Learning Objectives
By the end of this lesson, you will be able to:
- Show understanding of purpose and benefits of networking devices
- Show understanding of characteristics of a LAN and a WAN
- Explain client-server and peer-to-peer models of networked computers
- Show understanding of thin-client and thick-client and differences between them
- Show understanding of bus, star, mesh and hybrid topologies
- Understand how packets are transmitted between two hosts in given topology
- Show understanding of differences between and implications of use of wireless and wired networks
- Describe characteristics of copper cable, fiber optic cable, radio waves, microwaves, satellites
- Describe hardware that is used to support a LAN including switch, server, NIC, WNIC, WAP, cables, bridge, repeater
- Describe role and function of a router in a network
Key Terms
Network
A linked set of two or more computer systems capable of sharing resources
LAN
Local Area Network - contained within one building or small geographical area
WAN
Wide Area Network - connects computers over long distances (different cities/continents)
Client-Server Model
Network model with dedicated servers and client workstations
Peer-to-Peer Model
Network where each node can share files with all other nodes without central server
Thin Client
Device/software that needs constant connection to server for processing
Thick Client
Device/software that can work offline or online with local processing
Topology
Physical or logical arrangement of network nodes
Router
Hardware device that routes data packets between different networks
Switch
Device that connects network devices and directs packets to specific destinations
Hub
Device that connects network devices and sends data to all devices
Protocol
Set of rules for data transmission between devices
What is Networking?
A network is a linked set of two or more computer systems, which may be capable of sharing computer resources such as printers, CD-ROMs and databases. Networks may be wired or wireless.
Real-Life Example: School Computer Lab
Think of your school's computer lab:
- All computers are connected to school network
- Students can share files with teachers
- All computers use the same printers
- Teachers can control access to certain websites
- Work is backed up centrally
This is a Local Area Network (LAN) that makes sharing resources efficient!
Network Categories
Private Networks
Owned by a single company/organization (LANs/intranets) with restricted access requiring passwords/user IDs
Public Networks
Owned by communications carrier companies (telecoms), used by many organizations, usually no specific password requirements
Benefits of Networking
Cost Savings
- Devices like printers can be shared
- Network software licenses are cheaper than individual licenses
- Reduced hardware costs through sharing
Resource Sharing
- Users can share files and data
- Access to reliable data from central sources
- Centralized backup at end of each day
Communication & Control
- Users can communicate using email and instant messaging
- Network manager can oversee network and apply access rights
- Can restrict access to external networks like internet
Drawbacks of Networking
- Expensive initial outlay for cabling and servers
- Managing large networks can be complex and difficult
- Breakdown of devices like file servers can affect whole network
- Malware and hacking can affect entire networks
LAN vs WAN Comparison
| Local Area Network (LAN) | Wide Area Network (WAN) |
|---|---|
| Contained within one building or small geographical area | Connects computers over long distances (different cities/continents) |
| Owned by organization/company | Not owned by organization, leased from PSTN company |
| Transmission medium: twisted pair cable or Wi-Fi | Transmission medium: fiber-optic cable |
| Typical size: 10m to 1000m | Typical size: 100km to over 1000km |
| End-systems directly connected | No end-systems connected directly to WAN |
| Used within a site/branch | Used to connect sites/branches of an organization |
WAN Connection Visualization
How WANs work: A WAN connects multiple LANs over large distances. Each site has a switch that connects to the WAN, and transmission occurs from switch to switch using fiber-optic cables leased from PSTN companies.
Example: Bank ATMs in different cities connected to central banking servers.
LAN Hardware Components
Hub
Hardware device used to connect together a number of devices to form a LAN; directs incoming data packets to all devices on the network.
Like a teacher shouting to the whole class instead of whispering to individual students.
Switch
Hardware device used to connect together a number of devices to form a LAN; directs incoming data packets to a specific destination address only.
