Maintenance
4-17
3170-A2-GB20-20
December 1996
Starting a DTE Loopback
The DTE Loopback command (DLB) loops the
received signal on the DTE Drop/Insert port back to the
DTE without change.
A DTE loopback can be activated and deactivated
based on the state of an external contact on the DTE
Drop/Insert port. If this option is enabled with the DTE
Interface configuration option Extrn DLB, closing the
contact activates a DLB. The DLB remains active until
the contact is opened. Refer to the DTE Drop/Insert
Interface section in Appendix D, Pin Assignments, for
more information.
To perform a DTE loopback,
1. Press F2 to select Test from the top-level menu
screen.
2. From the Test screen, press F2 to select Lpbk.
F1
Test:
Rlpbk Lpbk
Ptrns
F2
F3
3. From the Loopback screen, press
once to
display the DLB selection on the screen.
F1
Loopback:
Abort
LLB
PLB
F2
F3
4. Press F3 to select DLB.
F1
Loopback:
LLB
PLB
DLB
F2
F3
Test Started appears on Line 2. If a DTE
loopback is already in progress, the Already
Active message appears. If an invalid combination
of loopbacks is in progress, the error message
Invld Test Combo appears (see Table 4-8 for
valid loopback test combinations).
Starting a Repeater Loopback
The Repeater Loopback command (RLB) loops the
signal being sent to the network back to the DTE
Drop/Insert and data ports. The signal is looped back as
close to the network interface as possible (after it has
passed through the framing circuitry of the E1
DSU/CSU). Therefore, framing CRCs and BPVs are
corrected.
To perform a Repeater loopback,
1. Press F2 to select Test from the top-level menu
screen.
2. From the Test screen, press F2 to select Lpbk.
F1
Test:
Rlpbk Lpbk
Ptrns
F2
F3
