Subject: [Megaco] Resolution of multiple resource reservation

From: milton mukhopadhyaya <[email-masked]>
Date: Fri, 21 Jun 2002 05:19:42 -0700 (PDT)

Hi all,
I have confusion about the following scenario where
multiple resources are reserved and I dont understand
how Media Gateway Controller is resolving the
situation.

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MGC TO MG1:
1.
MGC TO MG1

 Transaction=01{
 Context = 2000 {
         Modify = RTP/1 {
                    Media {
                         LocalControl {
                                 Mode = SendReceive,
                                 ReserveGroup = false,
                                 ReserveValue = true}   ; 
Local {
 v=0
 c=IN IP4 $		
 m=audio $ RTP/AVP 4 0
 
                         }
                 }
         }
 }

The above transaction specifies that if resources are available then MG1 should reserve resources for both the codecs (0 and 4)

2.
MG1 TO MGC
 
Reply =01{
Context=2000{
	Modify=RTP/1{
		Media{
		  Local{
			v=0
			c= IN IP4 125.125.125.222
			m= audio 2222 RTP/AVP 4 0
			}
		      }
		     }
	    }
	 }
As MG1 has resources to reserve resources for both the codecs, it reserves them and replies appropriately.

3.
MGC TO MG2

 Transaction=011{
 Context = 3000 {
         Add = $ {
                    Media {
                         LocalControl {
                                 Mode = SendReceive,
                                 ReserveGroup = false,
                                 ReserveValue = true}   ; 
			Local {
 				v=0
 				c=IN IP4 $		
 				m=audio $ RTP/AVP 4 0
 
       				}//end of local
			Remote {
 				v=0
 				c= IN IP4 125.125.125.222
 				m= audio 2222 RTP/AVP 4 0
 
       				}//end of remote
                 }//end of media
         }//end of add
 }//end of transaction

MGC has sent a request for a new rtp stream to MG2 with required parameters and remote descriptors specified.

4.

MG2 TO MGC
 
Reply =011{
Context=3000{
	Add=RTP/11{
		Media{
		  Local{
			v=0
			c= IN IP4 125.125.125.222
			m= audio 2222 RTP/AVP 4 0
			}
		      }
		     }
	    }
	 }
As MG2 has resources to reserve resources for both the codecs, it reserves them and replies appropriatly.

Now both MG1 and MG2 have reserved resources for both the codecs specified by RTP/AVP 0 and RTP/AVP 4. 
QQ1> Now when the media flow starts how will the Media Gateways      determine which codec to support?
QQ2> If later on MGC specifies a SINGLE codec say RTP/AVP 0 in another  Local descriptor, should MG1 AND MG2 deallocate resources reserved  for the other codec (in this case RTP/AVP 4)? If that is the case  then I dont see any real benefit of reserving resources for both the  codecs beforehand. If I am wrong please say what is right.