Nortel Networks 311 User Manual

Overview

Figure 14
Typical trunk interface unit block diagram

Coder/Decoder circuit

The coder/decoder (codec) performs Analog

to Digital (A/D) and Digital to Analog (D/A) conversion of the line analog
voiceband signal to and from a digital PCM signal. This signal can be coded
and decoded using either the A-Law or the µ-Law companding algorithm.
On some trunk cards the decoding algorithm depends of the type of codec
installed when the board is built. On others, it is an option selected using a
software overlay.

Variable gain filters

Audio signals received from the analog phone trunk

are passed through a low-pass A/D monolithic filter that limits the frequency
spread of the input signal to a nominal 200–3400 Hz bandwidth. The audio
signal is then applied to the input of the codec. Audio signals coming
from the CODEC are passed through a low-pass A/D monolithic filter that
integrates the amplitude modulated pulses coming from the CODEC, and
then filters and amplifies the result.

On some of the trunk cards, the gain of these filters can be programmed
by the system controller. This allows the system to make up for line losses
according to the loss plan.

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311

01.04

Standard

Release 5.0

23 May 2008