What is Data Communication?
Data communication is the transmission of electronic data over some media. The media may be cables, microwaves.
Elements of Data Communication
Four basic elements are needed for any communication system.
1. Sender. The computer or device that is used for sending data is called sender, source or transmitter. In modern digital communication system, the source is usually a computer.
2. Medium. The means through which data is sent from one location to another is called transmission medium. If the receiver and transmitter are within a building, a wire connects them. If they are located at different locations, they may be connected by telephone lines, fiber optics or microwaves.
3. Receiver. The device or computer that receives the data is called receiver. The receiver can be a computer, printer or a fax machine.
4. Protocols. There are rules under which data transmission takes place between sender and receiver. The data communication s/w are used to transfer data from one computer to another. The s/w follows same communication protocols can communicate and exchange data.
Data may be transfer from one device to another by means of some communication media. The electromagnetic or light waves that transfer data from one device to another device in encoded form are called signals. Data transmissions across the network can occur in two forms i.e.:
(i) Analog signal.
(ii) Digital signal.
Analog Signal. The transfer of data in the form of electrical signals or continuous waves is called analog signal or analog data transmission. An analog signal is measured in volts and its frequency is in hertz (Hz).
Advantages of Analog Signaling
- Allows multiple transmissions across the cable.
- Suffers less from attenuation.
Disadvantages of Analog Signaling
- Suffers from EMI.
- Can only be transmitted in one direction without sophisticated equipment.
The transfer of data in the form of digit is called digital signal or digital data transmission. Digital signals consist of binary digits 0 & 1. Electrical pulses are used to represent binary digits. Data transmission between computers is in the form of digital signals.
Advantages of Digital Signaling
- Equipment is cheaper and simpler than analog equipment.
- Signals can be transmitted on a cable bidirectional.
- Digital signals suffer less from EMI.
Disadvantages Digital Signaling
- Only one signal can be sent at a time.
- Digital signals suffer from attenuation.
Techniques of Data Communication
There are two possible techniques of sending data from the sender to receiver, i.e.:-
(1) Parallel transmission.
(2) Serial transmission.
Parallel Transmission. In parallel transmission each bit of character / data has a separate channel and all bits of a character are transmitted simultaneously. Here the transmission is parallel character by character.
Serial Transmission. In serial transmission, the data is sent as one bit at a time having a signal channel for all the bit, i.e.:
Types of Serial Transmission
On serial transmission it is very essential to know exactly where one character ends and the next begins. The necessary synchronization that helps determine which bit is the first bit of the incoming character may be synchronous or asynchronous.
Asynchronous Serial Transmission
Computer communication that occurs one bit at a time with start and stop bits at the beginning and the end of each character is called Asynchronous Serial Transmission. In this type of transmission, there is no fixed time relationship with one character.
Advantages of Asynchronous Serial Transmission
- This type of transmission is very simple.
- This type of transmission is cheaper.
Disadvantages of Asynchronous Serial Transmission
- This type of transmission is slow.
In this method a clock signal is used and the sending as well as the receiving devices are synchronized with this clock signals. It doesn’t use start and stop bits but the character are sent in character groups called block
Advantages of Synchronous Transmission
- It is very fast as compared to Asynchronous Series Transmission.
Disadvantage of Synchronous Transmission
- It uses more expensive and complex equipment.
Modes of Data Communication.
The manner in which data is transmitted from one location to another location is called data transmission mode.
There are three ways or modes for transmitting data from one location to another. These are:
(2) Half duplex.
(3) Full duplex.
In half duplex mode, data can be transmitted in both directions but only in one direction at a time. During any transmission, one is the transmitter and the other is receiver. So each time for sending or receiving data, direction of data communication is reversed, this slow down data transmission rate.In half duplex modes, transmission of data can be confirmed.
Half Duplex Mode
Wireless communication is an example of half duplex.
Advantages of Half Duplex
- Costs less than full duplex.
- Enables for two way communications.
Disadvantages of Half Duplex
- Costs more than simplex.
- Only one device can transmit at a time.
In simplex mode, data is transmitted in only one direction. A terminal can only send data and cannot receive it or it can only receive data but cannot send it. Simplex mode is usually used for a remote device that is meant only to receive data. It is not possible to confirm successful transmission of data in simplex mode.
This mode is not widely used. Speaker, radio and television broadcasting are examples of simplex transmission, on which the signal is send from the transmission to your TV antenna. There is no return signal.
Advantages of Simplex
- Cheapest communication method.
Disadvantage of Simplex
- Only allows for communication in one direction.
In full mode, data can be transmitted in both directions simultaneously. It is a faster mode for transmitting data because no time wastes in switching directions.
Full Duplex Mode
Example of full duplex is telephone set in which both the users can talk and listen at the same time.
Advantage of Full Duplex.
- Enables two-way communication simultaneously.
Disadvantage of Full Duplex.
- The most expensive method in terms of equipment because of two bandwidth channels is required.
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