[SIPForum-techwg] Could to-tag in 200 OK response be different with the to-tag in 180 ringing?

[mike xu]

Hi Dale,

Thank you for your reply.
It seems that the transaction/dialog match part in the UAC which I
used need to be enhanced to deal with such "forking" case.

Thanks again,
Mike

On 7/27/07, Dale Worley <dworley at pingtel.com> wrote:
> On Fri, 2007-07-27 at 12:49 +0800, mike xu wrote:
> > Do you know that in RFC3261, could the to-tag in 200 OK be different
> > with the one in 180 ringing?
>
> It is allowed, but it does not mean what you might expect.  Each to-tag
> represents one dialog.  The 180 has a to-tag value, and it is part of a
> dialog.  The 200 has a different to-tag value, and so it is part of a
> *different* dialog.  The 180's dialog never succeeds (because the dialog
> never returns a 200 response), and eventually the UAC deletes knowledge
> of it.  So from the UAC's point of view, this is an example of forking.
> (In general, a UAC must be able to track multiple early dialogs until it
> receives a 200.  After that, it may also receive 200 responses for other
> forks of the INVITE, which it must either handle or terminate by sending
> BYE.
>
> > Below is the case which I met, in step F1 (180 ringing), callee
> > generated one to-tag (46bf8) while in step F2 (200 OK) the sip server
> > generates a new to-tag which is "as5123fc8f", and my sip endpoint
> > didn't match this 200 OK response, the sip server will resend 200 OK
> > and I obveriously couldn't hear the voice mail info.
> >
> >    Caller        SIP_SERVER       Callee
> >      |                |              |
> >      |       INVITE    |             |
> >      |------------->|  INVITE      |
> >      |    (100 Trying)  |----------->|
> >      |<-------------|              |
> >      |                |180 Ringing F1 |
> >      |   180 Ringing   |<-----------|
> >      |<-------------|              |
> >      |                |   CANCEL     |
> >      |                |----------->|
> >      |                |   200 OK     |
> >      |                |<-----------|
> >      |                |487 Req Cancel |
> >      |                |<------------|
> >      |                |     ACK       |
> >      |                |------------>|
> >      |200 OK(SIP/SDP) F2|               |
> >      |<-------------|               |
> >      |    ACK         |               |
> >      |------------->|               |
> >      | voicemail RTP   |               |
> >      |<===============||               |
> >
> > Does any body know that the new to-tag in F2's 200 OK response is
> > valid or invalid? Does it comply to RFC3261?
>
> It looks like SIP_SERVER is doing what it should -- the 200 is
> establishing a different dialog than the one that the 180 was reporting
> on.
>
> Dale
>
>
>