"A Practical Guide to Selecting a Modem," by Seth Novogrodsky, Berkeley Computing, Volume 3, Number 4, May-June 1993, The Regents of the University of California. Contact: avante@garnet.berkeley.edu. At one time, choosing a modem to connect your computer to other computers over the telephone line was a fairly simple matter, but as technology has advanced, modems have become more and more complicated. To make things even more perplexing, the terminology used to describe modem features and capabilities is often bewildering, and there are many different kinds of modems on the market, not all of which may be appropriate for your computer. A modem (MOdulator/DEModulator) is a device that connects your computer to the telephone line and converts digital signals sent by the computer into audible tones that can be sent over the telephone line (modulating) and then converts the tones sent from the modem on the other end of the connection back into digital signals (demodulating). A modem can connect your computer to other computers no matter how far away they may be. Protocols Because such a wide variety of modems is now on the market, you can choose from a broad range of features and prices. But before you can decide what kind of a modem to get, you will need to know which communications protocols are used by the services that you will need to connect to. You will need to make sure that the modem you buy is compatible with those protocols. The ability to make sense out of the different protocols is something of a black art, but once you understand the basics you should be able to determine exactly what you need. Communications protocols (or standards) fall into three broad categories--modulation or speed, error correction, and data compression. (These protocols should not be confused with file transfer protocols and communications settings such as parity, the number of stop bits, character length, etc. Although it is important to know about those sorts of protocols and settings, they are software dependent and are not features built into modems.) Some standards are international standards set by the International Telegraph and Telephone Consultative Committee (CCITT), a United Nations committee based in Geneva, Switzerland; CCITT standards are normally designated by a capital letter "V" followed by a period (V.) and a number. Some early standards in the United States are Bell System standards established by AT&T. Other standards are proprietary standards created by modem manufacturers; some proprietary standards have been adopted by other vendors and incorporated into international standards. Speed or modulation. The speed of a modem determines how fast data, in the form of binary digits or bits, are transferred over telephone lines. Speed is normally measured in terms of the number of bits per second (bps). (In the past, modem speed was often described in terms of baud, which refers to the number of signaling events that take place in one second. In some modulation schemes, more than one bit is transferred per signaling event. The term "baud" is often inaccurately used as a synonym for "bps.") There are a number of different modulation standards in common use. Most of these are designed to provide asynchronous, full-duplex connections. In asynchronous communication, characters--normally made up of streams of 7 or 8 bits--are generally framed by start and stop bits and do not have to be transmitted in fixed time intervals. (The term synchronous describes a type of communication in which characters are transmitted in fixed time intervals.) Asynchronous communication is far more common on microcomputers and workstations than synchronous communication, and protocols that can operate synchronously can also operate asynchronously. A full-duplex connection is one in which data can be sent from the modem and received by the modem simultaneously; data can be sent only in one direction at a time in a half-duplex connection. (Full-duplex modems can operate in half-duplex mode.) These are the most commonly used modulation standards: + Bell 103. This standard provides asynchronous, full-duplex connections at speeds of 110, 136.5, 150, and 300 bps. The European standard for 300 bps and slower modems is the CCITT's V.21, which is not compatible with Bell 103, although most modern modems support both modulation schemes. + Bell 212A. This standard provides an asynchronous, full-duplex connection at 1200 bps. The European standard for 1200 bps communication is V.22, and this standard is very similar to Bell 212A; most 1200 bps modems can support both protocols. (The "A" in "Bell 212A" indicates that a modem also provides support for the Bell 103 standard at speeds of 300 bps or slower. The Bell 212 standard provides support only for 1200 bps connections.) + V.22bis. This worldwide full-duplex synchronous and asynchronous communication standard provides communication at up to 2400 bps. (The suffix bis is the Latin word for "twice," and it is used in CCITT standards to indicate a significant change or enhancement.) A modem that supports this protocol can automatically "fall