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Maintenance Description
9-26 Issue 1 December 1997
OC-3/OC-12 Path Switched Ring (0x1) 9
A DDM-2000 OC-3 ring shelf can function in a ring-on-ring application using the
0x1 interface capability of the OC-12 or FT-2000 OC-48 Lightwave System ring.
The OC-3 shelf functions in the normal path switched ring mode. VT/STS path
protection switching is done on the OC-3 shelf.
In single homing, the OC-3 ring shelf interconnects through its main-1/main-2 ring
interface either directly or through another OC-3 ring shelf to the low-speed OC-3
0x1 interface on a single OC-12 or FT-2000 OC-48 Lightwave System shelf.
In dual homing, the OC-3 ring shelf interconnects directly or through another
OC-3 ring shelf with the OC-3 interfaces on two separate and normally non-
colocated OC-12 or FT-2000 OC-48 Lightwave System shelves.
Status of ACTIVE LED on Rings 9
In ring applications, ACTIVE LEDs on each main OLIU are always lit because it is
not known if a signal on that OLIU is currently being selected by a far-end NE.
Loopbacks 9
The DDM-2000 OC-12 Multiplexer allows technicians to do loopbacks on all low-
speed DS3 and EC-1 interfaces. Low-speed DS3 and EC-1 electronic loopbacks,
directed toward the high-speed OC-12, are individually controllable from the CIT.
Facility loopbacks can also be set up towards the DSX on all low-speed DS3 and
EC-1 interfaces. Active electronic loopbacks are noted by the user panel's
abnormal (ABN) indicator and in the alarm and status report. See the
opr-lpbk-ds3, opr-lpbk-ec1, rls-lpbk-ds3, and rls-lpbk-ec1
commands in Section 11, "Commands and Reports."
Front access to the OLIU optical connectors allows an easy manual OC-3 and
OC-12 optical loopback. This loopback is performed by connecting a fiber jumper
from the OLIU output to its input. On the 21-type OLIUs, no optical attenuator is
required for this loopback. However, the optical output power switch on the 21G/
21G-U OLIU circuit pack must be set for low output power to prevent receiver
overload when an optical loopback is set up. On the 23G/23G-U OLIU, an external
optical attenuator is required to prevent receiver overload during manual optical
loopback.
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