There really aren't any rules for B2BUAs (other than the basic rule that
it must behave as a UA), and its hard to make any because there are so
many different purposes (good and bad) for them. What rules might be
appropriate depend on what the B2BUA is trying to do. In some cases a
B2BUA is acting in a role very similar to a proxy. In that case you
might argue that is should violate very few of the proxy rules. In other
cases the a B2BUA really should be thought of as the UA. And in yet
other cases it is a protocol fixer/mediator and needs to do whatever it
must.
There have been some initial steps to define certain categories, such as
SBC and conference focus. I think eventually there will be clear rules
for such categories. But we aren't really there yet.
Thanks,
Paul
Jeff Wright wrote:
> A B2BUA is a user agent, not a proxy. It acts as a user agent on behalf of
> other user agents (so it is involved in registration, call setup / teardown,
> etc.). Unfortunately the RFCs don't give a lot of direction to their
> specific implementation.
>
> That said, to me, a B2BUA should act so that any alteration of header fields
> or parameters should be within the spirit of maintaining the call flow
> originated by the UAs being served by the B2BUA. They should be as
> transparent as possible and not interfere with or disallow any features
> attempted by the UAs.
>
> Jeffrey Wright
> System Test Engineering Manager
> Aztek Networks
>
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED] on behalf of Stephan Steiner
> Sent: Sun 2/17/2008 4:34 AM
> To: [email protected]
> Subject: [Sip-implementors] Header fields in the B2BUA scenario
>
> Hi
>
> I have a SIP PBX which works in B2BUA mode and I've noted that when it comes
> to dealing with Header fields, it doesn't stick to the table 2 in chapter
> 20.1 of RFC 3261. Specifically, it is modifying some header fields which
> according to that table may not be modifed by a proxy. I contacted the
> manufacturer and they claim that since a B2BUA isn't a proxy, they don't
> have to follow the rules established in the RFC and I'm having a hard time
> countering that since to me, a B2BUA is a proxy seeing as it does what a
> proxy does (even if the RFC doesn't spell that out) but I'm wondering:
>
> Is there any type of UAS to which the header processing rules mentioned
> before do not apply? Is B2BUA really a loophole to not do things a proxy
> should do just because it isn't a real proxy per definition (even though it
> basically does the same things.. it just does more than a proxy does)?
>
> Regards
> Stephan
>
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