back" to V.22 at 1200 bps, although in practice V.22bis modems usually also support Bell 103 and Bell 212. + V.29. This is a half-duplex standard normally used only by modems that have facsimile capability to send and receive faxes using the Group III fax standard. V.29 can operate at 4800, 7200, and 9600 bps. (Another standard for faxes is V.17, which can operate at up to 14400 bps. Fax machines that can operate at this speed are not yet common.) + V.32. This standard provides full-duplex synchronous and asynchronous communication at 4800 and 9600 bps. + V.32bis. This extension to the V.32 standard adds support for a maximum speed of 14400 bps and fallback speeds of 7200 and 12000 bps. In addition, there are a number of proprietary modulation standards for high-speed modems (9600 bps or faster) that you might come across. The three best known proprietary modulation standards are the Hayes Express 96, which was used on the earliest 9600 bps modems from Hayes Microcomputer Products, Inc.; HST (High Speed Technology) from U.S. Robotics, Inc.; and PEP (Packetized Ensemble Protocol) from Telebit, Inc., which is a half-duplex protocol that is commonly used for UUCP (UNIX to UNIX copy) applications. These proprietary protocols are not compatible with each other or with the CCITT standards, although modems that use proprietary protocols now often support the international protocols as well. Apart from the protocols discussed above, new standards are being developed to provide even faster connections. A standard under development by the CCITT generally referred to as V.FAST will provide speeds of at least 19,200 bps and possibly as high as 28,800 bps. (This developing standard is sometimes referred to as V.32ter, although no official designation has been assigned to it yet. The word ter is Latin for "thrice.") Generally, modems that have the higher speed protocols built into them have the lower speed protocols as well. It is important to remember that modems on both ends of a connection must have at least one modulation protocol in common. Note that speed in this discussion of modulation protocols does not refer to the effective data transfer rate. The effective speed of a modem can be diminished or augmented by factors such as error correction protocols, which can reduce the effective data transfer rate in certain circumstances, and data compression protocols, which can often increase it. When you are evaluating a modem, you need to know whether a bps figure refers to the modulation speed or the maximum effective data transfer speed. Error correction. Error correction protocols, sometimes referred to as error control or error checking protocols, can detect when errors have occurred during the transmission of data and, if errors are detected, cause the affected data to be retransmitted. These are the most commonly used error correction protocols: + MNP (Microcom Networking Protocol) Classes 1 through 4. These error correction protocols were developed by Microcom Systems, Inc. MNP-1 is now effectively obsolete and is often not included on modems that support other MNP error correction protocols. + V.42. This CCITT standard incorporates a protocol called LAP-M (link access procedure for modems), which offers better performance than MNP-1 through MNP-4. For compatibility with modems that have only the MNP error correction protocols, the V.42 standard has MNP-2 through MNP-4 built into it as a fall-back alternative to LAP-M. Not all modems have error correction protocols built into them. Although certain types of error correction can be incorporated into software, error correction protocols that are built into modems can be extremely useful. Without error correction, noisy telephone lines and poor connections can result in garbled characters appearing on the screen and other, more serious corruption of data. Some error correction protocols, such as MNP-4 and V.42, can sometimes have the side benefit of increasing the effective data transfer rate, since these protocols can reduce the amount of data sent by grouping the data in packets and stripping out start and stop bits. Data compression. Data compression protocols can reduce the amount of data that needs to be sent over the phone lines. These compression techniques work by encoding the data in such a way that redundancies in the data are minimized. The two data compression protocols most commonly built into modems are the following: + MNP Class 5. This data compression protocol is often included in modems that have MNP error correction protocols. (MNP-5 in fact requires MNP-4.) This protocol can reduce the amount of data that needs to be transmitted to as little as half of its original size. + V.42bis. This protocol, which always includes the V.42 error correction protocol as a subset, can reduce the amount of data that needs to be transmitted to as little as one quarter of its original size. With either of these protocols, the amount of compression depends on the type of data being transmitted. For example, plain text files benefit most from compression, but interactive applications such as logging onto a remote