162 lines
7.2 KiB
HTML
162 lines
7.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>Wireless Howto: Background Knowledge </TITLE>
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<LINK HREF="Wireless-HOWTO-3.html" REL=next>
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<LINK HREF="Wireless-HOWTO-1.html" REL=previous>
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<LINK HREF="Wireless-HOWTO.html#toc2" REL=contents>
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</HEAD>
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<BODY>
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<A HREF="Wireless-HOWTO-3.html">Next</A>
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<A HREF="Wireless-HOWTO-1.html">Previous</A>
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<A HREF="Wireless-HOWTO.html#toc2">Contents</A>
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<HR>
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<H2><A NAME="s2">2. Background Knowledge </A></H2>
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<H2><A NAME="ss2.1">2.1 What about Wireless?</A>
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</H2>
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<P>Wireless is a new technology that can help you to connect computers at
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distance. It works with Wireless cards with a TX/RX inside at 2.4 GHz while
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the software interface is Ethernet-like, with an hardware address different
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for each card in the world. Typical transmit power is 10-20 mW till 100mW (see
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standard IEEE 802.11 and FCC/CEPT licenses).
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<H2><A NAME="ss2.2">2.2 What's the max distance between radio cards? </A>
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</H2>
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<P>The most important thing in Wireless communications is the line of sight
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clear: you MUST SEE (with eyes or with a binocular) the antenna from the other
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end or you can have (at most) a little tree between them.
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<P>The distance depends on the antenna and (eventually amplifier) used: 2-300
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meters with a omnidirectional antenna; 1 km with a directive one; 2-3 km with
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a omnidirectional amplified (200mW); some km with parabolic antenna. 50-60
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km with parabolic or directive antenna amplified (some Watts).
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<P>Be aware that it is not always legal to amplifier Wireless cards, cause
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you could violate FCC/CEPT (and also your country relative) specifics.
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<H2><A NAME="ss2.3">2.3 What's the difference between wired and Wireless network? </A>
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</H2>
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<P>Wired networks are very simple to setup (at least at low level). Wireless
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networks are very difficult to setup, to manage, to debug... Typical problem
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with wired networks like hardware install, software install, debug and so on
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become very critical with Wireless:
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<P>
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<OL>
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<LI>You have to choose the right Wireless card: there are many cards from many
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vendor with many requirement and specs. If you want to create a little LAN/WAN
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you have to buy IEEE 802.11 compliant Wireless cards with an Access Point.
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</LI>
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<LI>Many cards are PCMCIA, so you have to install pcmcia Linux source first.
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</LI>
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<LI>You have to test it with 2 running systems, first at very short distance,
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then you can get far. </LI>
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<LI>You should test it at any weather (typically rain). </LI>
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<LI>Finally be happy for setting up. </LI>
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</OL>
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<P>If you installed a repeater (Linux box that has many Wireless and wired
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cards) you may have problem editing its configuration at distance!
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<H2><A NAME="ss2.4">2.4 What I need to know to setup a Wireless network? </A>
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</H2>
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<P>There are a number of requirement to setup a Wireless network;
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<P>
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<PRE>
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software requirement:
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</PRE>
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<P>
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<OL>
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<LI>Generic network knowledge like IP address, netmask, routing... covered
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by generic Linux NET3-4-HOWTO; *</LI>
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<LI>Specific network knowledge like proxy arp, bridging, proc fs, contained
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in Proxy-ARP-Subnet, Bridge Mini-Howto and in Linux Kernel Source (2.2.x or
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2.4.x) under Documentation/networking/ ip-sysctl.txt) *</LI>
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<LI>Wireless network knowledge like access mode (ADHOC, INFRASTRUCTURE and
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ACCESS POINT), channel concept, outdoor and indoor defines and so on that you
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can find in any document concerning Wireless: IEEE standard 802.11, CEPT, etc.
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</LI>
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</OL>
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<P>
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<PRE>
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non software requirement:
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</PRE>
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<P>
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<OL>
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<LI>Minimal experience in antennas, physical mounting, pointing</LI>
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<LI>Pc hardware installation with particular attention to not produce interference
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between different Wireless Cards (if required). </LI>
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</OL>
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<P>finally a great luck!
