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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Packet assembler/disassembler</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">"X.29" redirects here. For similarly named topics, see <a href="../X29_(disambiguation)" class="mw-redirect mw-disambig" title="X29 (disambiguation)">X29</a>.</div>

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<p>A <b>packet assembler/disassembler</b>, abbreviated <b>PAD</b> is a communications device which provides multiple <a href="../Asynchronous_serial_communication" title="Asynchronous serial communication">asynchronous</a> terminal connectivity to an <a href="../X.25" title="X.25">X.25</a> (packet-switching) network or host computer. It collects data from a group of terminals and places the data into X.25 packets (assembly). A PAD also does the reverse, it takes data packets from packet-switching network or host computer and returns them into a character stream that can be sent to the terminals (disassembly). A <a href="../Frame_Relay_assembler/disassembler" title="Frame Relay assembler/disassembler">Frame Relay assembler/disassembler</a> (FRAD) is a similar device for accessing <a href="../Frame_Relay" title="Frame Relay">Frame Relay</a> networks.

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<div class="mw-heading mw-heading2"><h2 id="ITU-T_(Triple-X_PAD)">ITU-T (Triple-X PAD)</h2></div>

<p>The structure of a PAD is defined by the <a href="../ITU-T" title="ITU-T">ITU-T</a> in recommendations <a href="../X.3" title="X.3">X.3</a>, <a href="../X.28" title="X.28">X.28</a>, and X.29. Sometimes, this is referred to as a Triple-X PAD, due to the three X-series recommendations which define it:

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<ul><li><b>X.3</b> specifies the parameters for terminal-handling functions such as line speed, <a href="../Flow_control_(data)" title="Flow control (data)">flow control</a>, character echo, et al. for a connection to an X.25 host. The X.3 parameters are similar in function to present-day <a href="../Telnet" title="Telnet">Telnet</a> options.</li>

<li><b>X.28</b> defines the DTE-C (asynchronous character mode) interface to a PAD, including the commands for making and clearing down connections, and manipulating the X.3 parameters. The commands were very crude, a bit like (but not at all compatible with) the <a href="../Hayes_command_set" class="mw-redirect" title="Hayes command set">Hayes command set</a>. Many commercial PAD products provided completely different enhanced user interfaces.</li>

<li><b>X.29</b> defines the DTE-P (packet mode) interface to a PAD, i.e., how the PAD encapsulates characters and control information in X.25 packets.<sup id="cite_ref-X29_1-0" class="reference"><a href="#cite_note-X29-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup></li></ul>

<p>Connections are established using <a href="../X.121" title="X.121">X.121</a> 14-digit X.25 addresses.

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<div class="mw-heading mw-heading2"><h2 id="Green_Book_PAD">Green Book PAD</h2></div>

<p>One of the UK <a href="../Coloured_Book_protocols" title="Coloured Book protocols">Coloured Book protocols</a>, <b>Green Book</b>, also defines two PAD protocols. Green Book was developed by (UK) <a href="../Post_Office_Telecommunications" class="mw-redirect" title="Post Office Telecommunications">Post Office Telecommunications</a> in the 1970s. Although not identical to Triple-X, Green Book is sufficiently similar to X.3 and X.29 that generally the two will interwork. Green Book also specifies <b>TS29</b>, a very similar protocol which ran over the Yellow Book Transport Service, which is another of the Coloured Book protocols.

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<p><b>ITP</b> (Interactive Terminal Protocol) was an early PAD protocol for use over X.25 developed in the 1970s for use with <a href="../Post_Office_Telecommunications" class="mw-redirect" title="Post Office Telecommunications">UK GPO's</a> EPSS (Experimental Packet Switching System, the predecessor of <a href="../Packet_Switch_Stream" title="Packet Switch Stream">PSS</a>). ITP predated Triple-X, and is a completely different protocol. <a href="../Science_and_Engineering_Research_Council" title="Science and Engineering Research Council">Science and Engineering Research Council</a> (SERC) also used ITP on SERCnet and continued developing ITP after EPSS, although it eventually gave way to Triple-X.

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<ul><li><a href="../Terminal_node_controller" title="Terminal node controller">Terminal node controller</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.29/en">"X.29 : Procedures for the exchange of control information and user data between a Packet Assembly/Disassembly (PAD) facility and a packet mode DTE or another PAD"</a>. <i>www.itu.int</i>.</cite></span>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://www.chilton-computing.org.uk/ca/technology/networking/p001.htm">ITP: Protocols in the SERC/NERC Network"</a></li></ul></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2024-09-16" href="https://en.wikipedia.org/wiki/?title=Packet_assembler%2Fdisassembler&oldid=1245981799">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

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