computer and running a text editor may not benefit significantly. In addition, files that have already been compressed, such as those compressed by StuffIt or Compact Pro on the Macintosh, ARC or PKZIP on an IBM PC or compatible computer, or the compress command in UNIX, probably will not benefit from compression at all. (Most files available on bulletin board services and commercial information services, discussed below, and Internet archives are already compressed.) If a modem with MNP-5 attempts to compress already compressed data, the resulting data is likely to be increased in size rather than decreased. V.42bis will attempt to compress only data that will benefit from compression. Although data compression built into modems can be very useful for some applications, software compression utilities can sometimes be more efficient. These data compression protocols are independent of the modulation standard used. For example, the effective data transfer rate of a V.22bis (2400 bps) modem can theoretically reach a maximum speed of 9600 bps using V.42bis, and a V.32bis modem can theoretically reach a maximum speed of 57600 bps using V.42bis. In practice these maximum speeds are rarely attained. Deciding Which Protocols You Need The protocols that you will want to look for when choosing a modem will depend on what services you will want to connect to and what you will be doing with those services once you are connected. Connecting to campus computers using the general access dial-up lines. To connect to campus computers using the 1200 bps, 2400 bps, or the new high-speed (9600 or 14400 bps) dial-up lines, you will need to have a modem that uses the Bell 212, V.22bis, or V.32 or V.32bis modulation standards respectively, as discussed in the article above "Ask Dr. Micro: What Sort of Modem Should I Get to Connect to Campus Computers?" In addition, the campus 2400 bps V.22bis modem lines support MNP-3 error correction (although it is not necessary to have an MNP modem to use these lines). Although the high-speed modem lines that were announced in the April 1993 Berkeley Computing have both V.42 error correction and V.42bis data compression, it was not determined which special features of these modems would be enabled at the time this article was being prepared. A V.32bis modem will provide the most flexibility for connecting to campus computers, since these modems generally include the slower modulation speeds and V.42 error correction and V.42 data compression. In addition, there may be specialized departmental services, other than the standard dial-up numbers maintained by the campus Data Communication and Network Services department, such as AppleTalk Remote Access servers and direct links to departmental computers. If you would like to use these sorts of services, contact the department providing those services and ask what protocols your modem should have. Connecting to other services. Many campus computer users want a modem to communicate only with computers at the University, but there are also other types of services that users may wish to connect to: + Commercial information services. There are a number of commercial "information utilities" such as AppleLink, America Online, GEnie, and Prodigy that can provide a huge amount of information including current newspaper articles, movie reviews, online encyclopedias, and the latest news about computers. The largest of these information services typically support modulation speeds ranging from 300 to 9600 bps using the Bell and CCITT standards, although support for 300 bps connections is starting to become less common and support for 14400 bps connections will likely be widely available in the near future. These services often charge by the hour, and the rates are usually higher for connections at higher speeds. Whether or not it is cost-effective to use the higher-speed connections with these services depends on your application. Generally, if you are going to be receiving (generally referred to as downloading in telecommunications jargon) large files, it probably makes sense to use a high-speed connection. Otherwise, it may be more cost-effective to use a lower speed. + Bulletin board services. There are also many free bulletin board services (BBSes) that offer a tremendous variety of freeware, shareware, and public domain software. (Phone numbers of local BBSes are listed in free publications including MicroTimes and Computer Currents.) Many software and hardware vendors have bulletin board services that provide technical information and updates to software. Most commonly, BBSes use Bell and CCITT modulation standards, although some BBSes use proprietary standards such as U.S. Robotics HST. Although BBSes tend to be free, long distance charges may apply. If you plan on using these services extensively for downloading software, it would probably make sense to get a high-speed modem. + Individual microcomputers. It is also possible to exchange files with pretty much any other person who has a microcomputer and modem, since the ability to answer calls as well as originate them is now a standard