Networks and Connectivity

Networks: LAN and WAN

A Local Area Network (LAN) connects computers and devices within a small, defined area — typically a single building, school, hospital or office campus. All the hardware is usually owned and managed by the organisation itself. A Wide Area Network (WAN) connects devices across much larger geographical distances — cities, countries or even continents. The internet is the largest example of a WAN. Unlike a LAN, a WAN typically uses infrastructure owned and managed by third-party telecommunications companies, and the organisation leases access to those connections. The main differences to know are: LANs cover a small area and are owned by the organisation; WANs cover a large area and rely on external infrastructure.

Protocols

Protocols are the agreed rules and standards that control how data is sent, received and formatted across a network. Without protocols, devices from different manufacturers would be unable to communicate. The most important protocol suite is TCP/IP (Transmission Control Protocol / Internet Protocol), which governs how data is broken into packets, addressed and reassembled at the destination. HTTP (HyperText Transfer Protocol) governs how web pages are requested and delivered; HTTPS is its secure, encrypted version. FTP (File Transfer Protocol) is used to transfer files between computers. Email relies on protocols such as SMTP (for sending) and POP3 or IMAP (for receiving). Protocols allow a smartphone made in South Korea, a laptop running software from the USA, and a server hosted in the UK to exchange data seamlessly.

Internet, Intranet and Extranet

The internet is a global public network accessible to anyone — the network of all networks. An intranet is a private network that looks and works like the internet but is accessible only to people within a specific organisation, such as a company's employees. It might host internal documents, HR policies and staff forums. An extranet extends an intranet to give controlled, limited access to selected external users — for example, a supplier might be given access to a retailer's stock management system through an extranet, but cannot access the rest of the intranet. The key distinction is access: internet = public; intranet = private, internal; extranet = private, selectively external.

Network Topologies

A network topology describes how devices are physically or logically arranged and connected. There are three topologies to know. In a bus topology, all devices are connected to a single central cable called the backbone or bus. Data sent by one device travels along the bus in both directions until it reaches the intended recipient. Bus networks are cheap to install but if the backbone cable fails the whole network fails, and performance degrades as more devices are added because all devices share the same cable. In a star topology, every device connects to a central hub or switch. All data passes through the central device. Star networks are reliable because a single device failure does not affect others; they are easy to manage and fast because each device has a dedicated connection to the hub. The main disadvantage is that if the central hub or switch fails, the entire network goes down, and more cable is required than in a bus topology. In a ring topology, devices are connected in a loop and data travels in one direction around the ring, passing through each device until it reaches the correct destination. Ring networks avoid data collisions (since data travels in one direction), but if any single connection or device in the ring fails, the whole network is affected.

Devices Within a Network

Several hardware devices make a network function. A router directs (routes) data packets between networks — it is what connects your home LAN to the wider internet. A switch connects multiple devices within a LAN and directs data only to the device it is intended for, reducing unnecessary traffic. A hub is an older, less intelligent version of a switch that broadcasts data to all connected devices. A modem converts digital computer signals into a form that can travel over telephone or cable lines (and converts incoming signals back). A network interface card (NIC) is the hardware component inside each device that allows it to connect to a network. Wireless Access Points (WAPs) allow Wi-Fi-enabled devices to connect to a wired network wirelessly.

How Data Is Transferred and Threats to Data Transfer

When data travels across a network it is divided into small chunks called packets. Packets carry a data payload and header information such as source and destination addresses. Protocols that need ordered delivery, such as TCP, use sequence numbers so the receiver can reassemble data in the correct order. Packet switching allows networks to be more efficient because different packets can take different routes depending on congestion.

One significant threat to data in transit is packet sniffing. A packet sniffer is software (or hardware) that intercepts and reads packets as they travel across a network. On an unencrypted network, a malicious user running a packet sniffer can read usernames, passwords, email contents and financial data in plain text. Encryption (such as HTTPS) protects against packet sniffing by scrambling the data so that even if packets are intercepted, they cannot be read without the decryption key. Other threats include man-in-the-middle attacks and denial-of-service (DoS) attacks that flood a network with traffic to overwhelm it.

Cloud Computing versus In-house Servers

Cloud computing means storing data and running applications on remote servers accessed over the internet, rather than on hardware physically located in an organisation's own building. Benefits include: no need to buy and maintain expensive server hardware; storage can scale up or down as needed; data is accessible from anywhere with an internet connection; the provider maintains the underlying infrastructure, while the organisation remains responsible for its data, settings and access controls. Drawbacks include: dependence on a reliable internet connection; ongoing subscription costs; data is held by a third party (raising questions about privacy and legal jurisdiction); potential security risks if the cloud provider is breached. In-house servers give the organisation full physical control over its hardware and data, compliance with strict data regulations is easier to demonstrate, and there is no reliance on internet connectivity for internal systems. The trade-off is higher upfront cost, the need for specialist IT staff to maintain the hardware, and limited scalability.

Connectivity Methods

Devices connect to networks through a wide range of methods. Short-range wireless connections include: 802.11 (Wi-Fi) — the standard for wireless local networking, covering a building or campus; Bluetooth — connects devices like headphones and keyboards over short distances, often around 10 metres; NFC (Near-Field Communication) — works within a few centimetres for contactless payments; RFID — uses radio waves to identify tagged objects, used in library tracking and stock management. Medium-range wireless connections include mobile data networks: 3G (basic browsing), 4G (video streaming on smartphones) and 5G (very high speeds and low latency). Long-range wireless methods include: microwave transmission — line-of-sight radio signals between fixed tower antennas; satellite — data relayed via an orbiting satellite, enabling remote-area connectivity; latency depends on the satellite's orbit. Wired connections include: Ethernet — the standard for wired LANs using twisted-pair copper cable; USB-C — a reversible connector whose data speed and power delivery depend on the USB version and device; older USB-A and Micro USB connectors are still widely found on legacy devices.