[Asterisk-Dev] Early media in H.323 driver

[Warp]

Hi,

chan_h323 use only g723.1 without annex A , maybe here your problem?
Please check ast_h323.cpp (SetCapability) for more information. 

> Paul Cadach wrote:
> > 
> > This is because:
> > 1) H.323 allows different codec negotiated for opposite voice path while Asterisk have single codec for channel;
> 
> Yes in theoretically, but in my test environment,
> both the forward and reverse path use the same codec(G.723.1).
> 
> For the codec in Asterisk channel, it's still a mystery to me.
> It seems there are several variables associated with the codec of
> a channel: nativeformats, rawreadformat, readformat, rawwriteformat,
> writeformat. And some of them(readformat/writeformat ?)
> are changed during a call.
> Could someone explain them?
> 
> > 2) There is missed codec negotiation (???, not verified) between OpenH323 stack and Asterisk, so translation couldn't be
> > set up correctly.
> > 3) Asterisk currently isn't have codec preferences, so it could interfere with 1) and 2).
> > 
> > Usage of translation within oh323_write is complicated because state of the locks is unknown (sometime it calls with
> > locks held, sometime without ones).
> 
> As I tested, when A dials B, Asterisk generatd a local ringback tone
> to A. But when B sent early media packets to Asterisk, it
> stopped the local ringback tone and tried to pass back the early
> media packes, but failed due to codec imcompatible.
> 
> I also observed if I asked oh323_write to ignore imcompatible
> packets by changing the block
> 
>    if (!(frame->subclass & c->nativeformats)) {
>          ast_log(LOG_WARNING, ...
>          return -1;  <== change to 0
>    }
> 
> The call would not be hangup, but A can't hear the ringback
> tone from B (as expected).
> However, when B answered the call, A and B could talk without problem.
> It seems when a call be answered, Asterisk adjusts the
> read or writeformat of the channel(s) so A and B can be connected.
> 
> I guess we can have Asterisk to adjust the read/writeformat of channels
> when received early media packets to allow the early media be passed
> back to A, just like the call be answered.
> But I don't know how to do that.
> (I know how to detect early media packets in Openh323,
> but I don't know how to tell Asterisk. Any help?)
>