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<!DOCTYPE Article PUBLIC "-//OASIS//DTD DocBook V3.1//EN">
<Article id="index">
<ArtHeader>
<Title>DSL HOWTO for Linux</Title>
<PubDate>v1.71, 2002-07-21</PubDate>
<AuthorGroup>
<AUTHOR>
<FirstName>Hal</FirstName>
<SurName>Burgiss</SurName>
<Affiliation>
<Address>
<Email>hal@foobox.net</Email>
</Address>
</Affiliation>
</AUTHOR>
<AUTHOR>
<FirstName>Original Author: David</FirstName>
<SurName>Fannin</SurName>
<Affiliation>
</Affiliation>
</AUTHOR>
<Editor>
<firstname>Greg</firstname>
<surname>LeBlanc</surname>
<Affiliation>
<Address>
<Email>GLeblanc@cu-portland.edu</Email>
</Address>
</Affiliation>
</Editor>
</AuthorGroup>
<!--
Not supported...
<othercredit>
<firstname>Greg</firstname>
<surname>LeBlanc</surname>
<contrib>Help with layout, organization and various content suggestions.
</contrib>
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...and if co-author is not used or is inappropriate, you could use
the <othercredit> tag. Example:
<othercredit>
<firstname>Greg</firstname>
<othername>J</othername>
<surname>Ferguson</surname>
<contrib>Conversion to DocBook SGML; updated section on
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</othercredit>
This goes in the <artheader> (DocBook 3.x) or <articleinfo> (DocBook 4.x)
section.
-->
<RevHistory>
<Revision>
<RevNumber>v1.71</RevNumber>
<Date>2002-07-21</Date>
<Authorinitials>hb</Authorinitials>
<RevRemark>
Add another supported modem only.
</RevRemark>
</Revision>
<Revision>
<RevNumber>v1.7</RevNumber>
<Date>2002-07-14</Date>
<Authorinitials>hb</Authorinitials>
<RevRemark>
More small updates.
</RevRemark>
</Revision>
<Revision>
<RevNumber>v1.6</RevNumber>
<Date>2002-05-23</Date>
<Authorinitials>hb</Authorinitials>
<RevRemark>
Various small updates.
</RevRemark>
</Revision>
<Revision>
<RevNumber>v0.92</RevNumber>
<Date>1999-04-10</Date>
<Authorinitials>df</Authorinitials>
<RevRemark>
First release (ADSL mini HOWTO).
</RevRemark>
</Revision>
</RevHistory>
<KeywordSet>
<Keyword>DSL</Keyword>
<Keyword>xDSL</Keyword>
<Keyword>ADSL</Keyword>
<Keyword>RADSL</Keyword>
<Keyword>IDSL</Keyword>
<Keyword>G.Lite</Keyword>
<Keyword>SDSL</Keyword>
<Keyword>SHDSL</Keyword>
<Keyword>PPPoE</Keyword>
<Keyword>PPPoA</Keyword>
<Keyword>PPPoATM</Keyword>
<Keyword>DSLAM</Keyword>
<Keyword>VDSL</Keyword>
<Keyword>Broadband</Keyword>
<Keyword>Internet</Keyword>
<Keyword>Network</Keyword>
<Keyword>Alcatel</Keyword>
</KeywordSet>
<Abstract>
<Para>
<Comment>
aspell -H -c DSL-HOWTO.sgml
submit@tldp.org
export CVSROOT=:pserver:hal@cvs.tldp.org:/cvsroot
cvs -d $CVSROOT login
pword: XXXXXXXXXXXXXX
$cvs get LDP/howto/docbook/DSL-HOWTO.sgml
upload...
$ cvs commit DSL-HOWTO.sgml !!!!!!!!!!!!!!!!
(from the LDP/howto/docbook/ dir)
check here: http://cvs.pld.org.pl/LDP/howto/docbook/DSL-HOWTO.sgml
alex alex@bennee.com, user land A STUSB.
====================================================================
Submitted 1.71 07/21/02
Changes:
IteX PCI ADSL modem (Apollo 3 chipset) Dlink
Todo:
Add the ADSL Bandwidth HOWTO
Begin 1.7 07/10/02 SUBMITTED 07/14/02
Changes:
Added comments on ISDN microfilters being different.
cable modem now more secure.
http://eciadsl.sourceforge.net USB modems.
Add something on usepeerdns per Timo Karjalainen timo.karjalainen@myorigo.com
remove linuxfriendly ISPs???
Todo:
Begin 1.6 01/07/02 submitted 05/23/02
Changes:
new faq re: distance CO vs DSLAM
minor touch ups to DSL family.
Trouble: setup both chap and pap
Removed sympatico from ISPs.
Xpeed not in 2.4.
Made table of out of distance chart
Alarm re-write.
Released 1.5 to LDP 01/07/02
Begin 1.5 12/10/01
Changes:
new ISP (Tiscali)
new ATM page URL
new ISP (istop)
http://sourceforge.net/projects/speedtouch (new link)
Adv Routing tweaks! 12/28/01 HOT!
New FAQ (be my own ISP?)
PPP LCP tuning
LCP in glossary
new ISP (q-dsl)
fixed _screen_ tags 12/31/01
removed linux.com.sg/news/atm/
rewrite new tuning section on iproute 01/02/02
reworked SpeedTouch section again. (major)
ToDo:
See: http://ds9a.nl/lartc/HOWTO/cvs/2.4routing/output/2.4routing-15.html#ss15.8
cbq stuff
Begin 1.4 started 06/30/01
Changes:
new ISP (VIC)
new ISP FAQ: T-DSL
shorewall firewall added. 11/01/01
BT-Internet doc added
Minor note on interleaving per Juha
Removed references to Rhythms telco
shdsl update
Security URLs (mine)
Took out large chunk of security related stuff. It's in the
Security HOWTOs now, and better explained.
Re-worked the Alcatel USB section, removing Chris's HOWTO.
Todo:
Look at txt version. Some screen output is not spaced right.
Flesh out linux router. Add basic networking.
NAT'd ISPs????
http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc2923.html PMTUD, don't block
destination unreachable ICMP.
Submitted 1.3 06/30/01
Begin 1.3 Wed 03/28/01 06:57:01 PM
Changes:
Fixed a few broken links.
Feeble attempt to add some internalization to a few sections.
RWIN and interleaving in glossary.
Minor changes to comments on RBOC/independent shake out, and
remote terminals.
Updates to the SpeedTouch HOWTO in appendix
Added back the NTS FAQ.
Added a new dyn dns org.
Added bit about kernel mode PPPoE/rp-pppoe per David Skoll
<!--
<date>
<year>2000</year>
<month>12</month>
<date>11</date>
</date>
<glossary><title>Example Glossary</title>
<para>
This is not a real glossary, it's just an example.
</para>
<glossdiv><title>E</title>
<glossentry id="xml"><glossterm>Extensible Markup Language</glossterm>
<acronym>XML</acronym>
<glossdef>
<para>Some reasonable definition here.</para>
<glossseealso otherterm="sgml">
</glossdef>
</glossentry>
</glossdiv>
</glossary>
-->
</Comment>
</Para>
<Para>
This document examines the DSL family of high speed Internet services now
being deployed in various markets worldwide. Information is included on the
technology behind DSL as well as subscribing, installing, configuring, and
troubleshooting, with an emphasis on how this impacts Linux users.
</Para>
</Abstract>
</ArtHeader>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="intro">
<Title>Introduction</Title>
<Para>
DSL, or Digital Subscriber Loop, is a high-speed Internet access technology
that uses a standard copper telephone line (a.k.a. <Quote>loop</Quote> in
telco parlance). DSL provides a direct, dedicated connection to an ISP via
the existing telco network. DSL is designed to run on up to 80% of the
telephone lines available in the United States. By using line-adaptive
modulation, DSL is capable of providing data speeds of 8 Mbps or more.
</Para>
<Para>
DSL services are now being aggressively marketed for home and small business
use. DSL is typically priced below ISDN, and well below T1 service, yet can
provide potentially even greater speeds than T1 without the
cost, complexity, and availability issues of T1. Since DSL is a dedicated,
often <Quote>always on</Quote> service, it avoids the delays and use charges
that are common with ISDN. Making this quite a nice technology for the
bandwidth starved masses.
</Para>
<Para>
While all this sounds exciting, DSL does have some drawbacks. The quality of
the DSL signal, and thus the connection, depends on distance (the length of
the copper <Quote>loop</Quote>) and various other factors. Also, there is no
such thing as standard <Quote>DSL</Quote>. There are various flavors of DSL,
and many, many ways DSL providers are implementing their networks. In typical
fashion, Linux users are often left to fend for themselves, since the DSL
providers are often taking the easy way out, and catering only to
<Quote>mainstream</Quote> Operating Systems.
</Para>
<Para>
The topics included in this HOWTO include qualification and pre-installation,
installation, configuration, troubleshooting and securing a DSL connection. As
well as other related topics. There are also appendices including a
comprehensive <Link LinkEnd="overview">DSL Overview</Link>, <link
linkend="faq">Frequently Asked Questions</link>, a listing of <link
linkend="links">related links</link>, and a <link
linkend="glossary">glossary</link>. </Para>
<Para>
Due to the fast pace of change in the telco and DSL industries, please make
sure you have the latest version of this document. The current official
version can always be found at
<Ulink
url="http://www.tldp.org/HOWTO/DSL-HOWTO/">http://www.tldp.org/HOWTO/DSL-HOWTO/</Ulink>. Pre-release versions can be found at <Ulink
URL="http://feenix.burgiss.net/ldp/adsl/">http://feenix.burgiss.net/ldp/adsl/</Ulink>.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Document Structure and Reading Guidelines</Title>
<Para>
This document attempts to give a comprehensive discussion of DSL. All aspects
are hopefully addressed to one degree or another with what can be a complex
topic since it deals with networking, hardware, new fangled technologies, and
various approaches taken by various vendors. The core components of this
document are:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
The <Link LinkEnd="installation">Installation</Link> section covers
installation of DSL hardware and related components, including wiring
considerations, splitter or microfilter installation, modem and Network
card installation.
</Para>
</ListItem>
<ListItem>
<Para>
The <Link LinkEnd="configure">Configuring Linux</Link> section covers
mostly client and software aspects of getting the connection up and
running. The Network card configuration is actually covered mostly in the
above Installation section.
</Para>
</ListItem>
<ListItem>
<Para>
The <Link LinkEnd="secure">Securing Your Connection</Link> section covers
Security implications that are even more important with a full-time
connection. Linux users seem especially targeted by crackers, because
quite frankly, some don't understand how important security is, or don't
understand the finer points of this. And who wants to <quote>own</quote>
a Windows box?
</Para>
</ListItem>
<ListItem>
<Para>
The <Link LinkEnd="tuning">Tuning and Troubleshooting</Link> section
covers post-installation topics like how well is our connection performing,
and how to track down any show-stoppers or intermittent problems.
</Para>
</ListItem>
<ListItem>
<Para>
There is also a lengthy Appendix that covers various topics relating to
Linux and DSL. None of these are directly related to simply getting that
connection up and running, but may be of interest nonetheless.
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
To simplify the navigation of this document, below is a suggested reading
guideline. Everyone should read the Introduction. Please pay special
attention to the <Link LinkEnd="usage">Conventions and Terminology</Link>
section, as some of this terminology may be used somewhat differently in
other contexts. Also, there is a <Link LinkEnd="glossary">Glossary</Link> if
you get lost in the world of TA (telco acronyms) ;-).
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
If you don't know anything about DSL, you should probably read the entire
document. You may want to start with the <Link LinkEnd="overview">DSL
Overview</Link> section in the Appendix, and then the <Link
LinkEnd="faq">FAQ</Link>. The DSL Overview explains how the various pieces
of the puzzle fit together. DSL network implementations are more complex
than traditional dialup networks.
</Para>
</ListItem>
<ListItem>
<Para>
If you have already done some homework, but have not ordered service from
anyone yet, read the <Link LinkEnd="cproviders">Choosing
Providers</Link> section. Also, you might get a head start by reading the
<Link LinkEnd="configure">Configuring Linux</Link> section so you know
what lies ahead.
</Para>
</ListItem>
<ListItem>
<Para>
If you have ordered service already, and are awaiting delivery, you can
skip the sections on choosing a Provider. If you will be doing a
self-install, you should read the pertinent parts of the <Link
LinkEnd="installation">Installation</Link> section, the <Link
LinkEnd="configure">Configuring Linux</Link> section, and the <Link
LinkEnd="secure">Securing Your Connection</Link> section.
</Para>
</ListItem>
<ListItem>
<Para>
If the installation is complete, and you can't get a working connection,
skip right to the <Link LinkEnd="tuning">Troubleshooting</Link> Section.
If you are not clear on what protocols are required, or what software you
need to have installed, also read the <Link
LinkEnd="configure">Configuring Linux</Link> section. If not sure what
terms like <Quote>sync</Quote> mean in this context, then be sure to read
the <Link LinkEnd="overview">DSL Overview</Link> section first so you know
how it all fits together.
</Para>
</ListItem>
<ListItem>
<Para>
If trying to decide between cable and DSL, read the
<Link LinkEnd="cable">Cable vs DSL</Link> section, and possibly the
<Link LinkEnd="overview">DSL Overview</Link> section.
</Para>
</ListItem>
<ListItem>
<Para>
If you have never had a full-time Internet connection, or are not
absolutely sure you fully understand how to secure you connection,
be sure to read The <Link LinkEnd="secure">Securing Your Connection</Link>
section. If you don't understand some aspect of this, re-read it, or start
looking for other references.
</Para>
</ListItem>
<ListItem>
<Para>
There is a comprehensive <Link LinkEnd="links">Links section</Link> that
has references to some topics not touched on in the main body of the
Document itself.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>What's New</Title>
<para>
1.71: Add info on the IteX PCI ADSL modem only.
</para>
<para>
1.7: Added comments on ISDN line filters being different than POTS,
and other additions related to ADSL over ISDN in various places. Add another
supported modem: Eci Hi Focus ADSL Modem (and various related chipsets).
Removed the 'Linux Friendly ISP' section. The landscape has changed much
since this section was started. Back then there were few options for DSL in
many places, and all too often a non-compatible modem was the only thing
available. Also, the advent of microfilters and self-installation has helped
with the <quote>do-it-yourselfer</quote> approach, giving everybody more
freedom. Then, maintaining this number of links was a PITA too. I still
encourage new subscribers to shop their local markets if there are options.
Many large ISPs and telcos have very poor ideas of what an Internet
connection is and restrict severely what you can do with Linux. Or at least
try to ;-) Updated LDP links to tldp.org (from linuxdoc.org).
</para>
<para>
1.6: Several new Linux Friendly ISPs. Clarification on
problems with alarm systems. Minor touch ups to other sections, and fix some
broken links (never ending job :).
</para>
<para>
1.5: New Tuning sub-section using <application>iproute</application>. Hot
stuff! Other additions to the Tuning section. A few new ISPs. Alcatel
SpeedTouch USB section updates. Thanks to Alex Bennee for clarifying things.
Other minor updates to FAQ, Glossary and Tuning.
</para>
<para>
1.4: A few new and updated URLs, and catch ups. The Alcatel USB modem section
is revamped. A few new ISPs.
</para>
<Para>
Version 1.3: Updates to the SpeedTouch USB HOWTO in the appendix.
Minor update to PPPoE section, and two new Linux Friendly ISPs. A feeble
attempt to make the document a little less U.S.-centric. Various minor
updates.
</Para>
<Para>
Version 1.2 adds PPTP configuration section for Alcatel ethernet modems.
Also, added are two additional sections in the <Quote>Tuning</Quote> section
for the TCP Receive window, and ADSL/DMT interleaving. And the big news is
the release of open source drivers for the Alcatel USB modem as of March
2001. There is an Alcatel SpeedTouch USB mini HOWTO in the <Link
LinkEnd="SpeedtouchUSB">appendix</Link> by Chris Jones. A number of
miscellaneous updates as well.
</Para>
<Para>
Version 1.1 included quite a few minor corrections, updates,
and additions. Not much that is substantially new. There are finally two
Linux compatible DSL PCI modems from Xpeed. The drivers are now in the kernel
2.2.18 source (not ported to 2.4 as of this writing 05/23/02).
</Para>
<Para>
Version .99 addresses some of the many changes that have occurred since the
original ADSL mini HOWTO was published. Originally, ADSL was the primary DSL
technology being deployed, but more and more some of the other DSL flavors
are entering the picture -- IDSL, SDSL, G.Lite, and RADSL. Thus the renaming
from <Quote>ADSL mini HOWTO</Quote> to the <Quote>DSL HOWTO</Quote>. There
have been many other changes in DSL technology as well. PPPoE/A encapsulation
has become more and more common as many ISPs are jumping on this bandwagon.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Copyright</Title>
<Para>
DSL HOWTO for Linux (formerly the ADSL mini HOWTO)
</Para>
<Para>
Copyright &copy; 1998,1999 David Fannin.
</Para>
<Para>
This document is free; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
</Para>
<Para>
This document is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
details.
</Para>
<Para>
You can get a copy of the GNU GPL at <ULink
URL="http://www.gnu.org/copyleft/gpl.html">GNU GPL</ULink>.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Credits</Title>
<Para>
Thanks to all those that contributed information to this HOWTO. I have
anti-spammed their email addresses for their safety (and mine!). Remove the
X's from their names.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Emphasis remap="bf">B Ediger</Emphasis> (Xbediger@csn.net) Great
Description of loop impairment.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis remap="bf">C Wiesner</Emphasis> ( Xcraig@wkmn.com) List of many ADSL URLs.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis remap="bf">J Leeuw</Emphasis> ( Xjacco2@dds.nl) Many tips on ADSL,
especially in Europe
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis remap="bf">N Silberstein</Emphasis> ( Xnick@tpdinc.com) Info on
Netrunner and his experience with US Worst.
</Para>
</ListItem>
<ListItem>
<Para>
Many and various posters from comp.dcom.xdsl and
bellsouth.net.support.adsl, too numerous to mention individually.
(HB)
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis remap="bf">Juha Saarinen</Emphasis> for suggestions and
explanations on the TCP Receive Window, and related tuning topics.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis remap="bf">Chris Jones</Emphasis>
<email>chris@black-sun.co.uk</email> for his Alcatel SpeedTouch USB mini
HOWTO which was previously incorporated into the <Link
LinkEnd="SpeedtouchUSB">Appendix</Link>. Also, Alex Bennee for clarifying
the driver situation for this modem.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<sect2 id="disclaimer">
<title>Disclaimer</title>
<para>
The authors accept no liability for the contents of this document. Use the
concepts, examples and other content at your own risk. As this is a new
edition, there may be errors and inaccuracies. Hopefully these are few and
far between. The author(s) do not accept any responsibility for incorrect or
misleading information, and would certainly appreciate any corrections. Also,
this type of technology dates itself very quickly. What may be true today, is
not guaranteed to be true tomorrow.
</para>
<para>
All copyrights are held by their respective owners, unless specifically noted
otherwise. Use of a term in this document should not be regarded as affecting
the validity of any trademark or service mark.
</para>
<para>
References to any particular product, brand, service or company should
not be construed as an endorsement or recommendation. Excepting Linux
itself, of course!
</para>
</sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Feedback</Title>
<Para>
Any and all comments on this document are most welcomed. Please make sure you have
the most current version before submitting corrections! These can be sent to
<email>hal@foobox.net</email>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="usage">
<Title>Conventions, Usage and Terminology</Title>
<Para>
For the sake of simplicity and sanity, let's clarify some of the terminology
that we will be using in this document, so that we are all on the same page.
While many of the definitions below are not always 100% technically correct,
they are close enough for our purposes here. In fast moving technologies like
DSL, there are so many <Quote>ifs, ands, and buts</Quote> that it is
difficult to say anything with any degree of certainty and have it stick. And
there are exceptions to almost every rule. And sometimes exceptions to the
exceptions. We will be dealing with generalities to a large degree here,
please keep that in mind.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Quote>DSL</Quote> will be used to refer to the entire family of DSL
technologies now available -- ADSL, SDSL, IDSL, RADSL, etc. ADSL still
seems to be the most prevalent at this time, but the others are being
deployed as well. Where it is important to differentiate one type of
DSL from another, the full proper name will be used: e.g. RADSL. xDSL is
also commonly used to refer to the various DSL technologies as a group, but
we will be using just <Quote>DSL</Quote> here.
</Para>
</ListItem>
<ListItem>
<Para>
The term <Quote>telco</Quote> here refers to any potential DSL provider.
This includes the ILECs (Incumbent Local Exchange Carriers), a.k.a. the old
guard phone companies or state run phone companies, and where the
monopolies now have competition, the CLECs (Competitive Local Exchange
Carriers), or independent providers such as Covad in the U.S.
</Para>
</ListItem>
<ListItem>
<Para>
<Quote>CO</Quote> is the telco acronym for <Quote>Central Office</Quote>.
Traditionally this is a building where one end of your phone line
physically terminates. The other end terminates at your home, office, or
wherever. It will be used here to refer to the telco end termination point,
regardless of whether it is a traditional Central Office building or
another, smaller, remote structure or device.
</Para>
</ListItem>
<ListItem>
<Para>
<Quote>Loop</Quote> is telco speak for <Quote>phone line</Quote>.
Essentially, you should think of your loop as one dedicated pair of copper
wires that run uninterrupted from your residence or office directly to the
CO. This is perhaps an oversimplification, but will serve our purposes. DSL
availability, and signal quality, is tied directly to the characteristics
of your physical line -- or <Quote>loop</Quote> as they say.
</Para>
</ListItem>
<ListItem>
<Para>
<quote>POTS</quote> is the acronym for Plain Old Telephone Service. In other
words, traditional, non-digital devices like analog phones, faxes and answering
machines. ISDN is used for DSL in some areas, so POTS is not the only way
to piggy-back DSL. But certainly the most common in many places.
</Para>
</ListItem>
<ListItem>
<Para>
<quote>NID</quote>, or Network Interface Device, is the small telco
housing that is often typically attached to the outside wall of your house,
and is the service entrance for telco services, though may be placed
elsewhere depending on the phone company. This may variously also be
referred to as <quote>ONI</quote>, <quote>SNI</quote>, <quote>NIU</quote>,
<Quote>TNI</Quote> or other creative telco acronyms. It represents the
<quote>demarcation</quote> point that divides the customer's realm of
responsibility from the telco's. Commercial structures, and multi-family
housing will likely have something more sophisticated, and probably located
inside somewhere.
</Para>
</ListItem>
<ListItem>
<Para>
<Quote>DSLAM</Quote> is the sophisticated hardware device in the telco's CO
where your phone line physically terminates, and thus makes DSL happen.
Increasingly, telcos are making use of smaller devices like the
<Quote>mini-RAM</Quote> in remote locations. We'll use <Quote>DSLAM</Quote>
here as a catch-all for any device that enables DSL service from a telco.
These are now being manufactured by a number of companies.
</Para>
</ListItem>
<ListItem>
<Para>
<Quote>Modem</Quote> will be used to refer to the end user device that
enables a DSL connection. Your <quote>modem</quote> is connected to the
telco's DSLAM in the CO via your copper loop. When they are
<Quote>talking</Quote> DSL to each other, they are in <Quote>sync</Quote>.
Without <Quote>sync</Quote>, no connection to your ISP is possible.
</Para>
<Para>
<Quote>Modem</Quote> is indeed the correct terminology since there is
MOdulation and DEModulation of the signal, even though it doesn't
resemble an analog 56K modem like many of us have had before. These modems
incorporate other features too -- so they are more than just a
<quote>modem</quote>. Some ISPs and manufacturers may be marketing simply
<Quote>routers</Quote>, <Quote>bridges</Quote>, or even
<Quote>brouters</Quote> for this purpose. These are essentially DSL modems
with enhancements. A compatible <Quote>modem</Quote> of some kind is the
minimum hardware requirement at the customer's end of the connection. The
most commonly supplied modem is actually a combination bridge and modem.
</Para>
<para>
One distinction here may be where ADSL is provided over ISDN lines. In this
case, the term <quote>modem</quote> is not appropriate and the only
physical difference is that the ISDN Network Terminator (NT), is equipped
to handle DSL, but is still an NT. In any case, for brevity, we will take
license here to refer to all such devices as <quote>modems</quote>.
</para>
<Para>
Unless stated otherwise, we will also be assuming the <Quote>modem</Quote>
has an ethernet interface, and will connect to a standard ethernet Network
Card (NIC). This is far and away the most prevalent configuration for Linux
users, at least until more Linux drivers are available for PCI and USB
modems. USB modem are quite popular otherwise, because they are
<quote>plug 'n play</quote>, and arguably less expensive.
</Para>
<Para>
It is worth noting that <Quote>routers</Quote> as supplied by DSL providers
are typically modem/router combination devices. In our context,
<Quote>router</Quote> will refer to these devices as such. There are also
SOHO broadband routers available that are only dedicated routers and lack
the modem functionality.
</Para>
</ListItem>
<ListItem>
<Para>
Previous versions of this document referred to the modem as an
<Quote>ANT</Quote> (ADSL Network Termination). While this may be
technically correct terminology, it is not used by ISPs, manufacturers,
telcos, or most users to any extent. The <Quote>modem</Quote> will be just
called a modem, regardless of whatever other features it may incorporate (i.e.
router, bridge, etc.).
</Para>
</ListItem>
<ListItem>
<Para>
PPPoX will be used to refer to PPPoE (PPP over Ethernet) and PPPoA
(PPPoATM, or PPP over ATM) collectively. These protocols are being used by
many DSL providers now.
</Para>
</ListItem>
<ListItem>
<Para>
The information provided in this document is based mostly on the current
state of DSL in the U.S. I will assume there are enough similarities with
DSL services outside of the US that this document would still have some
merit for everyone. Correct me if I am wrong by emailing
<email>hal@foobox.net</email>.
