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Circuit Pack Descriptions
7-68 Issue 3 June 2001
The red FAULT LED lights by the SYSCTL on detection of BBG4/BBG4B DS3
circuit pack failure. In the event of an incoming DS3 signal failure, this LED will
flash on and off. The green ACTIVE LED lights when the circuit pack is active
(carrying service).
General Description of Operation 7
The BBG4/BBG4B DS3 circuit pack provides bidirectional transport of one DS3
signal through DDM-2000 OC-3 in either clear channel (CC) mode, violation
monitor and removal (VMR) mode, or violation monitor (VM) mode, by mapping
the DS3 into an STS-1 signal. The BBG4/BBG4B DS3 performs maintenance and
provisioning functions associated with the STS-1 and DS3 signals and provides
access to the STS-1 path overhead. It interfaces to the OLIU at the STS-1 rate, to
the DSX-3, and to the SYSCTL, and receives timing signals traceable to the TG
circuit pack. When provisioned for the CC mode, the DS3 can transport any DS3
rate signal that meets specified electrical interface requirements. When
provisioned for the VMR or VM mode, the DS3 signal must meet both electrical
and DS3 frame format requirements.
Detailed Description of Operation 7
Transmission Circuitry 7
Transmit Direction. 7Figure 7-26 provides an overall block diagram of the BBG4/
BBG4B DS3 circuit pack. The transmit direction is the direction towards the STS-1
signal, and receive direction refers to the direction towards the DSX-3. In the
transmit direction, the BBG4/BBG4B DS3 receives an incoming B3ZS encoded
DS3 signal from the DSX-3. A closed protection relay contact routes the DS3 to a
circuit that splits the signal and sends one output to the companion (standby)
circuit pack and the other to its own receiver. The BBG4/BBG4B DS3 receiver
performs equalization and clock recovery. The MUX circuitry performs B3ZS
decoding, optional automatic DS3 AIS insertion, and a provisionable VMR
function, then synchronizes and maps the DS3 to the STS-1 rate. The DS3 signal
is then synchronized to the STS-1 payload rate, STS-1 path overhead is inserted,
and an STS-1 rate signal is transmitted to an OLIU pair.
Receive Direction. 7The BBG4/BBG4B DS3 receives STS-1 data from both the
active and standby OLIUs, selects one STS-1, performs pointer interpretation,
processes and removes the path overhead, desynchronizes the embedded DS3,
provides a provisionable VMR function, and then B3ZS encodes the signal for
transmission to the DSX-3. A jumper allows the user to insert or remove an LBO
network (225 ft. of 734A-type cable equivalent) to provide the required signal level
and shape at the DSX-3.
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