363-206-285
Circuit Pack Descriptions
Issue 3 June 2001
7-27
General Description of Operation 7
The DS1 circuit pack terminates four bidirectional DS1 lines complying with
standard DSX-1 signal specifications. The DS1 circuit pack interfaces to the
MXRVO/STS1E circuit pack at the VT-G rate (6.912 MHz) and to the SYSCTL.
The BBF1 and BBF1B DS1 circuit packs are functionally equivalent. Either one
can be used to replace the other. The BBF1B has improved protection switching
performance on circuit pack removal and insertion.
Detailed Description of Operation 7
Transmission Circuitry 7
Transmit Direction. 7Figure 7-10 provides an overall block diagram of the DS1
circuit pack. The transmit direction points towards the VT-G and the receive
direction points toward the DS1s. In the transmit direction, the DS1 receives four
balanced DS1 bipolar signals. Each of these signals passes through a relay to a
DS1 interface circuit that converts it to unipolar nonreturn to zero (NRZ) format,
recovers its clock, and sends it to the multiplexer (MUX) circuit. The MUX circuit
converts each DS1 rate input into a 1.728 Mb/s VT1.5 signal, and then byte
interleaves the four VT1.5s to create a VT-G signal that it sends to the MXRVO/
STS1E pack using the frame sync and clock received from the MXRVO/STS1E.
Receive Direction. 7The DS1 receives a VT-G with clock and frame information from
the MXRVO/STS1E and demultiplexes the VT-G into four unique VT1.5 signals.
Each VT1.5 passes through circuitry that performs pointer interpretation, removes
the VT path overhead bits, the fixed stuff bits, and the overhead communications
channel bits, and desynchronizes the embedded DS1. The DS1 rate signal is AMI
or B8ZS encoded, pre-equalized with a selectable line buildout (LBO). It is then
sent as a balanced signal to a DSX-1 that may be located up to 655 feet from the
DDM-2000 OC-3.
Control Circuitry 7
The DS1 circuit pack interfaces with the SYSCTL via the intra-shelf control bus.
Redundancy in the intra-shelf control bus assures the level of control required to
perform protection switching and alarming of a faulty circuit pack. The DS1
provides maintenance elements for reporting the status of the circuit pack and the
incoming VT1.5 and DS1 signals, as well as the circuit pack inventory information
(
CLEI
code, date of manufacture, etc.). These maintenance elements are used by
the SYSCTL for fault detection and isolation. Conversely, the DS1 responds to
control signals from the SYSCTL (such as FAULT LED control).
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