Subject: Re: [Megaco] physical termination in context with no media descriptor

From: Christian Groves <[email-masked]>
Date: Wed, 10 Jan 2007 11:49:47 +1100

Hello Raphael,

If the Physical termination really has an empty media descriptor then I 
think you are correct media couldn't flow. However do the T.38 flows 
assume that the media descriptor has been pre-provisioned? In that case 
you wouldn't request it in an Add.req but it should be seen in the 
Add.reply.

Regards, Christian

Raphael Tryster wrote:
> " Within a context, StreamID is a means by which to indicate which media
> flows are interconnected: streams with the same StreamID are connected".
>
> Does this mean that if a physical and an ephemeral termination are added
> to a context, and only the ephemeral termination has a media descriptor,
> no media will be passed between them?
>
> Here is an example from the T.38 document (where else...?):
>
> MEGACO/1 [123.123.123.4]:55555
> Transaction = 11 {
>   Context = $ {
>     Add = DS0/1/1 {
>       Events = 1 {al/on, ctyp/dtone }
>         },  ; SCN termination prepared to listen for tones
>     Add = $ {
>       Media { 
>         Stream = 1 { 
>           LocalControl { Mode=ReceiveOnly, ReservedGroup=On,
> ReservedValue=On},
>           Local {
> v=0
> c=IN IP4 $
> m=audio $ RTP/AVP 18 0
> v=0
> c=IN IP4 $
> m=image $ udptl t38
>            }; IP termination for audio     
>          }                  
>        }
>      }    
>   }
> }  
>  
> In the call flow examples in H.248 itself, physical terminations are
> also added to contexts without a media descriptor being specified in
> that command, but it was specified in earlier commands.  In the four
> Megaco call flows given in the T.38 document, physical port DS0/1/1
> never gets a media descriptor in two of them, and in one of them it gets
> it after it is added to the context.
>
> Is this another error in the T.38 document?  Are there any scenarios in
> which it would be useful to add a termination to a context without a
> media descriptor?
>  
>  
> Raphael Tryster
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