Like a postman delivering mail to specific addresses instead of broadcasting to everyone.
Router
Hardware device which enables data packets to be routed between different networks (for example, can join LANs to form a WAN).
Like a traffic police directing cars to different roads/cities.
Modem
Modulator demodulator; device which converts digital data to analogue data (to be sent down a telephone wire) and vice versa.
Like a translator converting English to Spanish and back for international calls.
Network Size Comparison
Personal Area Network
1m to 10m
Local Area Network
10m to 1000m
Metropolitan Area Network
1km to 100km
Wide Area Network
100km to 1000+km
Activity 1: LAN vs WAN Identification
For each scenario below, identify whether it describes a LAN or WAN and explain why:
- A school with 50 computers connected within the same building, sharing printers and files.
- A bank with ATMs in London, New York, and Tokyo all connected to the central banking server.
- An office building with computers on 5 different floors connected to the same network.
- A multinational company connecting its offices in Paris, Berlin, and Madrid.
- Your home network connecting your laptop, phone, and smart TV.
Solution:
- LAN - All computers are within one building (small geographical area).
- WAN - ATMs are in different cities/continents (long distances).
- LAN - All floors are within the same building/small area.
- WAN - Offices are in different cities/countries.
- LAN - All devices are within one home (small area).
Key difference: LAN covers small geographical areas (buildings, campuses), while WAN connects locations over large distances (cities, countries, continents).
Check Your Understanding: Networking Basics
1. What is a network? [2 marks]
Answer
- [1 mark] A linked set of two or more computer systems
- [1 mark] Capable of sharing computer resources such as printers, CD-ROMs and databases
- [Additional] Networks may be wired or wireless
2. Give three benefits of networking over standalone computers. [3 marks]
Answer
- [1 mark] Devices such as printers can be shared, reducing costs
- [1 mark] Users can share files and data
- [1 mark] Data and files can be backed up centrally
- [Additional] Network software licenses are cheaper, users can communicate via email/IM, network manager can oversee and control access
3. What is the main difference between a hub and a switch? [2 marks]
Answer
- [1 mark] Hub directs incoming data packets to all devices on the network
- [1 mark] Switch directs incoming data packets to a specific destination address only
- [Additional] Switches are more secure and efficient than hubs
4. What is the role of a router in a network? [2 marks]
Answer
- [1 mark] Enables data packets to be routed between different networks
- [1 mark] Can join LANs to form a WAN
- [Additional] Takes data in one format from a network and converts it to a protocol understood by another network
5. Give two characteristics of a WAN. [2 marks]
Answer
- [1 mark] Used when computers/networks are situated a long distance from each other (different cities/continents)
- [1 mark] Transmission medium is fiber-optic cable
- [Additional] Not owned by organization, leased from PSTN, transmission is switch-to-switch, no end-systems connected directly
Network Models
Networks can be organized using different models that determine how devices communicate and share resources. The two main models are client-server and peer-to-peer.
Client-Server Model
Real-Life Example: School Network
Your school's network is likely a client-server model:
- Server: Central computer storing all student files, software, and email
- Clients: Classroom computers and student laptops
- Control: Teachers/IT staff control access to resources
- Security: Passwords required to log in
- Backup: Central backup of all important data
Key Features
Centralized Servers
Separate dedicated servers store files and manage resources
Client Workstations
Client computers connected to server(s) to access resources
Access Control
Server dictates which users can access which files using passwords/user IDs
Client-Server Model Simulation
How it works: In client-server networks, all requests go through central servers. Clients request resources (files, email, printing), servers process requests and return results. This allows for centralized control, security, and backup.
