[asterisk-dev] AST_FRAME_DIGITAL

[Sergio Garcia Murillo]

----- Original Message ----- 
From: "Steven Critchfield" <critch at basesys.com>
To: "Asterisk Developers Mailing List" <asterisk-dev at lists.digium.com>
Sent: Wednesday, September 12, 2007 9:52 PM
Subject: Re: [asterisk-dev] AST_FRAME_DIGITAL


> On Wed, 2007-09-12 at 08:25 +0200, Klaus Darilion wrote:
> > Russell Bryant schrieb:
> > > I can tell you right now that you will not be able to convince me that
we should
> > > add an opaque frame type for this situation.  It is completely against
the
> > > Asterisk architecture.  As you said, the stream you are handling is in
fact
> > > voice and video.  Asterisk has explicit handling for voice and video,
and the
> > > streams should be passed into Asterisk using those frame types.
> >
> > Hi Russel!
> >
> > A simple scenario: A Asterisk server is used as PBX and is connected to
> > the PSTN with a PRI (zap). Further, it has a BRI card to connect to
> > in-house BRI devices.
> >
> > Asterisk bridges calls between BRI and PRI, and sometimes this is a
> > digital call. As digital calls do not have proper treating yet, it will
> > happen that Asterisk thinks that PRI uses ulaw and BRI uses alaw and
> > starts transcoding - which is a very bad thing for digital connections.
>
> Not all BRIs are alaw. If there needs to be a conversion, it should
> happen. Your scenario proves why it should even happen. What if I was
> using European ISDN phones in my office here in the US where I need ulaw
> PRI. I need these calls to be transcoded if it is a voice call.
>
> The problem I see here is when does the channel driver determine if the
> data in the channel should be handled differently? Especially on the PRI
> line.
>
> Back a while ago, we used zapras a little for a backup BRI connection
> from a remote site into our network. Why should and how could the
> chan_zap driver know when I am getting a data ppp connection and when I
> am getting a data 3g video conference.

Just cheking q931 bearer capability:

pri debug span 1
Bearer Capability (len= 3)
 Ext: 1  Q.931 Std: 0  Info transfer capability:
         Unrestricted digital information (8)
 Ext: 1  Trans mode/rate: 64kbps, circuit-mode (16)
 Ext: 1  User information layer 1: H223/H245 data (38)

I think the translation is easy....
AST_FRAME_DIGITAL
AST_FORMAT_H223

As
Bearer Capability (len= 5)
Ext: 1  Q.931 Std: 0  Info transfer capability: Speech (0)
Ext: 1  Trans mode/rate: 64kbps, circuit-mode (16)
Ext: 1  User information layer 1:A-Law
Is
AST_FRAME_VOICE
AST_FORMAT_ALAW

Still can undestand the dificulty about handling it that way

Best regards
Sergio