This is modem12 (part 1 of 2 parts) >> From VM1.NoDak.EDU!wrair-emh1.army.mil!kipps Wed Sep 30 19:13:08 1992 >> From: What You Need To Know About Modems December 25, 1991 Version 1.0 ------------------------------------------------------------------- Copyright (c) 1991 Patrick Chen. All rights reserved. Distribution Notice: This document may be distributed by electronic bulletin boards and commercial on-line services. This document may not be edited or changed in any way for redistribution. CONTENTS Introduction Modulation Protocols 2400 bps modems High-speed modems V.32 V.32bis U.S. Robotics HST Telebit PEP Hayes Express 96 CompuCom CSP Things to come V.fast ISDN Error Control Protocols V.42 and MNP-4 V.42 & MNP-4 can provide error-free connections V.42 and MNP-4 can improve throughput Are MNP 4/V.42 useful? Data Compression Protocols MNP-5 & V.42bis Are MNP-5 & V.42bis useful? Compression by Software vs. MNP-5/V.42bis Local Flow Control and Data Buffering Macintosh and high-speed modems PC and UART Profiles of High-speed modems ATI 9600etc/e CompuCom SpeedModem Champ/Star/Storm Hayes modems Image Communications: Twincom 96/42 Intel 9600EX & 14.4EX Practical peripherals PM9600SA & PM9600 Prometheus modems Telebit modems U.S. Robotics modems Zoom V.32 Turbo Modems Things to come Buying a High-speed Modem Should you pay the extra for a V.32bis modem? Should you buy a modem with a proprietary modulation protocol? Should you buy a 2400 bps modem with V.42bis? Beware of the ads Setting Up Software to Work with High-speed Modems The Proper Software Setup Does Your Software Initialize the Modem Properly? Does Your Software Configure Itself to Match the Modem Settings? Why You May Need to Change the Initialization String Editing the Initialization String Match Software Settings To the Modem Settings Configuring Popular Communications Software to Work with High-speed Modems Procomm 2.0 Telix Qmodem HyperAccess 5 Crosstalk for Windows MicroPhone II (for Macintosh) ZTerm (for Macintosh) Other Settings for Your Communications Software Telephone Number Dial String: ATDT 8-N-1 or 7-E-1 (data bits-parity-stop bits) Half vs. Full Duplex: Local Echo Terminal Emulation Comm Port File Transfer Protocols ASCII Xmodem Xmodem-1K Ymodem Ymodem-g Zmodem Kermit Sealink Which file transfer protocol should you use? Appendix A: Resources Appendix B: How to reach the author Appendix C: About "The Joy of Telecomputing" ------------------------------------------------------ Introduction Buying and using a modem used to be relatively easy. Not so long ago, almost all modems are 1200 or 2400 bps units and they are all compatible with the Hayes Smartmodems (although some are more Hayes-compatible than others). How time has changed. Today, modems not only run faster, they are also loaded with features like error control and data compression. Suddenly, you are confronted with all the buzzwords: V.32, V.32bis, V.42, V.42bis, MNP-5, LAP-M, etc. What do they mean? And what do they mean to you? To make the most of a high-speed modem, you need to understand three different kinds of protocols and the relationships among them. They are the modulation protocols, error control protocols and data compression protocols. Modulation Protocols Modem stands for MOdulator/DEModulator. A modem converts digital signals generated by the computer into analog signals which can be transmitted over a telephone line and transforms incoming analog signals into their digital equivalents. The specific techniques used to encode the digital bits into analog signals are called modulation protocols. The various modulation protocols define the exact methods of encoding and the data transfer speed. In fact, you cannot have a modem without modulation protocols. A modem typically supports more than one modulation protocols. The raw speed (the speed without data compression) of a modem is determined by the modulation protocols. High-speed modems are modems that feature modulation protocols at 9600 bps or higher. A 2400 bps modem with data compression that can theoretically yield a 9600 bps throughput is not a high-speed modem. "CCITT" is a French acronym for the International Telegraph and Telephone Consultative Committee. CCITT, a United Nations agency, is an international telecommunications standards committee that makes recommendations on a broad range of subjects concerning data communications. 2400 bps Modems A 2400 bps Hayes-compatible modem typically supports the following modulation protocols: Bell 103 (300 bps U.S. Standard) Bell 212A (1200 bps U.S. Standard) CCITT V.22 (1200 bps standard used outside the U.S.) CCITT V.22bis (2400 bps International Standard) Some 2400 bps modems also support the following protocols: CCITT V.21 (300 bps standard used outside the U.S.) CCITT V.23 (1200/75 and 75/1200 bps, used in Europe) In the past, most 2400 bps modems do not support any error correction or data compression protocols. Recently, however, many modem manufacturers have introduced 2400 bps modems with extra features like data compression, error correction and fax capability. High-speed Modems There are two standard modulation protocols for high-speed modems: V.32 and V.32bis. Both are standards established by the CCITT. V.32 This is the standard for 9600 (and 4800) bps modems. CCITT V.32 is adopted by the CCITT in 1984. But the market has not taken off until recently. V.32 modems used to cost more than modems using proprietary modulation protocols (Hayes introduced the Smartmodem 9600, a V.32 modem, in 1988 with a $1999 price tag). But it is no longer true. At present, street prices for most V.32 modem are below $500. Every modem manufacturer is making V.32 