Subject: Re:

From: "Rahalkar, Suchitra (c)" <[email-masked]>
Date: Mon, 16 Nov 1998 15:18:42 -0700

> Hello,
	> 
	> I have worked quite a bit on H.323 and learning SIP currently.
	> However, I am not able to get any further technical details on the
	> following.
	> 
	> It is written in the SIP recommendations that -
	> 
	> SIP can also be used in conjunction with other call setup and
	> signaling protocols. In that mode, an end system uses SIP
exchanges to
	> determine the appropriate end system address and protocol from a
given
	> address that is protocol-independent. For example, SIP could be
used
	> to determine that the party can be reached via H.323 [7], obtain
the
	> H.245 [8] gateway and user address and then use H.225.0 [9] to
	> establish the call.
	> 
	> How exactly does this take place? Is there any middle agent that
	receives SIP on one hand and gives out H.323 on the other hand.

Regards
Suchitra

---

From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 17 Nov 1998 11:29:56 -0500

> Rahalkar, Suchitra (c) wrote:
> 
>      > Hello,
>      >
>      > determine the appropriate end system address and protocol from
>      a given
>      > to determine that the party can be reached via H.323 [7],
>      obtain the

This can happen in a number of ways:

1. a SIP server can be programmed to redirect calls to an h.323 URL.
This programming can take place either through a REGISTER message, or
through administrative configuration. Calls for the user will then get
redirected (i.e., 300 class response) back to the caller. THe caller can
then initiate an h.323 call using the supplied URL.

2. a SIP server can be programmed to act as an SIP to H.323 gateway. In
that case, the server would receive calls for sip:[email-masked],
for example, and determine from its configuration that calls for this
address should be converted to H.323, and the server/gateway should
initiate a call to a specified gatekeeper. I imagine one could
conceivably program a SIP server to do this by REGISTER'ing a SIP URL
and setting action=proxy.

3. A UAS can redirect calls to an h.323 URL. 

Additionally, things like the call processing syntax in iptel, or SIP
CGI, can be used to program a SIP server to do the above things (well,
case 1 at least with CGI, not case 2).

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
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EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen