01 tdm voice introduction

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Copyright © 2014 Huawei Technologies Co., Ltd. All rights reserved.
TDM Voice Introduction

Copyright © 2014 Huawei Technologies Co., Ltd. All rights reserved. Page 1
Foreword
 Traditional voice network uses TDM technology and narrow
band signaling to realize the voice transmission.
 This chapter describes the traditional voice network and basic
voice transmission knowledge.

Objectives
 Upon completion of this course, you will be able to:
 Understand the traditional voice network;
 Understand the components, interfaces and signaling in the
traditional voice network.

Phone Terminals
 Digital phone (Digital line)
 Advantages: more feature, easy to use, connect quickly
 Disadvantages: non-standard, expensive.
 Analog phone (Analog line)
 Advantages : universal, cheap
 Disadvantages: few feature, connect slowly
 Fax machine (Analog line)
PSTN
Phone:
 Digital Phone
 Analog Phone
 Fax
PBX
Fax
Terminal

PBX
 PBX: Private Branch Exchange
Trunk Card
Signaling
Processor
Trunk Card
Subscriber
Card
Control System
Subscriber
Card
Switched
Network

PBX
Switching
Matrix
Common
Control
Analog
Line Card
Digital
Line Card
Data
Line Card
ISDN BRI
Line Card
Analog
Trunk Card
Digital
Trunk Card
User Interface Analog Trunks
Digital Trunks
Analog phone
Digital phone
Digital terminal
ISDN terminal
PSTN or PBX
PSTN or PBX

Analog Line
 Electric currents are used to send analog signals.
 Each analog circuit is composed of a pair of wires.
Time
voltage
Analog Phone Central Office
Ground
Battery (ring)-48V

Digital Line
 Digital signals use discrete values to represent levels of voice
instead of a combination of electrical signals.
0
1
0
Central office
Digital connection
1 1 1 0 1
Time slot #1
Time slot #0
Time slot #0
Time slot #1
Time slot #31
… …
PBX
…

Type of Circuit
PSTN
PBX
Circuit Type
 Analog Circuit
 Digital Circuit
 Digital Circuit
 A digital circuit support multiple sessions at the same time
 Advantage: Digital signaling connect quickly, high port density, more
calling information
 Disadvantage: The rent is more expensive
 Analog Circuit
 An analog circuit support only one session at the same time
 Advantage: Apply for the number of circuit as your need, the rent is
more cheap
 Disadvantage: Analog signaling connect slowly, low port density, less
calling information

Analog Circuit
Analog Circuit
FXS (Foreign eXchange Station): It is analog voice interface, also called subscriber
interface, and it is the port that you plug a telephone, fax, or modem to provide
telephony service.
FXO (Foreign eXchange Office): It is the port on the device that connect to the CO or PBX,
the port maybe on a telephone, fax and router that connects to the FXS port.
Interface Call out Call in
Opposite
interface
FXS Loop current variety Receive ringing current FXO
FXO Close loop circuit Receive ringing current FXS
PSTN
PBXTelephone
FXO FXS FXO FXS

Digital Circuit/Trunk
PBX
E1
Type Bandwidth Area Number
Signaling
Channel
T1 1.544 Mbit/s
North America, Japan,
Hong Kong, Taiwan
24 23rd
E1 2.048 Mbit/s Europe, Asia 32 16th
E1
PSTN
T1 T1
64kbps/channel

Signaling
 Signaling is the exchange information between involved points
in the network that sets up, controls, and terminates each
telephone call.
 Types of signaling
 Line Signaling: Loop start signaling, Ground start signaling.
 Inter-office signaling: CAS, CCS.
Inter-office signaling
Line Signaling PBX
Phone PBX Phone

Loop Start Signaling
 Loop start signaling is a typical signaling between a user and
the exchange.
 Voice signaling can be classified into three general types:
 Supervisory
 Addressing (Dual-Tone Multi-Frequency (DTMF) and Pulse)
 Informational-indicates call progress
Analog phone Central office
Ground
-48V

Signaling - CAS
 CAS (Channel Associated Signaling): Signaling and audio are
encoded and transmitted in the same channel.
PSTN
T1/E1 T1/E1
Signaling and Audio
PBX

CAS - R2
R2 Signaling
Line Signaling
Inter-register Signaling
PSTN
E1 E1
Line Signaling
Audio+ Inter-register Signaling
PBX

Signaling - CCS
 CCS (Common Channel Signaling) transmits the signaling
information (control information) on a separate channel from
the audio. Signaling channel controls multiple audio channels.
 For example, PRA and SS7.
PSTN
T1/E1 T1/E1
SignalingAudio
PBX

CCS - SS7
 Signaling System No. 7 (SS7) is a set of telephony signaling
protocols which are used to set up most of the PSTN calls.
 The network can be made up of several link types and three
signaling nodes - Service Switching Point (SSPs), Signal Transfer
Point (STPs), and Service Control Point (SCPs).

CCS - PRA
 PRA consists of B-channel and D-channel;
 T1 PRA consists of “23B+D”, E1 PRA contain ”30B+D”.
PSTN
E1/T1 E1/T1
D-channel: 64kbps
23 or 30 B-channel: 64kbps
PBX

CCS - PRA
Q.931
I.431/I.430
Q.921(LAPD)
Point to
point user
signaling
PRA
1
2
3
4
5
6
7
OSI
 Physical Layer
Provides an electrical, mechanical, and procedural
interface to the transmission medium.
 Data Link Layer
Provides the functional and procedural means to
transfer data between network entities and might
provide the means to detect and possibly correct errors
that may occur in the physical layer.
 Network Layer
Responsible for packet forwarding including routing
through intermediate routers, whereas the data link
layer is responsible for media access control, flow
control and error checking.

PRA Basic Call Flow
SETUP
networkcaller
SETUP ACKNOWLEDGE
ALERTING
CONNECT
CALL PROCEEDING
CONNECT ACKNOWLEDGE

Traditional Voice Application Network
…
PBX
Phone Phone
New YorkBeijing
…
PBX
Phone Phone
PSTN
SS7/PRA
1
2
Phone
3

Fax Application
 Fax machine can transmit signal through the existing PSTN
telephone network.
 Fax machine needs modulation and demodulation for fax
communication.

Modem
 A modem (modulator-demodulator) is a device that modulates
an analog carrier signal to encode digital information, and also
demodulates such a carrier signal to decode the transmitted
information.
 The goal is to produce a signal that can be transmitted easily
and decoded to reproduce the original digital data.

Summary
 Traditional terminals and PBX structure.
 The narrow bandwidth trunk protocols about traditional voice
network.

01 tdm voice introduction

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