Category Self Image & Branding

What do you mean by Communication Network?

COMMUNICATIONS NETWORKS

Telephone calls, fax messages, e-mails, computer data – and often radio and television signals as well – all travel from place to place through a complex, worldwide telecommunications network. All the different forms of telecommunications are turned into signals that can travel through the network. They always travel between two points in the network (for example, two telephone receivers or fax machines), and are directed through it by electronic circuits at telephone exchanges. This sort of telecommunications network is called a switched network. Radio and television networks, where signals are sent to many receivers from one transmitter, are known as broadcast networks.

All the telecommunications devices (telephones, fax machines and home computers) connected to normal telephone lines are linked by the lines to a local telephone exchange. Each line has its own unique telephone number which the exchange uses to find it. All the local exchanges in one area are linked to a main exchange, which in turn is linked to other main exchanges to form a national network. Also linked into the network are special exchanges for mobile telephones and Internet service providers. Most information (speech, fax messages and computer data) travels to and from the local exchange in analogue form and between local exchanges in digital form.

There are several different ways of linking together telephone exchanges on a network. Some links are underground cables, either in the form of electrical cables or optical-fibre cables, in which signals are carried by light. Some links are made with microwaves. International links across oceans are made via satellites in orbit around the Earth, and through cables stretched across the sea bed.

THE INTERNET

The Internet is a vast computer network that stretches right around the world, made up of hundreds of millions of computers. Data can travel from any computer on the network to any other computer. The Internet began in the 1960s, when research agencies in the USA built their own communications network. Other organizations, such as universities, gradually joined. As home computers became cheaper and more popular in the 1990s, the Internet began expanding rapidly, with anybody being able to use it via a telephone line.

Internet use falls into two main areas – e-mail and the World Wide Web. With e-mail, it is possible to send a text message (with other data files, such as photographs, attached if needed) almost instantly to any other Internet user at their e-mail address. The World Wide Web (the “Web”) is a huge information-gathering system. It allows one computer connected to the Internet to ask for and copy files from another computer. The files are stored in standard form so that any computer can read them.

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What were various telecommunication modes?

 

TELECOMMUNICATIONS

Telecommunications is the sending and receiving of information using electricity, radio waves or light. The information can be sound, television pictures or computer data (which itself can be numbers, words, sounds and images). Forms of telecommunications include the telephone, fax, two-way radio, television and radio broadcasting, and the Internet. Most of these forms of communication require transmitting and receiving machines, and a network to link them together.

The first telecommunications device was the telegraph. Messages travelled along wires from a sending device to a receiving device as pulses of electricity, using some sort of code that both the sender and receiver understood. Practical telegraph systems were developed in the first half of the nineteenth century, and were first used for railway signalling. Early systems needed several connecting wires, but the system that eventually became standard, developed in the USA by Samuel Morse, needed just one wire. A network of telegraph lines, including undersea cables across the Atlantic, was quickly established right around the world.

In the early 1900s the telegraph was automated so that machines turned the message into code and back again. The sender could type messages on a keyboard and they would be printed out at the receiver’s end. To send a telegraph message, people had to visit a telegraph office. The message arrived at another office and was delivered by hand to the recipient.

The next major step in the development of telecommunications was the invention of the telephone, which could transmit speech, allowing people far apart to talk to each other. The first telephone receiver (the part that you talk into and listen to) was patented in 1876 by Alexander Graham Bell. This device both turned the sound of the user’s voice into an electrical signal, and an incoming signal into sound, which meant that the user could not talk and listen at the same time.

When the telephone was invented, there was no telephone network to link telephones in different places, but one soon grew up. All the telephone lines in an area meet at a telephone exchange, where they can be connected to one another, or to a line to another area’s exchange. The first exchange, opened in 1878 in Connecticut, USA, had just 21 lines. Like all early exchanges, it was operated by hand. A subscriber had to tell the operator which line he or she wanted to be connected to. The automatic exchange, which allowed people to dial numbers, was invented in the USA by Almon Strowger, and started working in 1897. Meanwhile, complex telephone networks grew in large cities. It took longer for different cities and countries to be linked, and until the middle of the twentieth century, the telegraph was still used for long-distance communication.

HOW A TELEPHONE WORKS

All telephone receivers are linked to a telephone exchange by a telephone line. When you lift or turn on the receiver, electronic circuits at the exchange detect it and wait for a number to be dialled. As you dial the number, the receiver sends signals to the exchange, which uses them to make a connection to the line of the person you are calling. The exchange makes the other telephone ring, and when it is answered, it connects the two lines together.

When you speak into the receiver’s mouthpiece, the sound makes a thin metal plate called a diaphragm vibrate. This movement affects the strength of an electric current, creating an electrical copy of the sound, which is called a signal. The signal travels through the connections in the telephone network to the other receiver, where it operates a tiny speaker in the earpiece, recreating the sound.

The signal travels in digital form for most of its journey through the network.

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What are Electromagnetic Radiations?

