Nortel Networks Circuit Card - Manual (Page 35)

Overview Page 35 of 906
Circuit Card Description and Installation
DS-30X loops
The line interfaces provided by the line cards connect to conventional 2-wire
(tip and ring) line facilities. IPE analog line cards convert the incoming
analog voice and signaling information to digital form and route it to the Call
Server over DS-30X network loops. Conversely, digital voice and signaling
information from the Call Server is sent over DS-30X network loops to the
analog line cards where it is converted to analog form and applied to the line
facility.
IPE digital line cards receive the data from the digital phone terminal as
512 kHz Time Compressed Multiplexed (TCM) data. The digital line card
converts that data to a format compatible with the DS-30X loop and transmits
it in the next available timeslot. When a word is received from the DS-30X
loop, the digital line card converts it to the TCM format and transmits it to the
digital phone terminal over the digital line facility.
A separate dedicated DS-30X network loop is extended between each IPE
line/trunk card and the controller cards within an IPE module. A DS-30X
network loop is composed of two synchronous serial data buses. One bus
transports in the Transmit (Tx) direction towards the line facility and the other
in the Receive (Rx) direction towards the CS 1000S, CS 1000M, and
Meridian 1.
Each bus has 32 channels for Pulse Code Modulated (PCM) voice data. Each
channel consists of a 10-bit word. See Figure 3 on
page 36 . Eight of the 10
bits are for PCM data, one bit is the call signaling bit, and the last bit is a data
valid bit. The eight-bit PCM portion of a channel is called a timeslot. The
DS-30X loop is clocked at 2.56 Mbps (one-half the 5.12 MHz clock
frequency supplied by the controller card). Thus, the timeslot repetition rate
for a single channel is 8 kHz. The controller card also supplies a locally
generated 1 kHz frame sync signal for channel synchronization.
Signaling data is transmitted to and from the line cards using the call signaling
bit within the 10-bit channel. When the line card detects a condition that the
switch needs to know about, it creates a 24-bit signaling word. This word is
shifted out on the signaling bit for the associated channel one bit at a time
during 24 successive DS-30X frames. Conversely, when the switch sends
signaling data to the line card, it is sent as a 24-bit word divided among 24
successive DS-30X frames.