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Circuit Pack Descriptions
7-144 Issue 3 June 2001
Receive Direction. 7In the receive direction for each OC-1, the optical receiver
converts the light pulses from an NRZ-encoded OC-1 signal to equivalent
electrical pulses. The output from the optical receiver goes into a timing recovery
device. The device recovers received clock and uses it to retime the received
data. The transport overhead processor circuit accepts the retimed STS-1 bit
stream, frames on the incoming signal, descrambles it, and processes OC-1
transport overhead. The overhead information is sent to the SYSCTL circuit pack
via the intra-shelf control bus and to the OHCTL circuit pack by the transport
overhead channel interface.
The STS-1 outputs from the transport overhead processor are sent to the STS-1
pointer processor which performs pointer interpretation and generation on each
received STS-1, using the local timing signals. The output of the STS-1 pointer
processor is two STS-1 signals, frame synchronous to each other, which are sent
to the VT1.5 pointer processor. VT1.5 pointer processing is performed on each
STS-1 that is to be VT1.5 cross-connected. STS-1 path overhead termination is
also done on these VT1.5 based signals. STS-1s that do not require VT1.5 cross-
connections are passed through without VT1.5 pointer processing or STS-1 path
overhead termination. The output from the VT1.5 pointer processor is sent to the
STS-1/VT1.5 router. The router cross-connects the appropriate VT1.5 tributaries
and sends the two STS-1 signals to the appropriate main or function unit slots.
Control Circuitry 7
The 27G-U/27G2-U OLIU circuit pack interfaces with the BBG8/BBG8B SYSCTL
and with the BBG9 OHCTL circuit packs.
The 27G-U/27G2-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 27G-U/27G2-U OLIU responds to control signals from the SYSCTL, such as
STS-1 routing, VT1.5 routing, protection switching, and LED control commands.
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