</Para>
</ListItem>
<ListItem>
<Para>
A <Quote>#</Quote> will be used to denote a command that typically is run
by the root user. Otherwise, a <Quote>$</Quote> will be used as the prompt
for non-root users.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="installation">
<Title>Installation</Title>
<Para>
Before actually ordering service, there are several things you may want to
explore. Please note, that there are many ways any given telco might
decide to handle qualification and installation procedures. Much of what
is described in this section, is how it is commonly done in the U.S.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Pre-Installation</Title>
<Para>
In many parts of the world, there is no choice on who you get DSL from: your
friendly local telco, of course! They own the copper wires, and thus they
hold all the cards.
</Para>
<Para>
However, in the U.S. de-regulation has opened this up somewhat. Beyond the
obvious consideration of price, there are reasons to investigate which
alternate providers may be offering DSL services in your area. The large
Telephone companies are everywhere, and may advertise the most. But
increasingly smaller ISPs and independents are getting into the act. This has
created some diversity in the DSL marketplace. A good thing of course, but
possibly creating a little confusion too. Conversely, in areas where there
is only one choice, then we have no choice but to accept whatever service
is being offered.
</Para>
<Para>
If your telco has a monopoly on phone service and DSL, you may skip the
rest of this section. And probably the next few sections. They will probably
control the installation and qualification processes, and you just wait
for them to get finished.
</Para>
<Para>
Not all DSL services are alike. Just because two local companies are offering
<Quote>ADSL</Quote>, does not mean that necessarily there is much in common
at all. In fact, there are potentially a number of factors that make one ADSL
provider's service significantly different from another's. Some things to
consider:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
Speed vs Price.
</Para>
</ListItem>
<ListItem>
<Para>
What hardware is provided, i.e. modem or router. It is best if this is
external ethernet in either case.
</Para>
</ListItem>
<ListItem>
<Para>
The ISP's Network architecture. PPPoX? Static IP? Servers allowed?
</Para>
</ListItem>
<ListItem>
<Para>
Is it an <Quote>always on</Quote> service, at least theoretically? Are
there supplemental usage fees, or idle timeouts?
</Para>
</ListItem>
<ListItem>
<Para>
Linux friendly, Linux hostile, or Linux agnostic? This is not as much of
a problem as it used to be in most areas. Some providers are still very
restrictive on allowing <quote>servers</quote>, and possibly even
LAN connections. Buyer beware. Talk to other users, and read their
TOS (Terms of Service) to get a feel for their attitude.
</Para>
</ListItem>
<ListItem>
<Para>
Quality of service. How is news, mail, etc.? News particularly seems
to be inconsistent with low-end broadband providers. Probably because
of the dramatic increase in binary news content, which is compounded by the
higher bandwidth and increased usage of such groups.
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
For a more lengthy discussion on some of these considerations and related
issues, see the <Link LinkEnd="overview">DSL Overview</Link> appendix for
more on <Link LinkEnd="dslmodems">modems</Link>,
<Link LinkEnd="qualify">qualifying for service</Link>, and
<Link LinkEnd="cproviders">choosing a provider</Link>.
</Para>
<Para>
Once you have chosen a provider, and ordered service, the next step is for
the telco to <Quote>qualify</Quote> your loop. This essentially means testing
your line to make sure it can handle the DSL signal, and possibly what level
of service may be available to you. This may take some time, especially if
the telco encounters problems with the loop. If no problems are found during
this phase, then possibly there will be a one to three week wait for the
installation. YMMV.
</Para>
<Para>
After the telco has qualified the loop and readied their end of the
connection, the next step is installation of the necessary components at the
customer's end of the connection: wiring modifications, splitter or filters,
and, of course the modem and any necessary software.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Installation Options -- Self Install or Not</Title>
<Para>
You may or may not have a choice on how the installation is done, or who
does it. This is totally at the discretion of the provider. In much of the
world, this is done by the telco, and there is little flexibility. Many
providers in the U.S. offer a <Quote>self install</Quote> option where you do
all the work. In this scenario, the provider will send a kit in order to save
them from sending a tech, and thus reducing cost. Typically, self install
kits will include microfilters for the POTS (Plain Old Telephone Service)
or ISDN (where ADSL over ISDN is used) phone jacks, the modem (and
maybe a NIC), and a CDROM with drivers, etc. on it. In some cases, a splitter
may be included instead of microfilters. In any case, some type of filtering
is necessary on the non-DSL lines. If not the noise generated by the DSL
signal may interfere with regula telco devices such as phones and answering
machines.
</Para>
<Para>
The other possibility is for the provider to do the installation. Again, this
may be your only option. Obviously, the cost is higher here, but it may have
the advantage of having a trained tech do any wiring. There is also a better
chance of getting a <quote>splittered</quote> installation with this option
(a good thing!). Another benefit is that if something is wrong with the line,
or the telco has not provisioned the line properly, an on-site tech may be
able to help sort out certain kinds of problems quickly.
</Para>
<Para>
The self-install kit should come with full instructions, regardless of whether
the installation will be splittered or filtered. So we won't go into much
detail on this aspect.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Wiring/Installation Options</Title>
<Para>
There are various wiring schemes depending on how your service is being
provided, who is providing it, and which DSL service is being provided.
If your telco is performing the installation, you may skip this section.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Emphasis>Dedicated Line</Emphasis>. Some DSLs require a dedicated, or
<Quote>dry</Quote>, wire pair, e.g. IDSL. This means a separate, physical
line without dial-tone for DSL and Internet connectivity. Also, DSL
services from CLECs (independent telcos like Covad), may use a
dedicated line, depending on their line sharing agreement with the local
incumbent carrier. (Instead the CLEC will actually lease a loop from the
ILEC.) On your end, this simply means using one of the unused wire pairs
in the telco wire bundle, and connecting it to the DSL jack.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Shared Line with Splitter</Emphasis>. For DSLs like ADSL, that
are provided over the same line as regular voice service, the signal
must be filtered somehow so that voice services are not adversely effected.
Installing a splitter splits the line into two pairs, and filters the DSL
signal from one of them. This results in a inside wiring scheme where DSL
goes to only one jack, and then regular voice type service to all other
jacks. This is considered by many to be a better type of installation than
<Quote>splitterless</Quote>, i.e. with microfilters instead. See below.
</Para>
<Para>
Splitters are available from various manufacturers and come in various
shapes and sizes. Some are small enough to fit in the NID itself (sometimes
called SNI, this is the telco phone box on the outside of your house),
while others have a housing as large as the NID itself. Typically this is
mounted near the NID, on the customer's side of the demarcation point.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Shared Line with Filters</Emphasis>. Again, for some DSLs that
piggyback on the POTS (or ISDN) line, the signal must be filtered or split at some
point. This is not necessary for g.lite or RADSL however. The other way of
doing this is by placing RJ11 <Quote>microfilters</Quote> in each phone
jack -- <Emphasis>except where the DSL modem will be</Emphasis>. These
filters are relatively small, plug-in devices and remove the higher
frequencies associated with DSL. This is obviously much easier since no
tools or wiring is required. This is often what is included in self-install
kits, and is often referred to as a <Quote>splitterless</Quote>
installation. This is a very common approach in the U.S. Note that
in areas where ADSL over ISDN is provided, filtering is required
also, but the filters themselves are quite different and are not
interchangeable with POTS filters!
</Para>
<Para>
Similar microfilters are sometimes used by some telcos to reduce the
excessive <Quote>whine</Quote> on the line that is produced by some modems.
This is a little different approach as the filter is put on the same
jack as the modem.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Shared Line, Splitterless and Filterless</Emphasis>. Some newer
DSLs, like G.Lite, have no adverse effect on regular POTS devices and thus
require no filters or splitters. This would seem to be the wave of the
future. Just plug and play. Though still not very common.
</Para>
</ListItem>
</ItemizedList>
</Para>
<BridgeHead renderas=sect3>
Figure 1: DSL Block Diagram with Splitter (NID not shown)
</BridgeHead>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
<--------Home/Office-----><---Loop---><--Central Office-->
POTS X-------+
phone, |
fax, |
etc, |
| CO
| -------
| | |
| | |
| ----- | |
POTS X-------+----Voice--=| S | | D |
| P | | S |=- Voice Switch
| L | 2 wire | L |
| I |=------------=| A |
| T | Local Loop | M |=- ISP --> INET
--------- | T | | |
Linux X--=| Modem |=-Data-=| E | | |
--------- | R | | |
----- | |
-------
</LiteralLayout>
</MSGText>
</Literal>
</Para>
<BridgeHead renderas=sect3>
Figure 2: DSL Splitterless (a.k.a. filtered) Block Diagram
</BridgeHead>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
<--------Home/Office-------><----Loop---><--Central Office-->
POTS X--Voice---[RJ11]------+
phone, (filter) |
fax, D CO
etc, a -------
t | |
a | |
POTS X--Voice---[RJ11]----- & | D |
(filter) V ----- | S |=- Voice Switch
o | N | 2 wire | L |
i-=| I |=-----------=| A |
c | D | Local Loop | M |=- ISP --> INET
e ----- | |
----------- | | |
Linux X--=| Modem |=-------| | |
----------- -------
</LiteralLayout>
</MSGText>
</Literal>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="wiring">
<Title>Self Install - Wiring</Title>
<Para>
If you are not doing a self-install, then you may skip this section
and move to <Link LinkEnd="configure">Configuring Linux</Link>. If you are
doing a self-install with microfilters, skip to the
<Link LinkEnd="micro">mircofilter section</Link>. The following procedures
are meant to illustrate the wiring process. Please note that your procedures
may be different at your location. Make sure you follow any warnings or
safety instructions provided, that you RTFM, and that you are familiar with
telco wiring procedures.
</Para>
<Para>
The first step will be to wire up the connections from your provider. Identify
the line on which service will be installed, and the locations of your
splitter and DSL jack(s). (For perhaps a better wiring scheme, see the
Homerun section immediately below.)
</Para>
<Para>
Be aware that typical telco wire has more than one pair per bundle. Often,
two pairs, but sometimes more. If you have but one phone line, the other
pair(s) are unused. This makes them available for use with wiring for DSL.
Wire pairs are color coded for easy identification. SDSL and IDSL require a
dedicated, or <Quote>dry</Quote>, pair. If an unused pair is available, then
no real re-wiring is required. It is just a matter of re-wiring an existing
jack for the correct pair of wires, and attaching the modem.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="homerun">
<Title>The Homerun</Title>
<Blockquote>
<attribution>A retired BellSouth ADSL installer</attribution>
<Para>
<quote>
<emphasis>
I would not use microfilters if I lived across the street from my CO. A
splitter is the only way to go.
</emphasis>
</quote>
</Para>
</Blockquote>
<Para>
The optimum method of wiring for the DSL modem is sometimes
called a <Quote>homerun</Quote>. It is called this because it is one,
straight shot from the splitter to the modem's DSL jack. What this does is
bypass the existing inside wiring altogether, and any problems that might be
lurking there -- like a corroded connection somewhere on a voice jack. Inside
wiring deficiencies can cause a degradation of the DSL signal.
</Para>
<Para>
This also allows you to route the cable to avoid any potential
RFI (Radio Frequency Interference) sources. RFI anywhere in the
circuit can be a DSL killer. Routing the cable away from items that
may have electric motors, transformers, power supplies, high
intensity lighting fixtures, dimmer switches and such, is a smart way
to go. And you are also less likely to have a failing microfilter
cause problems -- one potential point of failure instead of several. You can
also use a better grade of cable such as CAT 5.
</Para>
<Para>
If your existing installation is <quote>splitterless</quote> (i.e. using
microfilters) now, converting to a homerun will entail purchasing a splitter.
And, of course, will also mean some new wiring will need to be run.
Microfilters also add to the effective loop length -- as much as 700 ft per
filter in some cases! So if you have several microfilters installed, and your
sync rate or distance is marginal, eliminating these filters may result in a
significant improvement.
</Para>
<Para>
A poor man's splitter can be rigged by using a microfilter inside the NID.
This is not <quote>by the book</quote>, but seems to work just fine for many.
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Wire the Splitter</Title>
<Para>
If you have the splitterless design (i.e. using <Quote>microfilters</Quote>)
or a dedicated line, you may skip this part.
</Para>
<Para>
The splitter will typically consist of two parts, the splitter and a small
outdoor housing. Mount the splitter and accompanying housing per the telco's
instructions at the Network Interface Device (NID) point (also sometimes
called the SNI or ONI), usually the side of your house where the phone line
is located. Put it on your side of the NID. The phone company may need
to access the splitter for maintenance, so its advisable to locate it on the
outside where they can get at it, but outside is not absolutely
necessary.
</Para>
<Para>
The wire bundle should have at least two separate wire pairs. The splitter
takes one pair, and separates the signal onto two pairs. One pair in the
bundle will then go to all phone jacks, and the other to the modem's DSL wall
jack. So connect the incoming telco line to the LINE side of the splitter.
Then wire the inside pair for your telephone to the VOICE, and your inside
wire pair for the modem to DATA.
</Para>
<Para>
<Emphasis remap="bf">Checkstep </Emphasis> At this point, you should be able
to pull dial tone off the voice side of the splitter. If this doesn't work,
then you've wired it wrong. You can also plug the modem into the test jack in
the NID box (most should have this). Plug in the modem's power cord, and
if the line is provisioned correctly, you should <Quote>sync</Quote> in less
than a minute. This test only requires the modem. (Internal and USB modems
will require a driver to be loaded before syncing. This would mean having the
computer there too.)
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Wire the DSL Jack</Title>
<Para>
Wire the DSL wall jack (RJ11) at your computer location, which should already
be connected to the DATA side of the splitter. The specifics differ for each
situation, but basically you will have a wire pair that you will connect to
the DSL jack. Make sure you <Emphasis>read the directions</Emphasis>, as the
DSL-RJ11 wiring may be different for phones and DSL jacks.
<Emphasis>AND</Emphasis> -- different modems may expect the signal on
different pairs -- most on the inside pair, but some on the outside pair.
</Para>
<BridgeHead renderas=sect3>
Figure 3: RJ11 Wiring options
</BridgeHead>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
||
||
||
/ \
|RJ11|
| |
----
||||
^^ <-- Inside Most modems on inside pair
^ ^ <-- Outside Some on outside, e.g. Alcatel 1000, SpeedTouch Home
</LiteralLayout>
</MSGText>
</Literal>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id='micro'>
<Title>Installing Microfilters</Title>
<Para>
Pretty much a no-brainer here. If you are doing a
<Quote>splitterless</Quote>, self-install installation, then install the
provided microfilters in all phone jacks <Emphasis>except</Emphasis> the one
where the DSL modem will be connected. Don't forget devices like fax machines
and analog modems. The filters filter out the higher DSL frequencies and will
keep the DSL noise from interfering with POTS (or ISDN) equipment.
</Para>
<Para>
<Emphasis>Warning!</Emphasis>
Alarm systems can present various problems, depending on the type of alarm
and how it is installed. This may require telco help for proper installation
so the one does not interfere with the other. Common microfilters tend not to
work because most alarm boxes use a different size jack. Filters are now
available just for alarm boxes, though traditionally this has been handled
with a splitter type installation.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Installing an Ethernet Modem</Title>
<Para>
To install, connect the modem's (or router's) power cord, and connect
the phone line between the DSL wall jack and the modem. This cable should be
provided. If not, a regular phone cord will suffice. With the ethernet
interfaced modems, you may also connect the ethernet cable between the NIC
and the modem (but not really necessary at this point just to verify an
ethernet modem is working).
</Para>
<Para>
<Emphasis remap="bf">Checkstep </Emphasis> At this point, verify that
the modem syncs with the telco's DSLAM signal. Most modems have a
green LED that lights up when the signal is good, and red or orange
if not in sync. The modem's manual will have more details on the
LEDs. If it doesn't sync, then check your wiring, or make sure that
the DSL signal is being sent. Do this by calling your telco and
verifying they have activated the service. Or by testing the modem at
the test jack on the NID (see above). Note that having dial tone
on the line does NOT confirm the presence of the DSL data signal. And
vice versa -- perfectly possible to have dial tone and no DSL, or DSL
and no dial tone. There should also be no static or noise on the
voice line when everything is installed and functioning properly.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Installing the Ethernet Network Card (NIC)</Title>
<Para>
Ethernet modems will, of course, require an ethernet network card.
If you haven't already done so, install the NIC in your Linux machine,
configure the kernel, or load modules, etc., etc. This is sometimes the
biggest stumbling block -- getting the NIC recognized and working. See the
various Linux references for doing this, such as the <Ulink
url="http://www.tldp.org/HOWTO/Ethernet-HOWTO.html">Ethernet
HOWTO</Ulink> for more information. Also, see the <Link
LinkEnd="tuning">Troubleshooting Section</Link> below. This is certainly
something you could conceivably do ahead of time if you already have the NIC.
</Para>
<Para>
Be sure the RJ45 cable between the NIC and the modem is now connected. You
can <quote>hot plug</quote> this cable, meaning there is no need to power
down to do this.
</Para>
<Para>
We can do a few quick tests now to see if the NIC seems to be functioning
properly. First we'll attempt to bring up the interface. Then we'll see how
well it is responding by <Command>pinging</Command> it. And lastly use
<Command>ifconfig</Command> to check for errors:
</Para>
<para>
<Screen>
# ifconfig eth0 10.0.0.1 up
$ ping -c 50 10.0.0.1
PING 10.0.0.1 (10.0.0.1) from 10.0.0.1: 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_seq=0 ttl=255 time=0.2 ms
64 bytes from 10.0.0.1: icmp_seq=1 ttl=255 time=0.2 ms
64 bytes from 10.0.0.1: icmp_seq=2 ttl=255 time=0.1 ms
&lt;snip&gt;
- 10.0.0.1 ping statistics -
50 packets transmitted, 50 packets received, 0% packet loss
round-trip min/avg/max = 0.1/0.1/0.2 ms
$ ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:50:04:C2:09:AC
inet addr:10.0.0.1 Bcast:10.255.255.255 Mask:255.0.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:428 errors:0 dropped:0 overruns:0 frame:0
TX packets:421 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
Interrupt:10 Base address:0xc800
</Screen>
</para>
<Para>
If <Quote>eth0</Quote> comes up without errors, and you can
<Command>ping</Command> it without errors, and <Command>ifconfig</Command>
shows no errors, we most likely have all our hardware in working order now, and
are ready to start configuring Linux. If not, see the <Link
LinkEnd="tuning">Troubleshooting section</Link> below.
</Para>
<Para>
<Emphasis remap="bf">Gotcha:</Emphasis> A few modems may already be wired as
a 10baseT crossover, and require a direct Category 5 cable for a direct
connection to a NIC, rather than a crossover cable. I lost around 12 hours
figuring this one out, so don't make the same mistake - make sure you RTFM
first.
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Installing a USB Modem</Title>
<Para>
The physical installation of a USB modem is similar to an ethernet modem.
There is no ethernet card necessary obviously. So connect the phone
line between the DSL wall jack and the modem's DSL port, and attach the
USB cable to the computer's USB port.
</Para>
<Para>
USB modems will require vendor and model specific drivers in order to sync
and function properly. Assuming you are using the Alcatel SpeedTouch USB,
this will require both a binary firmware driver available from Alcatel's
driver page: <Ulink
URL="http://www.speedtouchdsl.com/support.htm">http://www.speedtouchdsl.com/support.htm</Ulink>,
and a separate modem driver.
</Para>
<Para>
This driver also supports both PPPoE and PPPoA, though the steps for getting
either to work are quite different. See the
<Link LinkEnd="SpeedtouchUSB">Appendix</Link> for more on this modem.
</Para>
<para>
The Eci Hi Focus ADSL Modem has some support in Linux now too. See
<ulink url="http://eciadsl.sourceforge.net/">http://eciadsl.sourceforge.net/</ulink>.
</para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="configure">
<Title>Configuring Linux</Title>
<Para>
After you have connected the modem and it's getting sync, then you're ready
to configure Linux and verify your connection to your ISP. Although I will
refer to a Linux System, you could conceivably connect any type of 10baseT
device to the modem. This includes a router, hub, switch, PC, or any other
system that you wish to use. We'll just cover the Linux aspects here.
</Para>
<Warning>
<Para>
<Emphasis>Before you connect to your ISP</Emphasis>, make sure you understand
all security issues of having a direct connection to the Internet via DSL.
Depending on your ISP, most outside users can access your system, and you
should setup any firewalls, deactivate ports/services, and setup any
passwords prior to connecting your machine to the world. See the <Link
LinkEnd="secure">Security section below</Link>, and the <Link
LinkEnd="links">links section</Link> for more on this <Emphasis>very
important</Emphasis> topic. Do not make this an afterthought! Be ready.
</Para>
</Warning>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="bridgevsppp">
<Title>Bridged vs PPPoX Networks</Title>
<Para>
Before we get too far into the final stages of installing and
configuring our system, let's look at how various DSL ISPs set up
their networks. It will be very important for you to know how your ISP does
this, as there is more than one possibility and the steps involved are quite
different for each. This may not be the kind of thing the ISP is advertising,
and since you are not using Windows, you may not have access to the setup
disk that the ISP provides. If you're not sure, ask the ISP's tech support
staff, or better, find other knowledgable users of the same service.
</Para>
<Para>
To muddy the waters even more, some ISPs may be offering more than one kind
of service (over and above the various bit rate plans). Example: Verizon
(formerly Bell Atlantic) originally offered static IPs with a Bridged
connection. Now all new installs use PPPoE with dynamic IPs. For installation
and configuration purposes, this is very different.
</Para>
<Para>
The two most common DSL network implementations are Bridged/DHCP and PPPoX.
Both have mechanisms for obtaining an IP address and other related networking
configuration details so we shouldn't have to worry about this. But there are
indeed other, less common, means of connecting. Our job will be finding the
right client, and doing what we have to, to get it up and running. The most
common ones are discussed below.
</Para>
<Para>
<Emphasis>Important!</Emphasis> You need to know beforehand how your ISP is
setup for connecting to his network. To re-iterate, the two main
possibilities are Bridged/DHCP and PPPoE. These are mutually exclusive
implementations. And there are indeed other possibilities as well. So you will
need to know exactly what this is beforehand. And it must be the right one or
you will waste a lot of time and effort. You cannot choose which one either.
It is a matter of how the ISP is doing his network. Note that PPPoE can run
over Bridged networks, so just knowing whether you are Bridged or not, is not
necessarily good enough. If your provider is giving you a router, there is a
good chance that the router's firmware will handle all of this for you.
</Para>
<Para>
If you are subscribing with one of the Baby Bells in the U.S., you can
count on that being PPPoE, and thus you will need a PPPoE client.
</Para>
<Para>
There are a few provider specific FAQs and HOWTOs in the <Link
LinkEnd="links">Links section</Link> below.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Bridged/DHCP</Title>
<Para>
In the good old days of a year or two ago, purely <Quote>Bridged</Quote>
connections were the norm. PPPoE had not been invented yet. This type of
network puts you on a local subnet just like a big LAN. You are exposed to
much of the local subnet traffic, especially ARP and broadcast traffic. The
typical means of authenticating in this set up, is via DHCP.
</Para>
<Para>
DHCP is a standard, established networking protocol for obtaining an IP
address and other important network parameters (e.g. nameservers). This is a
standard, well documented networking scheme and is very easy to set up
from the end user's perspective. It is also a very stable connection. You
can actually unplug the modem for say 10 minutes, plug it back in, let it
re-sync, and the connection is still there -- same IP and everything.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>PPPoX</Title>
<Para>
The main alternative now is PPPoX, meaning either PPPoE (PPP over Ethernet)
or PPPoA (PPP over ATM, aka PPPoATM). Both of these related protocols are
currently being deployed, but at the moment, PPPoE seems to be the more
common of the two. PPPoX is a relative newcomer, and, as the name implies, is
a variation of Point-to-Point Protocol that has been adapted specifically for
DSL networks.
</Para>
<Para>
There are several PPPoE clients for Linux (<Link LinkEnd="pppoe">see
below</Link>). PPPoX simulates a dialup type environment. The user is
authenticated by user id and password which is passed to a RADIUS server,
just like good ol' dialup PPP. A routable IP address, and other related
information, is returned to the client. Of course, no actual dialing takes
place. The mechanics of how this is handled, will vary from client to client,
so best to RTFM closely. Typically you will set up configuration files like
<Filename>pap-secrets</FileName>, etc.
</Para>
<Para>
It is worth noting that PPPoE will also work on non-ethernet devices like USB,
provided the correct drivers are installed.
</Para>
<Para>
From the ISPs perspective, PPP is much easier to maintain and troubleshoot.
From the end user's perspective, it is often more work to set up, often uses
more CPU, and the connection is maybe not as stable. So anyway, this seems to
be the coming trend. Many of the large telcos around the world, especially
the RBOCs (Baby Bells) in the U.S., have committed to PPPoX already. Setting
up a PPPoX connection is completely different from setting up a bridged/DHCP
connection.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>ATM</Title>
<Para>
Since the traffic on the wire from the DSLAM to the modem is typically ATM, a
raw ATM connection would seem to make sense. While possible, this is rare, if
it exists at all in the U.S, and would require a modem in addition to a PCI
ATM card, such as the Efficient Networks 3010. Recent 2.4 kernels
do have ATM support. (See the <Link LinkEnd="links">Links section</Link> for
more information.)
</Para>
<Para>
This may be a viable solution at some point, but it is just not
<Quote>there</Quote> yet, mostly because this is more costly to implement.
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Configuring the WAN Interface</Title>
<Para>
The most common configuration is a DSL modem in <Quote>bridging</Quote> mode.
Both PPPoX and DHCP can use this setup. In this scenario, the WAN interface
typically means your NIC. This is where your system meets the outside world.
(If you have a router see <Link LinkEnd="router">below</Link> for router
specific instructions.) So essentially we will be configuring the NIC,
typically <Quote>eth0</Quote> since it is an ethernet interface.
