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Circuit Pack Descriptions
7-128 Issue 3 June 2001
General Description of Operation 7
The 24G-U OLIU multiplexes twelve STS-1 signals to an STS-12, inserts the
SONET transport overhead bytes (line and section), and scrambles the resulting
signal. This STS-12 signal drives the laser transmitter to create the OC-12 output.
The received OC-12 signal is converted to an electrical STS-12. This STS-12 is
descrambled and demultiplexed into twelve STS-1 signals, and transport/path
overhead is accessed. Some of the overhead (for example, section DCC) is
passed via serial data links to the control packs, while other bytes (for example,
framing, parity check) are processed on board. The twelve STS-1 signals go
through a pointer processor to guarantee STS-1 frame alignment to the local
system clock before being routed to the other main and function unit slots. Any
three of the twelve STS-1s can be routed to the function unit slots.
If an incoming STS-1 signal from the fiber is to be VT1.5 cross-connected, VT1.5
pointer-processing is performed on this pack and STS-1 path overhead
termination is performed on these signals. All signals entering this pack from
either the backplane or from the optical interface may be routed as STS-1s. If
appropriate, VT1.5 routings may be established between STS-1s using a limited
VT1.5 cross-connection.
Each 24G-U OLIU provides timing signals to and receives timing signals from the
TG circuit packs.
Detailed Description of Operation 7
Figure 7-46 is a block diagram of the 24G-U OLIU.
Transmission Circuitry 7
STS-1 Router and VT1.5 Cross-Connect. 7The STS-1 router is used to select
STS-1s for both the transmit and receive directions. All incoming STS-1s are fed
to the limited VT1.5 cross-connect. Outgoing STS-1s may be sourced by this
VT1.5 cross-connect or sourced directly by an STS-1 input.
Transmit Direction. 7The STS-1 router selects up to three of the STS-1 signals
directly from the other main and function unit slots or from the VT1.5 cross-
connect. SONET path overhead is then added to STS-1s sourced by the VT1.5
cross-connect before the signals are sent to the multiplexer. The multiplexer takes
these three STS-1 signals and the remaining STS-1s from the ring (through the
faceplate connector), 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-12 format and is used to amplitude modulate the
laser transmitter, converting the electrical signal to an NRZ-encoded SONET
compatible OC-12 optical signal.
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