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Q1. What is data communication? Identify and explain the five components of a datacommunication system.

We all are acquainted with some sorts of communication in our day to day life.For communication of information and messages we use telephone and postalcommunication systems. Similarly data and information from one computersystem can be transmitted to other systems across geographical areas. Thus datatransmission is the movement of information using some standard methods.

These methods include electrical signals carried along a conductor, opticalsignals along an optical fibres and electromagnetic areas.

The five components are sender, receiver, protocol, medium and message

Q2. What are the basic elements of a communication system

The following are the basic requirements for working of a communicationsystem.1. The sender (source) who creates the message to be transmitted2. A medium that carries the message3. The receiver (sink) who receives the messageIn data communication four basic terms are frequently used. They are:Data : A collection of facts in raw forms that become information afterprocessing.Signals : Electric or electromagnetic encoding of data.

Signaling : Propagation of signals across a communication medium.Transmission : Communication of data achieved by the processing of signals.

Q3. Explain communication protocols.

The data communication software instructs computer systems and devices as to how exactly data is to betransferred from one place to another. The procedure ofdata transformation in the form of software is commonly known as protocol.The data transmission software or protocols perform the following functionsfor the efficient and error free transmission of data.1. Data sequencing : A long message to be transmitted is broken intosmaller packets of fixed size for error free data transmission.2. Data Routing : It is the process of finding the most efficient routebetween source and destination before sending the data.3. Flow control : All machines are not equally efficient in terms of speed. Hence the flow control regulates theprocess of sending data betweenfast sender and slow receiver.4. Error Control : Error detecting and recovering is the one of the mainfunctions of communication software. It ensures that data are transmittedwithout any error.

Q4. What are the advantages of Computerized Communication.

(a) Telephonic calls, using Internet, can be made to any part of the world with the same expenses as alocal telephone call made within the city.

(b) Pictures, sound and written matter can be sent within minutes and a confirmation about it reaching atthe destination can be obtained immediately.

(c) Message can be sent in coded form so that they are not understood by anybody else except theperson who is sending and the person who is receiving them.

(d) Message can be sent in any language from any place of world to any place.(e) Users need not take highly specialized training for sending or receiving message.

Q5 Explain data transmission modes.

There are three ways for transmitting data from one point to another.1. Simplex : In simplex mode the communication can take place in onedirection. The receiver receives the signal from the transmitting device.In this mode the flow of information is Uni-directional. Hence it is rarelyused for data communication.2. Half-duplex : In half-duplex mode the communication channel is usedin both directions, but only in one direction at a time. Thus a half-duplexline can alternately send and receive data.3. Full-duplex : In full duplex the communication channel is used in bothdirections at the same time. Use of full-duplex line improves theefficiency as the line turnaround time required in half-duplex arrangementis eliminated. Example of this mode of transmission is the telephoneline.

Q6 Discuss digital and analog signal transmission.

Data is transmitted from one point to another point by means of electrical signals

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that may be in digital and analog form. In analog signal the transmissionpower varies over a continuous range with respect to sound, light and radio waves.On the other hand, a digital signal may assume only discrete set of values withina given range. Examples are computer and computer related equipment. Analog signal is measured in Voltsand its frequency is in Hertz (Hz).A digital signal is a sequence of voltage represented in binary form. When digitaldata are to be sent over an analog form the digital signal must be converted toanalog form. So the technique by which a digital signal is converted to analog

form is known as modulation. And the reverse process, that is the conversion of analog signal to its digital form,is known as demodulation. The device, whichconverts digital signal into analog, and the reverse, is known as modem.1 0 0 0 0 0 0 1

Q7. What are the advantage of Digital Transmission over Analog Transmission

(a) The voice data, music and images can be interspersed to make more efficient use of the same circuits andequipment.

(b) Much higher transmission rates are possible using telephone lines.(c) Digital transmission is much cheaper than analog transmission.(d) Maintenance of a digital system is easier than maintenance of analog system.(e) A digital signal can pass through an arbitrary number of regenerators in with no loss in signal and thus

travel long distances with no information loss. In contrast, analog signal always suffer some informationloss when amplified, and this loss is cumulative.

Q8. Explain different Transmission Modes i.e. Simplex, Half-duplex and Full-duplex.

There are three modes of data transmission. These are:

(a) Simplex Simplex communication imply a simple method of communication. In simplexcommunications mode, there is a one way communication transmission. Television transmission is avery good example of this type of communication.

(b) Half-duplex - In half-duplex mode, both units communicate over the same medium, but only one unitcan send at a time. While one is in send mode, the other unit is in receiving mode. It is like two politepeople talking to each otherone talks, the other listens, but neither one talks at the same time.

(c) Full-duplex - In a half-duplex system, the line must be "turned around" each time the direction isreversed. This involves a special switching circuit and requires a small amount of time(approximately150 milliseconds). With high speed capabilities of the computer, this turn-around

Q9 Explain Asynchronous and Synchronous Transmission.

Asynchronous Transmission: -Asynchronous transmission is often referred to as start-stop transmission because of its nature, that is thesender can send a character at any time convenient and the receiver will accept it. Asynchronouscommunication lines remain in an idle state until the hardware on the line is ready to transmit. Since the line isidle, a series of bits have to be sent to the receiving node to notify it that there is more data coming. Whendata is finished, the node has to be notified that the transmission is complete and to go back to an idle state,hence the STOP bits are to be sent. This pattern continues for the duration of the time the link is operative. Thisis the characteristic of many terminals when on a terminal, the time spent between successive keystrokeswould vary. Thus, in asynchronous transmission, data is transmitted character by character at irregularintervals.Synchronous Transmission: -Synchronous devices need not use Start and Stop bits; so coordination between the two nodes, i.e. the senderand the receiver, is handled differently. In synchronous communications, there are two "channels" - one fordata and another for link Synchronization. The channel for synchronization uses the integral clock in thehardware for link synchronization between the two nodes when one of the nodes is ready to transmit data, aunique combination of bits called a Sync Character is sent to the receiver. Since the first character will probablyget trashed, a second one usually follows to ensure that synchronization is complete.

Q10. Compare between Asynchronous and Synchronous Transmission:

Synchronous communications tend to be more expensive than asynchronous ones as the hardwareinvolved is more costly due to integral clocking mechanism that have to be used as wellas moresophisticated engineering efforts.

Synchronous transmission is well suited to remote communication between a computer and suchdevices as buffered card readers and printers. It is also used for computer to computercommunications.

The primary advantage of synchronous transmission is its efficiency. Not only does it eliminate theneed for individual start-stop bits on each character, but much higher data rates can be used than withasynchronous transmission.

Asynchronous transmission is well suited to many keyboard type terminals. The advantage of this

method is that it does not require any local storage at the terminal or the computer as transmissiontakes place character by character. Hence it is cheaper to implement.