How Data Communication works, A Brief Introduction

Howdy folks, the term communication means to send or receive information. When we communicate we share any kind of information or data. Thus, a communication system can be elucidated as the collection of hardware and software that facilitates inter-system exchange of information between different devices.
Just as our brain tells our body parts the way to function and work together, the software governs the way devices on a network or link communicate with each other and perform functions.
Data Communication

Data communication is the exchange of data between two devices via some form of transmission medium/media. This transmission of data is done between a centralized computer and remote terminals or between two or more computer centers over established communication links. Data is transferred from one place to another in the form of signals.


There are 3-types of signals.

1. Digital Signal. Here data is transmitted in electronic form i.e. binary digits (0 or 1). Hence, digital data refers to information that has discrete states/values.

2. Analog Signal. Here data is transmitted in a continuous waveform that changes smoothly over time e.g. radio waves. Hence, analog data refers to information that is continuous.

For example, an analog clock shows the time in a continuous form where the movement of the hands are continuous but in a digital clock the time changes suddenly from 11:05 to 11:06.

3. Hybrid Signal. Hybrid signals have properties of both digital signal and analog signal.

Today’s world which is growing at a fast rate requires faster communication channels to move data from one place to the other. It was during the 20th century, the crux of the technology had been information gathering, processing and distribution. Other developments which we have witnessed is the installation of worldwide telephone networks, the birth and the inexplicable growth of computer industry and the launching of communication satellites. But as we have entered the 21st century, these gamut of areas are rapidly converging. This merging of the computers and communication channels has a profound impact on the way computer systems are organized. The older model of a single computer serving all our needs, is rapidly being replaced by the one in which a large number of separate but interconnected computers do the job.

Effectiveness of a Data communication system depends on 4 - fundamental characteristics :-

1) Delivery
2) Accuracy
3) Timeliness
4) Jitter
Note:Do As Told Joker” – remember it this way.
  • Delivery - Data must be delivered to the correct destination.
  • Accuracy - Data must be delivered accurately. Altered data is useless.
  • Timeliness - Data must be delivered in a timely manner. Data delivered late are useless.
  • Jitter - Variation in the data (packet) arrival time. E.g. – If in a video, data packets arrive with 20-ms delay and some arrive with 40-ms delay, then there will be uneven quality of video output.

There are 5 - components of Data communication :-

Components of Data Communication

1. Message – It is the information (data) to be communicated like - text, number, picture, audio and video.
2. Sender – Devices that sends the message. It can be a computer, workstation, telephone handset, etc.
3. Receiver – Device that receives the message. It can be a computer, workstation, telephone handset, etc.
4. Transmission medium – It is the path by which the message is transmitted E.g. – Twisted pair cable, Coaxial cable, Fiber optics cable and radio waves.
5. Protocol – Set of rules that govern the data communication. It is basically an agreement between the sender and receiver.

Data or information can be represented in forms like text, number, images, audio and video.

  • Text – It is represented by a bit pattern. Each text symbol is represented by a set of bits (0s or 1s) called code and the process of representing is called coding. E.g. – Unicode & ASCII are the coding systems.
  • Numbers – These are also represented by bit patterns. Numbers are directly converted to a binary number and here no coding system is used.
  • Images – These are also represented by bit patterns. Each pixel of an image is assigned a bit pattern. A black and white image made of only black and white dots can be represented by a 1-bit pattern. If the image includes gray scale then we can use 2-bit patterns like a black pixel can be represented by 00, a dark gray pixel by 01, a light gray pixel by 10 and a white pixel by 11. Color images are represented by methods called RGB (Red, Green & Blue) or YCM (Yellow, Cyan & Magenta) where intensity of each color is measured and a bit pattern is assigned to it.
  • Audio – It is in the form of sound or music and is continuous.
  • Video – It is in the form of a picture or movie and can be either continuous or it can be a combination of images that conveys the idea of motion.

 Digital and Analog Transmission 

Data is transferred from one point to another by means of electrical signals which may be in the Digital or Analog form.

Analog signals are continuous in nature and thus Analog data takes continuous values. Since it is continuous it becomes very difficult to remove any noise and distortion from them, which may be added during transmission or otherwise. The telephone lines used for data communication are usually analog signals.

Analog Signals

Digital signals are discrete in nature and thus Digital data takes discrete values. It is a sequence of voltage pulses represented in binary form. Data generated by computer is digital in form.

