Computer network basics
FoundationA network is computers connected to share things. A small one is a LAN (home, school); connect the whole world and you get the internet — the biggest WAN.
- A network = computers connected to share data
- LAN (small) → WAN (big); the internet is the biggest WAN
- Connect by Ethernet (fast, steady) or Wi-Fi (convenient)
§Text Passage
1A computer network links computers and devices so that they can exchange data and share equipment. By coverage, a local area network (LAN) serves a small area such as a school computer room or home Wi-Fi, while a wide area network (WAN) spans cities and countries; the internet is the largest WAN of all, with routers and switches directing and managing the traffic.
2At home, Wi-Fi is a typical LAN: the router beams out a wireless signal, and once your phone, computer and TV have joined, they reach the internet through the broadband line. When the browser receives a web address, DNS first translates the domain name into an IP address so the data reaches the right server; if the line drops or DNS fails, online lessons and printing homework stop immediately.
3Hong Kong example: estate broadband, free Wi-Fi at MTR stations and cafe hotspots are all networking in action. Once you can tell a LAN from a WAN, you can make a first guess at the cause of any problem: if only your own device cannot join the Wi-Fi it is probably a local issue, while if no website opens at all the cause may be DNS or your internet provider — check the router first, then call customer service.
1Summary 重點摘要
A network is computers connected to share things. A small one is a LAN (home, school); connect the whole world and you get the internet — the biggest WAN.
2Vocabulary cards Vocabulary
Two or more computers connected so they can share data.
A network in a small area, e.g. a home, classroom or office.
A network spanning cities or countries; the internet is the biggest WAN.
The device that directs traffic; your home router also gives each device an IP address.
Wi-Fi connects by radio waves; Ethernet uses cables — usually faster and steadier.
A server is an always-on computer that hands out data; the client is your machine asking for it.
The device that converts the signal so your home can reach the internet; its job differs from the router's.
The worldwide network of networks — the biggest WAN of all.
3Step by step Steps
- The value of a network: sharingA network's chief value is sharing: exchanging files, sharing one printer, letting many devices use one internet line. Two connected devices already form the simplest network — two classroom PCs swapping homework files make a minimal LAN. Everyday examples abound: casting phone photos to the TV at home, classmates beaming notes to each other, a whole office sharing one printer. All of these are sharing, the everyday reason networks exist.
- LAN versus WANA local area network (LAN) covers a small area such as a home or campus; a wide area network (WAN) joins LANs in different places, and the internet is the largest WAN of all. Judge by reach: thirty classroom PCs form a LAN, while a video call with classmates abroad carries data across an ocean over WANs. The home works the same way: joining the house Wi-Fi is LAN territory, while browsing foreign sites on mobile data steps out into the WAN.
- Wired versus wirelessTwo ways to connect. Wired Ethernet: a cable straight into the router — fast, steady and nearly immune to interference, the first choice for gaming and video calls. Wireless Wi-Fi: no cables and free movement, but the signal fades through walls and slows down when many people share it. Choose by need: desktop PCs and smart TVs in fixed spots suit cables; phones and tablets need wireless. The classic 'no Wi-Fi in the bedroom' problem is solved by a signal extender or by running a cable instead.
- What the router doesA home router has two jobs: it is the door between the home network and the internet, and it hands every device an inner IP address — like a door number for each flat — so the phone, computer and TV each get one and data reaches the right device. Most routers also include a firewall that blocks malicious connections from outside. When home internet fails, the first move is checking the router's lights; restarting the router fixes the majority of connection faults.
- Clients and serversWhen you open a page, your computer or phone acts as the client, asking the website's server for data; the server is the always-on, powerful machine answering those requests — YouTube's videos and the bank's records all live on servers. The split resembles a restaurant: clients order at the table, the kitchen keeps ingredients ready and serves. One server can serve thousands of clients at once, which is exactly why popular websites slow down at crowded peak times.
- Bandwidth and speed in numbersBroadband speed is measured in Mbps (millions of bits per second), say a 1000 Mbps fibre line into the flat; since 8 bits = 1 byte, 1000 Mbps is about 125 MB per second, so a 2 GB film takes roughly 16 seconds in theory. Bandwidth is shared by the household: at peak evening hours, simultaneous HD streams and game downloads thin it out into buffering. Note that the advertised '1000 Mbps' is a ceiling — real speed depends on line quality, Wi-Fi distance and how many people are online, and is generally below the headline figure.
4Diagrams Diagrams
5Worked example Example
Example: a school computer room has 30 PCs sharing one printer, then connecting to the internet by fibre. Which parts are the LAN and which the WAN?
- The 30 PCs and the printer connected within the room form the LAN.
- The fibre link out of the room to the whole world is the WAN (the internet).
- The printer is a shared device on the network, showing the sharing value of networking.
- The judging rule is coverage: inside the room is LAN, across large distances is WAN.
- Further thought: when the internet fails, decide first whether the fault is in the room's LAN or out in the WAN before fixing anything.
- Answer: The 30 PCs and printer inside the room form the LAN, while the fibre link out to the world is the WAN — when troubleshooting, first decide whether the fault is local or external, then check the router and cabling step by step.
6Common mistakes Mistakes
7Quick check Quick check
Q1The network inside a school computer room is a…? A. WAN B. LAN C. server
Q2Name one wired and one wireless way to get online.
Q3When you open YouTube, what are your computer and YouTube's computer called?
Q4With 4 devices online at home, which device hands each one its inner IP address?
Q5Your online game lags and family suggest plugging in a cable. Why is wired usually steadier?
8Recap Recap
- A network = computers connected to share data
- LAN (small) → WAN (big); the internet is the biggest WAN
- Connect by Ethernet (fast, steady) or Wi-Fi (convenient)
- Client asks, server answers; the router directs traffic
- When the internet breaks, first decide: your router or the provider