Nortel NT1R20 Description page 50

Page 26 of 290 Description
553-3001-105 Standard 5.00 June 1999
SL-1 Network loops
to conventional 2-wire (tip and ring) line facilities. Peripheral equipment (PE)
analog line cards convert the incoming analog voice and signaling
information to digital form and route it to the Meridian 1 common equipment
(CE) CPU over SL-1 network loops. Conversely, digital voice and signaling
information from the CPU is sent over SL-1 network loops to the analog line
cards where it is converted to analog form and applied to the line facility.
PE 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 SL-1 Network loop, and
transmits it in the next available timeslot. When a word is received from the
SL-1 Network loop, the digital line card converts it to the TCM format and
transmits it to the digital line facility.
Each loop has 32 timeslots for pulse code modulated (PCM) data. Each of the
32 channels is carried at 64 kbps (the standard rate for a digitized voice
channel). The total data rate is therefore 2.048 Mbps.
Data on the loop is "bit-interleaved" instead of byte-interleaved as it is on the
DS-30X loop. Instead of having a byte of data occupy eight successive
timeslots on the loop, the SL-1 Network loop has the first 32 successive
timeslots occupied (in order) by the sign bit from each channel. The next
32 successive timeslots are occupied by the most significant bit (MSB), and
so on, until eight "subframes" of 32 timeslots each have been completed (see
Figure 9).
An SL-1 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. When a terminal is enabled during a timeslot, its codec transmits
one bit of PCM data towards the Meridian 1 CE and, at the same time,
receives one bit of data from the Meridian 1 CE.
The timeslots are numbered 0 through 31. Timeslot 0 is reserved for signaling
information. Timeslot 1 is not used. Timeslots 2 through 31 are used for voice
data, giving a total of 30 usable timeslots for voice.
The line interfaces provided by the line cards connect