</Para>
<Para>
With PPPoX, once the connection comes up, there will be a
<Quote>ppp0</Quote>, or similar, interface, just like dialup. This will
become the WAN interface once the connection to the PPP server is up, but for
configuration purposes we will we be concerned with <Quote>eth0</Quote>
initially.
</Para>
<Para>
There are various ways an ISP may set up your IP connection:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
Static IP.
</Para>
</ListItem>
<ListItem>
<Para>
Dynamic IP on Bridged Network via DHCP.
</Para>
</ListItem>
<ListItem>
<Para>
Dynamic IP via PPPoX.
</Para>
</ListItem>
<ListItem>
<Para>
Static IP via PPPoX.
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
Let's look at these individually.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Static IP Configuration</Title>
<Para>
A <Quote>static</Quote> IP address is an IP that is guaranteed not to change.
This is the preferred way to go for those wanting to host a domain or run
some type of public server, but is not available from all ISPs. Note that
while there are some noteworthy benefits to having a static IP, the
disadvantage is that is more difficult to remain <quote>invisible</quote>. It
is harder to hide from those with malicious intentions. Skip this section if
you do not have a static IP, or if you have a router, and the router will be
assigned the static IP.
</Para>
<Para>
Configure the IP address, subnet mask, default gateway, and DNS server
information as provided by the ISP. Each Linux Distribution (Redhat, Debian,
Slackware, SuSE, etc.) has a different way of doing this, so check on your
distro's docs on this. Each may have their own tools for this. Redhat has
<Command>netcfg</Command> for example. You can also do this manually using
the <Command>ifconfig </Command> and <Command>route</Command> commands. See
the man pages on these or the <Ulink
url="http://www.tldp.org/HOWTO/Net-HOWTO">Net HOWTO</Ulink> for more
information and specifics. A quick command line example with bogus IPs:
</Para>
<para>
<Screen>
# ifconfig eth0 111.222.333.444 up netmask 255.255.255.0
# route add default gw 111.222.333.1 dev eth0
</Screen>
</para>
<Para>
Be sure to add the correct nameservers in <Filename>/etc/resolv.conf</FileName>.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Bridged/DHCP Configuration</Title>
<Para>
ISPs that have Bridged networks typically use DHCP to assign an IP addresses,
and authenticate the user. All distributions come with one or more DHCP
clients. <Command>dhcpcd</Command> seems to be the most common.
<Command>pump</Command> comes with Redhat based distributions as of Redhat
6.0. The DHCP client will obtain an IP <Quote>lease</Quote> from the ISP's
server as well as other related information: gateway address, DNS servers,
and network mask. The lease will be <Quote>renewed</Quote> at regular
intervals according to the ISP's configuration.
</Para>
<Para>
You will want the DHCP client started on boot, so use your distribution's
means of doing this. There generally is little to configure with DHCP as it
is fairly straightforward and easy to use. You may need to tell it which
interface to listen on if the NIC is something other than
<Quote>eth0</Quote>. You can also start it from the command line to get
started. See the respective man pages for more.
</Para>
<Para>
Unless you have a static IP, the ISP will need some way to know who you are
when you connect. There are two ways this authentication process is
accomplished with DHCP. The first and most common method is via the MAC (or
hardware) address of the network device. Typically this would be the NIC. The
MAC address is a unique identifier and can be found among the boot messages,
or with <Command>ifconfig</Command>, and looks something like
<Literal>00:50:04:C2:19:BC</Literal>. You will need to give the ISP the MAC
address before your first connection.
</Para>
<Para>
The other DHCP authentication method is via an assigned hostname. In this
case, the ISP will have provided you with this information. Your DHCP client
will need to pass this information to the server in order for you to connect.
Both <Command>dhcpcd</Command> and <Command>pump</Command> accept the
<Quote>-h</Quote> command line option for this purpose. See the client's man
page, or your distribution's documentation, for specifics.
</Para>
<note><title>Note</title>
<Para>
If your ISP uses MAC address authentication, and you change your network
device (e.g. NIC), you will need to register the new address with the ISP or
you won't be able to connect.
</Para>
</note>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="pppoe">
<Title>PPPoE Configuration</Title>
<Para>
PPPoE (PPP over Ethernet) is an alternate way for ISPs to control your
connection, and is becoming increasingly popular with ISPs. Setting this up
is quite different, and may be a little more work than with static IPs or
DHCP above. Recent distro releases are now shipping PPPoE clients. If this is
not the case for you, then you will have to download one. Check any Linux
archive site like <Ulink
URL="http://freshmeat.net">http://freshmeat.net</Ulink>, etc. or look below.
</Para>
<Para>
Some of the current GPL PPPoE clients available:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
The Roaring Penguin (rp-pppoe): <Ulink
URL="http://www.roaringpenguin.com/pppoe/">http://www.roaringpenguin.com/pppoe/</Ulink>,
by David F. Skoll. Reportedly very easy to set up, and get started with.
This is a popular Linux PPPoE clients due to it's reputation for ease of
installation, and is now being bundled with some distributions. rp-pppoe
works as a user-mode client on 2.0 and 2.2 kernels, and in kernel-mode
on 2.4 kernels.
</Para>
</ListItem>
<ListItem>
<Para>
PPPoEd: <Ulink URL="http://www.davin.ottawa.on.ca/pppoe/">
http://www.davin.ottawa.on.ca/pppoe/</Ulink> by Jamal Hadi Salim is
another popular Linux client and is also bundled with some
distros. This is a kernel based implementation for 2.2 kernels. A setup
script is now included so no patching is required, making installation
quick and easy. Also, less CPU intensive than user space alternatives like
rp-pppoe (2.0/2.2 kernels).
<Comment>
HB
jamal hadi@cyberus.ca pppoed author
very helpful on this part
"David F. Skoll" dfs at roaringpenguin.com
Some feedback too.
</Comment>
</Para>
</ListItem>
<ListItem>
<Para>
PPPoE Redirector: <Ulink
URL="http://www.ecf.toronto.edu/~stras/pppoe.html">
http://www.ecf.toronto.edu/~stras/pppoe.html</Ulink>. This is a redirector
which allows the use of PPPoE with pppd-2.3.7 or later. No recompiling of
other system components are required. It is meant as an interim solution
until the 2.4.x series, which will include kernel support of PPPoE/A. (Does
not seem to be under active development at this time.)
</Para>
</ListItem>
<ListItem>
<Para>
2.4.x kernels include native PPPoE support. The PPPoE for 2.4 page is
<Ulink
URL="http://www.shoshin.uwaterloo.ca/~mostrows/">http://www.shoshin.uwaterloo.ca/~mostrows</Ulink>
[link is dead, sorry, can't find new page] and is by Michal Ostrowski, the maintainer for kernel PPPoE. This
includes detailed instructions for installing and configuring kernel
mode PPPoE.
</Para>
</ListItem>
<ListItem>
<Para>
EnterNet is a non-GPL'd PPPoE client from NTS, <Ulink
URL="http://www.nts.com">http://www.nts.com</Ulink>, that is being
distributed by some ISPs as the Linux client. It does come with
source code but the it is not available for free download. (I haven't
found anyone that is impressed by this one.)
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
Depending on which client you have chosen, just follow the
<Filename>INSTALL</FileName> instructions and other documentation included
with that package (<Filename>README</FileName>, <Filename>FAQ</FileName>, etc.).
</Para>
<Para>
Once a PPPoE client connects, your connection should look something like the
below example from Roaring Penguin, where <Quote>eth0</Quote> is connected to
the modem:
</Para>
<para>
<Screen>
$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.0.254 * 255.255.255.255 UH 0 0 0 eth1
208.61.124.1 * 255.255.255.255 UH 0 0 0 ppp0
192.168.0.0 * 255.255.255.0 U 0 0 0 eth1
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
default 208.61.124.1 0.0.0.0 UG 0 0 0 ppp0
$ ifconfig
eth0 Link encap:Ethernet HWaddr 00:A0:CC:33:74:EB
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:297581 errors:0 dropped:0 overruns:0 frame:0
TX packets:266104 errors:1 dropped:0 overruns:0 carrier:2
collisions:79 txqueuelen:100
Interrupt:10 Base address:0x1300
eth1 Link encap:Ethernet HWaddr 00:A0:CC:33:8E:84
inet addr:192.168.0.254 Bcast:192.168.0.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:608075 errors:0 dropped:0 overruns:0 frame:0
TX packets:578065 errors:0 dropped:0 overruns:0 carrier:0
collisions:105408 txqueuelen:100
Interrupt:9 Base address:0x1200
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:3924 Metric:1
RX packets:1855 errors:0 dropped:0 overruns:0 frame:0
TX packets:1855 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
ppp0 Link encap:Point-to-Point Protocol
inet addr:208.61.124.28 P-t-P:208.61.124.1 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1
RX packets:297579 errors:0 dropped:0 overruns:0 frame:0
TX packets:266102 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:10
</Screen>
</para>
<Note><title>Note</title>
<Para>
PPPoE adds 8 bytes of extra overhead to the ethernet frames and the correct
initial maximum setting for the ppp0 interface MTU is 1492. If the MTU is
set too high, it may cause a fubar packet fragmentation scenario, known as
the Path MTU Discovery blackhole where the two ends of the connection fail
to communicate. A typical symptom would be the failure of some web pages to
load properly, and possibly other annoying problems. You may need to also
set the MTU for interfaces on any masqueraded LAN connections MTU to 1452.
This does not apply to PPPoA, bridged, or routed configurations, just PPPoE!
See rfc2923 for a technical explanation.
</Para>
</Note>
<Para>
Actually, for PPPoE the real setting should be at least 8 bytes less (the
extra PPPoE protocol overhead) than any interface between you and the
ultimate destination. All routers normally would be set to 1500, thus 1492 is
correct from your end. But, it may happen that somewhere a router is
configured at a lower setting, and this can cause problems, especially
with web pages loading, and other traffic failures. The way to test this is
to keep dropping the MTU until things 'work'.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="pppoa">
<Title>PPPoA</Title>
<Para>
PPPoA (PPPoATM, or PPP over ATM) is a cleaner solution than PPPoE since most
of the work is done in hardware, and since the raw DSL traffic is ATM. There
is no user space client necessary to manage the connection as with PPPoE, and
the additional ethernet protocol layer is not required. Authentication is
still the same: user id and password to connect, but the mechanics are
different since no ethernet encapsulation takes place.
</Para>
<Para>
PPPoA is either done completely in hardware or is implemented as a device
specific driver. There is no such thing as a generic PPPoA software client
like there is for PPPoE. There is an ATM patch for 2.2 kernels, support for
ATM in the 2.4.x kernel, and a project based on the Efficient Networks 3010,
as well as other ATM cards. The ATM on Linux homepage is here: <Ulink
URL="http://linux-atm.sourceforge.net/">
http://linux-atm.sourceforge.net/</Ulink>. And even more info is at <Ulink
URL="http://www.sfgoth.com/~mitch/linux/atm/pppoatm/">
http://www.sfgoth.com/~mitch/linux/atm/pppoatm/</Ulink> from the kernel
developer of this project. Existing PPPoA implementations are hardware/driver
based, and Linux PPPoA modem drivers are scarce as hen's
teeth at this time. The above modem does not seem to be available through
normal retail channels. This may be a problem, if this is the only protocol
an ISP delivers, and an external modem that supports PPPoA is not available.
</Para>
<Para>
If PPPoA is your ISP's only option, you might consider one of the
router/modems that can handle PPPoA connections, and let the hardware handle
everything.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="pptp">
<Title>PPTP/PPPoA with Alcatel Ethernet Modems</Title>
<Para>
Alcatel SpeedTouch Home ethernet modems (supersedes the Alcatel 1000)
support both bridged and PPPoA connections. The modem itself handles the
PPPoA protocol internally. When in PPTP/PPPoA mode (as opposed to RFC1483 bridging
mode), Linux will connect to the modem via PPTP (MS VPN). The Linux PPTP
homepage is <Ulink
URL="http://cag.lcs.mit.edu/~cananian/Projects/PPTP/">http://cag.lcs.mit.edu/~cananian/Projects/PPTP/</Ulink>,
and works well with this modem.
<!--
RPMs can be found as
<Filename>pptp*rpm</FileName> at freshmeat or other download locations.
-->
In addition to installing pptp, your kernel must also have support for PPP.
</Para>
<Para>
The modem has internal configuration pages than can be reached by pointing
a browser to the default IP address of http://10.0.0.138. (You will of course
have to have your NIC set up for a 10.0.0.0 network with similar IP such
as 10.0.0.1, in order to reach the modem's configuration pages.) For PPPoA,
the connection type is 'PPTP'. You will have to get the other settings from
your provider if the defaults do not work. Settings such as 'VPI/VCI' and
'encapsulation' can vary from provider to provider. Of course, if the modem
is coming from your provider, all this should be already configured.
</Para>
<Para>
The next step is to configure <Command>pptp</Command>, which is done by
configuring the <Command>pppd </Command>files
<Filename>/etc/ppp/pap-secrets</FileName> (or
<Filename>chap-secrets</FileName>) and <Filename>/etc/ppp/options</FileName>.
This is where the username and password is entered. For example:
</Para>
<Para>
<Filename>/etc/ppp/pap-secrets</FileName>:
</Para>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
# client secret server IP address
login@isp.com * my_password_here *
</LiteralLayout>
</MSGText>
</Literal>
</Para>
<Para>
and <Filename>/etc/ppp/options</FileName>:
</Para>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
name "login@isp.com"
noauth
noipdefault
defaultroute
</LiteralLayout>
</MSGText>
</Literal>
</Para>
<Para>
Once everything is configured properly, it should be just a matter of
starting pptp, pointing it to the modem's address:
</Para>
<para>
<screen>
#pptp 10.0.0.138
</screen>
</para>
<note><title>Note</title>
<Para>
Alcatel supplies many sub-models of these modems. These features may not be
available on all models, or may be altered from the defaults. This is
something to be aware of, if buying a used modem.
</Para>
<Para>
This modem only supports one concurrent PPTP connection.
</Para>
</note>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="router">
<Title>Modem/Router Configuration</Title>
<Para>
Some ISPs are providing <Quote>routers</Quote> as the connection device.
Essentially these are mini routers with built in modems. These are all
ethernet based devices too, so Linux should be good to go here as well.
Again, a compatible, working NIC should be all that is required to make this
work.
</Para>
<Para>
A <Quote>router</Quote> has many advantages. The better ones can handle the
connection management, IP encapsulation, and authentication, as well as
providing a means of segregating your LAN from outside traffic, and possibly
other features too. In short they can do it all. One big advantage is that
they can handle whatever protocols your ISP requires in order to connect.
</Para>
<Para>
If the ISP is requiring PPPoX, then this makes life a little easier since you
will not have to install or configure any additional software just to use
their network. The modem's firmware will handle this. The downside is that
most of these do not have the flexibility of a Linux router, or other
software solution. Of course, you could set up a Linux router behind the
router, and have the best of both worlds. The ones with more and better
features are also going to cost significantly more.
</Para>
<Para>
While the physical installation of a router is very similar to the modem
installation (see above), the router configuration itself is different
since your first <Quote>hop</Quote> will be the router's interface and not
the ISP's gateway. Routers will actually have two interfaces -- one that you
connect to from the LAN side, and one that connects to your ISP on the WAN
side. Your point of exposure here is the WAN interface of the router.
</Para>
<Para>
The router will also have a pre-configured, private IP address that you will
connect to from the LAN side. This will be your gateway. The public IP
address will be assigned to the WAN side interface. Typically these devices
also act as DHCP servers for the LAN side as well. So possibly all you have
to do is to start a DHCP client such as <Command>dhcpcd</Command> or
<Command>pump</Command> (Redhat based distros) to get up and running. Just
make sure the modem/router is syncing first. The appropriate steps and
configuration should be in the owner's manual, or available from your
provider.
</Para>
<Para>
If you are a PPPoX customer, and the router is handling this part of the
connection, then you will have to configure at least your user id and
password before connecting. If a Bridged/DHCP customer, you should just have
to activate DHCP on the router, and possibly register the MAC (hardware
address) of the router with your provider. Some routers have <Quote>MAC
cloning</Quote> which means that they will report the MAC address of the
attached NIC. If static IP, then you will have to configure this as well.
</Para>
<Para>
If you need to access the router directly, you will need to know the
manufacturer's default setting for its IP address. See the owner's manual, or
ask your provider. You will then have to set your NIC's interface to the same
network as the router. For instance, if the router has an IP of 10.0.0.1, set
your interface's address to 10.0.0.2 (typically eth0), and netmask to
255.0.0.0.
</Para>
<para>
<Screen>
# ifconfig eth0 10.0.0.2 up netmask 255.0.0.0
# route add -net 10.0.0.0
$ ping 10.0.0.1
</Screen>
</para>
<Para>
If everything is in working order, the router should respond to pings. How to
configure this permanently will vary from distro to distro. So check your
distribution's documentation. Now you should be able to ping the
modem/router, and, if all is well, beyond. Then use telnet or a web browser
to do any further configuration of the router.
</Para>
<Para>
Even if the ISP is not offering any router options, there are quite a few
available from third party manufacturers such as Netgear, Linksys, Cisco,
Zyxel, Cayman, Alcatel and others. These will have all the features already
mentioned and maybe more. Just make sure it matches your provider's DSL. This
is one good way around the PPPoX bugaboo.
</Para>
<Caution>
<Para>
Some manufacturers may be marketing these as having <Quote>firewall</Quote>
capabilities. In some cases, this amounts to nothing more than basic NAT
(Network Address Translation or masquerading). Not a full, true firewall by
most measures. Be sure to read the fine print before buying and make sure you
know how much real firewalling is included.
</Para>
</Caution>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="connect">
<Title>Connect</Title>
<Para>
Everything should be in place now. You probably have already tested your
connection. You should be seeing ping roundtrip times of 10-75 ms to the ISP's
gateway. If something has gone wrong, and you cannot connect, either
retrace the above steps, or see the <Link LinkEnd="trouble">Troubleshooting
Section</Link> below.
</Para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="secure">
<Title>Securing Your Connection</Title>
<Para>
This section is intended for those who have not previously dealt with the
security implications of having a full-time Internet connection. Or may not
understand some of the basic concepts of security. This is meant to be just a
quick overview, not a comprehensive examination of all the issues! Just
enough to give you a gentle shove in the right direction. Please see the <Link
LinkEnd="links">Links section</Link> for sites with more details. Also, your
distribution surely has plenty of good information as well.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Security Quick-start</Title>
<Para>
Before going on-line full-time, do not underestimate the need for securing
your connection. You will have two things that mischief makers and crackers
of the world are looking for: bandwidth, and a Unix-like OS. You instantly
become an inviting target. It is just a matter of time before someone
comes knocking. Possibly a very short time. A quick start:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
Turn off any daemons and services that aren't absolutely essential, and
can be accessed from outside. You can't get compromised through a port
that isn't open. Use <Command>ps</Command> and <Command>netstat</Command>
to see what services are running. (See man pages for specifics). Do you
really need <Command>named</Command>, <Command>sendmail</Command>,
<Command>telnet</Command>, <Command>ftp</Command> running and accessible
to one and all? If not sure, then they should not be running. Then take
whatever steps necessary to make sure they don't start again on the next
boot. See your distribution's documentation on this.
</Para>
<Para>
Many distributions start some well known services by default. You may not
have done anything yourself explicitly to start these. And may not even
realize these are indeed running. But it is up to you to know what is
running, and how safe it is. Don't rely on a <Quote>default</Quote>
installation of any distribution to do this for you, or to be secure.
Chances are it isn't.
</Para>
</ListItem>
<ListItem>
<Para>
If you decide some services are essential, make sure you are running the
most current version. Exploits are found, and then get fixed quickly.
Don't get caught with your pants down. A full-time connection makes
staying updated very easy -- and very important. Check with your
distribution to see what new packages are available. Then stay in
touch. If they have a security mailing list, get on it.
</Para>
</ListItem>
<ListItem>
<Para>
Take passwords seriously, using non-dictionary <Quote>words</Quote>. Use
shadow passwords (this should be a standard feature of newer
distributions). Do not allow remote root logins. See the
<Ulink URL="http://www.tldp.org/HOWTO/Security-HOWTO.html">Security
HOWTO</Ulink> for more details and ideas.
</Para>
</ListItem>
<ListItem>
<Para>
Use <Command>ssh</Command> instead of <Command>telnet</Command>
or <command>rsh</command>.
</Para>
</ListItem>
<ListItem>
<Para>
Set up a firewall to limit access, and log connection attempts. This will
be different depending on which kernel series you are using:
<Command>ipfwadm</Command> for 2.0, <Command>ipchains</Command> for 2.2,
and <Command>iptables</Command> for 2.4. See the below HOWTOs for a more
in depth discussion on this and other security related topics:
</Para>
</ListItem>
<ListItem>
<Para>
<ItemizedList>
<listitem>
<para>
<ulink url="http://tldp.org/HOWTO/Security-Quickstart-HOWTO/index.html">Security-Quickstart-HOWTO</ulink>
and for Redhat based distros
<ulink url="http://tldp.org/HOWTO/Security-Quickstart-Redhat-HOWTO/index.html">Security-Quickstart-Redhat-HOWTO</ulink>
</para>
</listitem>
<ListItem>
<Para>
<Ulink
URL="http://www.tldp.org/HOWTO/Firewall-HOWTO.html">Firewall
HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink
URL="http://www.tldp.org/HOWTO/Security-HOWTO.html">Security
HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink
URL="http://www.tldp.org/HOWTO/IPCHAINS-HOWTO.html">IPCHAINS
HOWTO</Ulink>
</Para>
</ListItem>
<listitem>
<para>
<ulink url="http://netfilter.samba.org">Netfilter/Iptables docs</ulink>
</para>
</listitem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/IP-Masquerade-HOWTO.html">IP
Masquerade HOWTO</Ulink>
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
Additional references are in the <Link LinkEnd="links">Links Section</Link>
below.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="tuning">
<Title>Performance Tuning and Troubleshooting</Title>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Tuning</Title>
<Para>
OK, now we are up and running, and we want to be running at warp factor nine.
No such thing as too fast, right?
</Para>
<Para>
Linux networking is pretty robust, even a default installation with no
<Quote>tuning</Quote>. You may well not need to do anything else. But if your
connection is not performing up to what you think it should be, then possibly
there is a problem somewhere. This may be a more worthwhile approach than
the pursuit of any magical <Quote>tweak</Quote>.
</Para>
<Para>
A <Emphasis>very</Emphasis> rough guideline on what you might reasonably
expect as a maximum sync rate, based on distance from DSLAM/CO:
</Para>
<!--
<LiteralLayout>
&nbsp;&nbsp;0-12 K ft &nbsp;(0-3.6 km) &nbsp;&nbsp;- 2000 Kbps or more (8100 max for ADSL)
12-16 K ft (3.6-4.6 km) - 1500 Kbps -&gt; 1000 Kbps
16-18 K ft (4.6-5.4 km) - 1200 Kbps -&gt; 512 Kbps
18-?? K ft (5.4-?? km)&nbsp; - &nbsp;&nbsp;512 Kbps -&gt; &nbsp;128 Kbps or less :(
</LiteralLayout>
-->
<informaltable label="Distances" pgwide="1">
<tgroup cols=2 align="left" colsep=1 rowsep=1>
<colspec colname=c1 align="center" colwidth="40">
<colspec colname=c2 align="center" colwidth="40">
<tbody>
<row>
<entry align="right" colname="c1">
0-12 K ft &nbsp;(0-3.6 km)&nbsp;&nbsp;&nbsp;
</entry>
<entry align="left" colname="c2">
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2000 Kbps or more (8100 max for ADSL)
</entry>
</row>
<row>
<entry align="right" colname="c1">
12-16 K ft (3.6-4.6 km)&nbsp;&nbsp;&nbsp;
</entry>
<entry align="left" colname="c2">
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1500 Kbps to 1000 Kbps
</entry>
</row>
<row>
<entry align="right" colname="c1">
16-18 K ft (4.6-5.4 km)&nbsp;&nbsp;&nbsp;
</entry>
<entry align="left" colname="c2">
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1200 Kbps to 512 Kbps
</entry>
</row>
<row>
<entry align="right" colname="c1">
18-?? K ft (5.4-?? km)&nbsp;&nbsp;&nbsp;
</entry>
<entry align="left" colname="c2">
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;512 Kbps to &nbsp;128 Kbps or less :(
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<Para>
There are many conceivable factors that could effect this one way or the
other. Newer generations of DSL will surely improve this, as will related
technologies like repeaters.
</Para>
<Para>
You will loose 10-20% of the modem's attainable sync rate to networking
overheads (TCP, ATM, ethernet). So a 1500 Kbps connection, is only going to
realize about 1100-1300 Kbps or so of real world throughput. No tweaking is
going to change the built-in protocol overheads. Also, if your
service is capped at a lesser speed by your provider, then you can't get
above that speed no matter what. <Emphasis>AND</Emphasis> -- that there are
numerous variables that can effect your loop/signal quality, and subsequently
your speed (aka sync rate). Some of these may be beyond your control.
</Para>
<para>
But there are a few things that you might want to look at.
</para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>TCP Receive Window</Title>
<Para>
For many of us, a default Linux installation is going to give something close
to optimum performance. Windows 9x users often get a big boost by increasing
their TCP Receive Window (RWIN). But this is because it is too small to start
with. This is just not the case with Linux where the default value is 32KB.
</Para>
<Para>
The exception here is if you have to routinely deal with a high latency
connection. For instance, if your provider has a satellite uplink that is
consistently adding unusual latency (250ms or greater?). Then a larger
TCP Window will likely help. For more on TCP Receive Window and related
issues, look at <Ulink
URL="http://www.psc.edu/networking/perf_tune.html">http://www.psc.edu/networking/perf_tune.html</Ulink>.
