Networks, the Internet and Connectivity
Why Connect Computers?
A computer network is two or more devices linked so they can exchange data and share resources. Without networks, every device would be an island: no email, no video calls, no shared printing in a school, no cloud storage. Networks enable collaboration at every scale — from two laptops in a bedroom to millions of servers spanning continents.
The advantages of networking are substantial. Files can be shared instantly without physical media. A single internet connection can be shared across many devices. Centralised storage makes backups simpler and more reliable. Users can communicate in real time. The disadvantages include the cost of hardware and ongoing maintenance, the risk of spreading malware to every connected device simultaneously, and the need for security measures to protect shared data from unauthorised access.
LAN and WAN
A LAN (Local Area Network) covers a small geographical area — a school building, a hospital ward, an office floor. The hardware (cables, switches, routers) is typically owned and managed by the organisation itself. Because devices are physically close together and the infrastructure is dedicated, LANs generally offer high-speed, reliable connections.
A WAN (Wide Area Network) covers a wide geographic area, connecting multiple LANs across cities, countries, or continents. WANs rely on third-party telecommunications infrastructure — leased telephone lines, undersea fibre optic cables, and satellite links — so no single organisation owns the entire network. The internet is the largest example of a WAN.
LAN vs WAN in three contrasts: Scale — LAN covers a small area (e.g. one building); WAN covers a large area (e.g. an entire country). Ownership — LAN hardware is owned by one organisation; WAN infrastructure is shared across multiple parties. Speed — LANs typically offer faster, more consistent connections because devices are physically close; WAN speeds depend on leased telecommunications links and vary significantly.
Unity College has a LAN connecting its computers across the school campus. The switches and cabling are owned by the school, giving speeds of up to 1 gigabit per second. Students at home connect to the internet (a WAN) via their broadband provider — speeds vary from 10 to 900 Mbit/s depending on the type of connection and distance from the exchange. Notice that:
- The school LAN is a single-owner, small-area network with dedicated infrastructure.
- The internet is a WAN owned by many parties — the school pays its ISP for a leased connection into this larger network.
- When a student at home uses the school’s virtual learning environment, their data travels first across their home LAN (router to device), then out across the WAN (internet), and into the school’s LAN at the other end.
How the Internet is Structured
The internet is a global network of interconnected networks. Two key elements hold it together: IP addressing and routers.
Every device on the internet is assigned an IP address (Internet Protocol address) — a unique identifier that acts like a postal address. When data is sent across the internet, each packet carries the source and destination IP address so that network equipment can forward it correctly.
router are the signposts of the internet. A router examines the destination IP address on each incoming packet and forwards it along the best available path towards its destination. Data sent from a device in Manchester to a server in New York may pass through many routers along the way, each making its own forwarding decision. This distributed design means the internet has no single point of failure — if one route is blocked, traffic can be rerouted.
Wired vs Wireless Connectivity
Wired networks use physical cables to carry data. Fibre optic cable transmits data as pulses of light and can achieve very high speeds (up to and beyond 1 Gbit/s) over long distances with minimal signal degradation. Copper cable (such as twisted-pair Ethernet cable) is cheaper and simpler to install but its speed and maximum range are more limited, and it is more vulnerable to electrical interference from nearby equipment.
Wireless networks transmit data using radio waves. The main benefit is mobility: devices can connect from anywhere within range without needing a physical cable. This makes wireless ideal for smartphones, tablets, and laptops that move around. However, wireless connections are generally slower and less reliable than their wired equivalents, more susceptible to interference from walls, other devices, and competing signals, potentially less secure because signals can be intercepted by anyone in range, and their quality degrades with distance from the access point.
Wired: faster, more reliable, more secure, less interference — but cables restrict mobility. Wireless: flexible and mobile — but slower, more interference, signals can be picked up by unauthorised devices, and range is limited. The characteristics that matter most are: speed, range, latency (the delay before data starts moving), and bandwidth (the amount of data that can be carried at once).
Network Speeds and Transmission Time
Network speeds are measured in bits per second. The units you need to know are:
- kilobit per second (kbit/s) — 1,000 bits per second
- megabit per second (Mbit/s) — 1,000,000 bits per second
- gigabit per second (Gbit/s) — 1,000,000,000 bits per second
Note that network speeds use decimal (1000-based) prefixes here — not binary. These are the standard units for measuring data transfer rates.
You also need to be able to calculate how long it takes to transfer a file. The relationship is:
Transfer time (seconds) = File size (bits) ÷ Transfer rate (bits per second)
File sizes are often given in bytes; remember that 1 byte = 8 bits. Convert before you calculate.
Question: A student wants to upload a 25 MiB video file to a school server. The school’s wired network has an upload speed of 100 Mbit/s. How long will the transfer take?
Step 1 — Convert file size to bits:
File size = 25 MiB = 25 × 1024 × 1024 bytes = 26,214,400 bytes
In bits: 26,214,400 × 8 = 209,715,200 bits
Step 2 — Convert transfer rate to bits per second:
100 Mbit/s = 100,000,000 bits per second
Step 3 — Calculate time:
Time = 209,715,200 ÷ 100,000,000 = 2.097 seconds (approximately 2.1 seconds)
Check: Does the answer make sense? A 25 MiB file at 100 Mbit/s should take about 2 seconds — this is consistent with common experience of school network speeds. Notice that the file size is given in binary MiB (mebibytes) but network speed uses decimal Mbit/s; the units must be handled separately.