Make your own free website on Tripod.com
Computer Appreciation

1.12 Networking Concept

Data Communications: No Need to Be There
  • Originally, computer hardware was all kept in one place
  • Decentralisation - telephone lines
  • Distributed data processing (DDP)
  • Value of computer communications

 Electronic Mail

  • Sending messages directly - one computer to another

 Teleconferencing

  • Part of CSCW technology (computer support co-operative work)
  • To bring people 'together' despite geographic barriers.
  • Videoconferencing

The Internet

  • It is the largest and most far-reaching network system of all time
  • A loosely organised collection of about 25,000 networks worldwide.
  • No one owns the Internet.
  • Needs a server with Internet protocol
  • Individuals are billed at an hourly or monthly rate
  • Research and education activities (original purpose) Vs business related (more than half)
  • Benefits for business
  • The future for business

Components of a typical Network:

Basic components of a data communications system:

    1. A sending device
    2. A communications link
    3. A receiving device.

 Design Considerations

  1. Data transmission speed
  2. Types of communication links
  3. Network topology:
      • Local area network
      • Wide area network
  4. Location of peripherals such as disks and printers

 

  1. Data Transmission Speed
  • Computer communication = digital transmission

= distinct pulses (in the form of on or off)

  • Media communications (voice transmission) = analog transmission

= continuous electric signal (in the form of a wave) 

  • Carrier wave to convert digital signals to analog form
  • Two flexible characteristics of a carrier wave:
  • Amplitude: the height of the wave
  • Frequency: the number of wave repetitions over a specific interval
  • Modulation: process of conversion from digital to analog signals
  • Demodulation: reverse
  • Modems: Converts a ‘DIGITAL’ signal to ‘ANALOG’ signal
  • Modem data speeds:
  • Old speed: 1200, 2400, and 9600 bps (bits per second)
  • Modem: 14,400 bps and 28,800 bps.

 BIT = A Binary Digit 

Types of Communications Links 

The physical medium used for data transmission (wires and cables)

 i. TWISTED PAIR

  • Sensitive to electrical pulses (copper)

 ii. FIBBER OPTICS

  • High-quality transmission - a single conductor wire
  • Made of glass fibres
  • Thinner than a human hair
  • Send data via light beams (all types of data voice, pictures, music, video at same time)
  • Materials are lighter and less expensive than wire cables
  • The University of Nottingham:
    • 1,200 (bits per second - bps) 1985
    • 2,400 (twisted pair)
    • 9,600
    • 28,000
    • 1,000,000 (fibber optics)
    • 10,000,000
    • 100,000,000 1998

iii. MICROWAVE TRANSMISSION

  • Line-of-sight transmission of data signals through the atmosphere, using relay stations (30 miles apart)
  • Speed, cost effectiveness, and ease of implementation.

iv. SATELLITE TRANSMISSION

  • Uses earth stations to send and receive signals from satellites
  • A satellite is hanging in space about 22,300 miles away.

 3. Network Topologies:

It is the physical layout of a network.

A. Local Area Networks (LAN)

  • A local area network (LAN) is a collection of computers, usually personal computers that share hardware, software, and data.
  • Cover short distances (one office or building)
  • Terminology:
  • Server - PC with large hard disk (holds shared files) – controls network
  • A node – A computer on a network
  • A network-interface card (NIC) – includes electronic components to send and receive massages

Three basic topologies:

  • Star network
    • A hub computer
    • All messages are routed through the central computer
  • Ring network
    • Circular manner
    • Data travel in one direction
    • Data is examined by the node to see if it is the addressee
    • If not, the data is passed on
    • If one node fails then the entire network fails.
  • Bus network
    • Has a single line
    • Nodes can be attached to or detached without affecting the network
    • If one node fails it does not affect the rest of the network


Two ways to organize the resources of a LAN:

  • Client/server: processing is done by the server, the results sent to the node
  • File server: processing is done by the node, the entire file is sent by server

B. Wide Area Networks (WAN)

  • A network of geographically distant computers and terminals.
  • Contain computer systems (Mainframe, minicomputer).

Copyright © 2001 Selfonline-Education. All rights reserved.