In this chapter, we will describe how we have arrived at this electronic global village. Computers, telephones, and wireless devices are being linked by network everywhere in the world of connectivity. We are rapidly coming into an era in which we can find almost anything we want online and reach almost anywhere, anytime. When we collaborate, we are sharing information.
This sharing can be local or remote. Between individual, local communication usually occurs face to face, while remote communication takes place over distance.
Data Communications is the exchange of data between two devices via some form of transmission media such as a wire cable. In other words, we can say that transfer of information or data from one location to another is called data communications. The term Data Communication can generally be defined as the movement of encoded information by means of electrical transmission systems from one computer or device to other computer or device through communication channels (such as cables, wireless media etc.
Figure 3.1: Five different components of Data Communication System.
Component of Data Communication
There are five components (see figure 3.1) in data communication.
- Message: The message is the information (data) to be communicated. It can consist of text, number, pictures, sound, video or any combination of these.
- Sender: The sender is the device that sends the data. It can be computer, workstation, telephone, video camera and so on.
- Receiver: The receiver is the device that receives the data. It can be computer, workstation, telephone, television and so on.
- Communication Channel: The Communication channel is the physical path by which a data travels from sender to receiver. It can be a twisted – pair wire, coaxial cable, fiber optic cable, or microwave etc.
- Encoder and Decoder: The encoder converts digital signals to form, which can pass through transmission medium and decoder again coverts signal from encoded form into digital form, which is understandable for receiver. Without these, two devices may be connected but not communicating, such as a student speaking Urdu cannot understand a student who speaks only German without a translator.
Signals
The electromagnetic or light waves representing data are called signals. These are used to transfer data from one device to another device through a communication medium. Data communication signals can be in analog or digital form.
Figure 3.2: (a) Analog signal
Figure 3.2: (b) digital signal
- Analog: The analogue data signals are continuous electrical signal in the form of wave. This wave is called a carrier wave. Two characteristics of analogue carrier waves that can be altered are frequency and amplitude (figure 3.2.a). Frequency is the number of times a wave repeats during a specific time interval. Amplitude is the height of wave within a given period of time.
- Digital: A digital signal uses on-off electrical pulses in discontinuous. Or discrete form. Most computers are digital in nature, represent data as patterns of binary numbers (figure 3.2.b).
Type of Data
Data can be represented in different ways such as in data communication, numbers, images, audio, and video etc.
- Text: The text consists of words, sentences, and paragraphs. Text processing refers to the ability to manipulate words, lines, and pages Typically, the term text refers to text stored as ASCII codes that is, without any formatting. Objects that are not text include graphics, numbers and program code.
- Numeric: Numeric data consist of digits from 0 to 9, +(positive) or – (negatives)sign and a decimal point. It can be integer type or real type data.
- Image: This type of data includes chart, graph, pictures and freehand drawings. The information in this form is more comprehensive. The data are sent as contiguous bits, which for transfer, are packed into the 8-bit transfer bytes. The receiving site must store the data as contiguous bits.
- Audio: Sound is a representation of audio. It is converted into digital code by sampling the sound waves 44,056 times per second and converting each sample into a 16-bit number.
- Video: Video can be produced either as a continuous entity (by a camera), or it can be a combination of images, each a discrete entity, arrange to convey the idea of motion. Video creates action and movements.
Data Representation
The computer works with binary numbers, binary means two digits. These are 0 and 1. An electrical pulse inside the computer represents each binary number. I is represented by a pulse of electrical inside the computer and 0 by an absence of a pulse. Each binary digit is called bit and it is the smallest element of data.
Define data communication: Data communications is a process of transferring data electronically from one place to another. Data can be transferred by using different medium.
List out different elements of data communication.
The basic elements of data communication are message, sender, receiver, medium and Encoder and Decoder.
Define the term ender in data communication?
Sender is device that sends message. It is also celled source or transmitter. Normally, is used as sender in data communication systems.
Define the term receiver in data communication?
Receiver is a device that sends the data message. It is also called sink. The receiver can be computer, printer, or another computer related device.
Differentiate between sender and receiver.
Sender is a device that sends the data massage. It is also called source. Sender is normally a computer. Receiver is a device that receives message. It can be computer, printer, or another computer related device. The receiver must be capable of accepting the message.
Define the term medium in data communication?
Medium us the physical path that connects sender and receiver. It is used to transmit data. The medium can be a copper wire, a fiber optic cable, microwave etc.
Define the term Encoder and Decoder.
Encoder is a device that converts digital signals in a form that can pass through a transmission medium. Encoder is a device that converts the encoded signals into digital form sender and receiver cannot communicate successfully without encoder and decoder.
What is signal?
