Subject: [Megaco] Need clarifications on behaviour of media gateway

From: "Prerna Nagar" <[email-masked]>
Date: Fri, 27 Apr 2007 20:21:07 +0530

Hi All,
 
I need some clarifications on issue described below:
 
Here Originating and Terminating gateway is same.
 
    Gateway              Configured List of codecs                Message
Local Descriptor                               Remote Descriptor
============================================================================
=====================
                              EncName / Payload / Preference
============================================================================
=====================
1. Originating GW    G.729/103 /2                                  Add
Request             m=audio $ RTP/AVP 106 102                        None
                              G.726/106 /1
a=rtpmap:106 G729a/8000/1
 
a=rtpmap:102 G723.1a-H/8000/1                                             
                                                                        
2. Originating GW     Same as above                             Add Response
m=audio 16402 RTP/AVP  106 102                  None
a=rtpmap:106 G729A/8000/1
 
a=rtpmap:102 G723.1A-H/8000/1
 
3. Terminating GW   Same as above                             Add Request
m=audio $ RTP/AVP $                      m=audio 16402 RTP/AVP 106 102
 
a=rtpmap:106 G729A/8000/1
 
a=rtpmap:102 G723.1A-H/8000/1
 
4. Terminating GW   Same as above                             Add Response
m=audio 16404 RTP/AVP 106 103     m=audio 16402 RTP/AVP 102 106
 
a=rtpmap:106 G723.1A-H/8000/1       a=rtpmap:106 G729A/8000/1
 
a=rtpmap:103 G729A/8000/1             a=rtpmap:102 G723.1A-H/8000/1

My query is "Can Terminating gateway change the preference order of payload
types in m line while replying to the Add?" 
If yes what can be the reason GW would need to modify a remote descriptor ? 
 
Regards,
Prerna
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---

From: [email-masked]
Date: Fri, 27 Apr 2007 17:35:47 +0200

Prerna,

the resource selection rules are defined in clause 7.1.8/H.248.1.

You got a single media group in your example, and your omitting
ReserveGroup & ReserveValue properties, thus following rule is applicable:

   If  ReserveGroup  is  "False"  and  ReserveValue is "False", then the MG
   should apply the following rules to resolve Local and Remote to a single
   alternative each:

   ?    The  MG chooses the first alternative in Local for which it is able
         to support at least one alternative in Remote.

   ?    If  the  MG  is unable to support at least one Local and one Remote
         alternative, it returns Error Code 510 ("Insufficient resources").

   ?   The MG returns its selected alternative in each of Local and Remote.

Saying that, I think that already step 2 is incorrect. The responsing GW
shall select one codec, and not respond with both in my understanding.

Albrecht

                      "Prerna Nagar"                                                                                                    
                      <[email-masked]         To:      <[email-masked]>                                                               
                      om>                      cc:                                                                                      
                                               Subject: [Megaco] Need clarifications on behaviour of media gateway                      
                      27.04.2007 16:51                                                                                                  

Hi All,

=================================================================================================
=================================================================================================

2. Originating GW     Same as above                             Add
Response           m=audio 16402 RTP/AVP  106 102                  None
a=rtpmap:106 G729A/8000/1
a=rtpmap:102 G723.1A-H/8000/1

Regards,
Prerna_______________________________________________
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https://www1.ietf.org/mailman/listinfo/megaco

---

From: "Prerna Nagar" <[email-masked]>
Date: Fri, 27 Apr 2007 21:33:26 +0530

Thanks Albrecht...
But Lets assume that Reserve Value = ON.
Now step 2 is correct... Right?

But as far as my understanding about protocol goes as of now... I think
Terminating gateway should never play with Remote descriptor. The intention
to send a remote descriptor is just to inform the terminating end about the
capabilities of originating end. So as per your third point.." MG returns
its selected alternative in each local and remote" I think whatever MG has
to respond should be a part of local descriptor..

Please correct me if my understanding of the protocol is wrong... Since I m
new newbie in this field..

Regards,
Prerna
-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] 
Sent: Friday, April 27, 2007 9:06 PM
To: Prerna Nagar
Cc: [email-masked]
Subject: ReserveGroup & ReserveValue properties; Re: [Megaco] Need
clarifications on behaviour of media gateway

Prerna,

You got a single media group in your example, and your omitting ReserveGroup
& ReserveValue properties, thus following rule is applicable:

Albrecht

                      "Prerna Nagar"

                      om>                      cc:

                                               Subject: [Megaco] Need
clarifications on behaviour of media gateway                      
                      27.04.2007 16:51

Hi All,

Regards,

---

From: "Raphael Tryster" <[email-masked]>
Date: Sun, 29 Apr 2007 14:11:48 +0200

>From 7.2.5 text describing the AuditValue command:

   ¸    To audit an individual property in the media descriptor the 
        relevant stream ID (optional), group ID(optional) and 
        propertyID are included. The current value of the property is 
        returned. Group ID is used in the case where the local control 
        Reserve Group flag is used. Group ID 1 corresponds to the first 
        group (session decription) reserved, Group ID 2 the next group 
        etcetera.

I see this groupID and propertyID described in ASN.1 but not in ABNF.  Does it / should it exist in ABNF?

Also, is it correct that it is possible to audit an individual property of a single stream or all streams in the media descriptor, but it is not possible to audit all properties of a single stream?
 
Raphael Tryster