Subject: question about supplementary services for SIP

From: [email-masked]
Date: Fri, 19 Mar 1999 10:50:16 -0800

Hello, all:

Does SIP support the following services:
   Message Waiting Indication
   Conference out of Consultation
   Call Completion on Busy Subscriber
If it does, how?  which header field(s) and what kind of messages should be used
for them?

Thanks for any information?

Hanlin

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From: Jonathan Rosenberg <[email-masked]>
Date: Fri, 19 Mar 1999 18:42:17 -0500

>    Message Waiting Indication

No, and its something I think is out of scope for SIP. Rather, something
like IMAP would probably be the right thing for this. I might have lots
of messages, in fact - voice, email, faxes. Using a voice specific
protocol for messaging seems a bad idea. In fact, I think there was a
BoF on VPIM that might be relevant (not sure).

>    Conference out of Consultation

Not in the base spec, but something that is defined in the call control
extensions. We're in the process of reworking this, as I mentioned
during the meeting. Expect the draft soon.

>    Call Completion on Busy Subscriber

There are several ways to implement this, some of which are supported in
the base spec.

Approach 1: Callee sends 181 Queued responses back to the caller until
they're not busy, and then sends a 200 OK when free.

Approach 2: Callee notes the call attempt, sends a 4XX response. When
the callee is free, it calls back the caller.

An alternate approach not available in the base spec is to use a
SUBSCRIBE/NOTIFY mechanism to have the caller ask for call state
updates. Once the callee is free, a NOTIFY gets sent to the caller, and
it can retry the callee.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX: (732) 834-5379                         Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

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