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COMSPHERE 3500 Series Data Service Units
3-12 January 1998 3510-A2-GN32-50
Local Loopback – DTE Test Message
The Local Loopback is a data disruptive test used to
determine the proper functioning of the DTE to DSU
connection.
Local Loopback Overview
This loopback uses a test message provided by your
DTE. The DTE sends the message to the DSU’s
transmitter, where it is looped back to the receiver and
returned to the DTE (Figure 3-6). Check the returned
message for errors. Errors should be detected,
appropriately reported, and the problem cleared. The DSU
front panel does not display the test results.
Make sure the DTE cable is connected to the DSU and
the DSU is powered on. The DSU is not required to be
connected to the network.
To start the loopback, press the LL test switch; the
DTE sends the test message. To return the DSU to normal
after the loopback result is determined, press the LL test
switch.
Local Loopback Procedures
Follow the procedure in Table 3-5 or Table 3-6 to
perform a Local Loopback – DTE Test Message.
Local Loopback Results
For proper operation, the test message should be
received error free.
Figure 3-6. Local Loopback – DTE Test Message Diagram