Subject: RE: [Megaco] Query on H.248 ReserveValue Implementation

From: "Kevin Boyle" <[email-masked]>
Date: Mon, 7 Nov 2005 15:09:53 -0500

Comments inline. [KJBII]

Kevin 

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Naveen Sujit Kumar
Sent: Tuesday, October 18, 2005 1:45 AM
To: [email-masked]
Subject: [Megaco] Query on H.248 ReserveValue Implementation

Hi All,
 I had few queries regarding MG's behaviour when ReserveValue was 'On'.

1. The Add message contains both local and remote descriptors with
   a list of codecs. There might be common codecs between the two
   descriptors. The message might be like this:

      Add = R$ {Media {
        LocalControl {Mode = ReceiveOnly,ReservedValue=ON},
        Local {
v=0
c=IN IP4 7.7.7.160
m=audio 20000 RTP/AVP 0 18 4		<<<<<
a=ptime:20
        },
        Remote {
v=0
c=IN IP4 7.7.7.123
m=audio 20000 RTP/AVP 0 18		<<<<<
a=ptime:20
        }
      }
    }
  }
}

	What exactly should we do when we have both local and
	remote descriptors..?? 
	* Should only one descriptor be considered..?? Or
	* Should MG go thro' both the lists and take only the 
	  common codecs ( 0 18 ) for consideration..?? Or
	* Should both the lists be treated seperately and resources
	  reserved for the same..??
	* Also, what should be the behaviour if there are no common
	  codecs between local and remote descriptors..??

Is there any such real world application for any of the above
conditions..??

[KJBII] With ReserveValue = ON, the MG is required to reserve resources
for as many of the codec options as it can. It also means that the MG
must be ready to process packets for the codecs returned to the MGC at
any time.  There is no protocol requirement that codec selection be
symmetrical.  Remember that the Local and Remote Descriptors are
independent of each other, each indicating one direction of a two-way
connection.  Many MG vendors have ensured that codec selection will be
symmetrical, but this is an implementation decision and not a protocol
requirement.

2. How does Ignore go with ReserveValue..?? The message might be 
   like this:

      Add = R$ {Media {
        LocalControl {Mode = ReceiveOnly,ReservedValue=ON},
        Local {
v=0
c=IN IP4 7.7.7.160
m=audio 20000 RTP/AVP -			<<<<<
a=ptime:20
        }
      }
    }
  }
}

	What needs to be done here..?? Should we return an empty
	descriptor as RFC says, since we cannot reserve any
resources..??
	Or should we return an error and what needs to be the error
	value..??

[KJBII] I do not believe this to be valid in the context of H.248.
Further, how can you have a packetization rate, if there is no codec
specified?  An error should be returned -- 515 appears to be the closest
reasonable error code.

TIA for any suggestions,
-Naveen

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