I have a MGW that has SIP interface towards UE and ISUP towards MSC. For a SIP->ISUP call:
1. MGW receives SIP INVITE from UE and sends IAM to MSC-A. 2. MGW receives backward ACM message with "called party status = free" from MSC-A. 3. MGW sends 180 Ringing towards SIP UE. 4. Called Party (on MSC-A) rings but does not answer 5. Call is now forwarded by MSC-A (this is the case of call forwarding after alerting the user) towards MSC-B. Thus, MSC-A sends IAM to MSC-B 6. MSC-B sends ACM message with "called party status = free" towards MSC-A 7. MSC-A transforms it to CPG (Alerting) and sends it towards MGW. 8. My question is: what MGW should do with 2nd CPG (Alerting) message? RFC 3398 (ISUP<->SIP interworking) mandates to send out 180 but as MGW has already sent out 180 (see #3 above), so it can not send duplicate 180 with same "tag". Thanks Kapil Saxena _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
