(http://www.faximum.com/technotes/117)
TITLE: #117 - Explanation of fax modem protocol compatibility errors
KEYWORDS: receive transmit modem compatibility errors code fhng
RELEASE: All
CLASSIFICATION: All
PROBLEM: Faxes are not being received or transmitted. Either the trace
indicates an FHNG error or the log shows errors of the form
"tx phase X:...".
CAUSE: Possible compatibility error between the fax modem and the
fax machine.
SOLUTION: When the fax modem detects a serious problem while sending or
receiving a fax, it will hang-up the phone and pass Faximum
a hang-up code. This code will appear in the system log and
will look something like:
faxcico tx phase B: received invalid command (22) on page 1
faxcico fax transmission failed
The hang-up code appears in parentheses (22). This is the
code the modem passes to the Faximum software as part of the
"FHNG" response. A complete table of FHNG responses may be
found in TechNote #038.
This TechNote describes how to determine if a problem is the
result of an incompatibility between the fax firmware and the
fax machine.
The protocol that governs the exchange of data and commands
between two fax machines or a fax modem and a fax machine is
specified by standards issued by the International
Telecommunications Union in Geneva (a branch of the United
Nations). The key fax protocol is defined by the standard
T.30 which is not only complex, but also not particularly well
documented either. To compound this problem many fax modems
and fax machines do not follow the protocol completely.
When a fax modem and a fax machine talk to each other, it is
possible that one or the other might not follow T.30 exactly,
or might take exception to a message that ought to be accepted.
In these cases we say there is a protocol incompatibility between
the fax modem and the fax machine. Sometime the fault is with
the modem, sometimes the fault is with the fax machine. And
sometimes (but rarely, since with Class 2 fax modems 95+% of the
protocol is handled by the fax modem) by the fax software itself.
The primary characteristic of a protocol incompatibility is that
the same error occurs (almost) every time a fax is sent to
(or received from) a given fax machine.
Many of the errors listed in TechNote #038 can be caused by
transient problems including noise on the phone line or the fax
machine jamming or running out of paper.
If, however, the same error occurs frequently and is associated
with a specific fax machine then it would indicate strongly a
possible protocol incompatibility between the fax modem and the
fax machine.
If a protocol incompatibility problem is suspected then the first
step is to contact the Technical Support Department of the modem
manufacturer. Provide them with the following information:
1) the make and model of your fax modem;
2) the firmware version of your fax modem (see below);
3) the make and model of the fax machine; and
4) the FHNG code that is being logged,
and ask them if they are aware of a problem with their modem that
might affect communications with this particular fax machine.
(To obtain the firmware revision of your fax modem, use the cu or
tip command to connect to the modem directly and record the
responses to the "AT+FREV?" and "ATI3".)
If they are not able to assist you, then please contact Faximum
Technical Support and provide the following information (by fax or
e-mail):
1) the make and model of your fax modem;
2) a trace of the attempted transmission or reception which
frequently fails (for Faximum PLUS, see Chapter 4 of your
Installation Guide and Release Notes, for Faximum Client/
Server, see TechNotes #082 and #112);
3) excerpts from the log file showing that the error occurs
frequently (see the file /usr/spool/fax/log or
/var/spool/fax/log, depending on your system);
4) the make and model of the fax machine;
5) the fax number of the fax machine with which you are having
problems communicating;
6) the name and fax number of the person in the Technical
Support Department of the modem manufacturer that you
have been working with.
While Faximum Software will try to identify the exact cause of the
problem and to work with the modem manufacturer to correct it,
Faximum obviously cannot be held responsible for the operation of
the modem nor the responsiveness of the modem manufacturer.
If you have any questions about analysing the output of a Faximum
trace, please fax or e-mail the entire trace to Faximum Technical
Support.
E-mail: support@Faximum.com
Fax: 1 (604) 926-8182
Tech Note: 117 - Copyright 1995 Faximum Software Inc., All Rights Reserved.
The complete set of Faximum TechNotes are available on the Internet at
http://www.faximum.com/TechSupport
© Copyright 2001 Faximum Software Inc. All Rights Reserved.