[OpenSIPS-Users] Opensips as front end for late offer handling

[sindrek]

Hi,

I'm working for a firm which are using the sip porta platform. This is fine
despite it does not support late offer. That is a client/pbx etc sending an
initial invite and possible re-invites with no sdp. This is legal, but
portaone does not support it (they will in a year or so, but until then ..).

The idea then is to put some sort of front end for these types of endpoints
and as a man in the middle ... detect invites with no sdp and insert a fake
sdp into it before it continues to the porta platform. This part is ok and I
have made it and it works.

The problem is all the other signalling, it sounds simple, but it is not
since all the signalling will go through this front end. The clients/pbxs
wil be directed to register and signal everything towards the front end's ip
address.

I have tried to do this for some weeks now using opensips as a proxy (not
b2bua). What I did was to let the register msg make entries in the front end
opensips proxy and then fwd the register message to porta which does all the
auth etc. 

If the registration is ok I'll keep it in the location table in opensips. If
not I wipe it again. This works fine, but what is difficult further is to
handle all the other signalling with replies and everything which passes
through. 

Porta thinks all endpoints that are registered via the opensips front end is
at the opensips front end's ip (the only way). Opensips them needs a lot of
logic to rewrite this and that from what it got in the location table (real
endpoint ip etc).  I came a step forward, but it gets more and more
complicated and I have concluded to stop for now.

Right now I'm looking into using opensips as a transparent b2bua instead
just looking for invites with no sdp. I'm not sure if this is possible or
simpler yet since I'm new to configuring it as a b2bua. So I'm asking you
experts for some advice .. ? 

Is this possible using opensips you think? If so in b2bua mode? If so again
any b2bua config examples would be very interesting to me :-) 

/BR
Sindre



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