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From: [email protected] (George Pajari)
Subject: Fax (comp.dcom.fax) Frequently Asked Questions (FAQ) [Part 1/2]
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Summary: Frequently asked questions about fax communications, protocols,
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Archive-name: fax-faq/part1

comp.dcom.fax FAQ (Frequently Asked Questions) -- Part 1 of 2
=============================================================

Introduction

The comp.dcom.fax FAQ is brought to you by Faximum Software Inc.

This article contains the answers to some Frequently Asked Questions
(FAQ) often seen in the USENET newsgroup comp.dcom.fax relating to
facsimile standards, software, and hardware. It will be posted
approximately monthly. Note that the World Wide Web (HTML) version
contains additional information that is not part of the monthly
posting. Also the WWW version is "master" copy and is updated
regularly. The posted version may lag by several months. The WWW
version may be reached at http://www.faximum.com/faqs/fax

If you would like to make any submissions or corrections to the FAQ,
please contact [email protected]. Your input is greatly appreciated.
Suggested questions need not be accompanied by suggested answers.
Areas that are in particular need of contributions are marked "[Need
more information]". Flames and other comments (constructive or
otherwise) are also welcomed.

Note that this FAQ is primarily concerned with fax standards in
general and computer-based fax in particular. It contains little
information on commercial fax machines and related paraphenalia. If
someone else would like to start and maintain such a section (or
separate FAQ) they are more than welcome to do so. Otherwise, please
send contributions to this FAQ.

My apologies for the somewhat strange format of this FAQ. As mentioned
elsewhere, this FAQ is now maintained in HTML (i.e. WWW) format and the
posted version is generated automatically using lynx and a shell script.

Obviously some more work is required in order to create a more visually
pleasing flat-text version.

How to Get a Current Copy of This FAQ

This FAQ is crossposted to news.answers. As a consequence, this text
will also be automatically archived on many FAQ servers all over the
world (e.g., anonymous ftp to rtfm.mit.edu in directory
/pub/usenet/news.answers). You'll also find there many other answers
to frequently asked questions. This faq is stored in the directory
fax-faq.

Most FAQs (including the posted flat-text version of this FAQ) are
available through Thomas Fine's WWW FAQ archive:
http://www.cis.ohio-state.edu:80/hypertext/faq/usenet/FAQ-List.ht
ml.

This FAQ is also available on the WWW at
http://www.faximum.com/faqs/fax . The WWW version is always the
most current version. The text version can lag by up to a month from
the html version.

The current text version is available by FTP:
ftp://ftp.faximum.com/pub/faqs/fax/fax-faq . You can also have
the current text version of this FAQ mailed to you. Send any message
(content not important) to [email protected]. regards
g.
[email protected] * http://www.faximum.com/ George Pajari *
Faximum Software * Tel: +1 (604) 925-3600 * Fax: ... 926-8182 1497
Marine Drive, Suite 300 * West Vancouver, BC * Canada V7T 1B8

Std. Disclaimers:

The content of this article is the sole responsibility of the
author(s) and contributors, and does not necessarily represent the
opinions or policies of their employers or other companies mentioned.

The information provided herein is believed to be correct but the
author and contributors cannot accept any liability for errors and
omissions. Readers are cautioned to verify any information before
making decisions or taking action based upon this information.

While every reasonable effort has been taken to maintain an objective
and unbiased approach in the collection and presentation of this
information, readers are advised that the author and possibly some of
the contributors work for or have an interest in commercial
organisations involved in the fax and/or computer industry.

==============================================================================

TABLE OF CONTENTS

A. INTRODUCTION

G. GLOSSARY AND BACKGROUND INFORMATION

Q. FREQUENTLY ASKED QUESTIONS

Q.1 Can I use my * data modem to send/receive faxes?
Q.1A Can my fax modem transmit data?
Q.2 How can I fax PostScript or PCL documents using computer-based
fax?
Q.3 How can I view incoming faxes on my computer?
Q.4 How can I print incoming faxes on my computer?
Q.5 Can fax modems also handle data or voice calls?
Q.6 What resolution are fax images?
Q.7 Can I take a fax file and edit it?
Q.8 Is there a standard program interface (API) for fax
communications?
Q.9 How can I share my single phone line with voice, fax, data,
etc.
Q.10 How can I send a fax over the Internet?
Q.11 What legal restrictions are there on the use of facsimile
devices?

I. SOURCES OF INFORMATION

I.1 Standards Related to Facsimile Communication
I.2 Where to Obtain Standards Documents and Related Information
I.3 Magazine Reviews of UNIX Fax Software
I.4 Magazine Reviews of DOS/Windows Fax Software
I.5 Magazine Reviews of Mac Fax Software
I.6 Magazine Reviews of Fax Modems (see also O/S specific reviews)

I.7 Magazine Reviews of Fax Machines
I.8 Publications Devoted to Fax and Telecommunications
I.9 Books on Fax
I.10 Other Sources of Information on Fax
I.11 Conferences on Fax
I.12 Associations Related to Fax Technology
I.13 Fax-on-Demand Phone Numbers
I.14 Related FAQs
I.15 Fax-Related URLs

P. PRODUCT INFORMATION

P.1 List of UNIX Fax Software
P.2 List of MS-DOS Fax Software
P.3 List of MacIntosh Fax Software
P.4 List of Windows Fax Software
P.5 List of OS/2 Fax Software
P.6 List of Fax Modem Vendors
P.7 List of Fax Board Vendors
P.8 List of Vendors of Secure Fax Equipment
P.9 List of Libraries and Related Information for Writing Fax
Servers
P.10 List of Vendors of Fax Protocol Test Equipment
P.11 List of Vendors of UNIX-Based Fax-On-Demand Software/Systems
P.12 List of Vendors of Fax-On-Demand Software/Systems
P.13 List of Vendors of Products Delivered by Fax

==============================================================================

G. GLOSSARY and BACKGROUND INFORMATION

ANSI/AIIM MS53-1993
The American National Standard File Format for Storage and
Exchange of Images - Bi-Level Image File Format: Part 1
(ANSI/AIIM MS53-1993) was approved in 1993. The standard
defines a format for a file containing one page with one image.
Page sizes and image sizes can be specified. Both definite
length and indefinite length are supported. Clipping of the
image can be specified. Image coding may be according to
ITU-T Recs. T.4 (one- and two-dimensional) and Rec.
T.6. Bitmap may also be specified. Both facsimile style
least significant bit and industry style most significant bit
mapping are supported.
(Definition courtesy of [email protected]
(herman.r.silbiger)

APPLI/COM
The name for the ITU-T API for computer-based facsimile. See
T.611 below for more information.

Bell 103
A standard for 300 bps full duplex dial-up modems. Popular in
the U.S. and Canada. In Europe the preferred standard is
V.21. (Not used in fax but frequently supported by modems
that handle fax.)

BFT or

Binary File Transfer
A method of transferring files using fax modems (as an
extension to the fax protocol). The ITU-T standard for BFT is
T.434. The US version is TIA/EIA-614.

Brooktrout Patent (taken from a press release from Brooktrout)
Brooktrout's patent (number 4,918,722), issued by the US patent
office in 1990, covers generally any method for the selection
of facsimile messages and their deliver to a particular
telephone number under control of commands entered through a
telephone, for example in the form of signals generated from
the telephone's touch-tone keypad. This method is employed in
many fax-on-demand systems, which provide business users and
service providers the ability to offer automated fax delivery
of specified information in response to requests from
customers, subscribers or other callers.
[Editor's note: this patent is the subject of litigation and
the current status or validity of this patent is not known.]

CAS
An API for fax devices invented by Intel and DCA and tied to
the Intel and MS-DOS architectures. The full text of the
specification may be obtained from
ftp://ftp.faximum.com/pub/documents/cas.txt.

CCITT
Comite Consultatif International Telegraphique et Telephonique
(a.k.a. The International Telegraph and Telephone Consultative
Committee). The old name for ITU-T, the body responsible for
setting the international standards for telecommunications
equipment. See ITU below.

CED or
Called Station Identifier
The distinctive tone generated by a Group III fax machine
when it answers the phone (2100 Hz).

Class 1
The Class 1 fax modem standard describes an extension to the
"Hayes Modem Command Set" to permit computers to send and
receive faxes using fax modems. The Class 1 standard is a
low-level specification in which most of the protocol work
(i.e. T.30) as well as image generation (rasterising and
T.4 compression) must be done by the computer (in software)
while the modem only handles the basic modulation as well as
converting the asynchronous data from the computer into the
synchronous packets used in fax communications.

The primary advantage of Class 1 modems is that fax protocol is
implemented in software which means that new extensions to the
fax protocol standard (i.e. T.30) can be implemented without
requiring a ROM change in the modem (or without waiting for the
modem manufacturer to get around to supporting the new
feature). Also software developers are not dependent on the
quality of the T.30 firmware in the modem (as are developers
who use Class 2 modems).

The primary disadvantages are (a) the software vendor has to
handle the complexity of the T.30 protocol and (b) Class 1 is
very sensitive to timing and multi-tasking operating systems
(such as *IX) have great difficulty in reliably meeting the
tight timing constraints and maintaining the fax connection.
Lifting this timing limitation is the primary motivation behind
the new proposed Class 4 standard.

The official standard for Class 1 is EIA/TIA-578. (Note that if
you are purchasing a copy of EIA/TIA-578 be sure to purchase
also the TIA/EIA Telecommunications Systems Bulletin 43 (TSB43)
which provides additional information missing from, or
incorrect in, the original EIA/TIA-578 standard.

Although the official standard is copyright EIA/TIA/ANSI, a
draft version has been published electronically by Supra and is
available from their BBS and FTP sites (see sections I.10,
and I.15) and from Sam Leffler at SGI (retrieve his FlexFax
package, described in section P.1).

Class 2
The Class 2 fax modem standard describes an extension to the
"Hayes Modem Command Set" to permit computers to send and
receive faxes using fax modems. The Class 2 standard is a
higher-level specification in which most of the protocol work
(i.e. T.30) is done by the modem while the computer is
responsible for managing the session and providing the image
data in the appropriate format (i.e. T.4).

The priimary advantage of Class 2 is that the low-level detail
work is handled by the modem. Not only does this mean that
software developers do not have to be burdened with having to
support the T.30 protocol, it also relieves the host computer
of all of the time-critical aspects of fax communications,
making support of Class 2 modems under *IX systems possible.

The biggest headache for software developers is that the Class
2 standard took a long time to be approved (more for political
than technical reasons, IMHO) and many companies did not wait
for the final version to be approved before shipping modems. As
a result we have a situation (as of 93Q4) in which all shipping
Class 2 modems adhere (more or less) to the first draft of the
TR29.2 committee (document SP-2388) and not to the standard as
it was approved. To compensate for this, the "new" Class 2 is
referred to as Class 2.0 and the "old" as plain Class 2.

(Warning - flame from a frustrated fax programmer on...)
Even more disconcerting is the fact that most companies who
have implemented (the old) Class 2 have done one or more things
wrong (they must have been smoking *and* inhaling) so we have a
further division of the standard into "true, old Class 2"
(which includes the Everex 24/96D and MultiTech modems) and
everything else (mostly based on the Rockwell chip which
differs from SP-2388 in a number of ways, although some other
chip makers, such as EXAR, have found even more ways than
Rockwell to depart from SP-2388). It's so bad that most modem
companies now implement the Rockwell version of Class 2 just
because so many of the *%#& things have been shipped (i.e.
Multitech has a special command which switches their modem from
proper Class 2 operation to Rockwell-like operation just so
they can interoperate with DOS software that expects
Rockwell-like operation). And of course no one at Rockwell or
EXAR or the other companies bothered to write down the
difference between their version of Class 2 and the TR29.2
document. (Flame off.)

The draft standard for the "old" Class 2 is SP-2388, Document
TR-29/89-21R8, dated March 21, 1990. This is available by
contacting the EIA/TIA directly. This is the standard
implemented by all Class 2 modems on the market prior to the
end of 1993.

The official standard for the "new" Class 2 (also referred to
as Class 2.0) is EIA/TIA/ANSI-592. This document is available
from Global Engineering Documents (see below).

As of 94Q4 the only modems known to the editor of this FAQ that
support 2.0 are those produced by USRobotics and ZyXEL.

Note that although many modems that implement Class 2 also
support Class 1, Class 1 is *not* a subset of Class 2. Also,
there are some modems that only support Class 2 and many that
only support Class 1.

Although the official standard is copyright EIA/TIA/ANSI, a
draft version has been published electronically by Supra and is
available from their BBS and FTP sites (see sections I.10,
and I.15) and from Sam Leffler at SGI (retrieve his FlexFax
package, described in section P.1).

Class 3
A class number reserved for a project to define a standard for
fax modems that would, in addition to handling the T.30
protocol (i.e. Class 2), also handle the conversion of ASCII
data streams into images (i.e. T.4). Although there are a
couple of fax modems that handle the ASCII to fax conversion,
no draft document has been circulated and the future of this
project is in doubt.

Class 4
Class 1 with intelligent buffering to reduce the need for the
host computer to respond instantly to the fax modem.

Class 8
Not a fax standard at all but an extension to the Hayes command
set to support voice.

CNG or
Calling Tone
The distinctive tone that a fax machine ought to generate when
placing a fax call (1100 Hz on for 1/2 second, off for 3
seconds). Note that the Group 3 fax standard only requires fax
machines in "automatic operation" to generate this tone so that
machines which require you to dial the number (either on the
keypad of the fax machine or using an attached phone) need not
generate this tone. The lack of CNG can cause some fax switches
(see Q.9 below) problems.

There has been a proposal to change the Group 3 standard to
mandate CNG on all fax calls.

CSI or
Called Subscriber Information
The "name" of the answering fax machine. An optional frame of
information sent to the calling fax machine during Phase B (see
T.30 below). Although many fax machines permit ASCII
information, the T.30 standard states that this is to contain
the international phone number of the fax machine, including
the plus symbol, the country code, the area code, and the
subscriber number using only digits, the plus symbol, and a
space.
(i.e. the North American fax number (604) 926-8182 ought to be
programmed into the fax machine as +1 604 926 8182).

DID or Direct Inward Dialling
A special type of phone line (trunk) provided by the telco
which associates multiple phone numbers with a single telephone
line and which send a signal down the line when a call arrives
which indicates which number was used to place this call.

In some sense DID can be viewed as the opposite of Caller ID.
With Caller ID the signal indicates which number placed the
call (i.e. the phone number of the originator of the call).
With DID the signal indicates which number was dialled (i.e.
the phone number of the destination of the call).

Note, however, that the signalling mechanism used for Caller ID
is different from the method used for DID. In other words,
equipment that can decode the Caller ID signals will not work
on a DID trunk.

Historically DID has been used by PBXs that provided direct
dialling to internal extensions. For example, dialling 555-1201
would ring on extension 101. Dialling 555-1202 would come in on
the same trunk to the PBX but the PBX would route the call to
extension 102.

Now DID is also used with fax modems and boards to provide
routing of inbound faxes. Each employee or department is given
a different fax number but all of the calls come in on the same
DID trunk. The fax board (or external DID decode box) decodes
the signal from the telco central office which indicates which
number was dialled and uses this number to route the fax to the
appropriate user or department.

ECM or
Error Correcting Mode
An extension to T.30 to permit the receiving fax machine to
request that portions of an image that were received with
errors be retransmitted.

