Networks ig

• Network


  An arrangement of two or more computers that are connected together for the purpose of sharing resources and data
• Devices that can be linked together in networks

  • Desktops
  • Laptops
  • Tablets
  • E-readers
  • Gaming systems
  • Shop tills
  • Internet of Things (IoT) devices
• Reasons for connecting devices on a network

  • Share data files
  • Share hardware devices
  • Share an internet connection and internet services
  • Communicate with each other
  • Work together using web-based software
  • Make use of centralised IT support services
  • Socialise online
• Local Area Network (LAN)


  Covers a relatively small area, often a single site, such as a home, a hospital or a factory
• Wide Area Network (WAN)


  Spans multiple sites over a large geographical area using a variety of transmission media
• LAN is connected to form a WAN


  Enables the hotel chain to operate its loyalty card scheme
• Hotel chain has a WAN

  Benefits: data synchronised and shared across the whole business, software applications and patches deployed easily, eliminates need for duplicated functions
• Hotel chain has a WAN

  Guests benefit: can log in to the network wherever they are, access shared systems and work together collaboratively
• Bandwidth


  Measure of the capacity of a network - the maximum volume of data that can be transferred per second
• Latency


  The time between the data being transmitted and the moment it reaches its destination, measured in milliseconds
• Bandwidth is more important than latency


  For downloading a large movie file
• Data transfer rate


  The speed at which data is transmitted from one device to another, measured in bits per second
• Calculating how long it takes to transfer a file

  1. Convert file size from mebibytes to bits

  2. Convert transmission speed from Mbps to bits per second

  3. Divide bits by bits per second
• Copper wire


  • Transmits data as electrical pulses
  • Short range up to 100 metres
  • High latency due to susceptibility to interference
• Fibre optic cable


  • Transmits data as pulses of light
  • Can transmit data over long distances with no loss of signal strength
  • High speed up to 100 Gbps
  • Low latency due to less susceptibility to interference
• Fibre to the cabinet (FTTC)


  Fibre optic cables run from telephone exchange to street cabinet, final stretch to customer's premises is copper cable
• Fibre to the premises (FTTP)


  Entire connection from exchange to customer's premises is fibre optic cable, providing a much faster broadband connection
• Wireless transmission


  • Uses radio waves, microwave or infrared signals to create connections between devices
  • Flexible, devices can move around without losing connection
  • Theoretical range of 100 metres but can be obstructed by physical objects and interference
  • Slower than wired, up to 3.2 Gbps, with bandwidth shared by all active devices
  • Performance can be inconsistent due to interference
  • Less secure, data needs to be encrypted
• Wireless hotspots are available in public locations such as airports, cafés and hotels
• Many networks use a combination of wired and wireless connections
• Bluetooth


  • Works at distances up to 10 metres
• Zigbee


  • Uses low-power radio waves to connect thousands of IoT devices
• RFID


  • Uses electromagnetic fields to identify and track tags attached to objects
• Near Field Communication (NFC)


  • Uses electromagnetic fields to create a high-speed connection between two devices in very close proximity, commonly used for contactless payments
• Wireless coordinator


  Connected by cable to the WLAN and acts as a bridge between the two networks
• End devices


  Connect to the coordinator directly or via routers
• Contactless payments


  One of the most common examples of NFC
• Wireless network technologies


  • Bluetooth
  • Zigbee
  • Radio-frequency identification (RFID)
  • Near field communication (NFC)
• Bluetooth


  • Works at distances of up to 10 metres, for example between a wireless mouse and a laptop
• Zigbee


  • Uses low-power radio waves and can connect thousands of IoT devices with radio transmitters/receivers embedded within them
• RFID


  • Uses electromagnetic fields to identify and track tags attached to objects. A radio transmitter/receiver is embedded in each tag
• NFC


  • Uses electromagnetic fields to create a high-speed connection between two devices in very close proximity. Cards don't have to have their own power supply, they are powered by the electromagnetic field produced by the reader
• Alexa, Google Home, Nest and Hive are examples of electronic assistants and smart home technologies appearing in more and more of our homes
• Wi-Fi and Bluetooth are not designed for low power applications or for meshing together many devices
• Zigbee can help enable devices to communicate over a range of 75 to 100 metres indoors. It creates a mesh of interconnected devices up to around 65 000 at any one time without the need for a centralised hub
• Alexa is a device which uses Zigbee to communicate with other devices
• Simplified CSMA/CD sending algorithm

  1. Check if bus is busy

  2. If not busy then send message, else go to step 1

  3. Listen to see if message received correctly

  4. If message not received correctly then wait random amount of time, go to step 1 to retry sending message
• Node


  Each device on a network
• Network topology


  Describes how different nodes on a network connect to one another
• Bus topology


  • All the nodes on the network are connected to a single cable, known as the backbone. Messages are sent along the cable in the form of electronic signals. A terminator at each end absorbs signals that have reached the end of the cable, preventing them from bouncing back and causing interference