[SIPForum-discussion] In which scenario Proxy will generate CANCEL ?

Tajinder Gulati gulati.tajinder at gmail.com
Fri Jun 18 08:56:32 UTC 2010


As soon as UAS responds with 180 Ringing , a timer starts at the proxy,
which waits for the final response.

Please refer section "Progress" in RFC 3261 where the following is

*A proxy has the option of canceling a transaction when there is a gap of 3
minutes between responses in a transaction. To prevent cancellation, the UAS
MUST send a non-100 provisional response at every minute, to handle the
possibility of lost provisional responses.*

On the expiry of this timer (i.e. on time out), proxy sends a *CANCEL*request.
*CANCEL *asks the UAS to cease processing the request and to generate an
error response to that request.Firstly UAS responds back with 200 OK
response confirming the receipt of CANCEL request then it sends the "487
Request Terminated" error response. This also ends the initial INVITE

**Please refer to section 9 "*Canceling a Request*" in RFC 3261.


On Thu, Jun 17, 2010 at 1:05 PM, seshagiri <seshgirik at gmail.com> wrote:

> Hi All
>  I came across a scenario to test CANCEL which should be generated by
> Proxy.
>  In the following scenarios, which scenario is valid?
>  1 UAC sends INVITE to Proxy, proxy forwards the request to UAS.
>  Now UAS responds with 180 ringing only  but no final response , so in
> this case *Proxy sends CANCEL to UAS  or which response ?*
>  Now the proxy sends 408 or 480 to UAC ?
>  Or in the *above scenario is valid only for Forking* *scenario only*,
> where Proxy tries to multiple locations?
> I am confused about the functionality.
>  Pl give your valuable suggestions.
>  Regards
> Sesh
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