Nortel Circuit Card Installation Manual page 70

Page 70 of 906 Overview
Figure 14
Typical trunk interface unit block diagram
DS-30X
Network loop
CODEC
Signaling
TS0
553-3001-211 Standard 3.00
trunk line through an impedance matching and balance network. The trunk
interface also includes the logic necessary to place outgoing call signaling
onto the trunk, or the logic to connect to special services such as recorded
announcement and paging equipment.
Figure 14 shows a typical example of the logic that performs these functions.
Each part of the trunk interface unit is discussed in the following section.
Variable gain
filters
logic
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.
August 2005
Isolation
transformer
2-wire
to
4-wire
conversion
and
balance
network
Tip
Interface
(protection)
Ring
Signaling
leads
(E&M,
DX, etc.)
553-6159