363-206-285
Circuit Pack Descriptions
Issue 3 June 2001
7-105
Each 22F-type OLIU provides timing signals to, and receives timing signals from,
the TG circuit packs.
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. While single-mode fiber is suggested for optimum performance,
multimode facilities are also supported as long as a single-mode jumper is placed
between the 22F-type OLIU optical output connector and the multimode fiber.
Detailed Description of Operation 7
Figure 7-40 is a block diagram of the 22F-type 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 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 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 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
laser transmitter, converting 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 OC-3 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 demultiplexer 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 three
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
To Next Page
Loading...
Need help?
General