Peer-to-Peer Model
Real-Life Example: File Sharing
Early file-sharing programs like Napster or BitTorrent use P2P:
- No central server - each computer is equal
- Direct sharing between users
- "Look up" computer helps find files
- Each peer is both supplier and consumer
- Used for small networks with few users
Key Features
No Central Server
Each node has its own data, no central storage or authentication
Equal Peers
Peers participate as equals, each can be both supplier and consumer
Service Discovery
'Look up' computer helps find which nodes can provide required services
Client-Server vs Peer-to-Peer
| Client-Server Model | Peer-to-Peer Model |
|---|---|
| Uses separate dedicated servers and client workstations | Each node can share files with all other nodes (no central server) |
| Central security databases control access (passwords/user IDs) | No central security system, little data security |
| Files stored on dedicated servers, centrally managed | Each node has its own data, no central storage |
| Can become bottlenecked with many client requests | Avoids congestion when many clients download files simultaneously |
| Better for large networks, easier to scale up | Better for small networks (few nodes), becomes complex with many nodes |
| Files better protected from malware (central scanning) | Less secure, no real authentication procedures |
Thin Client vs Thick Client
Thin Client
Device or software that needs constant connection to a powerful computer/server for processing.
- Web browser (needs server connection)
- Mobile phone apps requiring server access
- POS terminal at supermarket
Pros: Less expensive to expand, central updates/installation, server protection
Cons: High reliance on server, cannot work if server down, higher start-up costs
Thick Client
Device or software that can work offline or online, doing most processing independently.
- Normal PC/laptop (has own storage, RAM, OS)
- Computer game running independently
- Desktop applications like Microsoft Office
Pros: More robust (works offline), clients have more control, stores own programs/data
Cons: Less secure, individual updates needed, data integrity issues
| Thin Client Software | Thick Client Software |
|---|---|
| Always relies on connection to remote server/computer | Can run some features even when not connected to server |
| Requires very few local resources (SSD, RAM, CPU) | Relies heavily on local resources |
| Needs good, stable, fast network connection | More tolerant of slow network connection |
| Data stored on remote server/computer | Can store data on local resources (HDD/SSD) |
Activity 2: Network Model Selection
For each scenario, recommend whether to use client-server or peer-to-peer model and explain why:
- A small graphic design studio with 4 designers who need to share large design files occasionally.
- A hospital with 200 staff members needing secure access to patient records and medication systems.
- A university with 10,000 students needing email, file storage, and online learning platforms.
- A family wanting to share photos and videos between 3 computers at home.
- A large bank with 50 branches needing centralized customer account management.
Solution:
- Peer-to-peer - Small group, occasional sharing, no need for robust security or centralized control.
- Client-server - Large user base, needs proper access control, good security, protection from accidental loss.
- Client-server - Very large user base, needs network security, centralized management, scalability.
- Peer-to-peer - Very small network, simple file sharing, no security requirements.
- Client-server - Large organization, needs centralized data control, security, backup, multi-location access.
General rule: Client-server for large networks needing security/control; Peer-to-peer for small networks with minimal security needs.
Check Your Understanding: Network Models
1. What are the main differences between client-server and peer-to-peer models? [4 marks]
Answer
- [1 mark] Client-server uses dedicated servers; peer-to-peer has no central server
- [1 mark] Client-server has central security/authentication; peer-to-peer has little security
- [1 mark] Client-server is better for large networks; peer-to-peer for small networks
- [1 mark] Client-server stores data centrally; peer-to-peer stores data on individual nodes
2. Why would a company choose a client-server network model? [3 marks]
Answer
- [1 mark] The company has a large user-base
- [1 mark] Access to network resources needs to be properly controlled
- [1 mark] There is a need for good network security
- [Additional] Data needs to be backed up centrally, free from accidental loss
3. What is a thin client and give an example? [3 marks]
Answer
- [1 mark] A device or software that needs constant connection to a powerful computer/server
- [1 mark] Will not work unless connected at all times to computer/server
- [1 mark] Example: Web browser, mobile phone apps, POS terminal at supermarket
4. What are the advantages of a thick client over a thin client? [3 marks]
Answer
- [1 mark] More robust - can carry out processing even when not connected to server
- [1 mark] Clients have more control - they can store their own programs and data/files
- [1 mark] Can work offline or online independently
- [Additional] More tolerant of slow network connections
5. Why is peer-to-peer network not suitable for large organizations? [3 marks]
Answer
- [1 mark] Offers little data security since there is no central security system
- [1 mark] More nodes lead to performance and management issues
- [1 mark] No central control over file sharing or access rights
- [Additional] Difficult to maintain data consistency and backups
Network Topologies
Network topology refers to the physical or logical arrangement of network devices. Different topologies have different advantages, disadvantages, and methods of packet transmission.
