Subject: Re: [Sip] Forking: a modest proposal.

From: [email-masked]
Date: Fri, 13 Jul 2001 08:36:00 +0200

Maybe I'm missing something, but I have the feeling that you are always putting together the session control and the bearer control , which is very likely the case of real user agents, that is end-users, but definitely not the case of servers in the
network, and a B2BUA is defined as appearing as a proxy (RFC2543).
The splitting of the session layer and the bearer layer is the current trend of Next Generation Networks in the Telecom world, including obviously the UMTS environment.

So, when I was talking about a B2BUA providing services (which is still appearing as a proxy) I was not talking about bearer manipulation, codec insertion, etc. Instead, I was talking about services provided on top of the session layer, as e.g. conference,
meet-me, follow-me services, etc.

Now, if the B2BUA concept includes also the bearer handling (which in my personal opinion is going against history), this should be clearly stated in 2543, and the corresponding definition should be improved.

Henning Schulzrinne <[email-masked]> on 11/07/2001 14:48:06

 To:      Juan-Carlos ROJAS/FR/ALCATEL@ALCATEL                
                                                              
 cc:      Paul Kyzivat <[email-masked]>, Jay Batson       
          <[email-masked]>, [email-masked]                 

 Subject: Re: [Sip] Forking: a modest proposal.               

UAs (and B2B UAs) make sense when the UA also needs to terminate media,
as for large-scale conference bridges and anonymizers. I don't think
anybody is arguing with that, although for conference bridges, one would
hope that they are transient phenomena. (Despite the bad press,
multicast is slowly emerging as an option again, at least in selected
environments, such as Internet2.)

I have no idea why you would need B2B UAs for roaming or what they have
to do with QoS (except that they generally are likely to make QoS
worse.)

An additional use of B2BUAs is for media translation, but this is really
only likely for multiparty calls, as quality is much better if you can
avoid transcoding. (I may be underestimating the effect of the screwy
licensing for G.72x and various other low-rate codecs here, which also
could lead to more transcoding than is technically called for.)

[email-masked] wrote:
>
> The main reason for B2BUA is to take control over the service to be provided to the end user.
> So, if SIP is strictly used as a "rendez-vous" protocol over the public Best Effort Internet network, there is in principle no need for such functionality.
> This can become quite different if you need to handle the user plane, as in the case of conference controllers.
> This is still worse if you are intended to provide services having guaranteed characteristics, like confidentiality, QoS, roaming, etc. A simple SIP proxy can not provide that, then you need a more complex functionality (because the service is more
> complex) allowing you to take control over the user request, and that can be done with B2BUA servers.
> Best regards
> Juan Carlos
>
> Paul Kyzivat <[email-masked]> on 11/07/2001 00:36:46
>
>

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---

From: [email-masked]
Date: Fri, 13 Jul 2001 08:56:00 -0500

> -----Original Message-----
> From: [email-masked] 
> 
> Maybe I'm missing something, but I have the feeling that you 
> are always putting together the session control and the 
> bearer control , which is very likely the case of real user 
> agents, that is end-users, but definitely not the case of 
> servers in the
> The splitting of the session layer and the bearer layer is 
> the current trend of Next Generation Networks in the Telecom 
> world, including obviously the UMTS environment.
> 
> So, when I was talking about a B2BUA providing services 
> (which is still appearing as a proxy) I was not talking about 
> bearer manipulation, codec insertion, etc. Instead, I was 
> talking about services provided on top of the session layer, 
> as e.g. conference,

Forgive my agreeing with you, but maybe you *are* missing something.

I'd be very interested in the scenarios under which you beleive
a B2BUA can provide any value add in the conference and meet-me
scenarios without any corresponding node in the media path.

I'm also very interested in knowing how acting as a B2BUA instead
of a proxy when providing a find-me/follow-me service helps in
any way. Given that using a B2BUA destroys feature transparency,
the unnecssary insertion in this case seems very short sighted.

/a

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

Ok, I've had it with one little blurb in rfc2543bis03.

The line that gets quoted "a B2BUA appears as a proxy".

What's it really say?

from the draft:
Back-To-Back User Agent: Also known as a B2BUA, this is a logical entity
that receives an invitation,
and acts as a UAS to process it. In order to determine how the request
should be answered, it acts as
a UAC and initiates a call outwards. A B2BUA appears like a proxy, but
differs in that it maintains
complete call state and must remain in a call. Since it is nothing more than
a concatenation of other
logical functions, no explicit definitions are needed for its behavior.

THIS DOES NOT MEAN A B2BUA IS A PROXY. IT MEANS IT LOOKS LIKE A PROXY ON A
NETWORK SCHEMATIC DRAWING. Calls come in. Calls go out. Looks kind of like a
proxy, but it is NOT a proxy and not constrained by the rules of  aproxy.

A B2BUA is application logic which associates one or more calls. Note that
"one or more" is not "exactly two" -- I actually heard someone say recently
that a B2BUA could only deal with two calls at a time, because there are
only two "B"s in the acronym. One must be careful when using acronyms these
days.

So, what does this application logic do? That's up to the application! See
the line in the def that says "Since it is nothing more than a concatenation
of other
logical functions, no explicit definitions are needed for its behavior." The
logical functions are not defined by the SIP speciication, no more than the
specification of every program one could write in C++ is defined in the C++
standard.  One could make a B2BUA that acts like a proxy. Bill Marshall has
argued that a proxy is just a special case of a the more general B2BUA. One
could also use a B2BUA as a firewall controller, a signaling anonymizer, or
many other things.

So why do we have proxies and not just use B2BUAs for everything? Becasuse
the limitations on B2BUA that make it a "proxy" are there for a reason --
they provide for network and feature transparency. In other words, proxies
provide a way to make it relatively easy to add functionality at the edge of
the network and have a reasonable expectation that the new functionality
will actually work. Any B2BUA that does not conform to the rules of proxy
behavior needs to do so very carefully, and is extremely likely to break
some sort of functionality that wasn't considered in the design of that
B2BUA. This is DANGEROUS, and non-proxy B2BUAs must be used VERY CAREFULLY,
with DISRETION, and only when ABSOLUTELY NECESSARY.

--
Dean

----- Original Message -----
From: <[email-masked]>
To: <[email-masked]>; "Henning Schulzrinne"
<[email-masked]>
Cc: "Paul Kyzivat" <[email-masked]>; "Jay Batson" <[email-masked]>;
<[email-masked]>
Sent: Friday, July 13, 2001 8:56 AM
Subject: More B2BUA ranting (was RE: [Sip] Forking: a modest proposal.)

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Thu, 19 Jul 2001 12:37:45 -0500

What's it really say?

from the draft:

--
Dean

---

From: "Dean Willis" <[email-masked]>
Date: Fri, 20 Jul 2001 00:28:22 -0500

Looks there have been a bunch of repeats here. I'm sorry. It looks like some
sort of odd problem between kevlar.softarmor.com and odin.ietf.org . . .
odin kept giving an error response and kevlar kept retrying. Hmm. Any
experts out there?

--
Dean