Subject: RE: [Sip] To-tag Corner Case

From: [email-masked]
Date: Thu, 25 Apr 2002 09:12:36 +0200

The issue shouldn't be whether there are clear examples, but whether there 
is
clear specification text. In cases where the specification leads to 
difficult
to read text to make the text correct, examples can be given.

Regards,

Frank

Hi,

The main issue I have with 2543bis-09 is that it's not clear with clear
examples that case were To tag is needed and not, cause in latest call 
flows
draft which been updated to reflect 2543bis-09 it may contain missing To 
tag
which I hope it just an typing error, I already I sent an email early for
clarification about this.

To my understanding
* To tag is added to any provisional response and final responses to all
requests, like it shown in section 11.1 line 1783, were no to tag in 
OPTIONS
request but in section 11.2 line 1818 there's To tag, and so 2543bis-09 is
missing To tag in F2 message, section 24.1

* I don't think (a) is true, cause I can not find any statement in the
2543bis-.09 that prove it, plus in section 17.1.1.3 which state that ACK
message for non-2xx differ from the To header field in the original 
request
by the addition of the tag parameter, it does not state that a provisional
response was sent early in order to have a To tag in the ACK message

Hope this helps.

Thanks.

Hussam Jarada
Ulticom Inc.

 -----Original Message-----
From:            [email-masked] [mailto:[email-masked]]  On Behalf 
Of Tom-PT
Taylor
Sent:            Wednesday, April 24, 2002 2:14 PM
To:              [email-masked]'
Subject:                 [Sip] To-tag Corner Case

Section 8.2.6.2 of 2543bis says a To tag MUST be added to any provisional
response (except perhaps 100 Trying).  It goes on to say:

   The same tag MUST be used for all responses to that request, both
   final and provisional (again excepting the 100 (Trying)).

Section 12.1 says:

   Dialogs are created through the generation of non-failure responses
   to requests with specific methods. Within this specification, only
   2xx and 101-199 responses with a To tag to INVITE establish a dialog.

and of course, creation of a dialog involves the UAS adding a To-tag.

What I get out of this is:

(a) If the first response to an INVITE is a failure response, a To-tag 
MUST
NOT be added.

(b) If the first response to an INVITE is a 1xx (greater than 100), then a
To-tag MUST be present in that response and in ALL succeeding responses,
even if the final response is a failure response.

Some unexpected tags in the call flows document stimulated this 
observation,
which I present for your confirmation.

Tom Taylor
[email-masked]
Ph. +1 613 736 0961 (ESN 396 1490)

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This list is for NEW development of the core SIP Protocol
Use [email-masked] for questions on current sip
Use [email-masked] for new developments on the application of sip