</Para>
<Para>
The Receive Window is a buffer that helps control the flow of data. If
set too low, it can be a bottleneck and restrict throughput. The optimum
value for this depends completely on your bandwidth and latency. Latency being
what you would find as average roundtrip time (RTT) based on
<Emphasis>your</Emphasis> typical destinations and conditions. This can be
determined with <Command>ping</Command>. For example, the Linux default of
32KB is acceptable up to speeds of 2 Mbps and a typical latency of 125ms or so,
or 1.0 Mbps and latency of 250ms. Setting this value too high can also
adversely effect throughput, so don't over do it.
</Para>
<Para>
An example courtesy of Juha Saarinen of New Zealand:
</Para>
<Blockquote>
<Para>
The commonly used formula for working out the tcp buffer is the
<Quote>bandwidth delay product</Quote> one:
</para>
<Para>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Buffer size = Bandwidth (bits/s) * RTT (seconds)
</Para>
<Para>
In my case, I have roughly 8Mbps downstream, but the ATM network can only
support ~3.5Mbps sustained. I'm far away from the rest of the world, so to
squeeze in a sufficient amount of 1,500 byte packets, with average RTTs of
250ms, I should probably have a buffer of (3,500,000/8)*.25 = 106KB. (I've
got 128KB at the moment, which works fine.)
</Para>
</Blockquote>
<Para>
The Receive Window can be dynamically set in the /proc filesystem. This
requires entering a value that is twice the desired buffer size:
</Para>
<para>
<screen>
#echo 262144 > /proc/sys/net/core/rmem_default
#echo 262144 > /proc/sys/net/core/rmem_max
</screen>
</para>
<Para>
The above example actually sets the value to 128K. The Send Window can also
be set, but is not as likely to be a limiting factor on DSL connections as
the Receive Window:
</Para>
<para>
<screen>
#echo 262144 > /proc/sys/net/core/wmem_default
#echo 262144 > /proc/sys/net/core/wmem_max
</screen>
</para>
<Para>
These values can also be set using the <Command>sysctl</Command> command. See
the man page.
</Para>
<Para>
Other suggested kernel options for those who want to squeeze every last bit
out of that copper (selected entries only):
</Para>
<para>
<screen>
# sysctl -a
net.ipv4.tcp_rfc1337 = 1
net.ipv4.ip_no_pmtu_disc = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_fack = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_ecn = 0
</screen>
</para>
<para>
A brief description of these, and other, options may be found in
<filename>/usr/src/linux/Documentation/networking/ip-sysctl.txt</filename>,
in the kernel source directory.
</para>
</sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Interleaving</Title>
<Para>
<Quote>Interleaving</Quote> is an error control mechanism of ADSL with DMT
line encoding. DMT is now the standard for ADSL, and is by far and away the
most prevalent form of ADSL. Interleaving buffers the raw data and corrects
errors on the fly at the DSLAM. This can significantly help marginal loops
that may be prone to line errors. The downside is that this buffering also adds
significant latency to the connection. So for those with reasonable quality
lines, interleaving is of no real benefit, and may actually add unnecessary
latency.
</Para>
<Para>
Interleaving is an adjustable parameter and can be turned on or off by the
telco. Many telcos seem to like to have this on by default, since it probably
reduces tech support calls in those cases where it does help stabilize a line.
But everyone else pays a price.
</Para>
<Para>
How to know if your line is interleaved or not, and how to change it? Good
question. Generally speaking, if your first hop or two on a traceroute is
less than 25ms or so, you can pretty much figure that interleaving is off.
But there may be other factors such as how far away those hops actually are.
Unless your modem accurately reports this, the only other real way to know is
to talk to someone at the telco. This may prove easier said than done.
</Para>
<Para>
<Quote>FastPath</Quote> DMT is synonymous with <Quote>interleaving
off</Quote>. Again, this <Emphasis>only</Emphasis> applies to ADSL/DMT.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New section ~~~~~ -->
<sect3 id="bottlenecks">
<title>TCP Bottlenecks</title>
<para>
DSL connections may suffer performance degradations under certain
circumstances. Thankfully, Linux has very robust and flexible networking
tools to help us deal with these.
</para>
<para>
One such common situation is where traffic bottlenecks are created whenever
data from a fast network segment hits a slower one. Such as ethernet hitting
a DSL modem/router. This can cause short term traffic backlogs, known as
<quote>queues</quote> in the device. Queuing can result in degraded
performance, particularly for interactive protocols (like telnet or ssh) and
streaming protocols (like RealAudio), and increased latency for ICMP and
other network protocols. This is most evident when the upstream link is
saturated (since downstream data is queued at the ISP's end and we can't do
as much about that). The queued traffic is processed such that lower volume
traffic protocols (like ssh) often get drowned out so to speak, by the higher
volume, bulk traffic (like http or ftp), as there isn't any special
prioritizing in default usage.
</para>
<para>
And if the upstream queuing, or other factors, causes enough of a delay, it
can even decrease downstream bandwidth utilization by slowing the
ACKnowledgements (which are heading upstream), that are required to keep a
download moving at optimal rates. So it is possible that an upload can hurt
a simultaneous download.
</para>
<!--
<para>
Another effect can occur on asymmetric networks, like some ADSL offerings
where the downstream has significantly greater bandwidth than the upstream.
While both the up and down channels can be used at the same time, the
saturation of both can adversely effect the downstream performance under
some conditions. TCP necessitates a certain amount of back and forth
communication. So that during a download, for instance, there is always a
small percentage of upstream bandwidth being utilized by the downstream
traffic. The greater the downstream bandwidth being utilized, the more
upstream bandwidth is required to maintain the two-way TCP
<quote>conversation</quote>. It can happen that the combined upstream
pressures from both an upload, and a simultaneous download, degrades
performance and results in a reduction of available downstream bandwidth.
This is caused by the ACKnowledgements for the downstream traffic (which are
headed upstream), getting delayed or possibly even lost, on route for a
variety of reasons. The sender will only send as fast as we can tell it to.
If our communications to the sender are impeded, then so is our speed coming
back from the sender. This effect can be more pronounced on highly asymmetric
connections.
</para>
-->
<para>
Such effects can be largely mitigated with Linux's built-in traffic
shaping abilities. The user space tool for manipulating the kernel's
advanced traffic routing features is <application>iproute</application>,
sometimes packaged as <application>iproute2</application>. This includes various
tools that can classify and prioritize traffic with a considerable degree of
flexibility. It also requires various kernel config options to be turned on.
And is also fairly close to Black Magic ;-) The definitive document on this
is the Advanced Routing and Traffic Control HOWTO (<ulink
url="http://tldp.org/HOWTO/Adv-Routing-HOWTO.html">http://tldp.org/HOWTO/Adv-Routing-HOWTO.html</ulink>).
Pay particular attention to the <quote>Cookbook</quote> Section #15, and in
particular #15.8, <quote>The Ultimate Traffic Conditioner: Low Latency, Fast
Up & Downloads</quote>. A great read!
</para>
</sect3>
<!-- ~ End section ~ -->
<!-- ~~~~~ New section ~~~~~ -->
<sect3>
<title>Dropped PPP Connections</title>
<para>
PPPoE and PPPoA both rely on the venerable PPP protocol. This
protocol incorporates the Link Control Protocol (LCP), which is used to
maintain the viability of the connection. Each end can send LCP echoes to other
end, and if there is no response in the alloted time frame, the session is
presumed dead, and is torn down. Again, either end can initiate this process.
The client should then negotiate a new connection. But, this normally means a
new IP address is assigned along with the new session.
</para>
<para>
Perhaps this is undesirable? While you certainly can't control what happens on
the remote end in this regard, you can adjust PPP's very flexible way of
dealing with LCP echoes on your end, to increase the number of echoes, extend
the interval and timeout period on your end. This might help prolong the life
of an unstable connection in situations with marginal line conditions, or a
buggy peer on the other end. Read your client's documentation. YMMV.
</para>
<para>
Some providers may deliberately enforce some time limit. There is not much
you can do about this.
</para>
<para>
Also, frequently dropped connections are often an indication of a line
problem of some kind. This is something the telco should investigate.
</para>
</sect3>
<!-- ~ End section ~ -->
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="trouble">
<Title>Installation Problems</Title>
<Para>
Read this section, if you have no sync at all or are completely unable to
connect. See your modem's owner's manual for interpreting the modem's LEDs.
(Many will show a solid red (or orange) light if not in sync.)
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="nosync">
<Title>No sync</Title>
<Para>
The modem sync LED has never been green.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
If doing a self-install, the DSL jack may be wired wrong, or the splitter
may be wired wrong. Also, the modem may be wired differently than standard
telco devices. See above.
</Para>
</ListItem>
<ListItem>
<Para>
Is the modem Linux compatible? If ethernet interfaced, this should not be
a problem. But PCI or USB modems may require drivers just to achieve sync.
This could be a show stopper since many PCI and USB modems are not
Linux compatible.
</Para>
</ListItem>
<ListItem>
<Para>
Call your provider and make sure the line was provisioned. It is always
possible someone dropped the ball. They may even be able to run a remote
test on your line just to verify. There is a also remote possibility that
the DSLAM is down. They should know this as well.
</Para>
</ListItem>
<ListItem>
<Para>
Disconnect the modem power cord and disconnect the DSL cord from the wall
jack. Plug it into the test jack inside the NID (outside phone box), and
run an extension cord if necessary for power. Temporarily disconnect the
wiring to the inside phone circuit. This should effectively bypass any
inside wiring and environmental issues. The ethernet cable to the NIC does
not need to be connected to run this test (true <Emphasis>only</Emphasis>
for ethernet modems). The modem will sync fine without it. (Easier said
than done, I know.) But if possible, move enough of your system where you
can view the modem's diagnostics (if available) and get the sync rate. If
this works, there is probably something wired incorrectly inside, or a
short in a connection somewhere, or there is severe electrical
interference on the DSL line. Double check the splitter and wall jack
connections. If a splitterless installation, look for bad wiring, bad
(e.g. corroded) connections on <Emphasis>all</Emphasis> jacks, bad
splices, or defective microfilters!
</Para>
<Para>
If no sync on the above test, either the line was not readied, the
modem is defective, or the DSLAM is down. Note that PCI and USB
modems will need to load drivers before syncing, and thus make
this test a little more complicated.
</Para>
</ListItem>
<ListItem>
<Para>
If you installed microfilters, remove these temporarily and unplug
<Emphasis>all</Emphasis> telco devices, such as fax machines, etc. Possibly
a mircofilter is defective and shorting out the line.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Network Card (NIC) Problems</Title>
<Para>
Symptoms here are: NIC is not recognized, modules won't load, or
<Command>ifconfig</Command> shows the interface is not up, or is generating
lots of errors, etc.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
Turn off Plug 'n Pray in BIOS. This may be labeled as <Quote>non-Microsoft
OS</Quote> or similar. A sometimes symptom here is that the NIC is
assigned IRQ 0. Or there may be an error message like <Quote>resource
temporarily unavailable</Quote>.
</Para>
</ListItem>
<ListItem>
<Para>
Check for IRQ conflicts with <Command>cat /proc/interrupts</Command>. If
the NIC is sharing an IRQ, try moving cards around in slots, or tinker
with BIOS IRQ settings. If an ISA card, you may need to get the setup
utility from the manufacturer and use it to set IRQ, etc. This may
require booting to DOS. Modern systems should theoretically be
able to handle IRQ sharing, so it is not necessarily a problem in and of
itself. Only if something is misbehaving.
</Para>
</ListItem>
<ListItem>
<Para>
Possibly the wrong module is being loaded. Look through the kernel source
documentation in <Filename>/usr/src/linux/Documentation/*</FileName> for
your card or chipset. Also, for comments and update information in
<Filename>/usr/src/linux/drivers/net/*.c</FileName> for your respective
chipset. It is worth noting that there is more than one module for some
card types. This seems to be true of tulip and 3Com cards. Check boot
messages or use <Command>lspci -v</Command> to see how the kernel is
identifying your card. You can use <Command>insmod</Command>,
<Command>rmmod</Command>, and <Command>modprobe</Command> to test
different modules. See the respective man pages for more information.
</Para>
</ListItem>
<ListItem>
<Para>
Check the manufacturer's web site for Linux documentation. Or look at
Donald Becker's informative site at <Ulink
URL="http://www.scyld.com/network/">http://www.scyld.com/network/</Ulink>.
</Para>
</ListItem>
<ListItem>
<Para>
Some Linux NIC drivers reportedly work better as non-modular. In other
words, compile them into the kernel instead of as a module.
</Para>
</ListItem>
<ListItem>
<Para>
It is also possible that the card is bad, or the drivers just aren't up to
snuff. Try another card. And you don't need an expensive, high quality
card necessarily either.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>IP Connection Problems</Title>
<Para>
Read this section if you are sure the modem is syncing, the NIC is recognized
and seems to be working properly, client software is installed and running
without error, but the connection to the ISP fails. Verify the modem is indeed
syncing by the LED(s). An IP connection failure may be evidenced by
<Command>ifconfig</Command> not showing an active eth0 interface (or ppp0 for
PPPoX), or <Command>pinging</Command> gateway and other destinations
generates '<Literal>network unreachable</Literal>' or similar errors.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
Make sure you know which protocol your ISP is using. Are they using DHCP?
PPPoX? It is critical that you have this right. You may have to ask tech
support.
</Para>
</ListItem>
<ListItem>
<Para>
If you are using DHCP, does the ISP require MAC address authentication,
and if so, do they have the right address? Did they or you typo it? If
the ISP requires hostname authentication, is your DHCP client passing
the required hostname? This is done with the <Quote>- h</Quote> command
line option.
</Para>
</ListItem>
<ListItem>
<Para>
Look at <Filename>/var/log/messages</FileName> and see if any useful clues
are there. Also, run <Command>tcpdump</Command> while trying to initiate
the connection. <Command>tcpdump</Command> output is fairly cryptic, but
you should be able to determine if there is any response at all.
</Para>
</ListItem>
<ListItem>
<Para>
If PPPoX, is the ISP using <Literal>username</Literal> as an id, or
<Literal>username@isp.com</Literal>?
</Para>
</ListItem>
<listitem>
<para>
CHAP, PAP, or other? I would set up both CHAP and PAP (see
<command>man pppd</command>) just to be safe.
</para>
</listitem>
<ListItem>
<Para>
Try pinging the default gateway's address. Get this with '<Command>route
-n</Command>'. If you can <Command>ping</Command> by IP address (i.e.
111.222.333.444), but not by hostname, then likely nameservers are not
correctly setup in <Filename>/etc/resolv.conf</FileName>. This is
configurable as to whether your connection protocol (e.g. PPPoE) does this
automatically or not. And different distributions may have their own
way of setting this up, so check their documentation first. In a pinch,
just add them manually to <filename>/etc/resolv.conf</filename>.
<command>pppd</command> also has the <quote>usepeerdns</quote> option
that can be enabled.
</Para>
</ListItem>
<ListItem>
<Para>
For <application>rp-pppoe</application>, let the PPPoE client bring up the ethernet interface. Do not
have it come up on boot. Make sure there is no existing default route
before starting PPPoE. For rp-pppoe, David Skoll recommends that
<Filename>/etc/ppp/options</FileName> be left empty.
</Para>
</ListItem>
<ListItem>
<Para>
If running a firewall (e.g. with <application>ipchains</application>), try
temporarily taking it down. Possibly this is misconfigured, and not
allowing packets through.
</Para>
</ListItem>
<listitem>
<para>
Roaring Penguin has a very nice debug output with all kinds of
system info, and even tips for correcting problems. See the docs
for turning this well-done feature on.
</para>
</listitem>
<ListItem>
<Para>
If the modem was purchased from a source other than your ISP, it may the
wrong kind of modem. SDSL needs an SDSL modem, for instance. Also, for
ADSL there are CAP and DMT encodings, and these are incompatible with
each other.
</Para>
<Para>
The modem may need to be configured for your ISP's service. All modems
have configurations for VCI, VPI, encapsulation, etc. Call tech support
for this information. Modem configuration is usually done by either
telnetting or web browsing to the modem's IP address.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="synctr">
<Title>Sync Problems</Title>
<Para>
Read this section if you have had a working connection, but now have lost
sync, are intermittently losing sync, your sync rate has dropped
significantly, or are getting a <Quote>sync/no surf</Quote> condition.
(Better quality modems will have a way to report sync rate, usually via
telnet or a web browser interface. See the owner's manual.)
</Para>
<Para>
A loss of sync indicates a problem with the DSLAM, your line (inside or
outside) or your modem. DSLAMs typically have <Quote>shelves</Quote> with
<Quote>cards</Quote>. Alcatel DSLAM cards, just for instance, have a capacity
of four connections each. If the card goes bad, at most four customers are
effected. The point being that sync loss outages can be very isolated. Unlike
network outages that tend to effect large numbers of users. Sync outages are
a telco problem, not an ISP problem. If your service agreement is with the
ISP, you will need to contact them, who will in turn contact the telco.
</Para>
<Para>
Degraded sync rates, and disruption of the DSL signal, can cause various
problems. Obviously, you will never get your maximum throughput under these
conditions. But, the symptoms are not always obvious as to whether the
problem is on your end or the provider's.
</Para>
<Para>
For instance, a poor inside wire connection may result in retransmissions of
packets that have been dropped. This can really reduce throughput and slow a
connection down. It is tempting to think of packet loss as a traditional
networking problem, but with DSL it is possible to be the result of a bad
line, impaired signal, or even the modem itself.
</Para>
<Para>
Some things to try:
<ItemizedList>
<ListItem>
<Para>
Power cycle the modem. Turn off the power button/switch, and physically
unplug the cable to the wall jack for 30 seconds or so. Turn back on, and
re-attach to the wall jack. This will force a resync. Unfortunately, the only
way to power down a PCI modem, is to reboot. This may fix a
<Quote>sync/no surf</Quote> condition that is caused by the modem, and
maybe other conditions too.
</Para>
</ListItem>
<ListItem>
<Para>
See the <Link LinkEnd="nosync">above section</Link> on moving the modem
lock, stock and barrel to the NID and thus bypassing all inside wiring.
If the situation is improved there, then the problem is inside somewhere. If
not, it is a telco problem.
</Para>
</ListItem>
<ListItem>
<Para>
RFI Bear-hunt: The DSL signal is fragile. There are a number of
things that can degrade it. RFI, or Radio Frequency Interference,
from sources in and around the home/office is one common source of
reduced signal strength, intermittent sync loss, low
sync rates and high line error rates that can cause retransmissions and
slow things down. DSL frequencies just happen to be in a range that is
susceptible to many potential RFI sources. Our test tool here is simply a
portable AM radio. Tune it to any channel where you can get clear reception
-- it makes no difference where. The AM radio will pick up RFI that is in
the same frequency range as the DSL signal. It will sound like
<Quote>frying bacon</Quote> type static. Put it against your computer's
power supply. You should hear some static. Move it away and the static
should fade pretty quickly. This will give you an idea of what RFI sounds
like. A decent quality power supply should produce only weak RFI --
probably not enough to cause a problem. Use the radio like a Geiger counter
and move it around your modem and DSL line. If you hear static, follow it
to the source. Things to be suspicious of: power supplies, transformers,
ballasts, electric motors, dimmer switches, high intensity lighting. Moving
the modem, or rerouting cables is sometimes enough. Keeping the line
between the modem and the wall jack as short as possible is a good idea
too.
</Para>
</ListItem>
<ListItem>
<Para>
Chronic sync problems are often due to a line problem somewhere.
Sometimes it is something as simple as a bad splice or corroded jack, and
easily remedied if it can be found. Most such conditions can be isolated
by a good telco tech. Check with your provider, and politely harass them
if you have to. If you get the run-around, ask to go over their heads.
</Para>
</ListItem>
<ListItem>
<Para>
If you are near the distance limits of DSL, and having off and on sync
problems, try the <Quote>Homerun</Quote> installation. See <Link
LinkEnd="homerun">above</Link>. This can be effective in improving
marginal signal/sync conditions.
</Para>
</ListItem>
<ListItem>
<Para>
If using a surge protector, try it without the surge protector. Some may
interfere with the DSL signal.
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
Another possibility is a nearby AM radio station, or bandit ham radio
operator that are disrupting the DSL signal since they operate in a similar
frequency range. These may only cause problems at certain times of day, like
when the station boosts its signal at night. A good telco DSL tech may be
able to help minimize the impact of this. YMMV.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Network and Throughput Problems</Title>
<Para>
Read this section if your connection is up, but are having throughput
problems. In other words, your speed isn't what it should be based on your
bit rate plan, and your distance from the CO. <Quote>Network</Quote> here is
the WAN -- the ISP's gateway and local subnet/backbone, etc. Remember that a
marginal line can cause a reduced sync rate, and this will impact throughput.
See <Link LinkEnd="synctr">above</Link>.
</Para>
<Para>
The two factors we will be looking for are <Quote>latency</Quote> and
<Quote>packet loss</Quote>. Both are pretty easy to track down with the
standard networking tools <Command>ping</Command> and
<Command>traceroute</Command>. If either of these occur in our path, they
will impact performance. Latency means <Quote>responsiveness</Quote> or
<Quote>lag time</Quote>. Actually what we are interested in is abnormally
high latency, since there is always some latency. Packet loss is when a
packet of data gets dropped somewhere along the way. TCP/IP will know
it's been <Quote>lost</Quote>, and there will be a retransmission of the lost
data. Enough of this can really slow things down. Ideally packet loss should
be 0%.
</Para>
<Para>
What we really need to be concerned about is that part of the WAN
route that we routinely traverse. If you do a traceroute to several different
sites, you will probably see that the first few <Quote>hops</Quote> tend to
be the same. These are your ISP's local backbone, and your ISP's upstream
provider's gateway. Any problem with any of this, and it will effect
everywhere you go and everything you do.
</Para>
<Para>
We can start looking for packet loss and latency by pinging two or three
different sites, hopefully in at least a couple of different directions. We
will be looking for packet loss and/or unusually high latency.
</Para>
<para>
<Screen>
$ ping -c 12 -n www.tldp.org
PING www.tldp.org (152.19.254.81) : 56(84) bytes of data.
64 bytes from 152.19.254.81: icmp_seq=0 ttl=242 time=62.1 ms
64 bytes from 152.19.254.81: icmp_seq=1 ttl=242 time=60.8 ms
64 bytes from 152.19.254.81: icmp_seq=2 ttl=242 time=59.9 ms
64 bytes from 152.19.254.81: icmp_seq=3 ttl=242 time=61.8 ms
64 bytes from 152.19.254.81: icmp_seq=4 ttl=242 time=64.1 ms
64 bytes from 152.19.254.81: icmp_seq=5 ttl=242 time=62.8 ms
64 bytes from 152.19.254.81: icmp_seq=6 ttl=242 time=62.6 ms
64 bytes from 152.19.254.81: icmp_seq=7 ttl=242 time=60.3 ms
64 bytes from 152.19.254.81: icmp_seq=8 ttl=242 time=61.1 ms
64 bytes from 152.19.254.81: icmp_seq=9 ttl=242 time=60.9 ms
64 bytes from 152.19.254.81: icmp_seq=10 ttl=242 time=62.4 ms
64 bytes from 152.19.254.81: icmp_seq=11 ttl=242 time=63.0 ms
--- www.tldp.org ping statistics ---
12 packets transmitted, 12 packets received, 0% packet loss
round-trip min/avg/max = 59.9/61.8/64.1 ms
</Screen>
</para>
<Para>
The above example is pretty normal from here. (You probably have a very
different route to this site, and your results may thus be quite different.)
Apparently no serious underlying problems that would slow me down. The below
example reveals a problem:
</Para>
<para>
<Screen>
$ ping -c 20 -n www.debian.org
PING www.debian.org (198.186.203.20) : 56(84) bytes of data.
64 bytes from 198.186.203.20: icmp_seq=0 ttl=241 time=404.9 ms
64 bytes from 198.186.203.20: icmp_seq=1 ttl=241 time=394.9 ms
64 bytes from 198.186.203.20: icmp_seq=2 ttl=241 time=402.1 ms
64 bytes from 198.186.203.20: icmp_seq=4 ttl=241 time=2870.3 ms
64 bytes from 198.186.203.20: icmp_seq=7 ttl=241 time=126.9 ms
64 bytes from 198.186.203.20: icmp_seq=12 ttl=241 time=88.3 ms
64 bytes from 198.186.203.20: icmp_seq=13 ttl=241 time=87.9 ms
64 bytes from 198.186.203.20: icmp_seq=14 ttl=241 time=87.7 ms
64 bytes from 198.186.203.20: icmp_seq=15 ttl=241 time=85.0 ms
64 bytes from 198.186.203.20: icmp_seq=16 ttl=241 time=84.5 ms
64 bytes from 198.186.203.20: icmp_seq=17 ttl=241 time=90.7 ms
64 bytes from 198.186.203.20: icmp_seq=18 ttl=241 time=87.3 ms
64 bytes from 198.186.203.20: icmp_seq=19 ttl=241 time=87.6 ms
--- www.debian.org ping statistics ---
20 packets transmitted, 13 packets received, 35% packet loss
round-trip min/avg/max = 84.5/376.7/2870.3 ms
</Screen>
</para>
<Para>
High packet loss at 35%, and some really slow roundtrip times in there as
well. A little digging on this showed that it was a backbone router 13 hops
into the traceroute that was the problem. While making this site really slow
from here, it would only effect those routes that happen to hit that same
router. Now what would really hurt us is if something similar happens with a
router that we tend to go through consistently. Like our gateway, or maybe
the second hop router too. Find these with <Command>traceroute</Command>, by
just picking a random site:
</Para>
<para>
<Screen>
$ traceroute www.bellsouth.net
traceroute to bellsouth.net (192.223.22.134), 30 hops max, 38 byte packets
1 adsl-78-196-1.sdf.bellsouth.net (216.78.196.1) 14.86ms 7.96ms 12.59ms
2 205.152.133.65 (205.152.133.65) 7.90ms 8.12ms 7.73ms
3 205.152.133.248 (205.152.133.248) 8.99ms 8.52ms 8.17ms
4 Hssi4-1-0.GW1.IND1.ALTER.NET (157.130.100.153) 11.36ms 11.48ms 11.72ms
5 125.ATM3-0.XR2.CHI4.ALTER.NET (146.188.208.106) 14.46ms 14.23ms 14.40ms
6 194.at-1-0-0.TR2.CHI2.ALTER.NET (152.63.65.66) 16.48ms 15.69ms 16.37ms
7 126.at-5-1-0.TR2.ATL5.ALTER.NET (152.63.0.213) 65.66ms 66.18ms 66.39ms
8 296.ATM6-0.XR2.ATL1.ALTER.NET (152.63.81.37) 66.86ms 66.42ms 66.40ms
9 194.ATM8-0.GW1.ATL3.ALTER.NET (146.188.233.53) 67.87ms 68.69ms 69.63ms
10 IMVI-gw.customer.ALTER.NET (157.130.69.202) 69.88ms 69.25ms 69.35ms
11 www.bellsouth.net (192.223.22.134) 68.74ms 69.06ms 68.05ms
</Screen>
</para>
<Para>
The first hop is the gateway. In fact, for me the first two hops are
<Emphasis>always</Emphasis> the same, and the first three or four are often
the same. So a problem with any of these may cause a problem anywhere I go.