modems now. Packet-switching networks like Sprintnet (Telenet) and CompuServe are also starting to support V.32 modems. Companies that make modems with proprietary modulation protocols are making modems with "dual standard." U.S. Robotics, Telebit, Hayes and CompuCom all have modems that support V.32 and their own proprietary protocols. V.32bis V.32bis, established in early 1991, is the CCITT standard for 14400 bps modems. A V.32bis modem also can fall back to 12000, 9600, 7200 and 4800 bps. V.32bis is downwardly compatible with V.32. Unlike 2400 bps modems where a single modulation protocol (V.22bis) is supported by all modem makers, there are several proprietary modulation protocols used by modems from different manufacturers. U.S. Robotics HST (High Speed Technology) Until the recent surge of V.32 modems, the U.S. Robotics HST was the de facto standard in the PC-based BBS community. U.S. Robotics introduced the Courier HST modem in 1986 and pioneered the market for high-speed modems in the IBM PC environment. The immense popularity of the HST modems was partly due to the generous discount program U.S. Robotics offered to the BBS Sysops (SYStem OPerators). Many modem manufacturers have implemented similar Sysop discount programs, but most BBS sysops remain loyal to the U.S. Robotics modems. The original Courier HST modem ran at 9600 bps. U.S. Robotics later improved the speed of the Courier HST to 14400 bps. Although U.S. Robotics remains committed to the HST modems, there are now three different high-speed Courier modems available: the Courier HST (which only supports the HST protocol), the Courier V.32bis (which only supports V.32bis) and the Courier HST Dual Standard (which supports both the HST and the V.32bis protocols). Telebit PEP (Packetized Ensemble Protocol) Telebit introduced the TrailBlazer in 1985 that employed a proprietary modulation protocol called PEP. While the Courier HST is popular among BBS, Telebit modems dominate the UNIX UUCP and Usenet communities. (Usenet, UUCP and the Internet are discussed in Part II of "The Joy of Telecomputing"). The TrailBlazer Plus owes its success partly to its built-in support for the UUCP g-protocol, thus allowing efficient and flawless UUCP session. PEP also performs well even with noisy telephone lines. The actual throughput is around 14400 bps. The TrailBlazer Plus has an installed base of more than 120,000 units. Telebit also introduced a cheaper (and slower) PEP modem, the T1000, in 1988. Hayes Express 96 Hayes entered the high-speed modem arena in 1987 with the introduction of the V-series Smartmodem 9600. The modem used a proprietary modulation protocol called Express 96 (also known as Hayes "Ping Pong" protocol). The V-series modems have not been as successful as the U.S. Robotics or the Telebit modems. CompuCom CSP (CompuCom Speed Protocol) While every modem manufacturer is jumping on the V.32 bandwagon, CompuCom bucked the trend and came out with the SpeedModem Champ in early 1991. It's a 9600 bps modem with a proprietary modulation protocol called CSP. The SpeedModem Champ has one strong selling point. It is the only modem with a proprietary protocol that costs less than a generic V.32 modem. The internal SpeedModem Champ is priced at $169. An external version is available for $199. Hundreds of PC-based bulletin board systems have installed the SpeedModem Champ. The Champ also works as a Hayes-compatible 2400 bps modem with MNP 2-4 error control and MNP-5 data compression. Two modems can establish a connection only when they share a common modulation protocol. To connect at high speed, two modems have to support the same high-speed modulation protocol. Therefore, a modem with a proprietary modulation protocol can only establish a high-speed connection with another modem from the same manufacturer. A U.S. Robotics HST modem can only establish a high-speed connection (at 9600 or 14400 bps) with another HST or an USR Dual Standard modem. A Courier HST modem cannot establish a high-speed connection with a Courier V.32bis modem. They can only connect at 2400 bps. (All high-speed modems in the market support the CCITT V.22bis modulation protocol). On the other hand, two V.32 modems can talk to each other at 9600 bps. They do not have to be from the same manufacturer. Two V.32bis modems can talk to each other at 14400 bps. A V.32 modem can talk to a V.32bis modem at 9600 bps. Things to come V.fast CCITT is working on a new modem standard, dubbed V.fast. If all goes well, the next modem standard can materialize before 1993. A V.fast modem is expected to reach a raw speed of 19,200-24,000 bps over standard dial-up telephone lines. ISDN In a couple of years we may not need modems at all. Integrated Services Digital Network (ISDN) has been coming for years. When will ISDN really become available for the rest of us? It depends on your local telephone company. It is estimated that by the end of 1994 about half the telephone connections in the U.S. will has access to it. With ISDN, you won't need a modem since no modulation or demodulation will be necessary. You will need an ISDN adapter instead. An ISDN line carries three digital channels: two "B" channels that carry various kinds of data at 64,000 bps and a "D" channel at 16,000 bps that can carry control signals or serve as a third data channel. A single ISDN channel can transfer uncompressed data bidirectionally at 64,000 bps. Combine that with a data compression scheme and you will be able to transfer data at hundreds of kilobits per second. Eventually, ISDN will provide widely available, low-cost digital communications for voice and data communication. Until ISDN is firmly in place, high-speed