363-206-295
Circuit Pack Descriptions
Issue 1 December 1997 7-59
Transmission Circuitry 7
Transmit Direction. 7The STS-1 router selects three of the STS-1 signals received
from other main and function unit slots, or from TSI slots in the OC-12 shelf, and
sends them to the multiplexer. The multiplexer circuitry takes the three STS-1
signals from the output of the router, adds SONET transport overhead, then byte-
interleaves and scrambles the signal in a frame synchronous scrambler. The
output from the multiplexer is in the SONET STS-3 format and is used to
amplitude modulate the laser transmitter, which converts the electrical signal to an
NRZ-encoded SONET compatible OC-3 optical signal.
Receive Direction. 7In the receive direction, the optical receiver converts the light
pulses from an NRZ-encoded OC-3 signal to equivalent electrical pulses. The
output from the optical receiver goes into a timing recovery device. The device
recovers received clock (155.520 MHz) and uses it to retime the received data.
The demultiplexer circuit accepts the retimed STS-3 bit stream, frames on the
incoming signal, descrambles it, demultiplexes it into three STS-1 signals, and
processes SONET transport overhead. The overhead information is sent to the
SYSCTL pack via the intra-shelf control bus and the transport overhead channel
interface.
The STS-1 outputs from the demultiplexer are sent to the pointer processor which
performs pointer interpretation and generation on each received STS-1 using the
local timing signals. The output of the pointer processor is three STS-1 signals,
frame synchronous to each other. The STS-1 router sends each of the three
STS-1 signals to the appropriate main or function unit in the OC-3 shelf, or TSI
slots in the OC-12 shelf.
Control Circuitry 7
The 21G/21G-U/21G2-U OLIU circuit pack interfaces with the system controller
(SYSCTL) and with the overhead controller (OHCTL) circuit packs.
The 21G/21G-U/21G2-U OLIU provides maintenance elements for reporting the
status of the circuit pack, status of the incoming optical and electrical signals, as
well as inventory information (
CLEI
code, date of manufacture, etc.). These
maintenance elements are used by the SYSCTL for fault detection and isolation.
Conversely, the OLIU responds to control signals from the SYSCTL such as
STS-1 routing, protection switching, and LED control commands.
The 21G/21G-U/21G2-U OLIU accesses the SONET transport overhead and
routes it via the transport overhead channel interface to the AUXCTL slot and/or to
the SYSCTL. The transport overhead is routed from the main slots to both the
AUXCTL and SYSCTL slots and from the function unit slots to the AUXCTL slot.
Timing Circuitry 7
Each TGS circuit pack sends timing signals to each OLIU. Each OLIU monitors
the timing inputs from both TGS circuit packs. The OLIU normally selects the
timing signals from the active TGS circuit pack. Each OLIU provides timing signals
derived from the incoming optical signal to both TGS circuit packs for line
(formerly loop) timing and DS1 timing outputs (BITS).
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