Networks

• Internet


  A group of inter-connected networks
• World Wide Web


  A collection of web pages stored on computers all over the world, accessed via the Internet, with no central storage or owner
• URL (Uniform Resource Locator)


  A web address, all of which are unique
• Parts of a web address


  1. www

  2. .abc

  3. .co

  4. .uk

  5. /images/logo.jpg
• Domain names


  Top Level Domains (TLDs) such as .uk, .fr, .es, .de, .cz, .com, .org, .gov, .edu
• HTTP (HyperText Transfer Protocol)


  A protocol, a set of rules that web browsers and servers use to exchange information. If everyone follows the same set of rules, everything works.
• Data Packets


  Data transmitted over the Internet is broken down into smaller chunks or packets to be sent, with the destination and sender's addresses added, and each packet numbered and put in the right order again at the other end
• Packet switching


  Each knot is a node or router, and packets go the fastest way, not the shortest, which may differ for each packet
• Sending images as packets
• IP Addressing


  Every computer in the world has a separate, unique address, so data can be sent to these addresses to request or display a web page
• DNS (Domain Name Server)


  A DNS converts a web address or URL into the correct IP address for the computer that the web site sits on, making it easier to remember than the IP address
• The three main types of network topologies are bus, star, and ring.
• Network topology refers to the physical layout or arrangement of nodes (devices) and connections within a computer network.
• Network topology refers to how nodes are arranged within a network
• A network is a collection of devices connected by communication links.
• The internet is the largest computer network, connecting millions of computers worldwide
• Bandwidth


  The amount of data that can be carried at a time
• Calculating download speed


  1. Get file size and speed into same unit

  2. Divide file size over speed
• Calculating download speed


  • 1 MB file on 8Mbps connection: 1 second
  • 10 MB file on 8Mbps: 10 seconds
  • 700 MB music CD on 8Mbps: 11.66 minutes
  • 700 MB music CD on 2Mbps: 46.66 minutes
• Connection Speeds


  • Measured in Mbps (Megabits per Second)
  • 1 megabit is 10^6 or 1,000,000 bits
• Run a speed test: www.speedtest.net
• Upload vs Download Speed


  Download speeds are faster than upload speeds because most users spend more time downloading than uploading
• Broadband


  • A high-speed connection to the internet that has superseded the use of dial-up connections
  • Fibre optic glass thread is used in modern cables, with up to 1,000 fibres in a single cable
  • Potential bandwidth can be many terabytes per second
• Buffering


  • Occurs when a movie or music track plays faster than it downloads
  • Computer stores some of the file in a buffer until it can begin playing the whole thing
• Wireless connectivity


  • Must be close to a WiFi hotspot or router
  • Slower than a wired connection
  • Interference from walls and furniture
  • Greater security risk
  • No need to be physically connected
  • Can connect mobile devices
• First cable, 2,500 miles long, was laid across the Atlantic, after many difficulties including storms and cable breakages


  1858
• For each mile of cable, 133 miles of copper and iron wire was needed
• Total weight of the cable was one ton per mile
• Advantage of wireless connectivity

  There is no need to be physically connected
• Purpose of buffering


  Temporarily store downloaded data (e.g. a film or music)
• Network topology


  The arrangement of the elements (links, nodes, etc.) of a communication network
• Types of network


  • LAN (Local Area Network)
  • WAN (Wide Area Network)
• LAN (Local Area Network)


  • Usually operates on a single site or within a single building
• WAN (Wide Area Network)


  • Cover a large geographical area
  • Use cables, telephone lines, satellites and radio waves to connect
  • Used by international organisations
• Bus topology


  • Failure of one node does not affect the rest of the bus network
• Star topology


  • Easy to install and expand with extra nodes
• In a ring network


  Cable failure anywhere will affect the whole network
• In a ring network


  Need to 'break' the ring in order to add a new node
• All nodes must be switched on in a ring network for the nodes to communicate
• Router


  Traffic policeman for data packets, sends them on their way in the best direction