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4. Maintenance
Local Loopback Tests
The Local Loopback tests enable you to conduct circuit testing and fault isolation
for the digital line. The supported local loopback tests are:
T
T
T
T
T
T
The Line Loopback command can be activated and deactivated in response to
commands received over the network interface. The Network Interface
configuration option NET LLB controls whether the DSU/CSU responds to the
commands transmitted on the network interface to initiate LLBs (see
Configuration Options
The data port configuration option NET DCLB controls whether the DSU/CSU
responds to inband V.54 commands to initiate DCLB for that port (see
Configuration Options
Local loopback tests can be aborted (Abort Command) at any time.
No more than two local loopbacks can be active at any one time. An additional
restriction prohibits certain loopbacks from running at the same time. Valid
loopback combinations listed in
identified by YES.
Table 4-8.
4-22
Line Loopback (LLB)
Payload Loopback (PLB)
DTE Loopback (DLB)
Repeater Loopback (RLB)
Data Channel Loopback (DCLB)
Data Terminal Loopback (DTLB)
NOTE:
DLB does not appear when the DTE Drop/Insert (DSX-1) interface is disabled.
).
).
Valid Loopback Combinations
LLB
PLB
DLB
LLB
N/A
NO
YES
PLB
NO
N/A
YES
DLB
YES
YES
N/A
RLB
YES
NO
NO
DCLB
NO
NO
YES
DTLB
YES
YES
YES
February 2001
Table 4-8, Valid Loopback
RLB
DCLB
YES
NO
NO
NO
NO
YES
N/A
NO
NO
YES
(on separate ports)
YES
YES
(on separate ports)
Appendix C,
Appendix C,
Combinations, are
DTLB
YES
YES
YES
YES
YES
(on separate ports)
YES
(on separate ports)
3160-A2-GB21-90
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