Hi

we are using Kamailio 4.3.7 and I have a question concerning BYE handling.

We have the following situation:

A carrier a call to us. We are forwarding the call to the destination, but it does not pick up the call. We have call-forward active with use of tm module, so we forward the call to the new destination. The first call generates a to-tag in 180, let's call it TT1. The second call, so the c-destination also answer with 180 but with another to-tag (TT2). Both ringing are passed to the originating carrier.

When the timer for the first call is timed out, Kamailio cancels the branch with a CANCEL so it does not exist any more

Now the c-destination picks up the phone, and reply with 200 OK with TT2

The carrier then sends a BYE with TT1 to us, but Kamailio doesn't know anything about it, so it does not reply and the carrier sends a timeout and terminates the complete call.

So the question is, how handle such a situation. Is it possible to store the first branch, or fake a OK reply to the BYE request of the carrier as for my understanding this behaviour is not against RFC.

To clarify the situation here comes a call-flow diagram

A            Kamailio           B               C

|---INV Bob@P1->|               |               | |               |--INV Bob@B--->|               | |               |<-100----------|               | |<-100----------|               |               | |               |<-180 TT1------|               | |<-180 TT1------|               |               |

Forward after 10 seconds

|               |--CANCEL------>|               | |               |<-487----------|               | |               |<-200 OK-------|               | |               |--ACK--------->|               | |<-181 TT1------|               |               | |               |--INV Carol@C----------------->| |               |<-100--------------------------| |               |<-180 TT2----------------------| |<-180 TT2------|               |               | |               |<-200 OK TT2-------------------| |<-200 OK TT2---|               |               | |--BYE TT1----->|               |               | |--BYE TT1----->|               |               | |--BYE TT1----->|               |               | |--408--------->|               |               | |--ACK--------->|               |               | |               |--ACK------------------------->| |               |<-BYE TT2----------------------| |<-BYE TT2------|                               | |--481--------->|                               | |               |--481------------------------->|

To get around the the situation with the second to-tag, we passing every call through SEMS now, because its B2B function rewrites the to-tag, so there is always only one to-tag towards the carrier A. But it's not the gold solution.

I hope somebody can help me.

BR, Björn