Signal is an electromagnetic or light wave that represents data signals are used to transfer data from one device to another through a communication medium.
Define digital signal.
Digital signal is sequence of voltage represented in binary form. Digital signal are in the form of electrical pulses of ON and OFF. There signal are in discrete form. Digital signals are faster and efficient. All data communication between computers is in digital form.
Define analog signal.
Analog signal is a continuous electrical signal in the dorm of wave. The wave is known as carried wave. Sound wave is an example of analog signal.
Write is two characteristics of analog signal.
Two characteristics of an analog wave are frequency and amplitude. The number of times a wave repeats during a specific time interval is known as frequency. The height of wave within a given period of time is known as amplitude.
Differentiate between analog and signal. Which is popular?
Analog signal is continuous electrical signal is the form of wave. Sound wave is an example of analog signal. Digital signal is sequence of voltage represented in binary form digital signals is popular. The provide lower error rates, higher transmission speed and higher quality voice transmission.
How is data represented in computer?
Computer works with binary numbers. Binary number may be 0 or 1. The data inside the computer is represented as electrical pulses. The binary digit 1 indicates the presence of electrical pulse.
Define bit and byte.
A binary digit is called bit. It takes one storage location in memory. A collection of eight nits in called byte. It is used to store single character.
Write different encoding characters used to represent data in computer.
The process of converting data into binary form is known as encoding. Data can be converted into binary form by using different encoding techniques. These are BCD Code, EBCDIC Code, ASCII and. Unicode.
what is ASCII code?
ASCII is the most widely used coding scheme for personal computer. The 7-bit code displayed on computer screens. An 8-bit code can represent 256 characters. The extended 128 unique codes represent graphic symbols.
Why does ASCII code only provide 256 character combinations?
It is an 8-bit code, and 28=256.
What is Unicode?
Unicode is a 16-bit code. It can represent 65636 characters. It has started to replace ASCII code. It can represent the characters of all languages in the world.
Explain why Unicode is superior to ASCII code
ASCII code uses 8 bit. It is limited to 256 different characters. Unicode uses 16 bits. It allows over 65,000 codes. It can represent all major languages.
Define transmission modes.
The way in which data is transmitted from one place to another is called data transmission modes. Simplex, half duplex and full duplex are modes of data transmission.
Describe half duplex mode of data transmission.
In simplex mode, data can flow only in one direction. It operates in manner similar to a one- way street. The direction of never changes. A device with simplex mode can either send or receive data. Traditional television broadcast in an example of simple’s mode.
Describe half duplex mode of data transmission.
In half-duplex mode, data can flow in both directions but nor at the same time. It is transmitted one-way at one time. A device with half-duplex mode can send or receive data but not at the same time. So, the speed of half-duplex mode is slow. Internet surfing us an example of half duplex transmission.
Compare simplex and half duplex mode.
In simplex mode, data can flow only in one direction. Radio and television broadcasting are the examples of this mode. In half-duplex mode, data can flow in both directions but not at the same time.
What is full duplex data transmission mode?
In full-duplex mode, data can travel in both directions simultaneously. Full duplex mode is faster way of data transmission than half duplex. Time is not wasted in changing in the direction of data flow. Telephone conversation is an example of full duplex mode.
what do you know about parallel data transmission?
A method of transmission in which groups of bits are sent at the same time over multiple wires is called parallel transmission. It is usually unidirectional. Each bit is transmitted over a separate line. Data transmission between computer and printer is an example of parallel transmission.
what is serial data transmission?
A method of transmission in which data is sent one bit at a time is called serial transmission. Telephone lines se this method of data transmission. Each individual bit of information travels along its own communication path.
Differentiate between serial and parallel transmission.
Parallel transmission in faster because all bits are sent at the same time. Setial transmission is slower that parallel transmission because data is sent sequentially one bit at a time. Each individual bit of information travels along its own communication path.
Describe Asynchronous data transmission.
In synchronous mode, saved data is transmitted block by block. Each block nay consists of many characters. It uses a clock to control the timing of bits being sent. Synchronous transmission in much faster than asynchronous because there is no gap between characters.
How does asynchronous transmission take place?
In asynchronous transmission, data is transmitted character by character. It uses a special start signal. A start bit has a value of 0. The value of 0 indicates that a character is about to be transferred. It alerts the receiver and it gets ready to receive the character. It start but has a value1, it indicates that the line is idle.
Compare asynchronous and synchronous transmission.
In asynchronous transmission, data is transmitted one character at a time. The sender and receiver are not synchronized with each other. Synchronous transmission sends a block of characters at a time. It allows sender and receiver to be synchronized with each other synchronous transmission is typically more efficient than asynchronous communications.
Differentiate between bounded $ unbounded communication.