Normally the T.4/T.30 protocol is error detecting but not error
correcting. The receiving fax machine can usually tell when an
error has impaired the image but cannot selectively request
retransmission of the damaged portions of the image. The only
options are to (a) ignore the errors (if few in number), (b)
request that the page be resent (ignored by most fax machines),
or (c) give up.

EIA/TIA
The Electronics Industry Association and the Telecommunications
Industry Association. The U.S. bodies responsible for the
development of standards related to telecommunications in
general and for fax in particular.

EIA/TIA-465
The US version of T.4 (will probably be accepted as T.4 in
the near future).

EIA/TIA-466
The US version of T.30 (will probably be accepted as T.30
in the near future).

EIA/TIA-530
The US version of something or other related to fax. Need more
information.

EIA/TIA-578
See the definition of Class 1 (above).

EIA/TIA-592
See the definition of Class 2 (above).

EIA/TIA-602
The ANSI/EIA/TIA standard for the for modems.

EIA/TIA-614
The ANSI/EIA/TIA standard for Group I Fax
An old (now obsolete) standard for fax machines in which a page
was transmitted in about six minutes at a resolution of 98 scan
lines/inch. Group I devices frequently worked by attaching the
page to be transmitted to a rotating drum (at 180 rpm) along
which a photocell moves. Either amplitude modulation (the
blacker the pixel the louder the tone) or frequency modulation
(the blacker the pixel the higher the tone) can be used. The
gory details may be found in ITU-T Recommendation T.2.

Group II Fax
An old (now almost obsolete) standard for fax machines in which
a page was transmitted in about three minutes at a resolution
of 100 scan lines/inch. Group II uses vestigial sideband
amplitude modulation with phase shifts. A white pixel is
represented by a louder tone.

Group III
One of the current standards for fax machines in which a page
is transmitted in about one minute. See the definition of
T.30 (below) for more details.

Group IV
A standard for fax transmission using ISDN at 64kbps.

IS-101
The Interim Standard developed and published by the TIA 29.2
committee for voice modems (a set of extensions to the AT modem
command set to support voice recording and playback with
modems).

ITU and
ITU-T
The International Telecommunication Union (ITU) is the United
Nations specialized agency dealing with telecommunications.

The purposes of the ITU as defined in the Convention are:

+ to maintain and extend international cooperation for the
improvement and rational use of telecommunication of all
kinds;
+ to promote the development of technical facilities and their
most efficient operation with a view to improving the
efficiency of telecommunication services, increasing their
usefulness and making them, so far as possible, generally
available to the public;
+ to harmonize the actions of nations in the attainment of
those common ends.

The ITU works to fulfil these basic purposes in three main
ways:

1. international conferences and meetings;
2. technical cooperation;
3. publication of information, world exhibitions.

The ITU is an organization, a union, of Member countries. As of
1993 there were 166 Members. The Union's headquarters are in
Geneva, in the Place des Nations.

Before 1993, the ITU consisted organizationally of five
permanent organs: the General Secretariat, the International
Frequency Registration Board (IFRB), the International Radio
Consultative Committee (CCIR), the International Telegraph and
Telephone Consultative Committee (CCITT) and the
Telecommunications Development Bureau (BDT).

In early 1993, the ITU was reorganized into the General
Secretariat and three Sectors: Radiocommunication,
Telecommunication Standardization and Telecommunication
Development. The standards-making activities of the CCITT and
CCIR have been consolidated into the Telecommunication
Standardization Sector (ITU-T). The remainder of CCIR
activities were integrated with the activities of the IFRB into
the Radiocommunication Sector (ITU-R). The Development Sector
(ITU-D) facilitates telecommunications development by offering
technical cooperation and assistance. The ITU General
Secretariat supports the activities of the three Sectors. (This
description has been taken from material published by the ITU.)

The standards promulgated by the ITU-T are called
Recommendations and the recommendations of relevance to the fax
world are the T series which govern the fax protocols and the V
series which govern modem operation. (See also T.*, and
V.*, below.)

For more information on the ITU and the publications available
from them, see the description of ITUDOC in section I.10 in
Part 2 of this FAQ.

