
Troubleshooting Routers
6-26
2.
If the router’s connection to the modem is a 44-pin synchronous
interface, and the modem is a master, make sure the modem can send the
RI (ring indicator) signal from Pin 22 to the router interface in the
control off state (negative voltage).
Most RS232 modems support this control signal. If the modem does not
support this control signal, use the Configuration Manager to edit the
connector of the backup line, click on Modem, and disable ring indicator.
The RS232 pin assignments are
• RI (ring indicator) Pin 22
• DCD (data carrier detect) Pin 8
• DTR (data terminal ready) Pin 20
• DSR (data set ready) Pin 6
Troubleshooting V.35 Raise DTR Dial (Balanced)
If the DTR is up when it should not be, causing the modem or CSU to initiate a
dial sequence, do the following:
1. If the router’s connection to the modem or CSU is a 44-pin synchronous
interface, and the modem is a master, make sure the modem or CSU can
send the RI signal from Pin J to the router interface in the control off
state.
Some CSUs do not support the Pin J, RI signal. If the modem or CSU does
not support this control signal, use the Configuration Manager to edit the
connector of the backup line, click on Modem, and disable ring indicator.
If the CSU does not supply RI Pin J, you can create a custom cable to use
another signal, such as RLSD (received line signal detection) pin F, as RI
Pin J. RLSD is typically low until the modem establishes a connection, and
goes low again after DTR toggles.
2. Disconnect the local and remote CSUs from the DCE, and use a breakout
box to verify whether the DCE (modem or CSU) is sending a DSR (data
set ready) signal to the router interface in the on state (positive voltage).
Note: Disabling ring indicator on the router has no effect in this case. The
absence of the RI control signal at the master end causes DTR to go high.
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