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4-22
3160-A2-GB21-80
March 1999
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:
H Line Loopback (LLB)
H Payload Loopback (PLB)
H DTE Loopback (DLB)
H Repeater Loopback (RLB)
H Data Channel Loopback (DCLB)
H Data Terminal Loopback (DTLB)
NOTE:
DLB does not appear when the DTE Drop/Insert (DSX-1) interface is
disabled.
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.
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 Table 4-8 are identified by YES.
Table 4-8. Valid Loopback Combinations
LLB PLB DLB RLB DCLB DTLB
LLB
N/A NO YES YES NO YES
PLB
NO N/A YES NO NO YES
DLB
YES YES N/A NO YES YES
RLB
YES NO NO N/A NO YES
DCLB
NO NO YES NO YES
(on separate ports)
YES
(on separate ports)
DTLB
YES YES YES YES YES
(on separate ports)
YES
(on separate ports)