Subject: [SIP] tags in ACKs in rfc2543bis-00

From: "McMurry, Kathleen" <[email-masked]>
Date: Wed, 21 Jun 2000 13:42:00 +0000

I am confused about the new statement in Section 11.4 that states "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."

This seems to conflict with Section 4.2.2 which states "A proxy server
receiving an ACK request after having send a 3xx, 4xx, 5xx, or 6xx response
must make a determination about whether the ACK is for it, or for some user
agent or proxy server further downstream.  This determination is made by
examining the tag in the To field."

If the UAC doesn't copy the tag into the ACK, how is the proxy server
supposed to make the determination that the ACK request is for it?

Thanks, 

Kathleen McMurry

---

From: "Jo Hornsby" <[email-masked]>
Date: Wed, 21 Jun 2000 14:53:39 +0100

> I am confused about the new statement in Section 11.4 that states "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."
>
> This seems to conflict with Section 4.2.2 which states "A proxy
> server receiving an ACK request after having send a 3xx, 4xx, 5xx,
> or 6xx response must make a determination about whether the ACK is
> for it, or for some user agent or proxy server further downstream.
> This determination is made by examining the tag in the To field."
>

It does copy the tag into the ACK; it just doesn't copy the tag into
any other requests.  For instance, if the UA was to retry an INVITE
(with a different CSeq, or something) after having received a non-2xx
final response, it would be wrong for it to update the To header to
include a tag that was in the response; only if the INVITE succeeds
should the To header be updated.

HTH,

 - Jo.

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