1.1 · LAN vs WAN

Goal: distinguish LAN and WAN by coverage, ownership, speed and example.

Definitions

Type	Stands for	Coverage
LAN	Local Area Network	A single site (room, building, campus)
WAN	Wide Area Network	Multi-site / city / country / global

Side-by-side comparison

Feature	LAN	WAN
Coverage	< ~1 km	unlimited
Owner	Usually one organisation	Multiple parties; the Internet is a WAN of WANs
Speed (typical)	1 Gbps – 10 Gbps	10 Mbps – 1 Gbps per user, slower per hop
Cost	Low (Ethernet cables, switches)	High (leased lines, fibre between cities)
Latency	Sub-millisecond	Tens to hundreds of milliseconds
Examples	Office LAN, school computer lab	The Internet, a bank's branch network

Special networks worth knowing

Term	Coverage	Example
PAN Personal Area Network	A few metres around one person	Phone + Bluetooth headset + smartwatch
MAN Metropolitan Area Network	A city	Hong Kong public Wi-Fi (Y5ZONE legacy)
VLAN Virtual LAN	Logical subdivision of a physical LAN	School splits staff and student networks on the same switches
VPN Virtual Private Network	Secure tunnel over the Internet	Working from home and reaching the office LAN

Common services in a networked environment

The C&A Guide explicitly mentions:

• Internal communications (email, chat, video calls)
• Conferencing (Zoom, Teams)
• Resource sharing (files, printers, Internet bandwidth)

Worked example · A typical Hong Kong office

                Internet (WAN)
                     │
              ┌──── Router ────┐
              │                │
   Office A (HK Central LAN)   Office B (Kowloon Bay LAN)
   ├─ Switch                   ├─ Switch
   ├─ PCs, printers            ├─ PCs, printers
   └─ Wi-Fi AP                 └─ Wi-Fi AP

Each office is a LAN. Connecting them across the city makes a WAN.

Common student mistakes

• Calling the Internet a LAN — it is the world's largest WAN.
• Listing Wi-Fi as a separate type — Wi-Fi is just the wireless layer of a LAN.
• Mixing LAN with Ethernet — Ethernet is a LAN technology; not all LANs use Ethernet.

Exam-style question

Q (4 marks): Compare LAN and WAN in terms of coverage, ownership, and typical transmission speed. Give one example of each.

Sample answer:

• LAN: covers a small area (typically up to a building); owned and managed by a single organisation; high speeds (1–10 Gbps). Example: a school's computer lab connected via Ethernet and Wi-Fi.
• WAN: covers a large geographical area (cities, countries, continents); typically involves multiple organisations or ISPs; per-user speeds usually lower (10 Mbps – 1 Gbps) due to long-distance links. Example: the Internet.

Key takeaways

• LAN = local, fast, cheap, single-org.
• WAN = global, slower-per-user, multi-org.

➡️ Next: 1.2 IPv4 & IPv6