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Components of a Computer Network

Components of a Computer Network

  1. Nodes
    • End Nodes (Senders and Receivers)
    • Intermediate Nodes
      • e.g. 
      • Hub
        • Physical layer
        • One-to-all (broadcasts), it is not one-to-to(unicast)
        • Can't store or keep track of MAC addresses so can't unicast so may lead to unnecessary traffic in the network, not efficient!
        • Receives data packets from one port and broadcasts it to all other ports
        • e.g. a hub can have 8 or 4 or any number of ports and all these ports are connected to individual nodes(devices)
        • Can be used to create LANs
      • Repeater
        • Physical layer
        • Used to regenerate the signal over the same network before it becomes too weak
        • They do not amplify but increase the intensity of the signal
        • e.g. optic fibers can only be effective for sending signals without becoming weak for up to 60 km or so
        • Also do not concern themselves with the MAC addresses for the machine
      • Bridge
        • Data-link layer
        • Connects two LANs : One port - One LAN
        • Uses MAC addresses to forward the data
          • MAC addr. PC1 -> Port 1
          • MAC addr. PC1 -> Port 1
          • MAC addr. PC1 -> Port 1
          • MAC addr. PC1 -> Port 2
          • MAC addr. PC1 -> Port 2
          • MAC addr. PC1 -> Port 2
      • Switch
        • Data-link layer
        • basically a Hub with a MAC table
        • Used to connect nodes/devices in a network
        • It uses a MAC table to forward a packet
        • It can make Unicast (One-to-one), Multicast and Braodcast communications
        • Can be used to create LANs
        • When it recieves a data frame from any of its ports, it examines the destination address and sends the frame to the corresponding port
        • Smart-Switches can also be used as a layer 3 device ( network layer ) but can work only insde a network and are not inter-network
    • Router
      • Network Layer (layer 3)
      • It uses the IP address of the computers
      • Connects two networks/subnets
      • Intelligent device as it can decide the best route to forward the packets from the source to destination
      • Maintains a routing table to decide the path of a packet
      • It examines the destination address of a given packet header and compares with the entries of its routing table
      • Routing tables
        • Static (manually setup by the system administrator)
        • Dynamic
      • Can connect LAN to WAN and LAN to LA N
      • One Port/interface against one network in the routing table
      • The Routing Table is usually stored inside the Random Access Memory of forwarding devices, such as routers and network switches
    • Firewall
    • Wireless Access Points (WAP)
    • Gateways
    • Cellphone Towers
    • NIC (Network Interface Card)
      • Physical layer and data-link layer
      • It is the middleman between a computer and the network
      • It is a physcial card or chip which contains the MAC address, works as an identiity for the devices on the network
  1. Transmission Media
    • Wired
    • Wireless
  2. Services - (software)
    • Email server
    • WWW
    • instant messaging 
    • Telnet services
    • DNS services etc.

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