Bus Topology
Real-Life Example: School Announcement System
Think of old school PA (public address) systems:
- Single cable like the main announcement wire
- All classrooms connected to same line
- Principal's announcement goes to all rooms
- Each room listens for their name/address
- If main cable breaks, no one hears announcements
How Packets are Transmitted
In bus topology:
- Each node examines every packet on the bus
- Checks if recipient address matches node address
- If match: node accepts the packet
- If no match: packet is ignored
- Message must be broadcast even if intended for one node
Bus Topology Simulation
Key characteristics: Single shared link (multi-point connection), no direct connection between end systems, messages broadcast to all, resilient to single node failure but vulnerable to main cable failure.
Star Topology
Real-Life Example: Hotel Switchboard
Old hotel telephone systems used star topology:
- Central switchboard connects all rooms
- Each room has direct line to switchboard
- Operator routes calls to specific rooms
- If one room phone fails, others still work
- If switchboard fails, no calls work
How Packets are Handled
Depends on central device:
- If hub: All packets sent to every device
- If switch: Packets sent only to matching addresses
- Each end system has point-to-point connection to central device
- Transmission is duplex (both directions simultaneously)
- Messages can be unicast, multicast, or broadcast
Star Topology Simulation
Key characteristics: Each device connects to central hub/switch, failure of one device doesn't affect others, central device failure brings down entire network, reduces data collisions, more secure than bus.
Mesh Topology
Real-Life Example: Telephone Network
Traditional telephone systems use mesh concepts:
- Telephone exchanges connected to multiple other exchanges
- Multiple possible routes for calls
- If one line fails, calls rerouted
- Internet backbone routers use mesh topology
- Very reliable but expensive to install
Key Features
Fully Connected
Each end-system has point-to-point connection to every other end-system
Redundant
Multiple paths available, broken links don't affect other nodes
Complex
Large amount of cabling needed, expensive and time-consuming to set up
Topology Comparison
| Bus Topology | Star Topology | Mesh Topology |
|---|---|---|
| Single shared link (multi-point connection) | Each device connects to central hub/switch | Each device connects to every other device |
| Messages broadcast to all nodes | Hub: broadcast; Switch: direct to address | Messages can be unicast, multicast, or broadcast |
| If main cable fails, whole network down | If central device fails, whole network down | Broken links don't affect other connections |
| Not secure (packets pass through every node) | More secure (packets to specific addresses) | Secure (direct point-to-point connections) |
| Easy to expand, cheap cabling | Easy to expand, more cabling than bus | Difficult/expensive to expand |
| Performance declines under heavy load | Reduced data collisions, handles heavy traffic | Excellent performance, multiple paths |
Hybrid Networks
A hybrid network is a mixture of two or more different topologies (bus and star, bus and mesh, etc.). Main advantages and disadvantages depend on which types of network are used to make up the hybrid network, but the main disadvantage is that they can be very complex to install, configure and maintain.
A large office building might use star topology within each department (for easy management) but connect department switches in a bus topology (to save on cabling between floors).
