72 lines
4.7 KiB
HTML
72 lines
4.7 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 name="Robots" content="index,follow" />
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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="Digital services and DDS" />
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<meta name="abstract" content="You can use digital service and Digital Data Services (DDS) with PPP." />
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<meta name="description" content="You can use digital service and Digital Data Services (DDS) with PPP." />
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<meta name="DC.Relation" scheme="URI" content="rzaiyconnalts.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaiycsudsu.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaiysw56.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="rzaiydigital" />
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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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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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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>Digital services and DDS</title>
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</head>
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<body id="rzaiydigital"><a name="rzaiydigital"><!-- --></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">Digital services and DDS</h1>
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<div><p>You can use digital service and Digital Data Services (DDS) with
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PPP.</p>
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<div class="section"><h4 class="sectiontitle">Digital service</h4><p>With digital service, data travels
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all the way from the computer of the sender to the central office of the telephone
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company, to the long distance provider, to the central office, and then to
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the computer of the receiver in digital form. Digital signaling offers much
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more bandwidth and higher reliability than analog signaling. A digital signaling
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system eliminates many of the problems that analog modems must deal with,
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such as noise, variable line quality, and signal attenuation.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Digital Data Services</h4><p>Digital Data Services (DDS)
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is the most basic of digital services. DDS links are leased, permanent connections,
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running at fixed rates of up to 56Kbps. This service is also commonly designated
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as DS0.</p>
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</div>
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<div class="section"><p>You can connect to DDS using a special box called <dfn class="term">Channel
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Service Unit/Data Service Unit (CSU/DSU)</dfn>, which replaces the modem
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in the analog scenario. DDS has physical limitations that are primarily related
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to the distance between the CSU/DSU and the Telephone Company Central Office.
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DDS works best when distance is less than 9000 m (30 000 ft). Telephone companies
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can accommodate longer distances with signal extenders, but this service comes
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at higher cost. DDS is best suited for connecting two sites that are served
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by the same Central Office. For long distance connections that span different
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Central Offices, mileage charges can quickly add up to make DDS impractical.
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In such cases, Switched-56 may be better solution. Typically, you can connect
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to a DDS CSU/DSU over V.35, RS449, or X.21 serial interface with synchronous
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protocol at rates up to 56Kbps.</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 class="relref"><strong>Related reference</strong><br />
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<div><a href="rzaiycsudsu.htm" title="A Channel Service Unit (CSU) is a device that connects a terminal to a digital line. A Data Service Unit (DSU) is a device that performs protective and diagnostic functions for a telecommunications line. Typically, the two devices are packaged as a single unit, CSU/DSU.">CSU/DSU</a></div>
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<div><a href="rzaiysw56.htm" title="When you do not need a full-time connection, you can save money by using switched digital service, which is generally called Switch-56 (SW56).">Switched-56</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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