Re: [hylafax-users] receiving problem

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Matthias Reich wrote:

> I have a strange problem with receiving a fax from a destination.
> the communication is fine, according to the log, but the received fax
> (tif-file) is only 500 bytes.
> I tried two different modems on different servers with different 
> hylfax-versions.
>
> I have no idea what to do, to make the receiving from that destination work.
> As far as I understand the logs hylafax is receiving data for about 20 
> seconds, after that hylafax sends a RTN, but why is hylafax then telling me
> normal and proper end of connection when it received obviously nothing.

The logs are saying this:

That the session is normal up through the point when Phase C high-speed 
data carrier is raised.  However after 15 seconds or so of being there 
the receiver only detects a few (probably corrupted) scanlines.  The 
sender drops the carrier transmits EOP, and then the receiver responds 
to that with RTN (in hopes of getting the sender to retransmit).  
However, the sender sends DCN and hangs up.

The real problem: the V.17 modulators are apparently incompatible 
between the sender and the receiver.  To blame: your modem.

The fact that the sender transmits DCN and then hangs up causes the 
session error-message to say "Normal and proper end of connection".  
That's just wording that comes from the Class 2 specification.  The fact 
that we obviously didn't get any useful data is an indication of an error.

The unfortunate occurrance here is the unavoidable usage of RTN and the 
unavoidable behavior by the sender in response to that signal.  Imagine 
a sheet-fed fax machine that has a limited memory buffer, and so it 
essentially transmits page image data at the same time as it scans it.  
When it gets through with the page, having sent the page all the way 
through the feeder scanner, and then it encounters and RTN signal it 
cannot pick up the page and re-feed it into the scanner to send it 
again.  So, instead, it sends DCN, hangs up, and *maybe* sounds an error 
to the human sender to send it again.

There are a few of these kinds of "weaknesses" in the non-ECM fax 
protocol.  If the sender supports ECM then switching to Class 1 (which 
probably would require you to switch modems) would help greatly.  If the 
sender doesn't support ECM, then it's a matter of getting a new modem 
that doesn't have the incompatibility with the sender that your current 
modems do.

Thanks,

Lee.


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