363-206-295
Circuit Pack Descriptions
Issue 1 December 1997 7-33
General Description of Operation 7
The BBG11B 3DS3 circuit pack provides bidirectional transport of three DS3
signals through the DDM-2000 OC-12 Multiplexer 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 BBG11B 3DS3 circuit pack
performs maintenance and provisioning functions associated with the STS-1 and
DS3 signals and provides access to the STS-1 path overhead. The BBG11B
3DS3 circuit pack interfaces to the TSI circuit pack at the STS-1 rate, to the
DSX-3, and to the SYSCTL, and it receives timing signals from the TSI circuit
pack. When provisioned for the clear channel mode, the 3DS3 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 7-14 provides an overall block diagram of the
BBG11B 3DS3 circuit pack. The transmit direction is the direction towards the
STS-1 signal, and the receive direction refers to the direction towards the DSX-3.
In the transmit direction, the BBG11B 3DS3 receives three incoming B3ZS
encoded DS3 signals from the DSX-3. A closed protection relay contact routes the
DS3 signal 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 BBG11B
3DS3 receiver performs equalization and clock recovery, B3ZS decoding, optional
automatic DS3 AIS insertion, and a provisionable VMR function. The BBG11B
DS3 then synchronizes and maps the DS3 to the STS-1 rate, inserts STS-1 path
overhead and transmits the STS-1 rate signal to the TSI circuit packs.
Receive Direction. 7The BBG11B 3DS3 receives STS-1 data from both the active
and standby TSI circuit packs, selects one set of STS-1s, 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 a line LBO network (225 ft. of 734A-type cable equivalent) to provide the
required signal level and shape at the DSX-3.
Before the DS3 signal is B3ZS-encoded (receive direction) or decoded (transmit
direction), a VMR function can be provisioned via the control circuitry for one of
three possible modes:
■ VMR with DS3 AIS insertion (default)
■ VM and AIS insertion without removal of violations
■ CC
— With DS3 AIS insertion
— Without DS3 AIS insertion.
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