[asterisk-users] How do extensions "stay registered"

[Carlos Alvarez]

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.

You can enable a feature called NAT keep-alive on most endpoints to
overcome bad NAT in some routers.


On Mon, Nov 14, 2011 at 2:51 PM, Douglas Mortensen
<doug at impalanetworks.com>wrote:

> 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?****
>
> ** **
>
> 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.*
> ***
>
> ** **
>
> But am I oversimplifying it? Is there more to the process?****
>
> ** **
>
> Thanks,****
>
> -****
>
> Doug Mortensen****
>
> Network Consultant****
>
> *Impala Networks Inc*
>
> CCNA, MCSA, Security+, A+****
>
> Linux+, Network+, Server+****
>
> .****
>
> www.impalanetworks.com****
>
> P: (505) 327-7300****
>
> F: (505) 327-7545****
>
> .****
>
> ** **
>
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-- 
Carlos Alvarez
TelEvolve
602-889-3003
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