Nortel NT1R20 Description page 44

Page 20 of 290 Description
553-3001-105 Standard 5.00 June 1999
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/PE 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 Meridian 1 common equipment.
Each bus has 32 channels for pulse code modulated (PCM) voice data. Each
channel consists of a 10-bit word (see Figure 7). 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
Meridian 1 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
Meridian 1 switch sends signaling data to the line card, it is sent as a 24-bit
word divided among 24 successive DS-30X frames.