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Understanding Personal Computer Faxmodems This guide explores PC faxmodem technology to help you get the best data and fax communications for your PC. Communicating with Everyone Today's faxmodems are a growing class of PC enhancement that integrates data and fax communications into a single add-in product that handles both types of transmissions. By taking advantage of advances in digital signal processing technology and chip miniaturization, faxmodems provide more functionality than traditional data-only modems--with advances in technology continuing to drive down prices. Because faxmodems connect you to other modem-equipped computers and to more than 20 million fax machines worldwide, a faxmodem gives you far more communications flexibility than a data-only modem. But not all faxmodems are created equal. To ensure compatible, reliable, high-speed communications, faxmodems must clear a number of technical hurdles. This paper explains issues that affect how well a faxmodem performs, and also describes several technical issues that affect a faxmodem's overall usability. Compatible Communications: Implementing Standards For two telecommunication products to work together smoothly, they need standards that specify how to get the job done --and each product must implement the standards fully and carefully. For example, the high-speed data modem market began its explosive expansion in the late 1980s, when the V.32 standard for 9600 bps communications was widely adopted. Before then, most high-speed modems used proprietary schemes that worked only with another modem from the same vendor. Telecommunications standards can be: Formal standards such as V.32 and V.42bis, which are developed by government and industrial organizations and specify the interactions between two modems or faxmodems; or Defacto standards such as the Communicating Applications Specification (CAS) and the Hayes AT* command set, which describe ways for communications software to control the features of a modem or faxmodem. Standards specify items such as: Handshaking and modulation schemes for establishing communications and transmitting data. Methods of compressing data to achieve higher throughput. Techniques to identify transmission errors and try to correct them. Programming interfaces (APIs) between a software application and a faxmodem Tables 1 and 2 (on the next page) provide a reference list of relevant standards. For guaranteed compatible communications, faxmodems should conform fully to the appropriate standards and should be tested to verify connectivity with a variety of other modems and fax devices. Don't hesitate to ask a vendor what testing it performs to verify standards compliance and connectivity. Evolving Standards When technology is rapidly advancing, standards must evolve to keep pace. Future standards now under development include the "V.fast" modulation standard and fax applications interface (API) standards: V.fast is the working name of the proposal for the next-generation high-speed modem standard for ordinary phone lines. As of this writing, V.fast isn't far enough along the development path to have earned official nomenclature or for the CCITT to have determined what its top speed will be. So the 14,400 bps of V.32bis appears likely to reign as the high-speed king at least through 1993. Fax API standards are still emerging. The CCITT's T.611 specification will be the first international fax/application software interface if it is approved as expected in late 1992. Meanwhile, the Intel/DCA CAS interface is supported by over 100 applications and provides a comprehensive, high-level API for fax applications. The Class 1 standard (EIA 578), which extends the Hayes AT command set to allow control of a fax modem, is a new, low-level fax API that is quickly gaining in popularity among faxmodem vendors. The proposed Class 2 (PN2388) standard, which puts more of the intelligence on the faxmodem rather than in the PC, remains unratified at this time. Reliable Communications:Error Handling and Other Issues Telephone lines were designed for transmitting voices, and the ordinary background noise or static on a phone line can introduce errors in data and fax communications. Noise is a particular problem during high-speed transmissions, because each period of noise can damage so much data. Faxmodems can use sophisticated methods to ensure accurate transmissions of both data and faxes, including the methods specified by international standards and features such as intelligent buffering and adaptive handshaking. Standard Methods for Error Control For data communications, V.32 and V.32bis modems start with trellis-coded modulation (TCM), which attempts to identify errors and repair them as they come into the receiving modem. In addition, the V.42 standard defines a method called the Link Access Procedure for Modems (LAPM), and the MNP protocols provide a more rudimentary approach to error control. V.42 and MNP error control can be used with slower modems, as well. These methods vary in efficiency, but both provide for error-free data transfer between