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TSSNTelecommunications Switching System

Vidya sagar.pAssociate professor,

VBIT

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Communications

Communications may be defined as the transmissignal by way of a medium from sender to receive

Sender ReceiveSignal

Transmission

Medium

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Telecommunications

Telecommunications- the electronictransmission of signals for communication

Telephone

Radio

Television

http://images.google.co.in/imgres?imgurl=http://www.earlytelevision.org/images/tt5front.jpg&imgrefurl=http://www.earlytelevision.org/rca_tt5_story.html&h=270&w=360&sz=32&hl=en&start=3&tbnid=JZquPU_LwKgHxM:&tbnh=91&tbnw=121&prev=/images%3Fq%3Dfirst%2Btv%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DGhttp://images.google.co.in/imgres?imgurl=http://www.chennaimuseum.org/draft/gallery/08/03/image/radiotra.jpg&imgrefurl=http://www.chennaimuseum.org/draft/gallery/08/03/science4.htm&h=461&w=400&sz=91&hl=en&start=6&tbnid=FsuFHdLGDvFM4M:&tbnh=128&tbnw=111&prev=/images%3Fq%3Dfirst%2Bradio%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DGhttp://en.wikipedia.org/wiki/Image:CNAM-IMG_0564.jpg

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Telecommunications-Based Se

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Telecom services categorized

Communications teleworking, multimedia, mail

Knowledge distance education, databaseretrievals

Entertainment games etc. (getting increasingly

important!)

Information Marketing, yellow pages,catalogues

Service home shopping and banking,telemedicine

Remote control/remote

supervision

Automation applications

Category Important application

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Telecommunications Network

Atelecommunications network is a network oftelecommunications links and nodes arranged

messages may be passed from one part of the n

another over multiple links an through various

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MEDIUM SPEED C

TWISTED WIRE 300 BPS - 10 MBPS

MICROWAVE 256 KBPS - 100 MBPS

SATELLITE 256 KBPS - 100 MBPS

COAXIAL CABLE 56 KBPS - 200 MBPS

FIBER OPTICS 500 KBPS - 6.4 TBPS

BPS: BITS PER SECOND

KBPS: KILOBITS PS, MBPS: MEGABITS PS,

GBPS: GIGABITS PS, TBPS: TERABITS PS

SPEEDS & COST OF MEDIA

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World Numbering Plan

World Numbering Zones

Code Zone

1 N.A. & Carib.

2 Africa

3 & 4 Europe

5 S.A. & Cuba

6 South Pacific

7 Former USSR

8 N. Pac., E. Asia

9 Far & Mid East

0 Spare

Sample Country Codes

Code Country

20 Egypt

231 Liberia

33 France

351 Portugal

44 UK

55 Brazil

593 Ecuador

60 Malaysia

886 Taiwan

966 Saudi Ara

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Early telecommunications Homing pigeons have occasionally been used through history

different cultures. Pigeon post is thought to have Persians rootused by the Romans to aid their military. Frontinus said that JuCeasar used pigeons as messengers in his conquest of Gaul.

The Greeks also conveyed the names of the victors at the OlymGames to various cities using homing pigeons. In the early 19t

the Dutch government used the system in Java and Sumatra. A1849, Paul Julius Reuter started a pigeon service to fly stock prbetween Aachen and Brussels, a service that operated for a yeagap in the telegraph link was closed.

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Telegraph and telephone

Sir Charles Wheatstone and Sir William Fothergill Cooke inveelectric telegraph in 1837.Also, the first commercial electrical te

purported to have been constructed by Wheatstone and Cooke

on 9 April 1839.

Both inventors viewed their device as "an improvement to the

electromagnetic telegraph" not as a new device.

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Telegraph and telephone

Samuel Morse independently developed a version of the electrthat he unsuccessfully demonstrated on 2 September 1837. His

important advance over Wheatstone's signaling method. The fi

transatlantic telegraph cable was successfully completed on 27 J

allowing transatlantic telecommunication for the first time.

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Telegraph and telephone

The conventional telephone was invented independently by Aland Elisha Gray in 1876.

Antonio Meucci invented the first device that allowed the electrtransmission of voice over a line in 1849. However Meucci's delittle practical value because it relied upon the electrophonic effrequired users to place the receiver in their mouth to hear whsaid.

The first commercial telephone services were set-up in 1878 anboth sides of the Atlantic in the cities of New Haven and Lond

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Radio and television

In 1832, James Lindsay gave a classroom demonstration of wirtelegraphy to his students.

By 1854, he was able to demonstrate a transmission across the from Dundee, Scotland to Woodhaven, a distance of two milesusing water as the transmission medium.

In December 1901, Guglielmo Marconi established wireless

communication between St. John's, Newfoundland (Canada) anCornwall (England), earning him the 1909 Nobel Prize in physshared with Karl Braun).

