Fax (comp.dcom.fax) Frequently Asked Questions (FAQ) [Part 1/2]
George Pajari
comp.dcom.fax FAQ (Frequently Asked Questions) -- Part 1 of 2
=============================================================
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 fax...@faximum.com. 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.
HOT NEWS
--------
This FAQ is now maintained in HTML format and is available on the World-Wide
Web (see below for details).
Some of the aesthetics of translating from HTML to flat text still need to
be improved (which is why this FAQ is not as nicely formatted as the previous
postings.)
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.html>.
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 but 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 sendf...@faximum.com.
regards
g.
George...@Faximum.COM * 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
=================
----- Part 1 of 2 [This part] -----
G. Glossary and Background Information
----- Part 2 of 2 [The other part] -----
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 hr...@cbnewsi.cb.att.com (herman.r.silbiger)
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). This standard, which will be approved shortly, will be
referred to as T.434.
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.
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 "Hayes Command Set" for modems.
FaxBios
An industry consortium (including companies such as Everex, HP,
WordPerfect, etc.) that has published a specification for a FAX API.
Versions for DOS and WINDOWS have been developed and discussions continue
on adapting this API to other operating systems.
With the demise of Everex the association seems to have collapsed leaving
WordPerfect as the only significant company supporting and promoting the
FaxBios standard.
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.
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 mpa...@mv.us.adobe.com (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.
T.30
One of the 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:
agree on whether to use tones or binary codes to exchange
information on capabilities (most current fax machines use
binary codes)
(optionally) the called machine sends a CSI frame identifying it
to the calling machine.
the called machine sends a DIS frame telling the calling machine
what capabilities it has (i.e. resolution, page size, receiving
speed, etc.)
(optionally) the calling machine sends a TSI frame identifying
it to the called machine.
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).
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
the calling machine indicates what it wants to do next (send
another page, terminate the call, request operator intervention,
etc.).
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.
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.
Gray Associates (manufacturers of fax protocol testing equipment) also
have an in-depth discussion of fax protocols at
<http://www.grayfax.com/FAXSMNAR.html>.
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.
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.
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LEGAL NOTICE
COPYRIGHT 1994 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 entirety (including this
NOTICE) without any changes, and (b) the distribution is done for
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Electronic distribution of this FAQ (in its entirely) as part of electronic
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Including this FAQ in a printed book or CD-ROM is specifically not permitted
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almost always granted. It is just considered polite to ask.
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Please see part 2 of this FAQ for the list of contributors.