1

Telecommunication II

2

Course BooksUnderstanding Telecommunications, Part II

ISBN 91-44-00214-9Ericsson, Telia

Wireless Communications and NetworksWilliam Stallings

Introduction to Telecommunication Networks Engineering

Second EditionTarmo Anttalainen

3

Course Orientation

4

“The global telecommunications network is the largest and most complex technical

system that man has created”

Understanding Telecommunications, Part II ISBN 91-44-00214-9

Telecommunication Networks Basic purpose of a telecommunications

network: transmit user information in any form to another user of the network.

Many forms of networks, such as voice or data; subscribers may use different access network technologies to access the network, for example, fixed or cellular telephones.

Three technologies needed for communication through the telephone.

1) Transmission (2) Switching (3) Signaling.

5

Transmission Transmission is the process of transporting

information between end points of a system or a network.

Transmission systems use four basic media for information transfer from one point to another:

1. Wire-pair (copper) cables, such as those used in

telephone subscriber lines (access network)2.Optical fiber cables, such as those used in

high datarate transmission in telecommunications

networks (especially in transport networks)6

Transmission

3. Radio waves, such as microwave radio links, cellular telephones and satellite transmission.

4.Free-space optics, and infrared communications (limited application, e.g. PC-to-PC short range links).

7

8

Telephony Fundamentals Basic Telecommunication Network

Users of public networks, for example, a telephone network, are called subscribers

9

Telephony Fundamentals The telephone connector

Two wire line

10

Telephony Fundamentals Signaling is the mechanism that allows network

entities (user terminal or network switches) to establish, maintain, and terminate sessions in a network

Off-hook position The exchange notices that the subscriber has raised

the telephone hook and gives a dial tone to the subscriber

On-hook position The exchange notices that the subscriber has

finished the call (subscriber loop is disconnected), clears the connection, and stops billing

Dial Pad/Dial-plate The subscriber dials digits and they are received by

the exchange

11

Telephony Fundamentals Signaling is naturally needed between

exchanges as well because most calls have to be connected via more than just one exchange

The ordinary home telephone receives the electrical power that it needs for operation from the local exchange via two copper wires

The subscriber line, which carries speech signals as well, is a twisted pair called a local loop

The principle of the power supply coming from the exchange site makes basic telephone service independent of the local electric power network

12

Telephony Fundamentals Telephone exchanges supply dc voltage to

subscriber loops, and telephone sets use this supplied voltage for operation

On/Off hook switch Each telephone has a switch that indicates an

on- or off-hook condition When the hook is raised, the switch is closed

and an approximately 50 mA of current starts flowing

The control unit Rotary or Pulse dialing

In rotary dialing a local loop is closed and opened according to the dialed digits, and the number of current pulses is detected by the exchange

13

Telephony Fundamentals Slow Does not support supplementary services such

as call forwarding etc. The local-loop interfaces in telephone

exchanges have to support this old technology though it has been gradually replaced by tone dialing

Currently telephones include electronic circuits that make possible the implementation of better means for signaling

electronic circuitry, which is needed for number repetition, abbreviated dialing, and other additional features of modern telephone sets

14

Telephony Fundamentals DTMF Signaling

Each push button generates a tone with two frequencies

All frequencies are inside the voice frequency band (300–3,400 Hz) and can thus be transmitted through the network from end to end, when the speech connection is established

The subscriber is able to select with a switch on his telephone which

type of dialing is to be used. Tone dialing should always be selected if the

local exchange is a modern digital one

15

Telephony Fundamentals Rotary or Pulse dialing

Tone dialing It is quicker and dialing of all digits takes the same

time Additional push buttons are available (*, #, A, B, C,

D) for activation of supplementary services

16

Telephony Fundamentals 2W/4W Hybrid

Separates the transmitted and received signal Matches the impedance of 2W local loop to 4W

network circuit Cancels the echo