two modems. The T.30 fax standard specifies the ability to identify errors and indicate the need for a page to be retransmitted if errors reach a certain level. T.30 was later enhanced by the addition of an optional error correction mode (ECM) that defines techniques to ensure error-free faxing. Smart Data Buffering Standards such as V.42 and T.30 ensure accurate data and fax transmission across phone lines. But today's modems must also make sure high-speed data isn't lost getting from the modem to the PC if the PC is busy with another application or otherwise unable to keep up with the flow of incoming data. To reduce this possibility, some PC serial ports (and some internal modems) provide a serial interface that incorporates a small character buffer. While this feature helps reduce risk of high-speed modem-to-PC data loss, more advanced designs are required to make sure the CPU has fetched the data waiting in the serial port interface before the modem overwrites it with additional data. This is a capability that Intel refers to as "Smart UART Buffering." Speed Optimization High-speed modems have sophisticated methods of increasing both accuracy and performance by allowing the modems to operate at the fastest speeds that line conditions will safely permit. First, during the handshaking that occurs at the beginning of a connection, some high-speed modems can test line quality and use that information to help choose a line speed. This "adaptive handshaking" ensures that the modems can complete the error control negotiation process and establish the fastest error-controlled connection possible--even over poor lines. Second, once the connection is established, and transmission begins, some data modems can dynamically monitor the quality of the phone connection, slowing down (falling back) if too many errors occur. More advanced modems can also speed back up (fall forward) if conditions improve. Modems that support this feature vary in how quickly they are able to identify changes in line quality. High-Speed Performance: Modulation, Compression, Architecture In addition to features such as speed optimization and adaptive handshaking, communications throughput depends on what modulation and data compression standards a faxmodem follows. Throughput also depends on how well its architecture meets the performance demands of handling massive quantities of data very rapidly. Modulation Modulation is the method used to transform bits of information into an analog signal suitable for traveling over telephone lines. Modulation techniques have been on a rapidly rising curve since the early 1980s, when 300 bps was common. As we've seen, the fastest faxmodems standards today support transmitting data and faxes at 14,400 bps, with advanced data compression techniques raising effective throughput even higher. Although a faxmodem has a single modem chipset, it uses different modulation techniques for data and fax transmissions. Data and fax speeds are relatively independent, so a faxmodem can offer 2400 bps data and 9600 bps fax rates, for example. Data Compression Data compression increases effective throughput by recognizing patterns and reducing the data to a smaller number of bits without any loss of information. For data communications, the V.42bis standard allows data to be compressed up to fourfold, making it possible for a V.32bis modem to transmit data at effective rates of 57,600 bps. The MNP 5 protocol provides 2:1 compression, which, for example, gives a 2400 bps modem an effective throughput of up to 4800 bps. On the fax side, the T.4 standard specifies one-dimensional (Modified Huffman) encoding, which compresses the data in each horizontal scan line. T.4 also allows an optional 2D (Modified Read or MR) encoding, which compresses the image vertically as well as horizontally and can reduce fax transmission times and associated costs by up to 25%. MR encoding is widespread in stand-alone fax machines and is beginning to appear in advanced PC fax products. Avoiding Bottlenecks, Providing Background Faxing A faxmodem's actual throughput can vary considerably from the product's rated line speed. For example, keeping data flowing over the phone line at 14,400 bps means that a V.32bis faxmodem must execute compression algorithms up to four times that rate. Since V.32bis modems can send and receive simultaneously, that means the faxmodem has to be able to compress 57,600 bits and decompress another 57,600 bits each second. Bottlenecks occur and performance declines if the faxmodem isn't up to the job. So, look for a DTE rate that matches or exceeds the faxmodem's maximum throughput. High-speed faxmodems provide coprocessing power to handle this work-load efficiently. For example, some Intel SatisFAXtion faxmodems incorporate an Intel 80186 microprocessor, 512 Kbytes of on-board memory and a custom gate array to manage the flow of data between the faxmodem and the PC. Not only does coprocessing enhance performance, it allows fax communications to proceed smoothly as a background task. This makes communications more reliable and transparent by ensuring that users can continue working