Faximum's recommended Class 2 fax modem supplier.
Faximum's recommended Class 2 fax modem supplier.














Q. - Frequently Asked Questions about Fax

Q.1 Can I use my * data modem to send/receive faxes?

In a word, no. Unless your data modem has specific additional support for fax, you cannot communicate with fax devices using a data (only) modem.

Simply put, the problem is that the modulation methods (tones) used to communicate data are different from those used to communicate faxes.

Typically the modulation schemes used for fax are synchronous half-duplex while those used for data (at least by most UNIX and PC people) are asynchronous and full-duplex.

Also, data modems, once they have negotiated a modulation scheme, tend to continue with the same one through out the session. Fax modems switch before and after each page between a high-speed modulation scheme used to transmit the image data and a lower (300 or 2400 bps) scheme to exchange control information.

The following table outlines this briefly (see also part 1 of this FAQ for definitions of V.*).

Date Rate Data Modulation Std Fax Modulation Std
9,600 bps

Q.1A Can my fax modem transmit data?

In a word, maybe. There is a standard proposed by the EIA/TIA/ANSI called Binary File Transfer (BFT) that extends the fax Group III modulation and protocols for bulk data transfer.

The problem, of course, is that few fax modems or software packages provide support for this mechanism.

Q.2 How can I fax PostScript or PCL documents using computer-based fax?

In addition to the basic software to drive your fax modem/board, you will need specific software that can convert PostScript or PCL files into a raster image format compatible with your fax software package.

GhostScript, for example, is a publically available software package that can convert PostScript into raster image format (although there are varying opinions on the quality of the font support).

In the commercial world, most of the vendors of fax software provide software that can handle PostScript and/or PCL.

When purchasing such software (a) check how many different fonts are supported (it's a pain to be able to use, say, NewCentury on your laser printer only to find it is not included in your fax package), and (b) in the case of PCL, check which level of the language is supported (PCL-4 does not support scalable fonts, PCL-5 does).

Q.3 How can I view incoming faxes on my computer?

In the PD world, there are a number of image-viewing packages available for X (such as xv).

In the commercial world, most fax vendors provide support for the commonly available devices (in the case of UNIX, X; in the case of PC-UNIX, VGA and HGA support. Some vendors support other graphics-capable terminals such as the Wyse WY-160.)

Q.4 How can I print incoming faxes on my computer?

Most fax software packages include software to convert fax images into print data streams compatible with dot matrix, HP PCL, or PostScript printers.

Also the publically available (where?) pbmplus filter kit will handle most image formats.

Q.5 Can fax modems also handle data or voice calls?

Not all fax boards can handle data (some are fax only). Most (all?) external fax modems can handle data as well as fax.

Some (but not all) fax modems and software can automatically distinguish between data and fax calls and answer them appropriately.

Some DOS/WINDOWS based products can automatically distinguish between voice and fax/data calls and operate as a digital answer machine as well as a fax machine.

Also, several companies sell devices which can switch incoming calls between a fax machine, a telephone answering machine, and a modem.

[Suggestions anyone?]

Q.6 What resolution are fax images?

The standard resolution for faxes is 3.85 scan lines/mm (approx. 98 dpi vertically) with 1728 pixels across a standard scan line of 215 mm (approx. 204 dpi horizontally).

The optional "fine" resolution is 7.7 scan lines/mm (approx. 196 dpi vertically) with the same horizontal resolution.

Many Group III fax machines use non-standard frames to negotiate higher resolutions (typically 300x300 dpi and 400x400 dpi) with other fax machines by the same manufacturer.

Two fax machines (or modems) must negotiate a common resolution, page width, and page length before sending each page. The standard requires that all Group III fax machines suppport at least standard resolution and A4 size so that common ground can always be found.

Extensions to the Group III standard to support these higher resolutions in a standard way have been proposed. Their current status is not known [Need more information].

[Need more information on resolutions supported by Group IV].

Q.7 Can I take a fax file and edit it?

When faxes exchange information, it is done in the form of compressed images (with the exception of BFT). If you wish to edit or otherwise manipulate a received fax file you have two options:

  1. edit the file using a "paint" program that will accept the fax file (unfortunately there is a wide range of file formats for image files and you may have to work to find a format that is common between your fax application and your paint program).
  2. pass the file through an OCR program that will attempt to convert the image into ASCII (or word processing file format). The problem here is that most OCR programs are tuned to work with 300x300dpi images and faxes are either 98x204 or 196x204.

