Re: Selection of media (m=) at MG

I'm not familiar with the ISDN/SIP interwork spec [ETSI TS 183 036], but I guess that this could be the emulation of ISDN bearer service "UDI with support of tones/announcements" [ITU-T I.231.x].
The (optional?) capability of tones/announcements is just required during the call establishment phase, - before the communication phase.

1st Dependency on MG type
	a) TGW: no impact, because tone/announcement inserted by ISDN local exchange (terminating Q.931); TGW needs just clearmode support
	b) RGW/AGW [ETSI 183 002]: ... call-dependent procedures for specifying the details of the emulation service


2nd H.248 RGW/AGW profile [ETSI 183 002]
You don't find correspondent call dependent procedures, also due to historical reasons because this was the very first profile defined before the "ITU-T H.248 profile template" was developed.
On the other side, it could be transparent for the MG as you said.

E.g., MGC
-> call establishment phase: IF tones/announcements THEN H.248 Command.req for tone/announcement control plus media configuration with voice codec
-> after: H.248 Command.req for modification of the media configuration towards CLEARMODE

Thus, two media configurations in time series.

Regards
Albrecht

PS
My experience: the condition "IF tones/announcements" AND "ISDN bearer service UDI" seems to be very, very rare, thus just starting UDI bearer service emulation in CLEARMODE ...

 

> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Javi Muñoz
> Sent: Dienstag, 29. November 2011 18:40
> To: [email protected]
> Subject: [Megaco] Selection of media (m=) at MG
> 
> For the ISDN UDI-TA capability, [ETSI TS 183 036] proposes to 
> describe the media at MG using the next SDP description in 
> the Local/Remote
> descriptors:
> 
> m=audio <puerto> RTP/AVP <Dynamic_PT> 0 [8] 
> a=rtpmap:<Dynamic_PT> CLEARMODE/8000
> 
> 
> MG must use the codec:
> 
> * CLEARMODE: in the phase of the call of information transfer.
> 
> * Audio Code G.711-u/A: in the phase of the call of 
> establishment/release.
> 
> 
> The phase of the call is known by the MGC (using signalling 
> Q.931, not visible to the MG). But, with that SDP 
> description, how may MGC indicate to the MG which codec may 
> use at each instant?
> 
> Regards,
> 
> Javi
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