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<P>* All Howtos needed by this document can be retrieved from
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<A HREF="http://www.linuxdoc.org">http://www.linuxdoc.org</A><H2><A NAME="ss2.5">2.5 Why should I setup a Wireless network and what I expect from it? </A>
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</H2>
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<P>Why? Because you're not satisfied of wired network!
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<P>With Wireless cards you can go across garden, parks, houses, (but you MUST
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SEE the other end!).
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<P>High Level Protocol used in Wireless Cards are the same used in Ethernet
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cards: TCP/IP over Wireless Ethernet-like but make attention to Windows Sharing
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Application, cause if you use Linux to forward, you are warned that a ip forwarder
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doesn't let pass through broadcast messages (see more on NetBIOS protocol):
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in this case you should use a WINS server to support Network Browsing (see
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Samba doc).
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<P>Wireless let you create a little LAN/WAN with a central point of access
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(maybe with Internet Access!) and give access to anyone by air!
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<P>Imagine a country all cabled by radio machines.
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<P>Imagine a network that can connect all country people together, sharing
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files, audio applications, video applications at high bandwidth (like cable
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network).
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<P>All that can be done (and it's already done in some country) using Wireless
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cards with Wireless Access Point and Wireless Linux Boxes that can operate
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as repeater (at IP level such as router or, if you want, at data-link level,
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with bridge driver, see more at
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<A HREF="http://openrock.net/bridge">Bridge Http Link</A> or
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<A HREF="ftp://openrock.net/bridge">Bridge Ftp Link</A><H2><A NAME="ss2.6">2.6 What Wireless cards are covered by this howto? </A>
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</H2>
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<P>In this howto I start with a generic configuration (to introduce Wireless
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networking), then I describe an example for each card I knew directly, with
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some trick you can use to improve its performance.
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<P>
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<PRE>
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Wireless Card list:
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</PRE>
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<P>
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<OL>
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<LI>Proxim Symphony -
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<A HREF="http://www.proxim.com">http://www.proxim.com</A></LI>
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<LI>Webgear AviatorPRO 2.4 (pcmcia support needed) -
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<A HREF="http://www.webgear.com">http://www.webgear.com</A></LI>
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<LI>Lucent Wavelan I, II, Orinoco -
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<A HREF="http://www.lucent.com">http://www.lucent.com</A> and
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<A HREF="http://www.orinocowireless.com">http://www.orinocowireless.com</A></LI>
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<LI>Cabletron -
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<A HREF="http://www.cabletron.com">http://www.cabletron.com</A></LI>
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<LI>YDI am930_isa -
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<A HREF="http://www.ydi.com">http://www.ydi.com</A></LI>
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<LI>Siemens Radio Modem (Dect) -
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<A HREF="http://www.siemens.com">http://www.siemens.com</A></LI>
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<LI>RadioLan (5 GHZ) -
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<A HREF="http://www.radiolan.com">http://www.radiolan.com</A> </LI>
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</OL>
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<P>For a very more exhaustive list see
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<A HREF="http://www.hpl.hp.com/personal/Jean_Tourrilhes/Linux">Jean Tourrilhes Wireless Howto</A>.
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<P>Siemens Radio Modem is not a really 802.11 Wireless card, they are modems
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that you can attach to serial and they act as modem (at 1800 MHz, so DECT technology).
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Appendix B describe their use.
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<P>RadioLan cards work at 5.4GHz in a Windows 9x environment and with a RadioLan
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Access Point that bridges between Wired and Wireless networks (there are no
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Linux driver as I know).
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<H2><A NAME="ss2.7">2.7 How much do they cost? </A>
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</H2>
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<P>Wireless cards listed above are very low expansive: they start from very
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few hundred of dollars up to some thousand of dollars for Access Point that
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have 2 Wireless card (Lucent, for example) that can act as a bridge.
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<HR>
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<A HREF="Wireless-HOWTO-3.html">Next</A>
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<A HREF="Wireless-HOWTO-1.html">Previous</A>
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<A HREF="Wireless-HOWTO.html#toc2">Contents</A>
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