(The specifics of your own situation may be a little different than this
example.) A <Quote>normal</Quote> gateway ping (normal for me!):
</Para>
<para>
<Screen>
$ ping -c 12 -n 216.78.196.1
PING 216.78.196.1 (216.78.196.1) : 56(84) bytes of data.
64 bytes from 216.78.196.1: icmp_seq=0 ttl=64 time=14.6 ms
64 bytes from 216.78.196.1: icmp_seq=1 ttl=64 time=15.4 ms
64 bytes from 216.78.196.1: icmp_seq=2 ttl=64 time=15.0 ms
64 bytes from 216.78.196.1: icmp_seq=3 ttl=64 time=15.2 ms
64 bytes from 216.78.196.1: icmp_seq=4 ttl=64 time=14.9 ms
64 bytes from 216.78.196.1: icmp_seq=5 ttl=64 time=15.3 ms
64 bytes from 216.78.196.1: icmp_seq=6 ttl=64 time=15.4 ms
64 bytes from 216.78.196.1: icmp_seq=7 ttl=64 time=15.0 ms
64 bytes from 216.78.196.1: icmp_seq=8 ttl=64 time=14.7 ms
64 bytes from 216.78.196.1: icmp_seq=9 ttl=64 time=14.9 ms
64 bytes from 216.78.196.1: icmp_seq=10 ttl=64 time=16.2 ms
64 bytes from 216.78.196.1: icmp_seq=11 ttl=64 time=14.8 ms
--- 216.78.196.1 ping statistics ---
12 packets transmitted, 12 packets received, 0% packet loss
round-trip min/avg/max = 14.6/15.1/16.2 ms
</Screen>
</para>
<Para>
And a problem with the same gateway on a different day:
</Para>
<para>
<Screen>
$ ping -c 12 -n 216.78.196.1
PING 216.78.196.1 (216.78.196.1) : 56(84) bytes of data.
64 bytes from 216.78.196.1: icmp_seq=0 ttl=64 time=20.5 ms
64 bytes from 216.78.196.1: icmp_seq=3 ttl=64 time=22.0 ms
64 bytes from 216.78.196.1: icmp_seq=4 ttl=64 time=21.8 ms
64 bytes from 216.78.196.1: icmp_seq=6 ttl=64 time=32.0 ms
64 bytes from 216.78.196.1: icmp_seq=8 ttl=64 time=21.7 ms
64 bytes from 216.78.196.1: icmp_seq=9 ttl=64 time=42.0 ms
64 bytes from 216.78.196.1: icmp_seq=10 ttl=64 time=26.8 ms
--- adsl-78-196-1.sdf.bellsouth.net ping statistics ---
12 packets transmitted, 7 packets received, 41% packet loss
round-trip min/avg/max = 20.5/25.6/42.0 ms
</Screen>
</para>
<Para>
41% packet loss is very high, to the point where many services, like HTTP,
come to a screeching halt. Those services that were working, were working
very, very slowly.
</Para>
<Para>
It's a little tempting on this last real-life example to think this gateway
router is acting up. But, as it turned out, this was the result of a problem
in the DSLAM/ATM segment of the telco's network. So any first hop problem
with packet loss or high latency, may actually be the result of something
occurring before the first hop. We just don't have the tools to isolate
where it is starting well enough. Packet loss can be a telco problem, just as
much as an ISP/NSP problem. Or conceivably, even a modem problem. In which
case try resetting the modem by power cycling <emphasis>and</emphasis> by
unplugging/replugging the DSL cable (from the wall jack).
</Para>
<Para>
It is also quite possible for the modem itself to cause packet loss. The fix
here is to power cycle the modem, and resync by unplugging the DSL connection
for 30 seconds or so. In fact, any part of the connection can be a source of
packet loss -- modem, DSLAM, ATM network, etc.
</Para>
<Para>
If you do find a problem within your ISP's network, it's time to report the
problem to tech support.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Miscellaneous Network Problems</Title>
<Para>
Some odds and ends:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Emphasis>Some Web pages won't load.</Emphasis> For PPPoX users, the
MTU value could be too high. This will cause packet fragmentation,
and likely will cause misbehaving routers to fail to route your
requests per Path MTU Discovery specs.The correct ppp0 device setting
should be a maximum of 1492, but actually it needs to be 8 bytes less
than any router you pass through on the way to the site. If a router
somewhere is misconfigured, you could have problems. Try experimenting
with lower MTU values. Any LAN hosts behind the connection, may even need
to be even lower -- 1452 or maybe even 1412. If ECN is enabled, it might
also cause this problem. Cured with <quote>echo 0 > cat
/proc/sys/net/ipv4/tcp_ecn</quote>.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Ping by IP address</Emphasis> works, but not hostname. The
nameservers are not being setup correctly in
<Filename>/etc/resolv.conf</FileName>. Check your client's (DHCP, PPPoX)
documentation or enter these manually with a text editor. Get the
correct DNS server addresses from your ISP.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>PPPoX disconnects</Emphasis>. Unfortunately, PPPoX
is more likely to drop connections than routed or bridged networks. PPP
can be sensitive to any line condition which results in a temporary
interruption of the connection. This may not be completely solvable,
depending on what and where the problem is. Check your client's docs for
<quote>LCP Keepalive</quote> features. There generally is a timeout on
each end of the connection if the other end does not respond. If worse
comes to worse, set up a cron job to watch the connection, and
re-establish if necessary.
</Para>
<para>
Some providers may also be enforcing idle timeout disconnects. This is
a different issue altogether, since it is deliberate. The solution here is to
switch providers if you can.
</para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Interface or route goes down for no reason</Emphasis>. If
<Command>ifconfig</Command> and/or <Command>route</Command> show the
interface and/or route has automagically disappeared, it may be due to
a buggy NIC driver.
</Para>
</ListItem>
<ListItem>
<Para>
Sub-par performance, or errors with the interface (e.g. eth0), may
possibly be caused by a duplex mismatch. This would be most apparent when
maxing out the connection. Most DSL modems and routers typically are set
to half duplex, and your NIC that interfaces with the modem should be set
likewise.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="throughput">
<Title>Measuring Throughput</Title>
<Para>
One of the first things most of us do is check our speeds to make sure we
aren't getting short changed, and that our system is up to snuff. Doing this
accurately is easier said than done however. First, remember you are losing
10-20% right off the top due to networking protocol overhead. Just how much
is <Quote>lost</Quote> here depends on your provider's network architecture,
where and how you are measuring this and other considerations. Most of us may
wind up being closer to 20% than 10%.
</Para>
<Para>
Then, any time you hit the Internet, there is some slight degradation of
performance with each hop you take. Now this may not amount to much, as long
as you are not taking too many hops and all the components -- your system,
your ISP's network, your ISP's upstream provider, and the destination itself
-- are all working like well oiled machines. But there's the rub -- how do
you really know with so many variables in the mix? One flaky interface, on
one router, on one hop along the path, may cause misleading results.
</Para>
<Para>
Your absolute max speed is going to be at your point of connection to your
ISP -- the ISP's gateway. It can only go downhill from there, not up! So the
ideal test is as close to home as possible. This eliminates as many unknown
variables as possible. If your ISP has a local ftp server, this is an
excellent place to run your own tests. (Run a traceroute though just to see
how local it really is.)
</Para>
<Para>
If your ISP does not have this, look for an ftp site that is close -- the
fewer the hops, the better. And look for one that isn't too busy, or you will
get misleading results. Find a large file -- like 10 Megs -- and time the
download. Try this over several days, and at different times of day. The
server, and the backbone, are going to be busier at certain times of day,
which can skew results and you want to eliminate these variables as much as
possible. Your provider cannot compensate for heavy backbone traffic,
backbone bottlenecks, slow or busy servers, etc.
</Para>
<Para>
There are many test sites scattered around the web. Some are better than
others, but take these with a grain of salt. There are just too many
variables for these tests to reliably give you an accurate snapshot of your
connection and throughput. They may give you a general picture of whether you
are in the ballpark of where you think you should be or not. One good speed
test is <Ulink
URL="http://www.dslreports.com/stest/0">http://www.dslreports.com/stest/0</Ulink>.
Another test is <Ulink
URL="http://speedtest.mybc.com/">http://speedtest.mybc.com/</Ulink> (both are
Java). I find these to be better than some of the others out there.
</Para>
<Para>
Now keeping in mind that we are limited by the ~10-20% networking overhead rule,
here is an example. My speed is capped at 1472 Kbps sync rate. Minus the ~15%
is 1275 Kbps. My sync rate is known to be good and my distance to the CO is
about 11,000 Ft, which is close enough that I should be able to hit my real
world maximum throughput of 1275 Kbps or roughly 1.2-1.3 Mbps -- all other
things being equal. From dslreports.com speed test:
</Para>
<para>
<Screen>
Test running..Downloaded 60900bytes in 5918ms
Downloaded 696000bytes in 4914ms
First guess is 1133kbps
fairly fast line - now test 2mb
Downloaded 1679100bytes in 11090ms
Upload got ok 1 bytes uploaded
Uploaded 1bytes in 211ms
Upload got ok 1 bytes uploaded
Uploaded 1bytes in 205ms
Upload got ok 1 bytes uploaded
Uploaded 1bytes in 207ms
Upload got ok 50000 bytes uploaded
Uploaded 50000bytes in 2065ms
Upload got ok 100000 bytes uploaded
Uploaded 100000bytes in 3911ms
** Speed 1211(down)/215(up) kbps **
(At least 24 times faster than a 56k modem)
Finish.
</Screen>
</para>
<Para>
1.211 Mbps is probably about as good as I can realistically expect based on
my service. There is no reason for me to go troubleshooting or looking for
tweaks.
</Para>
<Para>
<Emphasis>Big Caution</Emphasis>: my ISP uses a caching proxy server for
web pages. This is a big equalizer for these kinds of web based
tests. Without that, I surely would have been significantly slower on this
test. The effect of the proxy is that you are actually testing throughput
from the proxy -- NOT the test site. Just FYI. Another note: at the same time
I tried another test site and was consistently getting 600-700 Kbps. So YMMV
with these tests. (Usually I get the same on each, more or less.) Timing a
large ftp download from two different sites, I calculated about 1.25 Mbps.
</Para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="overview">
<Title>Appendix: DSL Overview</Title>
<Para>
DSL is a telephone loop technology that uses existing copper phones lines,
and provides a dedicated, high speed Internet connection. One of the big
advantages of some DSLs (notably ADSL), are that they can co-exist on the
same line with a traditional voice service such as <Quote>POTS</Quote> (Plain
Old Telephone Service), and even ISDN. This is accomplished by utilizing
different frequency ranges above the voice range (voice is up to 4KHz).
Essentially, this gives two lines in one: one for voice, and one for Internet
connectivity. When all is working normally, there should be no interference
between the two <Quote>lines</Quote>. This gives DSL a potentially broad
consumer base, and helps minimize costs for service providers.
</Para>
<Para>
DSL is positioned for the Home and Small Office (SOHO) market that is
looking for high speed Internet access at reasonable prices. Since it also
typically provides dedicated, <Quote>always on</Quote> access, it can be used
for interconnecting low to mid range bandwidth servers, and provides a great
access solution for small LANs. It is also great for those Linux power users
that just want a fat pipe :-).
</Para>
<Para>
Phone companies, and other independent telecommunications providers (CLECs),
are now deploying DSL to stay ahead of the Cable
companies -- the main consumer and SOHO competition for DSL providers. This
mad rush to get <Quote>a piece of the pie</Quote>, is bringing much
competition (a good thing!), much diversity, and some confusion, into the
consumer market. The DSL provider (often, but not always, the phone company)
will provide the DSL infrastructure. This would include your line, the DSLAM,
and physical connection to the outside world. From there it is typically
picked up by an ISP, who provides the traditional Internet services.
</Para>
<Para>
Consumer DSL plans are typically <Quote>best effort</Quote> services. While
boasting speeds approaching T1, and even surpassing that in some cases, it is
not necessarily as reliable as T1 however. Business class DSL offers more
reliability at a higher cost than consumer plans, and is a good compromise
where both reliability and bandwidth are at a premium. All in all, the cost
of DSL compared to traditional telco services, such as T1, is attractive and
substantially more affordable for home and small business users.
</Para>
<Para>
DSL providers often do not have service contracts for home users,
while business class DSL services typically do include similar SLAs (Service
Level Agreements) to that offered for a T1 line.
</Para>
<Para>
The downside is that DSL is not available everywhere. Availability, and
available bit rate (speed), are purely a function of where you live, where
the telco has installed the prerequisite hardware, how far you are from the
DSLAM/CO, and the quality of your phone line (loop). Not all loops are
created equal, unfortunately. The primary limitation is distance.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="family">
<Title>The DSL Family</Title>
<Para>
<ItemizedList>
<ListItem>
<BridgeHead renderas=sect3>ADSL</BridgeHead>
<Para>
Asymmetric Digital Subscriber Loop currently supports downstream rates up
to 8 Mbps, and upstream of 1024 Kbps, hence the <Quote>asymmetric</Quote>.
ADSL is far and away the most widely deployed consumer DSL, and was
specifically developed for the home and SOHO markets. The higher downstream
rates lends itself to those not running serious servers -- at least
anything more than a small, personal web site. ADSL is capable of sharing
data with a POTS (or ISDN) voice line, so an additional line is not
required. A big selling point. ADSL, like other DSLs, is limited by
distance. 18,000 ft (5.5 km) is a typical cut-off point for telcos. ADSL
does typically require either a splitter or filters to isolate the DSL
signal from POTS. Sometimes referred to as <Quote>full rate</Quote> ADSL in
order to differentiate it from G.Lite DSL. There are two line encodings for
ADSL: DMT and CAP. DMT (a.k.a. Alcatel compatible) has won the standards
battle and is now the standard and the most common. Also, note that modems
must be compatible with the encoding. In other words, a CAP modem will not
work with a DMT service, and vice versa. Also, ISDN requires
<quote>modems</quote> (NTs), and related hardware such as filters, that are
specific to that type of line since the signal on the line is very
different for POTS and ISDN.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>G.Lite</BridgeHead>
<Para>
G.Lite is sometimes referred to as <Quote>DSL Lite</Quote>,
<Quote>Universal DSL</Quote> or <Quote>splitterless ADSL</Quote>, is a
slower version of ADSL that requires no splitters <Emphasis>or</Emphasis>
filters. G.lite uses a <Quote>fast retrain</Quote> technique to negate the
various signal disturbances caused by normal POTS usage. Currently G.Lite
supports speeds up to 1.5 Mbps/512 Kbps, and at one time was expected to
become the dominant consumer DSL service. As of this writing, it is not
nearly as wide spread as <Quote>full rate</Quote> ADSL however.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>SDSL</BridgeHead>
<Para>
Single-pair Digital Subscriber Loop, or also sometimes referred to
as <Quote>Symmetric Digital Subscriber Loop</Quote> since it is indeed
symmetric with a current maximum rate of 1.5 Mbps/1.5 Mbps. SDSL requires a
dedicated line, and thus true SDSL is not as readily adaptable to the
consumer market as ADSL. SDSL also uses a 2B1Q encoding (same as ISDN and
some T1) which is considered more robust than the DMT or CAP encoding of
ADSL. True SDSL is generally considered more of a server quality DSL, and
is typically marketed as a business class service. It is worth noting that
some providers may be promoting a <Quote>SDSL</Quote> service that is
really ADSL pinched so that upstream/downstream are the same. Or vice
versa, SDSL with asymmetrically allocated bandwidth. Wasn't all this
confusing enough already?
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>IDSL</BridgeHead>
<Para>
ISDN Digital Subscriber Loop, 144 Kbps/144 Kbps is really a new and
improved ISDN from Lucent Technologies and uses the same 2B1Q line encoding
as ISDN, SDSL and others. IDSL does require a dedicated line however. The
benefits are that it is an <Quote>always on</Quote> technology, like other
DSLs, and provides an additional 16 Kbps over traditional ISDN. It is being
marketed by some DSL providers as a low end bit rate option, where line
quality is not sufficient for higher speeds such as that of ADSL.
Ironically, IDSL is generally priced significantly higher than ADSL.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>RADSL</BridgeHead>
<Para>
Rate Adaptive Digital Subscriber Loop was developed by Westell and has a
potential of 2.2 Mbps downstream and 1.0 Mbps upstream. What makes RADSL
more flexible is that the sync rate can be dynamically adjusted up or down
as line conditions change. This makes it more of a viable alternative where
line conditions are marginal due to distance or other factors. In many
respects, RADSL is an enhanced ADSL to meet a more diverse set of line
conditions. Like ADSL, RADSL can piggyback on the POTS line. RADSL does not
require any splitters or filters.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>HDSL</BridgeHead>
<Para>
High bit-rate DSL was one of earliest versions of DSL. HDSL
requires multiple, dedicated wire pairs, and is symmetric at 1.5
Mbps/1.5 Mbps (the speed actually depends on number of wire pairs
used). Not a viable alternative for the consumer or SOHO markets.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>VDSL</BridgeHead>
<Para>
Very high rate Digital Subscriber Loop is a DSL still in development
with a current downstream capacity of 52.8 Mbps, and upstream of
2.3 Mbps. At this time, VDSL is limited to very short loop lengths,
and is not yet a viable alternative. It may find application where
there is fiber to the neighborhood, and thus the copper loop
segment is relatively short.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>UDSL</BridgeHead>
<Para>
Unidirectional Digital Subscriber Loop is a proposal from Europe that is
not yet in use.
</Para>
</ListItem>
<ListItem>
<BridgeHead renderas=sect3>G.SHDSL</BridgeHead>
<Para>
The standards for G.SHDSL have just recently been finalized. SHDSL
includes many enhancements, including better reach, better rate adaptation,
and better upstream bandwidth. G.SHDSL is symmetric with speeds up to 2.3
Mbps, and will more than likely be marketed as an SDSL alternative.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>The DSLAM</Title>
<Para>
This technology is made possible by the placement of DSLAMs, or Digital
Subscriber Loop Access Multiplexers, from such suppliers as <Ulink
url="http://www.alcatel.com">Alcatel</Ulink> and
<Ulink
URL="http://www.cisco.com/warp/public/cc/pd/si/6000/prodlit/c6160_ds.htm">Cisco</Ulink>,
in the telco's Central Office, or sometimes a suitable remote location.
DSLAMs come in various shapes and sizes, and are the one, single complex and
costly component of a DSL connection. When a qualified phone line is
connected to a modem at the user's end of the loop, a high speed digital
connection is established, typically over ATM, or sometimes frame relay. The
DSLAM splits the signal back into separate voice and data channels. The voice
channel stays within the telco network, whereas the data is picked up by an
ISP (typically).
</Para>
<BridgeHead renderas=sect3>
Figure 4: A Typical DSL Connection Path
</Bridgehead>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
Voice -+ +---> Voice
|<-- copper loop --> DSLAM/CO <--{ATM cloud}--->|
modem -+ | +---> Inet
| | |
ether..|..... DSL/ATM here ....|.... raw ATM here .....|.. TCP/IP ..
| |
SOHO...|............ telco (ILEC or CLEC) .............|.. ISP ..| NSP
</LiteralLayout>
</MSGText>
</Literal>
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Sync</Title>
<Para>
A good, working connection to the DSLAM is referred to as
<Quote>syncing</Quote>. This is typically indicated by LEDs on the modem.
Without sync, nothing happens. The modem will establish a sync rate which is
often throttled by the provider at a predefined limit. This limit, or
<Quote>cap</Quote>, is at the provider's discretion and is part of the
service that is being provided. Your modem may well sync at a higher rate
than the <Quote>cap</Quote>, but your speed will be limited to whatever
<Quote>cap</Quote> the provider is enforcing. So while ADSL has an upward
theoretical limit of 8 Mbps, you will not see that speed -- unless of course
your provider is selling an 8 Mbps plan. Most plans are well below this.
</Para>
<Para>
Below is the status information from a SpeedStream 5660 modem/router via the
built-in telnet interface. In this example, the customer is on a 1.5 Mbps/384
Kbps service:
</Para>
<para>
<Screen>
Command-> show dslstatus
--- Channel Info ATU-R ATU-C
Current TX Rate - 384000 1500000
Previous TX Rate - 0 0
CRC Block Length - - -
Interleave Delay - - -
--- Physical Layer Info ATU-R ATU-C
Current Attainable Rate - 448433 3890243
Current SNR Margin - 10.5 17.0
Current Attenuation - 54.5 31.5
Current Output Power - 3.0 16.0
Current Status:
Defects detected - No No
Loss of Framing - No Loss No Loss
Loss of Signal - No Loss No Loss
Loss of Power - No Loss No Loss
Loss of Signal Quality - No Loss No Loss
--- ATU-R Line Status
Line Coding - DMT
Line Type - Fast or Interleaved
Command->
</Screen>
</para>
<Para>
First notice the <Quote>Current Attainable Rate</Quote> in the
<Quote>ATU-C</Quote> column. This is the downstream sync rate negotiated by
the modem and DSLAM, which is over 3.5 Mbps. The actual speed is limited,
however, to 1.5 Mbps/384 Kbps from the first row <Quote>TX Rate</Quote>. This
is the theoretical limit of this connection. This limit, or
<Quote>cap</Quote>, can be enforced at the DSLAM, as is the case the here, or
further upstream. Had the first row <Quote>TX Rate</Quote> been lower than
the provider's imposed limit, then this would indicate some kind of problem
with the connection, perhaps due to distance or some kind of line impairment.
</Para>
<Para>
The attainable sync rate is the result of a number of factors, including wire
distance to the DSLAM, quality of both inside and outside wiring, the loop
wire gauge and various other factors within the loop. Actual measurable,
real world throughput, on the other hand, is first of all dependent on sync
rate. Low sync rate means low throughput. In the above example, had the sync
rate been lower, say 500 Kbps, then that would be the maximum for that
connection, even though the customer is paying for a 1.5 Mbps service.
</Para>
<Para>
Secondarily, throughput will depend also on the ISP's network, and then the
ISP's upstream provider. You will lose approximately 10-20% of potential
throughput to networking overhead. In the above example where the connection
is throttled at 1.5 Mbps, the actual, real-world maximum throughput would be
somewhere around 1.2-1.3 Mbps when overhead is taken into account. Moreover,
once you hit the Internet proper, all bets are off as there are any number of
factors that may impact throughput. A overloaded or busy server is likely to
be slow no matter how fast your DSL connection is.
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="dslmodems">
<Title>DSL Modems</Title>
<Para>
The <quote>modem</quote> is the last piece of the connection. The modem is
connected directly to the DSLAM via the copper loop on the telco end, and
plugs into a wall jack on your end. When all is well, the modem
<Quote>syncs</Quote> with the DSLAM, and then makes an IP connection to the
ISP, and off we go!
</Para>
<Para>
For Linux users, <Emphasis>the modem is a very important
consideration</Emphasis>! There are many modems supplied by ISPs that are not
Linux compatible. Your best bet is an external, ethernet interfaced modem (or
modem/router combo) that connects via a standard ethernet NIC, since many
other modem options (PCI, USB, onboard) will not work due to a lack of
drivers at this time! All ethernet based modems will work fine. (See the
<Link LinkEnd="modems">Modems Section</Link> for an up-to-date list of
compatible modems.) ISDN users will need a modem (NT) designed specifically
for DSL over ISDN.
</Para>
<Para>
With ethernet modems, the only potential compatibility issue is the Network
Card (NIC). (And really any compatible ethernet NIC should do just fine --
100 Mbps is not even necessary.) You are probably better off anyway, since PCI and
USB modems can be more problem prone. If your chosen provider does not
offer a compatible modem as an option, then you either need to look
elsewhere, or you will have to buy one outright from a third party.
</Para>
<Para>
As always, there are exceptions. <Ulink URL="http://www.xpeed.com">Xpeed</Ulink>
now has drivers for two PCI modems included with the kernel drivers (as of
2.2.18, not in 2.4 yet though AFAIK). These are the first open source Linux DSL modem
drivers, and is welcomed news. <Ulink
URL="http://www.alcateldsl.com">Alcatel's</Ulink> ADSL SpeedTouch USB modem
now has Linux drivers. And more recently, the Eci Hi Focus ADSL USB Modem
has drivers (and some related chipsets are supported as well, see
<ulink url="http://eciadsl.sourceforge.net/">http://eciadsl.sourceforge.net/</ulink>).
IteX PCI ADSL modems, based on the Apollo chipset, have Linux drivers.
(Modems using this chipset are sold under a number of various brand names.)
Diamond also makes [made?] an internal PCI modem which has binary-only
drivers, but it is not in widespread use, and seems to be discontinued at
this point. It is also possible to make a direct ATM connection using a modem
plus an ATM network card, though this delivery system is not used in the U.S.
as far as I know, and should not be considered as a viable option. This would
also require a 2.4 kernel.
