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AQA 7517 · Paper 2 · 4.9.2a

LAN, WAN &
Network Topologies

Star, bus, mesh, ring · Switches, routers · Section 4.9

WHAT YOU'LL LEARN
LAN vs WAN · Star/bus/mesh/ring topologies · Advantages and disadvantages · Network hardware
AQA SPEC LINK
4.9.2 — Networks: LAN, WAN, star, bus, mesh, ring topologies
LAN vs WAN

LAN & WAN

LAN — Local Area Network
Covers a small geographical area (building, campus). Owned and managed by one organisation. High speed (1–40 Gbps). Uses: Ethernet, WiFi.
WAN — Wide Area Network
Covers large areas (country, global). Uses third-party infrastructure (ISP leased lines, fibre, satellite). Slower, higher latency. The Internet is the largest WAN.
Star Topology

Star Topology

All devices connect to a central switch or hub. Data travels via the switch to the destination.
ADVANTAGES
Easy to add devices / Fault in one node doesn't affect others / Central management / Fast with switch
DISADVANTAGES
Central switch failure = entire network down / More cabling needed / More expensive
Bus Topology

Bus Topology

All devices connect to a single backbone cable. Data broadcast to all; terminators at each end prevent signal bounce.
ADVANTAGES
Simple, cheap to install / Uses less cable / Easy to extend
DISADVANTAGES
Cable fault = whole network fails / Collisions at high traffic / No fault isolation / Now largely obsolete
Mesh Topology

Mesh Topology

Full mesh: every device connects to every other. Partial mesh: some connections. Highly resilient — multiple paths exist.
ADVANTAGES
Very robust / Multiple paths for redundancy / No single point of failure / Used in Internet routing
DISADVANTAGES
Very expensive (n(n-1)/2 cables for n nodes) / Complex to configure and manage
Ring Topology

Ring Topology

Devices connected in a closed loop. Data travels around the ring in one direction (token ring). Each device acts as a repeater.
ADVANTAGES
Equal access for all devices / No collisions (token passing) / Predictable performance
DISADVANTAGES
One device failure = whole network fails (in basic ring) / Difficult to reconfigure / Mainly historical
Network Hardware

Key Network Devices

Switch
Connects devices in a LAN. Uses MAC addresses to forward frames to the correct port only. Reduces collisions.
Router
Connects different networks. Uses IP addresses to forward packets. NAT, DHCP, firewall built in on home routers.
Wireless Access Point (WAP)
Extends a wired LAN wirelessly. Broadcasts SSID; manages wireless client connections.
Comparison

Topology Comparison

TopologyKey AdvantageKey Disadvantage
StarFault isolationSwitch is single point of failure
BusCheap, simpleBackbone fault = total failure
MeshHigh resilienceVery expensive
RingEqual accessOne failure = whole ring fails
AQA Exam Style

Practice Question

AQA 7517 — Paper 2 Style
(a) A school has 30 computers. Explain ONE advantage and ONE disadvantage of using a star topology. [2]
(b) The Internet uses a mesh topology for its core routing infrastructure. Explain why. [2]
(c) Describe the difference between a switch and a router. [2]
[6 marks]
2 marks
(a) Advantage: if one computer fails it doesn't affect others [1]. Disadvantage: if the central switch fails the whole network goes down [1]
2 marks
(b) Mesh provides multiple paths between nodes [1]; if one connection/router fails, data can be rerouted, ensuring the Internet remains operational [1]
2 marks
(c) A switch connects devices within a LAN using MAC addresses to direct frames to the correct device [1]; a router connects different networks and uses IP addresses to forward packets between networks [1]
Summary

Key Points to Remember

LAN — small area, one org, fast; WAN — large area, third-party infrastructure, slower
Star — central switch; fault isolation but switch = single point of failure
Mesh — multiple paths; resilient; expensive — used in Internet core
Bus — cheap, single backbone; ring — equal access; both largely obsolete
Switch: MAC addresses, LAN. Router: IP addresses, connects networks.
🎉 Lesson complete — move to the quiz!