363-206-285
Circuit Pack Descriptions
7-146 Issue 3 June 2001
The 27G-U/27G2-U OLIU accesses the SONET transport overhead and routes it
via the transport overhead channel interface to the OHCTL. The 27G-U/27G2-U
OLIU accesses the STS-1 path overhead and routes it via the intra-shelf control
bus to the SYSCTL circuit pack.
Timing Circuitry 7
Each TG circuit pack sends timing signals to each 27G-U/27G2-U OLIU. Each
27G-U/27G2-U OLIU monitors the timing inputs from both TG circuit packs. The
27G-U/27G2-U OLIU normally selects the timing signals from the TG selected by
the SYSCTL. When inserted in main or function unit C slots, each 27G-U/27G2-U
OLIU provides timing signals derived from the incoming optical signal to both TG
circuit packs for line timing and DS1 output (BITS).
Protection Circuitry 7
Optional 1+1 nonrevertive unidirectional line protection switching compliant with
SONET specifications is provided. The 27G-U/27G2-U OLIU is protection
switched by the SYSCTL in response to an external command, incoming optical
signal failure, or internal equipment fault. The 27G-U/27G2-U OLIU circuit pack is
protection switched by the SYSCTL when the SYSCTL detects a fault on the
active 27G-U/27G2-U OLIU and the companion 27G-U/27G2-U OLIU is good.
The 27G-U/27G2-U OLIU interfaces with STS-1 signals from the circuit packs in
the main and function unit slots. It selects the signals from the service or
protection slot of each pair as directed by the SYSCTL.
The 27G-U/27G2-U OLIU provides selectors for timing signals from the TG circuit
packs, monitors these inputs, and autonomously selects either TG circuit pack.
The SYSCTL can inhibit autonomous selection and make its own selection.
Fault Detection Circuitry 7
The 27G-U/27G2-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 OLIU circuit pack is inserted or recovers from a transient
failure.
The 27G-U/27G2-U OLIU has provisionable VT signal degrade and STS signal
degrade BER threshold capabilities for path protection switching.
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