[Sip] RFC 5626 (Outbound) hard to understand non-register request processing

Iñaki Baz Castillo <ibc@aliax.net> Fri, 14 October 2011 11:52 UTC

Return-Path: <ibc@aliax.net>
X-Original-To: sip@ietfa.amsl.com
Delivered-To: sip@ietfa.amsl.com
Received: from localhost (localhost []) by ietfa.amsl.com (Postfix) with ESMTP id 7BABC21F8B29 for <sip@ietfa.amsl.com>; Fri, 14 Oct 2011 04:52:25 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.541
X-Spam-Status: No, score=-2.541 tagged_above=-999 required=5 tests=[AWL=0.136, BAYES_00=-2.599, FM_FORGED_GMAIL=0.622, MIME_8BIT_HEADER=0.3, RCVD_IN_DNSWL_LOW=-1]
Received: from mail.ietf.org ([]) by localhost (ietfa.amsl.com []) (amavisd-new, port 10024) with ESMTP id qquXzEDrbzeg for <sip@ietfa.amsl.com>; Fri, 14 Oct 2011 04:52:25 -0700 (PDT)
Received: from mail-qw0-f44.google.com (mail-qw0-f44.google.com []) by ietfa.amsl.com (Postfix) with ESMTP id E97DB21F886A for <sip@ietf.org>; Fri, 14 Oct 2011 04:52:24 -0700 (PDT)
Received: by qadb12 with SMTP id b12so960160qad.31 for <sip@ietf.org>; Fri, 14 Oct 2011 04:52:24 -0700 (PDT)
MIME-Version: 1.0
Received: by with SMTP id th10mr4954016obb.44.1318593143925; Fri, 14 Oct 2011 04:52:23 -0700 (PDT)
Received: by with HTTP; Fri, 14 Oct 2011 04:52:23 -0700 (PDT)
Date: Fri, 14 Oct 2011 13:52:23 +0200
Message-ID: <CALiegfkV2vup6a4FrRqkuUQJPox6ErcJda5sgX0Wg7Vnw=2ihw@mail.gmail.com>
From: =?UTF-8?Q?I=C3=B1aki_Baz_Castillo?= <ibc@aliax.net>
To: sip@ietf.org
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Subject: [Sip] RFC 5626 (Outbound) hard to understand non-register request processing
X-BeenThere: sip@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Session Initiation Protocol <sip.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/sip>, <mailto:sip-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/sip>
List-Post: <mailto:sip@ietf.org>
List-Help: <mailto:sip-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/sip>, <mailto:sip-request@ietf.org?subject=subscribe>
X-List-Received-Date: Fri, 14 Oct 2011 11:52:25 -0000

Hi, RFC 5626 section 5.3 "Forwarding Non-REGISTER Requests" says:

5.3.  Forwarding Non-REGISTER Requests

   When an edge proxy receives a request, it applies normal routing
   procedures with the following additions.  If the edge proxy receives
   a request where the edge proxy is the host in the topmost Route
   header field value, and the Route header field value contains a flow
   token, the proxy follows the procedures of this section.  Otherwise
   the edge proxy skips the procedures in this section, removes itself
   from the Route header field, and continues processing the request.

And then in section 5.3.2 "Processing Outgoing Requests" (which is
*into* section 5.3) it talks about:

   If the edge proxy receives an outgoing dialog-forming request, the
   edge proxy can use the presence of the "ob" URI parameter in the
   UAC's Contact URI (or topmost Route header field) to determine if the
   edge proxy needs to assist in mid-dialog request routing.

The problem is that an initial INVITE/SUBSCRIBE sent from a outbound
SIP client won't have a flow token in a Route header, so the text in
5.3 suggests doing nothing special for such request. The reader could
then ignore section 5.3.2 in which, clearly, the edge proxy should
assist in-dialog request routing for this initial request (by adding a
flow token in the Record-Route).

Do I miss something? or the text is indeed confusing?


Iñaki Baz Castillo