Q.8 Is there a standard program interface (API) for fax communications?

There are many API's that are used for fax communications. Words marked by -word- are further explained in the glossary in Part 1 of this FAQ.

At the hardware level, the two standards that govern the exchange of commands between a host computer and a fax modem are EIA-578 (-Class 1-) and EIA-592 (-Class 2-).

At the software level there is one "official" standard and a number of "industry standards". The one "official" standard is ITU-T T.611 ([need more information on this standard]).

The most widely known industry standards are -CAS- (Communicating Applications Standard (?)) invented by Intel and DCA and tied closely to the Intel architecture, and -FaxBios- (developed by an industry consortium) which is less machine-dependent (implementations for MS-DOS and WINDOWS have been published and sporadic work on UNIX and other bindings is underway).

Q.9 How can I share my single phone line with voice, fax, data, etc.

There are a number of devices on the market (suggestions from happy campers welcome) that will try to distinguish between an incoming voice, fax, or data call and route the call appropriately.

These fax switches attach to the phone line and then the other devices (your normal voice phone/answering machine, fax machine, data modem, etc.) are attached to the fax switch).

All devices work on one of two general principles: listening for CNG or voice, or listening for distinctive ring patterns (cadences).

In the first case the device will answer the phone and try to guess what it should do based on what it hears. Some machines play back a sound of a phone ringing so that humans dialling in think the phone is still ringing when in fact the fax switch is listening to see if the call is from a fax machine or a human. If the CNG tone (see Part 1 for a definition of CNG) from the calling fax machine is heard, then the switch connects the call to the fax machine, otherwise the call is deemed to be a voice call and is connected to your phone/answering machine.

A slightly more sophisticated approach is for the fax switch to answer the phone and play a short recorded announcement. If, during the announcement the CNG tone is heard, then the call is switched to the fax machine. If no CNG tone is heard but sound is heard after the announcement, then the call is assumed to be voice and switched appropriately. If nothing is heard then the switch either considers the call a data call and switches it to a modem or considers it a fax call from a machine that does not generate a CNG and switches it to the fax machine.

The other approach relies upon an optional service available from some telcos called "SmartRing", "Distinctive Ring", "RingMaster", "Ident-a-Ring", etc. This feature allows one to have more than one phone number associated with the same phone line. Incoming calls using the different phone numbers can be differentiated by the different ringing patterns (i.e. one long ring, two short rings, three short rings, etc.) The fax switch distributes the call based on the ring cadence it detects.

The advantage of the first approach is that one does not have to send more money to the phone company (or depend upon the availability of the "SmartRing" feature being available). The disadvantage is that it is not always reliable (especially in the face of fax machines that do not generate CNG tones).

The advantage of the second approach is that it is very very reliable. The disadvantage is that it requires the availability of the "SmartRing" feature from one's telco as well as sending more money to the telco every month.

Q.10 How can I send a fax over the Internet?

There are several services (commercial as well as free) that offer to accept e-mail messages and fax them to the specified phone number.

To obtain information on the free service, see http://www.tpc.int/

To obtain information on the commercial services, see:



See also http://www.savetz.com/fax/

Q.11 What legal restrictions are there on the use of facsimile devices?

Note that the following is provided for your information only and is not to be considered or taken as legal advise. You are recommended to contact a lawyer in your jurisdiction should you need information on the legal issues related to facsimile communications.

American (USA) Law

***** FCC January 11, 1993 Public Notice *****


PUBLIC NOTICE (31291 / DA 92-1716) January 11, 1993


The Telephone Consumer Protection Act (TCPA) is a federal statute that was enacted on December 20, 1991, to address concerns about the growing volume of unsolicited telephone marketing calls and the increasing use of automated and prerecorded telephone calls. The TCPA imposes restrictions on the use of automatic telephone dialing systems ("autodialers"), artificial or prerecorded voice messages, and telephone facsimile machines to send unsolicited advertisements. The TCPA also directs the FCC to adopt regulations to protect residential telephone subscribers' privacy rights to avoid receiving telephone solicitations to which they object.

The FCC adopted rules and regulations, effective December 20, 1992, implementing the TCPA. The FCC will be monitoring complaints about automated calls and unwanted telephone solicitations to determine whether additional action to limit or to prohibit such calls would be appropriate.


