35
MULTIPORT CSU/DSU
To perform a LAL test, follow these steps:
1. Activate LAL, in one of two ways:
a. Move the front panel toggle switch up to “Local,” or,
b. Activate the “LLB” signal on the DTE. If you are not sure which lead is the
LLB signal, refer to
Appendix A
.
2. Verify that the data terminal equipment is operating properly and can be
used for a test.
3. Perform a V.54 BER (bit error rate) test as described in
Section 5.3.3
. If the
BER test equipment indicates no faults, but the data terminal indicates a fault,
follow the manufacturer’s checkout procedures for the data terminal. Also,
check the interface cable between the terminal and the CSU/DSU.
5.3.2 O
PERATING
R
EMOTE
D
IGITAL
L
OOPBACK
(RDL)
The Remote Digital Loopback (RDL) test checks the performance of both the
local and remote CSU/DSUs, as well as the communications link between them.
Any characters sent to the remote CSU/DSU in this test mode will be returned
back to the originating device (characters typed on the keyboard of the local
terminal will appear on the local terminal screen after having been passed to the
remote CSU/DSU and looped back).
Figure 5-3. Remote Digital Loop.
To perform an RDL test, follow these steps:
1. Activate RDL, in one of two ways:
a. Move the front panel toggle switch DOWN to “Remote,” or
b. Active the “RDL” signal on the DTE. If you are not sure which lead is the
RL signal, refer to
Appendix A
.
Local CSU/DSU
Remote CSU/DSU
