Faximum TechNote #117

Faximum TechNote #117


TITLE:    #117 - Explanation of fax modem protocol compatibility errors

KEYWORDS: receive transmit modem compatibility errors code fhng



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
		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 

	  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 

Copyright 2001 Faximum Software Inc. All Rights Reserved.