Subject: Re: MEGACO & SIP

From: Peter Blatherwick <[email-masked]>
Date: Mon, 16 Oct 2000 12:55:38 -0400

Megaco/H.248 and peer-to-peer protocols such as SIP or H.323 are
orthogonal.  They solve different aspects of the overall problem of
Internet communication systems.

Megaco/H.248 is a master/slave protocol for control of gateway functions at
the edge of packet networks, for example to control interface functions on
IP-PSTN trunking gateways, analog lines gateways, etc.  Megaco Protocol
(IETF name) and H.248 (ITU-T name) are a single identical protocol solution
jointly developed by both ITU and IETF as a single international open
standard.  The main function of Megaco/H.248 is to allow gateway functions
to be decomposed into a call agent part (master), known as Media Gateway
Controllers (MGC),  containing all call control intelligence, and an
gateway interface part (slave), known as Media Gateways (MG), which have no
call control intelligence and simply handle making of connection, simple
configuration, and possibly user interface.  The MGC slave part is dumb
from an application perspective, and can therefore be highly optimized for
its interface function, and can be physically located separately from the
call control intelligence.

On the other hand, both SIP and H.323 are peer-to-peer protocols for call
control, or more generally multi-media session control.  They compete with
each other in this space.  They both operate at a different level (call
control layer) from Megaco/H.248 in a decomposed network, and are thus
unaware of whether or not Megaco/H.248 is being used underneath for
master/slave control.   While Megaco/H.248 is not absolutely necessary in a
system to support SIP or H.323 gateway functions, it does allow some very
important properties when used (see next).

Megaco/H.248 and peer protocols (SIP or H.323) are complementary in nature
and entirely compatible within the same system.  At a system level,
Megaco/H.248 allows for overall network cost and performance optimization,
protection of investment by isolation of changes at the call control layer,
freedom to geographically distribute both call function and gateway
function, and adaptation of legacy equipment.  Megaco/H.248 also has a lot
of potential for interesting applications in the area of end-user device
control, such as master/slave based Internet telephone control.

I hope that helps,
Peter Blatherwick

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Monday, October 16, 2000 05:08
To: [email-masked]
Subject: MEGACO & SIP

Hello there,
Can you explain the difference between MEGACO & SIP/H.323?

I don't know whether MEGACO is a signaling protocol or not.
Is MEGACO alway necessary to implement a SIP gateway or H.323 gateway, If
that is not a signaling protocol?

If MEGACO is not alway necessary, what's their purpose(Reason for using
MEGACO)?

Thanks.

from Eungdon Lee

------------------------------------------------------------------
Eungdon Lee
ETRI(Electronics & Telecommunications Research Institute)
Tel : 82-42-860-3904
E-mail : [email-masked]

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From: Tom-PT Taylor <[email-masked]>
Date: Wed, 25 Oct 2000 09:20:03 -0400

You may be interested in my tutorial in the current issue of IEEE
Communications Magazine.  I'll warn you that this article is probably a bit
controversial -- it's written from my personal point of view.
Tom Taylor, "Megaco/H.248: A New Standard For Media Gateway Control", IEEE
Communications Magazine, Vol. 38 No. 10 (October 2000), pp. 124-133.

> Sent: Monday, October 16, 2000 5:08 AM

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From: "Roy, Radhika R, ALCOO" <[email-masked]>
Date: Wed, 25 Oct 2000 10:59:22 -0400

Hi, Tom:

I do appreciate your viewpoints although it is personal and controversial.
In fact, I feel that it will be remembered one of the best articles that
bridges the gap between the history of progressive standard development and
the actual standard that people usually see.

My personal thanks to you for a well written paper.

Radhika R. Roy