Subject: [Sip] Why 439 for only ob supported UAC?

From: "Rockson Li (zhengyli)" <[email-masked]>
Date: Wed, 3 Dec 2008 13:52:28 +0800

Hi,
 
draft-ietf-sip-outbound-16 sec 6.

<snip> 
   When receiving a REGISTER request, the registrar MUST check from its
   Via header field if the registrar is the first hop or not.  If the
   registrar is not the first hop, it MUST examine the Path header of
   the request.  If the Path header field is missing or it exists but
   the first URI does not have an ob URI parameter, then outbound
   processing MUST NOT be applied to the registration.  In this case,
   the following processing applies: <NOTE> if the REGISTER request
contains
   the reg-id and the outbound option tag in a Supported header field,
   then the registrar MUST respond to the REGISTER request with a
439</NOTE>
   (First Hop Lacks Outbound Support) response; otherwise, the registrar
   MUST ignore the reg-id parameter of the Contact header.  See
   Section 11.6 for more information on the 439 response code.
</snip>

I just wonder why 439 is a must if  reg-id and the outbound option tag
in a Supported header field present in incoming REGISTER.
I think if registra thinks it cannot apply ob, it just follow normal
RFC3261 behavior and does not insert outbound into Require header of REG
response.

Moreover, If the registra does not understand ob, how could it responds
with 439?

I thinks this must-respond-439 opertion only applies to outbound option
tag in a Require header field in incoming REGISTER

Any thoughts?

Thanks

Regards,
-Rockson
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