</Para>
<Para>
The most common type of modem in use today is actually a combination
<Quote>bridge</Quote> and modem device. The bridge is a simple device,
typically with little configuration. Network traffic passes blindly across
the ATM to ethernet bridge in either direction. Your point of exposure is the
interface (typically a NIC) that is connected to the modem/bridge.
</Para>
<Para>
Some ISPs are also offering <Quote>routers</Quote>. These are basically
combination modem/routers that can handle NAT, and may have other feature
enhancements such as port forwarding, a built in hub, etc. These are all
external, so should work too. But probably not a big deal for Linux users,
since Linux can do anything these do, and more. A locked down Linux box makes
a most excellent firewall/gateway/proxy!
</Para>
<Para>
To confuse things even more, there are also all-in-one devices: combo
bridge+router+modem, sometimes called <Quote>brouters</Quote>. In this case,
the modem can be configured for either bridged or routed modes -- but it
can't be both at the same time.
</Para>
<Para>
All providers should make available a modem of some sort. Many ISPs will have
more than one modem option. Some may give away the modem at no additional
charge. Some may offer a free base model, and charge the difference for the
better models with more features. Many of the modems that ISPs supply are not
available through normal retail channels. Should you want to buy one
yourself, this leaves used equipment outlets (e.g. ebay), or possibly buying
a modem that your ISP may not support (i.e. a possibility of no tech support
if you have a problem).
</Para>
<Para>
While some ISPs provide modems that are not readily available through normal
retail channels, there are a number of manufacturers that are getting on the
DSL modem bandwagon, and offering a good selection. Most have a
number of enhancements. At this time Alcatel (now owned by Thomson), Intel,
Zyxel, Cisco, 3Com, and Cayman have products available. Depending on model
and feature set, prices range from a little over $100 US to $800 and up. Many
of these handle their own authentication and encapsulation (DHCP, PPPoE,
etc).
</Para>
<Para>
Are some modems better than others? Short, easy answer: no. Modems are not
much of a factor in speed in most cases. But some do have enhanced features,
such as diagnostics or the combo modem/routers. Ethernet modems are
generally considered the most reliable. Fewer IRQ hassles, no buggy drivers,
etc. So the fact that Linux users are mostly relegated to ethernet modems is
a blessing in disguise really. Are any of these better than others? Hard to
say since most of this is so new there is not enough of a track record to
compare brands and models with any degree of assurance. In other words, any
old external, ethernet modem should do -- provided it matches your
provider's DSL, and is configured for that service. Remember, there can be
differences here.
</Para>
<Warning>
<Para>
Make sure any third party modem or router you may purchase is compatible with
your DSL provider. There are two major line encodings for ADSL (CAP and DMT
a.k.a. Alcatel compatible), and several options for IP encapsulation. And
different DSLs (SDSL, IDSL, etc) will require their own modems too, as will
ISDN lines. Your provider should have a list of compatible options. It may
well have to be configured for your ISP's service too. Don't expect it to
work right out of the box either (unless it does indeed come from your
provider). Many are accessible via telnet, or a web browser, where the
configuration options are available. See the owner's manual for this.
</Para>
</Warning>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="ispconn">
<Title>The ISP Connection</Title>
<Para>
The modem connects to the DSLAM, and then the DSLAM is connected to the
telco's ATM network (or frame relay), where it is picked up by the ISP. The
ISP typically will take over at what we <Quote>see</Quote> as the first hop on a
<Command>traceroute</Command>. Everything up to that point is in the hands
of the telco/DSL provider. The ISP will connect to the telco's ATM network
via a high-speed data connection, usually ATM over a DS3 (45 Mbps) or
possibly an OC-3 (155 Mbps). The important thing here is that an ISP must
<Quote>subscribe</Quote> with your telco to provide this connection. The ISP
will provide traditional ISP type services: email, DNS, news, etc. It is
really a two step connection -- DSL from one provider, Internet from a second
-- even though these may be combined into one billing.
</Para>
<Para>
The Baby Bells (RBOCs) in the U.S. all own ISPs. These, of course, are
connected to their DSLAMs, and are providing Internet services via the
telco's ISP subsidiary. Many independent ISPs are availing
themselves of the ILEC's DSL services, and in essence
<Quote>reselling</Quote> the DSL services of the ILEC. While the underlying
infrastructure is the same in this case, having more than one ISP working out
of a CO may mean a better selection of features and prices for the consumer.
</Para>
<Para>
CLECs (independent telcos) are now installing their own DSLAMs in many U.S.
markets. This makes them a direct competitor to the ILEC. In this scenario,
there would be two (or more) DSL providers in the same CO, each with their
own DSLAM(s), and each competing against each other. This complicates the ISP
situation even further, as each DSL provider will be <Quote>partnered</Quote>
with one or more ISPs. If you are lucky here, you will have many choices of
plans and pricing structures.
</Para>
<Para>
At this time, there is a shake out going on in the U.S. market. The
independents are all struggling to match the deep pockets of the regional
phone companies. The independents that have survived are now focusing more
on small business and higher-end consumer customers. This means, it will
cost more, but you should also expect to get more. Especially, in the
quality department.
</Para>
<Para>
Typically, your service agreement is with the ISP, and not the DSL
provider. This makes the actual DSL provider a <Quote>behind the
scenes</Quote> player. This may vary, and in some cases, you may wind up
with a separate service agreement for both the DSL provider and the ISP.
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Availability</Title>
<Para>
Who can get DSL? The first requirement is that a telco has installed the
necessary hardware somewhere on their end. Typically this is in the CO. You
have no choice on which CO is yours -- it is wherever your loop terminates.
If your CO has a DSLAM, and the necessary other components, then DSL may be
available to you. This is often known as <Quote>pre-qualifying</Quote>, and
is Step One in getting service.
</Para>
<Para>
More and more <Quote>remote terminals (aka DSLAMs)</Quote> are being
deployed. This is certainly good news for those that are a long way from
the CO. CO distance is not the limiting factor it once was.
</Para>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Ordering</Title>
<Para>
Before ordering service, check to see what providers there are in your area.
Look for options on both the telco/DSL side and the ISP side. You may have
several options, including the large phone companies, as well as smaller,
local ISPs. Once an order is placed, you must wait for the qualification
process before a provider will agree to provide service.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="qualify">
<Title>Qualifying</Title>
<Para>
Once local availability is established, the next step is
<Quote>qualifying</Quote> your loop. The provider will run various tests to
make sure that your loop can handle the DSL signal. This is to determine how
suitable your line is for DSL, and maybe what level of service will be
available to you. You probably will have to order service just to find out
this much. It can be a fairly involved process, with a variety of different
tests being run. There are a number of things that may
<Quote>disqualify</Quote> a line. The most common limitation is distance.
</Para>
<Para>
All DSLs have distance limitations. ADSL is limited
to a loop length of roughly 18,000 ft (5.5 km), but the actual cut off point
will vary from provider to provider. The further away you are, the weaker the
signal, and the potential for poor connections is greater. With ADSL, if you
are within approximately 12,000 ft (3.7 km), you should be able to get at
least 1.5 Mbps -- all other things being equal. IDSL has even greater reach,
mainly because the maximum speed for IDSL is considerably lower at 144
Kbps/144 Kbps.
</Para>
<Para>
Still even if you're close enough, there are a number of potential
impediments that may disqualify a line. Two such common impediments
are load coils and bridge taps. These are aspects of the old telco
infrastructure that once were deemed beneficial, but now are getting
in the way of the newer, digital technologies. <comment>This next
sentence could stand rephrasing. HB - ??? sounds good to me?</comment>
Whether you hit a snag like this or not, is pretty much hit or miss. Fiber
anywhere in the loop is also a disqualifier. The provider may take steps to
<Quote>clean</Quote> the line. Just how far they are willing to go will vary
from provider to provider, and this will likely add additional time to the
installation process.
</Para>
<Para>
Once the line is <Quote>qualified</Quote>, the next step is deciding on which
plan is suitable for your situation. The provider may have differing plans
available depending on how strong a signal they think your line can handle.
If you are marginal, you will not be qualified for the higher speed plans.
And if price is a factor, having a tiered pricing structure is good also
since the lower end plans are obviously less expensive. How this is
structured also varies wildly from provider to provider. Since, DSL is a new
service, and providers are trying to find the right price/feature
combinations that will attract the most users and thus gain a competitive
edge.
</Para>
<Para>
Some common data rates:
</Para>
<Para>
<BlockQuote>
<LiteralLayout>
Downstream/Upstream
128 Kbps/128 Kbps
256 Kbps/256 Kbps
384 Kbps/128 Kbps
640 Kbps/90 Kbps
1.5 Mbps/384 Kbps
2.0 Mbps/512 Kbps
7.1 Mbps/1024 Kbps
</LiteralLayout>
</BlockQuote>
</Para>
<Para>
and a near infinite number of other possibilities. The cost of different
plans generally goes up with their speed.
</Para>
<Para>
Should you be disqualified, and have other options, get a second opinion.
Calculating the effective loop length is by no means an exact science. There
is plenty of room for errors. Also, some providers may go to greater lengths
to <Quote>clean</Quote> the loop than others. And, if you have more than one
phone line, and are disqualified, then try the other line. Just because they
both terminate at your location, does not necessarily mean they are the same
length! The telco network is full of surprises.
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="cproviders">
<Title>Choosing Providers</Title>
<Para>
Should you have more than one choice, here are some things to keep in mind
when comparing services from different providers. If you are in a populous
area, chances are you do have a number of choices. There is a dizzying array
of possibilities at this time. Remember too, that it is a two step
connection: DSL provider and ISP. You may have choices for each.
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Emphasis>A compatible modem</Emphasis>. For now with Linux (or any
alternative OS) this essentially means an ethernet interface. (There are
rare exceptions.) <Quote>Routers</Quote> (i.e. combo modem/routers) should
be OK too since these seem to be all ethernet devices.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Installation</Emphasis>. A self-install option, of course, let's
anyone get up and running, and is less expensive. But if there is no
self-install available, will the provider install onto a Linux only
site? Many will not! Having a Windows (or Mac) box temporarily available
is a work around here. Even a laptop may be enough.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Static vs Dynamic IP Address</Emphasis>. If wanting to run
servers, or hosting your own domain, static is the way to go. A dynamic
IP, on the other hand, makes you a little harder to find should you wish
to remain <Quote>invisible</Quote>, or a least harder to keep track of.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Encapsulation</Emphasis>. Is the connection
<Quote>Bridged</Quote> or <Quote>PPP</Quote>. PPPoX has the reputation of
being not as stable a connection, and not <Quote>always on</Quote>. PPPoE
requires client software to manage the connection, so one more layer of
code.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Server Policy</Emphasis>. Some ISPs are fairly open about this,
while others forbid any servers -- even personal web sites. Others may even
go so far as to block certain ports.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Contract</Emphasis>. Is there a contract, and what are the out
clauses? Cancellation fees?
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Connection Limits</Emphasis>. Is it <Quote>always on</Quote> (at
least theoretically :-)? Are there session limits, or idle timeouts? Is
bandwidth metered and limited to so much per month? Do they forbid a LAN
behind the connection (dumb!)?
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Linux Support</Emphasis>. A few ISPs may offer some degree of
tech support for Linux, but most will not. This isn't so bad, as long as
they don't go overboard and refuse to help with anything just because you
run a non-supported OS. (<Quote>Supported</Quote> means like <Quote>tech
support</Quote>.) If they say <Quote>we don't care</Quote>, you should be
good to go.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Free Dialup Account</Emphasis>. A nice thing to have if the
connection is down, or you just need to check mail from another location.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Setup program</Emphasis>. A few ISPs may have a setup program you
are required to run the first time you connect in order to setup your
account. This will likely not have a Linux version. (BellAtlantic.net was
doing this at last report.) Other than this, there is nothing proprietary
about DSL, and related protocols.
</Para>
</ListItem>
<ListItem>
<Para>
<Emphasis>Reliability and Quality of Service</Emphasis>. Ask around in your
local area from those that have the same DSL provider and ISP. A local LUG
is a good place to get this kind of info. How much down time (hopefully not
much)? Are mail and news services good? Backbone routing? Tech support?
</Para>
</ListItem>
</ItemizedList>
</Para>
<Para>
There are a number of other options and features that might be worth looking
at too: multiple IPs, domain hosting (DNS), free web space, number of
email accounts, web mail, etc. All things considered, the better plans
are probably going to cost more for a reason.
</Para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="faq">
<Title>Appendix: FAQ</Title>
<Para>
Some Frequently Asked Questions about DSL and Linux.
</Para>
<Para>
<OrderedList>
<ListItem>
<Para>
Q. Does DSL work with Linux?
</Para>
<Para>
DSL is a technology, or more correctly, a group of related technologies.
This is akin to asking if Linux works with telephones. The technology
itself does not care. So, the short answer is <Quote>Yes, of
course!</Quote>. The long answer is that if there are any impediments, they
are being imposed by the provider. There are things they may do, that can
make getting Linux up and running, more of a challenge than it needs to be.
Not having a compatible modem option available is one common gotcha. Also,
if the telco or ISP is doing the installation, they may require a Windows
or Mac system to be available. This saves them the costs of training their
techs on various alternative OSes. Buyer beware!
</Para>
<Para>
Basically all DSL does, is facilitate a high speed Internet connection. At
some point, it is all TCP/IP, and Linux, of course, handles TCP/IP quite
well.
</Para>
</ListItem>
<ListItem>
<Para>
Q. Where can I find drivers for my PCI (or USB) modem?
</Para>
<Para>
With a few exceptions, you probably can't, because they are just not
available. Your best bet is an external, ethernet interfaced modem for all
intents and purposes. If your provider does not offer one, you will have
to find another provider, or buy your own modem outright. Just make sure
it is compatible with your provider's flavor of DSL.
</Para>
<Para>
The are exceptions to every rule. See the <Link LinkEnd="modems">Modems
Section</Link> for a list of compatible modems as of this writing.
</Para>
<Para>
If an incompatible modem puts you in a bind, hopefully you will take the
time to politely harass the manufacturer ;-).
</Para>
<Para>
This situation is changing for the better. <Ulink
URL="http://www.xpeed.com">Xpeed</Ulink> now has drivers included in the
kernel for source for their PCI IDSL and SDSL modems. This is good news!
<Ulink URL="http://www.alcateldsl.com">Alcatel</Ulink> has
released drivers for the Alcatel SpeedTouch USB ADSL modem. IteX has
also released drivers for their PCI ADSL modem. Hopefully
more will follow suit. (Make sure you are reading the latest version of
this document, as I have intentions of keeping this situation updated as
needed.)
</Para>
</ListItem>
<ListItem>
<Para>
Q. How fast or good of a network card do I need?
</Para>
<Para>
Any card that is compatible with Linux should work fine. Remember even
low-end cards are 10 Mbps, and no consumer class DSL is near that at this
time. I would suggest a reasonably good quality card, just to help
eliminate the possibility of errors and premature failure.
</Para>
</ListItem>
<ListItem>
<Para>
Q. How can I find out when DSL will be available in my area?
</Para>
<Para>
Just where and when DSL gets deployed is totally in the hands of
your friendly local telco. They obviously can't do everyone at
once, so they probably are selecting areas based on competitive
factors. Getting a straight answer from a telco on this question
can also be a challenge. Probably so as not to tip their hand to
competitors. Unfortunately, it is a question only they can answer.
</Para>
</ListItem>
<ListItem>
<Para>
Q. I was disqualified because I am too far away. What can I do?
</Para>
<Para>
Move? Seriously, there isn't much you can do. If there are other providers,
get another opinion. You never know. Determining the loop length is an
inexact science, and there is room for errors. Many use databases for
this, and these databases routinely have some inaccuracies. Some providers
too, may be more aggressive in taking steps to help you out and clean up
the line. Also, some providers offer low-end speed services that have
greater reach. Maybe this will become available in your area. Or, the telco
may install, at some point, remote devices for customers who are now too
far away.
</Para>
</ListItem>
<ListItem>
<Para>
Q. I am told I am 20,000 ft from the CO. Isn't that too far? Will my
speeds be really bad?
</Para>
<Para>
Not necessarily. This distance limitation is not where the CO is, but
where the DSLAM is. These are often installed in CO's, but more and more
are being installed in remote locations in order to expand the reach
of DSL service.
</Para>
</ListItem>
<ListItem>
<Para>
Q. What are the speed tweaks for Linux?
</Para>
<Para>
This may not be necessary. Linux is pre-tweaked for the most part,
unlike some versions of Windows that really need some registry hacks to get
optimum performance. If you have a high latency connection, you may
benefit from increasing the TCP Receive Window. See the <Link
LinkEnd="tuning">Tuning</Link> section.
</Para>
<Para>
Now if you are convinced you are not getting the performance you should
based on your distance and line conditions, then there might be a problem
somewhere. See the <Link LinkEnd="tuning">Troubleshooting</Link> section for
more. What you may need is a fix, more than a tweak.
</Para>
</ListItem>
<ListItem>
<Para>
Q. My service is limited to 640K (for example). Can I get better speed by
getting a faster modem? Any way around this?
</Para>
<Para>
No, and no. The modem has little bearing on how fast your connection is for
all intents and purposes. The provider has a mechanism in place for
limiting your speed somewhere in the pipe before you hit the Internet.
There is no way to defeat this.
</Para>
</ListItem>
<ListItem>
<Para>
Q. Can I download and upload at the same time? Is one effected by the
other?
</Para>
<Para>
The upstream and downstream channels use separate frequency ranges within
the DSL signal, so simultaneous upload/download is not a problem and
available bandwidth is not normally impacted.
</Para>
<Para>
Where there may be somewhat of an adverse impact, is with asymmetric DSLs
like ADSL, <Emphasis>and</Emphasis> both the upstream and downstream are
simultaneously saturated. This is a TCP 'feature' and not DSL related
though. This can adversely effect the faster stream (i.e. the downstream).
How much of an impact depends on a slew of factors and is beyond the scope
of this document, but is more pronounced with higher ratios of downstream
to upstream (e.g. 640/90). See the <link linkend="bottlenecks">Tuning</link>
on how to mitigate this effect.
</Para>
</ListItem>
<ListItem>
<Para>
Q. I am paying for 768 Kbps service, and the best I ever get is 640 Kbps or
so. Why? Is the service oversold? I am not getting what I pay for.
</Para>
<Para>
You will lose 10-20% of the rated capacity due to the overhead inherent
in the various protocols utilized. Most of us will probably fall closer to
20%. This is just a fact of life for everybody. Just how much is lost here
depends on various factors. You seem to be close to your maximum when this
is taken into consideration. Also, if you read the fine print, many ISPs
are advertising speeds <Quote>up to</Quote> such and such. Check your
service agreement and see if there are any guarantees. If there are, they
may be well below the advertised maximum speed, and may be based on sync
rate instead of actual throughput. Though this may vary from provider to
provider as well.
</Para>
<Para>
Also, be careful how you test this. Some of the so-called test sites can be
pretty unreliable. There can be many factors between you and that site that
can impact your throughput and skew results -- not the least of which is
how many people might be trying that same test at the same time. The best
test is via FTP download from a known good, close, not too busy site.
</Para>
</ListItem>
<listitem>
<para>
Q. Can DSL work with ISDN, and how is this different?
</para>
<para>
Yes, there have been DSL capable modems and service providers for some
time. In fact, this is common in parts of Europe. So this is not an issue.
</para>
<para>
What makes ISDN different is the underlying signal on the line is
fundamentally different than a POTS line. This means that any physical
layer hardware has to be compatible with ISDN (and conversely it is
incompatible with POTS lines). So this means the NT (modem), filters, etc,
all have to be designed for ISDN. Other than these low level issues, the
other aspects of DSL implementation are the same (e.g. network protocols).
</para>
</listitem>
<ListItem>
<Para>
Q. Why does PPPoX have such a bad rap?
</Para>
<Para>
The occasional disconnects is one of the biggest gripes. PPP seems to be
sensitive to any interruptions in the connection. Generally a disconnect
means a new IP. And there are those that say PPP, by its very nature, was
never meant to be an <Quote>always on</Quote> protocol. PPP is a session
management protocol at heart, that requires a user to initiate a
connection and authenticate him or herself. PPPoE/A are not yet
particularly mature protocols either. They do not have much of a history
or track record. Some would say the telcos and hardware manufacturers have
rushed this out the door. PPPoE also requires an additional layer of
software just to maintain the connection. This is one more layer of code
and one more potential point of failure. Also, more system overhead is
utilized to manage the connection.
</Para>
<para>
The impact of the disconnect problem can potentially be eased by adjusting
the PPP LCP-echo settings to extend the period before the local end of
the connection decides to terminate the session. Each end of the
connection uses LCP echoes to make sure the other end is still
<quote>there</quote>. Nothing much can be done if the remote end decides
to tear down a session (other than to do what you can to make sure you are
responding to it's LCP echoes).
</para>
</ListItem>
<ListItem>
<Para>
Q. Why PPPoX? This seems like a bad idea!
</Para>
<Para>
PPP gives several advantages to the provider: they can use their existing
infrastructure and hardware that they now use for their (larger) dialup
customer base. It is easier to control user authentication and potential
abuse situations, and easier to manage their network and related issues. In
fact, it most boils down to its just easier for them. Easier, means saves
man hours, and therefore saves costs (at least from their perspective).
</Para>
<Para>
It is not a conspiracy to conserve IP addresses, or thwart heavy users. IP
address costs are insignificant in the overall scheme of things.
</Para>
</ListItem>
<ListItem>
<Para>
Q. The only provider in my area does not support Linux. What can I do?
Will I have to use Windows?
</Para>
<Para>
NO! <Quote>Support</Quote> here is support as in <Quote>tech
support</Quote>. They are just saying that they will not give you tech
support when and if you have problems. This does not mean you cannot use
Linux on their network. Just that you may have to fend for yourself when
and if a problem does arise. Anything that is forbidden will be in their
Acceptable Use Policy (AUP), or Terms of Service (TOS) agreement.
</Para>
<Para>
I have heard stories where a new tech or installer has misinterpreted their
own company's policy on this and told someone <Quote>you can't use Linux
here</Quote>. Same with NT server. But this is almost always a misinformed
individual.
</Para>
<Para>
But -- if a provider does not support Linux, they may balk at installing
onto a Linux box. Hopefully, they will have a self-install option to get
around this annoyance. YMMV.
</Para>
</ListItem>
<ListItem>
<Para>
Q. My fax software does not work with my DSL modem. Why is that?
</Para>
<Para>
Faxes are normally transmitted over typical analog phone lines by dialing
the fax machine on the other end. Analog modems can handle this, but
DSL <Quote>modems</Quote> have no dialing capability. Don't throw out that
56K yet!
</Para>
</ListItem>
<ListItem>
<Para>
Q. What does <Quote>FastPath</Quote> mean? Is it better? Faster? What is
interleaving? How can I get better ping times?
</Para>
<Para>
Interleaving is a feature of DMT line encoding. Essentially it is a form
of error correction that is configurable at the DSLAM. The side effects are
a slower connection, especially higher latency. With FastPath (or sometimes
called non-interleaved) DMT, gateway pings can be in the 10-25 ms range. With
interleaving, this is more likely to be in the 40-75 ms range depending on
the degree of interleaving that has been enabled.
</Para>
<Para>
On the positive side, a marginal line is more stable and less prone to
errors with interleaving. Many telcos have interleaving on by default since
increased stability would seem to be a good thing. But this is only
beneficial for marginal lines, and everyone else is paying a latency tax
for this. Some telcos may be amenable to turning this feature on/off. YMMV.
</Para>
</ListItem>
<ListItem>
<Para>
Q. How fast and powerful of a computer do I need for DSL? My ISP says I
need at least a Pentium 200. Why?
</Para>
<Para>
At the most basic level, a 386 will work fine. In most situations, you are
connected to what is essentially an ethernet based network. So
theoretically anything that can handle a very slow ethernet connection
would work. No comment on how well Netscape will run on a 386 though ;-)
But as far as just managing a raw connection, a 386 is indeed workable.
What else you can do with it, is another matter.
</Para>
<Para>
Where this gets a little more complicated is the modem, and the client
that the ISP may require. Any PCI or USB modem is going to require
drivers, which means more CPU and system resources. Also, PPPoE does even
more processing, so again the potential CPU load is increased. Windows
tends to be not so efficient with all this going on, hence the requirement
for mid range Pentiums by some ISPs.
</Para>
<Para>
With Linux it will depend on what you are going to do. A low end Pentium
should be fine for most uses. A 386/486 should do nicely for just a
firewall/gateway box in most situations. Just remember if you are running
PPPoE, you may take a performance hit on low end hardware.
</Para>
</ListItem>
<ListItem>
<Para>
Q. I just got my DSL installed, and my speed sucks, and/or my connection
constantly drops. What is the problem?
</Para>
<Para>
Not enough information to say, really. There are many, many things that
can cause a poor connection. The list is too long to mention them all.
</Para>
<Para>
One of DSL's weaknesses is that the signal can be fairly fragile. Many
things can degrade the signal, making for poor connections, and thus
speed. This can be caused by poor or substandard inside wiring, a wiring
problem outside (like bad splice), RFI from any number of sources, AM
radio signal interference from a nearby station, bridge taps on your
line, excessive distance from the DSLAM and so on. Not to mention possible
hardware problems with your modem, NIC, or the telco's DSLAM, etc. Not
always easy to sort out.
</Para>
<Para>
Your provider should be able to assist you. First, make sure the problem
isn't with your setup as they likely won't help solve a Linux problem. Then
be persistent, and don't hesitate to go over someone's head if the help is
not forthcoming. Most problems are solvable. The trick is isolating it. A
good telco tech, trained for DSL, can find all kinds of obscure wiring
problems.
