Summary:ASTERISK-11230: Attempt To Add T38 Gateway Support As A Codec Translator
Reporter:Gregory Hinton Nietsky (irroot)Labels:
Date Opened:2008-01-13 23:52:10.000-0600Date Closed:2011-06-07 14:02:44
Versions:Frequency of
Description:Ok this is somthing that may or may not be possible or feasiable but im throwing it out here and going to attempt to do just this ...

please note this is related and tied into the brilliant work by dimas on christmas day (ASTERISK-11094)

there will be a few things required for me to do to make it suitible for our application

1)Define T38 as a codec (change to frame.h add it as a audio codec)
2)Create a codec translator (codec_t38fax) that will do conversion to and from SLIN
3)to allow T30<->SIP(T38/UDPTL)<->IAX(RTP/T38)<->ZAP(ALAW/T30) ill need to allow this new codec to pass on RTP
4)Dial will need to be updated to allow MODEM/T38 frame types as voice ... (AST_FORMAT_T38FAX)

this is a brief overview im sure there will be headaches along the way.


due to licencing issues hacking T38 Gateway onto the Dial command is not feasiable and i do not feel that a second dial command just for T38 is justifiable.the architecture of the codec translators lends itself to this approach of using a translator for the T30(audio/SLIN) to T38(data) conversion.

the idea is as follows using Steve Underwoods spandsp add a codec_t38fax file to the addons package that will accompany the newly T38 enabled app_fax to handle the gateway function.

slintot38fax is is achived by reading a T30 frame passed to the converter from the Zap/mISDN/.... channel and writing it to a buffer via the t38fax gateway handler call back.

t38faxtoslin is achived by processing  incoming t38 ifp packets and writing them to a buffer with the t38 tx function.

all of the above is relitivly straightforward ... what is not straight forward however is preventing licencing isues and initilising the private structure (t38_gateway_init) make_compatible will need to make sure the same private structure is is used on both channels (t38state) and will possibly need to be locked.all the T38 bits need to be kept in codec_t38fax in the addons/GPL side asterisk must however make sure the private structure for T38 is on both sides.

this all seems great in theory and if im missing something or if this proposal is not acceptable please let me know ... ill be working on the bits over the next few days if there no objections.
Comments:By: Jason Parker (jparker) 2008-02-14 19:09:52.000-0600

No patch here...  any luck?

By: Gregory Hinton Nietsky (irroot) 2008-02-15 07:52:09.000-0600

it is still in the good ideas dept. unfortunately we have been extremely busy and i have had to focus on some other issues this is something that needs to be done there is a requirement for it please be patient it i have every intention of doing  this.

so far i have spent a good chunk of time pouring over the spandsp bits and have belive it can be done of course the masters at digium need to be pleased ;)

By: Joshua C. Colp (jcolp) 2008-06-02 14:39:10

Suspending for now. Discussion is probably best for the -dev list so more people can see and participate.