ELECTROMAGNETIC RADIATION

Radio waves, microwaves, light and X-rays have different characteristics, but they are all forms of electromagnetic radiation. Together with other forms, they make up a family called the electromagnetic spectrum. These forms of radiation can also be thought of as waves moving through space, in the same way as waves move across the surface of water. They all travel at the speed of light. Forms of electromagnetic radiation can be grouped according to their wavelengths – the distance between one wave crest and the next.

In reality, the wavelength at the left-hand end of the spectrum is a million million million times the wavelength at the right-hand end.

RADIO WAVES

The longest waves of the electromagnetic spectrum are radio waves. They have wavelengths ranging from more than 100 kilometres down to less than a metre. Radio waves are produced when an electric current changes strength or direction. Radio waves are important in communications through air and space. Microwaves are high-frequency radio waves also used in communications. Some microwave frequencies can be used in cooking.

Electromagnetic waves have amplitude and a frequency. Amplitude is the height or strength of a wave. Frequency is the number of wave crests that pass a point every second. To make a radio wave carry sound, it has to be modulated. This can be done by modulating (varying) either the strength of a wave – amplitude modulation or AM – or the speed of a wave – frequency modulation or FM.

LIGHT

In the middle of the electromagnetic spectrum is a small group of waves that our eyes detect, which is called visible light. It has wavelengths of around a thousandth of a millimetre. Waves with slightly different wavelengths appear as different colours, which together make up the colour spectrum. Light and especially laser light is very important in modern communications. Where practical, it is used in place of electricity and radio waves, because it can carry far more information without problems of interference.

 

INFRARED AND ULTRAVIOLET

To the left of visible light on the spectrum is infrared (IR) radiation. This is the radiation you feel as heat from hot objects. It is one of ways in which heat energy travels. Infrared radiation is used for short-range communications, such as in television remote controls, video camera autofocus and remote locking in cars.

To the right of visible light on the spectrum is ultraviolet (UV) radiation. It carries more energy than visible light. Ultraviolet radiation from the Sun is mostly absorbed by the atmosphere, but it still causes tanning of the skin and sunburn.

X-RAYS AND GAMMA RAYS

To the right of ultraviolet radiation are two more forms of electromagnetic radiation – X-rays and gamma rays. They both have very short wavelengths (less than a millionth of a millimetre) and extremely high frequencies (more than a million million million cycles per second). This means that X-rays and gamma rays have extremely high energies, and they can pass right through some solids. This makes them useful for investigating what is inside solid objects, such as human bodies, or closed suitcases at an airport security checkpoint.

X-rays were discovered by the German physicist Wilhelm Rontgen in 1895. They have a wide range of applications. In medicine, they are used to see the structure of bones and other organs by placing the patient between an X-ray source and a photographic film or camera. X-rays and gamma rays are also used in radiotherapy for treating cancers. However, in high doses they can damage tissues. X-rays are given off by high-energy, distant objects in space. X-ray telescopes can detect them.

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When was Happy Curriculum launched in India?

On July 2, 2018, the Delhi Government launched the ‘Happiness Curriculum’ for students from nursery to class VIII in schools run by it, in an effort to shift the focus from students’ academic achievement to their emotional well-being. The best part of the ‘Happiness Curriculum’ is that there is no homework, no exam or no marks.

In the last two years, the system has garnered attention with representatives from other Indian states and countries visiting the schools. After the U.S, First Lady Melania Trump attended one of the sessions of the ‘Happiness Curriculum’ during her recent visit to India, there has been a renewed interest in the programme.

Whose initiative is the Happiness Curriculum?

The ‘Happiness Curriculum’ is a flagship programme of the Arvind Kejriwal-led AAP government in Delhi. It was envisioned by the Education Minister of Delhi, Manish Sisodia. The content of the programme was designed by a committee of members including Delhi government teachers, lecturers from the District Institute of Education and Training (DIET) and principals, and organisations working in the area of child psychology.

What is Happiness Curriculum?

Instead of focussing only on the IQ (intelligent quotient), the Happiness Class focusses on students’ EQ (emotional quotient) and SQ (social intelligence quotient) as well. The curriculum incorporates meditation, mental exercises and storytelling in teaching for a holistic development of the students.

Manish Sisodia, in his book Siksha, lists the three main aspects of the curriculum: mindfulness meditation, inspirational stories to make children responsible and mature and activity-oriented discussions where children are encouraged to introspect and react.

How are the classes conducted?

The ‘Happiness Class’ takes place in all schools run by the Delhi government during the first period of the day, from Monday to Saturday. It breaks away from traditional teaching methodology and involves a combination of meditation, value education, and creative activities which prompt a student to think. On Mondays, mindfulness exercises are done, while on Tuesdays and Wednesdays, students are told stories which are followed by discussions. Students participate in creative activities on Thursdays and Fridays. And Saturdays are reserved for self-expression, when the students speak their mind and reflect on their behavioural changes.