</Para>
</ListItem>
<ListItem>
<Para>
Q. My provider's tech support staff is clueless. What can I do?
</Para>
<Para>
Common complaint. Seems to be the nature of the beast. First line tech
support is an entry level position, and mostly filled by young people
with little technical or networking knowledge. Grin and bear it, or try
calling back.
</Para>
</ListItem>
<ListItem>
<Para>
Q. Now that I have a dedicated line, do I really need an ISP?
Can't I be my own ISP?
</Para>
<Para>
Yes, and no. Linux has everything needed to run a small ISP. But even
though the <quote>line</quote> is a dedicated connection, it is only
dedicated to the telco end-point equipment. You still need someone to sell
you bandwidth, and gateway access to the Internet. So, traditional ISPs
still have their role. You might see if there is a local provider of some
kind that will just sell you the bandwidth without all the frills (e.g.
email and news). But this probably will not save any costs.
</Para>
<para>
It is also technically possible to connect two DSL modems via
a <quote>dry</quote> copper line. In some areas, a dry line (with
no dial tone), is fairly inexpensive (but in others areas it's not).
And then you need someone on the other end who is willing to provide
the bandwidth and whatever services may be needed. Not all DSL modems
support this (some common SDSL modems apparently do). This is also going to
require dealing with the local phone company for something that is not a
consumer type service (read: might be a real PITA). There is also a
significant start up investment, that may not come with any telco
guarantees for the intended use.
</para>
</ListItem>
<ListItem>
<Para>
Q: Are there ADSL Standards?
</Para>
<Para>
Sort of. The U.S. Bell Operating Companies have standardized on Discrete
Multi-Tone (DMT) (ANSI T1.413) in their current roll-out. Most others
should follow their lead in the states. There are other types of modems, most
notably Carrier-less Amplitude Phase Modulation (CAP), which of course, is
incompatible with DMT.
</Para>
<Para>
A biased comparison from an DMT-based vendor on this subject can be found at
the <ULink URL="http://www.aware.com">http://www.aware.com</ULink>. Still,
it provides the best detail on this issue I have seen so far.
</Para>
<Para>
A rather expensive copy of the ANSI standard can be ordered at: American
National Standards Institute <ULink URL="http://www.ansi.org">ANSI Home
Page</ULink>
</Para>
<Para>
Asymmetric Digital Subscriber Loop (ADSL) Metallic Interface
</Para>
<Para>
ANSI TI.413-1995
</Para>
<Para>
Note: ANSI TI.413 Issue 2 was released September 26, 1997
</Para>
</ListItem>
<ListItem>
<Para>
Q: Can I use ATM to connect to DSL?
</Para>
<Para>
Technically speaking, you can. Some DSL modems (at least the Alcatel
version) has a ATM Forum 25Mbps interface, which connects to a PCI ATM
card. But this is rarely done in practice since many Operating Systems
can't speak ATM natively, and the cost of ATM cards is more than ethernet.
See <Ulink
URL="http://linux-atm.sourceforge.net/">http://linux-atm.sourceforge.net/</Ulink>
for more details.
</Para>
</ListItem>
<ListItem>
<Para>
Q: Why does DSL have all these bit rates (384/1.5/7.1M/20M/etc) options?
</Para>
<Para>
The basic problem is the 100 year old design of the copper loop. It works
great for analog phone, but it presents a real challenge for higher
performance signals like DSL. Remember that the distance of a loop is
inversely proportional to the data rate that it can carry. Rate adaptive
technologies are great for making a digital signal work in many situations,
but it can't provide a consistent bandwidth for all applications,
especially for very long (over ~15,000 ft) loops. The different bandwidths
that you see advertised reflect various marketing battles of vendors
equipment, and the telco struggle to finalize on a standard set of data
rates. The bottom line is for the telco to be able to reach as broad a
customer base as possible.
</Para>
<Para>
Check out the next question on the loop impairments that cause this to
happen.
</Para>
</ListItem>
<ListItem>
<Para>
Q: What are all these loop impairments (bridge taps, load coils, DLCs) that
could disqualify my line from DSL? (thanks to Bruce Ediger)
</Para>
<Para>
Load coils: in-line inductances that improve voice-frequency transmission
characteristics of a telephone circuit. Essentially, a "load" steals energy
from high frequencies and gives it to lower frequencies. Typically only used
in very long (&gt; 9,000 ft) phone lines.
</Para>
<Para>
By "bridges" I assume you mean "bridged taps". In older neighborhoods, the
phone wiring will have been used by more than one customer. Perhaps these
customers lived at different (though near-by) addresses. The unconnected
"spur" of wiring is a "bridged tab" on the currently connected circuit.
</Para>
<Para>
DLCs, Digital Loop Carriers: there's a bunch of systems for carrying more
than one voice transmission on a single pair of wires. You can shift the
frequencies up or down, or you can digitize the voice transmissions and
divide the telephone circuit by time or code or something. The more
general term is "pair gain".
</Para>
<Para>
These things cause different problems for high-frequency communications.
</Para>
<Para>
Load coils will completely mess up things by filtering high frequencies and
passing low frequencies. They probably also change the "delay envelope",
allowing some frequencies to arrive before others. One byte's tones will
interfere with the next byte's.
</Para>
<Para>
Bridged taps act as shunt capacitances if they're long in relation to the
signals wavelength, and they'll actually act as band pass filters if they're
about 1/4 wavelength of the signal. That is, they'll pass particular
frequencies freely. Particular tones of a DMT modem might get shunted back,
rather than passed along to the receiving modem, reducing bandwidth for that
telephone line.
</Para>
<Para>
Pair gain, digital or analog, limit the bandwidth available to one
transmission in order to multiplex several on one wire. High and low tones
of a DMT transmission get filtered out by the apparatus.
</Para>
<Para>
The book "Subscriber Loop Signaling and Transmission Handbook", by Whitham D.
Reeve, , IEEE Press 1992, ISBN 0-87942-274-2 covers the math of how to
calculate the effect of line length, bridged tap, etc on the transmission
characteristics of a telephone line. It's pretty expensive, however.
</Para>
</ListItem>
<ListItem>
<Para>
Q. Can I run a web server with my DSL connection?
</Para>
<Para>
Sure. You are connected to a TCP/IP network, so theoretically you can run
any service that the protocols allow -- mail, ftp, ssh, irc, etc. Where
there may be problems, is with the ISP's TOS (Terms of Service). Some ISPs
are pretty open on this, while others forbid any type of server, and may
even block certain ports. You should research this, or ask the ISP before
making any plans. ISPs that are selling a consumer service are not
going to allow any high volume servers -- just personal, or low traffic
services at best. If this does not fit the bill, then you can check with
any local Business class DSL providers. This will cost more, but the
Terms of Service, and guarantees, are generally much more suited to
higher bandwidth usages.
</Para>
<Para>
If you do not have a static IP, you can get around this with one of the
many Dynamic DNS services that are out there for just this purpose. See the
<Link LinkEnd="links">links</Link> section.
</Para>
</ListItem>
<ListItem>
<Para>
Q: Do you have examples of DSL Modems?
</Para>
<Para>
Short Answer: Yes. Real Answer: The evolution of this technology is
moving too rapidly for anyone to keep up to date in a HOWTO.
Check <Ulink
URL="http://dslreports.com/information/equiprated/all">http://dslreports.com/information/equiprated/all</Ulink> for up to date information.
</Para>
<Para>
However, below is a list of some of the current modem offerings as of
January 2002. All are ADSL modems with DMT encoding (a.k.a. Alcatel
compatible), unless specified otherwise. [Note: Some items retained from
original list dated June 1998.]
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
Router/Modems with 10/100baseT Ethernet Interface:
</Para>
<Para>
Examples: Flowpoint 2000 DSL(CAP), 3COM Viper-DSL (CAP), Westell
ATU-R-Flexcap (CAP), Aware x200, Zyxel P641, Efficient Networks
SpeedStream 5660 and 5861, Cayman 3220H, Cisco 673 (SDSL), Cisco 675
(ADSL/CAP), Cisco 677 (ADSL/DMT), Alcatel SpeedTouch Pro
</Para>
</ListItem>
<ListItem>
<Para>
Bridge/Modems with 10/100baseT Ethernet Interface:
</Para>
<Para>
Examples: Alcatel 1000, Alcatel SpeedTouch Home [note: Home == ethernet,
there are also USB and PCI SpeedTouch versions!], Westell ATU-R-Flexcap2
(CAP), Efficient Networks SpeedStream 5260, Efficient Networks SpeedStream
5251 (SDSL), Westell WireSpeed.
</Para>
</ListItem>
<ListItem>
<Para>
Modems with ATMF Interface:
</Para>
<Para>
Examples: Alcatel 1000, Alcatel SpeedTouch Home, Cisco 677 (DMT), Ariel
Horizon II
</Para>
</ListItem>
<ListItem>
<Para>
Bridge/Modems with V.35 Serial Interface (T1, Serial Router)
</Para>
<Para>
Examples: Westell ATU-R
</Para>
</ListItem>
<ListItem>
<Para>
Modems with USB Interface:
</Para>
<Para>
Efficient Networks SpeedStream 4060, Intel 3100, Alcatel SpeedTouch USB
</Para>
</ListItem>
<ListItem>
<Para>
PCI Modems:
</Para>
<Para>
Examples: Cisco 605, Efficient Networks SpeedStream 3060/3061, Intel 2100,
Xpeed X200 (IDSL), Xpeed X300 (SDSL), Alcatel SpeedTouch PCI
</Para>
</ListItem>
<ListItem>
<Para>
Wireless Modems (IEEE 802.11b):
</Para>
<Para>
Examples: Alcatel SpeedTouch Wireless
</Para>
</ListItem>
<ListItem>
<Para>
Dedicated Router (no built in modem) with 10/100baseT Ethernet Interface:
</Para>
<Para>
Examples: Netgear RT311, SMC 7004BR, Linksys BEFSR11
</Para>
</ListItem>
</ItemizedList>
</Para>
</ListItem>
</OrderedList>
</Para>
<Para>
This is but a very small sampling and should not be construed as
endorsements of the products listed. It is just a simple illustration
of a few of the available products.
</Para>
<Warning>
<Para>
Modem manufacturers often ship modems to meet an ISP's specifications.
Features are sometimes enabled or disabled as requested by the ISP. There are
conceivably numerous, possible variations on each model. Something to
consider if buying one second-hand.
</Para>
</Warning>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<Sect1 id="appendix">
<Title>Appendix: Miscellaneous</Title>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="links">
<Title>Links</Title>
<Para>
<ItemizedList>
<ListItem>
<Para>
Other related documentation from the Linux Documentation Project:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/Firewall-HOWTO.html">Firewall HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/Security-HOWTO.html">Security HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/IPCHAINS-HOWTO.html">IPCHAINS HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/IP-Masquerade-HOWTO.html">IP Masquerade HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/mini/Home-Network-mini-HOWTO.html">Home Network mini HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/Ethernet-HOWTO.html">Ethernet HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/Networking-Overview-HOWTO.html">Networking Overview HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/Net-HOWTO/">Net HOWTO</Ulink>,
previously named the NET3-4-HOWTO, the definitive, in-depth guide to
various Linux networking topics.
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/Adv-Routing-HOWTO.html">Linux
2.4 Advanced Routing HOWTO</Ulink>. All the great features of Linux's
sophisticated traffic management capabilities are explained here,
including performance enhancing ideas relevant to DSL.
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/mini/DHCP/">DHCP HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/VPN-HOWTO.html">VPN HOWTO</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.tldp.org/HOWTO/VPN-Masquerade-HOWTO.html">VPN Masquerading HOWTO</Ulink>
</Para>
</ListItem>
</ItemizedList>
</Para>
</ListItem>
<ListItem>
<Para>
More on the 2.4 kernel packet filtering from The Netfilter Project at <Ulink
URL="http://netfilter.samba.org/">http://netfilter.samba.org/</Ulink>.
Several good HOWTOs for the new features available with 2.4 kernels
and <application>iptables</application>.
</Para>
</ListItem>
<ListItem>
<Para>
Check your security and see what ports are open at
<Ulink
URL="http://hackerwhacker.com/">http://hackerwhacker.com/</Ulink>. This
is one of the better sites for this. Some only test a relatively few
ports.
</Para>
</ListItem>
<ListItem>
<Para>
SuSE's Linux PPPoE page is at <Ulink
Url="http://www.suse.de/~bk/PPPoE-project.html">http://www.suse.de/~bk/PPPoE-project.html</Ulink>.
Good information on most of the available Linux PPPoE implementations.
</Para>
</ListItem>
<ListItem>
<Para>
Bob Carrick's definitive PPPoE site is at <Ulink
Url="http://www.carricksolutions.com/">http://www.carricksolutions.com/</Ulink>.
His Linux PPPoE page is at <Ulink
URL="http://www.carricksolutions.com/linuxpppoe.htm">http://www.carricksolutions.com/linuxpppoe.htm</Ulink>.
It has some other DSL related information as well. All OSes are covered.
</Para>
</ListItem>
<ListItem>
<Para>
The NTS EnterNet for Linux documentation can be found at <Ulink
URL="http://support.efficient.com/KB/NTS/Docs/ENLinux13rel.html">
http://support.efficient.com/KB/NTS/Docs/ENLinux13rel.html</Ulink>. This is a
non-GPL'd PPPoE client that is distributed by some ISPs.
</Para>
</ListItem>
<!--
Funky URL 06/21/01
<ListItem>
<Para>
A white paper from Redback on the technology and rationale behind PPPoE can
be found at
<Ulink URL="http://www.redback.com/en-US/frameset.jsp?flash=true&javascript=true&page=home/home.html">http://www.redback.com/</Ulink>.
This is how the ISPs see it. (Redback is the leading manufacturer of PPPoX
termination routers.)
</Para>
</ListItem>
-->
<ListItem>
<Para>
ATM on Linux: <Ulink URL="http://linux-atm.sourceforge.net/">
http://linux-atm.sourceforge.net/</Ulink>. Where to find the latest info on
PPPoA and raw ATM connections.
</Para>
</ListItem>
<!--
<ListItem>
<Para>
A step by step report on getting Linux going with raw ATM is here: <Ulink
URL="http://linux.com.sg/news/atm/">http://linux.com.sg/news/atm/</Ulink>.
</Para>
</ListItem>
-->
<ListItem>
<Para>
FreeSwan, <Ulink
URL="http://www.freeswan.org">http://www.freeswan.org</Ulink>, is an
IPSec and IKE VPN implementation for Linux.
</Para>
</ListItem>
<ListItem>
<Para>
VPN and Masquerading on Linux: <Ulink URL="http://www.tldp.org/HOWTO/VPN-Masquerade-HOWTO.html">http://www.tldp.org/HOWTO/VPN-Masquerade-HOWTO.html</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
PPTP-linux allows you to connect to a PPTP server with Linux. The home page is
<Ulink URL="http://cag.lcs.mit.edu/~cananian/Projects/PPTP/">http://cag.lcs.mit.edu/~cananian/Projects/PPTP/</Ulink>.
</Para>
</ListItem>
<ListItem>
<Para>
Justin Beech's
<Ulink Url="http://dslreports.com">http://dslreports.com</Ulink>, a great
site for anything and everything related to DSL. If it's not there, then
there is a link to it. (Site runs on Linux.)
</Para>
</ListItem>
<ListItem>
<Para>
John Navas's Cable and DSL site, <Ulink
Url="http://cable-dsl.home.att.net">http://cable-dsl.home.att.net</Ulink>,
has good general info, tweaks, troubleshooting, hardware info, etc. for
all OSes.
</Para>
</ListItem>
<ListItem>
<Para>
TCP Performance Tuning tips: <Ulink
URL="http://www.psc.edu/networking/perf_tune.html">
http://www.psc.edu/networking/perf_tune.html</Ulink>. Tips on Linux, and
other OSes.
</Para>
</ListItem>
<ListItem>
<Para>
A great Linux security site is <ulink
url="http://linuxsecurity.com">http://linuxsecurity.com</ulink>. Good
docs, and references for Linux. Another is <Ulink
URL="http://linux-firewall-tools.com/linux/">
http://linux-firewall-tools.com/linux/</Ulink>. Lots of info from Robert
L. Ziegler, author of <CiteTitle>Linux Firewalls</CiteTitle>. Many links
to other security related sites as well.
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.seifried.org/lasg/">
http://www.seifried.org/lasg/</Ulink>, The Linux Administrator's
Security Guide by Kurt Seifried. Good tutorials on a variety of
topics -- not just firewalls, but the big picture.
</Para>
</ListItem>
<ListItem>
<Para>
The Seattle firewall is a packet filtering firewall that can be used on a
dedicated masquerading firewall machine (including LRP), a multi-function
masquerade gateway/server or on a stand-alone Linux system. The
<application>ipchains</application> project is
located at <Ulink
URL="http://seawall.sourceforge.net/">http://seawall.sourceforge.net/</Ulink>.
And for <application>iptables</application>:
<ulink url="http://shorewall.sourceforge.net/">http://shorewall.sourceforge.net/</ulink>.
</Para>
</ListItem>
<ListItem>
<Para>
Here a few pages dedicated to using Linux with specific providers. (I
could use some submissions for more please.)
</Para>
<Para>
<ItemizedList>
<!--
no findo 06/21/01
<ListItem>
<Para>
Bell Canada's Sympatico:
<Ulink URL="http://www.sympaticousers.org/faq/opsys_software.htm#unix">
http://www.sympaticousers.org/faq/opsys_software.htm#unix</Ulink>
</Para>
</ListItem>
-->
<ListItem>
<Para>
Verizon:
<Ulink URL="http://www.panix.com/~dfoster/prog/linux/pppoe.html">
http://www.panix.com/~dfoster/prog/linux/pppoe.html</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
Southwestern Bell:
<Ulink URL="http://home.swbell.net/sdboyd56/DSL/connect1.html">
http://home.swbell.net/sdboyd56/DSL/connect1.html</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
BellSouth:
<Ulink
URL="http://personal.bellsouth.net/sdf/h/b/hburgiss/dsl/survival/linux.htm">
http://personal.bellsouth.net/sdf/h/b/hburgiss/dsl/survival/linux.htm</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
HomeChoice (UK):
<Ulink URL="http://www.maxuk.net/hc/faq.html">http://www.maxuk.net/hc/faq.html</Ulink>. (This gets my vote for the strangest ADSL service anywhere.)
</Para>
</ListItem>
<ListItem>
<Para>
BT-Internet (UK):
<Ulink URL="http://www.tldp.org/HOWTO/mini/BTI-PPP/index.html">http://www.tldp.org/HOWTO/mini/BTI-PPP/index.html</Ulink>
This covers both dial-up and ADSL connections.
</Para>
</ListItem>
<listitem>
<para>
German T-DSL:
<ulink url="http://www.datenhighway.com/adsl/">http://www.datenhighway.com/adsl/</Ulink>
</para>
</listitem>
<ListItem>
<Para>
France T<>l<EFBFBD>com's Netissimo:
<Ulink
URL="http://www.rhapsodyk.net/adsl/HOWTO/">http://www.rhapsodyk.net/adsl/HOWTO/</Ulink>. Good information on setting up PPTP with Linux for Alcatel modems.
</Para>
</ListItem>
<ListItem>
<Para>
Austrian Highspeed Internetconnection & Linux HOWTO:
<Ulink
URL="http://www.members.aon.at/heimo.schoen/at-highspeed-howto.html">http://www.members.aon.at/heimo.schoen/at-highspeed-howto.html</Ulink>.
</Para>
</ListItem>
<listitem>
<para>
Israel (various ISPs covered):
<ulink url="http://vipe.technion.ac.il/~mulix/adsl-howto.txt">http://vipe.technion.ac.il/~mulix/adsl-howto.txt</ulink>
</para>
</listitem>
</ItemizedList>
</Para>
</ListItem>
<ListItem>
<Para>
Now that you have a full-time connection, want a routable hostname for
your computer? Dynamic DNS services can do this, even if your IP changes from
time to time. Just a few of the many available services:
</Para>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Ulink URL="http://dyndns.org">http://dyndns.org</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://tzo.com">http://tzo.com</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.easydns.com">http://easydns.com</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://no-ip.com">http://no-ip.com</Ulink>
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink URL="http://www.microtech.co.gg/dns">http://www.microtech.co.gg/dns</Ulink>
</Para>
</ListItem>
</ItemizedList>
</Para>
</ListItem>
<!--
kaput????
<ListItem>
<Para>
ADSL Forum Home Page: <ULink
URL="http://www.adsl.com">http://www.adsl.com</ULink> A comprehensive web
site created by the ADSL vendors. Fairly complete for reference information
on ADSL.
</Para>
</ListItem>
-->
<ListItem>
<Para>
<ULink URL="http://conk.com/world/dsl/">ADSL
Deployment 'round the World</ULink> Claims to have a complete list -
looked accurate for my area - gives providers, prices, speeds, etc.
</Para>
</ListItem>
<ListItem>
<Para>
<ULink
URL="http://homepage.interaccess.com/~jkristof/xdsl-faq.txt">comp.dcom.xdsl
FAQ</ULink>. Actively maintained, and a great technical reference for DSL
technologies.
</Para>
</ListItem>
<ListItem>
<Para>
<Ulink Url="news://comp.dcom.xdsl">comp.dcom.xdsl</Ulink>, DSL discussions,
vents, and flames on Usenet. Good place to get technical questions answered
that your ISP can't.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id="glossary">
<Title>Glossary</Title>
<Para>
A dictionary of some of the jargon used in this Document, and in the
telco and DSL industries.
</Para>
<Para>
<VariableList>
<VarListEntry>
<Term>ADSL</Term>
<ListItem>
<Para>
Asymmetric Digital Subscriber Loop. <Quote>Asymmetric</Quote> in that the
downstream potential is greater than the upstream. ADSL is capable of
sharing on a single telco wire pair. Maximum speed is 8 Mbps, though
typically is limited by the provider to lesser speeds. The most popular
DSL at this time.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ANT</Term>
<ListItem>
<Para>
ADSL Network Termination (a.k.a. the ADSL modem).
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ARP</Term>
<ListItem>
<Para>
Address Resolution Protocol. Converts MAC addresses to IP addresses.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ASAM</Term>
<ListItem>
<Para>
Alcatel's terminology for a DSLAM.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ATM</Term>
<ListItem>
<Para>
Asynchronous Transfer Mode - provides high-speed packet switching from 155
Mbps to (currently) 2Gbps. Used to provide backbone switching for the
Internet, and by many telcos since it can carry both voice and data. This
is a common transport protocol for many telco DSL networks.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ATMF-25Mbps</Term>
<ListItem>
<Para>
ATM Forum Interface - 25Mbps speed, provided by a PCI NIC card. One of the
interfaces used between the modem and PC.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>brouter</Term>
<ListItem>
<Para>
A combination DSL modem that can be configured to act as either a bridge
or a router.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>CAP</Term>
<ListItem>
<Para>
Carrierless Amplitude Phase. A proprietary ADSL line encoding technique,
that is (or was) in competition with <Quote>DMT</Quote>. DMT has won the
standards battle. CAP and DMT modems are not compatible with each other.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>Central Office, or CO</Term>
<ListItem>
<Para>
Usually refers to one of two meanings: 1) The local Telco building that
houses telephone equipment, and where local loops terminate. 2) The Telco
voice switch that provides dial tone. Often referred to as just
<Quote>CO</Quote>. Typically, the CO houses one or more DSLAMs that
make DSL possible. But, increasingly, DSLAMs are being deployed remotely.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>CLEC</Term>
<ListItem>
<Para>
Competitive Local Exchange Carrier. <Quote>Competitors</Quote> to the
ILECs. They do not own any lines, and must lease their lines from ILEC in
order to provide any service.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>CPE</Term>
<ListItem>
<Para>
Customer Premises Equipment - The Telco term for customer owned equipment
(i.e. the stuff you are responsible for fixing). Examples are analog
modems, fax machines, and your telephone.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>DHCP</Term>
<ListItem>
<Para>
Dynamic Host Configuration Protocol - A protocol used to distribute
dynamically assigned IP addresses and other important networking
parameters. The DHCP server <Quote>leases</Quote> an IP from its pool to
clients on request. The lease is renewed at regular intervals. This is a
common protocol on bridged DSL networks, and cable modem networks.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>DMT</Term>
<ListItem>
<Para>
Discrete Multitone Technology. This is a line encoding common among ADSL
deployments, and now is the standard. Sometimes referred to as
<Quote>Alcatel compatible</Quote>. Most telcos in the U.S. are now
standardizing on DMT. The other, less common, ADSL encoding is
<Quote>CAP</Quote>. CAP and DMT modems are incompatible with each other.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>DS0</Term>
<ListItem>
<Para>
The basic digital circuit for Telcos - offered at 56 Kbps or 64 Kbps. Can
support one analog voice channel.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>DSLAM</Term>
<ListItem>
<Para>
Digital Subscriber Loop Access Multiplexer - The Telco equipment installed
at the CO that concentrates and multiplexes the DSL lines. One end of the
copper loop connects to the DSLAM, the other to your modem. The DSLAM
is essentially what makes DSL work. Increasingly, smaller devices that
perform similar functions, are being deployed in remote locations in order
to extend the reach of DSL.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>DSL</Term>
<ListItem>
<Para>
Digital Subscriber Loop - A term describing a family of
DSL services, including ADSL, SDSL, IDSL, RADSL, HDSL, VDSL, SHDSL, etc.
that enable high speed Internet connections over standard copper
telephone lines. The main limitation is distance.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>G.DMT</Term>
<ListItem>
<Para>
Synonymous with <Quote>full rate</Quote> ADSL. Used to distinguish between
full rate ADSL, CAP based ADSL and G.Lite. See <Link LinkEnd="family">DSL
Family</Link> for more.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>G.Lite</Term>
<ListItem>
<Para>
A lesser version of ADSL that has lower maximum speeds, and requires no
splitter or filters. Not DMT compatible. See <Link LinkEnd="family">DSL
Family</Link> in this HOWTO for more. </Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>HDSL</Term>
<ListItem>
<Para>
High bit rate DSL. See <Link LinkEnd="family">DSL Family</Link> in
this HOWTO for more.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ILEC</Term>
<ListItem>
<Para>
Incumbent Local Exchange Carrier. The Regional phone company that
physically owns the lines. Examples: Bell Atlantic and Pacific Bell. FCC
regulations are forcing the ILECs to open up their networks to independent
providers. This is allowing an independents like Covad to
offer competitive services. This is a good thing for consumers IMHO.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>Interleaving</Term>
<ListItem>
<Para>
Interleaving is a tunable aspect of DMT/ADSL line encoding. It essential
controls the 'interleaving' of bits in the transmission, and is used
as a form of error correction. As interleaving increases, so does
stability of marginal lines. It also increases latency.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>IP</Term>
<ListItem>
<Para>
Internet Protocol. Also, often used to simply refer to an IP address.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>ISP</Term>
<ListItem>
<Para>
Internet Service Provider. Even full-time connections require an ISP to
provide basic Internet services and connectivity.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>LAN</Term>
<ListItem>
<Para>
Local Area Network. A network of computers that are segregated from the
WAN (Wide Area Network, i.e. the Internet). Often using private,
non-routable IP addressing, e.g. 192.168.1.1 or 10.0.0.1.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>LCP</Term>
<ListItem>
<Para>
Link Control Protocol, one of the sub-protocols used by PPP, and
derivative protocols like PPPoE. As the name sounds, it used by
both the client and server to determine if the connection is
viable. Either end may terminate the session if LCP indicates
the connection is not responsive.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>Loop</Term>
<ListItem>
<Para>
The two wire twisted pair from the telco Central Office that terminates at
a customer location. For DSL, a <Quote>clean</Quote> copper loop within
the distance limitations is required.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>MAC Address</Term>
<ListItem>
<Para>
Media Access Control Address. Sometimes also called
<Quote>hardware</Quote> address, it is a unique identifier of network
devices and is an important aspect of some network environments.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>mini-RAM</Term>
<ListItem>
<Para>
Remote Access Multiplexer, a mini DSLAM. Typically with very few
connections -- eight is common. Used for remote areas too far from a CO.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>MTU</Term>
<ListItem>
<Para>
Maximum Transmission Unit, the largest packet size, measured in bytes,
that a network can transmit. Any packets larger than the MTU are divided
into smaller packets, or <quote>fragmented</quote>, before being transmitted.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>NAT</Term>
<ListItem>
<Para>
Network Address Translation is a means of allowing computers on a LAN to
access the WAN while <Quote>masquerading</Quote> with the IP address of a
host with a suitable address and configuration. With Linux this is called
<Quote>ip-masquerading</Quote>. Often used to share one public, routable
IP address among hosts located on a LAN behind a masquerading proxy where
the local addresses are private and non-routable.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>NID</Term>
<ListItem>
<Para>
Network Interface Device - The telco housing on the side of your house.
