Subject: [Sip] Of-hook and On-hook @ sip?

From: "F.S.Salloum" <[email-masked]>
Date: Wed, 26 Feb 2003 14:30:42 +0200

Dear all,

One simple question is there a similar message
in SIP which works like on-hook and off-hook on 
the PSTN world (Q-931)?

I know that this can be implemented playing with
the state machines of the hard-sip-phone but we were
wondering if this has been investigated from you guys.

Thanks
F.S.Salloum
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From: "Dean Willis" <[email-masked]>
Date: Wed, 26 Feb 2003 15:22:56 -0600

> wondering if this has been investigated from you guys.

In short, no. But the long answer, is "maybe, depending on what you want to
do with it".

On/off hook are valid terms in the confined space of a traditional phone
line, which is either "in use" or "not is use". We tend to assume that if a
line is on-hook, then there is no session on that line and the  phone
attached to it (if any -- the line is usually on-hook even if there is no
phone) may be rung to request a new session to the phone. We also tend to
assume that if a line is off-hook, that there is no session on that line and
the phone may NOT be rung to request a new session, and that only signaling
on that line (such as call waiting tones) or preemption on that line
(barge-in) can be used to communicate with the user.

So there are a couple of questions that might be asked here:

1) Is the user of the phone busy with another call right now?
2) Is all the bandwidth available to a phone in-use right now?

Sometimes, in SIP-land, these concepts make no sense. For example, I have
100Mb/s to my phone. I can juggle six different calls simultaneously. And
sometimes I wach a video stream, set up with SIP, on my PC at the same time.

But sometimes, they do make sense.

Imagine a single-line phone adapter such as the Cisco box distributed by
Vonage. On one side, an rj-45 for ethernet. On the other side, an rj-11 for
a phone. Assume a really simple version, with no call waiting.

Let's say we want an upstream server to, if there's a session on my UA,
automatically forward any new session requests to my voice mail. The
question is (as #1 or #2), hows does it KNOW I'm in a session?

Seveal options come to mind.

Option 1: The upstream server is a dialog-stateful proxy. If I have an
ongoing INVITE dialog, it automagically diverts new INVITEs to my voice
mail.

Option 2: The upstream server is a B2BUA, which is by definition
dialog-stateful, and it does the same diversion thing.

Option 3: We use an event package, and the upstream server subscribes to the
session state of my adapter. When my adapter starts a session, it sends a
NOTIFY to the server saying "I have a session, for which I have an
identifier.". When my adapter stops a session, it sends anotehr NOIFY saying
"This session (using identifier) has ended".

--
Dean

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From: "Vijay K. Gurbani" <[email-masked]>
Date: Wed, 26 Feb 2003 15:51:41 -0600

Dean Willis wrote:
[...]
> "This session (using identifier) has ended".

One such event package is specified by the SPIRITS protocol.  For
implementation experience, see:
http://www.ietf.org/internet-drafts/draft-gurbani-spirits-implementation-00.txt

Cheers,

- 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