RE: [Sip] B2BUA & Max-Forwards

["Paul Long" <plong@packetizer.com>]

Adam,

FWIW, a B2BUA operates identically in this regard to an H.323 routing 
gatekeeper. The gatekeeper must contain H.323 endpoint functionality 
facing each of the two "real" endpoints with "application logic" in 
between the two functional endpoints, although this is not made 
explicit in any of the Recommendations. Vendors have wedged all sorts 
of applications in between these two virtual endpoints within the 
gatekeeper. Interestingly, some H.323 vendors have undergone the same 
initial naivete as some of the posters on this reflector. The bottom 
line is that you must fully terminate the connections on both sides and 
not simply pass everything or even selectively some things through and 
hope for the best.

Paul

> Unless you were merely trying to agree at length with the
> final paragraph of my previous message, I'm afraid that
> you missed my point rather broadly.
> 
> I'll reiterate the main point concisely: a B2BUA is a UAS
> attached to a UAC by application logic.
> 
> Read that carefully: Part of a B2BUA is a UAS.
> 
> That UAS is bound by RFC 3261 to certain behaviors.
> 
> One of those behaviors is honoring "Require" headers.
> 
> /a
> 
> > -----Original Message-----
> > From: Juan-Carlos.Rojas@alcatel.fr 
> > [mailto:Juan-Carlos.Rojas@alcatel.fr]
> > Sent: Wednesday, December 04, 2002 1:51
> > To: Adam Roach
> > Cc: 'Padma Suresh'; vkg@lucent.com; pete@tech-know-ware.com;
> > sip@ietf.org
> > Subject: RE: [Sip] B2BUA & Max-Forwards
> > 
> > 
> > 
> > Hello,
> > 
> > As it was already stated in this discusion thread, a B2BUA is an
> > *application* linking several UAs
> > As such, the behaviour of a B2BUA cannot be standardised.
> > 
> > Therefore, one cannot say that "A B2BUA needs to propagate some of 
the
> > headers received".
> > However, you can say that the application "x" behaves as a 
> > B2BUA, and that
> > the application "x" "needs to propagate" the a-header or the 
> > b-header etc.
> > for the needs of the application. This is the choice of the 
> > application,
> > that's all.
> > 
> > Best regards
> > Juan Carlos
> > 
> > 
> > 
> > 
> > 
> > Adam Roach <adam@dynamicsoft.com>@ietf.org on 04/12/2002 01:36:50
> > 
> > Sent by:  sip-admin@ietf.org
> > 
> > 
> > To:   "'Padma Suresh'" <padma_suresh@hotmail.com>, vkg@lucent.com,
> >       pete@tech-know-ware.com
> > cc:   sip@ietf.org
> > Subject:  RE: [Sip] B2BUA & Max-Forwards
> > 
> > 
> > -----Original Message-----
> > From: Padma Suresh [mailto:padma_suresh@hotmail.com]
> > 
> > > A B2BUA needs to propagate some of the headers received in a
> > > request/response to the other endpoint. Example: Require...
> > 
> > No. As emphatically as possible: NO. This is completely wrong,
> > and it appears to be a growing -- and dangerous -- misconception.
> > 
> > A B2BUA cannot transparently pass Require through. It must
> > understand and invoke the extension indicated.
> > 
> >   "The Require header field contains a list of option tags, 
> > described in
> >    Section 19.2.  Each option tag defines a SIP extension that MUST 
be
> >    understood to process the request."
> > 
> > A back to back user agent *is* a UAS, and *is* bound by this
> > provision.
> > 
> > Whether the UAC portion then turns around and imposes the same
> > requirement on the UAS it contacts is a local decision.
> > 
> > /a
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