Subject: [SIP] clarification on tags in the BYE request.

From: Sunitha Kumar <[email-masked]>
Date: Thu, 19 Oct 2000 10:42:14 -0700

With respect to section 11.3 and 11.4 in September 4, SIPbis,

It is given that all subsequent requests of the same callLeg  contains
the same To header field, including the *tags*.
It is also given here, that a UAC copies the tag from the final response
into the ACK, but it *MUST NOT* copy the tag into any subsequent
requests unless the response was a 200 class response to an INVITE
request.

Does this mean:
UAC -------send INVITE------------->UAS
UAC<------send 200 OK with tag in To----UAS
UAC-------send ACK, with same tag as in To of 200 OK-->UAS
UAC<-------RTP---------------------->UAS

Now , if BYE is sent from UAC to a UAS, should UAC tag the To field of
the BYE , the same as the 200 OK that it received.
If yes, why, isn't this another transaction?

I agree that if the BYE were to be sent instead of the ACK( in order to
cancel the call), then it needs to be tagged in the To field. But, not
if the BYE was sent independently, after establishing the call.
The FAQ had no explanation of this. Could someone explain this?

Thanks much.

--
Sunitha Kumar
http://www.vovida.com

---

From: Billy Biggs <[email-masked]>
Date: Thu, 19 Oct 2000 16:22:07 -0500

Sunitha Kumar ([email-masked]):

> the same To header field, including the *tags*.  It is also given
> here, that a UAC copies the tag from the final response into the ACK,
> but it *MUST NOT* copy the tag into any subsequent requests unless the
> response was a 200 class response to an INVITE request.

  Yes, the tag is only valid for the active call.

> the BYE , the same as the 200 OK that it received.

  Yes, you include the tag in all future transactions on the call-leg.

> If yes, why, isn't this another transaction?

  Huh?  The BYE is definitely a subsequent request, and a 200 class
response was received.  Sounds like this meets the requirements.

> I agree that if the BYE were to be sent instead of the ACK( in order
> to cancel the call), then it needs to be tagged in the To field. But,
> not if the BYE was sent independently, after establishing the call.

  Say the original INVITE forked to two UACs, and both 200 responses
were sent back to the caller.  Then the caller would have created two
active calls.  Say the caller keeps talking on both calls and now wishes
to hang up one of them.  If the BYE does not have a tag, and the phones
at the other end didn't put in a Contact (or are having both of their
calls handled the same proxy), how can the BYE be distinguished at the
far end?

  The tags conclusively define the call leg.

-- 
Billy Biggs, 3Com               Email: [email-masked]
http://www.div8.net/billy/      Phone: [email-masked]

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