SIP normally doesn't use TCP, it uses UDP, and is sessionless in that context. The exact mechanics of a registration can get deeply involved, so I'm going to give a very cursory overview. The endpoint tells the server (Asterisk, or whatever) that it would like to register, with a username and password, and what its IP address and port are. The server puts this in a list, and when it has a call for that endpoint, sends UDP packets to the known IP and port. There it typically encounters a NAT rounter, which had opened the port during the original registration and hopefully still has it open.<div>
<br></div><div>You can enable a feature called NAT keep-alive on most endpoints to overcome bad NAT in some routers.</div><div><br><br><div class="gmail_quote">On Mon, Nov 14, 2011 at 2:51 PM, Douglas Mortensen <span dir="ltr"><<a href="mailto:doug@impalanetworks.com">doug@impalanetworks.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal">I know this is probably a very basic question for many on this list. But in troubleshooting an issue, I wanted to take a step back & ask the question. In Asterisk (or maybe all SIP), how do extensions stay registered with the SIP server?<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Do the extensions simply register repeatedly as a means of telling asterisk “I’m still here”, or are there actual keepalive packets that are transmitted to actually keep a TCP session alive? My guess is the former.<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">But am I oversimplifying it? Is there more to the process?<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p><p class="MsoNormal">Thanks,<u></u><u></u></p>
<p class="MsoNormal">-<u></u><u></u></p><p class="MsoNormal"><span style="font-size:14.0pt">Doug Mortensen<u></u><u></u></span></p><p class="MsoNormal">Network Consultant<u></u><u></u></p><p class="MsoNormal"><b>Impala Networks Inc<u></u><u></u></b></p>
<p class="MsoNormal"><span style="font-size:10.0pt">CCNA, MCSA, Security+, A+<u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt">Linux+, Network+, Server+<u></u><u></u></span></p><p class="MsoNormal">
.<u></u><u></u></p><p class="MsoNormal"><span style="font-size:10.0pt"><a href="http://www.impalanetworks.com" target="_blank"><span style="color:blue">www.impalanetworks.com</span></a><u></u><u></u></span></p><p class="MsoNormal">
<span style="font-size:10.0pt">P: <a href="tel:%28505%29%20327-7300" value="+15053277300" target="_blank">(505) 327-7300</a><u></u><u></u></span></p><p class="MsoNormal"><span style="font-size:10.0pt">F: <a href="tel:%28505%29%20327-7545" value="+15053277545" target="_blank">(505) 327-7545</a><u></u><u></u></span></p>
<p class="MsoNormal">.<u></u><u></u></p><p class="MsoNormal"><u></u> <u></u></p></div></div><br>--<br>
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