Nortel Networks Circuit Card - Manual (Page 66)

Page 66 of 906 Overview
553-3001-211 Standard 3.00 August 2005
DS-30X loops
The interfaces provided by the line and trunk cards connect to conventional
2-wire (tip and ring) line facilities. IPE analog line and trunk cards convert
the incoming analog voice and signaling information to digital form, and
route it to the Common Equipment (CE) CPU over DS-30X network loops.
Conversely, digital voice and signaling information from the CPU is sent over
DS-30X network loops to the analog line and trunk cards where it is
converted to analog form and applied to the line or trunk 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 (or the
controller circuits on a network/DTR card in a CE module). A DS-30X
network loop is composed of two synchronous serial data buses. One bus
transports in the transmit (Tx) direction toward the line facility and the other
in the receive (Rx) direction toward the common equipment.
Each bus has 32 channels for pulse code modulated (PCM) voice data. Each
channel consists of a 10-bit word. See Figure 12 on
page 67 .
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 8-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