Re: [Sip] B2BUA & Max-Forwards

A B2BUA is an intermediate network element and MUST maintain the expectations of the endpoints involved in the session.

Not forwarding the Require or Expires headers (and some more) would break the above which would not be quite acceptable.

However, yes, the B2BUA can choose to step out of the signalling path by setting the contact header to the appropriate endpoint.

Vijay I agree that the ambiguity of choosing which header to pass on and which not, could be well avoided.

Regards

Padma

>From: "Vijay K. Gurbani"

>To: Padma Suresh

>CC: pete@tech-know-ware.com, sip@ietf.org

>Subject: Re: [Sip] B2BUA & Max-Forwards

>Date: Wed, 04 Dec 2002 09:21:11 -0600

>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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