Telecommunication Network to Computer Network

Telecommunication Network

to

Computer Network

What is Telecommunication?

Telecommunication networks carry information signals among entities which are geographically far apart. An entity may be computer, human being, a facsimile machine, a teleprinter, a data terminal, and so on.

Historical Backdrop

The field of telecommunications has evolved from a stage when signs, drum beats and semaphores were used for long distance communication to a stage when electrical , radio and electro-optical signals are used.

Let’s a Look Back

Contd...

• 1837 Telegraphy introduced in GB & 1845 n France

• 1876: Alexander Graham Bell invents the telephone 1881: First telephone Yellow Pages directory 1891: First dial phone 1887: First coin-operated telephone installed in the Hartford Bank by the payphone's inventor, William Gray. 1915: The first "official" coast-to-coast call is made from Alexander Graham Bell in New York City to Thomas Watson in San Francisco.

Alexander Graham Bell

Point-to-Point Telephone Connection

In telephonic conversation, the one who initiates the call is known as calling subscriber and the one for whom the call is destined is known as called subscriber.

Fully Connected Network

10 point-to-point links for connecting 5 entities

In general, for connecting n entities we need to have n (n-1)/2 links

Problem in Point to Point Connection

• Networks with point to point links among all the entities are known as fully connected networks.

• The number of links required in a fully connected network becomes very large.

Contd... • Practical use of Bell’s invention on a large scale

even on a moderate scale was not possible and it demanded the application of switching system or switching office or the exchange. With the introduction of switching system, the subscribers are not connected directly to one another, instead via the switching system. The functions performed by a switching system in establishing and releasing connections are known as Control functions. Functionally, the communication channels between switching system are referred to as trunks.

Birth of Switching System

Basic Components of Telecommunication System

Telecommunication system consists of four main components. They are:

End system or Instruments

Switching system

Signalling

Transmission media

End System

Rotary Dial Telephone

• Pulse Dialling (1895)

• The number of pulses in a train is equal to the digit value it represents

• Dialling 1 means 1 pulse and subsequently

• Only 0 creates 10 pulses

• Takes 12 seconds for dialling 7 digits

Touch Tone Telephone

Multifrequency Dialling (1950)

Or Dual-tone Multifrequency (DTMF) Diallng

Touching a button generates

a tone which is combination

of 2 frequencies –one from

lower band and the other

from upper band

DTMF Tone Decoding

Switching System

4 types of connections in Switching System

Local call connection between 2 subscribers in the system

Outgoing call connection between a subscriber and an outgoing trunk

Incoming call connection between an incoming trunk and a local subscriber

Transit call connection between an incoming trunk and outgoing trunk

Classification of Switching System

Manual Switching System

Energy Requirement in Exchanges

Local Battery (LB) Exchange Microphone needs to be energised in order to produce electrical signals corresponding to the speech waveform

• 1917 wall telephone, open to show magneto and local battery

• The use of magneto generator alternatively called as magneto exchange

Central Battery (CB) Exchange

Today's all exchanges

are CB Exchanges

Automatic Switching System

• It was the first automatic switching system developed by Almond B. Strowger in 1889

Advantages of Automatic Switching System

Language independent

A greater degree of privacy

Control function is faster

Load on the system = total time required to establish & release a call

Disadvantages of Strowger Switching System

• Regular maintenance

• Skilled manpower

• Strowger switching system has been the basis of telephone switching system for almost 70 years after ts inception in 1889

• Crossbar switching system was designed on the Principle of Common Control Concept

Contd...

• Principle of Common Control Concept was originated for mainly for 2 reasons:

• Identification no. of a subscriber is route dependent

• User must have the knowledge of topology of the network

• Overcoming this problem:

• Routing is done by the exchange

• A uniform numbering scheme is presented

• A Subscriber number has 2 parts

• Exchange Identifier + Subscriber line identifier within the exchange

Crossbar Switching System

• A crossbar switching system is a collection of switches arranged in a matrix configuration formed of relays & latches

Disadvantages of Crossbar Switching System

• Electromechanical component’s operational speed is slow

• lifetime is limited

• This subsystem have limited capability

• Impossible to provide additional functionalities

Electronic Switching System • Control function of the

exchange s performed by a computer or a processor

• Carrying out the exchange control function through programs stored in the memory of a computer led to nomenclature Stored Program Control (SPC)

• New facilities can be added to SPC system by changing the control program

Categorization of Electronic Switching System

• Space Division Switching

Here a dedicated path is established between the calling as well as called subscriber.

Crossbar system + SPC = electronic switching system

It was originally designed for analog network but now it is used both in analog and digital network.

