Chapter: Network Types & Topologies
Welcome to this guide on Network Types and Topologies! Have you ever wondered how your smartphone talks to your smartwatch, how your school computer prints to a shared printer down the corridor, or how computers across continents share information? It all comes down to computer networks. Don't worry if networking terms feel unfamiliar at first—we will break down every single concept step-by-step with clear examples.
Note: This chapter is part of the "Communication and the internet" unit. While we focus here on network types, models, connectivity, speeds, and topologies, other topics like protocols, internet routing, and security are covered in detail in companion chapters.
---1. Why Computers are Networked
A computer network is formed when two or more computing devices are connected together using communication links so they can share data and resources.
Key Reasons for Networking Computers:
• Resource Sharing: Hardware devices (such as high-end printers, scanners, and storage drives) can be shared among many users, saving money and physical space.
• Data and File Sharing: Multiple users can access, view, and collaborate on files stored centrally without passing around physical drives.
• Centralised Management: Software updates, security patches, backups, and user access rights can be managed centrally by network administrators from a single machine.
• Communication: Users can communicate rapidly via messaging, email, and video calls.
• Centralised Backups: Critical data can be backed up automatically to a single central location, reducing the risk of lost work.
Quick Review: Computers are networked to share hardware, files, and internet connections, to communicate, and to allow central security and backup control.
---2. Network Types by Geographical Scale: LAN, WAN, and PAN
Networks are commonly classified by the geographic area they cover. A simple way to remember the progression in size from smallest to largest is: PAN → LAN → WAN.
A. Personal Area Network (PAN)
• Geographical Area: Centred around a single person, typically within a range of a few metres (e.g. inside a single room).
• Typical Use: Connecting personal devices such as a smartphone to wireless earphones, a smartwatch, or a laptop.
• Common Technologies: Often relies on short-range wireless connections like Bluetooth.
B. Local Area Network (LAN)
• Geographical Area: Covers a small, limited geographical area, such as a single room, a home, an office, a school, or a single building site.
• Infrastructure Ownership: The communication hardware (cables, switches, routers) is typically owned and maintained by the organisation or individual using it.
• Typical Use: Connecting classroom computers to a school server and network printer.
C. Wide Area Network (WAN)
• Geographical Area: Covers a large geographical area, such as across cities, countries, or even globally.
• Infrastructure Ownership: Uses external telecommunication links and infrastructure provided by third-party telecom carriers (such as telephone lines, undersea cables, and satellite links), rather than entirely private cabling.
• Typical Example: The Internet is the largest and most well-known example of a WAN. A multinational bank connecting its branches in London, Tokyo, and New York also forms a WAN.
Memory Trick:
• PAN = Personal (just you and your devices)
• LAN = Local (one building/room)
• WAN = Wide (countries/continents/worldwide)
Common Exam Mistake to Avoid: Confusing the geographical ownership! In a LAN, the organisation usually owns all the cables. In a WAN, third-party telecommunication infrastructure is rented or used because no single company owns all the transatlantic cables and satellites.
---3. Network Usage Models: Client-Server vs. Peer-to-Peer
Once devices are connected, how do they interact and share responsibilities? There are two primary usage models: Client-Server and Peer-to-Peer.
A. Client-Server Network Model
In this model, computers have designated roles:
• Server: A powerful central computer that provides services, manages resources, holds central files, or controls security and user logins.
• Client: A computer or device used by a user to request data or services from the server (e.g., requesting a webpage, logging into an account, or retrieving a file).
Advantages of Client-Server:
• Centralised backups: All essential files are stored on the server, so backup routines only need to run on the server.
• Centralised security and access control: User accounts and permissions are managed centrally; a user can log into any workstation with their credentials.
• Easy software deployment: Upgrades and antivirus definitions can be installed centrally from the server.
Disadvantages of Client-Server:
• Single point of failure: If the main server crashes or goes offline, clients cannot access central files or services.
• Cost and complexity: Dedicated server hardware and network operating systems are expensive to buy and require specialist IT staff to maintain.
B. Peer-to-Peer (P2P) Network Model
In a peer-to-peer network, there is no central server. Every computer (known as a peer) has equal status and can act as both a client (requesting files) and a server (sharing its own files and connected hardware).
Advantages of Peer-to-Peer:
• No central point of failure: If one machine turns off or fails, the remaining computers can continue to communicate.
• Cheaper to set up: No expensive dedicated server hardware or specialist server operating software is required.
• Simpler maintenance: Easy to configure for small groups of computers without needing professional network technicians.
Disadvantages of Peer-to-Peer:
• Decentralised backups: Files are scattered across individual machines, making regular backups difficult and prone to being forgotten.
• Decentralised security: Each peer must maintain its own passwords, permissions, and virus scanning.
• Performance hit: If other users access files from your computer while you are working, your computer may slow down.
Key Takeaway: Choose Client-Server when you need high security, central control, and reliable backups for many users. Choose Peer-to-Peer for small, low-cost setups where users trust each other and equal access is sufficient.
---4. Connectivity: Wired and Wireless
Devices can connect to a network using physical cables (wired) or radio waves (wireless).
Wired Connections
• How it works: Physical cables (such as copper Ethernet twisted-pair cables or fibre-optic cables) run directly between network devices.