modems will be with us for a while. Error Control (Error-Correcting, Error Correction) Protocols Besides high-speed modulation protocols, all current models of high-speed modems also support error control and data compression protocols. V.42 and MNP-4 There are two standards for error control protocols: MNP 4 and V.42. The Microcom Networking Protocol, MNP, is developed by Microcom. MNP 2 to 4 are error correction protocols. MNP-5 is a data compression protocol. V.42 is established by CCITT. V.42 actually incorporates two error control schemes. V.42 uses LAP-M (Link Access Procedure for Modems) as the primary scheme and includes MNP-4 as the alternate scheme. Therefore, a V.42 modem will be able to establish an error-controlled connection with a modem that only supports MNP 4. A modem that uses a proprietary modulation protocol may also use a non-standard error control protocol. For example, Hayes V-series Smartmodem 9600 supports an error control protocol called LAP-B. CompuCom's SpeedModem Champ also uses a non-standard error control protocol. V.42 & MNP-4 can provide error-free connections Modems without error control protocols, such as most 2400 bps Hayes-compatible modems, cannot provide error-free data communications. The noise and other phone line anomalies are beyond the capabilities of any standard modem to deliver error-free data. V.42 (and MNP 2-4) copes with the phone line impairments by filtering out the line noise and automatically retransmitting corrupted data. If you have used a standard Hayes-compatible modem, you probably notice some garbled characters (like "@8d_\nw`[ce") show up on your screen from time to time. When two modems establish an error-controlled connection, they are said to have a reliable link and are capable of filtering out those garbled characters caused by the line noise. Notice that the line noise is still there, it just does not show up on your screen or the screen on the remote system. The filtering process used by V.42 (and MNP 2-4) is similar to the error correction scheme used by file transfer protocols (such as Xmodem). The two modems use a sophisticated algorithm to make sure that the data received match with the data sent. If there is a discrepancy, the data is resent. What is the difference between error control protocols (such as V.42) and file transfer protocols (such as Xmodem)? For one thing, file transfer protocols provide error detection and correction only during file transfers. File transfer protocols do not provide any error control when you are reading e-mail messages or chatting with other people online. In other words, an error control protocol is "on" all the time during your online session and file transfer protocols are "on" only some of the times, namely when you are sending or receiving files. Even though an error control protocol is "on" all the time, we still need file transfer protocols when two modems establish a reliable link. A modem works with bit streams, timing and tones. It does not understand what a file is. When you download or upload a file, your communications software needs to take care of the details related to the file: the filename, file size, etc. This is handled by the file transfer protocol which does more than error-checking. Some file transfer protocols, most notably Ymodem-g and Imodem, are developed to handle file transfer without performing any error-checking. The idea of using a protocol like Ymodem-g is to eliminate the redundancy thus improve the transfer speed. Ymodem-g and Imodem should only be used with modems that provide built-in error control protocols. These file transfer protocols do not provide any error-detection or recovery capability. If a problem occurs during the file transfer, the transfer session will be aborted. Protocols like Ymodem-g or Imodem depend on the modems to provide assurance for the integrity of data being transferred. However, you should know that a reliable link between two modems does not provide absolute guarantee for the data integrity during file transfer. When you call a remote computer, there are really three links involved in the process. Besides the link between the two modems, there are still one link between your computer and your modem and another link between the remote modem and the remote computer. When two modems make a reliable connection using V.42 or MNP 4, only the data integrity between the two modems is ensured. It is still possible for errors to occur at either end between the serial port and the modem (in the cable) or in the computer itself. (Fortunately, such errors are rare.) For extra protection, you may still want to use a file transfer protocol - such as Zmodem - which also performs error checking even if you have a reliable link with the remote system. There is a common misconception that Ymodem-g is much faster than other file transfer protocols. Although Ymodem-g is significantly faster than Ymodem, it offers little over Zmodem. Zmodem has proven to be extremely efficient. (See benchmark below) Filename Ymodem Ymodem-g Zmodem ------------------------------------------------------- the-wave.txt 1527 cps 3261 cps 3296 cps dayrpt.arc 761 1042 1025 dayrpt.wks 1244 2314 2337 sunset.arc 745 987 965 sunset.pic 1297 2594 2588 text109k.arc 814 1089 1064 text109k.txt 1351 2812 2885 Note: The seven test files used throughout this article are available on the Hayes BBS (800-874-2937). It is an excellent source for information about Hayes products. The BBS also provides a database for thousands of BBS in the U.S. Best of all, it is free. Unless noted otherwise, the results are obtained by using the following: Computer: Mac SE with Mobius Two Page