feature of modems. In addition, there are software packages for microcomputers that allow you to take control over a remote microcomputer and use it as though you were sitting in front of it. For these types of remote control applications, it is generally best to use a high-speed modem. It is a good idea to get a modem that is likely to work well with any service that you are likely to use for as long as you plan to own the modem. Choosing the best protocols for your application. Before you buy a modem, you need to think about what you are likely to want to use it for in addition to the specific services you will be connecting to, since most services support multiple protocols. The first choice that you will want to make is whether to get a high-speed modem that can operate at a modulation speed of 9600 bps or faster. To put these speeds into perspective, a transmission rate of 1200 bps translates roughly to 120 characters per second (cps), a rate of 2400 bps translates to roughly 240 cps, and so on. (This is because it typically requires 10 bits to transmit a single character or byte-a stream of eight bits--plus a start and stop bit.) A rate of 1200 bps may be an adequate speed for some applications, but it is very slow for transferring large files. If you are going to be using a simple text editor on the remote computer, then 2400 bps would likely be an acceptable speed. A transmission speed of 9600 bps or 14400 bps may not provide a significant advantage over 2400 bps for most screen-oriented text editing, but would likely be a much better choice for transferring large volumes of data. For example, if you want a modem to connect to a campus computer occasionally to check your electronic mail, a fairly simple 2400 bps modem might be an acceptable choice for you. If you plan to take advantage of certain new technologies that can provide access to capabilities not previously generally available via modem, then you will very likely want to get a more sophisticated high-speed model. For example, AppleTalk Remote Access, mentioned above, can provide access to all of the services available on an AppleTalk network, including AppleShare file servers and networked printers. Likewise, new networking protocols such as PPP (point-to-point protocol) and SLIP (serial line Internet protocol) can connect your computer directly to a network such as the Berkeley campus network; these types of services may not perform acceptably at speeds less than 9600 bps. (AppleTalk Remote Access, described in the article "AppleTalk Remote Access Brings the Campus Network to You" in the November-December 1992 issue of Berkeley Computing, is not currently provided as a general service by the campus. The campus is looking at providing access to the network via PPP and SLIP.) It is very important that you read the sales literature carefully to make sure that a modem that you are considering purchasing has the specific protocols that you need. If someone tells you that a modem will operate at 9600 bps, it may mean that the modem uses the V.32 modulation standard or a proprietary 9600 bps modulation protocol, that the modem uses the V.22bis (2400 bps) modulation standard and has V.42 data compression (which is unlikely to achieve the theoretical maximum compression ratio of 4:1), or even that the modem is a 2400 bps model with 9600 bps (V.29) fax capability. For most users, a high-speed modem is likely to be a better investment than a lower-speed model. Although high-speed modems cost more than lower-speed modems, prices have fallen dramatically within the past couple of years. It is now possible to buy a high-speed modem for less than $300. (For comparison, 2400-bps modems typically range in price from about $40 to $150 depending on the features.) The additional money that you spend on a high-speed modem now may be more than offset by the savings you may accumulate in reduced connect-time charges if you use commercial information services, depending on the rate-structure of the service, or in long distance phone charges if you use computers that require dialing a long distance number. If you decide to buy a high-speed modem, it is a good idea to look for one that has both the V.32bis modulation protocol and the V.42 and V.42bis error correction and data compression protocols. At this time, there is often little difference in price between V.32 and V.32bis modems, even though V.32bis can provide speeds that are 50 percent faster. V.42 and V.42bis error correction and data compression protocols are now pretty much standard features for these modems. Proprietary modulation standards such as HST may be useful in certain circumstances, but it is probably not worth paying extra for such features unless you know that you will be taking advantage of them. Likewise, some modem manufacturers are already advertising "V.FAST" compatibility or upgradeability, even though the V.FAST standard is still under development. It may not be worth paying extra for this feature either, since it will likely be some time before the V.FAST standard is finalized and even longer before these modems are widely