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------------------------------------------------------------------------ Searchlight BBS Guide To High Speed Operations Using the US Robotics Courier HST ------------------------------------------------------------------------ The following document discusses in detail the setup and use of the US Robotics Courier HST modem with Searchlight BBS, including the use of "high speed locked DTE" mode as implemented in Searchlight versions 1.73 and later. While the specific command strings and switch settings given here are for the US Robotics modem, the concepts discussed should apply equally to other high speed modems, such as the Hayes 9600. There are two distinct modes of operation supported by the US Robotics high speed modems, called "variable DTE" mode and "locked DTE" mode. In variable DTE mode (DTE refers to the baud rate used for communication between your computer and the modem), the USR operates exactly like most standard 1200/2400 baud modems, except of course with the addition of a 9600 baud speed. Most software, including all versions of Searchlight, support the USR in this mode. Locked DTE mode is a special mode which can allow the HST, under good line conditions, to provide data speeds of up to 14.4k baud (when connected to another HST) and to provide somewhat better throughput at all speeds, due to data buffering and compression. However, the locked DTE mode is more difficult to set up and has some drawbacks. We strongly suggest that you read your US Robotics manual and this document carefully, and fully understand how locked DTE mode works, before you attempt to use it on your BBS. -- (I) Dip Switch Settings --------------------------------------------- The following dip switch settings are recommended for all modes of operation: Switch Setting Function ------ ------- -------- 1 Up Enables normal DTR operations. 2 Up Enables verbal result codes. 3 Down Displays result codes. 4 Up Modem echos commands. 5 Up Enables auto-answering. 6 Up Enables true normal Carrier-Detect function. 7 Up Enables result codes in all modes. 8 Down Normal AT command set recognition. 9 Up Escape code recognition. 10 Up Loads configuration from NRAM at power-up. -- (II) Variable DTE Operations ---------------------------------------- The following communications parameters (as set via Menu #3 in the Searchlight CONFIG program) are recommended for normal, variable DTE rate operations: 2. Support 300 Baud .............. Yes 3. Support 1200 Baud ............. Yes 4. Support 2400 Baud ............. Yes 5. Support 4800 Baud ............. Yes 6. Support 9600 Baud ............. Yes 7. Support 19200 Baud ............ No 8. Remote Init String ............ ATM0H0X1S0=1&B0&H0! 9. Local Init String ............. ATH1! 10. Baud Detect Method ............ Modem Msg 11. Locked Baud Rate .............. None 12. Hardware Flow Control ......... Off 13. Hardware Modem Breaks ......... Off 14. Output Buffering Factor ....... (any value) Note the following: Support for 300 baud may be disabled if you wish. The init strings given assume that the factory defaults are in place for the remaining parameters. If you are unsure, you may want to reset your modem to its factory defaults (using the AT&F command) before you begin. If your modem will be used primarily with Searchlight BBS, you may want to write the above initialization parameters to the modem's nonvolatile memory (use the AT&W command). For additional parameters, refer to your HST manual. The "Modem Msg" baud detect method will work correctly as long as any "X" modem command, except X0, is in force. You can use the "Key Hit" method if you wish. Please notice that because the HST modem tries to establish a number of things each time it connects to another modem, such as the MNP level, it takes longer for the HST to connect after answering the telephone than a standard 1200/2400 baud modem. This is normal. The output buffering factor may be set to any appropriate value for your system, as described in the Searchlight documentation. As always, we recommend setting the buffering factor to zero if you experience any unusual system lockups or modem problems when running Searchlight. In this mode, the HST modem will behave much like a standard Hayes- compatible 300/1200/2400 baud modem. When you start Searchlight BBS, it opens the communications port at 9600 baud, issues the remote init string to the modem, and waits for a connection. When the modem receives a call and establishes a connection, it will issue a "CONNECT xxxx" message, indicating the speed of the connection, and immediately change to that speed. Searchlight, after reading the CONNECT message, will also switch speeds, and the call will proceed at the specified baud rate of 300, 1200, 2400 or 9600 