Display with 68030 accelerator Modem: ATI 9600etc/e (the modem is set as V.32 with V.42bis enabled) Operating System: System 7.0 Communication Software: ZTerm (Comm port speed set to 38400 bps) File Transfer Protocol: Zmodem All results are reported by ZTerm. (I use several communication programs on both IBM PC and Mac. All of them show the average throughput while file transfer is in progress, but ZTerm actually produces a report after the transfer is completed). V.42 & MNP-4 can improve throughput The other benefit of V.42 (or MNP 4) is that it can improve throughput. Before sending the data to a remote system, a modem with V.42 (or MNP 4) assembles the data into packets and during that process it is able to reduce the size of the data by stripping out the start and stop bits. A character typically takes up 1 start bit, 8 data bits and 1 stop bit for a total of 10 bits. When two modems establish a reliable link using V.42 or MNP 4, the sending modem strips the start and stop bits (which subtracts 20% of the data) and sends the data to the other end. The receiving modem then reinserts the start and stop bits and pass the data to the remote computer. Therefore, even without compressing the data you can expect to see as much as 1150 characters per second on a 9600 bps connection. (Although the modem subtracts 20% of the data, the speed increase is less than 20% due to the overhead incurred by the error control protocol.) Here are the test results obtained by downlaoding the same file (1) without any error control protocol, (2) with MNP-4, and (3) with V.42. No data compression protocol is used. Filename No EC MNP-4 V.42 ------------------------------------------------------------------ the-wave.txt 935 cps 1151 cps 1128 cps dayrpt.arc 863 1023 1002 dayrpt.wks 898 1071 1052 sunset.arc 838 971 953 sunset.pic 903 1080 1065 text109k.arc 908 1085 1064 text109k.txt 937 1150 1127 Are MNP4 and V.42 useful? Absolutely. Anyone that has ever used a standard modem can appreciate the benefit of an error-free connection. And the increase in data throughput, though modest, is nothing to sneeze at. Data Compression Protocols Besides error control protocols, all current high-speed modems also support data compression protocols. That means the sending modem will compress the data on-the-fly and the receiving modem will decompress the data to its original form. MNP-5 and V.42bis There are two standards for data compression protocols, MNP-5 and CCITT V.42bis. Some modems also use proprietary data compression protocols. A modem cannot support data compression without utilizing an error control protocol, although it is possible to have a modem that only supports an error control protocol but not any data compression protocol. A MNP-5 modem requires MNP 4 error control protocol and a V.42bis modem requires V.42 error control protocol. Also note that although V.42 include MNP-4, V.42bis does not include MNP-5. However, virtually all high-speed modems that support CCITT V.42bis also incorporate MNP-5. The maximum compression ratio that a MNP-5 modem can achieve is 2:1. That is to say, a 9600 bps MNP-5 modem can transfer data up to 19200 bps. The maximum compression ratio for a V.42bis modem is 4:1. That is why all those V.32 modem manufacturers claim that their modems provide throughput up to 38400 bps. Are MNP-5 and V.42bis useful? Don't be fooled by the claim. It is extremely rare, if ever, that you will be able to transfer files at 38400 bps. In fact, V.42bis and MNP-5 are not very useful when you are downloading files from online services. Why? How well the modem compression works depends on what kind of files are being transferred. In general, you will be able to achieve twice the speed for transferring a standard text file (like the one you are reading right now). Decreasing by 50% means that you can double the throughput on the line so that a 9600 bps modem can effectively transmit 19200 bps. V.42bis and MNP-5 modem cannot compress a file which is already compressed by software. In the case of MNP-5, it will even try to compress a precompressed file and actually expand it, thus slow down the file transfer! Here are the test results obtained by downloading the three compressed files using (1) MNP-4 without data compression, (2) MNP-5, (3) V.42 without data compression, and (4) V.42bis. Filename MNP-4 MNP-5 V.42 V.42bis ------------------------------------------------------------------- dayrpt.arc 1023 cps 946 1002 1010 sunset.arc 971 935 953 950 text109k.arc 1085 988 1064 1053 If you have ever downloaded files from a BBS or online service, you know that almost all files are in a compressed format. Therefore, you should only expect to see an actual throughput between 950 to 1100 cps even if your V.32/V.42bis modem is supposed to offer throughput "up to" 38400 bps. Most PC files are in the ZIP format. Macintosh files are typically in the .SIT (Stuffit) or .CPT (Compact Pro) format. Amiga files are usually in the ZOO, ARC or LZH format. Note that GIF files are also in a compressed format. Compression by Software vs. MNP-5/V.42bis There are several reasons why compression software programs (such as PKZIP or Stuffit) are superior to MNP-5 or V.42bis. 1. Compressed files save disk storage space. 