Chapter 7 - Troubleshooting
The Modem Cannot Connect When Answering
•The default DTR Control command (&D2) inhibits autoanswer. To enable autoanswer, change DTR Control to &D0, and make sure &Q0, &Q1, &Q5, or &Q6 is also set. For more information, see the &D command in the AT Command Reference Guide on the CD shipped with your modem. For information on changing the modem’s default configuration, see “Step 3: Install and Configure Your Software” in Chapter 2.
•Autoanswer might be disabled. Turn on autoanswer in your datacomm program or send the command ATS0=1 (ATS0=2 if you have Caller ID service) to your modem in terminal mode.
File Transfer Is Slower Than It Should Be
•You might have an older UART. For best throughput, install a 16550AFN UART or a
•If you are running under Windows 3.1 and have a 16550AFN UART, you must replace the Windows serial driver, COMM.DRV, to take full advantage of the UART’s speed.
•If you are using a slow transfer protocol, such as Xmodem, try Zmodem or Ymodem/G instead.
•Is your line noisy? If there is static on your line, the modem has to resend many blocks of data to insure accuracy. You must have a clean line for maximum speed.
•Are you downloading a compressed file with MNP 5 hardware compression enabled? Since hardware data compression cannot compress a file already compressed by an archiving program, the transfer can be marginally slower with data compression enabled than with it disabled.
•Does your Internet service provider (ISP) use the same 56K protocol as your modem? The default setting of your modem is to connect using either the 56K or the V.90 protocol, depending on which one the ISP modem is using. If your ISP uses the X2 protocol, the maximum speed you will be able to connect at is 33,600 bps. Check with your ISP to see which protocols it supports, and check the
•Try entering the &V1 command to display information about the last connection, making a screen print of the connection statistics, and checking for parameters that might be unacceptable.
Data Is Being Lost
•If you are using data compression and a high speed serial port, set the serial port baud rate to four times the data rate.
•Your UART might not be reliable at serial port speeds over 9600 bps or 19,200 bps. Turn off data compression, reset your serial port speed to a lower rate, or replace your serial port with a faster one.
•Make sure the flow control method you selected in software matches the method selected in the modem. If you are using the modem with a Macintosh, you might have the wrong cable for hardware flow control.
•Try entering the &V1 command to display information about the last connection, making a screen print of the connection statistics, and checking for parameters that might be unacceptable.
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