[Asterisk-Users] Softfax/spandsp

[Lee Howard]

On 2004.03.18 06:06 Steve Underwood wrote:

>    Some fax machines send a little less than the specified 1.5 
> seconds of training test data, so the training test failed every 
> time. I now only look for 1.25seconds of training test data.

You may even have to go as low as 1.00 sec., by the way.

>    Some fax machines do not correctly initialise the scrambler in 
> their V.29 transmit modem. I have changed the software to tolerate 
> this.

This is probably off-topic on-list (feel free to respond privately), 
but can you elaborate?

>    Some fax machines send a burst of ones before the burst of zeros 
> that forms the training test data.

This is actually quite normal.  And in the case of a Class 1 
transmitter, it is virtually impossible to avoid.  For example, a DTE 
using a Class 1 modem can send TCF by issuing the AT+FTM=145 followed 
by the transmission of the requisite zero-fill as soon as the CONNECT 
response is received.  However, per T.31 spec (8.3.3), the Class 1 
modem will already have transmitted a series of consecutive 1s before 
the 0s begin.  I know of no way to avoid this.

Lee.