2. Compression software programs are more versatile. Most of them allow you to group several files in a compressed file archive to ensure that all the related files get transferred at the same time. 3. Software compression is more efficient than on-the-fly modem compression. In the case of a small file, this may not make much difference. But the difference can be significant when you are transferring large files. Filename Size Time Throughput ----------------------------------------------------------------- the-wave.txt 143579 bytes 43 seconds 3296 cps dayrpt.arc 8423 bytes 8 seconds 1010 cps dayrpt.wks 19712 bytes 8 seconds 2337 cps sunset.arc 5084 bytes 5 seconds 950 cps sunset.pic 16391 bytes 6 seconds 2643 cps text109k.arc 29775 bytes 28 seconds 1053 cps text109k.txt 111386 bytes 39 seconds 2822 cps As we can see from the test results, it is about 30% faster to transfer the compressed file text109k.arc than to download the text file with V.42bis. Hayes BBS does not provide a compressed version for the file the-wave.txt. Using PKZIP (for PC) and Stuffit (for Macintosh), we obtain the following results: the-wave.zip: 6812 bytes (PKZIP) the-wave.sit: 6081 bytes (Stuffit) Assuming a transfer speed of 1000 cps, the compressed file can be downloaded in 7 seconds. That's six times faster than downloading the text file with V.42bis! Here is another example. Spider Island Software BBS (714-730-5785) has a test file called One-Minute Max. It is a Macintosh TIFF file (file size 206,432 bytes). According to Spider Island Software, the file can be downloaded in 56 seconds (with an effective throughput of 3745cps) with a V.32/V.42bis modem. The result may seem impressive at first. However, the file can be compressed to 6065 bytes (with Compact Pro) or 7385 bytes (with Stuffit). Assuming a transfer speed of 1000 cps, it would only take 6-8 seconds to transfer. Again, it is seven to nine times faster than downloading the file with V.42bis. On-the-fly modem compression does have one advantage. It is more convenient. You can send a file without compressing it first and the recipient does not need to decompress the file. Local Flow Control and Data Buffering To get the most from a modem with data compression, you'll want to send data from your PC to the modem as quickly as possible. If the modem is idle and waiting for the computer to send data, you are not getting the maximum performance from the modem. For example, you have a V.32/V.42bis modem and you want to send a text file to a remote system which also has a V.32/V.42bis modem. Let's assume the modem is able to send the file at 20000 bps using V.42bis. If your computer is sending data to your modem at 9600 bps, your modem will have to stop and wait to receive data from your computer. To get the maximum performance, you want to set the computer to send data to the modem at 38400 bps (the maximum a V.32/V.42bis modem can achieve). Since the modem can only send the file to the other modem at 20000 bps, it will never have to wait. Here are the test results for downloading the text file the-wave.txt by setting the communication port at different speeds: the-wave.txt: 946 cps (modem port speed 9600 bps) 1885 cps (modem port speed 19200 bps) 3296 cps (modem port speed 38400 bps) However, there is a new problem. Since your computer is sending data faster than the modem can handle, there needs to be some ways for the modem to ask the computer to stop sending data. Otherwise, data loss is sure to occur. This is where local flow control comes into play. A high-speed modem typically supports two kinds of local flow control: hardware handshaking (CTS/RTS) and software handshaking (XON/XOFF). Of the two, hardware flow control is the preferred method. We have mentioned earlier that there are three links involved when you are connected to a remote system: 1. The link between your computer and your modem 2. The link between the modems 3. The link between the remote modem and the remote computer Local flow control is used for the first and third links. Notice that the first link may not use the same kind of flow control as the third link. Hardware flow control (or hardware handshaking) works by altering voltage levels on the RTS (Request To Send) and CTS (Clear To Send) signal lines at the RS232 serial interface between the modem and the computer. CTS is used by the modem on the sending end of a transmission. When the local modem is ready to receive data, it sends the CTS signal to the local computer and the computer starts transferring data. If the modem is unable to accept the data as fast as it is received from the computer, the modem will disable the CTS to inform the computer that the modem buffer is almost full (A high-speed modem typically contains a small amount of RAM which is used to provide data buffers). The computer will then suspend data transfer. Once the local modem has emptied its buffer by transmitting data to the remote modem, it will enable CTS again. RTS is used by the computer on the receiving end of a transmission. When the computer cannot accept data at the rate at which the modem is passing data, it will disable RTS. The computer enables RTS again when it is ready to resume receiving data from the modem. Software flow control (or software handshaking) is achieved by embedding control character in the data stream. XON and XOFF are the most commonly used control characters. XON is also known as Control-Q or DC3 (ASCII 19) while XOFF is known as Control-S or DC1 (ASCII 17). The use of XON and XOFF during data transfer can create problem when a binary file contain the Control-S (^S) character as a legitimate part of the data. Do not use this method if ^S and ^Q are part of the transmitted data. Macintosh and High-speed Modems If you use a Macintosh with a high-speed modem, you will need a special modem cable that is wired correctly to support hardware handshaking. You can order the cable from most mail-order companies that sell high-speed modems. I got mine from Maya Computer (800-541-2318) for $10 (plus $2.50 for shipping & handling). Unfortunately, the cable did not work