without worrying about lockouts, line drops or performance slowdowns: faxing doesn't interrupt you, and you don't interrupt a fax. Usability Issues for Faxmodems In addition to providing reliable, compatible communications with high effective throughput, faxmodems may offer a number of other technical features that enhance the product's ease of use and effectiveness. These range from intelligent phone-line management to easy faxing from any application. Internal or External? Faxmodems are available as external devices and as boards that install in your PC. External products are easy to move from one computer to another, and their lights provide a convenient indicator of the faxmodem's activities. Internal products are better able to support the maximum throughput of the faxmodem architecture since they're not limited by the bandwidth of the PC's serial port. Smart Line Sharing Some faxmodems provide a smart line sharing capability that allows a single phone line to serve for data, fax and voice calls. By answering each incoming call and ringing the appropriate device, smart answering saves the $50 to $100 cost of a "black box" or line switcher. With distinctive ring service from your phone company, more than one phone number can be assigned to a single line. Calls are distinguished since they ring your phone in different ways. Some faxmodems can take advantage of this service with Smart Line Sharing. Software and Ease of Use Faxmodems vary in the software --and ease of use--that they provide. Most faxmodems come with fax software that includes time-delayed faxing, broadcast faxing to a list of recipients, and other capabilities. A key function to look for is the ability to fax from within your DOS or Windows applications; Intel's WYPIWYF interface (What You Print Is What You Fax*), for example, lets you send a fax in just a few keystrokes from within any application. It's also valuable to have data communications software included, to save the cost of purchasing it separately. Printer Emulation and Fax Output Quality Some PC fax products simply format faxed documents as ASCII text files, losing virtually all the formatting that today's programs can provide. Others emulate popular printers, but with widely varying accuracy. For best results, consider a faxmodem that emulates a richly featured printer like the printer you normally use. For example, if you use a LaserJet* Series II or III printer, you'll want to look for a faxmodem with HP PCL 4 and 5 emulation. Scanner Support Scanners make it possible to incorporate non-PC documents, photographs and other graphics into your faxes. Many faxmodems can send documents captured from leading full-page scanners, and a few offer an on-board hand-scanner interface that saves the need for a separate scanner interface board. Fax-to-Text Conversion Ordinarily, received faxes are stored as bit-mapped images in a graphics file format such as TIFF or PCX. Fax software that incorporates optical character recognition (OCR) allows you to convert these faxes to character-based files that you can bring into your word processor and edit. Memory Usage Even in PCs with plenty of memory, the first 640 Kbytes of "conventional" PC memory is still a scarce resource. To monitor incoming calls, faxmodems rely on terminate and stay resident (TSR) programs that can require up to 130 Kbytes of conventional memory. If memory usage is a concern, look for a product that uses the Expanded Memory Specification (EMS) to reduce its use of conventional memory. This frees up conventional memory for use by other applications. In Conclusion The right PC faxmodem - one that meets the technical challenges of compatibility, reliability, throughput and usability - can give you all the features of a data-only modem, plus the convenience and quality of full-featured faxing. And it provides unprecedented flexibility in communications - it puts you in touch with everyone. Intel offers a broad family of faxmodems that deliver high quality data and fax communications to fit any budget. Intel also provides a full line of data-only modems. __________________________________________________________________________ Table 1 Standards for Data Communications Category Standard Developed By Description Modulation V.32bis CCITT Int'l standard for 14,400, 12,000, 9600, 7200 and 4800 bps V.32 CCITT Int'l standard for 9600 and 4800 bps V.22bis CCITT Int'l standard for 2400 and 1200 bps V.22 CCITT Int'l standard for 1200 bps V.21 CCITT Int'l standard for 300 bps "V.fast" CCITT Working name for the proposed next- generation high-speed communication standard Bell 103 AT&T US defacto standards 212A, etc for low-speed communications Error Correction/Data Compression V.42bis CCITT Int'l standard for data compression (up to 4:1) protocols V.42 CCITT Int'l error control standard MNP 1-5 Microcom* Defacto standards for error control and data compression. Applications Interface TIA-602 TIA/EIA2 US standard command set for modem software to control a Hayes AT-compatible modem 1 International Consultative Committee for Telephone and Telegraph (known as the CCITT after its French initials) - a United Nations-sponsored organization that is the primary international standard-setter for the telecommunications industry. 