[asterisk-dev] AST_FRAME_DIGITAL

[Matthew Fredrickson]

Russell Bryant wrote:
> Klaus Darilion wrote:
>> What about G3 fax. It is rather the same as 3G video:
>>   fax delivers images over a telephone line
>>   3G video deliver audio and video over a telephone line
>>
>> In case of G3 fax, the image data is modulated
>> In case of 3G video, the audio/video is multiplexed with H223.
>>
>> Currently fax is handled inside an application. Taking your argument, 
>> the fax decoder should be in the channel driver and deliver 
>> AST_FRAME_IMAGE (maybe one per page) to Asterisk's core. But I think the 
>> current implementation which is a single application is much better then 
>> adding modem functionality to each channel driver.
>>
>> IMO it is much more flexible only add support for generic data 
>> (AST_FRAME_DIGITAL) to channel drivers. Then, new services and features 
>> can be added as application without touching the code of channel drivers.
> 
> Faxes are passed into Asterisk using the VOICE frame type, indicating that it is
> audio.  In the case of T.38, it uses the AST_FRAME_MODEM type.

So perhaps we could use our AST_FRAME_MODEM type for this (I'd prefer if 
we did this to rename it to something more appropriate, like 
AST_FRAME_DIGITAL or something like that), and use subclasses for the 
different types (H223, T38).  An extension of the translator 
architecture will allow us to do transcoding from that to audio/video as 
neccessary.  What's nice about that is you could also do T38 gateway 
(T38->[u,a]law) through a codec module as well.

-- 
Matthew Fredrickson
Software/Firmware Engineer
Digium, Inc.