COURIER HST CHAPTER 1 INTRODUCTION ADVANCED FEATURES The USRobotics Courier HST modem represents powerful, advanced electronic design that gives you optimal speed and accuracy. Trellis Coded Modulation Trellis coded modulation is a convolutional coding technique that makes data transmission less vulnerable to errors caused by phone network impairments. It can tolerate twice the telephone channel noise power as 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. Asymmetrical Modulation At top speed, data flows in one direction at 9600 bits per second and at 450 bits per second in the other. The modems automatically switch the high-speed channel on demand, i.e., depending on which transmitter has the most data to transmit. In practice, the modems seldom need to reverse channels, since the asymmetric design reflects typical communications sessions -- brief messages typed at one end of the link, files sent from the other. The asymmetrical approach provides the most efficient and economical strategy for using ordinary phone channels at high speeds. Error Control The MNP protocol is a widely used, sophisticated method of ensuring data integrity at 2400 and 1200 bps. A USRobotics proprietary protocol similar to MNP is used at 9600, 7200 and 4800 bps. With error detection and retransmission of errored data blocks, plus flow control, you can be assured that your data is sent and received with reliability. Data Compression/Throughput Gains The Courier HST compresses data to pack more information into each second of your calls, enabling throughput of up to 19.2K bits per second. In addition, the implementation of larger data blocks eliminates much of the added overhead (protocol information) associated with less powerful error-control protocols. Rate Selection/Flow Control The Courier HST modem's flow control buffer allows you to set your computer/modem rate as high as 19.2k bits per second, for 1-1 COURIER HST even greater performance. Flow control settings protect transmissions from data loss. Online Fallback/Fall Forward During 9600-bps communications, if severe line impairments threaten the integrity of data transfer, the modems fall back and retrain at 7200 bps. If necessary, they fall back further to 4800 bps. As line improvements occur, the modems automatically shift up to the next higher speed. Programmable Nonvolatile Memory You can tailor your own default settings for the Courier HST and store them in nonvolatile random access memory (NRAM). Each time the computer is powered on, the modem operates at the settings you've specified. Diagnostics After each call, you can display a Link Diagnostics screen containing information about the call. Two S-Registers also store information on the reason for a call's disconnect. Shorter Response Time 9600-bps modems are generally most efficient for file transfers. You'll find that the Courier HST also offers faster response times during interactive sessions. THE COURIER PRODUCT FAMILY In addition to the Courier HST's new features, the modem incorporates the same popular capabilities of other products in the USRobotics Courier line: Link Negotiation Fallback The Courier HST automatically falls back to 2400, 1200, and 300 bits per second, in both Originate and Answer Modes, to match a lower rate of a remote modem. You can optionally set local interface and link rates at fixed speeds. 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. 1-2 COURIER HST 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 Display On command, the modem displays its current settings, a handy way to check your transmission rate, S-registers and other operational controls. HELP Screens You can also display screens that summarize the command sets, Dial command options, and S-register functions. Bottom Panel Reference Operational 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 requirements. Automated Redialing You can put the modem into Repeat Mode to automatically 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 "number," such as 800-"DIAL USR" (USRobotics' Sales Department). Adaptive Dialing You can set the modem to first try Touch-Tone dialing. If tone dialing doesn't work on the line, the modem automatically switches to the slower type, pulse (rotary). Automatic Retraining Retraining (a resynchronization with the remote modem) occurs if the modem detects line disturbances that might affect data reliability. Retraining occurs at 9600 and 2400 bps. (Appendix E-3 contains more information.) 1-3 COURIER HST COURIER HST COMPATIBILITY The Courier HST offers upgrading to 9600 bps while maintaining compatibility with most installed 2400/1200/300 bps, dial-up modems and existing software. Its compatibility features include the following: o Can be used with any computer or terminal that is compatible with the RS-232C standard interface. o Can be used with any computer or terminal that uses ASCII, the standard character code supported by most equipment manufacturers. o Connects with any modem whose signal scheme is compatible with the following standards at the given data rate: 300 bps Bell 103 1200 bps Bell 212A 2400 bps V.22bis 9600 bps USR-HST o Uses the HST error control protocol at 9600 bps and the MNP error control protocol, Service Levels 1-5, at 2400 and 1200 bps. o Is fully FCC-certified for the uses described in this manual. 1-4