Fundamentals of Computer Networks

A computer network is a group of connected devices that can communicate and share data, resources and services. Networks allow users to share files, printers, internet connections and other resources, but they also create security risks and depend on suitable hardware and protocols.

A Personal Area Network (PAN) covers a very small area around one person. For this specification, Bluetooth is the main PAN technology students need to know. A Local Area Network (LAN) covers a relatively small geographical area such as a home, school or office and is often controlled by one person or organisation. A Wide Area Network (WAN) covers a large geographical area and may connect many LANs. The Internet is the largest example of a WAN.

Networks can be wired or wireless. Wired networks commonly use copper or fibre-optic cables. They can provide reliable, fast connections and are generally less affected by interference, but installing cables can be inconvenient and expensive. Wireless networks are easier to install and allow mobility, but their performance may be affected by interference, distance and security issues.

A network interface card, or NIC, allows a device to connect to a network. A NIC may support wired or wireless communication. Each network interface has a MAC address, which is a physical address associated with the network adapter and can be used to identify or control access to devices on a network.

A network switch connects devices within a LAN and directs data to the intended device. It uses addressing information to forward data more efficiently than simply sending it to every connected device.

A network protocol is an agreed set of rules that devices follow when communicating. Protocols specify how data is formatted, transmitted, received and interpreted so that different devices and software can communicate successfully.

TCP, or Transmission Control Protocol, is responsible for reliable communication between devices. It helps establish communication, divides data into packets where required and ensures that transmitted data can be received correctly and in the correct order.

IP, or Internet Protocol, is responsible for addressing and routing data across networks. An IP address identifies a device or network interface for communication so that packets can be routed towards the correct destination.

HTTP, or Hypertext Transfer Protocol, is used to transfer web pages and related data between web servers and browsers. HTTPS is the secure version of HTTP and uses encryption to protect data transmitted between the user and the website.

SMTP, or Simple Mail Transfer Protocol, is used when sending email. IMAP, or Internet Message Access Protocol, is used to access and manage email stored on a mail server.

Network security is required because networks may be exposed to unauthorised access, data theft, interception and other threats. Different security methods can be combined to improve the overall protection of a network.

Authentication verifies the identity of a user or device before access is granted. This may involve usernames, passwords or other authentication methods. Authentication helps prevent unauthorised users from accessing network resources.

Encryption converts data into a form that cannot easily be understood without the correct key. It protects data from being read if it is intercepted while travelling across a network.

A firewall monitors incoming and outgoing network traffic and allows or blocks traffic according to security rules. Firewalls help prevent unauthorised access and can work together with authentication, encryption and other security measures.

MAC address filtering allows or blocks devices according to the MAC address of their network interface. It can be used as one part of network access control, although it should normally be combined with other security methods.

The TCP/IP model has four layers: application, transport, internet and link. The application layer includes network applications and protocols such as HTTP, HTTPS, SMTP and IMAP. The transport layer manages communication between hosts and includes TCP. The internet layer handles addressing and routing using IP. The link layer deals with local network communication and hardware such as network interface cards.