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Circuit Pack Descriptions
Issue 1 December 1997 7-55
21D/21D-U OLIU Quick Reference Summary 7
Transmit Functions 7
Major transmit functions of the 21D/21D-U OLIU circuit pack are as follows:
■ Selects STS-1 inputs from TSI circuit packs
■ Adds SONET transport overhead
■ Byte-interleaves and scrambles the three selected STS-1 or optional
STS-3c signals to produce an STS-3 or STS-3c signal
■ Converts the STS-3 or STS-3c signal to an IS-3 or IS-3c optical signal for
transmission over the optical fiber.
Receive Functions 7
The following are major receive functions of the 21D/21D-U OLIU circuit pack:
■ Receives an optical IS-3 or IS-3c signal and converts it to an electrical
STS-3 or STS-3c signal
■ Extracts STS-3 or STS-3c clock and retimes the received data
■ Demultiplexes the STS-3 or STS-3c signal into three STS-1 signals
■ Extracts transport overhead
■ Processes the STS-1 or STS-3c pointers and frame-synchronizes the
STS-1 signals
■ Sends the three STS-1 signals to both TSIs.
Control Functions 7
The major control functions are as follows:
■ Protection switching for TSI circuit packs
■ Transport overhead processing
■ Inventory information (
CLEI
code, date of manufacture, etc.).
Maintenance Signal Functions 7
The major maintenance signal functions are as follows:
■ Inserts and detects STS-1 path AIS
■ Inserts STS-1 path unequipped signal
■ Inserts and detects IS-3 line AIS
■ Inserts and detects far-end receive line failure (FERF)
■ Detects IS-3 line failures (LOS, LOF, AIS, and BER)
■ Detects IS-3 line signal degrade BER.
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