Yes. Effective December 20, 1992, FCC rules ban the transmission of unsolicited advertisements to telephone facsimile machines. An "unsolicited advertisement" is defined as a transmission advertising the commercial availability or quality of property, goods or services without the prior express invitation or permission of the person or entity receiving the transmission.

Unsolicited advertisements may not be transmitted by any device to a telephone facsimile machine unless the person receiving the facsimile has given prior express invitation or permission to receive it. If the sender and the recipient have an established business relationship, an invitation or permission to receive unsolicited facsimile advertisements is presumed to exist. However, the recipient may end an established business relationship by requesting that no further unsolicited advertisements be sent, thus revoking any invitation or permission to receive further transmissions.


FCC rules require that each transmission to a telephone facsimile machine must clearly contain, in a margin at the top or bottom of each transmitted page or on the first page of the transmission, (1) the date and time the transmission is sent (2) the identity of the sender and (3) the telephone number of the sender or of the sending machine. All telephone facsimile machines manufactured on or after December 20, 1992 must have the capacity to clearly mark such identifying information on the first page or on each page of the transmission.

[Note, according to the FCC January 13, 1993 Public Notice, the requirement to mark faxes with the above identifying information on applied to fax machines and not for fax cards used in computers pending reconsideration proceedings.]


The person on whose behalf a facsimile transmission is sent will ultimately be held liable for violations of the TCPA or FCC rules.


The TCPA specifically preempts state law where it conflicts with the technical and procedural requirements for identification of senders of telephone facsimile messages or automated artificial or prerecorded voice messages.

The TCPA and the FCC's rules do not preempt state law which imposes more restrictive requirements or regulations for (1) the use of facsimile machines or other electronic devices to send unsolicited advertisements, (2) the use of autodialers, (3) the use of artificial or prerecorded voice messages, or (4) the making of telephone solicitations.

Thus, depending on state law, the TCPA, the FCC's rules and/or state laws could apply to your company's services. You should contact the state public utilities commission in each state where your company provides the services listed in the previous paragraph to determine what laws apply in those states.


Copies can be ordered from the FCC's contractor for public records duplication: Downtown Copy Center, 1990 M Street, N.W., Suite 640, Washington, D.C. 20036 (telephone: (202) 452-1422). You should ask for copies of the Telephone Consumer Protection Act and the Report and Order in CC Docket No. 92-90 released by the Commission on October 16, 1992 (In the Matter of Rules and Regulations Implementing the Telephone Consumer Protection Act of 1991).

Canadian Law

OTTAWA-HULL, Nov. 7 (Canada NewsWire) -- The CRTC today approved proposals to limit the hours during which uninvited facsimile calls can be made for the purpose of solicitation in Bell Canada and BC TEL territories. The Commission also shortened the interval during which telemarketers must comply with a consumer's request not to be faxed again (Telecom Order CRTC 96-1229).

``With the growing presence of fax machines in Canadian homes, there have been many consumer complaints about the misuse of fax advertising,'' said CRTC Chairperson Francoise Bertrand. ``Large numbers of consumers have complained about facsimile calls waking up their families in the middle of the night or tying up their machines with unwanted ads, and about the time taken by some telemarketers to comply with do not fax' requests.''

``Under the Telecommunications Act, the Commission has the responsibility to protect citizens' privacy and prevent undue inconvenience or nuisance from unsolicited telecommunications, while taking into account the legitimate uses of such communications and the guarantee of freedom of expression set out in the Charter of Rights. Overall, we believe the measures approved today constitute an appropriate balance between the protection of citizens' privacy and commercial freedom of expression.''

``Nonetheless,'' Ms. Bertrand concluded, ``the CRTC will continue monitoring consumer complaints regarding the use of facsimile calls and will address the issue again if public annoyance continues to be significant.''

As a result of today's decision, uninvited fax advertising in the areas served by Bell and BC TEL will be permitted only during the following hours: between 9 a.m. and 9:30 p.m. from Monday to Friday; and between 10 a.m. and 6 p.m. on Saturday and Sunday. These hours refer to the time zone of the called party.

In addition, telemarketers must remove names and numbers from their faxing lists within seven days -- instead of the current 30 -- after a consumer asks. A subscriber's do not call' request remains in effect for three years.

