Re: Trouble receiving faxes from certain sources

On 05/08/2019 09:59 AM, Jason Rissler wrote:
> I am having a problem that I can not receive faxes successfully from a=20
> few senders. I'm attaching a log from one of the sessions in hopes that=
=20
> someone can tell me what setting I could tweak or what the problem migh=
t=20
> be. I can receive fine from this sender when using an HP Officejet Pro=20
> multifunction machine but not with HylaFAX+.

TCF is a signal which is sent by the sender to the receiver and is a
1.5-second series of zeroes using the selected carrier modulation.=A0 So,
here is a list of modulation speeds and the number of bytes that should
be zeroes in a TCF signal:

14400 bps: 2700 bytes
12000 bps: 2250 bytes
9600 bps: 1800 bytes
7200 bps: 1350 byes
4800 bps: 900 bytes
2400 bps: 450 bytes

The fax receiver is required to use the reception of the TCF signal to
determine if its demodulator is properly trained on the signal from the
sender.=A0 If it is not trained properly then it will not be able to
demodulate the page image data and will need to be retrained
successfully before fax protocol can proceed to receive page image data.

In order to determine if the TCF signal indicates a proper training of
the demodulator (the modem) HylaFAX looks at two different things in the
TCF signal:

1) the percentage of non-zero data found in the signal (Class1TCFMaxNonZe=
ro)
2) the length of the largest run of zero data found in the signal
(Class1TCFMinRun)

Both of those settings can be tweaked in the modem config file.=A0 (See
the hylafax-config man page for details.
https://hylafax.sourceforge.io/man/hylafax-config.php)=A0 By default,
Class1TCFMaxNonZero is 10 (meaning up to 10% can be non-zero) and
Class1TCFMinRun is 1000 (meaning 1000 ms of uninterrupted zeroes) which
is modified by Class1TCFMinRunECMMod to 500 for ECM sessions.

If you look at your session log, then, you'll see the following results
from TCF signals in various training attempts:

14400 bps: RECV: TCF 2842 bytes, 96% non-zero, 1 zero-run
12000 bps: RECV: TCF 2368 bytes, 94% non-zero, 1 zero-run
7200 bps: RECV: TCF 1459 bytes, 54% non-zero, 1 zero-run
4800 bps: RECV: TCF 865 bytes, 96% non-zero, 1 zero-run
2400 bps: RECV: TCF 493 bytes, 60% non-zero, 2 zero-run
2400 bps: RECV: TCF 493 bytes, 60% non-zero, 3 zero-run
2400 bps: RECV: TCF 493 bytes, 60% non-zero, 3 zero-run

These are very bad results and indicate that the modem is not training
practically at all on the signals from the sender.=A0 I don't think there
is anything you can reasonably do to Class1TCFMaxNonZero or
Class1TCFMinRun to get things working.=A0 The problem isn't with your
configuration.

The problem is that the modem is not training properly on the sender's
signal.=A0 So, it's a problem with the line audio quality on the call or =
a
problem with the modulator/demodulator compatibility between the sender
and the receiver.

If you're not having a problem receiving from most other senders, and if
this sender can send to most other receivers, then it would most likely
be a problem with the firmware programming on your modem.=A0 The solution
would be to change modems (preferably to one with a different chipset or
better firmware).

Thanks,

Lee.



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