363-206-305
Circuit Pack Descriptions
7-16
Issue 3 June 2000
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 OLIU
circuit pack at the VT-G rate (6.912 MHz) and to the SYSCTL.
Detailed Description of Operation
7
Transmission Circuitry
7
Transmit Direction.
7
Figure 7-7 provides an overall block diagram of the DS1
circuit pack. The transmit direction points toward 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 OLIU pack
using the frame sync and clock received from the OLIU.
Receive Direction.
7
The DS1 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). It is then sent as a
balanced signal to a DSX-1 that may be located up to 655 feet from the system, or
to a DS1 termination located up to 1310 feet from the system.
Control Circuitry
7
The DS1 circuit pack interfaces with the SYSCTL via the intrashelf control bus.
Redundancy in the intrashelf 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. The DS1 responds to control signals
from the SYSCTL for functions including protection switching and FAULT light-
emitting diode (LED) control.
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