Subject: [Sipping] transparent B2BUAs

From: "Jeroen van Bemmel" <[email-masked]>
Date: Sun, 11 Mar 2007 01:35:12 +0100

Regarding draft-marjou-sipping-b2bua-00:

section 4.1.3 describes an example (KPML usage of dialog identifiers) which 
clearly illustrates why it is fundamentally impossible to construct such a 
"transparent B2BUA": it would have to know about and implement all current 
and _future_ extensions that somehow rely on the signaling elements it 
rewrites (e.g. call-id, tags, etc.)

In other words: the draft should highlight that a B2BUA can only be 
transparent with respect to a fixed, well-defined finite set of extensions, 
and can therefore never be future proof

Regards,
Jeroen 
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From: "Xavier Marjou" <[email-masked]>
Date: Mon, 12 Mar 2007 15:23:08 +0100

> rewrites (e.g. call-id, tags, etc.)

Yes. There are also SIP headers like In-Reply-To, Join, Refer-To,
Replaces, and Target-Dialog that lead to similar problems. It may be
that regular expressions could automate the substitution of dialog
identifiers, but it is impossible to be certain that this is the
wanted behavior for future SIP extensions.

> and can therefore never be future proof

Ok I'll do that.

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