MH or Modified Huffman compression
Also known as Group III one-dimensional compression. See
T.4.

MR or Modified READ compression
Also known as Group III two-dimensional compression. See
T.4.

One-Dimensional Compression
See T.4

PostScript Fax
PostScript Fax has to be considered in two pieces:

First, we added G3 fax compatability to printers. The device
accepts PS jobs from the Mac, PC, and Unix hosts (we have host
driver support for all three) rasterizes these jobs at G3
resolutions with optional cover pages and captions, and then
sends the fax. You get all of the usual bells and whistles like
broadcast, delay, whatever. This differs from a "normal" fax
machine in that you avoid printing and rescanning and thus get
to transmit very high quality without extra effort. It differs
from a PC fax modem because it is network shareable thus saving
hardware and phone line charges. Our testing shows that our
imaging is higher quality than popular PC fax programs, but
there's no intrinsic reason they couldn't do just as well.
Also, the fax modems tend to drag down the PC while sending or
receiving, whereas we offload the really hard work of
controlling the modem to the printer (yes, you can still print
while transmitting).

When we receive a G3 we automatically print it out, scaled to
fit the available paper if necessary. This plain paper output
is much nicer than a roll-fed device can produce. There's a
trade-off vs. a PC fax modem. With PS Fax you don't have to
leave your PC on to receive faxes, just your printer (which
probably has a sleep mode), and you don't have to deal with the
very slow printing speed that many fax modem packages seem to
suffer from. But, if you wanted that file on the PC so you
could edit it or re-transmnit it or... Well, we don't support
receiving back to the PC yet.

One obvious difference from a traditional fax machine is that
PS Fax printers do not yet offer a scanner. Unless you have a
scanner for your PC, there's no way to fax clippings or
handwritten documents with PS Fax. Obviously, the "wonder box"
printer, fax, copier, scanner is our next target.

The other half of the equation is a thing called Postscript
File Transfer. If both you and the person you're communicating
with have PS Fax devices then the PS file gets sent rather than
a G3. This usually results in a shorter phone call and it
always results in significantly higher document quality
including high resolution (ex 600 dpi), large format, color,
etc. Compared to 30 million G3 units the PS Fax installed base
is small, so the PSFT trick is only likely to work in closed
environments. It's been most successful either in big
corporations who use it to communicate between offices or for
consultants who have a need to transmit very high quality
output to their clients and can talk their clients into buying
a PS Fax receiver. Courtesy of [email protected] (Mike
Parker). You can also obtain more information on PostScript Fax
from Adobe's WWW server:
http://www.adobe.com/PS/PSFax.html.

SP-2388
The first draft standard for Class 2 that was implemented by
many companies while waiting for the final standard to be
approved (see also the definition for Class 2 above).

T.2
See Group I Fax. Not to be confused with T-1, a digital
telephony standard that runs at 1.544 Mb/s (at least in North
America).

T.3
See Group II Fax.

T.4
One of the ITU-T recommendations (i.e. standard) for Group
III fax. In particular, this recommendation covers the page
size, resolution, transmission time, and coding schemes
supported for Group III fax. (See also the definition of
T.30 below.)

The basic coding scheme (called in the recommendation
"One-dimensional coding scheme" but also known in the
industry as MH or Modified Huffman) takes each scan line of
pixels and compresses it by (a) converting the raster in a
sequence of run lengths (the number of white pixels followed by
the number of black pixels followed by the number of white
pixels etc. and etc. until the entire raster has been converted
into runlengths) and (b) encoding each run length into a unique
variable-length bit string. The code words used for white and
black runlengths are different and have been chosen in order to
do a reasonable job of compressing a "typical" fax page.

For example, in one dimensional encoding the following raster:
OOOOOOOOOO****OOOOOO**OOOOOOO*OOOOOOOOO***...

converted into run lengths:
10 4 6 2 7 1 9 3 ...

encoded into MH bit strings:
00111 011 1110 11 1111 010 10100 10

(spaces have been added for readability and are not part of the
MH bit string)

Since our example has unusually short white run-length it does
not accurately illustrate the degree of compression which can
be achieved. For example, a normal fine resolution fax image
contains about 3,800,000 pixels (464K). Using one-dimensional
encoding this can be reduced to between 20K - 50K.