Transmission Modes
Simplex
One direction data transmission only
Keyboard to CPU, computer to printer, television/radio broadcast
Half-Duplex
Both directions but not at same time
Walkie-talkie (one person talks at a time)
Full-Duplex
Both directions simultaneously
Telephone (both parties can talk at once), broadband connection
Message Types
Unicast
One-to-one communication between two devices
Server to client communication
Multicast
One-to-group communication
Group email or SMS, video conference
Broadcast
One-to-all communication
Network announcement, emergency alert
Activity 3: Topology Selection
For each scenario, recommend the most suitable network topology (bus, star, or mesh) and explain why:
- A small office with 5 computers that needs a simple, low-cost network setup.
- A university computer lab with 30 computers that needs reliable connections and easy management.
- Internet backbone routers that need maximum reliability and multiple redundant paths.
- A home network where the family wants to add gaming consoles and smart devices easily.
- A military communications system that must remain operational even if some connections are destroyed.
Solution:
- Bus topology - Small number of devices, low cost, simple setup, light traffic expected.
- Star topology - Moderate number of devices, needs reliability, easy to manage and expand, handles heavier traffic.
- Mesh topology - Needs maximum reliability, redundant paths essential, cost less important than reliability.
- Star topology - Easy to add/remove devices, central router/switch manages connections, common for home networks.
- Mesh topology - Maximum redundancy, can withstand broken links, critical for military applications.
Key considerations: Bus for simple/small networks, Star for most practical applications, Mesh for critical reliability needs.
Check Your Understanding: Network Topologies
1. Describe how packets are transmitted in a bus topology. [3 marks]
Answer
- [1 mark] Each node looks at each packet on the bus
- [1 mark] Determines if recipient address matches node address
- [1 mark] If match: node accepts packet; if no match: packet ignored
- [Additional] Message must be broadcast even if intended for one node
2. What is the main vulnerability of star topology? [2 marks]
Answer
- [1 mark] If the central hub/switch fails
- [1 mark] Then the whole network goes down
- [Additional] Failure of individual nodes doesn't affect others, but central device is single point of failure
3. What are the advantages of mesh topology? [3 marks]
Answer
- [1 mark] Easy to identify where faults have occurred
- [1 mark] Any broken links don't affect other nodes
- [1 mark] Network is relatively easy to expand
- [Additional] Highly reliable with multiple paths, secure direct connections
4. What is the difference between unicast, multicast, and broadcast messages? [3 marks]
Answer
- [1 mark] Unicast: One-to-one communication (server to client)
- [1 mark] Multicast: One-to-group communication (group email)
- [1 mark] Broadcast: One-to-all communication (network announcement)
5. Explain the difference between simplex, half-duplex, and full-duplex transmission. [3 marks]
Answer
- [1 mark] Simplex: One direction only (keyboard to CPU)
- [1 mark] Half-duplex: Both directions but not simultaneously (walkie-talkie)
- [1 mark] Full-duplex: Both directions simultaneously (telephone)
Transmission Media & Hardware
Networks use various transmission media (wired and wireless) and hardware components to enable communication between devices. Each has different characteristics, advantages, and disadvantages.
