Unit 3. Network & Security

• Network


  More than one computer system connected together allowing for communication and sharing of resources
• Advantages of Networks


  • Easily share files, software and hardware between computers
  • Log in from any connected computer and access your data and files
  • An administrator can monitor network activity and control security settings
  • Data from computers on the network can be automatically backed up on central storage
• Disadvantages of Networks


  • There is an initial cost because network devices like routers are required. Larger companies will need to buy and maintain a server
  • A network manager / administrator might need to be employed to maintain the network
  • Security breaches are more likely and malware, such as worms, can spread quickly across the network
  • If the web server fails, all connected computers won't be able to access files or log on
• Local Area Network (LAN)


  Computer systems situated geographically close together, usually within the same building or small site, like a school or office
• Personal Area Network (PAN)


  A personal network for an individual, such as a photographer connecting a smartphone, desktop computer and printer together
• Metropolitan Area Network (MAN)


  Larger than a LAN but smaller than a WAN and typically covers a relatively large area like a university campus, town or city
• Wide Area Network (WAN)


  Computer systems situated geographically distant to each other, possibly across a country or even across the world
• Virtual Private Network (VPN)


  Allows for a secure and encrypted connection to a public network like the internet. It is often used to protect an individual's privacy by concealing their real location
• Wired Connections


  • Use physical cables, such as copper or fibre optic wires, and require a network interface card (NIC) to connect to a network
  • Use a wired connection protocol - most commonly Ethernet
• Wireless Connections


  • Use no cables but require a wireless network interface card (WNIC)
  • Generally have a slower speed and can be affected by the computer's distance from the wireless router as well as obstacles like walls or bad weather
• Network Topology


  Layout of computer systems on a network. Devices in a network topology diagram are often called 'nodes'

  
• Bus Topology


  • The nodes are connected to a bus (a central cable along which all data is transferred across the network)
  • Terminators are required at both ends of the bus to mark the end of the cable
  • Because of the simple layout, it is easy to attach another system to the main cable without disrupting the whole network
  • A bus topology is quick to set up once the main cable has been established making it optimal for temporary networks
  • It is cost-effective because it usually requires no additional hardware (like a hub or switch)
• Ring Topology


  • Computer systems are connected together in a single loop
  • Data packets are transferred around the ring in one direction, passing from one computer system to the next in a loop
  • Data collisions are avoided as data packets are transmitted in one direction around the ring
  • Attaching more systems to a ring topology won't affect the transfer speed (bandwidth) as much as other layouts like a bus topology because the data is transferred at a consistent speed

  
• Star Topology


  • Each computer system is connected to a central device, usually a hub or switch
  • The hub or switch looks at the destination address and transfers the packets directly to the intended computer
  • New systems can be attached directly to the central system so the network doesn't need to be shut down. System failures of attached computers won't usually cause complete network failure
  • Transfer speeds are generally fast in a star topology as there are minimal network collisions
• Mesh Topology


  • In a full mesh network, each computer system is connected to every other computer system
  • Data packets are transferred to the destination address along the quickest path, travelling from node to node
  • If a pathway is broken, there are many alternative paths that the packets can take
  • Because of the large possible number of systems and connections, a mesh topology can usually withstand large amounts of data traffic
  • New systems can be added to the network without disrupting the entire topology

  
• Data Packet


  When sending data across a network, files are broken down into smaller parts called data packets. Whole files are too large to transfer as one unit so data packets allow data to be transferred across a network quickly

  
• Contents of a Data Packet

  • Source Address
  • Destination Address
  • The Data
  • Tracking Information
  • Checksum to check corruption
  • Information to reassemble data back into original form
• Packet Switching


  With a packet-switched network the data is split into packets. The data packets are transmitted over a network and may take different routes

  
• Advantages of Packet Switching

  • Transmission is more secure as it is harder for a hacker to intercept complete data because it can take different routes
  • If a network device fails the data packets can take an alternative route
  • Data packets can be sent efficiently and individually across less busy routes
• Disadvantages of Packet Switching

  • Reassembling the data takes longer because packets may arrive out of order
  • It is less reliable than circuit switching as some data packets may not reach the destination (this is called packet loss)
• Circuit Switching


  Information is sent along the same route in one continuous stream
• Advantages of Circuit Switching

  • Reassembling the data is quick because the packets arrive in the order that they were sent
  • It is more reliable than packet-switching because data is sent in one continuous stream
  • The transmission is fast and should encounter fewer errors - once the connection has been securely established
• Disadvantages of Circuit Switching

  • Less secure as hackers could intercept the data and more easily access the data as it all takes the same route
  • Establishing a connection takes time to set up
  • If any device fails on the route then the whole connection breaks and data transfer will be incomplete
• An algorithm is a set of instructions used by computers to solve problems or perform tasks
• A program is an instruction that tells the computer what to do