used. (By the time true V.FAST modems are in widespread use, new technologies such as ISDN [Integrated Services Digital Network] may be able to provide a superior method for connecting to remote computers. For information on ISDN, please see the articles "ISDN Holds Promise of New Communications Services" and "An Introduction to ISDN" in this issue of Berkeley Computing.) The only significant drawback of a high-speed modem is that some software and some computers, particularly older systems, cannot take advantage or full advantage of the higher speeds, as discussed in the section below. Choosing a Modem That Will Work with Your Computer When you are evaluating modems, it is important to think about how it will be connected to your computer and whether it will work properly with the software that you want to use to connect to remote computers. How a modem connects to your computer. A modem may be a standalone device that sits next to your computer or a plug-in board mounted in an expansion slot inside the computer's case. Standalone modems normally connect to the personal computer via a standard serial interface. (The term serial refers to communication in which bits are transmitted one at a time sequentially as opposed to parallel communication in which multiple bits are sent over several lines simultaneously.) The serial interfaces normally conform to the RS232-C standard. (Macintosh computers have serial ports that use the RS422 standard, which is compatible with the RS232-C standard.) Although many personal computers include a serial port as a standard feature (including all Macintoshes and most IBM compatibles), you may need to buy the serial interface separately for some computers. Generally, you will have to purchase a serial cable to connect the modem to the serial port, although sometimes the cable is included with the modem. (A few tiny portable modems plug directly into a serial port without the need for a cable.) In some cases, you may need a custom cable, since not all serial ports use the same signaling scheme and some use nonstandard connectors. Internal versus external (standalone) modems. If you have a computer such as a Macintosh II or an IBM PC with a free expansion slot, you might consider buying an internally mounted modem. An internally mounted modem requires no additional desk space and can perform just as well as a standalone model. (Some standalone modems are designed to fit underneath telephones or answering machines, so the amount of desk space a modem uses may not be much of an issue in some cases.) Because an internal modem draws its power from the computer's power supply, it does not require a free electrical outlet. (Many standalone modems have power transformers that are so large that they effectively take up two electrical outlets.) Internal modems are particularly useful for users of laptop and notebook computers, although there are now a number of very small external modems available that have been designed specifically to be used with portable computers. Another advantage is that internally mounted modems often include communications software at no additional charge, whereas standalone modems often do not. For IBM PCs and compatible machines, an internal modem can in some situations help sidestep certain compatibility problems, as discussed below. Internal modems also tend to be less expensive than standalone modems, since they cost less to manufacture. (Internal modems for Macintoshes tend to cost a bit more than standalone models, since they are not all that popular among Macintosh users.) There are, however, two potential disadvantages to internally mounted modems. First, whereas external modems often have a set of indicator lights that show the status of the modem and the connection to the remote computer, internally mounted modems do not. These indicator lights often provide information such as whether the modem is receiving a signal from a remote computer, whether the modem is set to receive incoming calls, whether the modem is sending or receiving data, and so forth. In addition, a few standalone modems have alphanumeric displays that provide ongoing information in words about the status of the connection, the protocols being used, and so forth. These indicator lights and displays can be very useful in troubleshooting problems Second, a standalone modem will be compatible with any computer that has a standard serial port. If you buy an internal modem and outgrow your present computer system, it will not be possible to use your modem with a new computer system unless the new machine can accommodate the same plug-in peripheral boards as the old one. Likewise, if you own two different computers, you may want to get a standalone modem so that you will be able to use the modem with either system. For most users, a standalone modem is likely to be a better investment than an internal model. Choosing a modem to use with a Macintosh. Modems are usually connected to a Macintosh via a cable that plugs into the "modem" serial port on the back of the computer. In order to establish reliable connections at modulation speeds