Wired Transmission Media
Lowest cost
Medium cost
Highest cost
| Characteristic | Twisted Pair | Coaxial | Fibre-Optic |
|---|---|---|---|
| Cost | Lowest | Higher | Highest |
| Bandwidth/Data Rate | Lowest | Higher | Much higher |
| Attenuation at high frequency | Affected | Most affected | Least affected |
| Interference | Worst affected | Less affected | Least affected |
| Need for repeaters | More often | More often | Less often |
| Transmission capacity compared to twisted pair | 1x (baseline) | 80x | 26,000x |
Twisted Pair Cable
- Most common in LANs
- Lowest data transfer rate
- Suffers most from external interference
- Cheapest option
- Uses copper for transmission
- Types: Unshielded (residential), Shielded (commercial)
Coaxial Cable
- Common in MANs and cable TV
- Higher cost than twisted pair
- Better data transfer rate
- Less affected by interference
- 80x capacity of twisted pair
- Not usually for long-distance telephone
Fibre Optic Cable
- Used for long distances
- Best data transfer rate
- Smallest signal attenuation
- High resistance to interference
- 26,000x capacity of twisted pair
- Main drawback: high cost
- Uses light pulses, not electricity
Wireless Transmission
| Characteristic | Radio Waves | Microwaves | Infrared |
|---|---|---|---|
| Frequency range | 3kHz – 3GHz | 3 – 300GHz | 300GHz – 400THz |
| Penetration through walls | Best | Medium | Worst (stopped by walls) |
| Attenuation (signal reduction) | Medium | Affected by rain | Low (but affected by rain/walls) |
| Bandwidth (data capacity) | Lowest | Medium | Largest |
| Typical use | Wi-Fi, Bluetooth, radio | Satellite, long-distance | Remote controls, short-range |
Wired vs Wireless Networks
Wired Networking
Advantages
- More reliable and stable
- Faster data transfer rates
- Cheaper overall (despite cable costs)
- More secure (harder to intercept)
Disadvantages
- Devices not mobile (cable limits)
- Tripping hazards from cables
- Overheating of connections
- Permission needed for underground cables
Wireless Networking
Advantages
- Easier to expand networks
- Increased device mobility
- No cable installation needed
- Flexible device placement
Disadvantages
- More interference from external sources
- Less secure (easier to intercept)
- Slower data transmission rates
- Signals stopped by thick walls
Wi-Fi vs Bluetooth
Bluetooth
- Sends/receives radio waves in 79 different frequencies
- Devices automatically detect and connect
- Each communicating pair uses different channel
- Uses Spread Spectrum Frequency hopping
- If channel busy, randomly picks another channel
- Short range, lower data transfer rates
Wi-Fi
- Uses spread spectrum technology
- Best for full-scale networks
- Much faster data transfer rates than Bluetooth
- Better range and better security
- Access internet wirelessly at WAPs or "hot spots"
- Range up to 100 metres
Satellites
GEO Satellites
- Geostationary Earth Orbit (highest altitude)
- Over equator, orbits at same speed as Earth spins
- Used for long-distance telephone and network communication
- Only 3 needed for global coverage
- Altitude: ~35,786 km
MEO Satellites
- Medium Earth Orbit
- Some provide Global Positioning System (GPS)
- 10 needed for global coverage
- Altitude: ~5,000-15,000 km
LEO Satellites
- Low Earth Orbit
- Work in "constellations"
- Supplement mobile phone networks
- 50 needed for full global coverage
- Currently hundreds in orbit
- Altitude: up to ~2,000 km
Satellite Disadvantages
The greater transmission distance causes transmission delays, which can cause technical problems for the network. This is because signals must travel to space and back (to GEO: ~35,786 km up and down = ~71,572 km total distance).
You might notice a slight delay in satellite phone calls or live broadcasts from reporters in remote locations - this is the signal traveling to space and back!
