On 9/14/16 7:05 AM, Harrison, Jason, Vodafone UK wrote:
Hi,
I have an issue and I can't identify if the behaviour is wrong:
Here is a working call
Provider Customer
SBC SBC
INVITE (SDP offer)-->
<--100 Trying
<--180 Ringing (SDP answer)
PRACK -->
<-- 200OK (PRACK)
<-- UPDATE
200OK UPDATE -->
<--200OK (INVITE)
ACK -->
And here is a failed call
Provider Customer
SBC SBC
INVITE -->
<--100 Trying
<--180 Ringing (SDP)
PRACK -->
<-- 200OK (PRACK)
<-- UPDATE
<--200OK (INVITE)
200OK (UPDATE) -->
ACK -->
BYE -->
<--200OK (BYE)
In the failed call I am being told by the provider that their SBC sent a BYE
because the 200OK for the INVITE was received before it managed to send the
200OK for the UPDATE, I have checked the RFCs and can't find if the customer
SBC is breaking any rules by sending an 200OK for the INVITE before it received
a response for the UPDATE
I don't think the second flow should be considered an error. It is valid
for the UPDATE to occur before the INVITE completes (as in the first
flow), and it is also valid for the update to occur after the INVITE
completes. Nor is there anything that the update will do that will have
a different effect whether it is completed before or after the INVITE
completes.
ISTM that by generating the error the implementation is indicating that
it is coupling the state machine for the UPDATE with that for INVITE.
That is dubious behavior.
Thanks,
Paul
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