363-206-305
Circuit Pack Descriptions
7-70
Issue 3 June 2000
General Description of Operation
7
The 22-type OLIUs multiplex three STS-1 signals to an STS-3, insert the SONET
transport overhead bytes (line and section), and scramble the resulting signal. For
the 22D-type OLIU, this STS-3 signal drives the LED transmitter to create an IS-3
output. For the 22F-type and the 22G-type OLIUs, this STS-3 signal drives the
laser transmitter to create the OC-3 output.
The received IS-3 or OC-3 signal is converted back to an electrical STS-3. This
STS-3 is descrambled and demultiplexed into three STS-1 signals, and transport/
path overhead is accessed. Some of the overhead (for example, section datacom
channel) is passed via serial data links to the control packs, while other bytes (for
example framing, parity check) are processed on-board. The STS-1 signals go
through a pointer processor to guarantee STS-1 frame alignment before being
routed to the main slots.
For 22D-type OLIUs, the output must interface with multimode fiber.
For 22F-type OLIUs, fiber access is via a pair of
ST
lightguide cable connectors
from the OLIU faceplate. The 22F-type OLIU photonics comply with SONET
intermediate-reach specifications.
Detailed Description of Operation
7
Figure 7-29 is a block diagram of the 22-type OLIU circuit pack.
Transmission Circuitry
7
STS-1 Cross Connect.
7
The STS-1 cross connect is used to select STS-1s for both
the transmit and receive directions.
Transmit Direction.
7
The STS-1 cross connect connects three of the STS-1
signals from the main slots. The multiplexer takes the three STS-1 signals, adds
SONET transport overhead, then byte-interleaves and scrambles the signal with a
frame synchronous scrambler. The output from the multiplexer is in the SONET
STS-3 format and is used to amplitude modulate the LED transmitter, converting
the electrical signal to an NRZ-encoded SONET compatible IS-3 optical signal for
22D-U and an OC-3 optical signal for 22F-types and 22G-types.
Receive Direction.
7
For all 22-type OLIUs, in the receive direction the optical
receiver converts the light pulses from an NRZ-encoded OC-3 or IS-3 signal to
equivalent electrical pulses. The demultiplexer circuit accepts the STS-3 bit
stream, frames on the incoming signal, descrambles it, demultiplexes it into three
STS-1 signals, and processes OC-3 or IS-3 transport overhead. The overhead
information is sent to the SYSCTL circuit pack via the intra-shelf control bus.
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