[OpenSIPS-Users] SST module: 422 returned on the min(client-Min-SE, client-Session-Expires) <RFC 4028>

[joel.oliveira]

Hello all,

As often, I am fighting this problem for quite a few days and did not manage
to find a solution. So here it goes my cry of help to the world.

I have various clients registered to my OpenSIPs solution, and negotiate via
SIP with a Cisco Media Gateway when recieving/making calls. No problems
until a week ago when I found out that clients behind Asterisk would have
inbound calls dropped after 15 minutes, and this happened with all of them
when they use 1.6+ version of Asterisk. 

This happens because of Re-Invites associated with Session-timers. I know
how to solve this on the client side by doing some configuration on the
Asterisk but of course I don't want to do that as I want to have a general
solution without have to control the client-side.

Ok, going right to the point: After doing some research on the SST module I
decide to add on the "Re-Invite part of the route" a treatment on the
Session-timer Re-Invite. So, my problem now occurs when Opensips answer to a
Re-Invite with a "422 - Session Timer Too Small" when, in my opinion, this
shouldn't happen. Asterisk sends the right Session-expires: 1800 and the
Min-SE: 90, where the Opensips Min-SE is 1800.

The Asterisk's request and the OpenSIPs response can be seen on
http://pastebin.com/wQFvv4ta

As I come to understand, and according to Bogdan, OpenSIPs is following  the
RFC 4028 as it should by answering back a 422 when comparing the proxy's
Min-SE with the minimum between the client's Min-SE and the Session-Expires
headers. ( info found on
http://opensips-open-sip-server.1449251.n2.nabble.com/sst-min-se-problem-td2582335.html
).

For me it doesn't make sense to have OpenSIPs to look into the client's
Min-SE. If Asterisk's Session-Expires is greater or equal to the proxy's
Min-SE so why do we need to look into Asterisk's Min-SE? I just read the RFC
http://tools.ietf.org/html/rfc4028#section-6 and it does seem to me that it
should only look into the client's Session-Expire.

Maybe I am understanding this all wrong and Asterisk should be changing the
Min-SE as well, but of course I don't know this for sure and don't
understand why should it change it. Can someone enlighten me. Thanks for
your time on reading all this text.

Best Regards,
Joel Oliveira

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