Circuit Pack Descriptions
Issue 8.0 July 2002
7-77
Loopbacks. 7The OC12 (1.3 STD) circuit pack provides facility and equipment
loopbacks for fault isolation testing.
â– A facility loopback bridges the OC-12/12C line input back to the
OC-12/12C line output via a loop connection in the STS12 MUX/DEMUX.
The facility loopback includes the receiver and laser transmitter modules.
â– An equipment loopback bridges the STS-12/12C transmit data drive to the
laser module back to the OC-12/12C receive input via a loop connection in
the STS12 MUX/DEMUX. The equipment loopback path includes all the
transmission devices on the circuit pack except the optical receiver module
and the laser module. Also, the DCC transmit data input from the overhead
controller will be looped back to the DCC receive data output to the
overhead controller.
These loopbacks are implemented in response to craft interface terminal (CIT)
commands (via the SYSCTL and LNCTL circuit packs) and controlled by the
board controller.
Performance Monitoring. 7The OC12 (1.3 STD) circuit pack monitors the following
performance-monitoring parameters:
â– Laser bias current
â– Optical transmit power
â– Received optical power
â– Loss of signal
â– Loss of frame
â– Bit error rate thresholds
When an incoming OC-12 signal defect from the lightguide cross-connect panel is
detected, the OC12 (1.3 STD) circuit pack inserts STS-1 path AIS in each STS-1
tributary of the four STS-3/3c signals (155.52 Mb/s) transmitted toward the OC-48
TRMTR circuit pack.
When an incoming OC-48 signal defect is detected by the OC48 RCVR circuit
pack or an STS-1 loss of pointer is detected by the OC12 (1.3 STD) circuit pack in
any of the 155.52 Mb/s signal received from the OC48 RCVR circuit pack, the
OC12 (1.3 STD) circuit pack inserts STS-1 path AIS in each STS-1 tributary of the
OC-12 signal transmitted toward the lightguide cross-connect panel.
When an internal fault is detected, the OC12 (1.3 STD) circuit pack inserts STS-1
path AIS in each STS-1 tributary of the STS-3/3c signals transmitted toward the
OC48 TRMTR circuit pack and in the OC-12 signal transmitted toward the
lightguide cross-connect panel.
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