Subject: RE: [Sip] B2BUA

From: [email-masked]
Date: Tue, 3 Dec 2002 18:18:19 +0100

Dean,

I fully agree with you. I've never said that the definition in 3261 is
wrong, just that it could be completed (or improved, etc.) to avoid
confusion.
After reading the mails in this discusion thread, what could be added is
that:
1) A B2BUA handles two or more UAs (each one behaving as UAC/UAS, as
described in 3261 for UAs)
2) The SIP protocol specification does not mandate for any behaviour of
such B2BUA, i.e. on how to "link" (or "concatenate") two or more UAs.

As a consequence, you cannot standardise the behaviour of a B2BUA, since a
B2BUA is an application "and that can  do anything that one can imagine an
application doing".
But you can still standardise an application or a class of applications
that behave as B2BUA. These applications exhibit a UA behaviour for each
concerned UA, according to SIP rules defined in 3261. But this is yet
another story.

Best regards
Juan Carlos

P.S.: The "something BETWEEN the B2BUA and  the conformant proxy" story
should be handled in a separate discusion thread, to avoid to mix all
problems in the same thread.

"Dean Willis" <[email-masked]>@ietf.org on 03/12/2002 07:00:19

Sent by:  [email-masked]

To:   "'Mary Barnes'" <[email-masked]>, Juan-Carlos
      ROJAS/FR/ALCATEL@ALCATEL
cc:   <[email-masked]>
Subject:  RE: [Sip] B2BUA

Mary said:
 -----
 So, I guess you're  suggesting that the term "concatenation" is not
accurate or is misleading and I  guess that depends upon how loosely one
applies the term concatenation here; my  assumption had been that it meant
that they were "linked" (consistent with  Webster's definition of
concatenate) in some manner which is unprescribed, so I  think your point 2
below isn't a problem with the current definition.  My  understanding of
the current definition is that there isn't anything more for  the SIP
protocol to prescribe about the operation of a B2BUA other than what is
required from a protocol perspective to function as a UAC and a UAS. From a
protocol perspective, it is a logical entity and thus whether there's one
or  multiple doesn't seem to apply.  I think what you (and perhaps others)
are  suggesting is that there's a definition of a B2BUA that more closely
parallels  the definition of a Proxy Server since in many cases the
physical rendition of  the logical B2BUA functionality would be replacing a
Proxy Server in a network.  And I think this is where the problem begins,
as many are opposed to this model  (as it increases the complexity, etc.)
and this is why the logical definition  has remained.
------

Well,  I think the argument is being made that this definition doesn't (for
some reason  that I seem incapable of comprehending) work for some people,
and that therefore  we should clarify it. At the fundamental level, I think
some people do not find  the implications of this definition obvious. There
are several ways we might  address this. We might add examples. We might
add "In other words, the only  relationship between the UAC and the UAS is
the application logic, and that can  do anything that one can imagine an
application doing", or we might just use  better wording.

I  don't think the argument is being made that the definition in 3261 is
wrong,  just that we can make it better for those who don't get it the way
it is  written. Of course, if we discuss it here long enough, maybe most of
them WILL  get it -- but that doesn't help the ones who aren't "here"  yet.

I  think that Bill is suggesting that there is also something BETWEEN the
B2BUA and  the conformant proxy, and that the world would be a better place
(ok, maybe not  THAT much better) if our taxonomy also included this
"between"  thing.

--
Dean

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