In accordance with previously established conditions for unsolicited facsimile calls, telemarketers must provide sufficient information to allow the subscriber to follow up on the call. They are also required to display the originating calling number, or an alternate number where they can be reached, unless number display is unavailable for technical reasons. Sequential dialing is prohibited, and callers using random dialing must ensure that no calls are made to emergency lines and healthcare facilities. Callers who violate any of the above conditions may have their service terminated by Bell or BC TEL after two business days' notice.

Facsimile calls made for purposes other than solicitation (e.g. emergency and other public service announcements, account information, and market or survey research) are not subject to the new rules. Similarly, these rules do not preclude facsimile calls by businesses responding to messages or requests by telephone subscribers.

Copies of today's telecom order are available through our Internet home page (http://www.crtc.gc.ca) or by contacting the public examination room of any CRTC office:
Halifax (902) 426-7997 (902) 426-6997 (902) 426-2721
Montreal (514) 283-6607 (514) 283-8316 (514) 283-3689
Ottawa-Hull (819) 997-2429 (819) 994-0423 (819) 994-0218
Winnipeg (204) 983-6306 (204) 983-8274 (204) 983-6317
Vancouver (604) 666-2111 (604) 666-0778 (604) 666-8322

For further information: CRTC Public Affairs, Ottawa, K1A 0N2, Tel: (819) 997-0313, TDD: (819) 994-0423, Fax: (819) 994-0218/

Q.12 How Can Received Faxes be Routed to the Intended Recipient?

One of the problems with computer-based facsimile that was never anticipated by the developers of the original fax standard was the need to be able to route incoming faxes to the appropriate user on a computer system or network.

Faxes arrive at a fax machine with no electronic addressing information and only a typed or handwritten name on the cover sheet.

There are several methods available or proposed for the routing of received faxes. They are listed below along with some of their advantages and disadvantages.

1. Manual Routing
2. OCR (Optical Character Recognition)
3. ICR (Intelligent Character Recognition)
4. T.30 Sub-Addrssing
5. NEST (Novell Embedded Systems Technology)
6. Bar-Code Routing
7. Transmitting Station Identification Routing
8. Received Fax Line Routing
9. DID (Direct Inward Dialling)
10. DDI (Direct Dialling In)
11. DTMF Routing

1. Manual Routing


Received faxes are examined at a workstation by an operator who manually decides who ought to receive the fax. Depending on the software being used this can be done using:

  1. a proprietary fax client
  2. an email client
  3. a web browser

The general concept is that the user can view the cover sheet of each received fax and select the intended recipient from a pull-down list. With well designed software it is possible to route a fax in a matter of seconds -- far faster than manually sorting, collating, and delivering hardcopy faxes.

  • almost 100% reliability
  • no special action or hardware required by sender
  • no special hardware/software/telephone line required by receiver
  • efficiency far higher than manual sorting of paper faxes
  • manual intervention required

2. OCR (Optical Character Recognition)


With this method an OCR software package tries to convert the image of the cover sheet into text which is then scanned for the name of the user the fax is to be routed to.

  • manual intervention not required
  • no special action or hardware required by sender
  • no special hardware/telephone line required by receiver
  • low reliability (especially with standard resolution faxes)
  • extra-cost software (about $1,600) needed
  • only typed cover sheets

3. ICR (Intelligent Character Recognition)


With this method an ICR software package tries to convert the image of the cover sheet into text which is then scanned for the name of the user the fax is to be routed to.

The difference between ICR and OCR is that ICR uses more powerful (but much slower) neural net algorithms which can handle standard resolution faxes as well as handwriting (printed).

  • manual intervention not required
  • no special action or hardware required by sender
  • no special hardware/telephone line required by receiver
  • better recognition than OCR (even with standard resolution faxes and some handwriting).
  • extra-cost software required (anywhere form $2,000 to $20,000 depending on package and platform) required
  • reliability not 100%

4. T.30 Sub-Addressing


A mechanism has been added to the T.30 fax protocol (in 1994) to allow the sender of a fax to key in an extension number which can be used by the receiver to route the fax.

For example, if a particular individual were to be associated with fax extension 215, then the sender would dial (say): 9268182#215

The fax machine would dial 9268182 and send the extension number (215 in this example) as the sub-address.

  • manual intervention not required
  • no special software/telephone line required by receiver
  • 100% reliability (assuming the sender enters the extension number).
  • sender required to have a new fax machine with support for subaddressing
  • sender required to know how to use new fax machine and how to enter sub-address
  • fax modem which supports T.30 subaddressing required

5. NEST (Novell Embedded Systems Technology) Routing


This method of routing is similar to T.30 sub-addressing in that the sender enters a fax extension number when dialling the number (i.e. 9268182#215). Technology never brought to market by Novell.

