✓ Free · Component 1 · 1.3.3 Networks
1.3.3a Network Topologies, Types and Hardware
OCR H446 · A Level Computer Science · ~12 min read
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Network Types

A network is a collection of devices (nodes) connected together to share resources and communicate. Networks are classified by their geographical size:

TypeFull nameTypical rangeExample
PANPersonal Area Network~1 mBluetooth between phone and earbuds
LANLocal Area NetworkSingle building/siteSchool network, home WiFi
MANMetropolitan Area NetworkCity/townCity council network linking sites
WANWide Area NetworkCountry/globalThe Internet; company linking offices across countries

A LAN is typically owned by a single organisation and uses private cabling. A WAN spans large distances using infrastructure (e.g. telephone lines, fibre, leased lines) owned or rented from telecoms providers.

Network Topologies

A topology describes the physical or logical arrangement of devices in a network. The main topologies at A Level are star, bus, ring, and mesh.

Star Topology

All devices connect to a central switch or hub. Each device has its own dedicated connection to the switch.

  • Advantages: if one cable fails, only that device is affected; easy to add/remove devices; performance is not affected by other devices (using a switch, not a hub); easy to manage and troubleshoot.
  • Disadvantages: requires more cable than bus; if the switch fails, the entire network goes down; higher installation cost.

Bus Topology

All devices share a single central cable (the bus/backbone). Data travels along the bus and is received by all devices — only the addressed device processes it.

  • Advantages: simple and cheap to install; less cable needed.
  • Disadvantages: if the backbone cable fails, the whole network fails; performance degrades with more devices (collisions); difficult to troubleshoot; not suitable for heavy traffic.

Ring Topology

Devices are connected in a closed loop. Data travels in one direction around the ring (or both directions in dual ring). Each device acts as a repeater, amplifying the signal.

  • Advantages: data flow is orderly — no collisions; performs well under heavy load; can span longer distances than bus.
  • Disadvantages: if any device or cable fails, the whole network is affected (unless dual ring); adding devices disrupts the network; slower than star for large networks.

Mesh Topology

Devices are interconnected — each device connects to multiple others. In a full mesh every device connects to every other; in a partial mesh only some devices have multiple connections.

  • Advantages: very high fault tolerance — multiple alternative paths; no single point of failure; fast and reliable for critical systems.
  • Disadvantages: expensive — large amount of cabling required; complex to install and manage; not practical for large numbers of devices.
Exam tip: The most commonly used topology in practice is star — it is reliable (switch failure aside), easy to manage, and performance is not shared. Bus topology is now largely obsolete in real networks but still tested theoretically. Mesh is used in WANs (e.g. the internet) and critical systems.

Wired vs Wireless Networks

Wired (Ethernet/UTP/fibre)Wireless (WiFi/802.11)
SpeedHigher — up to 10 Gbps (fibre)Lower — typical ~600 Mbps max, drops with distance
ReliabilityVery reliable — no interferenceSubject to interference (walls, other devices, channels)
SecurityMore secure — physical access requiredLess secure — signals travel through air (encryption needed)
MobilityDevices must be physically connectedDevices can move freely within range
InstallationCostly to install cablingCheaper to deploy (no cabling runs)

Network Hardware

NIC (Network Interface Card)

Hardware component inside every networked device that provides the physical interface to the network. Contains a unique MAC (Media Access Control) address — a 48-bit hardware identifier burned in at manufacture. Used for communication within a LAN (Layer 2 addressing). Format: 6 pairs of hex digits, e.g. 3C:22:FB:01:A8:D0.

Switch

Connects devices within a LAN and uses a MAC address table to forward frames only to the correct destination port. This means bandwidth is not wasted — only the recipient sees the data. Operates at Layer 2 (data link layer). Most modern networks use switches (not hubs).

Router

Connects different networks together (e.g. LAN to WAN). Uses IP addresses to route packets — examines the destination IP and selects the best path. Operates at Layer 3 (network layer). A home broadband router connects the home LAN to the ISP's WAN. Routers maintain routing tables to determine which path to send packets down.

Hub

An older device that broadcasts incoming data to ALL devices on the network — no intelligence. Causes collisions and wastes bandwidth. Largely replaced by switches. Operates at Layer 1 (physical layer).

WAP (Wireless Access Point)

Extends a wired network to wireless devices. Connects to the switch or router via a wired connection and creates a wireless network that devices can join. Used to provide WiFi coverage in schools, offices, etc.

