Please check this thread. The CANCEL will get a 2xx response.

https://lists.cs.columbia.edu/pipermail/sip-implementors/2006-May/012974.html


On 5/25/06, Nataraju A B <[EMAIL PROTECTED]> wrote:
>
>
> Thanks & Regards,
> Nataraju A.B.
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of Madhuri
> Sakhare
> Sent: Thursday, May 25, 2006 7:40 PM
> To: [email protected]
> Subject: [Sip-implementors] Query Regarding Collision case of CANCEL.
>
> Hi,
>
>
> Consider this call flow:
>
>    UAC                      UAS
>
>     |         INVITE         |
>
>     |----------------------->|
>
>     |      180 RINGING       |
>
>     |<-----------------------|
>
>     |        CANCEL          |
>
>     |----------------------->|
>
>     |      200 OK CANCEL     |
>
>     |<-----------------------|
>
>     |                        |
>
>
>     This is a collision case of a reliable 180 response and a CANCEL
> Request. The application on the callee side has sent a 200 OK response,
> and the response is left pending in the SIP stack.  Then the collision
> occurs and the CANCEL is indicated to the application, but since it has
> already sent a final response, it has no way of sending another one. The
> call is not freed.
>
> How should the SIP stack responds to this?
> [ABN] This scenario has been discussed in the list quite a few times...
> if the callee UA had already sent 200OK for INVITE then 200OK will not
> be sent for CANCEL. CANCEL would be rejected with 481 responses...
>
> The call will go through...
>
> The caller's SIP stack has to initiate the BYE request to terminate the
> call once the INV/200/ACK transaction is completed... if the user had
> hung up the call...
>
> Regards,
> Madhuri
>
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