74 lines
4.7 KiB
HTML
74 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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<meta name="DC.Title" content="T1/E1 and fractional T1" />
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<meta name="abstract" content="T1/E1 and fractional T1 are two kinds of valid connection alternatives." />
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<meta name="description" content="T1/E1 and fractional T1 are two kinds of valid connection alternatives." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>T1/E1 and fractional T1</title>
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</head>
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<body id="rzaiytone"><a name="rzaiytone"><!-- --></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">T1/E1 and fractional T1</h1>
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<div><p>T1/E1 and fractional T1 are two kinds of valid connection alternatives.</p>
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<div class="section"><h4 class="sectiontitle">T1/E1</h4><p>A T1 connection bundles together twenty-four
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64 Kbps (DS0) time-division multiplexed (TDM) channels over 4-wire copper
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circuit. This creates a total bandwidth of 1.544 Mbps. An E1 circuit in Europe
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and other parts of the world bundles together thirty-two 64-Kbps channels
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for a total of 2.048 Mbps. TDM allows multiple users to share a digital transmission
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medium by using pre-allocated time slots. Many digital private branch exchanges
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(PBX) take advantage of T1 service to import multiple call circuits over one
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T1 line instead of having 24 wire pairs routed between the PBX and telephone
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company. It is important to note that T1 can be shared between voice and data.
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A telephone service may come over a subset of the 24 channels of a T1 link,
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for instance, leaving remaining channels for Internet connectivity. A T1
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multiplexer device is needed to manage the 24 DS0 channels when a T1 trunk
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is shared between multiple services. For a single data-only connection, the
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circuit can be run unchannelized (no TDM is performed on the signal). Consequently,
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a simpler CSU/DSU device can be used. Typically, you can connect to a T1/E1
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CSU/DSU or multiplexer over V.35 or RS 449 serial interface with synchronous
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protocol at rates at a multiple of 64 Kbps to 1.544 Mbps or 2.048 Mbps. The
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CSU/DSU or multiplexer provides the clocking in the network.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Fractional T1</h4><p>With Fractional T1 (FT1), a customer
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can lease any 64-Kbps sub-multiple of a T1 line. FT1 is useful whenever the
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cost of dedicated T1 will be prohibitive for the actual bandwidth customer
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uses. With FT1 you pay only for what you need. Additionally, FT1 has the following
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feature that is unavailable with a full T1 circuit: Multiplexing DS0 channels
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at the central office of the telephone company. The remote end of an FT1 circuit
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is at a Digital Access Cross-Connect Switch that is maintained by the telephone
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company. Systems that share the same digital switch can switch among DS0 channels.
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This scheme is popular with ISPs that use a single T1 trunk from their location
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to the digital switch of a telephone company. In these cases, multiple clients
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can be served with FT1 service. Typically, you can connect to a T1/E1 CSU/DSU
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or multiplexer over V.35 or RS 449 serial interface with synchronous protocol
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at some multiple of 64 Kbps. With FT1, you are pre-allocated a subset of the
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24 channels. The T1 multiplexer must be configured to fill only the time slots
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that are assigned for your service.</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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