Contd... • Time Division Switching

• Here, sampled values of speech signals are transferred at fixed intervals

Time Division Switching is again 2 types-

1. Analog 2. Digital

In analog switching system, the sampled voltage

level are transmitted whereas , in digital

Switching system , they are binary coded &

transmitted

Signalling

A switching system provides for 3 different forms of signalling:

Subscriber loop signalling

Interexchange signalling

Intraexchange signalling

Five Signaling Functions By Operator

1. Respond to the calling subscriber to obtain the identification of the called party.

2. Inform the calling subscriber that the call is being established.

3. Ring the bell of the called party.

4. Inform the calling subscriber, if the called party is busy.

5. Inform the calling subscriber, if the called party line is not obtainable for some reason.

Dial Tone

1.Indicates that the exchange is ready to accept dialed digits from the subscriber.

2.The subscriber should start dialing only after hearing the dial tone.

3.Else, initial dial pulses may be missed by the exchange which may result in the call landing on a wrong number or exchange timing out

Transmission Media

• There are 2 basic categories of

Transmission Media: • Guided Transmission Media -

uses a "cabling" system that guides or bounds the data signals along a specific path. The data signals are bound by the "cabling" system. Guided Media is also known as Bound Media. Guided media is basically 3 types:

• Twisted Pair • Coaxial Cable • Optical Fibre

Twisted Pair

Coaxial Cable

Optical Fibre

Contd...

• Unguided Transmission Media - consists of a means for the data signals to travel but nothing to guide them along a specific path. The data signals are not bound to a cabling media and as such are often called Unbound Media.

• Radio transmission is the example of unguided transmission media

Radio Transmission

Radio is the wireless transmission of signals through free space by electromagnetic radiation in the frequency range of 3 KHz to 300 GHz. These waves are called the Radio Waves

Radio Wave Uses

• TV broadcasting, radio broadcasting, mobile communication, etc. • Navigation of the ships and aircrafts.

• Global Positioning Satellite to precisely pin point the location of the targets.

• The radio telescopes are used to study the radio waves emitted by the far flung

galaxies and the star to understand their origins and characteristics.

• The radio waves (20 Hz to 2000 Hz) are used by us to communicate with each other.

• Remote control of toys.

• Echolocation by bats

• To detect the sea objects and also used to detection of flaws in the manufactured products.

• Ultrasound, which lies in the radio wave range, is used in medical science to detect several diseases.

Few Features of Radio Waves

• The radio waves are used to carry information from one place to another by the use of air as a medium.

• The speed of radio waves is equal to the speed of the light.

• The radio wave can travels larger distance with very less attenuation and hence can be used for communication without the need of the wired medium.

Dangers of Radio Waves

• The constant exposure to radio waves may cause cancer. The other dangers are 1. Headaches, 2. Eye Discomfort, 3. Facial redness, 4. Fatigue, 5. Dizziness, 6. Sleep Disturbances, 7. High Blood-pressure, 8. Pain in the joints and muscles, 9. Immune system abnormalities 10. Allegies.

Categories of Radio Communication

Ionospheric communication

Microwave communication

Tropospheric scatter communication

Satellite communication

Mechanism of Radio Transmission

Microwave Transmission

Microwave transmission is considered a Line of Site technology. This is because

the proper functioning of microwave transmission requires that the airspace between two microwave towers in clear of mountains, buildings, and other objects that could possibly block signals from being intercepted by the towers. Microwave transmission is limited by this need for a clear line of sight, in addition to being susceptible to attenuation by the atmosphere.

Contd...

Satellite Communication

Contd...

Contd...

Contd...

Contd... • Basic Components of a Satellite Solar Panel Antenna

Transponder Satellites are Geostationary at 36000 Km above the

equator Every Satellites is provided with Attitude & Orbit Control System (AOCS) 3 frequency bands are allocated for commercial satellite

communication • C, Ku & Ka Band Of them C is widely used because it has least

atmospheric effect.

Technological Evolution • Voice Transmission Data Transmission

• PSTN ISDN

PSTN normally carries voice or analog signal

But they can however be used for data

Transmission using suitable interfaces like MODEM (modulator/demodulator)

Modem as Interface

Computer (D)

Modem (D to A)

Telephone Network (A)

Modem (A to D)

Computer (D)

Differences between voice and data transmission

Voice Traffic

1. Continuous

2. Low bandwidth for long duration

3. Typical line utilization is 85%-95%

4. Half Duplex

5. Real time

6. Loss acceptable

7. Error tolerable

Data Traffic

1. Bursty

2. High bandwidth for short duration

3. Typical line utilization is 5-15%

4. Half or full duplex

5. Non-real time

6. Loss unacceptable

7. Error unacceptable

Switching Technique for data transmission-

1. Circuit Switching

2. Store & forward switching

-Message Switching

-Packet Switching

To recognize the diverse characteristics of voice & data traffic, switching technique for data transmission was developed

A typical Packet Format

Header

User Data

Destination id Source id Message id Packet id Control