Subject: [Enum] VOVI and H.323

From: Orit Levin <[email-masked]>
Date: Wed, 12 Mar 2003 14:40:03 -0500

Hi guys!

My answer is that I don't see major conceptual differences between SIP and
H.323 in respect to this long thread. For those who would like to read the
details, they are provided at the bottom of the mail. My opinion is that
both protocols should be addressed by ENUM in the same way.

I also think that a clarification about the main ENUM motivation(s) and
consequently the prevalent ENUM usage cases would contribute to a more
focused discussion than the technical details of the call signaling
protocols.

What is the ENUM's objective?
1. Being an enabler for smooth user experience in communications involving
GWs? [i.e involving non-IP users who are identified by a phone number only
(for incoming calls) and are restricted to dialing phone numbers only (for
outgoing calls).]
2. Being an enabler for using phone numbers (instead of URIs) for pure IP
phones/services?
3. Both? At what ratio?

---------------------------------------------------------
I would like to clarify two H.323 specifics that have been referred to
during the VOVI thread and are different from SIP:

1. H.323 as a standard doesn't distinguish between a user and its device(s).
An H.323 entity can represent either and can be identified by an array of
"identifiers" - among them ASCII string, phone number, ...., URI.
Gatekeepers (i.e. statefull signaling proxies) are allowed for any ID
interpretation, substitution, association, routing, forking, line-hunting,
load balancing, etc. (Gatekeeper can also assign a new identifier to an
H.323 entity and the "entity" MUST use it.)
That said, in practice, it works very much like SIP. H.323 device REGISTERs
with its ID (name). The Gatekeeper makes an association between the devices
under its responsibility (and registration) and the users/services (using
any sort of DB and containing local policies).
When an H.323 call is placed from the outside of the Gatekeeper authority
(i.e. zone), the call would usually be destined either to a user (not a
device) or to a service (such as "conferenecing"). At this point the GK
performs the mapping between the user/service and its current
available/suitable device.

2. In H.323, you can NOT express media (voice/video/data) capabilities or
preferences using the REGISTRATION procedure or retrieve them afterwards
(using LOCATION requests). You do it only during a call establishment (where
the expression granularity is very high)... That said the Gatekeeper usually
knows the preferences and the capabilities of its users since it is an
important part of the (preconfigured) local policy.

Orit Levin
Chief Architect
RADVISION
Phone: +1.201.6896330
Video: +1.201.6896430

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