In bounded media, communication device are directly connected via physical media like wire coaxial cable and fiber optics are examples of bounded media. In unbounded signal etc. microwave and satellite are examples of unbounded media.
Name some bounded media.
Some examples of bounded media are wire pairs, coaxial cable and fiber optics.
Name some unbounded communication media.
Some examples of unbounded communication media are microwave system and communication satellite.
What is wire pair?
Wire pair is a communication media made up of copper. Wire pair is usually made up of copper. The pair of wires is twisted it is used for short distance digital data communication. Its speed is 9600 bits per second in a distance of 100 meter.
What is coaxial cable.
Coaxial cable consists of a copper wire core covered by insulating material. The insulated copper wire is covered by copper mesh. It protects the cable from electromagnetic waves. It is used for long-distance telephone lines and local area networks.
What is fiber optics?
Fiber optics uses binary method of data transfer. It is made up of a thin glass fiber. It is thinner than hair. Data transfer rate of fiber optics is very fast. There is no chance of data loss.
Write two advantages and two disadvantages of fiber optics cable.
The advantages are that it provides faster data transmission and better security for signal during transmission. The disadvantage are that is difficult to install and very costly.
Define refraction.
An important characteristic of finer optics refraction. Refraction is a characteristic of a material to pass or reflect light.
Describe the roles of core and cladding in optical fiber.
The core carried the light signal. Cladding reflects the signal back into the core with perfect internal reflection so that no light escapes form the core.
Write a short note on microwave transmission.
Microwave are radio waves that are used to provide high-speed transmission. Data is transmitted through the air form one microwave station to another similar to radio signals. Microwave used line-of-sight transmission
How does microwave system work?
Microwave uses line-of-sight transmission. It means that the signals travel in straight path and cannot bend. Microwave stations are placed within 20 to 30 each other. Each station receives signal from previous station and transfer to the nest station.
What is the disadvantage of microwave system?
A disadvantage of microwave is that it is limited to line-of- sight transmission. This means that microwave signals must be transmitted in a straight line. There can be no obstruction such as buildings or mountains, between microwave stations.
What is communication satellite?
Communication satellite is a space station. It receives microwave signals from earth station. It amplifies the signals and retransmits them back to earth. It is established in space about 22.300 miles above the earth.
Write one advantage and one disadvantage of communication via satellite.
The advantage is that a satellite can allow long distance wireless communications. The disadvantage is the high cost to put a communications satellite in orbit.
Which units are used to measure the transmission rate of modems?
The unit of measure is bits per second (bps).
Define demodulation. Why is it necessary?
The process of converting digital signal into analog signal is called modulation. It is converted from digital to analog from.
Define demodulation. Why is it necessary?
The process of converting analog signal into digital signal is called demodulation the modem on receiving computer receiver data in analog form. The incoming analog data is converted back into digital format to be used by the computer.
How does a modem allow computers to communicate over telephone lines?
Modem translates computer data into signals compatible with the telephone system.
Define baseband.
Baseband is a communications technique in which digital signals are placed on the transmission line without change in modulation. It transmits up to a couple of miles. It does not require complex modems. Digital signals are commonly called base band signals.
Define broadband.
Broadband is a technique to transmit large amounts of data over log distance. It can send data by modulating each signal onto a different frequency. It transmits several streams of data simultaneously using FDM (Frequency Division Multiplexing) technique.
Compare broadband and In broadband transmission
data is carried on high-frequency carrier waves. Several channels may be transmitted over a signal cable. It allows one medium to be used to a variety of transmission needs. Baseband transmission does not use a carrier wave. It sends data along channel by voltage fluctuations. It cannot transmit multiple channels on one cable but it is less expensive than broadband as it can use less expensive cable and connectors.
Describe FDM.
FDM stands for Frequency Division Multiplexing. It divides the bandwidth of a communication line into smaller frequency bandwidths. Each part of the communication line can be used for transmitting data separately.
Explain external modem.
External modem is attached to the system unit as an external device through telephone line. This modem is connected to computer using serial cable to COM1 or COM2 port. It requires external power supply. It is easy to setup.
Explain internal modem.
Internal modem is a circuit board that is inserted into an expansion slot on the motherboard. It cannot be moved from one computer to another easily. It is difficult to setup than other types of modem.
What do you know about wireless modem?
Wireless modem transmits the data signals through air instead of cable. It is also known as radio-frequency modem. It is designed to work with cellular technology and wireless local area networks.
What is start signal? Write its different states.
Asynchronous transmission uses a special start signal. It is transmitted at the start of each message. It is sent when the character is about to be transmitted. A start bit has a value of 0. It is called space state. It the start bit has the value1; it indicates that the line is idle.