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

[Dale Worley]

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