363-206-295
Circuit Pack Descriptions
7-60 Issue 1 December 1997
Protection Circuitry 7
Optional 1+1 nonrevertive unidirectional line protection switching compliant with
SONET specifications is provided. The 21G/21G-U/21G2-U OLIU is protection
switched by the SYSCTL in response to an external command, incoming signal
failure, or internal equipment fault. The 21G/21G-U/21G2-U OLIU circuit pack is
protection switched with the optical line.
The 21G/21G-U/21G2-U OLIU interfaces with STS-1 signals from the circuit
packs in the main and function unit slots in an OC-3 shelf, or TSI slots in an OC-12
shelf, and selects the signals from the service or protection slot of each pair as
directed by the SYSCTL.
The 21G/21G-U/21G2-U OLIU provides selectors for timing signals from the TGS
circuit packs, monitors these inputs, and autonomously selects either one. The
SYSCTL can inhibit autonomous selection and make its own selection.
Fault Detection Circuitry 7
The 21G/21G-U/21G2-U OLIU circuit pack has in-service and out-of-service built-
in test capability. In-service testing is continuous and errors are reported when
they occur to the SYSCTL via the intra-shelf control bus. An out-of-service test is
performed whenever the 21G/21G-U/21G2-U OLIU circuit pack is inserted or
recovers from a transient failure.
Performance Monitoring 7
The 21G/21G-U/21G2-U OLIU provides PM circuitry for the following performance
parameters:
■ Laser bias current threshold (21G and 21G-U only)
■ Transmit optical power threshold (21G and 21G-U only)
■ SEFS
■ Line parameters derived from B2 coding violations.
Power Circuitry 7
Power for the 21G/21G-U OLIU circuit pack is provided by two DC-to-DC
converters located on the 21G/21G-U OLIU circuit pack. One converter supplies
+5 volts and the other supplies −5.2 volts. Both A and B −48 volt backplane
busses supply power to the converters through diode ORed circuit pack-mounted
power select circuits and a circuit pack-mounted fuse. Failure of the fuse or either
converter causes the red FAULT LED to light.
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