In two-dimensional encoding, the first line of a group of lines
is compressed using one-dimensional coding (see above) and
subsequent lines are compressed using an algorithm that
describes line n in terms of line n-1. Since there is usually a
high-degree of correlation between the pixels of adjacent scan
lines, this usually results in significant compression.

Since the basic fax protocol (T.30) is error detecting (but not
error correcting), there is a limit on the number of
two-dimensionally compressed scan lines that can follow a 1-D
line. This is to limit the propagation of errors through an
image. This limit is referred to as 'k' in the standard and is
2 for standard-resolution faxes and 4 for high-resolution
faxes.

Unfortunately, this method of compression is computationally
intensive and most (inexpensive) fax machines do not support
it.

See Standards Related to Facsimile Communication for
information on how to obtain a copy of the T.4 standard.

T.6
The recommendation that covers the image compression algorithm
used for Group IV fax machines.

T.6 is essentially the two-dimensional compression algorithm
from T.4 (see above) except that 'k' is infinite (i.e. all
lines are two dimensionally compressed). This can be done
because Group IV fax machines operate over an error-free
communications channel.

See Standards Related to Facsimile Communication for
information on how to obtain a copy of the T.6 standard.

ITU-T recommendations (i.e. standard) for Group III fax. In
particular, this recommendation covers the protocol used to
manage the session and negotiate the capabilities supported by
each fax machine. The details of the image format are covered
by the T.4 recommendation (see above). The protocol
describes each fax call as proceeding through five phases:

A: Call Set-Up

This phase covers the placing of the call on the PSTN and
the distinctive tones the calling and called stations are
to emit.

B: Pre-Message Procedure for Identifying and Selecting Facilities

During this phase the two fax machines:

o agree on whether to use tones or binary codes to
exchange information on capabilities (most current fax
machines use binary codes)
o (optionally) the called machine sends a CSI frame
identifying it to the calling machine.
o the called machine sends a DIS frame telling the calling
machine what capabilities it has (i.e. resolution, page
size, receiving speed, etc.)
o (optionally) the calling machine sends a TSI frame
identifying it to the called machine.
o the calling machine sends a DCS frame telling the called
machine what capabilities are in effect for this
document (based on the calling machine's capabilities
and the information received in the DIS frame).
o the two machines determine the maximum baud rate that
the communications link will reliable sustain (training
& phasing)

C: Message Transmission

The fax is sent. The end of the last scan line is marked
by a RTC code (return to control).

D: Post-Message Procedure including End-of-message, Confirmation,
and Multi-Page Procedures

o the calling machine indicates what it wants to do next
(send another page, terminate the call, request operator
intervention, etc.).
o the called machine indicates its response to the page
and command just received (o.k., o.k. but retrain, not
o.k., give up, etc.)

At this point the machines go to one of phase B, C, or E
depending on the exchange of commands and responses
during phase D.

E: Call Release

Hang up the phone.

See Standards Related to Facsimile Communication for
information on how to obtain a copy of the T.30 standard.

Gray Associates (manufacturers of fax protocol testing
equipment) also have an in-depth discussion of fax protocols at
http://www.grayfax.com/faxsminar.html.

T.411 - T.418
Open document architecture (ODA) and interchange format
standards.

See Standards Related to Facsimile Communication for
information on how to obtain a copy of the T.41x standards.

T.434
The standard for Binary File Transfer Format (a method of
encoding documents and sending them by fax without converting
them to image format first.

See Standards Related to Facsimile Communication for
information on how to obtain a copy of the T.434 standard.

T.611
Programmable communication interface (PCI) APPLI/COM for
facsimile group 3, facsimile group 4, teletex and telex
services. (i.e. an API for fax services).