of 9600 bps or higher (or lower speeds using MNP-5 or V.42bis data compression), it is generally necessary to use a special "hardware-handshaking" cable. Not all Macintosh modem cables support hardware-handshaking. Be sure to inquire whether any modem cable that you are considering purchasing has this capability. The original Macintosh models--the Macintosh 128K, 512K, and 512KE-- cannot use a "hardware-handshaking" cable, and cannot use the same cables as later Macintosh models because the serial ports on those machines use different connectors. If you own one of these early Macintoshes, it would probably be best for you to buy a 2400 bps modem. Choosing a modem to use with an IBM PC or compatible computer. Unless you are using an internal modem, you will need to have one free serial port to connect a modem. Some PCs do not come with a serial port, as was the case with the original IBM PC. Today most PCs come with two serial ports. If your computer's serial ports are already being used (perhaps by a serial mouse and a serial printer) or if your computer does not have a serial port, you can plug a serial interface card (sometimes called an "asynchronous communications adapter") into a free expansion slot or use an internal modem instead. You should be aware that DOS was originally designed to support a maximum of two serial ports (COM1: and COM2:). It nevertheless is possible to have a COM3: and COM4:, but the way additional serial ports are accessed is not completely standardized. If you need to use COM3: or COM4: for your modem, you will need to make sure that the communications program that you are using will be able to access it. You may also need to change the default port address or interrupt request (IRQ) line to avoid conflicts with other hardware. (There are often switches or jumpers on serial interface cards that allow you to change the IRQ and whether the port is addressed as COM1:, COM2:, COM3:, or COM4:. For information on how you might do this, you will need to consult the manual that came with your computer or serial interface card.) Note that these issues also apply to internal modems; internal modems in effect have a serial port built into them that must be addressed as COM1:, COM2:, COM3:, or COM4:. There is one other issue related to serial ports that you may need to be aware of when connecting a modem. The original IBM PC, IBM PC XT, and older compatible computers normally use a serial communication chip called an 8250 UART (Universal Asynchronous Receiver/Transmitter) that is designed to operate at a maximum of 9600 bps. Communications between the modem and PC normally go through this UART chip. Note that if you are using a modulation speed of 9600 bps and are using data compression protocols, the serial port must be able to operate at speeds greater than 9600 bps. The IBM PC AT and many computers compatible with the PC AT use a more advanced chip called a 16450, which can operate at higher speeds. Nevertheless, even the 16450 can cause performance problems, particularly on computers that are running Microsoft Windows. The more recent 16550 UART, which is used on many newer IBM compatible computers, provides much better performance, although not all communication software (particularly older software) can take advantage of the increased performance of this chip. If your computer has an older UART, you can sometimes simply remove the old UART from its socket and plug in a new one. (All three of these UARTs fit into the same sockets. The new UARTs are fully backwards compatible with the older ones.) However, if the UART is soldered onto the computer's motherboard or serial interface card, you may have to use a plug-in serial interface card with a newer UART or use an internal modem with its own UART. Software compatibility. One additional consideration in selecting a modem is software compatibility. A modem will perform functions such as dialing a phone number or answering a call only when it is given an instruction to do so, generally by the communications software running on the microcomputer or workstation. Most communications programs only support the instructions used by the most popular modems. Virtually all modems currently on the market use some variant of the "AT" command set originally developed by Hayes Microcomputer Products, Inc. (This command set is referred to as the "AT" command set because each sequence of commands normally begins with the letters "AT," which stand for "attention.") The AT command set has been extended to take advantage of advances in modem technology (such as higher speeds, new error correction and data compression protocols, and the ability to send and receive faxes), but these extensions often differ from manufacturer to manufacturer. In order for some communications software to run properly (particularly if you are going to use your modem's advanced features), it must be configured for the specific model of modem used. In particular, if you are considering buying a high-speed modem, it is a good idea to find out if the software that you want to use with it has been tested with that particular