Re: Selection of media (m=) at MG

An aditional comment,

if, as we said, we admit the following behavior:

+ call establishment phase: H.248 Command.req for tone/announcement 
control plus media configuration with voice codec
+ information phase: H.248 Command.req for modification of the media 
configuration towards CLEARMODE


The following could happen:

1º Call starts and command.req for tone/announcement is applied.

2º When MGC needs to change to the information phase, the MG responds it 
does not support the CLEARMODE due to insufficient resources (MGC may 
audit the MG before the call to check it supports CLEARMODE, but MGC can 
not know how its resources will change during the call).

In that case, it would not be possible to continue a call that has 
already begun, which should not happen. The SDP description should 
ensure to the MGC that the MG reserves the resources needed by the call 
prior to the establishment of it.

If this is true, it would not be valid to use the modify command between 
the establishment and information phases.

Regards,

Javi


El 30/11/2011 18:44, Javi Muñoz escribió:
>
>> well spotted, thus just a single media configuration ('Clearmode') 
>> would be already sufficient to emulate that ISDN bearer service
> However, two comments:
>
> (a) In the "call establishment phase": what must be created at the 
> MG?: would it be necessary to create a context, or would it be enough 
> to create only an ISDN termination in the null context (which would 
> generate that tone/announcement, and then, MGC would apply a modify 
> command to create the context for the information phase)?
>
> (b) I believe, the announcement do not necessarily have to be recorded 
> in AGW, but that may come from an announcement server (I guess this 
> would also be possible for DTMF tones). Could this justify the 
> creation of such IP termination with voice codec G.711 in the 
> establishment phase, or that communication with the announcement 
> server does not belong to the ISDN call and, therefore, it should not 
> be involved in its Megaco context?
>
> Regards,
>
>
>
>> PS
>> Your previous email was related to ISDN-to-SIP interworking at call 
>> control level, a subject which is out of scope of MEGACO.
>> Thus, something for SIPPING, SIP-IMPLEMENTERS, ... (or TISPAN WG3 
>> list) in my understanding.
>>
>>> -----Original Message-----
>>> From: Javi Muñoz [mailto:[email protected]]
>>> Sent: Mittwoch, 30. November 2011 18:13
>>> To: [email protected]
>>> Cc: Schwarz, Albrecht (Albrecht)
>>> Subject: Re: [Megaco] Selection of media (m=) at MG
>>>
>>> A second comment,
>>>
>>> If:
>>>>>      a) TGW: no impact, because tone/announcement inserted by ISDN
>>>>> local exchange (terminating Q.931); TGW needs just
>>> clearmode support
>>>
>>> (I agree)
>>>
>>> then, why?
>>>>> E.g., MGC
>>>>> ->   call establishment phase: IF tones/announcements THEN H.248
>>>>> Command.req for tone/announcement control plus media configuration
>>>>> with voice codec
>>> That "media configuration with voice codec" (G.711) would be
>>> done at the MeGaCo termination of the IP side of the MG, not
>>> at the termination of the ISDN side. If tone/announcement is
>>> inserted (in the UNI ISDN) by this MG, the termination of the
>>> IP side of the MG would not be used, so that "voice codec"
>>> would not be relevant (no media would be transported over the
>>> IP network).
>>>
>>> am I wrong?
>>>
>>> Regards,
>>>
>>> Javi
>>>
>
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