Hi Jeroen,
Thanks for the clarification, it's very helpful.
Ok, so let's make it a bit more complicated. If there is a stateless
proxy in the chain, for example:
UA Stateless Stateful UA
Proxy Proxy
Initial Request
INVITE INVITE INVITE INVITE
via A --> via B --> via C --> via D
via A via B via C
via A via B
via A
So, the CANCEL will look like this -
CANCEL CANCEL
via A --> via ZZ -->
via A
200 OK 200 OK (Stateful proxy sends response back)
<-- via A <-- via ZZ
via A
CANCEL (Stateful proxy forwards CANCEL to next hop)
via C -->
200 OK
<-- via C
The point I'm trying to clarify here is that the receiver of the CANCEL
should use the branch id of the final via header to identify the
transaction, as stateless elements sitting in between will handle the
CANCEL in an end-to-end fashion, rather than hop-by-hop.
Am I interpreting RFC3261 correctly here too?
Thanks.
Best Regards,
Ben
Jeroen van Bemmel wrote:
> Ben,
>
> It also applies to proxies. So if you have the following scenario:
>
> UA->proxy
> INVITE
> Via: branch=b1
>
> proxy->onwards
> INVITE
> Via: branch=b2
> Via: branch=b1
>
> then if UA sends CANCEL, it becomes
>
> UA->proxy
> CANCEL
> Via: branch=b1
>
> proxy->onwards
> CANCEL
> Via: branch=b2 <= Note: only 1 Via header here
>
> When the proxy starts forking, each forwarded INVITE gets its own
> branch. So for two targets {A,B} it becomes:
>
> proxy->onwards_A
> INVITE
> Via: branch=b2
> Via: branch=b1
>
> proxy->onwards_B
> INVITE
> Via: branch=b3
> Via: branch=b1
>
> A subsequent CANCEL must have matching top branch again, so <b2>
> towards A and <b3> towards B
>
> Hope this clarifies,
>
> jeroen
>
>
> ----- Original Message ----- From: "Ben Papworth"
> <[EMAIL PROTECTED]>
> To: <[email protected]>
> Sent: Wednesday, February 22, 2006 4:40 PM
> Subject: [Sip-implementors] Stateful Proxies Forwarding CANCELs
>
>
>> Hi,
>>
>> I'm currently writing a call stateful SIP proxy. I've got a question
>> about how I should handle CANCELs...
>>
>> The SIP book (SIP: Understanding the Session Initiation Protocol) says
>> that CANCELs should have the same branch id as the request that's being
>> cancelled. Does this only apply to the UA that created the request and
>> issued the CANCEL, or should intermediate proxies use the same branch id
>> their via header for both the forwarded request and the forwarded
>> CANCEL?
>>
>> This proxy may also be capable of forking requests at a later date. In
>> this instance, is it desirable to use the same branch ids for requests
>> and their CANCELs?
>>
>> Thanks for any help!
>>
>> Best Regards,
>> Ben Papworth
>>
>>
>>
>> _______________________________________________
>> Sip-implementors mailing list
>> [email protected]
>> https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
>
_______________________________________________
Sip-implementors mailing list
[email protected]
https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
