Hi,
My idea was to parse the SDP and determine if transcoding is needed on the
invite and/or on the responses. Then given what is read, if transcoding is
required:
Alice --- media-proxy --- transcoding card --- media-proxy --- Bob
if no transcoding is required:
Alice --- media-proxy --- Bob
It's the simplest way I found to be able to decide to use transcoding or not on
the fly. What do you think of this approach ? I agree it's complicated but
re-INVITEs come with their own issues in heterogeneous environments.
Best regards,
Dominique
Le 26 août 2010 à 16:44, Saúl Ibarra Corretgé a écrit :
> Hi,
>
> On 08/26/2010 04:31 PM, Richard Revels wrote:
>> I was thinking the media relay would modify the SDP as per normal but set
>> the trancoder IP/port as one side (user configurable?) of the audio stream
>> rather than itself. Then it would tell the transcoder to send to itself so
>> the packets could be forwarded to the endpoints as usual.
>
> Alright, putting the transcoder between the network and the relay could
> do. However...
>
>>
>> And now that I reread your email, having the connection tracking rules send
>> and receive from the transcoder in the middle of the two sides of the media
>> relay would be much nicer. The SDP would still have the relay IP/ports
>> advertised to each side.
>>
>> Good point about the whole SDP mangling thing. I was thinking only of the
>> case where you know, say, G-729 is available on one side and not the other.
>> You know you need transcoding so you send rtp through the transcoder and
>> tell each side it is using what it wanted. In reality the SDP has to be
>> looked at from both ends and then a choice made to use the transcoder if
>> nothing matches, and then modify the SDP for the far end to reflect what it
>> is getting. It would not be desired to send rtp streams through the
>> transcoder if both sides were already supporting a given codec.
>>
>
> ... lets assume the standard scenario: Alice calls Bob. Alice offers
> G711, G722 and G729. When the INVITE arrives at the proxy and *before*
> it goes out to Bob, MediaProxy module kicks in and mangles the SDP. At
> this point we don't know what Bob's answer will be, so what should we
> put in there, the transcoder IP and port or the relay?
>
> We can only know this once Bob answers, but the it'd be too late to
> activate MediaProxy for Alice.
>
>> I bet this gets a lot more complicated than I was picturing up until now. :>
>>
>
> Feels like it ;-)
>
>> However, I'm thinking there might be a demand for this so Sangoma may have a
>> compelling reason to invest the work required for it.
>>
>
> In a B2BUA scenario this would make more sense, since you can start
> without the transcoder and if you detect it's needed, you could reINVITE
> both parties and put the transcoder in the middle. In a proxy scenario,
> OTOH, I find it utterly complicated.
>
> Anyway, don't take my word for granted, there could be something obvious
> which I am overlooking here.
>
>
> Regards,
>
> --
> Saúl Ibarra Corretgé
> AG Projects
>
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