[Asterisk-Users] Development news :: T38 passthrough support

[Olle E Johansson]

Friends in the Asterisk.org community,

There is a lot of cool stuff going on in Asterisk development, things  
that will change Asterisk and
make it work better in your organisation, make it easier to sell in  
your area or give you more
consulting oppurtunities - in short, functionality that will make a  
lot of sense for you users.

However, developers can't really get anywhere without a dialog with  
the users. You know
what you need, you know what is missing and how you would like to  
make Asterisk a better
choice.

I am planning to send out a description of new features now and  
then,  to inform you about
what is going on, but also to get some feedback. The bug tracker is  
not only a tool for developers,
but also for testers and users to react to changes and contribute.

*** ITU T.38 -- Fax over VoIP

Fax over VoIP is a hot issue. VoIP service providers encourage people  
to switch to VoIP,
but often forget to mention that faxing over VoIP is like russian  
roulette. On a local LAN,
it might work if you pick a clear channel codec like G.711. Steve  
Underwood, member of
the Asterisk developer team, has writen a good article about the  
problems involved and
the solutions for it on his web site, the URL is http://soft- 
switch.org/foip.html

T.38 is an ITU standard for fax over VoIP. To simplify, the idea is  
to decode the fax audio
stream at the ingress point, convert it to a data stream that is not  
sensitive towards jitter
or delays and encode it into audio again if needed at the other end  
of the call - if you
can't convert it to an image somewhere in the middle and print it  
directly, or send it by
e-mail.

*** T.38 PASSTHROUGH in Asterisk

Steve is the main contributor behind the work for T38 support in  
Asterisk. He's also
the author of spandsp - the fax application that many use in  
Asterisk. The first part
is to be able to send T38 calls to your Asterisk PBX and make  
Asterisk recognize
this and forward the data stream to another endpoint that supports T.38.

Asterisk won't be an T.38  endpoint, but will handle T.38 calls  
properly, regardless
if the T.38 was offered in the original call setup, or if the caller  
suddenly sends a fax
in the middle of a call (a re-invite). The requirement is that the  
incoming channel
and the outbound channel both supports T38. If not, the call will be  
declined
in a proper way.

When this is tested and stable, work will continue to see if we can make
Asterisk an T.38 endpoint.

This is a very important addition to Asterisk. There is code for  
testing available.
If you are interested, please check this URL in the bug tracker:
http://bugs.digium.com/view.php?id=5090

I think this is a big step for Asterisk. Do you?
If so, don't forget to say "thank you" to Steve Underwood - Coppice!


Have a nice weekend!

/Olle

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* Olle E. Johansson - oej at edvina.net
* Asterisk Training http://edvina.net/training/