On 3/13/19 5:45 PM, AXE MSC wrote:
Hi,
PCSCF has two realms. One is facing Core network and another is facing
Access network. I have a scenario where PCSCF sends the INVITE to the
handset facing Access realm. But no TCP ACK or SIP provisional response
received from the handset. After 15 seconds wait time SCSCF asks PCSCF core
realm to clear the call by sending a Cancel. PCSCF replies back with 200 Ok
for the Cancel. But PCSCF kept the transaction alive for the handset due to RFC
3261, Section 9.1: "If no provisional response has been received, the
CANCEL request MUST NOT be sent; rather, the client MUST wait for the
arrival of a provisional response before sending the request."
Is the PCSCF acting as a proxy or B2BUA?
After 4 minutes, handset replies back with TCP ACK. PCSCF then re-transmits
INVITE and and gets 183 back from handset. However, because calling party
side call was already cleared at 15th second, this is causing a ghost call
for B party after 4 minutes of the original call.
Can PCSCF destroy the transaction at 15th second without sending the Cancel
to handset? Later if handset comes with provisional response then PCSCF
can just reply back with SIP 481(transaction does not exist).
To be correct you need to maintain the transaction until you get
something back or it times out. If PCSCF is acting as proxy, then the
SCSCP should be retransmitting the INVITE (according to timers) until
something comes back or the transaction times out. Sending CANCEL and
receiving a 200 to it doesn't mean you can avoid this. If the CANCEL
succeeds then a 487 should be received for the INVITE, ending the
transaction.
OTOH, if the PCSCF is acting as a B2BUA, then the PCSCF *may* send a 487
to the INVITE when it gets the CANCEL. It will then have to handle the
transaction to the handset itself. It will still need to do all the
above on its own. If that then results in the handset accepting the call
it can send a BYE to terminate it.
Thanks,
Paul
_______________________________________________
Sip-implementors mailing list
Sip-implementors@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