with my SE. The cable is good since it worked fine on a Mac IIsi. It just refused to work on my SE. I was disappointed but not surprised. After all, my SE is equipped with a 25 Mhz 68030 accelerator. (Well, it is actually both an accelerator and a video adapter for a 19 inch dual-page monitor.) Since I will never want to run my SE without the accelerator, I have no choice but to use software handshaking. PC and UART (8250, 16450, 16550) Your PC's serial port has a UART (Universal Asynchronous Receiver/Transmitter) chip to control the input/output. The XT usually has an 8250 UART, the AT usually has a 16450 UART. If you are running Windows, Desqview, OS/2 or any other multitasking environment, you should upgrade your UART with the 16550 (if your PC does not already have one). The 16550 is standard in most IBM PS/2 and many 386-based computers. The 16550 UART has a 16 bytes FIFO (first in, first out) buffer that helps to prevent degradation when several programs are running at the same time. If you use an external modem, the UART is in your computer (either on the motherboard or on an I/O card that has the serial port). If you use an internal modem, the UART is on the modem. (Both internal modems from Practical Peripherals and Zoom use the 16550 UART. The Twincom 96/42 uses a 16450. The CompuCom SpeedModem Champ, due to its unique design, does not use a standard UART.) Even if you have a 16550 UART, the communication software that you use will need to support it. Fortunately, the most recent versions of popular communications programs are all designed to support the 16550 UART. Hayes ESP (Enhanced Serial Port) Hayes makes an adapter called Enhanced Serial Port (ESP) that has two serial ports complete with an on-board coprocessor. The ESP can save your PC's CPU from having to manage the work load. If a 16550 UART is not good enough for you, the ESP may be the only answer. Profiles of High-speed Modems Here are profiles of some high-speed modems. The list is not comprehensive, nor is it intended to be. Unless noted otherwise, the street price quoted are from PC Connection (800-243-8088) in PC Magazine (12/31/91). PC Connection generally does not offer the lowest price, but the service is excellent. I have dealt with PC Connection and MacConnection (800-800-4444) for years and have yet to be disappointed with their services. Unless noted otherwise, a V.32/V.42bis modem supports V.32, MNP2-5, V.42/V.42bis. And a V.32bis/V.42bis modem supports V.32bis, MNP 2-5, V.42/V.42bis. Most modems listed here are introduced in the past eighteen months. ATI 9600etc/e ATI Technologies is well known for their video adapters. But they also make a V.32/V.42bis external modem. As of this writing, it is the least expensive external modem from an established manufacturer. It is a generic high-speed modem that works well. The street price for the ATI 9600etc/e is $379. I have been using an ATI 9600etc/e for several months now and I am very pleased with it. I will not hesitate to recommend it to anyone looking for an affordable V.32/V.42bis modem. There are two things I really like about the ATI modem: * It has a slide volume control on the outside so you can easily adjust the volume by hand. * It has factory settings for three different modes: V.32 only, V.32 with MNP-5, V.32 with V.42bis. It is very convenient if you need to initialize the modem in different ways. CompuCom SpeedModem Champ/Star/Storm The SpeedModem Champ is a 9600 bps high-speed modem with CompuCom's proprietary CSP modulation protocol. It is introduced in early 1991. It can be ordered from CompuCom directly at a discount price of $169. The CompuCom Champ is supported by hundreds of BBS in the U.S., including heavyweights such as EXEC-PC and Channel 1. CompuCom also markets the SpeedModem Combo which is a SpeedModem Champ with fax and voice mail capabilities. The current price is $269. The SpeedModem Storm is a dual-mode modem. It supports both CSP and V.32/V.42bis. The discount price is $299 (internal) and $339 (external). The Storm is also available with fax and voice mail options for an additional $90. The SpeedModem Star is also a dual-mode modem. It supports both CSP and V.32bis/V.42bis. The discount price is $499 (internal) and $539 (external). The Star is also available with fax and voice mail options for an additional $90. Hayes Modems V-series Smartmodem 9600. Introduced in 1987, this is a high-speed modem that supports the proprietary Hayes Express 96 modulation protocol. The V-series Smartmodem 9600 is still available from various mail order vendors. There is also an internal unit called V-series Smartmodem 9600B. Smartmodem 9600. Introduced in 1988, the Smartmodem 9600 is a V.32 modem. It does not support any error control or data compression protocol. Don't confuse this unit with the V-series Smartmodem 9600. Ultra 96 is a dual-mode modem from Hayes. Introduced in 1990, the Ultra 96 supports both V.32/V.42bis and the Hayes Express 96 modulation protocol. Ultra 96 has many unique features that are not needed if you are calling BBS or online services. The current street price is $669. Introduced in Fall 1991, Ultra 144 is a dual-mode modem that supports both V.32bis/V.42bis and the Hayes Express 96 protocol. The current street price is $799. Optima 96 is a plain vanilla V.32/V.42bis modem. This is Hayes' answer to the "generic" V.32/V.42bis modem. The current street price is $479. Image Communications: Twincom 96/42 The Twincom 96/42 is an internal V.32/V.42bis modem. It lists for $299. (Don't expect to get discount on the price.) It just won a 1991 Best Buy Award from Computer Shopper. Notice that it has a 16450 UART, not a 16550. Furthermore, you