Typically where the telco's responsibility ends, and the owner's begins.
Also, sometimes called the <Quote>SNI</Quote>, <Quote>TNI</Quote> or
<Quote>ONI</Quote> or other descriptive acronyms.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>NIC</Term>
<ListItem>
<Para>
Network Interface Card - An internal PC card that supports the
required network interface. Often an ethernet 10/100baseT or an
ATMF-25Mbps card in this context.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>NSP</Term>
<ListItem>
<Para>
Network Service Provider. An ISP's upstream provider or backbone
provider.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>OC-3</Term>
<ListItem>
<Para>
A fiber optic line capable of 155 Mbps.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>POTS</Term>
<ListItem>
<Para>
Plain Old Telephone Service - The service that provides a single analog
voice line (i.e. a traditional phone line).
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>PPPoA (PPPoATM)</Term>
<ListItem>
<Para>
Point-to-Point Protocol over ATM (RFC 2364) is one of the PPP
protocols being used by some DSL providers. This is really a device
specific driver, and in many respects quite different from PPPoE. A
hardware device, i.e. a combination modem/router, is one alternative if
this is the only option available to you.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>PPPoE</Term>
<ListItem>
<Para>
Point-to-Point Protocol over Ethernet (RFC 2516). Another PPP protocol in
use by providers. This one is more common, and there are several Linux
clients available. See the <link LinkEnd="links">Links section</link> for
more. Not to be confused with PPPoA (PPPoATM) since there are fundamental
differences.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>PPPoX</Term>
<ListItem>
<Para>
Used to refer to PPPoE and PPPoA collectively.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>RADSL</Term>
<ListItem>
<Para>
Rate Adaptive DSL. See <Link LinkEnd="family">DSL Family</Link> in
this HOWTO for more.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>RBOC</Term>
<ListItem>
<Para>
Regional Bell Operating Company. The <Quote>Baby Bells</Quote>. The U.S.
phone companies that have had a state sponsored monopoly since the break
up of AT&amp;T.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>RFI</Term>
<ListItem>
<Para>
Radio Frequency Interference. DSL is susceptible to RFI if in the right
frequency range, and if close enough to the DSL signal. This can
disrupt and consequently degrade the DSL signal. Unfortunately, DSL
seems to operate in the frequency range of quite a few potential
disrupting influences.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>RWIN</Term>
<ListItem>
<Para>
Shorthand for 'Receive Window', aka the TCP Receive Window, a tunable
aspect of TCP network stacks.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>SDSL</Term>
<ListItem>
<Para>
Single Line DSL. Or, sometimes also <Quote>Symmetric DSL</Quote>.
See <Link LinkEnd="family">DSL Family</Link> for more.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>SNI</Term>
<ListItem>
<Para>
Subscriber Network Interface - The Telco term for the phone wiring housing
on the side of your house. It designates the point between the Telco side
and the Inside Wire. This is also called the Demarcation Point. Sometimes
called a <Quote>NID</Quote> also.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>Splitter</Term>
<ListItem>
<Para>
The passive device (low-pass filter) at or near the NID that
splits the DSL signal into separate voice and data channels. Filtering is
required for most DSLs that share a regular voice phone line (whether POTS
or ISDN).
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>Splitterless</Term>
<ListItem>
<Para>
A DSL installation that does not require a splitter. For higher
speeds, a RJ11 filter (sometimes called microfilters) is placed on every
extension phone jack where an analog phone or other non-DSL device is
used, thus filtering the DSL signal at the jack, rather than at the
NID. For lower speeds, no filter is necessary. Without a filter or
splitter, the DSL signal tends to cause audible interference on voice
phones. G.Lite needs no splitter, nor filter, but this is the exception to
the rule.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>SOHO</Term>
<ListItem>
<Para>
Small Office HOme
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>Sync Rate</Term>
<ListItem>
<Para>
The speed as negotiated by the DSL modem and the telco's DSLAM. This
represents the theoretical maximum speed of the connection before any
networking protocol overhead is taken into account. Real world throughput
is always something less than the modem's sync rate.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>T-DSL</Term>
<ListItem>
<Para>
German Telekom's ADSL implementation. See <Link LinkEnd="family">DSL
Family</Link> for more.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>T1</Term>
<ListItem>
<Para>
a.k.a DS1 - A digital dedicated line at 1.544 Mbps comprised of 24
channels, used for both voice (24 DS0s) and data.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>T3</Term>
<ListItem>
<Para>
a.k.a DS3 - T1's big brother, a digital dedicated line at 44.736 Mbps,
used for both voice (672 DS0s or 28 DS1s) and data.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>VPI/VCI</Term>
<ListItem>
<Para>
VPI is <Quote>Virtual PATH Identifier</Quote> and is part of an ATM
cell header. VCI is <Quote>Virtual Circuit Identifier</Quote>, also part of
an ATM cell header which contains circuit information. Technically
speaking, these are really remote VPI and VCI (RVPI, RVCI). They are both
important configuration aspects for modems and routers attached to ATM
networks. They must match what the provider is
using. Frequently used VPI/VCI pairs include 0/32, 0/35 and 8/35.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>VDSL</Term>
<ListItem>
<Para>
Very high bit rate DSL. See <Link LinkEnd="family">DSL Family</Link> for
more.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>VoD</Term>
<ListItem>
<Para>
Video on Demand.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>VoDSL</Term>
<ListItem>
<Para>
Voice over DSL.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>WAN</Term>
<ListItem>
<Para>
Wide Area Network, a large publicly accessible network. For example, the
Internet.
</Para>
</ListItem>
</VarListEntry>
<VarListEntry>
<Term>xDSL</Term>
<ListItem>
<Para>
Used to refer to the entire DSL family of related technologies: ADSL,
SDSL, IDSL, etc.
</Para>
</ListItem>
</VarListEntry>
</VariableList>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title>Other Consumer Class High Speed Services</Title>
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3 id="cable">
<Title>Cable Modem vs DSL</Title>
<Para>
The Telcos see DSL as a competitor to the Cable Company's Cable
Modem, and as such, are providing competitive pricing and configuration
offerings. Although Cable Modems are advertised as having 10-30Mbps potential
bandwidth, they use a shared transmission medium with many other users on the
same line, and therefore performance may vary, sometimes greatly, with the amount
of traffic, time of day, and number of other users on the same node. But YMMV.
</Para>
<Para>
It is often heard that DSL has an advantage in that it is a private pipe to
the Internet, with dedicated bandwidth. This is mostly a myth. You do have a
private pipe to the DSLAM, but at that point, you enter the telco's ATM (or
frame relay) network, and start sharing bandwidth. You are at the mercy of
how well your DSL provider and ISP manage their networks. The consensus seems
to be that DSL providers and ISPs are mostly doing a better job of managing
bandwidth than the Cable companies. It is easier for them to add and adjust
bandwidth as needed to meet demand. You are less likely to have speed
fluctuations due to other users being on line at the same time. But, again,
this gets down to how well the specific network and bandwidth are managed.
</Para>
<Para>
DSL probably has a small security advantage too. With most Cable modem
networks, it is like being on a big LAN. You are sharing your connection (and
bandwidth) right at the point of connection. But if you are not doing
something to filter incoming connections already, you are asking for trouble
either way. And, the cable companies are addressing this now, with more
secure approaches. This should not now be a major deciding factor.
</Para>
<Para>
There also seems to be a better chance of having ISP alternatives with DSL
than Cable. At least, in the U.S. this is true. Choice is a good thing, and
so is competition. It seems most Cable outfits give you just one choice for
an ISP. If you don't like it, you are out of luck. The number of options with
DSL probably varies greatly by geographic areas. Populous areas, like
Northeast U.S., seem to have many options.
</Para>
<Para>
So which is better? The differences aren't as much with the technology, as they
are with the implementations. If you look around, you can find plenty of
horror stories on either. And plenty of happy customers too. The way
to know what may be the best for you, is to do comparative shopping based on
experiences of other users in your area. Don't base your choice on one
person's opinion. This is statistically invalid. Likewise, don't base your
choice on someone's opinion who has had a particular service for only a short
time. Again, statistically not worth much. Get as many opinions from those
that are using the <Emphasis>exact same services</Emphasis> that you are
looking at.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Fiber in the Loop (IFITL or FTTC, and FTTH)</Title>
<Para>
In some areas, newer neighborhoods are being built with fiber optic cable
instead of the traditional telco copper lines. While the fiber is a definite
problem for DSL services, it has it's own potential advantages. Existing
fiber is potentially capable of 100 Mbps, and it looks like this could easily
go up soon.
</Para>
<Para>
So while telco fiber customers are being shut out of the DSL market
(since DSL is a copper only technology), they may have much to look forward
to. Technologies are under development, and in some cases just now being
deployed, to take advantage of fiber telco phone loops. Known as
<Quote>FTTC</Quote> (Fiber To The Curb), or <Quote>IFITL</Quote> (Integrated
Fiber In The Loop), this technology is another high speed service that telcos
can offer. The speeds are sufficient for VoD (Video on Demand) and VoDSL
(Voice over DSL), and other high bandwidth services. One nice advantage here
is, that since there is no DSL signal on the wire, the only required CPE is a
network card. In other words, no modem -- just connect a NIC to the wall jack
and off you go! This will also allow the telco to provide other digital
services such digital TV.
</Para>
<Para>
FTTC is Fiber To The Curb. The last leg into the house is still copper. FTTH
(Fiber To The Home), on the other hand, is an all fiber loop with even higher
potential.
</Para>
</Sect3>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect3>
<Title>Wireless</Title>
<Para>
There is a lot of buzz about wireless technologies these days. Wireless would
certainly seem to have a place in the broadband market, especially for areas
that don't have ready access to cable or telco networks. There are still
some inherent problems with the current state of this technology that may prevent
it from becoming a major player in the near term however. Weather can still
impact the wireless signal -- heavy cloud cover or rain for instance. Also,
there is some pretty hefty latency if the uplink is via satellite. Surely
these drawbacks will improve over time. But how soon?
</Para>
</Sect3>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2 id='modems'>
<Title>Compatible Modems</Title>
<Para>
This list is limited to those modems and delivery systems that are readily
available, and should work with any current Linux distribution without having
to go to extraordinary lengths. Alpha and Beta projects are not included. All
modems listed are POTS (analog) modems at this time.
</Para>
<Bridgehead>Ethernet Interface</Bridgehead>
<Para>
<ItemizedList>
<ListItem>
<Para>
<Emphasis>All</Emphasis> external, ethernet based modems, and modem
combination devices, will work (provided they match the provider's DSL).
The only requirement is a compatible ethernet network card. This is the
preferred way to go.
</Para>
</ListItem>
</ItemizedList>
</Para>
<Bridgehead>PCI (Internal)</Bridgehead>
<Para>
<ItemizedList>
<ListItem>
<Para>
Xpeed X200 IDSL <Ulink
URL="http://www.xpeed.com/Products/x200/x200_c.html">http://www.xpeed.com/Products/x200/x200_c.html</Ulink> (as of kernel 2.2.18)
</Para>
</ListItem>
<ListItem>
<Para>
Xpeed X300 SDSL <Ulink
URL="http://www.xpeed.com/Products/x300/x300_c.html">http://www.xpeed.com/Products/x300/x300_c.html</Ulink> (as of kernel 2.2.18)
</Para>
</ListItem>
<listitem>
<para>
IteX PCI ADSL modem based on the Apollo chipset, also sold under various
other brand names such as Dlink and ALH110. <ulink
url="http://www.itexinc.com/">http://www.itexinc.com/</ulink>.
</para>
</listitem>
</ItemizedList>
</Para>
<Bridgehead>USB</Bridgehead>
<Para>
<ItemizedList>
<ListItem>
<Para>
Alcatel SpeedTouch USB (ADSL):
<Ulink
URL="http://www.speedtouchdsl.com/support.htm">http://www.speedtouchdsl.com/support.htm</Ulink>.
The driver is kernel module and requires a 2.4 kernel. See the <link
linkend="SpeedtouchUSB">Appendix</link> for driver information.
</Para>
</ListItem>
<ListItem>
<Para>
Eci Hi Focus ADSL Modem:
<ulink url="http://eciadsl.sourceforge.net/"></ulink>. This project
seems to support several modems and chipsets, including ez-usb an2131qc,
gs7070 and gt3180.
</Para>
</ListItem>
</ItemizedList>
</Para>
</Sect2>
<!-- ~ End Section ~ -->
<!-- ~~~~~ New Section ~~~~~ -->
<Sect2>
<Title id="linrouter">Setting up Linux as a Router</Title>
<Para>
Depending on your local setup, you should consider some other issues. These
include a firewall setup, and any associated configurations. For my setup,
shown in Figure 5 below, I use an old i486 machine configured as a
firewall/router between the DSL connection and the rest of my home network.
I use private IP addresses on my private LAN subnet, and have configured my
router to provide IP Masquerading and Firewalling between the LAN and
WAN connections.
</Para>
<Para>
See the <Ulink
URL="http://www.tldp.org/HOWTO/IP-Masquerade-HOWTO.html">IP
Masquerade HOWTO</Ulink> , and <Ulink
URL="http://www.tldp.org/HOWTO/Firewall-HOWTO.html">Firewall
HOWTO</Ulink> for more information. For 2.4 kernels see the <Ulink
URL="http://www.tldp.org/HOWTO/Adv-Routing-HOWTO.html"
>Linux 2.4 Advanced Routing HOWTO</Ulink>. My experience is that Linux is more
flexible and provides superior routing/firewalling performance. It is
much less expensive than a commercial router -- if you find an old 486 machine
that you may be using as a doorstop somewhere. There any number of
brands of <quote>DSL/Cable</quote> routers on the market as well. These
might be the way to go for pure ease of use, but lack the sophistication
of what Linux can do.
</Para>
<BridgeHead renderas=sect3>
Figure 5: A typical SOHO Network Setup
</BridgeHead>
<Para>
<Literal>
<MSGText>
<LiteralLayout>
<--Private Subnet/LAN-> Linux <-----ISP's Public Subnet----><--inet-->
192.168.1.0
X--+ --------
| | | -------- (eth0:0)---------
+--=| Hub/ | | Linux | +------=| DSL |=-DSL-> ISP's
X-----=|Switch|=-----=| System |=----+ | Modem | Gateway
+--=| | eth1 |(Router)| eth0 ---------
| -------- | -------- |
X--+ | IP_Masq |
| IP_Firewall |
| | Gateway |
| | |
| V V
V 192.168.1.1 Dynamic or
192.168.1.x LAN Gateway Static IP
LAN Addresses IP Address from ISP pool
</LiteralLayout>
</MSGText>
</Literal>
</Para>
<Para>
What I did is setup a Linux router (Redhat Linux 5.0 on a i486) with two
ethernet interfaces. One interface routes to the ISP subnet/gateway (eth0 in
above example), and the other interface (eth1 above) goes to a hub (or switch)
and then connects the LAN with private network addresses (e.g. 192.168.1.x).
Using the private network addresses behind your router/firewall allows some
additional security because it is not directly addressable from outside. You
have to explicitly masquerade your private addresses in order to connect to
the Internet from the LAN. The LAN hosts will access the Internet via the
second NIC (eth1) in the Linux router. Just set their gateway to the IP
address of the second NIC, and assign them addresses on the same network.
</Para>
<Para>
<Emphasis remap="bf">Caution</Emphasis> Make sure your kernel is complied
with IP forwarding and the IP forwarding is turned on. You can check this
with '<Command>cat /proc/sys/net/ipv4/ip_forward</Command>'. The value is
<Quote>1</Quote> for on, and <Quote>0</Quote> for off. You can change this
value by echoing the desired value into this file:
</Para>
<para>
<Screen>
# echo 1 > /proc/sys/net/ipv4/ip_forward
</Screen>
</para>
<Para>
You will also need to set up <Quote>IP Masquerading</Quote> on the Linux
router. Depending on your kernel version, this is done with
<Command>ipfwadm</Command> (2.0), <Command>ipchains</Command> (2.2), or
<Command>iptables</Command> (2.4). See the documentation for specifics on
each. AND -- do not forget to have that firewall set up too!
</Para>
<Para>
There are also several projects that are devoted specifically to using Linux
as a router, just for this type of situation. These are all-in-one solutions,
that include security and various other features. Installation and
configuration, is reportedly very easy. And these will run on very minimal
hardware -- like a floppy drive only. The best known is <Ulink
URL="http://www.linuxrouter.org">http://www.linuxrouter.org</Ulink>. You
might also want to look at <Ulink
URL="http://www.freesco.org">http://www.freesco.org</Ulink> and <Ulink
URL="http://www.coyotelinux.com">http://www.coyotelinux.com</Ulink>. There is
also <Ulink URL="http://www.clarkconnect.org/index.html">http://www.clarkconnect.org/index.html</Ulink>,
which is a similar concept but more full-featured and is designed to be
monitored and configured with a set of Windows based utilities.
</Para>
</Sect2>
</Sect1>
<!-- ~ End Section ~ -->
<!-- ~~~~~~~~ New Section Header ~~~~~~~~~ -->
<!--
Begin adaptation of Chris's Jones' HOWTO for appendix of the DSL-HOWTO
General notes on adaptation for the DSL_HOWTO.
Renumbered section id's so it would fit into one appendix page.
Added preface section.
Added note on VPI/VCI in PPP options configuration area.
Corrected various typos and links (fed back to Chris mostly).
Changes are commented and identifiable by 'HB'.
we don't need this ...
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook V3.1//EN"[]>
<article id="SpeedtouchUSB">
-->
<sect1 id="SpeedtouchUSB">
<title>Appendix: The Alcatel SpeedTouch USB ADSL Modem</title>
<comment> HB: shortened title, made it 'SpeedTouch' which is I think correct
spelling.</comment>
<!--
HB: not allowed here, sorry, we will fudge it below...
<authorgroup>
<author>
<firstname>Chris</firstname>
<surname>Jones</surname>
<affiliation>
<address>
<email>chris@black-sun.co.uk</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2001</year>
<holder>Chris Jones</holder>
<email>chris@black-sun.co.uk</email>
</copyright>
http://benoit.papillault.free.fr/speedtouch/user.en.php3
http://perso.wanadoo.fr/ed.gomez/docs/SpeedTouch-HOWTO-en.html
http://sourceforge.net/projects/speedtouch
Chris's SGML: <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
http://www.linuxdude.co.uk/docs/Alcatel-Speedtouch-USB-mini-HOWTO.sgml
-->
<para>
The Alcatel SpeedTouch USB modem is one of a very few non-ethernet modems with
Linux drivers. This modem is quite popular in Europe (Alcatel's home turf),
and is widely used elsewhere as well. Hats off to Alcatel!
</para>
<para>
For this to work, you will essentially need three things: the Alcatel modem
firmware and management utility (supplied directly by Alcatel in
closed source, binary form), a properly configured kernel and PPP daemon,
and the Linux modem driver and related configuration. The modem driver itself
is open source. There are currently two distinct, unrelated drivers available.
</para>
<para>
When drivers were first released, the installation process required a fair
amount of patching and rebuilding to make things work. Since then, things
have progressed, and it can now be done without any patching (see below).
How well all the pieces go together may depend on how old your Linux
installation is, the kernel and PPP versions, and possibly what patches your
vendor may have applied to their own packages. Recent Linux releases
<emphasis>probably</emphasis> have most, if not all, of this already done,
and hence you may not need to do any patching. I believe this is true of
recent SuSE, Mandrake, and Debian (and probably others as well). You still
need the Alcatel binary firmware, and a driver for the modem (if
your distro does not include this). I would suggest checking your distro's
web site, and search their archives for documents relating to this modem, and
go from there as a first step. YMMV.
</para>
<para>
One obvious requirement is a kernel with USB support. USB and ATM support are
better in recent kernels, and I would suggest if not using a very current
Linux distribution, then at least get a recent kernel. And a quick note
on kernels and patching: if using the kernel source supplied with a Linux
distribution, it is most likely very heavily patched already. Applying
patches to these can be hit or miss.
</para>
<para>
As always with Linux, there is more than one way to skin a cat. This is
true of this modem and is resulting in some confusion since there
are various documents circulating on this modem with various approaches
taken. Some are more current than others too. Keep this in mind if you run
into conflicting recommendations. Again, your distribution is probably the
best source of documents.
</para>
<para>
There are two separate driver projects for this modem. The installation
and configuration are completely different, as is the code base. Both are
open source and GPL. One is a kernel module solution, originally developed by
Alcatel, and now maintained by Johan Verrept. His HOWTO is located at <ulink
url="http://linux-usb.sourceforge.net/SpeedTouch/howto.html">http://linux-usb.sourceforge.net/SpeedTouch/howto.html</ulink>.
I think most would agree that the installation of this driver is the more
complex of the two, and more than likely will require some patching (unless
your distro has already done this). But, it may have some slight performance
benefits since it runs mostly in kernel space.
<!--
404
There is also the
Alcatel-Speedtouch-USB-mini-HOWTO from Chris Jones, <Ulink
URL="http://www.linuxdude.co.uk/docs/Alcatel-Speedtouch-USB-mini-HOWTO/">http://www.linuxdude.co.uk/docs/Alcatel-Speedtouch-USB-mini-HOWTO/</Ulink>.
-->
This driver can potentially support both PPPoE and PPPoA connections.
</para>
<para>
The other driver is by Benoit Papillault and friends. This one has a less
complicated installation, and can be done with <emphasis>no
patching</emphasis>. All the important parts here are done in user space. For
inexperienced users, or just plain ease of use, this may well be the most painless
way to go. The home page is <ulink
url="http://sourceforge.net/projects/speedtouch">http://sourceforge.net/projects/speedtouch</ulink>
and related docs are <ulink
url="http://speedtouch.sourceforge.net/docs.php">http://speedtouch.sourceforge.net/docs.php</ulink>.
This driver can also work with 2.2 kernels (2.2.17 or later). PPPoE is not
an option with this driver at this time. This driver also does not use
the management utility that is part of the Alcatel supplied binary package.
It extracts the modem firmware, and then does its own
<quote>management</quote>, so less dependent on proprietary code. Mandrake is
reportedly including an RPM of this driver now.
</para>
<para>
Since this modem potentially supports both PPPoE and PPPoATM connections,
which one is better? Which ever is supported by your ISP, and then
which ever works best for you! If your ISP supports both (some do and
some don't), you might try each approach and make your own decision.
There is no absolute right or wrong on such things. There are just too
many variables. Theoretically at least, PPPoA should utilize a little
less overhead and system resources.
</para>
<para>
There are other USB modems on the market that use an Alcatel chipset,
such as the Efficient Networks 4060. Do not expect either of these drivers to
work with other modems. They won't. You should get a compatible ethernet
modem in such situations. There are other USB modems with Linux drivers also.
See <ulink
url="http://eciadsl.sourceforge.net/">http://eciadsl.sourceforge.net/</ulink>.
</para>
</sect1>
</Article>
<!-- ~~~~~~~~~~~~~~~~~~~~ finis ~~~~~~~~~~~~~~~~~~~~~~~~~ -->
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