1.3.3 Networks

• Networks are the name given to two or more computers connected together with the ability to transmit data between each other
• Two main types of networks are Local Area Networks (LANs) and Wide Area Networks (WANs)
• Physical topology refers to the physical layout of the wires and components in a network, while logical topology shows how data flows
• In a bus topology, all terminals are connected to a backbone cable, with the ends plugged into a terminator
• Advantages of Bus Topology:

  • Relatively inexpensive to set up
  • Doesn't require any additional hardware
  • All computers can see the data transmission
• Disadvantages of Bus Topology:

  • If backbone cable fails, the entire network gets disconnected
  • As traffic increases, performance decreases
• In a star topology, a central node, often a switch, directs data through the network with every device connected to the switch
• Advantages of Star Topology:

  • Performance is consistent even with heavy network traffic
  • Easy to add new stations
• Disadvantages of Star Topology:

  • Expensive due to switch and cabling
  • If the central switch fails, the rest of the network fails
• In a mesh topology, every node is connected to every other node, commonly found in wireless technology like Wi-Fi
• Advantages of Mesh Topology:

  • If using a wireless network, there is no cabling cost
  • Nodes are automatically incorporated
• Disadvantages of Mesh Topology:

  • If using a wired network, a large quantity of cable is required compared to other network topologies like bus and star
  • Maintaining the network is difficult
• Protocols are a set of rules defining how two computers communicate with each other, ensuring all devices have a designated method of communication
• Examples of commonly used protocols:

  • HTTP: Used for web page rendering
  • TCP/IP: A networking protocol used in routing packets through networks
  • POP3 and IMAP: Mailing protocols for email access
  • FTP: Used for file transmission over networks
• The Internet is a network of networks allowing global communication, with continents connected using large international backbone cables
• The TCP/IP stack consists of networking protocols working together to pass packets during communication
• The TCP/IP stack layers:

  • Application Layer: Specifies the protocol for the application being sent
  • Transport Layer: Establishes end-to-end connection and splits data into packets
  • Network Layer: Adds source and destination IP addresses
  • Link Layer: Adds MAC addresses identifying Network Interface Cards
• The OSI model is a conceptual model that describes how data is communicated between two devices on a network

  
• The OSI model is divided into seven layers, each with a specific function:

  • Physical layer: responsible for the physical connection between devices
  • Data link layer: ensures data is transmitted and received correctly
  • Network layer: routes data between devices
  • Transport layer: ensures reliable data delivery
  • Session layer: establishes and maintains connections
  • Presentation layer: formats data for understanding
  • Application layer: provides user access to the network
• Packet switching is a method of communication where data is communicated using packets across a network, sent across the most efficient route which can vary for each packet
• Advantages of packet switching:

  • Multiple methods to ensure data arrives intact (e.g., checksums and cyclic redundancy checks)
  • Multiple routes can be used between devices
• Disadvantages of packet switching:

  • Time is spent deconstructing and reconstructing data packets
  • Must wait for all packets to arrive before data can be received
• Circuit switching is a method of communication where a direct link is created between two devices, maintained for the entire conversation between devices
• Advantages of circuit switching:

  • Data arrives in a logical order for quicker reconstruction
  • Enables two users to hold a call without delay in speech
• Disadvantages of circuit switching:

  • Bandwidth is wasted during periods of no data transmission
  • Devices must transfer and receive data at the same rate
• A firewall is a device designed to prevent unauthorized access to a network, consisting of two network interface cards between the user and the Internet
• Packet filtering/static filtering limits network access according to administrator rules and policies by examining source IP, destination IP, protocols, and ports
• Encryption is a way of keeping data secure when transmitting over the Internet, making data unreadable if intercepted and using keys for encryption and decryption
• Network interface cards (NIC) connect devices to a network, assigning a unique MAC address to each device
• A switch directs the flow of data across a network, commonly used in networks with a star topology
• A wireless access point (WAP) allows a device to connect to a network, often combined with a router for internet access, used in mesh networks
• A router connects two or more networks together, allowing private networks to connect to the Internet
• A gateway is used when protocols differ between networks, translating protocols so networks can communicate by removing the header from packets before adding data using the new protocol
• Client-server networks consist of terminals (clients) connected to a central, powerful computer (server) that holds important information and resources
• Advantages of client-server networks:

  • More secure as data is stored centrally
  • Central backups are carried out
  • Data and resources can be shared between clients
• Disadvantages of client-server networks:

  • Relatively expensive to set up
  • Functionality depends on the server; if it fails, performance falls
  • Trained staff are required to maintain the server
• Peer-to-peer networks connect computers to share files, each device acting as both a server and client, used in piracy due to difficulty in tracing file origins
• Advantages of peer-to-peer networks:

  • Cheaper to set up
  • Allows users to share resources
  • Easy to maintain
  • Not dependent on a central server
• Disadvantages of peer-to-peer networks:

  • Poorer security
  • May be difficult to locate resources
  • Backups must be performed separately
• Give three advantages to the business of connecting computers together in a LAN. (3 marks)

  • Can monitor user activity
  • Centralised security
  • Share internet connection
  • Central maintenance