cannot replace the 16450 with a 16550, the Twincom 96/42 will not support a 16550 UART at all. Intel 9600EX & 14.4EX The 9600EX is a V.32/V.42bis modem. The 14.4EX is a V.32bis/V.42bis modem. PC Connection is selling the 9600EX for $499 and the 14.4EX for $549. If you decide to buy an Intel modem, the 14.4EX is obviously a better deal. Practical Peripherals PM9600SA & PM9600 The PM9600SA is a V.32/V.42bis modem. It is designed to be compatible with the Hayes Ultra 96. That means you can tell your communications software that you have a Hayes Ultra 96. However, the PM9600SA only responds to a subset of the commands supported by the Hayes Ultra 96. Any commands specific to the Hayes Ultra 96 that are not implemented in the PM9600SA will be ignored. Some early PM9600SA units have quite a few problems connecting to other V.32 modems. (Make sure you send in the warranty card.) Practical Peripheral has since sent out several ROM upgrades and the current shipping units seem to be working fine. Practical Peripherals also makes an internal modem that features a 16550 UART. You can get the PM9600SA for $469 and the internal PM9600 for $399. Prometheus Modems Prometheus modems are available from many Macintosh mail order companies. Until recently, Prometheus is the only manufacturer that makes high-speed modems with fax capability. Promodem 9600 Plus is a V.32/V.42bis modem. It can also send and receive Group III fax at 9600 bps. Prometheus Ultima is a V.32bis/V.42bis fax modem. It can also send and receive Group III fax at 9600 bps. MacConnection sells the Ultima for $689. Telebit Modems Telebit makes several modems. The prices quoted for the Telebit modems are their new list prices. TrailBlazer Plus. $849. Introduced in 1985, the Trailblazer has been the de facto standard in the UNIX UUCP and Usenet communities. With the new pricing, you should consider the T2500 or the T3000 instead of the TrailBlazer Plus if you need to connect to a Telebit PEP modem. T1000. Introduced in 1988, the T1000 is the little brother of the TrailBlazer Plus. The T1000 supports PEP at a slower speed. The actual throughput is about 9600 cps. The current list price is $699. Unlike the TrailBlazer Plus, the T1000 does not have callback or password security. T2500. $949. Introduced in 1989 when V.32 modems started to enter the market, the T2500 supports both V.32/V.42bis and PEP. The maximum throughput is 19,200 bps due to the limitation imposed by the older Rockwell chipset used. T1600. $699. The T1600 is a V.32/V.42bis modem introduced in 1991. It provides built-in support for UUCP and offers password and callback security. T3000. $949. This is the top of the line model from Telebit. The T3000 is a V.32bis/V.42bis modem. PEP upgrade is available for $99 until 3/31/92. After that date, the upgrade will be $199. QBlazer. $745. If I am going to buy another high-speed modem today, this will be it. (I use a notebook computer). QBlaser is the first portable V.32/V.42bis modem (2.3"x2.4"x2.4"). It works with a 9-volt battery for about two hours. Note that T1600, T2500, T3000 all offer the following features: * Built-in support for UNIX UUCP, Xmodem, Ymodem, Kermit file transfer protocols * Two types of dial-access security: password security and callback security * Remote management and diagnostics U.S. Robotics Modems Courier HST. This is the modem that made U.S. Robotics the king of PC-based BBS communities. Unless you are only going to communicate with other USR HST modems, it is probably not a good idea to purchase this unit. The street price for a 14400 bps HST is $550-$600. Telemart (800-521-1973) sells either the internal or the external version for $559. Courier V.32bis. Introduced in 1990, this is a V.32bis/V.42bis modem. It does not support HST. Telemart offers the external version for $565 and the internal version for $535. Courier HST Dual Standard. This unit is introduced in 1990. If you need to connect to HST modems and also want to be able to talk to other V.32/V.32bis modems, this is the modem to buy. Its current street price is around $800. Telemart sells the HST Dual Standard for $799. (Note that earlier HST Dual Standard modems only support V.32 and not V.32bis.) The HST Dual Standard is considered by many PC users as the best modem money can buy. The only reservation I have about the Courier modems is their size. The external Courier modems are rather bulky: 8.3" wide, 12.65" deep, 1.57" tall. I would not want to carry one of these with me when I travel. (It's bigger than my notebook computer.) Sportster 9600 V.42bis. This unit is introduced in 1991. The Sportster 9600 is an entry level V.32/V.42bis modem from U.S. Robotics. The list price is $645 for the external version. ($595 for the Internal version). WorldPort 9600 V.32. The WorldPort 9600 is a portable pocket modem. Originally made by Touchbase Systems, the WorldPort 9600 is a V.32/MNP-5 modem. It does not support V.42/V.42bis. The WorldPort 9600 works with a 9-volt battery. The list price is $699. Zoom V.32 Turbo Modems Zoom has been making Hayes-compatible modems for a long time. The V.32 Turbo is their entry into the high-speed modem arena. The V.32 Turbo is a V.32/V.42bis with a 12000 bps turbo mode which is compatible with a V.32bis modem at 12000 bps. Zoom also makes an internal version of the V.32 Turbo that features a 16550 UART. PC Connection sells the internal model for $399. Things to come Every modem manufacturer makes at least one V.32/V.42bis modem now. And soon every manufacturer will also make a V.32bis/V.42bis modem. The price for V.32 and V.32bis modems will continue to drop. In fact, Supra has announced an external V.32 fax modem (SupraFaxModem V.32) for $299 and an external V.32bis fax modem (SupraFaxModem V.32bis) for $399. These prices are for the modems only. Communication and fax software will be bundled with the modem for an additional $50-$70. (These modems won't be available at least until January 1992.) Buying a High-speed Modem V.32 and V.32bis modems are clearly the standards of high-speed modems today. You should buy a V.32 or a V.32bis modem unless 1. Your application requires a high-speed modem with a proprietary modulation protocol. In this case, you should consider a dual-mode modem that support both the proprietary protocol and V.32 (or V.32bis). 