[asterisk-users] fax / t38 gateway

[JD]

Gordon Henderson wrote:
> but it's very do-able, given good Internet connections.
[...]
> 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
>   

Fair enough. However, my experience has been that defining "good 
Internet" for faxing over G.711 is not entirely self-evident.

I've seen some really lagged environment work with FAX over G.711 like a 
dream. And some fast ones break badly:

While I don't have full explanations for this, it _seems_ like the 
following holds true:

good ping time sequence for faxes--no jitter (all times in ms):

   40, 40, 40, 40, 40, 40, 40, 40...

A bad one -- high jitter low latency:

  5, 10, 5, 20, 18, 7, 12, ...

A _really bad_ one -- "shifting" jitter:

  20, 20, ... , 20, 20, 30, 30, 30,...

No provable explanation as to why.

John