baud. After the call terminates, the modem is reset to 9600 baud for the next call. The advantages of using variable DTE mode are simplicity of setup and compatibility with other software, such as external transfer protocols or DOOR programs, which may not support locked DTE operations. Since the HST does not use extensive modem buffering and flow control in this mode, it will not interfere with Searchlight's flow control operations, as it can in locked DTE mode. -- (III) Locked DTE Operations ----------------------------------------- Locked DTE means that the baud rate at which Searchlight BBS opens and sends data to the communications port is "locked" at a fixed, high rate of speed, such as 19,200 baud, rather than being variable depending on the speed of the connection. During a locked DTE call, Searchlight will ALWAYS communicate with the modem at the "locked" baud rate, even though the HST may be communicating with the remote modem at any baud rate from 300 to 14.4k baud. In order for Searchlight to be able to send data to the HST modem at speeds faster than the modem is transmitting, the HST provides a method of "flow control". Flow control means that when the HST has all the data that it can handle at one time, it can ask Searchlight to stop transmitting data for a short period of time until it is ready to begin accepting data again. To use locked DTE, set your CONFIG parameters as follows: 2. Support 300 Baud .............. Yes 3. Support 1200 Baud ............. Yes 4. Support 2400 Baud ............. Yes 5. Support 4800 Baud ............. Yes 6. Support 9600 Baud ............. Yes 7. Support 19200 Baud ............ No 8. Remote Init String ............ ATM0H0X1S0=1&B1&H1&K0&Y0S15=8S38=2! 9. Local Init String ............. ATH1! 10. Baud Detect Method ............ Modem Msg 11. Locked Baud Rate .............. 19200 or 38400 12. Hardware Flow Control ......... On 13. Hardware Modem Breaks ......... Off [SEE NOTE BELOW] 14. Output Buffering Factor ....... 0 Please note the following: In NO CASE should field 7 (Support 19200 Baud) be set to "Yes", since this rate of speed is NOT supported by the modem. All calls which are completed by the HST at high speed (9600 baud or 14.4k baud) will be reported by the HST, and recorded by Searchlight, as 9600 baud calls. The &B1 parameter is the switch that sets the HST for locked baud rate operations. Field 11 should be set to 19,200 or 38,400 for best performance, but only if your communications ports can handle those speeds. See note below. Hardware (CTS) flow control MUST be enabled for reliable high speed operations. WARNING: Your serial port and modem cable MUST support this feature. If they do not, your entire system can EASILY hang while Searchlight sits waiting for a clear-to-send from the modem! The only way out if this happens is to reboot and try it again. The &K0 modem command DISABLES modem data compression. I recommend this setting because data compression works only on textual data, such as when reading messages interactively, and tends to degrade the transmission of archived or binary files. Usually, file transfer speed is considered most important. If you don't do many file transfers (or if most of your files are text files), use &K1 to enable compression. Field 13, Hardware Modem Breaks, enables Searchlight to use "hard" RS232 breaks to control the modem's output buffers. I suggest leaving this Off for now, because it appears to lock-up some systems during non- MNP calls. Output buffering (field 14) should be set to zero when using locked DTE, since the modem provides its own buffering in locked modes. See the discussion below for more information. Modem register S15 is used to configure the modem's buffer size to 128 bytes during a non-MNP 1200 or 2400 baud call. This is the recommended setting as it will reduce hot key delays. Register S38 sets a hangup time delay for the modem after DTR is dropped. If your remote users report that your logoff screens or closing messages are not being fully received before the system hangs up, set S38 to a larger value. NOTE: The S15 and S38 registers are not available on some older model HST's. There are four main reasons why the HST modem can provide better perfomance in Locked DTE mode: (1) Buffering. The HST provides up to 3.5k of RAM output buffering while in locked mode, enabling the BBS to perform other operations while data is being transmitted. HOWEVER, Searchlight BBS also performs output buffering (when a nonzero Output Buffering Factor is specified). Therefore, this advantage is not as important when using Searchlight BBS as it is for those using other bulletin board software. (2) High Speed Connections. The HST is capable of communicating at baud rates of up to 14,400 baud with compatible HST modems. Because the communications