2. You cannot afford a V.32 modem. In this case, your only choice for a high-speed modem is the CompuCom SpeedModem Champ. Should you pay the extra for a V.32bis modem? A V.32bis modem is faster than a V.32 modem but it also costs more. Should you pay the extra for the speed difference? That depends on two factors: what's the price difference and how do you want to reach the remote system. If the price difference is $50, I would buy the V.32bis modem. But what if the price difference is $200? Assuming the remote system support V.32bis, a V.32bis modem will pay for itself rather quickly if you are placing long distance calls to the remote system. However, it may be more cost-effective for you to use some packet-switching networks to reach the remote system by calling a local number. A V.32bis modem will be wasted since none of the packet-switching networks currently support V.32bis. In fact, they are just starting to offer 9600 bps access service. Part III of "The Joy of Telecomputing" provides a comprehensive discussion of the issues involved. Should you buy a modem with a proprietary modulation protocol? With the exception of the CompuCom SpeedModem Champ, it is generally not a good idea to purchase a modem which only supports a proprietary modulation protocol. If you have to connect to a modem that uses a proprietary modulation protocol, you should consider getting a modem that supports dual modulation protocols (USR Courier Dual Standard, Telebit 2500 or 3000, Hayes Ultra). Should you buy the SpeedModem Champ? It certainly costs much less than even the least expensive generic V.32 modem in the market today. Assuming the systems you are calling support both V.32 and the CompuCom Champ modems, should you save the money and buy the Champ? Unfortunately, there is no clear-cut answer to the question. The answer again depends on how you are going to reach the remote systems. If you want to reach the remote systems via a packet-switching network, the CompuCom Champ may not be a good choice. The CompuCom Champ is generally not supported by packet-switching networks (The only company that supports the CompuCom Champ is Connect-USA). As a result, you will only be able to connect at 2400 bps with the packet-switching networks. You would be forced to place a long distance call if you want to connect at 9600 bps. See Part III of "The Joy of Telecomputing" for the various issues involved. Should you buy a 2400 bps modem with V.42bis? If you are thinking of purchasing a 2400 bps modem with V.42bis data compression, think again. We have mentioned earlier that V.42bis and MNP-5 are useless for downloading compressed files. There is one more reason why a 2400 bps with V.42bis is generally not useful when you are calling commercial online services or BBS. Online services and BBS usually have separate phone numbers for 2400 bps and high-speed modems. Most of them do not support V.42bis on their 2400 bps lines. Therefore, you won't be able to make a connection with V.42bis if you call their 2400 bps modem lines. Couldn't you call their 9600 bps lines? Well, not really. Commercial online services, as well as many bulletin board systems, typically do not allow you to call their high-speed modem lines with a 2400 bps modem. You won't be able to make a connection even if you try. You should seriously consider the CompuCom SpeedModem Champ instead of a 2400 bps modem with V.42bis. The CompuCom Champ will probably give you much more for your money (especially if you need to pay more than $100 for the V.22bis/V.42bis modem). Beware of the Ads Current V.32 modems typically support MNP 2-5 and V.42/V.42bis. However, there are still some earlier models of V.32 modems in the market which 1. may not support any error control or data compression protocol (Hayes Smartmodem 9600). 2. may support MNP 2-5 but not V.42/V.42bis. 3. may support proprietary data compression protocol (Microcom MNP-9). 4. may support V.42 but not V.42bis (Prometheus). When a modem is said to offer a 38400 bps speed (or throughput), it may mean that 1. it is a V.32 or V.32bis modem with V.42bis 2. it is a V.32 modem with proprietary data compression protocol (some Microcom modems) 3. it is a high-speed modem with proprietary modulation protocol and V.42bis (U.S. Robotics Courier HST) 4. it is a high-speed modem with proprietary modulation protocol and proprietary data compression protocol (CompuCom Champ) An ad that says "USR modem, 38400 bps throughput, V.42bis" does not tell us anything except that the modem is made by U.S. Robotics. It could be any one of the three Courier modems. It could even be a Sportster 9600. When a modem is said to offer a 9600 bps speed (or throughput), it may mean several things: 1. it is a V.32 modem 2. it is a high-speed modem using proprietary modulation protocol (Hayes V-series Smartmodem 9600, Telebit 1000, etc). 3. it is a 2400 bps modem with V.42bis data compression. 4. it is a 2400 bps modem with 9600 bps fax 5. it is a 2400 bps modem both V.42bis and fax /end of part 1 of 2 parts/