[Sems] Problem when redirecting to Sems from Opensips

[Stefan Sayer]

Hello,

o Eli Hayun [06/22/09 11:24]:
> Hi
> I am trying to get MusicOnHold. When I find out an HOLD request I am
> doing the following in OpenSips
> 
>         append_hf("P-App-Name: announcement\r\n");
>         rewritehostport("myhost:5080");
>         t_relay();
>         exit;
> But I am getting an error 
> 
> SIP/2.0 481 Call leg/Transaction does not exist
> 
> I think the problem is that I am in a middle of a transaction, but I
> don't know how to avoid that error and actually run the application

Generally speaking, you can not break into an established SIP dialog, 
you need either support from the endpoints (telephones) for that, or a 
B2BUA in the call from the beginning.

Consider what would be happening if you just stripped the To-Tag in your 
proxy, and sent the call to the moh server. The moh server would create 
its dialog state locally and set it's own to-tag, which would not match 
the one from the endpoint sending the reinvite.

If you would be making the media server take the To-tag as given, and 
reply with 200 OK, things would break if the phone wants to unhold - the 
other endpoint would think CSeq is lower.

Have a look at sip service examples [1],[2]. Note that for historical 
reasons, SEMS does not yet support call flows with empty INVITE/SDP 
offer in 200/answer in ACK.

BR
Stefan

[1] http://tools.ietf.org/wg/sip/draft-ietf-sip-service-examples/
[2] http://tech-invite.com/Ti-sip-service-1.html
> 
> Thanks
> 
> Eli Hayun
> 
> _______________________________________________
> Sems mailing list
> Sems at lists.iptel.org
> http://lists.iptel.org/mailman/listinfo/sems

-- 
Stefan Sayer
VoIP Services

stefan.sayer at iptego.com
www.iptego.com

IPTEGO GmbH
Wittenbergplatz 1
10789 Berlin
Germany

Amtsgericht Charlottenburg, HRB 101010
Geschaeftsfuehrer: Alexander Hoffmann