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

PBX Telephone

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

Signaling Audio

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

network caller

SETUP ACKNOWLEDGE

ALERTING

CONNECT

CALL PROCEEDING

CONNECT ACKNOWLEDGE


Traditional Voice Application Network

…

PBX

Phone Phone

New York Beijing

…

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.

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