Class 11 Computer Science Chapter 3 Notes

• Define Data Communication and Describe its Five Components.
• Define Signal, explain Analog and Digital Signals.
• Describe FIVE Types of Data.
• Describe Data Representation.
• Define Data Encoding ? Describe Five Data Encoding Schemes.
• Describe THREE Modes of Data Communication.
• Explain Types of Data Transmission.
• Define Bandwidth? Describe Two Types of Bandwidth.
• Define and Classify Communication Media.
• Define Modem? Describe Transmission Rate and Speed. 
• Describe Various Types of Modems.
• Component of Data Communication: There are five components 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 a 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.
• 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.

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