[Devel] CANCEL to INVITE after183, Call flow question

[Sumeet Gupta]

Hello,

I am having an issue regarding a particular call flow through OpenSER. I was 
hoping someone could clarify. Basically this vendor claims that it is 
incorrect to send a CANCEL in response to a negative INVITE even after it 
has recieved a provisional response like a 183.

Call from Party A to Party B

Call flow 1:
(A) INVITE
(B) 100
(B) 183
(B) 503
(A) ACK
(A) CANCEL


Vendor claims it should be like this with no CANCEL.
Call Flow 2:
(A) INVITE
(B) 100
(B) 183
(B) 503
(A) ACK

Which flow is correct?

Thanks,
Sumeet

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