NWF test revision

• Computer networks


  Connect computers, printers and other peripherals together, allowing people to communicate or share resources
• Basic elements of networks

  • Devices
  • Media
  • Messages
  • Rules
• Devices


  • Used for exchange messages with each other
• Media


  • A means of interconnecting devices
• Messages


  • Information that travels from one device to another
• Rules


  • How messages are sent, directed, received and interpreted
• Types of devices


  • End devices
  • Intermediary devices
• End devices

  Devices that often originate/consume messages in our communication
• End devices

  • computers
  • servers
  • IP phones
  • network printers
  • IP cameras
• Intermediary devices


  Devices used for directing and managing messages across the network
• Intermediary devices

  • Switches
  • routers
  • firewall devices
  • modems
• Media types


  • Wired (copper cables, optical fibres)
  • Wireless (Earth's atmosphere, space)
• Wired media


  Copper cables carry electrical signals, optical fibres carry light signals
• Wireless media


  Signals are microwaves
• Types of messages


  • web pages
  • e-mail
  • instant messages
  • telephone calls
  • other forms of communication enabled by the Internet
• Protocols


  The rules that the networked devices use to communicate with each other
• Protocols


  • TCP/IP (Transmission Control Protocol/Internet Protocol)
• Types of networks


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

  Used within small areas (e.g. within an office, building), provide services and applications to people within a common organizational structure
• Wide Area Network (WAN)


  Span very large geographic area (e.g. country), connects 2 or more LANs/MANs together using relatively slow-speed connections
• Internet


  The most well-known and widely used publicly-accessible internetwork, created by the interconnection of networks belonging to Internet Service Providers (ISPs)
• Intranet


  A private connection of LANs and WANs that belongs to an organization, accessible only by the organization's members, employees, or others with authorization
• Hubs


  Simple star topology network, performance is slow because data is sent to all computers connected to the hub (bandwidth is shared)
• Switches


  Send data only to the intended recipient, not all computers connected to it, improve network performance, connect multiple segments of a LAN together
• Routers


  Used to route messages among sub-networks on a computer network, find the best path for data packets from the source to the destination network, also used to connect computer network to the Internet
• Models of Distributed Computing

  • Client-server model
  • Peer-to-peer model
• Client-server model


  A number of client computers request for resources from the central server, dedicated computer running Server OS, centralized management and control, scalable, high level of security
• Peer-to-peer model


  Each node is a client as well as a server, all peers provide resource to other nodes, meant for small networks < 15 users, low cost, no centralization, no need for network administrator
• Hub


  A device that connects multiple devices together in a single network.
• Star Topology


  A network configuration where all devices connect to a central device (the "star" or Hub).
• Slow Network Performance


  Caused by broadcasting data to all devices connected to the hub, leading to bandwidth sharing and contention.
• Faster Performance


  A setup or technology that allows for faster data transfer and reduced contention in a network.
• DNS stands for Domain Name System

  
• Most of us find it hard to remember IP addresses
• Domain names


  Used to represent IP addresses

  
• DNS service


  Service to resolve domain name to IP address

  
• How DNS service works

  1. Domain name query sent

  2. DNS Server returns IP address

  3. Web browser requests web-page

  
• DNS service is responsible for domain name to address resolution

  
• DNS service


  • Uses servers to resolve domain names
  • Client/server service
  • Supports name resolution for other network applications

  
• DNS servers manage a massive database that maps domain names to IP addresses