[Asterisk-Users] T.38 Pass-Thru?

[Steve Underwood]

Matthew Boehm wrote:

>What happens if asterisk receives a T.38 call? Will asterisk pass it thru?
>
>I've seen a few ATA devices that support T.38 and I'm wondering what happens
>if a fax is sent thru one of these ATAs into asterisk.
>
>Maby I have the terminology wrong. Is T.38 a protocol like SIP or is T.38 a
>compression like G729 using SIP?
>  
>
Right now it does not get handled. I think it looks like an unknown codec.

SIP is a signalling protocol. T.38 is more like a cross between a codec 
(e.g. G.729) and a transport (e.g. RTP). It defines its own UDP or TCP 
messages (although a proposal for using RTP as the transport exists). It 
defines a scheme for demodulating the modem tones, send their contents 
through the transport, and remodulating out the other end. If an 
endpoint is within a computer the demodulating and remodulating is 
skipped, and you get a T.38 package like the t38modem add on for OpenH323.

Regards,
Steve