CHAPTER ONE. FEATURES AND COMPATIBILITY INTRODUCTION Congratulations! The Courier modem you've purchased represents powerful, advanced electronic design that offers exceptional reliability, compatibility and flexibility at all standard rates up to 14,400 bits per second (bps). Courier HST modems connect with each other up to 16,800 bps. The transmission rate between the computer and modem, depending on your equipment and software support, can be as high as 57,600 bps. The following features and capabilities assure you of superior reliability and performance. High Speed CallsêAdaptive Speed Leveling (ASL) All Courier high speed modemsêHST, V.32 bis and Dual Standardêconnect at 9600, 12K and 14.4K bps, with 16.8K the maximum rate on HST-to-HST connections. In addition, our high-speed modems monitor phone line quality and perform Adaptive Speed Leveling. Like most high speed modems, Courier modems fall back to the next lower speed, for example, 12K, then 9600, if poor line conditions warrant. Unlike other modems, however, that stay at the lower rate for the rest of the call, Courier modems detect improved line conditions and shift upward again to the next higher speed. ASL keeps the modems online, always operating at the highest possible speed, and constantly ensuring data integrity. Error ControlêV.42/MNP Data integrity is ensured when the modems connect with remote modems that use the V.42 (LAPM), USR-HST, or MNP error control protocols. Error control is available on calls at 1200 bps and above. Data CompressionêV.42 bis/MNP5 Data compression enables potential throughput of well over 50K bps on 14.4K or 16.8K bps connections. Couriers connecting under V.42 or HST error control use V.42 bis compression. Couriers connecting under MNP error control use MNP Level 5 compression. Achievable throughput of text and other types of files is listed in Appendix A. Flow Control/Variable Interface Rates Flow control, required under error control, also allows the local computer interface rate to be set higher than the link rate, enabling greater efficiency and throughput. If your equipment and software support high rates, data can be sent from the computer to the modem at 57.6K, 38.4K or 19.2K bps, regardless of the link rate. Voice/Data Switch Users have always been able to phone and make arrangements with another user before turning control of the call over to the modems. A new feature, a switch on the modem's front panel, allows you to change from voice to data and back again, without issuing a command. If you don't ordinarily use voice and data in the same call, you can assign the switch a different function that normally requires a command, such as resetting the modem. See Appendix E, Voice/Data, for instructions on voice/data switching. Trellis Coded Modulation At speeds above 7200 bps the Courier uses trellis coded modulation. This technique makes high speed data transmission less vulnerable to errors caused by the phone network. The modems can tolerate twice the amount of noise in the telephone channel than they could with conventional modulation (quadrature amplitude modulation, or QAM), so there are fewer error control retransmissions. Trellis coded modulation is also less susceptible to impulse-type noise. Asynchronous/Synchronous Capability Courier high speed modems operate synchronously as well as asynchronously. A personal computer equipped with a syn- chronous interface adapter can call computers that use standard synchronous protocols. See Chapter 7 for more information. Programmable Nonvolatile Memory You can tailor your own default settings and store them in nonvolatile random access memory (NVRAM). Each time the Courier is powered on, it operates at the settings you've specified. Link Rate Negotiation The Courier automatically lowers its link rate to match a lower rate of a remote modem, in both Originate and Answer Modes, allowing connections with a wide range of installed modems. Link Diagnostics After each call, you can display a Link Diagnostics screen containing information about the last call, including the number of data characters transferred, line statistics, the call's rate and the reason the call was disconnected. Modem Diagnostics New CCITT V.54 loopback testing with the &T command options, and earlier Courier Register S16 test options are available. The modem performs three loopback tests: analog, digital, and remote digital. See Appendix F for information. Inactivity Timer You can set the modem to automatically hang up after a specified number of minutes if there is no activity on the phone line. Call Duration Reporting The modem records the duration of your calls in hours, minutes, and seconds. This feature enables you to display and print an audit of your calling activities. You can optionally use the modem clock as a real-time clock. Call Progress Detection An optional set of result codes (screen messages) lets you know when a line is busy, a person rather than a modem has answered the phone, there is no dial tone, or the distant phone is ringing. Modem Settings Displays On command, the modem displays its current settings, a handy way to check your transmission rate, S-Registers and other operational controls. The modem also displays the defaults stored in nonvolatile memory and the factory defaults stored permanently in read-only memory. HELP Screens The modem displays screens that summarize the command sets, Dial command options, and S-register functions. Bottom Panel Reference Command summaries and other information are printed on the bottom of the modem case. A Dual In-Line Package (DIP) switch guide makes it easy to tailor the switch settings to your terminal or software requirements. Dialing the Last Dialed Number The modem has a buffer that stores each dialed number until it is cleared by another Dial command. A few keystrokes cause the modem to redial the number in the buffer without your having to enter the number again. Automated Redialing You can put the modem into Repeat Mode to continuously redial if a previous dial attempt fails to connect. This is especially useful in dialing services whose lines are often busy. Quote Mode Set the modem to Quote Mode if you want it to dial an alphabetic acronym instead of a numeric number. COMPATIBILITY The Courier adheres to the following standards, ensuring compatibility with a wide base of installed modems. Unless otherwise indicated, HST, V.32 bis and Dual Standard modems all conform to the listed standard. USR-HST 16.8K, 14.4K/12K/9600/7200/4800 bps (Dual Standard and HST modems) CCITT V.32 bis 14.4K/12K/9600/7200/4 800 bps (Dual Standard and V.32 bis modems) CCITT V.32 9600/4800 bps (Dual Standard and V.32 bis modems) CCITT V.22 bis 2400 bps Bell 212A 1200 bps (also CCITT V.22) CCITT V.23 1200 bps with 75 bps back channel (British phone system) CCITT V.25 Answer sequence for calls originating outside the U.S. and Canada Bell 103 300 bps (CCITT V.21 optional) CCITT V.42 LAPM error control, 1200 bps and higher CCITT V.42 bis Data compression, 1200 bps and higher MNP Levels 2, 3 and 4 error control, level 5 data compression, 1200 bps and higher CCITT V.54 Analog, digital and remote digital loopback testing Other compatibility features include the following standards and certification: ù Can be used with any computer or terminal that is compatible with the RS-232 standard interface. ù Can be used with any computer or terminal that uses ASCII, the standard character code supported by most equipment manufacturers. ù Connects with older systems whose equipment operates at rates varying between 110 and 300 bps. ù Connects in synchronous mode at standard rates with any system using a synchronous protocol compatible with your synchronous interface equipment. ù Is fully FCC- and DOC-certified for the uses described in this manual.