System information

Troubleshooting Dialin Connections
Book Title
16-360
Dialin: Modem Cannot Send or Receive Data
Symptom: After a dialin connection is established, a modem cannot send or receive data of any
kind.
Table 16-9 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 16-9 Dialin: Modem Cannot Send or Receive Data
Modem control is not enabled on the
access server or router
Step 1 Use the show line exec command on the access server or router. The
output for the auxiliary port should show inout or RIisCD in the
Modem column. This indicates that modem control is enabled on the
line of the access server or router.
For an explanation of the show line output, see the “Using debug
Commands” section earlier in this chapter.
Step 2 Configure the line for modem control using the modem inout line
configuration command. Modem control is now enabled on the
access server.
Note: Be certain to use the modem inout command instead of the
modem ri-is-cd command while the connectivity of the modem is in
question. The latter command allows the line to accept incoming
calls only. Outgoing calls will be refused, making it impossible to
establish a Telnet session with the modem to configure it. If you
want to enable the modem ri-is-cd command, do so only after you
are certain the modem is functioning correctly.
Incorrect cabling
Step 1 Check the cabling between the modem and the access server or
router. Confirm that the modem is connected to the auxiliary port on
the access server or router with a rolled RJ-45 cable and an MMOD
DB-25 adapter. This cabling configuration is recommended and
supported by Cisco for RJ-45 ports. (These connectors are typically
labelled “Modem.”)
There are two types of RJ-45 cabling: straight and rolled. If you hold
the two ends of an RJ-45 cable side-by-side, you’ll see eight colored
strips, or pins, at each end. If the order of the colored pins is the same
at each end, then the cable is straight. If the order of the colors is
reversed at each end, then the cable is rolled.
The rolled cable (CAB-500RJ) is standard with Cisco’s 2500/CS500.
Step 2 Use the show line exec command to verify that the cabling is correct.
See the explanation of the show line command output in the section
“Using debug Commands” earlier in this chapter.
Possible Causes Suggested Actions