Subject: RE: [Sip] B2BUA

From: "Mary Barnes" <[email-masked]>
Date: Tue, 3 Dec 2002 07:35:26 -0600

Bill et al, 

My comments are embedded below [MB]:

-----Original Message-----
From: William Marshall [mailto:[email-masked]]
Sent: Tuesday, December 03, 2002 7:29 AM
To: [email-masked]
Cc: Barnes, Mary [NGC:B602:EXCH]; [email-masked];
[email-masked]
Subject: RE: [Sip] B2BUA

Dean wrote:
> 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.

To further elaborate, there certainly exists on paper a box that does
some abritrary and weird algorithm, not conformant with any of the
rules in rfc3261, that transforms requests and response and breaks
everything that goes through it.  Call it "Dean's devilish-B2BUA".

But I don't think anyone builds such a box.  At least not intentionally.

What is built instead are boxes that are close to the definition of
proxies, but not quite.  They serve a real need in the market (and
vendors tend to build what sells).  But due to various details, like
looking at the attachment (a proxy-no-no) to open pinholes in the firewall,
they don't strictly qualify as proxies.

[MB]: And I think this is where we get into problems trying to agree what
defines this in-between thing, as everyone has something that is likely
slightly different.  

Saying there are only two types of boxes, proxies and devilish-B2BUAs,
ignores the reality.

The writing of an accurate definition of a B2BUA is only the first step.
Unfortunately there is interaction with definition of new services.  The
definition of proxy is very restrictive for a reason, so that it leaves
wide open the possibilities for designs of new services.  But the
not-quite-proxy boxes will exist, and endpoints will need to interoperate
with them.  So services will also need to work through them.  This will
impose some restrictions on how new services are defined.  I think the
objective should be to minimize those restrictions; to do that the
variations
in not-quite-proxy behavior need to be documented and made predictable so
that services can be defined to interwork with them.

[MB]: Well, perhaps the most reasonable way forward would be to put together
an informational draft defining the various "flavors" of these in-between
things and categorizing the issues for service interworking introduced by
each of the variations.  Some of this, of course, will lead us back to the
list of the reasons why some folks consider these things "evil", but would
this also not lead us down the road of being very prescriptive about how
services work in SIP? 

Having services work through the "something BETWEEN the B2BUA and the
conformant proxy" would certainly make the world a much better place
(yes, THAT much better).

Bill Marshall
[email-masked]

-----original message-----
From: "Dean Willis" <[email-masked]>
To: "'Mary Barnes'" <[email-masked]>,
        <[email-masked]>
Cc: <[email-masked]>
Subject: RE: [Sip] B2BUA
Date: Tue, 3 Dec 2002 00:00:19 -0600

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