Subject: [Megaco] (no subject)

From: "Ron Gilaad" <[email-masked]>
Date: Mon, 14 May 2007 21:28:39 +0300

Hi,

1. H.248 say that one SDP can not contain more than one m= line, but
doesn't say that in one m= line there can not be an fmt list (more than
one coder). Is it possible to have more than one coder in one m= line?
2. When the MGC asks the MG to create a media, it sends to the MG a
Local descriptor (in the Media desc). Is this Local desc is based just
on previous Audit commands which the MGC has asked the MG, or it may be
based on other considerations not pertaining to the MG? In the 1st case
(the Local desc is based solely on information received from the MG),
then the MG can simply ignore this desc and build a new Local desc in
the reply to the MGC which describes it's configuration and
capabilities. What do you think? 
Thanks in advance,
Ron

Ron Gilaad
RAD Data Communications.
24 Raoul Wallenberg St.
Tel Aviv 69719
Tel: 972-3-6455411 
mailto:[email-masked]

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From: "Stephen Mell \(CV/ETL\)" <[email-masked]>
Date: Wed, 16 May 2007 20:29:46 +0200

Point 2
 
Unlike MGCP (from which I believe you are drawing a parallel here). The
MGC does not "audit" the MG to establish codec support
instead the H.248 MGC Sends Local and remote descriptors with
Under/Overspecified Parameter Values (Lists or Choose) the
ReserveValue=True (or ReserveGroup=true), in the Local Control
Descriptor.
 
This mechanism reserves a number of different codecs at one time, The
Gateway returns only what it has resources for at that particular moment
in time
 
When negotiation is complete. The excess codecs (not required for the
call) can be released by setting ReserveValue=Off (or ResrveGroup=Off)
 
This has the advantage over the MGCP mechanism, of being able to account
for limited resources for certain types of media/codec resources of a
Gateway. The MGCP model assumed that if a Gateway could encode/decode a
high compression codec then it would be able to do it for every line.
That may hold true for Packet Cable RGW's and the like but it does not
hold true for larger gateways.
 
The MG cannot legally ignore the LD, if the MGC puts CHOOSE into the LD
fields and turns ReserveValue=On then the MG effectively builds a
descriptor which describes its capabilities (at that moment in time!!!!)
 
If the MGC specifies a single codec in the LD (or RD) then MG must
comply.
 
Have a good long read of sections 7.1.7 and 7.1.8 and it will be clear.
The use of Reserve Properties is key.
 
Steve 

 

________________________________

From: Ron Gilaad [mailto:[email-masked]] 
Sent: Monday, May 14, 2007 19:29
To: [email-masked]
Subject: [Megaco] (no subject)

Hi,

Thanks in advance,

Ron

Ron Gilaad

RAD Data Communications.

24 Raoul Wallenberg St.

Tel Aviv 69719

Tel: 972-3-6455411 

mailto:[email-masked] <mailto:[email-masked]>