This is caused by your DSL/cable modem buffering the data internally. To
resolve this you need to feed the modem at a data rate that prevents it from
buffering. I solved this by using a shaping bridge server that does nothing but
control the data in and out of the internet connection. I have steady 21ms ping
times to the server that my RTP traffic comes from.
I do faxing over VOIP every day and it works! But it only works if you have a
stable internet connection with an SLA, which I have. Also having an ISP that
only uses a pure IP network makes a big difference. Some DSL providers use ATM
to transport IP and this causes high packet loss when their network is busy.
T.38 is a great idea but we need large scale implementation of it, with
standards for it to work.
Here is my hylafax log from last week. I removed the numbers for privacy
reasons.
Facsimile received since last week:
Pages Time Pg/min Errs TypRate TypData
1 3:17 0.3 0 14400 2-D MMR
26 16:55 1.5 0 9600 1-D MH
2 0:46 2.6 0 14400 2-D MMR
13 5:13 2.5 0 14400 2-D MMR
14 5:48 2.4 0 14400 2-D MMR
5 2:33 2.0 0 14400 2-D MMR
1 0:28 2.1 0 14400 2-D MMR
1 0:31 1.9 0 14400 2-D MMR
------------------------------------------------------------------------------------------
Total 63 35:31 1.8 0
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JD
Sent: Tuesday, October 28, 2008 2:20 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [asterisk-users] fax / t38 gateway
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
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