Subject: Re: [Enum] SIP as SRS questions

From: Jonathan Rosenberg <[email-masked]>
Date: Thu, 07 Nov 2002 13:41:06 -0500

more inline.

Peterson, Jon wrote:
> inline.
> 
> Jon Peterson
> NeuStar, Inc.
> 
> 
>>-----Original Message-----
>>From: Jonathan Rosenberg [mailto:[email-masked]]
>>Sent: Thursday, November 07, 2002 9:17 AM
>>To: Lawrence Conroy
>>Cc: [email-masked]
>>Subject: Re: [Enum] SIP as SRS questions
>>
>>
> 
> [snip]
> 
>>>(ii) How does the caller specify the features/teleservices in which they
>>
> 
>>>are willing
>>>to engage? (This is what we have in the past called their "services of 
>>>interest").
>>
>>Yes, but not just with caller prefs.
>>... [snip]
> 
> 
> It is probably also worth mentioning the role that SDP plays in this
> process. This isn't just a matter of the caller expressing general
> preferences for communication to proxy servers - a lot of specific feature
> negotiation takes place at the SDP level directly between the caller's user
> agent and the callee's user agent(s).

Very true, and very important for the topic at hand. Thanks for pointing 
this out, Jon.

I'll also add to that some more. Negotiation on features occurs directly 
between agents during call setup time, but can also be done once the 
call is established. That is, once an audio call is set up, a user can 
renegotiate to add video, for example. This renegotiation can happen at 
both the SDP level and within SIP. For example, feature sets and 
capabilities can be renegotiated. When would this happen? One case is 
when a UA changes its logical role; morphing from a plain-old user agent 
into a conference server, for the purposes of supporting an ad-hoc 
conference. Such a change might result in renegotiation of capabilities 
and feature sets.

I'm not sure how relevant it is, but worth noting.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                72 Eagle Rock Ave.
Chief Scientist                             First Floor
dynamicsoft                                 East Hanover, NJ 07936
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

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---

From: "Peterson, Jon" <[email-masked]>
Date: Thu, 7 Nov 2002 13:09:36 -0500

inline.

Jon Peterson
NeuStar, Inc.

[snip]

Finally, many features entail extension support. Extension negotiation
includes the use of Require/Supported headers and the like. Support for
particular extensions may be necessary to use features in intermediaries or
endpoints (i.e. hBh or e2e).

Incidentally, my SIP enumservice draft discusses (or at least mentions)
caller preferences, SDP and extension support in this context. I'm happy to
talk about this Atlanta, if there's some interest.

> hth,
> Jonathan R.