[SIPForum-discussion] A question about INVITE fork

[Tomasz Zieleniewski]

Hi,

If proxy is stateful it holds the information about incoming request, the
requests which
it sends as the result of this request processing by proxy core and request
responses.
In case when proxy forks the request, there may be many outgoing requests
and responses
corresponding to different destinations.
In such case there are some rules about proxy behavior. When proxy forks the
request, it
tries to choose the best answer for the request with the exception of 1xx
and 2xx responses.
Any provisional response, except 100 which is sent hop by hop, must be sent
upstream to UAC
immediately. But still proxy is unable to decide which transaction  will
complete first.
That's why whenever proxy receives first 2xx response it forwards it
immediately upstream to UAC
and cancels any other transactions it established downstream towards the
destination.
So UAC will not receive second 180 response because this transaction would
be canceled by proxy.

Kind regards,
- Tomasz Zieleniewski


2009/5/6 Sunny <guangu.he at gmail.com>

> Hi allI have a question about INVITE fork. see follow picture.
>
> UAC                     Proxy            UAS1             UAS2
>    |---------INVITE----->|                      |                     |
>    |                          |-------INVITE--->|                     |
>    |                          |----------------------|-------INVITE-->|
>    |                          |<-------200--------|                     |
>    |<--------200---------- |                      |                     |
>    |----------ACK------->|                       |                    |
>    |                          |---------ACK----->|                    |
>    |                          |                       |
>  |
>    |                          |<-------------180---|--------------------|
>    |<------180-------------|
>
> when UAC received UAS2 180, the UAC have not corresponding transaction,the
> UAC will discard 180 or other?
>
> --
> Thanks
>
> Sunny
>
> _______________________________________________
> This is the SIP Forum discussion mailing list
> TO UNSUBSCRIBE, or edit your delivery options, please visit
> http://sipforum.org/mailman/listinfo/discussion
> Post to the list at discussion at sipforum.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://sipforum.org/pipermail/discussion/attachments/20090508/0ed266d2/attachment-0002.html>