LAN and WAN

A network is two or more devices connected together to share data and resources. The two main types differ by size and ownership:

• LAN (Local Area Network) — covers a small geographic area on one site (home, school, office). The infrastructure (cables, switches) is owned by the organisation.
• WAN (Wide Area Network) — covers a large geographic area (between cities/countries). It uses third-party infrastructure that is hired (e.g. telephone lines, leased fibre). The internet is the biggest WAN.

Nail it: the key differences are size and who owns the hardware. A LAN is one site & self-owned; a WAN spans distances & uses hired infrastructure.

LAN or WAN?

Network hardware

Key hardware that builds a network:

• NIC (Network Interface Card) — lets a device connect to a network; each has a unique MAC address.
• Switch — connects devices on a LAN and sends data only to the intended device using MAC addresses.
• Router — connects different networks together (e.g. your LAN to the internet) and directs data between them using IP addresses.
• Wireless Access Point (WAP) — lets devices connect wirelessly; transmission media = copper cable, fibre-optic cable or radio waves.

Switch vs router: a switch connects devices within one network; a router connects separate networks together.

The internet: DNS, hosting & the cloud

The internet is a global network of networks. Some key services:

• DNS (Domain Name System) — translates a human-friendly domain name (e.g. bbc.co.uk) into the IP address of the server. Like a phone book for the web.
• Hosting — storing files/websites on a powerful, always-on server so others can access them over the internet.
• The cloud — using remote servers over the internet to store data or run software, instead of on your own machine. Benefits: access anywhere, easy sharing, no local maintenance. Drawbacks: needs internet, ongoing cost, security/privacy concerns.

DNS: you type a domain name → DNS looks up the matching IP address → your browser connects to that server.

What does DNS do?

Star & mesh topologies

A topology is how devices are arranged/connected. OCR covers two:

• Star — each device has its own cable to a central switch. Fast, reliable (one cable failing only affects one device), easy to add devices — but needs lots of cable and depends on the central switch.
• Mesh — devices connect to many others, so data has multiple routes. Very reliable (no single point of failure), but expensive/complex (lots of connections). Wireless mesh is common for IoT.

Star, mesh — or both?

Tap a statement, then tap where it belongs.

Wired & wireless networks

Devices connect with cables or with radio waves.

• Wired (e.g. Ethernet copper, fibre) — usually faster, more reliable and more secure, but not portable and needs cabling.
• Wireless (e.g. Wi-Fi, Bluetooth) — convenient and portable, no cables — but can be slower, less secure and affected by range, walls and interference.

Nail it: wired = faster/more secure; wireless = more convenient/portable. Bandwidth & the number of users also affect real network speed.

Protocols & layers

A protocol is a set of rules for how devices communicate. Key protocols to know:

• TCP/IP — the core rules for sending data across the internet (TCP splits/reassembles data; IP addresses & routes packets).
• HTTP / HTTPS — for web pages (HTTPS is HTTP + encryption).
• FTP — transferring files. SMTP — sending email. IMAP / POP — retrieving email.

Protocols are organised into layers — each layer does one part of the job. Layering makes networks easier to develop, maintain and troubleshoot, and lets different manufacturers work together.

OCR note: you need to explain what layers are and why they are used (self-contained, independent, easier to develop & fix) — you are not required to name individual layers.

Which protocol?

Packet switching

When data is sent across a network it is broken into small packets. Each packet has a header (source & destination IP addresses, packet number) and the payload (the actual data).

• Packets can travel by different routes to the destination (whichever is quickest/free).
• They may arrive out of order, so they are reassembled in the correct order using their packet numbers.
• If a packet is lost, it can be re-sent.

Why: packet switching uses the network efficiently and is resilient — if one route fails, packets take another.

Why packet numbers?

Match device/term to its job

Tap a term on the left, then its matching job on the right.

The big ideas to know

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