modem. Generally, if you buy a modem from a major manufacturer, you should not run into too many compatibility problems. You should also be aware that some communications software may not perform adequately on certain computers. In particular, at higher modulation speeds, particularly when data compression is also being used, older microcomputers may not be able to keep up with the amount of data being transmitted. For example, some terminal emulation programs running under Microsoft Windows on slower computers cannot keep up at higher modulation speeds. You may have to experiment with more than one communications program before you find one that performs adequately with your computer. In some cases, it might be best for you not to use the maximum modulation speeds and data compression capabilities offered by your modem. The Workstation Software Support Group (WSSG) on campus distributes terminal emulation software for both Macintoshes and IBM PCs and compatible machines free of charge, but WSSG has not yet tested these programs extensively at higher modulation speeds. These programs are basically no-frills applications that work reasonably well with campus computers for most applications, but it is not clear how these programs will perform at high speeds in all cases. WSSG is currently evaluating other terminal emulation programs for the campus that might be easier to use, provide more features, or offer better performance. Other Features to Look for When Selecting a Modem There are a number of specific features that you might want to look for when selecting a modem: + Built-in speaker. A built-in speaker will allow you to monitor the progress of a call, so that you will know immediately if you, for instance, reach a wrong number, or if the line is busy. Although speakers are found on most modems now being sold, the built-in speakers on some modems have volume levels so low that it is impossible to hear them in a moderately noisy office. In most cases you can turn off the speaker if it becomes distracting, but some modems that include speakers do not have adjustable volume. Standalone modems sometimes come with a volume control similar to that on a portable radio. Often the volume can be adjusted through software. + Indicator lights and displays. As mentioned above in the discussion of internal versus standalone modems, indicator lights on a standalone modem can be a very useful feature. Many external modems have eight or more indicator lights, and some models, as mentioned above, have alphanumeric displays. + Non-volatile memory. Many modems include circuitry to store configuration information such as phone numbers and communications settings in non-volatile memory. Although most communications programs allow you to store this type of information on a disk, it may still be a convenience to have this information stored in the modem itself. + Special circuitry for noisy lines. Some modems provide special circuitry to work well even on very noisy phone lines. If you are going to be making long distance connections with remote computers, then you should find out whether a modem you are considering will work adequately on noisy phone lines. In general, modems are more affected by line noise at higher speeds than at lower speeds. + Security features. Some modems have security features designed to prevent unauthorized users from connecting to a remote computer. For example, some modems can automatically hang up after answering an incoming call and receiving a password, and the modem that received the call can then automatically call the user back. + Fax capability. Even if you are planning to use a modem just to connect to other computers, it still might be worth considering a modem with fax capability because the difference in price is often slight. If you choose to get a fax modem, you should be aware that you will need special software in order to use the fax capability. Generally, fax modems come bundled with software for this purpose. Note that some fax modems can send faxes but not receive them; if you want to send and receive faxes, you will need to make sure that the modem has that capability. Also, if you plan on making extensive use of fax capabilities, you might want to think about getting a fax modem that uses the V.17 protocol, which can send faxes at up to 14400 bps (compared with 9600 bps for modems that use the more common V.29 protocol). + Voice and automatic switching capabilities. Some modems can determine whether an incoming call is a voice call, a modem call, or a fax, and route the call accordingly. Some modems even offer voice-mail capabilities (such as the ability to store digitized voice messages). + Macintosh-specific and PC-specific bundles. A number of modem manufacturers offer bundles that include a standalone modem and cable (or an internal modem) and software designed to work with a specific type of computer. Sometimes the bundled software is not of the highest quality, but the convenience of having everything together in one package is often worth the fairly small extra cost. (Sometimes the bundled software is of good