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OCR H446 · Component 1 · 1.3.3

Network Topologies,
Types & Hardware

OCR A Level Computer Science · cszone.co.uk
H446 SpecA Level
Learning Objectives

By the end of this topic you will be able to:

Distinguish LAN, WAN, MAN and PAN by scale and ownership
Compare bus, star, ring and mesh topologies including fault tolerance and cost
Describe the role of network hardware: switch, router, hub, NIC, WAP
Understand client-server and peer-to-peer network models
Network Types

LAN, WAN, MAN and PAN

By Scale
PAN – Personal Area Network. Very short range (Bluetooth, USB). Connects personal devices around one person.
LAN – Local Area Network. Single site (school, office). Usually owned and managed by the organisation.
MAN – Metropolitan Area Network. City-wide. Often connects multiple LANs across a campus or city.
WAN – Wide Area Network. Spans countries/continents. Uses leased lines or internet. The internet is the largest WAN.
Key Distinction
LAN infrastructure is owned by the organisation. WAN infrastructure uses third-party leased connections (ISPs, telecoms). This affects cost and control.
Client-server: dedicated servers handle requests from client machines. Peer-to-peer: all devices are equal, sharing resources directly with each other.
Topologies

Network Topologies

Bus
All devices share a single backbone cable with terminators at each end. Simple and cheap to install. Single point of failure — if the bus breaks, the whole network fails. Collisions increase with more devices.
Star
All devices connect to a central switch. Most common in modern LANs. If one cable/device fails, only that node is affected. Requires more cable than bus. Performance degrades if the switch fails.
Ring
Each device connects to exactly two others forming a ring. Data travels in one direction (or both in dual ring). A single break disrupts the whole network. Token passing avoids collisions.
Mesh
Every device connects to every other (full mesh) or some others (partial mesh). Extremely fault tolerant — multiple paths exist. Very expensive to cable. Used in WANs and critical infrastructure.
Hardware

Network Hardware

Switch: operates at Layer 2 (Data Link). Receives frames and forwards them only to the intended MAC address destination. Reduces unnecessary traffic. Replaces hubs in modern networks.
Router: operates at Layer 3 (Network). Connects different networks and routes packets using IP addresses. Maintains a routing table. Connects a LAN to the internet.
Hub: Layer 1 device. Broadcasts all incoming data to every connected device — creates unnecessary traffic and collisions. Largely replaced by switches.
NIC (Network Interface Card): hardware that connects a device to a network. Has a unique MAC address burned into it at manufacture.
WAP (Wireless Access Point): provides Wi-Fi connectivity. Connects wireless devices to a wired LAN. Uses radio waves; range limited by obstacles and interference.
Exam Practice
OCR H446 Style · 4 marks
Compare a bus topology with a star topology. Include one advantage and one disadvantage of each.
[4 marks]
1
Bus advantage: cheaper and simpler to install — only one backbone cable is needed, reducing cabling costs.
1
Bus disadvantage: a single break in the backbone cable brings down the entire network; it is a single point of failure.
1
Star advantage: if one cable or node fails, only that device is affected — the rest of the network continues to function.
1
Star disadvantage: requires more cable than a bus topology; if the central switch fails, the entire network loses connectivity.
Common Mistakes

Don't Lose Marks

!
Confusing switch and hub — a hub broadcasts to all devices (creates collisions); a switch intelligently forwards data only to the correct MAC address destination. Modern networks use switches, not hubs.
!
Saying a star topology has no single point of failure — the central switch IS a single point of failure. If the switch fails, all devices on that star network lose connectivity. Only the individual cable/node failure is isolated.
!
Confusing router and switch — a switch works within a network using MAC addresses; a router connects different networks using IP addresses. A home broadband router combines both functions but they are conceptually distinct.
1.3.3a Complete
Well done! ✓
Network Topologies, Types and Hardware
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