Digital Signals

When digital data is to be sent over an analog facility, the digital signals are converted to analog signals. This technique of converting digital signal to analog signal is known as Modulation and the reverse of it i.e. converting analog signal to digital signal is known as Demodulation.

 Serial and Parallel Transmission 

Serial transmission of data involves transmission as one bit at a time in a continuous stream along the communications channel. Here for each direction of data flow, only one wire is used, which is similar to the flow of traffic down a one-lane street. Serial transmission is typically slower than parallel transmission as data is sent sequentially in a bit-by-bit fashion unlike parallel transmission where several bits of data are sent in one-go.

Serial Transmission

Parallel transmission of data involves transmission of several bits of data concurrently through separate communication lines. This is done using many wires with each wire carrying one bit, which is similar to the flow of traffic on a multi-lane highway. Transfer of binary data in a computer uses parallel mode. So, if a computer uses a 64-bit internal structure all the 64 bits of data are transferred simultaneously on 64-lane connections. Data transmission between a computer and a printer commonly uses a parallel data transmission mode.

Parallel Transmission

 Simplex, Half-Duplex, Full-Duplex Transmission 

Based on the direction of data transmission the transmission systems can be classified into
3-modes – simplex, half-duplex or full-duplex.

Simplex - In Simplex mode of transmission, data flows in one direction only. As the communication is unidirectional only one of the two devices on a link can transmit and the other can only receive. E.g. – Radio, Television, Keyboard, Traditional monitors. (Keyboard can only do input and the monitor can only accept output). Here the entire capacity of the channel is used to send data in one direction. This mode of transmission is not very popular as most modern computers require a two-way interchange of data and information.

Simplex Transmission

Half-Duplex - In half-duplex mode of transmission, data flows in two directions, but not simultaneously. Both the devices on a link can transmit and receive but not at the same time. When one device is sending the other can only receive and vice versa. E.g. – Walkie-Talkies, citizen band radios. Here the entire capacity of the channel is used to send or receive data but not at the same time.

Half Duplex Transmission

Full-Duplex - In full-duplex mode of transmission, data flows in both the directions simultaneously. Both the devices on a link can transmit and receive simultaneously. E.g. – Telephone network, Mainframe computers. (When two people communicate on a telephone line both can talk and listen at the same time. Thus, this type of communication can be thought of as a flow of traffic on a 2-lane road).

Full Duplex Transmission

Here the data going in one direction share the capacity of the link with data going in the other direction. This sharing of the link can occur in 2-ways. Either the link contains 2-physically separate transmission paths, one for sending and the other for receiving or the capacity of the link is divided between the data signals travelling in both directions.
Full-duplex communication is made possible by devices called Multiplexers and is therefore the fastest of the modes.

 Asynchronous and Synchronous Transmission 

In asynchronous transmission, data is transmitted one-bit at a time, usually in a group of characters. Each character is transmitted separately, i.e. one character at a time. Each character has a start bit at the beginning and stop bit at the end. The start bit tells the receiving device where the character coding begins and the stop bit, tells the receiving device where the character coding ends. At the same time, there is an irregular time gap between each character. The start and stop bits allows the sending and receiving devices to synchronize the transmission. E.g. – Keyboard.

Asynchronous Transmission

Advantage – Accuracy. Does not require complex and costly hardware.

Disadvantage – Slow transmission time caused by the greater number of start and stop bits. If the channel is noise prone, false recognition of start and stop bits can occur.

In synchronous transmission, data is transmitted in a continuous sequence without start and stop bit and without any time gaps. If there are gaps, in between the data stream then the sender device must insert ‘idle’ bytes as ‘padding’ to fill the gaps. The data bytes are sent one after the other at regular intervals. The receiver counts the data bits as they arrive and group them in 8-bit units. Without gaps or start and stop bits there is no way for the receiving device to adjust its bit synchronization midway. Therefore, timing becomes very important because the accuracy of the received information is completely dependent on the ability of the receiving device to keep an accurate count of bits as they arrive.

Synchronous Transmission

Advantage – Faster transmission, as fewer bits are needed to identify the beginning and end of the character coding.

Disadvantage – Inaccuracy. Requires high-quality communication channels (hardware) as there is no room for error. When a receiver goes out of synchronization, losing track of where individual characters start and end, correction of errors takes additional time.

Another mode called – isochronous, involves synchronous transmission of asynchronous format.


Transmission of data has found its application in various fields which has led to the communities in the world to be not isolated anymore. It has given way to the system called computer networks which involves introducing interconnection of autonomous computers.

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