From 7f1ed056baf2d1f00f39c5b1bd2e5a7fd8f080d8 Mon Sep 17 00:00:00 2001
From: Peter Saint-Andre <stpeter@jabber.org>
Date: Wed, 26 Sep 2007 22:51:20 +0000
Subject: [PATCH] initial version

git-svn-id: file:///home/ksmith/gitmigration/svn/xmpp/trunk@1240 4b5297f7-1745-476d-ba37-a9c6900126ab
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+<?xml version='1.0' encoding='UTF-8'?>
+<!DOCTYPE xep SYSTEM 'xep.dtd' [
+  <!ENTITY % ents SYSTEM 'xep.ent'>
+%ents;
+]>
+<?xml-stylesheet type='text/xsl' href='xep.xsl'?>
+<xep>
+  <header>
+    <title>Stream Compression with LZW</title>
+    <abstract>This document specifies how to use the LZW algorithm in XML stream compression.</abstract>
+    &LEGALNOTICE;
+    <number>0229</number>
+    <status>Draft</status>
+    <type>Standards Track</type>
+    <sig>Standards</sig>
+    <dependencies>
+      <spec>XMPP Core</spec>
+      <spec>XEP-0138</spec>
+    </dependencies>
+    <supersedes/>
+    <supersededby/>
+    <shortname>N/A</shortname>
+    &stpeter;
+    <revision>
+      <version>1.0</version>
+      <date>2007-09-26</date>
+      <initials>psa</initials>
+      <remark>Per a vote of the XMPP Council, published as Draft.</remark>
+    </revision>
+    <revision>
+      <version>0.0.1</version>
+      <date>2007-08-30</date>
+      <initials>psa</initials>
+      <remark>Copied text from XEP-0138.</remark>
+    </revision>
+  </header>
+
+  <section1 topic='Introduction' anchor='intro'>
+    <p>&xep0138; specifies an extensible framework for XML stream compression and defines a registry for compression methods (see &COMPRESSMETHODS;). However, <cite>XEP-0138</cite> registers only the ZLIB method (see &rfc1950;). This document specifies usage of the LZW compression method.</p>
+  </section1>
+
+  <section1 topic='Background' anchor='background'>
+    <p>The "LZW" compression algorithm was originally developed by Abraham Lempel and Jacob Ziv, subsequently improved by Terry Welch <note>See "A Technique for High-Performance Data Compression", <cite>Computer</cite> (June 1984), pp. 8-19.</note>, and patented by Sperry Corporation (later Unisys Corporation) as U.S. Patent Number 4,464,650 <note>See &lt;<link url='http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=4,464,650'>http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=4,464,650</link>&gt;.</note>. This patent expired on June 20, 2003 <note>See &lt;<link url='http://www.unisys.com/about__unisys/lzw'>http://www.unisys.com/about__unisys/lzw</link>&gt;.</note>. Therefore implementations of LZW are no longer patent-encumbered.</p>
+    <p>The algorithm is specified by Ecma International in &ecma151; under the name "DCLZ".</p>
+  </section1>
+
+  <section1 topic='Definition' anchor='definition'>
+    <p>If the receiving entity (server) supports the LZW algorithm, it MUST include a &lt;method/&gt; element whose XML character data is "lzw" in the compression stream feature, as follows.</p> 
+    <example caption='Receiving Entity Offers Stream Compression Feature, Including LZW Method'><![CDATA[
+<stream:features>
+  <starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>
+  <compression xmlns='http://jabber.org/features/compress'>
+    <method>zlib</method>
+    <method>lzw</method>
+  </compression>
+</stream:features>
+    ]]></example>
+    <p>If the initiating entity wishes to use the LZW algorithm, then it MUST specify that method.</p>
+    <example caption='Initiating Entity Requests Stream Compression Using LZW'><![CDATA[
+<compress xmlns='http://jabber.org/protocol/compress'>
+  <method>lzw</method>
+</compress>
+    ]]></example>
+    <p>The initiating entity and receiving entity then MUST attempt to negotiate use of the LZW algorithm in accordance with <cite>XEP-0138</cite>.</p>
+    <p>If the use of the LZW algorithm is negotiated, the usage SHOULD follow the definition in <cite>ECMA-151</cite>.</p>
+  </section1>
+
+  <section1 topic='Optionality' anchor='optionality'>
+    <p>The LZW algorithm is OPTIONAL to implement for <cite>XEP-0138</cite> implementations and this specification does not define a mandatory-to-implement technology.</p>
+  </section1>
+
+  <section1 topic='Security Considerations' anchor='security'>
+    <p>The security considerations specified in <cite>XEP-0138</cite> apply to usage of the LZW algorithm.</p>
+  </section1>
+
+  <section1 topic='IANA Considerations' anchor='iana'>
+    <p>This document requires no interaction with &IANA;. </p>
+  </section1>
+
+  <section1 topic='XMPP Registrar Considerations' anchor='registrar'>
+    <section2 topic='Compression Methods Registry' anchor='registrar-methods'>
+      <p>The &REGISTRAR; maintains a registry of compression methods at &COMPRESSMETHODS;.</p>
+      <p>The LZW algorithm is already registered. This specification updates the registry submission as follows:</p>
+      <code><![CDATA[
+<method>
+  <name>lzw</name>
+  <desc>the LZW (DCLZ) compression method</desc>
+  <doc>XEP-0229</doc>
+</method>
+      ]]></code>
+    </section2>
+  </section1>
+
+</xep>