70 lines
3.2 KiB
HTML
70 lines
3.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
|
|
<HTML>
|
|
<HEAD>
|
|
<META NAME="GENERATOR" CONTENT="LinuxDoc-Tools 0.9.21">
|
|
<TITLE> Modem-HOWTO: Appendix E: Cable and DSL modems </TITLE>
|
|
<LINK HREF="Modem-HOWTO-26.html" REL=next>
|
|
<LINK HREF="Modem-HOWTO-24.html" REL=previous>
|
|
<LINK HREF="Modem-HOWTO.html#toc25" REL=contents>
|
|
</HEAD>
|
|
<BODY>
|
|
<A HREF="Modem-HOWTO-26.html">Next</A>
|
|
<A HREF="Modem-HOWTO-24.html">Previous</A>
|
|
<A HREF="Modem-HOWTO.html#toc25">Contents</A>
|
|
<HR>
|
|
<H2><A NAME="other_modems"></A> <A NAME="s25">25.</A> <A HREF="Modem-HOWTO.html#toc25">Appendix E: Cable and DSL modems </A></H2>
|
|
|
|
<H2><A NAME="ss25.1">25.1</A> <A HREF="Modem-HOWTO.html#toc25.1">Introduction</A>
|
|
</H2>
|
|
|
|
<P> This HOWTO only deals with the common type of analog modem used to
|
|
connect PC's to ordinary analog telephone lines. There are also
|
|
higher speed analog modems that use special types of lines: cable and
|
|
DSL modems. There is also the ISDN "modem" which uses digital signals.
|
|
While this HOWTO doesn't cover such modems, some links to documents
|
|
that do may be found at the start of this HOWTO. The next 3
|
|
sub-sections: DSL, Cable, and ISDN, briefly discuss such modems. For
|
|
both DSL and Cable modems, the basic QAM modulation method is similar
|
|
to ordinary analog analog modems. See
|
|
<A HREF="Modem-HOWTO-21.html#QAM_">Combination Modulation</A> </P>
|
|
|
|
<H2><A NAME="ss25.2">25.2</A> <A HREF="Modem-HOWTO.html#toc25.2">Digital Subscriber Line (DSL)</A>
|
|
</H2>
|
|
|
|
<P> DSL (often ADSL) uses the existing twisted pair line from your
|
|
home/office to the local telephone office. This can be used if your
|
|
telephone line can accept significantly higher speeds than an ordinary
|
|
modem would use. It replaces the analog-to-digital converter at the
|
|
local telephone office with one which can accept a much faster flow of
|
|
data (in a different format of course). The spectrum of the twisted
|
|
pair line is divided up into various channels. Each channel uses QAM
|
|
modulation like ordinary modems do. Data is sent over multiple
|
|
channels. The device which converts the digital signals from your
|
|
computer to the analog signal used to represent digital data on what
|
|
was once an ordinary telephone line, is a DSL modem. The DSL modem
|
|
is often external (takes up space on your desk) and connects to
|
|
your computer via either an ethernet port or a USB port.</P>
|
|
|
|
<H2><A NAME="ss25.3">25.3</A> <A HREF="Modem-HOWTO.html#toc25.3">Cable Modems</A>
|
|
</H2>
|
|
|
|
<P> The coaxial cables that provide for cable television in homes have
|
|
additional bandwidth not used for television, mostly at frequencies
|
|
higher than used for cable TV. This extra bandwidth may be used for
|
|
connecting computers to ISP's. However, many computers need to share
|
|
the same cable. The spectrum of the free bandwidth is split up into
|
|
channels (frequency division multiplexing) and each channel is given
|
|
time slots to which individual computers are assigned (time division
|
|
multiplexing). The cable modem converts the digital date from your
|
|
computer (from a network card: NIC) to the required analog signal, and
|
|
only broadcasts within it's assigned time slots on it's assigned
|
|
channel.</P>
|
|
|
|
|
|
<HR>
|
|
<A HREF="Modem-HOWTO-26.html">Next</A>
|
|
<A HREF="Modem-HOWTO-24.html">Previous</A>
|
|
<A HREF="Modem-HOWTO.html#toc25">Contents</A>
|
|
</BODY>
|
|
</HTML>
|