quality.) In addition, these bundles often include subscriptions or discounts to services such as CompuServe. + Support. Most modems come with warranties of at least two years, but five-year and seven-year warranties are not uncommon. Some vendors even offer lifetime warranties. In addition to warranty information, you should also find out what sort of support the vendor provides. Some vendors provide toll-free help lines and bulletin board systems. Also, find out if the vendor has an upgrade policy, particularly if you are buying a high-speed modem. High-speed modems have become popular only fairly recently, and the technology is still fairly new. Vendors often release upgrades in the form of new "firmware" or read-only memory (ROM) chips in response to problems that are discovered. As with any purchase, you should try to get a thorough demonstration of any modem that you are seriously considering. It is also a good idea to look at the documentation to see whether it is comprehensible. Educational Discounts In addition, at the time this article was being prepared, The Scholar's Workstation, the campus computer store, was investigating the possibility of selling high-speed modems to the campus community at a significant educational discount. Before making a purchase, it would be a good idea to check to see if educational prices on modems are available. For More Information This article just scratches the surface of the subject of modems and telecommunications. If you would like more information, there are a number of very good books on this subject. A few that were useful in the preparation of this article were the following: Becker, Philip L., with Mike Robertson, Mark Chambers, Phil James, and Alan C. Elliott. Introduction to PC Communications. Carmel, Indiana: Que Corporation, 1992. Dvorak, John C., and Nick Anis. Dvorak's Guide to PC Telecommunications, 2nd ed. Berkeley, California: Osborne McGraw-Hill, 1992. Freed, Les, and Frank J. Derfler, Jr. PC Magazine Guide to Modem Communications. Emeryville, California: Ziff-Davis Press, 1992. Taylor, Stephen. Telecommunications: The Macintosh Modem Book. New York: MIS:Press, 1992. In addition, there are three very useful documents available in electronic form: + comp-sys-mac-comm-faq.txt. This frequently-asked question list is posted periodically to the comp.sys.mac.comm Usenet newsgroup. It includes extensive information about modems from a Macintosh perspective, including information on how to make a "hardwarehandshaking" modem cable, Macintosh file formats, and filetransfer protocols. + Handouts from the "Using Your Macintosh and Modem to Connect to Campus Computers" short course. These handouts prepared by Aron Roberts include an excellent discussion of modems in addition to information specific to the Macintosh Kermit terminal emulation package. + What You Need to Know About Modems. This document written by Patrick Chen provides an excellent discussion of modem protocols, considerations for using modems with Macintoshes and IBM PCs and compatible computers, and discussions of specific modems and software. These documents are available for campus Macintosh users on the Information Central volume of the campus AppleShare file server Cornucopia in the folder "Technical info:Modem info." The "Using Your Macintosh and Modem to Connect to Campus Computers" handouts are in a folder called "Modem short course handouts." The What You Need to Know About Modems document is in a text file called "Modem Guide." For information on accessing Cornucopia, please see the handout Software for your Macintosh via the Cornucopia File Server (MIC 2.4.10), available from Workstation Consulting. You can also obtain copies of these online documents by bringing blank disks to the Workstation Consulting office in 264 Evans Hall, which is open weekdays from 10 a.m. to 4 p.m. Both What You Need to Know About Modems and comp-sys-mac-commfaq.txt are also available via anonymous FTP from sumexaim.stanford.edu in the directory /info-mac/report under the titles "comp-sys-mac-comm-faq.txt" and "modem-guide-11.hqx." The file "modem-guide-11.hqx" is a StuffIt file in BinHex format (an earlier version of this guide is available in plain text form under the title "modem-guide-10.txt"). If you need information on how to access these online documents, feel free to contact Workstation Consulting. If you are unable to access these documents online, some of them are available as handouts from the Workstation Consulting office. If you would like more information or have questions about modems, feel free to contact Workstation Consulting. ************************************************************************ CCNEWS Copyright Notice If you use any of these articles, in whole or in part, in printed or electronic form, you are legally and morally obligated to credit the author and the original publication name, date, and page(s). We suggest that you also inform the author or editor of your intention to use this article, in case there are updates or correction that he or she might wish to suggest. 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