• Advantages: Typically offers faster transmission speeds, greater reliability (less prone to interference from walls or electronic devices), and higher physical security (someone must physically tap into the cable to intercept data).
• Disadvantages: Requires expensive and messy cabling installations; devices are tethered and lack mobility.
Wireless Connections
• How it works: Uses radio frequency signals (such as Wi-Fi) to transmit data through the air without physical cables.
• Advantages: Great mobility and flexibility—users can move freely with laptops and mobile phones; easy to add new devices without laying new cables.
• Disadvantages: Generally lower speeds than high-end wired connections; signals can be weakened by walls, furniture, and radio interference; lower inherent security as signals travel through open space and can be intercepted if not properly encrypted.
5. Measuring Network Data Speeds
When measuring how fast data travels through a network, we measure the rate of data transfer.
Important Exam Rule: Network data speeds are measured in bits per second (bps), not bytes per second! (Storage capacity uses bytes; transfer speed uses bits).
Common Speed Units:
• Mbps: Megabits per second (\(1\text{ Mbps} = 10^6\text{ bits per second}\) or \(1,000,000\text{ bits per second}\)).
• Gbps: Gigabits per second (\(1\text{ Gbps} = 10^9\text{ bits per second}\) or \(1,000,000,000\text{ bits per second}\)).
Example: A connection speed of \(100\text{ Mbps}\) means that 100 million individual bits of data can travel along that connection every second.
Mobile Communication Standards:
Data transmission speeds on mobile networks have evolved over time through successive standards: 3G, 4G, and subsequent generations (such as 5G). Each new generation provides higher data transfer speeds, reduced latency, and greater capacity for connected mobile devices.
6. Network Topologies
A network topology describes the physical or logical layout of how nodes (computers, printers, servers) are arranged and connected to one another. The four key topologies you must master are: Bus, Ring, Star, and Mesh.
A. Bus Topology
In a bus topology, all devices are connected along a single central cable known as the backbone. Both ends of the backbone must have a terminator to absorb signals and prevent them from reflecting back and causing errors.
• How data travels: Data is sent along the shared backbone. Every workstation sees the data, but only the machine with the matching destination address accepts it.
• Advantages: Simple and inexpensive to install; uses very little cabling compared to other layouts.
• Disadvantages: If the main backbone cable breaks, the entire network stops working; as more devices are added, data collisions increase, slowing down performance.
B. Ring Topology
In a ring topology, each device is connected to exactly two neighbours, forming a closed continuous circular loop.
• How data travels: Data packets travel in one direction (unidirectional) around the loop from device to device until they reach the correct destination.
• Advantages: No data collisions because traffic moves in only one direction; consistent performance even under heavy loads.
• Disadvantages: If a single cable breaks or one workstation fails, the ring is broken and the entire network goes down; adding or removing a computer temporarily halts the whole network.
C. Star Topology
In a star topology, every node is connected via its own individual cable directly to a central hub or switch.
• How data travels: Any device wanting to send data sends it to the central switch, which forwards it to the intended recipient.
• Advantages:
– High fault tolerance: If one cable breaks or one computer disconnects, only that single device is affected; the rest of the network operates normally.
– Easy expansion: New devices can be added or removed without disrupting existing network users.
– Better performance: Minimal data collisions when using a central switch.
• Disadvantages:
– Central point of failure: If the central switch/hub fails, the entire network is disabled.
– Cabling cost: Requires significantly more cabling than a bus topology, making installation more expensive.
D. Mesh Topology
In a mesh topology, devices are interconnected with multiple redundant connections. In a full mesh, every single node connects directly to every other node. In a partial mesh, some nodes connect to all others, while some connect only to those they exchange the most data with.
• How data travels: Data can take multiple alternate paths to get from sender to receiver.
• Advantages:
– Extremely robust and resilient: If any single cable or node fails, data can simply be rerouted through another path.
– High performance: Data can travel simultaneously across different routes without bottlenecks.
• Disadvantages:
– Very high cost and complexity: In a full mesh of \(n\) nodes, the number of individual connections is \(\frac{n(n - 1)}{2}\). For example, connecting just 10 computers in a full mesh requires \(45\) separate cables! It is complicated to wire and expensive to install.
7. Summary Comparison of Network Topologies
• Bus: Single backbone cable with terminators. Cheap and simple, but backbone break collapses the entire network.
• Ring: Closed loop, unidirectional flow. Orderly with no collisions, but a single node/cable break takes down the entire loop.
• Star: All nodes connect to a central switch. Very reliable (one device failure does not affect others), but central switch is a single point of failure.
• Mesh: Interconnected nodes with multiple alternate routes. Highly resilient with no single point of failure, but very expensive and complex to cable.
8. Practice Review Questions
Try answering these questions to test your understanding before your exam:
1. State the difference between a LAN and a WAN in terms of geographical scale and communication infrastructure.
2. Give two advantages of using a star topology over a bus topology.
3. Explain one disadvantage of a client-server network compared to a peer-to-peer network.
4. State the unit used to measure network transmission speed, and write out what the abbreviation Mbps stands for.
5. A hospital needs a network layout where communication will never fail even if an individual cable is severed. Identify the most suitable topology and give a reason for your choice.