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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>The Need for VoIP Protocols</title><link rel="stylesheet" href="styles.css" type="text/css" /><meta name="generator" content="DocBook XSL Stylesheets V1.69.1" /><link rel="start" href="index.html" title="Asterisk™: The Future of Telephony" /><link rel="up" href="asterisk-CHP-8.html" title="Chapter 8. Protocols for VoIP" /><link rel="prev" href="asterisk-CHP-8.html" title="Chapter 8. Protocols for VoIP" /><link rel="next" href="asterisk-CHP-8-SECT-2.html" title="VoIP Protocols" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">The Need for VoIP Protocols</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="asterisk-CHP-8.html">Prev</a> </td><th width="60%" align="center">Chapter 8. Protocols for VoIP</th><td width="20%" align="right"> <a accesskey="n" href="asterisk-CHP-8-SECT-2.html">Next</a></td></tr></table><hr /></div><div class="sect1" lang="en" xml:lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="asterisk-CHP-8-SECT-1"></a>The Need for VoIP Protocols</h2></div></div></div><p>The basic premise of VoIP is the <a id="I_indexterm8_tt1089" class="indexterm"></a>packetization<sup>[<a id="asterisk-CHP-8-FN-1" href="#ftn.asterisk-CHP-8-FN-1">101</a>]</sup> of audio streams for transport over Internet Protocol-based
networks. The challenges to accomplishing this relate to the manner in
which humans communicate. Not only must the signal arrive in essentially
the same form that it was transmitted in, but it needs to do so in less
than 150 milliseconds. If packets are lost or delayed, there will be
degradation to the quality of the communications experience, meaning that
two people will have difficulty in carrying on a conversation.</p><p>The transport protocols that collectively are called “the Internet”
were not originally designed with real-time streaming of media in mind.
Endpoints were expected to resolve missing packets by waiting longer for
them to arrive, requesting retransmission, or, in some cases, considering
the information to be gone for good and simply carrying on without it. In
a typical voice conversation, these mechanisms will not serve. Our
conversations do not adapt well to the loss of letters or words, nor to
any appreciable delay between transmittal and receipt.</p><p>The traditional PSTN was designed specifically for the purpose of
voice transmission, and it is perfectly suited to the task from a
technical standpoint. From a flexibility standpoint, however, its flaws
are obvious to even people with a very limited understanding of the
technology. VoIP holds the promise of incorporating voice communications
into all of the other protocols we carry on our networks, but due to the
special demands of a voice conversation, special skills are needed to
design, build, and maintain these networks.</p><p>The problem with<a id="I_indexterm8_tt1090" class="indexterm"></a> packet-based voice transmission stems from the fact that
the way in which we speak is totally incompatible with the way in which IP
transports data. Speaking and listening consist of the relaying of a
stream of audio, whereas the Internet protocols are designed to chop
everything up, encapsulate the bits of information into thousands of
packages, and then deliver each package in whatever way possible to the
far end. Clearly, some way of dealing with this is required.</p><div class="footnotes"><br /><hr width="100" align="left" /><div class="footnote"><p><sup>[<a id="ftn.asterisk-CHP-8-FN-1" href="#asterisk-CHP-8-FN-1">101</a>] </sup>This word hasn’t quite made it into the dictionary, but it is a
term that is becoming more and more common. It refers to the process
of chopping a steady stream of information into discrete chunks (or
<span class="emphasis"><em>packets</em></span>), suitable for delivery independently of
one another.</p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="asterisk-CHP-8.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="asterisk-CHP-8.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="asterisk-CHP-8-SECT-2.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 8. Protocols for VoIP </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> VoIP Protocols</td></tr></table></div><div xmlns="" id="svn-footer"><hr /><p>You are reading <em>Asterisk: The Future of Telephony</em> (2nd Edition for Asterisk 1.4), by Jim van Meggelen, Jared Smith, and Leif Madsen.<br />
This work is licensed under the <a href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Attribution-Noncommercial-No Derivative Works License v3.0</a>.<br />
To submit comments, corrections, or other contributions to the text, please visit <a href="http://oreilly.com/catalog/9780596510480/">http://www.oreilly.com/</a>.</p></div></body></html>
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