ports on the IBM-PC can only be operated at fixed speeds of 9600 or 19,200 baud, using a locked baud rate of 19,200 is the ONLY way in which to allow the HST to make use of its special, high-speed connect rates. (3) Online Fallback. If the HST is operating at high speed but detects that the telephone connection is unusually "dirty" or unreliable, it can automatically "step-down" the transmission speed to the next lower baud rate (it will also "step-up" the baud rate if the line becomes clean again). This feature is only possible in locked DTE mode. (4) Data Compression. The HST can perform MNP data compression on most textual data transmitted through it. However, in order for data compression to have any effect on the total speed of the transmission, locked DTE rate must be used. Before you decide to use a locked DTE baud rate on your system, however, please note well the following comments and remarks: (1) The single most important concept to realize when dealing with the HST in "locked" mode is that the HST is a BUFFERED modem. Buffering means that it can accept data from the computer, store it in a RAM buffer, and transmit it to the remote user at a later time. While this has the effect of increasing throughput, it has the side effect of REDUCING, in some cases severely, the response time of Searchlight's own flow control commands- such as ^C, ^S, spacebar, and "hot" keys. For example, suppose a user requests to read a certain message. Searchlight will bring up the message and, almost instantly, "dump" the message into the modem's buffer at a high rate of speed. At this point, Searchlight, assuming the message has been sent, draws its usual options menu at the bottom of the screen, and waits for a response. Meanwhile, the modem is still transmitting the text in its buffer to the remote user. If the remote user decides to press a hot key, or pause or abort the message during this time, his request will NOT be honored- because Searchlight thinks the message has already been sent! Fortunately, the HST has certain commands which can be used to reduce the likelyood of this happening. However, you will always notice a delay in the response time to hot keys when using locked baud rates; the delay is most noticeable at lower baud rates, and when using MNP modems. (2) Many computers DO NOT support high speed (19,200 or 38,400 baud) operations! In particular, many older PC's and XT's cannot support these speeds. If your computer cannot support high speed, it may lock up or fail to operate correctly if high speed operations are attempted. You may have to purchase a replacement RS232 card capable of supporting high speed before you can use high-speed locked DTE on your BBS (try to obtain a board which uses the 164500 UART chip). (3) The data compression and error checking performed by the HST in high speed modes can speed up normal, interactive communications a great deal, but it can also slow down file transfers, particularly when you are transferring compressed files, binary files, or when using a protocol that employs small data packets (such as Xmodem or Kermit). You must determine which aspect of your BBS system is most important to yourself and your users. Use &K0 (disable data compression) in your modem init string if you want high-speed binary file transfers; use &K1 if you want compression of textual data. To minimize file transfer times, use a long-block protocol (such as Zmodem or Xmodem/1K) during an error checked (/ARQ) connection, and disable error checking if you need to use Xmodem or Kermit frequently. (4) Any external protocols you use, as well as any DOOR programs you use which perform their own modem i/o, MUST be able to recognise the "locked" baud rate and to perform the proper flow control handshaking with the modem. In particular, DOOR programs written for PCBoard version 12.0 systems will probably NOT run if the baud rate is locked at 19,200 or above. DOOR programs which use the PCBOARD.SYS files or the %B command-line parameter will be passed the correct (ie. locked) baud rate, but MUST perform CTS handshaking with the modem. DOOR programs which use Searchlight's modem support are not affected. (5) VERY IMPORTANT: The speed at which your BBS system operates is dependent on MANY factors besides the modem! The speed of your disk drives, your CPU, modem ports, operating system, etc. can all affect the total speed of your system. Even with high-speed modems attached, your BBS system may not be able to achieve the highest data speeds possible, due to these factors. In many cases, the benefits of running in locked mode aren't significant compared to straight 9600bps communications. Experiment to see what works best for you! ------------------------------------------------------------------------ Frank LaRosa 4/15/89