However small-scale radio communication had already been dein 1893 by Nikola Tesla in a presentation to the National ElectAssociation

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Telephone System

Early telephone system

Powered by self-contained local battery

Ringing created by cranking generator

Todays telephone system

Powered through the line by battery at the central office (-48V)

Circuit is closed when handset is liftedfrom the cradle (off hook) Transmitter carbon granule microphone

Air pressure of sound waves impact on diaphragm, varying pressure on car

Resistance of electrical current passing through carbon granules varies the c

Receiver

Varying electrical current passing through windings on magnet, moves a diaas in a music loudspeaker.

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Basic Telephone SystemsPOTS is the plain old telephone system that connects most homes and sm

POTS lines were designed to transmit the human voice, which has a bandw

4000 Hz.

A telephone conversation requires two channels, each occupying 4000 Hz

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Various telelphone channels and their assignment of freque

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PSTN - The IstTelecommunication N

PSTN (public switched telephone network) is the wocollection of interconnected voice-oriented public tenetworks, both commercial and government-owned.referred to as the Plain Old Telephone Service (POT

Most of the Telephone lines provided by Public Swi

Telephone Network had analog connections which tdata in the form of electrical pulses.

Now the trend is towards digital technology

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Early Signaling and Telegraphy

1856 - Western Union Telegraph Company was founded. 1861 Over two thousand telegraph offices operated across th

States.

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Telephone Technology

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Telephone Technology

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Bandwidth requirements of various applic

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ELEMENTS OF COMMUNICATIONSWITCHING SYSTEM

The purpose of a telecommunication switching system is to provide the meinformation from any terminal device to any other terminal device selected

Telecommunication system can be divided into four main parts. They are

1. End system or Instruments

2. Transmission system

3. Switching system

4. Signaling

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End Systems or Instruments. The end system or instruments are a transmitter or

receiver that are responsible for sending information

or decoding or inverting received information or

message into an intelligible message. End systems in

the telelphone network have evolved from analog

telephones to digital handsets and cellular phones.

However, endless arrays of other devices are being

attached to telephone lines, including computerterminals used for data transmission

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Development of telephone

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Telelphone System

Transmitter. The transmitter consists of a box containing a powder of smallcarbon granules. One side of the enclosure is flexible and is mechanically

attached to a diaphragm on which sound wave impinges. The diaphragm

causes the carbon granules to compress or allow them to expand.

Consequently the resistance of the carbon granules decreases or increases in

the box. The carbon granules conduct electricity and the resistance offered

by them is dependent upon the density with which they are packed. If a

voltage is applied to microphone, the circuit in the circuit varies according to

the vibrations of the diaphragm. The varying electrical signal is similar to the

varying sound signal. For this reason, it is called an analog signal. The theory

of the carbon microphone indicates that the microphone functions like an

amplitude modulator

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Receiver. The varying signal from the handset A (calling subscriber) is couplereceiver of the handset B (called sibscriber). The receiver is an electrom

accompanying magnetic diaphragm. The electromagnetic usually have two coils of

with nominal resistance of 400 ohms. The receiver diaphragm must always be

direction from its unstressed position.

It must be positioned with an air gap between it and the poles of the elec

diaphragm is made of cobalt iron and it is slightly conical shaped near the ear for u

distribution and hence the sound.

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Central Battery SystemThe microphone requires to be energized in order to produce the electrical signal

the speech waveform. The minimum current required for proper operation of

microphone is about 23 mA. In early system, local batteries at the subscriber pre

This local battery system uses a dry cells to power the microphone, a magn

generate required a.c to indicate the exchange for service and an autotransfo

impedance matching between transmitter, line and receiver. The local batter

practically obsolete due to the necessity of frequent replacement of dry cells

procedure of magneto generator.

The local battery system was completely replaced by the central battery system whe

secondary cells is provided at the telephone exchange. Thus, a battery of 5

exchange powers the subscriber loop.

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Telephone Base UnitThe modern telephone set circuits

includes keypad, dialler IC, sound

amplifier IC, associated circuits,

ringer IC, buzzer, buzzer volume

control and ringer switch which is

operated during the on hook or off

hook of the telephone handset. The

above circuits are usefull in effectiveconversation between subscribers.

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Elemental Telecommunication SysteA simplest telephone communication system betweentwo subscriber is shown in Fig there is a quiescent

current flowing even in the asbence of sound.

This quiescent current is necessary for faithful sound

reproduction. The inductor L offers no dc resistance

but is nominally opposes the voice frequencies.

The audio signal transmitted from calling subscriber

not only heared at called subscriber receiver, but alsoat senders receiver. The audio signal heared at the

generating end is called.

Basic telecommuni

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Modern telecommunication sys

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Classification of switching system

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Telephone Technology 1878- The first telephone

exchange opened in New

Haven, Connecticut.

Connected 21 separate

lines.

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Strowger Switch--Example

crossbar switch

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crossbar switch