The programme groups children into three categories: kindergarten to grade two, grades three to five, and grades six to eight. The curriculum has been designed catering to each group.

What is the aim of the programme?

According to the Delhi Government, the objectives of the ‘Happiness Curriculum’ are to enable children to develop self-awareness and mindfulness, critical thinking and communication skills. The Curriculum also teaches them to express themselves freely and creatively, to develop empathy, and to ensure healthy relationships with family, peers and teachers. Besides, it aims at helping learners to apply life skills to deal with stressful situations.

Kejriwal termed the ‘Happiness Curriculum’ as the third stage of reforms in the education sector initiated by his government after focussing on infrastructure development and motivation of teachers in the government schools.

Why did Melania Trump show interest in the ‘Happiness Curriculum’?

The Happiness Curriculum is similar to the Be Best programme initiated by her in the U.S. to teach children and young adults to not bully others, avoid drugs and take care of themselves.

 

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HOW DOES A TELEPHONE WORK?

A telephone works by sending and receiving electrical signals that represent sounds, including the human voice. When the required number is dialled, a signal passes to the called telephone, causing it to ring, buzz, flash a light, or even vibrate to attract the attention of the person using it. When the telephone is picked up or switched on, a connection is made, and a conversation can take place.

Messages reach the right telephone by means of a dialled number. Pressing the keys of the telephone causes different electrical pulses or varying tones to pass to electronic equipment at the telephone exchange. This “reads” the pulses or tones and routes the call to the correct area and telephone.

The Transmitter of a telephone serves as a sensitive “electric ear.” It lies behind the mouthpiece of the phone. Like the human ear, the transmitter has an 14 eardrum.” The eardrum of the telephone is a thin, round metal disk called a diaphragm. When a person talks into the telephone, the sound waves strike the diaphragm and make it vibrate. The diaphragm vibrates at various speeds, depending on the variations in air pressure caused by the varying tones of the speaker’s voice.

Behind the diaphragm lies a small cup filled with tiny grains of carbon. The diaphragm presses against these carbon grains. Low voltage electric current travels through the grains. This current comes from batteries at the telephone company. The pressure on the carbon grains varies as sound waves make the diaphragm vibrate. A loud sound causes the sound waves to push hard on the diaphragm. In turn, the diaphragm presses the grains tightly together. This action makes it easier for the electric current to travel through, and a large amount of electricity flows through the grains. When the sound is soft, the sound waves push lightly on the diaphragm. In turn, the diaphragm puts only a light pressure on the carbon grains. The grains are pressed together loosely. This makes it harder for the electric current to pass through them, and less current flows through the grains.

Thus, the pattern of the sound waves determines the pressure on the diaphragm. This pressure, in turn, regulates the pressure on the carbon grains. The crowded or loose grains cause the electric current to become stronger or weaker. The current copies the pattern of the sound waves and travels over a telephone wire to the receiver of another telephone. For more modern phones that have a telephone answering service, the sound wave is captured on a recording device which allows for the operator of the phone to playback at a later time.

The Receiver serves as an “electric mouth.” Like a human voice, it has “vocal cords.” The vocal cords of the receiver are a diaphragm. Two magnets located at the edge of the diaphragm cause it to vibrate. One of the magnets is a permanent magnet that constantly holds the diaphragm close to it. The other magnet is an electromagnet. It consists of a piece of iron with a coil of wire wound around it. When an electric current passes through the coil, the iron core becomes magnetized. The diaphragm is pulled toward the iron core and away from the permanent magnet. The pull of the electromagnet varies between strong and weak, depending on the variations in the current. Thus, the electromagnet controls the vibrations of the diaphragm in the receiver.

The electric current passing through the electromagnet becomes stronger or weaker according to the loud or soft sounds. This action causes the diaphragm to vibrate according to the speaker’s speech pattern. As the diaphragm moves in and out, it pulls and pushes the air in front of it. The pressure on the air sets up sound waves that are the same as the ones sent into the transmitter. The sound waves strike the ear of the listener and he hears the words of the speaker.

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WHAT IS SEMAPHORE?

Semaphore is a means of signalling using pairs of flags. Different flag positions stand for different letters and numbers. Semaphore signals are useful when the signaller is within sight of the receiver of the message but too far away to call out. It was widely used between ships sailing near each other in the days before ship-to-ship radio.

In programming, especially in UNIX systems, semaphores are a technique for coordinating or synchronizing activities in which multiple processes compete for the same operating system resources. A semaphore is a value in a designated place in operating system (or Kernel) storage that each process can check and then change. Depending on the value that is found, the process can use the resource or will find that it is already in use and must wait for some period before trying again. Semaphores can be binary (0 or 1) or can have additional values. Typically, a process using semaphores checks the value and then, if it using the resource, changes the value to reflect this so that subsequent semaphore users will know to wait.

Semaphores are commonly used for two purposes: to share a common memory space and to share access to files. Semaphores are one of the techniques for interprocess communication (IPC). The C programming language provides a set of interfaces or “functions” for managing semaphores.

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