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76 lines
2.7 KiB
76 lines
2.7 KiB
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<book id="sl" xmlns:xi="http://www.w3.org/2001/XInclude">
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<bookinfo>
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<title>The SL Module - Statless request handling</title>
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<authorgroup>
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<author>
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<firstname>Bogdan</firstname>
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<surname>Iancu</surname>
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<affiliation><orgname>FhG FOKUS</orgname></affiliation>
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<address>
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<email>iancu@fokus.fraunhofer.de</email>
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</address>
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</author>
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<author>
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<firstname>Daniel-Constantin</firstname>
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<surname>Mierla</surname>
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<affiliation><orgname>asipto.com</orgname></affiliation>
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<address>
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<email>miconda@gmail.com</email>
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</address>
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</author>
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</authorgroup>
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<copyright>
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<year>2003</year>
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<holder>FhG FOKUS</holder>
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</copyright>
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</bookinfo>
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<toc></toc>
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<chapter>
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<title>Admin Guide</title>
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<section id="sl.overview">
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<title>Overview</title>
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<para>
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The <acronym>SL</acronym> module allows the SIP server to act as a stateless
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UA server and generate replies to SIP requests without keeping
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state. That is beneficial in many scenarios, in which you wish not
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to burden server's memory and scale well.
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</para>
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<para>
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The <acronym>SL</acronym> module needs to filter ACKs sent after a
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local stateless reply to an INVITE was generated. To recognize such
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ACKs, ser adds a special "signature" in to-tags. This signature is
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sought for in incoming ACKs, and if included, the ACKs are
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absorbed.
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</para>
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<para>
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To speed up the filtering process, the module uses a timeout
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mechanism. When a reply is sent, a timer us set. As long as the
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timer is valid, the incoming ACK requests will be checked using TO
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tag value. Once the timer expires, all the ACK messages are let
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through - a long time passed till it sent a reply, so it does not
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expect any ACK that have to be blocked.
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</para>
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<para>
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The ACK filtering may fail in some rare cases. If you think these
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matter to you, better use stateful processing (<acronym>TM</acronym>
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module) for INVITE processing. Particularly, the problem happens when a UA
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sends an INVITE which already has a to-tag in it (e.g., a
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re-INVITE) and the server want to reply to it. Then, it will keep the
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current to-tag, which will be mirrored in ACK. SER will not see
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its signature and forward the ACK downstream. Caused harm is not
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bad--just a useless ACK is forwarded.
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</para>
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</section>
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<xi:include href="sl_params.xml"/>
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<xi:include href="sl_functions.xml"/>
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<xi:include href="sl_stats.xml"/>
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</chapter>
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</book>
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