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RE: [Sip] B2BUA & Max-Forwards
Pete,
By sheer coincidence at the time I wrote that email I was writting some code to access a media server directly, via a B2BUA ;). Although adding Max-Forwards wouldn't hurt, I could absolutely guarantee the request wouldn't loop so just left the default value in from our "Message Factory". The fact that there is no general B2BUA is my whole point, you need the Max-Forwards to be strictly decreasing across your B2BUA, I don't and can guarantee I don't and still have both sides conform to rfc3261 without risk of looping.
Despite actually using B2BUAs I'll have to add my voice to the "remove all references to B2BUAs" camp. Personally I found the definition easy to comprehend (even the name tells you what it is), but it is obviously a source of confusion; also letting people build two UAs that conform to the spec and linking them together by whatever innovative applications they can think of doesn't strike me as an area suitable for standardisation.
James
> -----Original Message-----
> From: Pete Cordell [mailto:pete@tech-know-ware.com]
> Sent: 05 December 2002 15:48
> To: James Undery; sip@ietf.org
> Subject: Re: [Sip] B2BUA & Max-Forwards
>
>
> James,
>
> Thanks for your comments.
>
> I think in general you CAN'T guarantee that an element you
> route to won't
> proxy (or be a B2BUA). And therefore loop detection is a problem.
>
> Propagating Max-Forwards even when you know the precise
> routing should not
> cause you any problems.
>
> Pete.
>
> ----- Original Message -----
> From: "James Undery" <jundery@ubiquity.net>
> To: "Pete Cordell" <pete@tech-know-ware.com>; "Dean Willis"
> <dean.willis@softarmor.com>; <sip@ietf.org>
> Sent: 05 December 2002 13:21
> Subject: RE: [Sip] B2BUA & Max-Forwards
>
>
> Hi,
>
> I think your confusion comes from mixing two email threads; the first
> statement in context says if a specific B2BUA demonstrates header
> transparency it doesn't change headers; the second statement
> is about B2BUAs
> in general and says they can do whatever they want (without
> commenting on
> the desirability of their actions).
>
> Max-Forwards probably are an important case for your
> particular application,
> in general they may not be required (e.g. routing to an
> element you can
> guarantee not to proxy).
>
> Your comment on Max-Forwards highlights well the difficulties faced in
> defining a B2BUA more specifically than the definition in 3261.
>
> James
>
> > -----Original Message-----
> > From: Pete Cordell [mailto:pete@tech-know-ware.com]
> > Sent: 05 December 2002 12:10
> > To: Dean Willis; sip@ietf.org
> > Subject: Re: [Sip] B2BUA & Max-Forwards
> >
> >
> > Dean,
> >
> > Firstly, your statement that "The B2BUA doesn't change
> > headers that transit
> > it." seems inconsistent with the statement "It does the same
> > thing as ...
> > ANY 500-pound gorilla does". I don't understand.
> >
> > Secondly, I think max-forwards is a special case. It is
> > important for the
> > protection of SIP systems as it prevents loops.
> >
> > Indeed, there is a major difference between a UAS and a B2BUA
> > and that is
> > that the former terminates a request, and the latter
> > terminates a request
> > AND ALSO forwards an associated request (or more). The
> impact of this
> > difference should be covered in the spec in the interests of
> > protecting
> > other SIP systems.
> >
> > Pete.
> >
> > ----- Original Message -----
> > From: "Dean Willis" <dean.willis@softarmor.com>
> > To: "'Pete Cordell'" <pete@tech-know-ware.com>; <sip@ietf.org>
> > Sent: 05 December 2002 01:23
> > Subject: RE: [Sip] B2BUA & Max-Forwards
> >
> >
> > > > One issue that the recent B2BUA discussion has raised in my
> > > > mind is what a B2BUA (whatever its decided that should be)
> > > > should do with Max-Forwards.
> > >
> > > It does the same thing as it does with any other header or
> > body part,
> > > which is the same thing that ANY 500-pound gorilla does to
> > somebody's
> > > body parts -- whatever it wants.
> > >
> > > What you're asking is "what is the transparency of this node with
> > > respect to max-forwards", which is "#4 -- Header
> Transaprency" in my
> > > top-10 list. The specification of a back-to-back user
> agent doesn't
> > > mandate any level of transparency on this or any other header.
> > >
> > > --
> > > Dean
> > >
> > > _______________________________________________
> > > Sip mailing list https://www1.ietf.org/mailman/listinfo/sip
> > > This list is for NEW development of the core SIP Protocol
> > > Use sip-implementors@cs.columbia.edu for questions on current sip
> > > Use sipping@ietf.org for new developments on the
> application of sip
> >
> > _______________________________________________
> > Sip mailing list https://www1.ietf.org/mailman/listinfo/sip
> > This list is for NEW development of the core SIP Protocol
> > Use sip-implementors@cs.columbia.edu for questions on current sip
> > Use sipping@ietf.org for new developments on the application of sip
> >
>
>
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