System information

Troubleshooting Dialin Connections 16-361
Dialin: Modem Cannot Send or Receive Data
Possible Causes Suggested Actions
Modem speed setting is not locked
Step 1 Use the show line exec command on the access server or router. The
output for the auxiliary port should indicate the currently configured
Tx and Rx speeds.
For an explanation of the output of the show line command, see the
“Using debug Commands” section earlier in this chapter.
Step 2 If the line is not configured to the correct speed, use the speed line
configuration command to set the line speed on the access server or
router line. Set the value to the highest speed in common between
the modem and the access server or router port.
To set the terminal baud rate, use the speed line configuration
command. This command sets both the transmit (to terminal) and
receive (from terminal) speeds.
Syntax:
speed bps
Syntax Description:
• bps—Baud rate in bits per second (bps). The default is 9600 bps.
Example:
The following example sets lines 1 and 2 on a Cisco 2509 access
server to 115200 bps:
line 1 2
speed 115200
Note: If for some reason you cannot use flow control, limit the line
speed to 9600 bps. Faster speeds are likely to result in lost data.
Modem speed setting is
not locked
Step 3 Use the show line exec command again and confirm that the line
speed is set to the desired value.
Step 4 When you are certain that the access server or router line is
configured for the desired speed, initiate a reverse Telnet session to
the modem via that line. For more information, see the section
“Establishing a Reverse Telnet Session to a Modem” earlier in this
chapter.
Step 5 Use a modem command string that includes the lock DTE speed
command for your modem. See your modem documentation for
exact configuration command syntax.
Note: The lock DTE speed command, which might also be referred
to as port rate adjust or buffered mode, is often related to the way in
which the modem handles error correction. This command varies
widely from one modem to another.
Locking the modem speed ensures that the modem always
communicates with the Cisco access server or router at the speed
configured on the Cisco auxiliary port. If this command is not used,
the modem reverts to the speed of the data link (the telephone line)
instead of communicating at the speed configured on the access
server.