Transmission Media

  • Twisted pair copper (UTP/STP): most common LAN cable; cheap; susceptible to interference; typical speeds up to 1 Gbps (Cat5e/Cat6).
  • Coaxial cable: older; shielded; used in cable broadband.
  • Fibre optic: uses light pulses; very high speed (up to 100+ Gbps); long distances; immune to electromagnetic interference; expensive to install.
Exam tip: Know the difference between hub (broadcasts to all — Layer 1), switch (forwards to correct device using MAC table — Layer 2), and router (routes between networks using IP — Layer 3). This is a classic exam question.
⚠ Common Mistakes
  • Saying a switch broadcasts to all — only a HUB does this. A switch uses its MAC address table to forward frames to the correct port only.
  • Confusing MAC addresses with IP addresses — MAC = hardware address on NIC (Layer 2, permanent, used within LAN). IP = logical address assigned by network (Layer 3, can change, used for routing between networks).
  • Saying 'if one device fails in a ring network the whole network stops' is always true — only in a single ring. A dual-ring (like FDDI) can reroute around the failure.
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Worksheet — 1.3.3a Network Topologies

8 questions · 20 marks · instantly marked

Q1Explain the difference between a LAN and a WAN. Give one example of each.[4 marks]
✓ Mark scheme
LAN (Local Area Network): covers a small geographical area such as a single building or site [1]; typically owned and managed by a single organisation and uses private cabling [1]; example: school network, home WiFi [1]. WAN (Wide Area Network): spans a large geographical area — country or global [1]; uses infrastructure (telephone lines, fibre, leased lines) owned or rented from telecoms providers [1]; example: the Internet; a multinational company linking offices across countries [1]. Max 4 marks.
Q2Describe the star topology. Give TWO advantages and ONE disadvantage compared to a bus topology.[4 marks]
✓ Mark scheme
Star: all devices connect to a central switch; each device has its own dedicated cable to the switch [1]. Advantages (any 2): if one cable fails only that device is affected — other devices continue to work [1]; switch forwards data only to the intended device — no wasted bandwidth/collisions [1]; easy to add/remove devices without disrupting the network [1]; easy to troubleshoot — each device is independently connected [1]. Disadvantage (any 1): if the central switch fails the entire network goes down [1]; requires more cabling than bus — one cable per device [1]; higher cost to install [1].
Q3Explain why bus topology is considered unsuitable for networks with heavy traffic. What happens when two devices transmit simultaneously on a bus?[3 marks]
✓ Mark scheme
In a bus topology all devices share the same single backbone cable [1]; when two devices transmit simultaneously their signals collide — both transmissions become corrupted/garbled and must be retransmitted [1]; as more devices transmit there are more collisions — performance degrades significantly under heavy load, making it unsuitable for high-traffic networks [1].
Q4A hospital wants to install a network with very high fault tolerance, where a single cable failure does not interrupt any communication. Which topology would you recommend? Justify your choice.[3 marks]
✓ Mark scheme
Mesh topology (full mesh) [1]; each device connects to multiple other devices so there are multiple alternative paths for data to travel [1]; if any cable or device fails, data is automatically rerouted through an alternative path — no single point of failure, which is critical for a hospital where system availability is essential [1].
Q5Explain the difference between a network switch and a network hub. Why are switches preferred in modern networks?[3 marks]
✓ Mark scheme
Hub: broadcasts incoming data to ALL devices on the network regardless of destination — all devices receive all data; wastes bandwidth and causes collisions [1]. Switch: uses a MAC address table to forward data only to the specific port where the destination device is connected — only the intended recipient receives the data [1]. Switches are preferred because: they do not waste bandwidth; they reduce/eliminate collisions; they are more secure (other devices don't receive frames not addressed to them); they allow full-duplex communication [1].
Q6What is a MAC address? How is it different from an IP address?[3 marks]
✓ Mark scheme
A MAC (Media Access Control) address is a unique hardware identifier assigned to a NIC at manufacture — it is a 48-bit address expressed as 6 pairs of hex digits (e.g. 3C:22:FB:01:A8:D0) [1]. MAC address: permanent hardware address; used for communication within a LAN (Layer 2); cannot be easily changed [1]. IP address: logical address assigned by the network; used for routing between networks (Layer 3); can change (dynamic IP via DHCP) [1].
Q7Compare wired and wireless networks in terms of speed, security, and mobility.[3 marks]
✓ Mark scheme
Speed: wired is faster and more consistent — up to 10 Gbps via fibre; wireless speeds are lower and degrade with distance and interference [1]. Security: wired is more secure — physical access is required to intercept data; wireless signals travel through the air and can be intercepted more easily — encryption (WPA3) is essential [1]. Mobility: wireless allows devices to move freely within range of an access point; wired requires devices to be physically plugged in — no mobility [1].
Q8Explain the role of a router in a network. How does a router differ from a switch?[3 marks]
✓ Mark scheme
A router connects different networks together (e.g. a home LAN to the Internet/WAN) and forwards packets between them [1]; it uses IP addresses to determine the best path for each packet and consults a routing table to select the appropriate next hop [1]. Switch vs router: a switch operates within a single LAN using MAC addresses to forward frames between devices on the same network (Layer 2); a router connects different networks and forwards packets between them using IP addresses (Layer 3) — it operates at a higher level and can make decisions about inter-network routing [1].
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