363-206-285
Circuit Pack Descriptions
Issue 3 June 2001
7-85
The red FAULT LED lights by the SYSCTL on detection of BBG19 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 BBG19 DS3 circuit pack provides bidirectional transport of one DS3 signal
through DDM-2000 OC-3 in either CC mode, VMR mode, or VM mode, by
mapping the DS3 into an STS-1 signal. The BBG19 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 data services device, 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 7-33 provides an overall block diagram of the BBG19
DS3 circuit pack. The transmit direction is the direction towards the STS-1 signal,
and receive direction refers to the direction towards the data services device. In
the transmit direction, the BBG19 DS3 receives an incoming B3ZS encoded DS3
signal from the data services device. BNC connectors on the faceplate of the
BBG19 provide input and output for the data services signal. The BBG19 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 BBG19 DS3 receives STS-1 data from the 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 data services
device. 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
data services device.
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