HP ProCurve 7000dl Series Basic Management And Configuration Manual page 294

Configuring Serial Interfaces for E1- and T1-Carrier Lines
Troubleshooting a Serial Connection
5-22
The router transmits the following signals to the CSU/DSU:
data terminal ready (DTR)
request to send (RTS)
The router receives these signals from the CSU/DSU:
clear to send (CTS)
data carrier detected (DCD)
data set ready (DSR)
test-mode (TM)
Using these signals, the ProCurve Secure Router and the CSU/DSU negotiate
data transfer and signal each other to control data flow. If the CSU/DSU drops
the CTS signal, the ProCurve Secure Router stops sending data. In turn, if the
ProCurve Secure Router must pause incoming data, it drops RTS, and the CSU/
DSU holds the data stream until it once again receives RTS.
The ProCurve Secure Router follows set protocols for dealing with inserted
and dropped signals. You can, however, reconfigure the router to respond to
dropped signals in different ways. For example, by default, when the serial
interface loses the DCD signal, it does not attempt to reestablish a connection.
You can configure the serial interface to ignore the DCD status and continue
trying to make a connection without the DCD signal. To do so, enter the
following command from the serial interface configuration mode context:
ProCurve(config-ser 1/1)# ignore dcd
To return the interface to the default setting, enter:
ProCurve(config-ser 1/1)# no ignore dcd