363-206-285
Circuit Pack Descriptions
Issue 3 June 2001
7-35
General Description of Operation 7
The DS1PM circuit pack terminates four bidirectional DS1 lines complying with
standard DSX-1 signal specifications. The DS1PM circuit pack interfaces to the
MXRVO/STS1E circuit pack at the VT-G rate (6.912 MHz) and to the SYSCTL.
The DS1 and DS1PM circuit packs are, with respect to transmission, functionally
equivalent. In addition to performing all of the functions of the DS1 circuit pack,
the DS1PM circuit pack provides PM for the DS1 rate transmit signals.
Detailed Description of Operation 7
Transmission Circuitry 7
Transmit Direction. 7Figure 7-13 provides an overall block diagram of the DS1PM
circuit pack. The transmit direction points towards the VT-G and the receive
direction points toward the DS1s. In the transmit direction, the DS1PM receives
four balanced DS1 bipolar signals. Each of these signals passes through a relay
to a DS1 interface circuit that converts it to unipolar NRZ format, recovers its
clock, and sends it to the MUX and framing (framer) circuits. 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 circuit pack, using the frame sync and clock received from the MXRVO/
STS1E.
Receive Direction. 7The DS1PM 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 LBO, and
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 DS1PM circuit pack interfaces with the SYSCTL over 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
DS1PM 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 DS1PM
responds to control signals from the SYSCTL (such as FAULT LED control). The
PM processor collects information from the framing circuitry and generates DS1
PM parameters which are sent to the SYSCTL.
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