363-206-305
Circuit Pack Descriptions
Issue 3 June 2000
7-23
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
OLIU 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 performance monitoring for the DS1 rate transmit
signals.
Detailed Description of Operation
7
Transmission Circuitry
7
Transmit Direction.
7
Figure 7-10 provides an overall block diagram of the DS1PM
circuit pack. The transmit direction points toward 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 nonreturn to zero (NRZ)
format and sends it to the multiplexer (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 OLIU
circuit pack, using the frame sync received from the OLIU.
Receive Direction.
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The DS1PM receives a VT-G with frame information from the
OLIU 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, preequalized with a selectable line build out (LBO), and then sent as a
balanced signal to Alternate Mark Inversion a DSX-1 that may be located up to
655 feet from the system.
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