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Re: [Sip] B2BUA & Max-Forwards
Padma Suresh wrote:
Vijay,
You are right -
A B2BUA needs to propagate some of the headers received in a
request/response to the other endpoint.
Choosing which headers should be passed by a B2BUA and which not is
exactly the ambiguity that we should AVOID, as I pointed out in my
my response to the original poster. As others have expressed, we may
try to taxonomize different types of B2BUAs, but each will have a
different manner of handling the headers (depending on the application
being realized by that particular B2BUA).
An anonymizer B2BUA may change To, From, Contact, etc, for instance (and
maintain internal state). A network-hiding B2BUA may scrap all Via
headers coming in and only expose one Via header going out. The
possibilities are endless.
Example: Require, Expires to name a few. This is because these
headers actually are relevant end to end.
A B2BUA may decide to consume the Require and change the Expires header
(maybe decrease its value) before sending it downstream, thus causing
havoc with the expectations of the sending UAC.
However, some of the other headers like Contact should be set by the
B2BUA as itself.
Likewise, I can imagine a B2BUA which rendezvous two users and steps
out of subsequent signaling. Thus the Contact it sends to each of
the users is that of the other peer.
I would strongly *stay away* from prescribing which headers must be
passed by a B2BUA and which must not.
Regards,
- vijay
--
Vijay K. Gurbani vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566 Voice: +1 630 224 0216
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