2 Telecommunications Industries Association /Electronic Industry Association - the main telecommunications standards-setting body for the U.S. ___________________________________________________________________________ Table 2. Standards for Fax Communications Category Standard Developed By Description Overall Fax Specifications Group 3 CCITT International standard for fax communications over ordinary phone lines Group 4 CCITT International standard for faxing over digital telephone networks Modulation V.17 CCITT International standard for 14,400, 12,000, 9600, 7200 and 4800 bps V.29 CCITT International standard for 9600 and 7200 bps V.27 CCITT International standard for 4800 and 2400 bps V.ch 2 CCITT International standard for 300 bps Higher Level T.30 CCITT International standard for establishing a connection, negotiating protocols and controlling errors. Advanced error correction mode (ECM) added in 1988. T.4 CCITT International standard for fax image format, 1D or 2D image compression and fax transmission T.6 CCITT Advanced 2D image coding scheme; formulated for Group 4 but also usable by Group 3 products with T.30 ECM Applications Interface (API) Class 1 TIA TR 29.1 U.S. standard adding fax (EIA 578) Committee API commands to the AT command set. Implements T.4 on faxmodem, T.30 on host. Class 2 TIA TR 29.2 Evolving U.S. standard (PN 2388) Committee adding fax API commands to the AT command set. Implements T.4 and T.30 on faxmodem, for improved performance over Class 1. CAS Intel, DCA* Defacto standard high- level fax API T.611 CCITT Proposed international high-level fax API standard INTEL SATISFAXTION MODEM FEATURE GUIDE ----------------------------------------------------------------------------- | Model | Model | Model | Model | MODEL | 400 | 400e | 200 | 100 | -------------------|------------|--------------|------------|---------------| TYPE | 2/3 Length | External | 2/3 Length | 1/2 Length | | Board | | Board | Board | -------------------|------------|--------------|------------|---------------| Max Line Speed/ | 14,400 bps/| 14,400 bps/ | 2400 bps/| 2400 bps | Max. Throughput | 57,600 bps | 57,600 bps | 9600 bps | 2400 bps | Max. DTE Speed |115,200 bps | 115,200 bps | 9600 bps | 9600 bps | -------------------|------------|--------------|------------|---------------| Data Compression | V.42bis | V.42bis | V.42bis | | | MNP5 | MNP5 | MNP5 | | -------------------|------------|--------------|------------|---------------| Error Control | V.42* | V.42 | V.42 | | | MNP4 | MNP4 | MNP4 | | -------------------|------------|--------------|------------|---------------| Automatic | | | | | Speed Optimization | Yes | Yes | N/A | N/A | Modem S/W Included | Yes | Yes | Yes | Yes | -------------------|------------|--------------|------------|---------------| Fax Send/ | 14,400 bps/| 9600 bps/ | 9600 bps/| 9600 bps/ | Receive Speed | 14,400 bps | 9600 bps | 9600 bps | 4800 bps | (Maximum) | | | | | -------------------|------------|--------------|------------|---------------| Coprocessed Faxing | Yes | No | Yes | No | -------------------|------------|--------------|------------|---------------| Fax Compression | Advanced | Basic | Basic | Basic | -------------------|------------|--------------|------------|---------------| HP LaserJet II/III | Yes | Yes | Yes | No | (PCL 5) Emulation | | | | (Option) | -------------------|------------|--------------|------------|---------------| Epson Emulation | Yes | Yes | Yes | Yes | -------------------|------------|--------------|------------|---------------| S/W included for: | | | | | Windows | Yes | Yes | Yes | Yes | DOS | Yes | Yes | Yes | Yes | -------------------|------------|--------------|------------|---------------| API Support | CAS |CAS, Class 1 | CAS | CAS, Class 1| -------------------|------------|--------------|------------|---------------| Smart Line | Yes | No | Yes | No | Sharing for Phone, | | | | | Fax and Modem | | | | | -------------------|------------|--------------|------------|---------------| Scanner Port** | Yes | No | Yes | No | -------------------|------------|--------------|------------|---------------| EMS Support | Yes | Yes | Yes | Yes | -------------------|------------|--------------|------------|---------------| Network Fax | | | | | S/W Available | Yes | No | Yes | No | -------------------|------------|--------------|------------|---------------| * Intel SatisFAXtion Modem/400 also includes high-speed data-loss protection. ** Intel SatisFAXtion Hand Scanner or Logitech Scanman 256 only Call 1-800-538-3373 for the dealer nearest you. Available Product Information North America 800-538-3373 Europe 44-793-431155 Worldwide 503-629-7354 What You Print Is What You Fax is a trademark, and Intel, SatisFaxtion, and WYPIWYF are registered trademarks of Intel Corporation. *Other brand and product names are trademarks of their respective owners. This literature is subject to change without notice. Intel assumes no responsibilities for errors or ommissions herein. c 1992 Intel Corporation. All rights reserved.