Re: [hylafax-users] Incomplete outgoing faxes

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

On 2004.05.13 08:54 Tortoise@xxxxxxxxx wrote:
> Hello!
> I would like to solve my problem. With latest Hylafax and Class 1
> faxmodem I am experiencing problems with outgoing faxes, because they
> are incomplete.
> Try to imagine that Letter or A4 page is divided into about six
> horizontal stripes, like this:
> +-------------+
> |Stripe 1     |
> +-------------+
> |Stripe 2     |
> +-------------+
> |Stripe 3     |
> +-------------+
> |Stripe 4     |
> +-------------+
> |Stripe 5     |
> +-------------+
> |Stripe 6     |
> +-------------+
>
> What target fax receives looks like this:
> +-------------+
> |Stripe 1     |
> +-------------+
> |Stripe 3     |
> +-------------+
> |Stripe 5     |
> +-------------+
>
> What is especially annoying when some agreements were sent and because
> were only some (whole) paragraphs missing (those on parts 2,4 and 6),
> it didn't look incomplete!
>
> I checked postscript files from the Hylafax queue and they are -
> according to my expectations - complete and without problems. This
> problem occurs always - no matter, which kind of fax device is on the
> other side.
>
> I would like to ask for following:
> 1. Is it known problem?

I've seen this happen (it's only possible in non-ECM faxing) when the 
modem didn't properly support the designated flow control (XON/XOFF) 
and the baud rate (ModemRate) was sufficiently higher than the 
negotiated baud rate that the DTE-to-DCE data actually overflowed the 
modem's buffer.

What modem (make, model) are you using?

> If so, is somewhere posted solution how to fix
> it?

In the cases where I've seen this I changed ModemFlowControl from 
xonxoff to rtscts and it worked fine.  Note, that this may not be an 
option if you are running an external modem off of a non-standard 
multiport serial expander (i.e., Cyclades).

> 2. If it is not known problem, which debug parts I should turn on to
> detemine where is the problem?

It was really nasty to debug.  I had to enable tracing of all modem 
communications (set 'TracingMask: 0x11' and then 'SessionTracing: 
0xFFF'), and then sent a fax from HylaFAX to another port on the same 
HylaFAX system.  I then compared the two sets of data and found that 
portions were simply missing.  Because the receiver only sees one 
corrupt scan line at each "break" it generally will accept the data as 
"acceptable".

When faxing legal documents, etc., I highly recommend using ECM, since 
it nearly guarantees that the data will be exactly as the original.  
Non-ECM faxing only requires an "acceptable" quality level.  You can 
get ECM in Class 1 by using HylaFAX 4.2.0 (now 4.2.0beta2).

Lee.

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