80 lines
4.9 KiB
HTML
80 lines
4.9 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Analog telephone lines" />
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<meta name="abstract" content="The analog connection, which uses modems to carry data over leased or switched lines, sits at the bottom of the point-to-point scale." />
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<meta name="description" content="The analog connection, which uses modems to carry data over leased or switched lines, sits at the bottom of the point-to-point scale." />
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<meta name="DC.Relation" scheme="URI" content="rzaiyconnalts.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzaiyanalog" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Analog telephone lines</title>
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</head>
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<body id="rzaiyanalog"><a name="rzaiyanalog"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Analog telephone lines</h1>
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<div><p>The analog connection, which uses modems to carry
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data over leased or switched lines, sits at the bottom of the point-to-point
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scale.</p>
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<div class="section"><p>Leased lines are full-time connections between two specified locations,
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while switched lines are regular voice-telephone lines. The fastest modems
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today operate at an uncompressed rate of 56 Kbps. Given the signal-to-noise
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ratio on unconditioned voice-grade telephone circuits, though, this rate is
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often unattainable.</p>
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</div>
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<div class="section"><p>Modem manufacture claims of higher bit-per-second (bps) rates
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are typically based on a data compression (CCITT V.42bis) algorithm that is
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utilized by their modems. Although V.42bis has the potential to achieve as
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much as four-fold reduction in data volume, compression depends on the data
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and rarely reaches even 50%. Data already compressed or encrypted may even
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increase with V.42bis applied. X2 or 56Flex extends the bps rate to 56 Kbps
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for analog telephone lines. This is a hybrid technology that requires one
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end of the PPP link to be digital while the opposite end is analog. Additionally,
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the 56 Kbps applies only when you are moving data from the digital toward
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the analog end of the link. This technology is well suited for connections
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to ISPs with the digital end of the link and hardware at their location. Typically,
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you can connect to a V.24 analog modem over an RS-232 serial interface with
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an asynchronous protocol at rates up to 115.2 Kbps.</p>
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</div>
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<div class="section"><p>The V.90 standard put an end to the K56flex/x2 compatibility issue.
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The V.90 standard is the result of a compromise among the x2 and K56flex camps
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in the modem industry. By viewing the public switched telephone network as
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a digital network, V.90 technology can accelerate data from the Internet to
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a computer at speeds of up to 56 Kbps. V.90 technology differs from other
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standards because it digitally encodes data instead of modulating it as analog
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modems do. The data transfer is a asymmetrical method, so upstream transmissions
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(mostly keystroke and mouse commands from a computer to the central site,
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which require less bandwidth) continue to flow at the conventional rates of
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up to 33.6 Kbps. Data sent from a modem is sent as an analog transmission
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that mirrors the V.34 Standard. Only the downstream data transfer takes advantage
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of the high-speed V.90 rates.</p>
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</div>
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<div class="section"><p>The V.92 standard improves on V.90 by allowing upstream rates
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of up to 48 Kbps. Additionally, connection times may be reduced due to improvements
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in the hand-shaking process, and modems that support a "hold" feature can
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now remain connected while the telephone line accepts in coming call or uses
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call-waiting.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaiyconnalts.htm" title="PPP can transmit datagrams over serial point-to-point links.">Connection alternatives</a></div>
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</div>
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</div>
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</body>
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</html>
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