Section 4 : Troubleshooting

Q427: Retrain Negative problem with some modems

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Re: RTN problem with some modems ?

Date: Mon, 04 Jan 1999 19:31:17 +0100
From: David Woolley <>
Subject: Re: New problems with 3Com/USR Voice Faxmodem

> Jan 02 23:01:43.09: [ 5807] : <-- data [2]
> Jan 02 23:02:00.24: [ 5807] : --> [5:ERROR]
> Jan 02 23:02:00.24: [ 5807] : SEND recv RTN (retrain negative)

I think RTN is geusswork here as it doesn't seem to have received a very
informative error status (the 5 in front of the word ERROR is simply the
number of characters in the message). However real RTNs should be generated
if the receiver thinks that the transmission was of too poor quality for an
acceptable image. The intention was that this should be used when the
telephone line properties had changed during the transmission and therefore
the modems needed to train their equalisers for the new properties.

However, a systematic coding error might be intepreted the same way by a
receiver that didn't actually monitor the analogue quality of the signal.

There is a known bug in the tag line processing in HylaFAX that causes
systematic errors which are sufficient to make some recivers issue RTN.
This bug was fixed in version 4.1.

Coding errors may also be introduced by overruns at the transmitting end,
due to inadequate flow control.

In a real retrain, the system should find a speed that produces acceptable
quality. HylaFAX doeswn't force this by default, although the modem should
not train faster than the line will tolerate. If the problem is not the
line quality, the modem will always retrain to the same speed. People have
reported that another patch, which causes the speed to be backed off
explicitly, does improve matters.

Various workrounds have also been suggested :
Date: Thu, 25 Mar 1999 09:01:51 +0800 (HKT)
From: Hong Kong Observatory <>
Subject: Re: First page sent 3 times

First try to force the modem to use a slower transmit signal rate (using
'-B 9600' or '-B 4800' with the sendfax command). If the problem still exists,
you may also try to specify a larger scanline time (using '-M 20ms' or
'-M 40ms' with the sendfax command).

Sam has also commented on this problem :
Date: Thu, 01 Aug 1996 10:03:23 -0700
From: Sam Leffler <>
Retraining during a fax session is required when the receiver requests it
through the post-page message response--in this case "RTN" or ReTrain Negative
(acknowledgement of the received page data).  Problems of this sort are typically
caused by a poor phone connection but sometimes may be due to improperly encoded
page data or, if ECM is being used, a bug in the ECM protocol.  The session
log that was supplied indicated ECM was not being used so the only reasonable
possibilities would seem to be bad data or a bad phone connection.  The
former is highly unlikely and the original poster did not indicate if the
problem was reproducible or if they'd tried a different phone line.


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