[asterisk-users] fax / t38 gateway

[Gordon Henderson]

On Tue, 28 Oct 2008, JD wrote:

> Steven's writeup is great and explains a lot of this.
>
> A shorter answer from a different perspective:
>
>  The folks that devloped the fax V.protocols took into acount typical
> copper problems like noise or echo. But what they never conceived of as
> even being possible is that a call might shift around in the time
> domain. Thanks to jitter/latency, the delay time of a call can change in
> the middle of the call. That isn't possible with copper technologies.
> This makes faxing over even G.711 a dice roll.
>
> IMO, with a sufficiently large buffer and a rock-solid quartz clocking
> system that goes way beyond what is typically seen, it might be
> theoretically possible to send a fax over VOIP.


I've not really been paying much attention to this thread, so forgive me 
if I'm repeating something said before, however, I have sent several faxes 
via VoIP over the public Internet. I'm not saying I'd ever sell this to a 
customer, but it's very do-able, given good Internet connections. (Which 
we seem to have in the UK --- IF you pay for it) My particular setup was 
when I was testing RxFAX and my fax to email software. This was primarrily 
aimed at sites with ISDN, but we thought we'd give it a go over IP, so I 
had a friend 300 miles away with an analogue fax machine talking to an ATA 
which was an extension on my local asterisk PBX, sending FAXes to an 
extension that was doing RxFAX and emailling the TIF file back to him.

I'd never say it was reliable enough to trust in a commercial setting, but 
I think your statements were just a bit too strong - I agree 
wholeheartedly about the V. protocols and copper, but I've found in 
practice that faxing over IP is not just theoretically possible, but quite 
do-able, and is someone wanted to send me a fax (I have no fax machine, 
they're so 80's :), then I'd not hesitate to setup a VoIP DID and give 
them the number...

Gordon