Computer networks

• Computer network


  An interconnected system that connects computers/hosts allowing them to exchange data
• Networked computing devices (nodes)


  • Pass data to each other along network links (data connections)
• Data transfer


  In the form of packets
• Connections between nodes


  Established using either cable media or wireless media
• The best known computer network is the Internet
• Components of a computer network system

  • Message
  • Sender
  • Receiver
  • Transmission medium
  • Protocol
• Message


  The information (data) to be communicated
• Sender


  The device that sends the data message
• Receiver


  The device that receives the message
• Transmission medium


  The physical path by which a message travels from sender to receiver
• Protocol


  A set of rules that govern data communications
• Types of data flow (transmission mode)

  • Simplex
  • Half-duplex
  • Full-duplex
• Simplex


  Communication is unidirectional, only one device sends and the other only receives
• Half-duplex


  Each station can both transmit and receive, but not at the same time
• Full-duplex


  Both stations can transmit and receive simultaneously
• Types of connection


  • Point-to-point
  • Multipoint
• Point-to-point


  Provide a dedicated link between two devices
• Multipoint


  More than two devices share a single link
• Physical topologies


  • Mesh
  • Star
  • Bus
  • Ring
  • Tree
• Mesh topology


  • Each device has a dedicated point to point link to every other device
  • Robust, meaning one link failure does not halt entire system
  • Privacy or security: When every message travels along a dedicated line only the intended recipient can receive the message
  • Adding additional devices does not disrupt data transmission between other devices

  
• Star topology


  • Centralized management of the network, through the use of the central controller
  • Robustness: If one computer on the network fails, the rest of the network continues to function normally
  • Less expensive than mesh (requires less cabling)
• Bus topology


  • Works well when the network is small
  • Easiest network topology to connect nodes in a linear fashion
  • Requires less cable than mesh or star topologies
• Ring topology


  • Easy to install and reconfigure: adding or deleting a device requires changing only two connections
  • In a unidirectional ring network all data flows in one direction, reducing the chance of packet collisions
  • If one device does not receive the signal within a specified period, it issue an alarm that alerts the network operator to the problem and its location
• Tree topology


  • Point-to-point wiring for individual segments (branches)
  • Supported by several hardware and software venders
• Categories of networks


  • PAN (Personal Area Network)
  • LAN (Local Area Network)
  • MAN (Metropolitan Area Network)
  • WAN (Wide Area Network)
• PAN (Personal Area Network)


  Network organized by the individual user for its personal use
• LAN (Local Area Network)


  • Group of interconnected computers within a limited area to a few kilometers (room, building, campus)
  • Two or more PC's can from a LAN to share files, folders, printers, applications and other devices
  • Coaxial or CAT-5 cables are normally used for connections
  • Due to short distances, errors and noise are minimum
  • Data transfer rate is 10 to 100 Mbps
  • Can be of topology: Bus, ring , star or hybrid

  
• MAN (Metropolitan Area Network)


  • Design to extend over a large area of entire city
  • Single network or connecting number of LAN's to form larger network, so that resources can be shared
  • Owned by organization or individual
  • Data transfer rate is low compare to LAN
• WAN (Wide Area Network)


  • Provide long-distance transmission of data over large geographical areas (country or continent)
  • Contains multiple LAN's and MAN's
  • Uses satellites and microwave relays
  • Data transfer rate depends upon the ISP (Internet Service Provider)

  
• LAN


  Two or more PC's can form a LAN to share files, folders, printers, applications and other devices
• LAN connections


  • Coaxial or CAT-5 cables are normally used
  • Due to short distances, errors and noise are minimum
  • Data transfer rate is 10 to 100 Mbps
• LAN topology


  Bus, ring, star or hybrid
• MAN (Metropolitan Area Network)


  • Designed to extend over a large area of an entire city
  • Single network or connecting number of LANs to form larger network, so that resources can be shared
  • Owned by organization or individual
  • Data transfer rate is low compared to LAN
• MAN example


  • Organization with different branches located in the city
• WAN (Wide Area Network)


  • Provides long-distance transmission of data over large geographical areas (country or continent)
  • Contains multiple LANs and MANs
  • Uses satellites and microwave relays
  • Data transfer rate depends upon the ISP (Internet Service Provider) and varies over the location

  
• WAN examples


  • Enterprise Network: a WAN that is wholly owned and used by a single company
  • The Internet itself is a type of WAN, because it covers the entire globe
• Internet


  A collection of interconnected networks
• The Advanced Research Projects Agency (ARPA) in the U.S. Department of Defense (DoD) showed interest in finding a way to connect computers to share research findings


  1960's
• ARPA presented its ideas for ARPANET


  1967
• ARPANET was a reality. Software called the Network Control Protocol (NCP) provided communication between the hosts


  1969