[Asterisk-Users] Fax with SPA-2000's?

[Lee Howard]

On 2004.06.24 18:28 Kevin P. Fleming wrote:
> Lee Howard wrote:
> 
>> I stand corrected.
>> 
>> After a little bit of work with the fax application to adjust the 
>> timings (increasing all of the pauses), all is well with V.17 also.
> 
> I assume you're using no compression (G711u) between the X100P and 
> the SPA-2000, then.

That is correct.

> Are you finding this to be a reliable combination?

For small to average faxes when ECM is used, yes, it is reliable.  When 
ECM is not used I see more image corruption than when I had a direct 
fax line into the analog device.  ECM compensates for that, which is 
why it's not noticeable when ECM is used.  But if I send or receive a 
large fax (lots of image data on the page), then it seems that even ECM 
has an extremely difficult time compensating for the "jitters" or 
whatever.

So, to clarify my previous posts, there is no incompatibility with V.17 
or any other fax modulation protocol that I can tell.  Neither is there 
a limitation to the speed at which data can be passed (at least within 
the bounds of faxing speeds).  However, there is a noticeable amount of 
"noise" that is created by the analog-to-digital-to-analog conversions, 
and it only gets worse when the fax devices "train down"/"slow down" to 
compensate.  So it works fine if it can get through without triggering 
a speed reduction, but once the speed reductions start going then it's 
downhill from there.

I wouldn't recommend doing this in a production deployment unless you 
have a shortage of telco lines and an abundance of FXS ports.  
Otherwise, it's simply a better solution to have a dedicated fax line 
going straight from the telco to the fax device.

> We are about to deploy a VOIP solution and we are planning on 
> avoiding the FAX issue for the time being, but if it _can_ be 
> reliable using G711u we might play around with it some more.

You may want to look into it, if it will be useful to you.  Just don't 
get your expectations too high.  Now, if we had a T.38 driver, then I 
suspect that things could be different.

Lee.