Subject: [Sip] Bis-04 inconsistency.

From: "Fairlie-Cuninghame, Robert" <[email-masked]>
Date: Tue, 4 Sep 2001 14:47:44 -0700

I don't believe the following paragraph in the ACK method description
(Section 5.1.1) is correct:

   A proxy server receiving an ACK request after having sent 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 tag in the ACK To header field matches the tag in the To header
   field of the response, and the From, CSeq and Call-ID header fields
   in the response match those in the ACK, the ACK is meant for the
   proxy server. Otherwise, the ACK SHOULD be proxied downstream as any
   other request. However, an ACK not destined for the proxy SHOULD NOT
   be retransmitted.

ACK's for non-2xx responses are hop-by-hop and the UAC does not copy the
tags from the non-2xx response into the ACK message, as described in Section
15.4:

   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.

Robert.

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---

From: "Brett Tate" <[email-masked]>
Date: Tue, 4 Sep 2001 18:30:16 -0400

>    response was a 200-class response to an INVITE request.

You are misreading the paragraph.

The tag is copied into the ACK for 2xx, 
3xx, 4xx, 5xx, and 6xx responses.  It 
isn't copied into subsequent requests 
unless the response was a 200-class 
response to an INVITE request.

---

From: "Jo Hornsby" <[email-masked]>
Date: Wed, 5 Sep 2001 14:51:56 +0100

>    response was a 200-class response to an INVITE request.

Looks fine to me.  The "MUST NOT" applies to re-INVITEs,
etc. (which don't exist unless there was a 2xx).

 - Jo.