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27 — Loopbacks
Procedure 27-3 To set a 2B1Q circuit loopback
where pp is 1 or 9, and c is A or B
27.3
DNIC circuit loopbacks
DNIC modules support remote connection of data devices through 2600 MainStreet
series DTUs.
For 2602 and 2603 MainStreet DTUs that support super-rate, super-rate circuit
loopbacks can only be applied while the circuit is connected. If a loopback is applied
to either port while neither is connected, the system displays the following error
message: "Connect super-rate circuit before applying loopbacks." If a loopback is
applied to one port while the other is involved in a super-rate connection, the system
displays the following error message: "Loopback invalid: other port involved in
super-rate connection."
Loopback A for two-port DTUs
For two-port DTUs, loopback A occurs on both lines (Port A and Port B)
simultaneously (see Figure 27-5). Loopback A extends from the DX on the Control
card and loops back on the DNIC line driver located on the DNIC module.
27-6
ON_CIRCUIT
<pp-c> ↵
LOOPBACK_A
LOOPBACK_B
MAINT
UNDO_MAINT
LOOPBACK_E
UNDO_LPK
2902 MainStreet Technical Practices
90-2906-01
SK000541
May 2002
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