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7.6
DSU and Communications Line Testing
After determining that the channel-device-to-MultiMux portion of the multiplexer network is operating properly, the next
steps are to check the operation of the local DSU, the communications line and the remote DSU. By performing the
procedures in Table 7-4, the MultiMux can send data (keystrokes) from the channel device and have them echoed
through the composite link, remote DSU and back to the channel devices monitor.
Table 7-4. DSU and Communications Line Testing Procedure
Step Procedure
1 Set the source and destination nodes on the local MultiMux to the same node number.
2 Place the remote MultiMux unit in Test Mode 5 (Digital Loopback test) by entering the following command.
AT&5 (hit Return)
The supervisory console will display the following message:
REMOTE DIGITAL LOOP - TEST #5
3 Enter data on the keyboard of each channel device on the local MultiMux and, if the network is operating
correctly, the data will be correctly displayed on the local channel device monitor. If the channel device is
equipped with an active local echo feature, double characters will be displayed.
4 When you have verified that the communications link is operating correctly, enter the following to end the test:
ATZ (hit Return)
or
AT&T0 (hit Return)