[OpenSIPS-Users] Transfer issue

Iñaki Baz Castillo ibc at aliax.net
Tue Nov 17 01:38:21 CET 2009

El Lunes, 16 de Noviembre de 2009, Bogdan-Andrei Iancu escribió:
> I agree that a b2bua is more complex than a proxy, but I guess the idea 
> is to identify all these buggy cases and fix them.

A very important issue in most of the existing B2BUA's:

Imagine the b2bua routes/generates the call to a proxy which does parallel 
forking so b2bua receives two 183 with different To-tag and, of course, 
different SDP (sess-id, sess-version...).

The b2bua replaces the received To-tags in an *unique* new To-tag to be used 
in the upstream leg.

This is a bug since the UAC will receive two 183 with same To-tag but 
different SDP so it must ignore the second SDP (a SDP cannot change during an 

I've issued this problem. The solution is "easy":

For each received 1XX response (different To-tags) the b2bua must create so 
many different To-tags for the 1XX it sends to the UAC.

If the b2bua doesn't replace the To-tag then the problem automatically 
dissapears, but then it's not a b2bua :)

Iñaki Baz Castillo <ibc at aliax.net>

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