computer organisation subject, Study notes of Computer science

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Introduction

DATA COMMUNICATIONS

• The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data.
• Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable or may be wireless.

Components of a Data Communication

System

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Five Components:

• Message- Text, Number, Image, Audio, Video
• Sender
• Receiver
• Transmission Medium
• Protocol

NETWORKS

• A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.
• A link can be a cable, air, optical fiber, or any medium which can transport a signal carrying information.

Network Criteria

• Performance
  • Depends on Network Elements- Transmit time, Response Time, Number of users, type of transmission medium, hardware, software.
  • Measured in terms of Delay and Throughput
• Reliability
  • Failure rate of network components.
  • Time to recover from a failure.
  • Measured in terms of availability/robustness
• Security
  • Data protection against corruption/loss of data due to:
    • Errors
    • Malicious users/ Unauthorized access.

Types of connections: point-to-point and

multipoint

Uses of Computer Network

• Business Applications
• Home Applications
• Mobile Users
• Social Issues

Business Applications (1)

A network with two clients and one server

Business Applications (2)

The client-server model involves requests and replies

Home Applications (2)

Some forms of e-commerce

Mobile Users

Combinations of wireless networks and mobile computing

PROTOCOLS

• A protocol is synonymous with rule. It consists of a set of rules that govern data communications. It determines what is communicated, how it is communicated and when it is communicated.
• The key elements of a protocol are
  • Syntax
  • Semantics
  • Timing

Elements of a Protocol

• Syntax
  • Structure or format of the data
  • Indicates how to read the bits - field delineation
• Semantics
  • Interprets the meaning of the bits
  • Knows which fields define what action
• Timing
  • When data should be sent and what
  • Speed at which data should be sent or speed at which it is being received.