See Standards Related to Facsimile Communication for
information on how to obtain a copy of the T.611 standard.

TIFF (Tagged Image File Format)

The TIFF specification was developed by Aldus (now part of
Adobe) and Microsoft as a general file format for storing
raster images. A PostScript version of the specification may be
obtained from ftp://ftp.faximum.com/pub/documents/TIFF6.ps

The relevance of TIFF to fax is explained in the following
entry.

TIFF/F (Tagged Image File Format, Class F)

The TIFF specification is an extremely general and extensible
one which makes it difficult to write programs which can
dependable handle all possible TIFF files. To simplify the
problem somewhat the authors of the TIFF specification have
developed the concept of TIFF classes.

A TIFF class defines the tags that are required to be written
by TIFF writers (i.e. those tags that TIFF readers may depend
upon) and defines those tags (and tag values) which all TIFF
readers of that class must be able to handle.

TIFF Class F was developed by Joe Campbell while he was at
Everex developing the first Class 2 fax modem. The Class F
specification defines those tags (and by extension, those TIFF
file formats) which ought to be used and supported by fax
software.

Many fax software companies support TIFF F files and some use
it as their native file format for received and transmitted
faxes (i.e. Faximum Software).

A flat-text version of the TIFF-F specification may be obtained
from i ftp://ftp.faximum.com/pub/documents/tiff_f.txt

TSI or

Transmitting Subscriber Information
The "name" of the calling fax machine. An optional frame of
information sent by the calling fax machine during Phase B (see
T.30 above). See CSI (above) for details on the recommended
format.

Two-Dimensional Compression
See T.4.

V.17
The ITU-T recommendation for 14,400 bps *synchronous*
half-duplex modems. Used during the image transmission phase of
fax communications. Optional (most fax machines do not support
V.17).

V.21
The ITU-T standard for 300 bps full duplex dial-up modems.
Popular in Europe. In U.S. and Canada the preferred standard is
Bell 103. (Not used in fax but frequently supported by
modems that handle fax.)

V.22bis
The ITU-T recommendation for 2400 bps asynchronous
full-duplex modems. (Not used in fax but frequently supported
by modems that handle fax.)

V.27ter
The ITU-T recommendation for 2400 and 4800 bps
*synchronous* half-duplex modems. Used during the image
transmission phase of fax communications.

V.29
The ITU-T recommendation for 7200 and 9600 bps
*synchronous* half-duplex modems. Used during the image
transmission phase of fax communications.

V.32
The ITU-T recommendation for 9600 bps asynchronous
full-duplex modems. (Not used in fax but sometimes supported by
modems that also handle fax.)

V.32bis
The ITU-T recommendation for 14,400 bps asynchronous
full-duplex modems. (Not used in fax but sometimes supported by
modems that also handle fax.)

V.42
The ITU-T recommendation for error-checking and correction.
(Not used in fax but sometimes supported by modems that also
handle fax.)

V.42bis
The ITU-T recommendation for data compression. (Not used in
fax but sometimes supported by modems that also handle fax.)

X.5
The ITU-T recommentation for a Fax PAD facility in a public
data network.

X.38
The ITU-T recommentation for a Group 3 fax equipment/DCE
interface for equipment accessing the fax PAD facility in a
public data network.

X.39
The ITU-T recommentation for procedures for the exchange of
control information and user data between a fax PAD facility
and a packet mode DTE.

==============================================================================

FAX FAQ LEGAL NOTICE

COPYRIGHT 1994, 1995 George Pajari ALL RIGHTS RESERVED.

The FAQ has been written in part, and compiled by, George Pajari.
While reasonable efforts have been made to verify the information in
this document, no liability can be accepted by George Pajari, Faximum
Software, or the many contributors for the correctness of the
information herein. Readers are cautioned to take such measures as
they deem necessary to verify the information herein before taking any
action based on this information.

Limited permission is granted to copy or distribute this faq for
non-commercial purposes as long as: (a) the FAQ is reproduced in its
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