The development of personal computers brought about tremendous changes in business, industries, science & education.

  1. Business today relies on computer networks and the internet.
  2. Mails, documents, files are reached to our computers almost instantaneously from any part of the world.

Exchange of Data between two devices via some form of a transmission medium

  1. Data Information (in some format) that two devices want to exchange with each other
  2. The communication process of sharing information
  3. Sharing Local (face-to-face) or remote (long distance)
  4. Telecommunication (Tele ‘far’ in Greek) Communication involving telephony, telegraphy, television

Components of Data Communication

Message: Data to be communicated, popular forms include text, pictures, audio, video.

Sender: The device that sends data messages, can be a computer, telephone, video camera…

Receiver: The device that receives data message, can be a computer, telephone, handset, TV

Transmission medium: Physical path by which a message is transferred from sender to receiver, wired, wireless…

Protocol: Mutually agreeable set of rules that govern data communication between the communicating devices. Without protocols, two devices may be connected but may not communicate.

Example: A person speaking Spanish cannot understand what is said by a person in Japanese



Communication Data Flow:

Simplex: One device will always transmit and the other will always receive such as, Keyboard can only input and monitor can only accept output

Half-duplex: Both devices can transmit and receive BUT not at the same time. When one transmits, other has to wait till it finishes its transmission eg. walkie-talkies

Full-duplex: Both devices can transmit and receive simultaneously. The capacity of a communication channel must be divided between two directions Such as communication over the telephone, both can talk and listen at the same time.


Network: A Network is a set of devices (also referred to as nodes) connected by communication links.

A node may be a computer, printer, or any other device capable of sending and receiving messages/ data generated by other nodes on the network.

Network Criteria: Performance [depends on # of network users, type of Transmission medium, capabilities of connected hardware, and efficiency of software]

  • Transit time
    • The time required for a message to travel from one device to another
  • Response time
    • The elapsed time between a query and a response
  • Throughput
    • The average rate of successful message delivery over a communication channel (bits/sec)
  • Delay
    • How long it takes for a bit of data to travel across the network from one node or endpoint to another
  • Reliability
    • Reliability is measured by
      • Frequency of Network failure
      • Time takes by a link to recover from failure
      • Network’s robustness in a catastrophe
  • Security
    • Security includes protecting data from
      • Unauthorized access
      • Damage
      • Development & implementing policies for recovery from breaches and data losses