Maintenance
4-15
3170-A2-GB20-20
December 1996
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:
•
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 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 E1 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 E1 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)
