Subject: RE: [Sip] B2BUA

From: Phil Reynolds <[email-masked]>
Date: Mon, 2 Dec 2002 16:19:54 -0000

Can we not define B2BUAs as a SIP entity that exhibits the behaviour of a
UAC and UAS combination. i.e. it can not be distinguished externally from a
properly conforming UA, thus not constraining it's internal functionality or
implementation.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: 02 December 2002 14:20
To: William Marshall
Cc: [email-masked]; [email-masked]
Subject: Re: [Sip] B2BUA

William,

"Many actual B2BUAs are not "fully independent of the SIP protocol rules",
and the above definition seems to say they must be..." The proposed
definition states that User Agents MUST behave as UAC ans UAS according to
SIP rules (this MUST could be enforced in the definition). This is SIP
standard, nothing else. All what is added is that the way of linking User
Agents in a B2BUA is not related to SIP rules, and is not subject to SIP
standardisation. As Dean pointed out in his mail, they are User Agents, they
can do anything they want to do, and we don't want to standardise their
behaviour. You can define a B2BUA whose behaviour is based on SIP rules, but
this is a special case for a specific B2BUA implementing a well defined
application. However, this cannot be generalised to any B2BUA.

Concerning your statement "there needs to be another type of SIP entity
defined for what exists in practice", my feeling is that today there are two
SIP entity types: Proxy and B2BUA, and that seems to be enough (Am I missed
something ?)

Best regards
Juan Carlos

William Marshall <[email-masked]>@ietf.org on 02/12/2002 15:06:13

Sent by:  [email-masked]

To:   [email-masked]
cc:   [email-masked]
Subject:  Re: [Sip] B2BUA

Dean,

you wrote:
> Juan-Carlos said:
> > Back-to-Back User Agent: A SIP element being able to handle a 
> > collection of "n" User Agents (behaving each one as UAC and UAS, 
> > according to SIP rules), which are linked by some application logic 
> > that is fully independent of the SIP protocol rules.
>
> This seems like a reasonable definition.
>

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