COURIER HIGH SPEED MODEMS CHAPTER 3. QUICK STARTêASYNCHRONOUS OPERATIONS ASYNCHRONOUS/SYNCHRONOUS COMMUNICATIONS Courier high speed desktop and rack modems are capable of asynchronous and synchronous communications. Terminals are usually capable of one type of communications or the other. The typical personal computer, however, is equipped to communicate only asynchron- ously. Most of the operational information in this manual is organized around asynchronous communications. During asynchronous communications, the computer adds Start and Stop bits to each data character before sending it to the modem over the serial port, and expects received data to be in the same format. Synchronous data transfer is based on synchronized timing between two communicating devices, not on data format, and is usually required by mainframes and other large computers. To exchange data synchronously, a personal computer requires specialized equipment, including the installation of a synchronous communications card with a synchronous port. If you will be making synchronous connections, you'll find the modem easy to use. Just follow the instructions in Chapter 7. INITIAL MODEM SETTINGS This manual covers the operation of three Courier models, the Courier HST Quick Start 3-1 COURIER HIGH SPEED MODEMS Dual Standard, Courier V.32 bis, and Courier HST. The modems are factory-set for compatibility with their own type of modem. ù Dual Standard modemsêB0êso that they connect at high speeds with both V.32 bis and HST modems ù V.32 bis modemsêB0êto connect at high speeds with V.32 bis and V.32 modems ù HST modemsêB1êto connect at high speeds with HST modems The above settings do not affect how the modems connect at speeds of 2400 bps and below. Leave the modems set to their factory defaults, B0 or B1. The exception is when an HST modem is to answer overseas calls, in which case you should set it to B0. 3-2 Quick Start COURIER HIGH SPEED MODEMS The modem is shipped ready for use except for Transmit Data flow control. This type of flow control is required for calls under error control, and when the computer sends data to the modem faster than the modem can send it over the phone link. How you set your modem depends on whether or not your machine or software support flow control, and what type of flow control they allow. Use the guidelines that follow. Recommended Settings The following modem settings, plus the factory defaults, are recommended for data reliability and for the best throughput. Check the Settings Supplement that came with the modem to see if your communications program is listed and what it supports. Check your computer or terminal documentation as well to see if your machine supports the recommended settings. If not, see Alternative Settings, after this section. Modem Setting Result &H1 Hardware flow control: the modem uses Clear to Send (CTS) at the RS-232 interface to control the data flow from the computer. This is the more reliable type of flow control. &B1 The data rate between the modem and the computer (Data Terminal Quick Start 3-3 COURIER HIGH SPEED MODEMS Equipment, or DTE) is fixed; it does not switch to match the phone link rate when the modem connects with a remote modem. Software Setting Result 19.2K bps The rate between the modem and the computer (DTE) Fixed rate is always 38.4K or 19.2K bps. This allows calls at the maximum speed of 14.4K bps on the phone line. The 38.4K rate provides the greatest efficiency when a call is under error control and data compression. NOTE: If you use an IBM PC or compatible and your software supports the above settings, we recommend that you write them to nonvolatile memory with the &W command as defaults. If 3-4 Quick Start COURIER HIGH SPEED MODEMS one of these conditions isn't true, review the following alternatives and guidelines. Alternative Settings 1. Your machine or software doesn't support Clear to Send, but your software supports XON/XOFF signaling: &H2 The modem sends the DTE Ctrl-S and Ctrl-Q (XOFF/XON) characters to control the flow of data. But see Guideline #2 below. &B1 As above, under Recommended Settings, providing your software supports a fixed DTE rate. 2. Your machine or your software does not support Clear to Send, and you're using an Xmodem-type file transfer protocol: &H0 Flow control disabled (factory setting). Do not use software flow control (&H2) because the protocol control characters will be misinterpreted as flow control characters, and you risk losing data. &B0 The DTE rate switches to match the connection rate of each call. Required because there is no flow control. NOTE: We do not recommend the use of Ymodem-G or Zmodem without the use of error control and flow control. Quick Start 3-5 COURIER HIGH SPEED MODEMS 3. Your system doesn't support either Clear to Send or XON/XOFF signaling: &H0 Flow control disabled (factory setting). &B0 The DTE rate switches to match the connection rate of each call. Required because there is no flow control. &M0 Error control disabled; recommended because there is no flow control. NOTE: We recommend that this configuration not be used for calls above 2400 bps. 3-6 Quick Start COURIER HIGH SPEED MODEMS 4. Your software does not support a fixed rate: &B0 Factory setting. The DTE rate switches to match the connection rate of each call. This does not affect error control or flow control. You will not, however, gain the throughput efficiency possible when the DTE rate can be fixed at a higher rate than the link rate. In addition, at the factory setting for data compression, &K1, the modem disables compression when the link rate is set to &B0. 5. Your maximum computer rate is 9600 bps: S34=3 This disables higher-speed V.32 bis modulation. The modem operates as a V.32 modem, with a maximum DTE and link rate of 9600 bps. (Does not apply to HST modems.) &H1 Hardware flow control (CTS), or &H2 for software flow control. &B1 Fixed DTE rate of 9600 bps, recommended for HST modems. &M4 Error control factory setting required, or &M5. 6. You are calling a non-MNP modem: S27=16 Disable MNP handshaking. A non-MNP modem may misinterpret the MNP link request and prevent a Quick Start 3-7 COURIER HIGH SPEED MODEMS successful connection. This does not apply for remote V.42 modems with error control enabled. 7. You are transferring compressed files: &K3 This disables MNP compression, which does not work successfully with files that are already compressed. If V.42 bis compression is negotiated, you will gain optimal throughput. DATA FORMAT The Courier and the remote modem must use the same ten-bit data format. The following table lists the allowable word lengths, parity and Stop bits. If a remote modem requires 2 Stop 3-8 Quick Start COURIER HIGH SPEED MODEMS bits and the format totals 11 bits, the second Stop bit is not counted. StartWord Parity Stop BitsLength (1 Bit) Bits 1 7 Even, Odd 1 Mark, Space 1 7 None, Even, Odd, 2 Mark, Space 1 8 None 1, 2 STORING DEFAULTS IN NONVOLATILE MEMORY Write your default configuration to nonvolatile memory (NVRAM) with the &W command. The following example sets the modem for the current session and also stores the settings as defaults. The defaults are loaded from NVRAM when the modem is powered on if DIP switch 10 is UP. Be sure to insert &W last in the string, before the Carriage Return. AT &B1 &H1 &W DIALING Use the following command format. The modem defaults to pulse dialing: the T in the command enforces tone dialing. The maximum number of characters in a command string is 40. ATDT phonenumber To redial the number, which the modem stores in a last-dialed number buffer, use the following command: Quick Start 3-9 COURIER HIGH SPEED MODEMS ATDL LINK RATE NEGOTIATION During link negotiation (handshaking), the modems negotiate the highest possible rate, depending on each modem's capabilities. The Courier automatically switches rates to match the rate of the remote modem, within the following rate ranges: 14.4K, 12K, 9600, 7200, 4800, 2400, 1200 bps and, without error control, 300 bps. For more detailed information on handshaking, see Appendix A. ONLINE FALLBACK When online at high speeds, the modems perform Adaptive Speed Leveling. They monitor the condition of the phone line. If they sense disturbances that threaten data integrity, they fall back and retrain (resynchronize) at the next lower speed in their fallback range: 14.4K, 12K, 9600, 7200, 4800 bps. If conditions remain poor, Courier modems continue to fall back to the next lower speed. As line improvements occur, they fall forward to the next higher speed, up to the link rate of the call. 3-10 Quick Start