[Users] Re: [Devel] New module: SIP Session Timer (sst)

[Ron Winacott]

Greg,
	The SST module sits in the middle and will update the timeout value of the 
dialog module. If the dialog times out, the proxy is free to release all 
locally held resources and delete the dialog. (from its point of view) It 
may, but I am fuzzy on this RFC point, also be able to send a BYE. The 
current SST module does not suppport sending the BYE.

SST is mainly used by SIP proxies to tell when a call has abnormally 
terminated and all BYEs/CANCELs/etc have been lost. In most cases, the SIP 
proxy have allocated a bunch of local resources (memory, database records, 
etc) that need to be released on call/dialog termination. Think of it as SIP 
ping or better still, SIP keep-alive. In the case where I am currently using 
the SST module is to close the firewall rules and release the QOS resources 
that were setup for the call in a SIP proxy server that stays in the middle 
of the SIP messaging.

If both uac's support SST (expire) then the proxy can see the expire: header 
going bay and set the dialog timeout to the correct value. If either or both 
uac's do not support SST, the dialog timeout value is left at its default 
value (in the case of OpenSER 12 hours unless you set the AVP to a different 
value)

I hope this answered your questions, and I too am not the greatest at reading 
RFCs. I think the only people that are good at reading them, are the 
authors. :-)

Ronw

On Monday 18 September 2006 11:05, Greg Fausak wrote:
> Ron,
>
> I just skimmed the RFC.  This is
> a great feature!  I have a question about
> what it does with respect to the OpenSER proxy.
>
> Does the sst module refresh the session, or does this module
> sit in the middle, monitor dialog time remaining, and remove reference
> to the dialog if the timer value goes negative?  That is, it looks
> like to me the session timer stuff is between the uas and the uac, but
> I never have been very good at reading the RFCs :-)
>
> -g
>
-- 
Ron Winacott - SOMA Networks, Inc.

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