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Local Loopback Tests
3166-A2-GB20-20
The Local Loopback tests enable you to conduct circuit testing and fault isolation
for the digital line. The supported local loopback tests are:
H
Line Loopback
(LLB)
H
Payload Loopback
(PLB)
H
Repeater Loopback
H
Data Channel Loopback
H
Data Terminal Loopback
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 Appendix C,
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
Appendix C,
Configuration Options
Local loopback tests can be aborted (Abort Command) at any time.
Local loopback tests cannot be run if send pattern or remote loopback tests are
active. In most cases local loopbacks cannot run with each other. Table 4-7
shows valid combinations of local loopbacks.
Table 4-7. Valid Loopback Combinations
LLB
LLB
NO
NO
PLB
YES
RLB
NO
DCLB
YES
DTLB
March 1999
(RLB)
(DCLB)
(DTLB)
).
PLB
RLB
NO
YES
NO
NO
NO
NO
NO
NO
YES
YES
Monitoring and Testing
DCLB
DTLB
NO
YES
NO
YES
NO
YES
NO
NO
NO
NO
4-19
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