  • manual intervention not required
  • no special software/telephone line required
  • 100% reliability (assuming the sender enters the correct extension number).
  • sender not required to replace fax machine with newer model (Novell intended to sell add-on devices for roughly $50 which will add NEST routing to existing fax machines).
  • no special modem or hardware required on receiving end
  • sender required either to have a new fax machine with support for NEST addressing or to have a NEST addressing device added to their fax machine (neither of which ever reached the market)
  • sender required to know how to use NEST addressing
  • requires that vendor pay significant licence fees to Novell
  • widespread acceptance of Novell's scheme is in doubt since it has not been adopted by any official standards body (but T.30 subaddressing has) and does not seem to provide any advantages over T.30 subaddressing.

6. Bar-Code Routing


With this method the sender of the fax places a bar code (like those found on groceries) on the cover sheet indicating the name of the intended recipient.

  • manual intervention not required for routing
  • no special hardware/telephone line required by receiver
  • reliability approaching 100%
  • sender required to:
    • be able to generate bar codes
    • be willing to place bar code stickers on faxes or be willing to use cover sheets provided by recipient
  • routing covered by a patent and not generally available without special licensing

7. Transmitting Station Identification Routing


With this method the TSI of the sending fax machine (i.e. the phone number of the sender's fax machine) is used to route the fax.

In other words, every fax from machine X goes to person Y.

  • manual intervention not required for routing
  • no special action or hardware required by sender
  • no special hardware/software/telephone line required by receiver
  • high reliability (100% when the sending fax machine is properly configured with the correct TSI)
  • requirement that the sending fax machine's TSI be properly set
  • faxes from the same machine not permitted to go to different people (i.e. the sender is not permited to select the recipient...all faxes from a given machine end up being routed to the same user)

8. Received Fax Line Routing


With this method the system has multiple fax lines and modems and all faxes that are received on a given fax line are routed to a particular user (or group of users).

  • manual intervention for routing not required
  • no special action or hardware required by sender
  • 100% reliability
  • separate phone line and fax modem for each user who wishes to receive faxes required

9. DID (Direct Inward Dialling)


Telephone companies in North America (and some other areas) can provide a special telephone line (trunk) which is associated with multiple phone numbers.

For example, a company could obtain a DID trunk from the telco with a block of numbers (say 926-8110 through 926-8119).

If any of these nine numbers is dialled, the call will come in on the same DID trunk. The difference is that before ring signal is sent, the telco central office sends a special signal down the line identifying which of the (in this case nine) numbers was dialled.

In this manner the receiving device can differentiate between a call to 926-8110 and 926-8115 (even though the two calls would come in on the same phone line) and can route all calls (faxes) to 926-8110 to one person and all calls (faxes) to 926-8115 to someone else.

  • manual intervention not required
  • sender not required to have special fax machine or hardware
  • 100% reliability (assuming the sender uses the correct fax number).
  • requirement for a special phone line from telephone company that is more expensive that a standard (POTS) phone line.
  • DID line not able to be used to outgoing faxes (requires an additional standard phone line, although a single modem can be shared between the DID and POTS line for both incoming and outgoing faxes)
  • special hardware and modem to intercept DID signalling information required

10. DDI (Direct Dialling In)


Telephone companies outside of North America (and some other areas) can provide a special ISDN telephone line (trunk) which is associated with multiple phone numbers. (DDI is the ISDN equivalent of DID, see above.)

  • manual intervention not required
  • sender not required to have special fax machine or hardware
  • 100% reliability (assuming the sender uses the correct fax number number).
  • requirement for a special services on top of an ISDN phone line from telephone company that may be more expensive that a standard ISDN phone line.
  • special hardware and/or modem to intercept DDI signalling information required

11. DTMF Routing


DTMF routing requires the sender to manually dial the fax modem and once the modem answers, type in a special routing code before pressing the send button the fax machine.

The fax software at the receiving end looks up the number in a table of users to determine the intended recipient.

  • manual intervention not required on receiving end
  • sender not required to have special fax machine or hardware
  • 100% reliability (assuming the sender enters the correct DTMF number).
  • requires sender to go through contortions to manually dial fax number, wait for answer, and then type in DTMF routing code
  • requires modem that can recognise DTMF tones



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