Subject: RE: [Megaco] A query ....

From: "Tom-PT Taylor" <[email-masked]>
Date: Sat, 20 Jul 2002 18:11:24 -0400

Sounds like an exam question, but here's a quick answer: Megaco/MGCP has a
different function from SIP/H.323.  The latter are call signalling
protocols.  Media gateway control is something the call processing
application does as a result of requests made by call signalling.  In the
usual network diagram, SIP/H.323 operate horizontally between call
processing entities, while Megaco/MGCP operates vertically between a call
processing entity and its subordinate media gateways.

-----Original Message-----
From: Rahul Pande [mailto:[email-masked]]
Sent: Friday, July 19, 2002 4:11 AM
To: [email-masked]
Subject: [Megaco] A query ....

Hi,

  A very basic query :

  "The architecture of MEGACO/MGCP with respect to media gateway
controller and the various media gateways can be brought out using
SIP/H323 protocols also using there respective servers like SIP Proxy and
H323 Gatekeeper.

  In what all ways MEGACO/MGCP is different than the SIP/H323 protocols
and how it might be better suited for deployment." 

 The main point refered at many places is that the Media Gateway is quite
small and most of the functionality complety only goes at the Controllers
end.

Thanks and Regards,
      rahul

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From: Rajeev K R <[email-masked]>
Date: Mon, 22 Jul 2002 09:26:48 +0800

Hi Rahul,
Maybe you are confused because of some network diagrams which shows H323
gatekeeper/SIP proxy operating vertically to H323/SIP terminals.(Ref: The
first statement in your query).  This may give an impression that it works
similar to MGC-MG. But that is not the case.  Since Tom did not emphasize on
this perspective let me try to explain.

    From the protocol perspective an H323/SIP terminal does not have a
master-slave relationship with the gatekeeper/proxy as in the case of MGC
and MG. In H323 and SIP protocol,  terminals are peer entities to gatekeeper
and proxy. This is evident when you see that a SIP terminal can make a call
to another SIP terminal without the help of a call processing entity. They
need the help of proxy when they cannot locate the other entity directly,
eg: you want to use an E164 number to call the other terminal. The proxy
will resolve the E164 number to a SIP URL and place a call to the other
terminal.

    An MG cannot make a call to another MG without the help of an MGC. In
reality the MG cannot even originate a call like a SIP terminal. The first
offhook notification from the MG is just an event notification (since the
MGC has requested to notify it) and NOT a call origination request. The same
offhook notification can mean an answer when the phone is ringing. All these
are decided by the MGC. When a SIP terminal send an INVITE, it is
originating a call. The difference between SIP/H323 and MGCP/MEGACO starts
right from here.

Regards,
Rajeev

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From: Rajeev K R <[email-masked]>
Date: Mon, 22 Jul 2002 09:26:48 +0800

Hi Rahul,

Regards,
Rajeev