System information

Troubleshooting Dialin Connections
Book Title
16-372
Flow control is not enabled, is
enabled only on one device (either
DTE or DCE), or is misconfigured
Syntax Description:
• none—Turns off flow control.
• software—Sets software flow control. An optional keyword
specifies the direction: in causes the Cisco IOS software to listen
to flow control from the attached device, and out causes the
software to send flow control information to the attached device. If
you do not specify a direction, both are assumed.
• lock—Makes it impossible to turn off flow control from the
remote host when the connected device needs software flow
control. This option applies to connections using the Telnet or
rlogin protocols.
• hardware—Sets hardware flow control. An optional keyword
specifies the direction: in causes the software to listen to flow
control from the attached device, and out causes the software to
send flow control information to the attached device. If you do not
specify a direction, both are assumed. For more information about
hardware flow control, see the hardware manual that was shipped
with your router.
Example:
The following example sets hardware flow control on line 7:
line 7
flowcontrol hardware
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.
Step 3 After enabling hardware flow control on the access server or router
line, 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.”
Flow control is not enabled, is
enabled only on one device (either
DTE or DCE), or is misconfigured
Step 4 Use a modem command string that includes the RTS/CTS Flow
command for your modem. This command ensures that the modem
is using the same method of flow control (that is, hardware flow
control) as the Cisco access server or router. See your modem
documentation for exact configuration command syntax. Figure 16-1
shows the hardware flow control command string for a
Hayes-compatible modem.
Congestion or line noise
Step 1 If the network is congested, dial-up connections can freeze for a few
seconds. The only solution is to reduce congestion on the network by
increasing bandwidth or redesigning the network.
Step 2 Line noise can also freeze up a dialup connection. For information
on how to account for line noise on your modem, refer to the vendor
documentation.
Old PC UART This problem applies only to PC-to-router dialin connections.
Step 1 Use the DOS program MSD to see what PC UART is on your comm
port. Older PC UARTs, such as the 8250, cannot run at speeds over
19200 bps.
Step 2 If you have an older UART, try lowering your connection speed or
get a faster serial card for your PC.
Possible Causes Suggested Actions