Network Hardware Components
Repeater
Devices added to transmission systems to boost signals so they can travel greater distances:
- Amplify signals on both analogue (copper) and digital (fibre optic) links
- Used on wireless systems to prevent "dead spots" in Wi-Fi zones
- Hubs with repeaters are called repeating hubs
- All signals fed to hub are boosted before sending to devices
- Increases operational range of network
Bridge
Devices that connect one LAN to another LAN that uses the same protocol:
- Connect different parts of a LAN to function as single LAN
- Can be wired or wireless
- Stores network addresses for end-systems in two segments it connects
- Often used to connect LAN segments in different buildings
Gateway
Network point that acts as an entrance to another network:
- Connects two or more dissimilar LANs (different protocols)
- Converts data packets from one protocol to another
- Can act as routers, firewalls, or servers
- Allows traffic to flow in and out of networks
- Wired or wireless devices
Router Functions
Key roles of routers in networks:
- Restrict broadcasts to a LAN
- Act as a default gateway
- Perform protocol translation (wired to wireless)
- Move data between networks
- Calculate best route to network destination address
- Join LANs to form WANs (sometimes called brouters)
| Routers | Gateways |
|---|---|
| Forward packets of data from one network to another | Convert one protocol/data format to another |
| Read each incoming packet and decide where to forward it | Act as entry and exit point to networks |
| Can route traffic between networks | Translate from one protocol to another |
| Join LANs to form WANs, connect LANs to internet | Connect dissimilar LANs (different protocols) |
| Offer dynamic routing (different routes) | Do not support dynamic routing |
Network Interface Card (NIC)
- Needed to allow device to connect to network/internet
- Usually part of device hardware
- Frequently contains MAC address generated at manufacturing
- Each device on network has unique MAC address
Wireless NIC (WNIC)
- Same as NICs but for wireless connections
- Used to connect devices to internet/networks wirelessly
- Use antenna to communicate via microwaves
- Plug into USB port or internal integrated circuit
Public Switched Telephone Network (PSTN)
Originally carried analogue voice data. Digital data could be transmitted using modems to convert digital to analogue and back. These 'dial-up' connections provided modest-speed, shared access.
Modern PSTNs have upgraded to fibre-optic cable with digital technology, offering:
- Broadband network connections for traditional access
- WiFi hotspot technology with wired network connections
- Improved leased line services to ISPs
Activity 4: Transmission Media Selection
For each scenario, recommend the most suitable transmission media (twisted pair, coaxial, fibre optic, radio, microwave, or satellite) and explain why:
- Connecting computers within a school computer lab on the same floor.
- Transmitting internet across the Atlantic Ocean between Europe and North America.
- Cable television connection to a residential home.
- Wireless connection between a smartphone and wireless earbuds.
- Backbone connection for a large university campus connecting multiple buildings.
- Remote weather station in the Arctic sending data to research center.
Solution:
- Twisted pair cable - Short distance, low cost, suitable for LANs, adequate speed for school lab.
- Fibre optic cable or Satellite - Very long distance, fibre for high capacity underwater cables, satellite if cable not feasible.
- Coaxial cable - Traditionally used for cable TV, good bandwidth for video, less interference than twisted pair.
- Bluetooth (radio waves) - Short-range personal area network, low power, device-to-device communication.
- Fibre optic cable - High bandwidth needed for campus backbone, connects multiple buildings, future-proof.
- Satellite - Remote location with no infrastructure, long-distance communication, can reach isolated areas.
Key factors: Distance, bandwidth requirements, cost, interference susceptibility, and existing infrastructure.
Check Your Understanding: Transmission Media & Hardware
1. Compare twisted pair, coaxial, and fibre optic cables. [3 marks]
Answer
- [1 mark] Twisted pair: Cheapest, lowest data rate, worst interference, common in LANs
- [1 mark] Coaxial: Higher cost, better data rate, less interference, used in MANs/cable TV
- [1 mark] Fibre optic: Highest cost, best data rate, least interference, used for long distances
- [Additional] Fibre has 26,000x capacity of twisted pair, uses light not electricity
2. What is the purpose of a repeater in a network? [2 marks]
Answer
- [1 mark] To boost signals so they can travel greater distances
- [1 mark] To prevent signal attenuation/loss over long distances
- [Additional] Used on both wired and wireless systems, prevents "dead spots" in Wi-Fi
3. What are the differences between routers and gateways? [3 marks]
Answer
- [1 mark] Routers forward packets between networks; gateways convert protocols between networks
- [1 mark] Routers support dynamic routing; gateways do not
- [1 mark] Gateways connect dissimilar LANs (different protocols); routers connect similar networks
- [Additional] Gateways act as entry/exit points; routers calculate best routes
4. What are the three types of satellites and their uses? [3 marks]
Answer
- [1 mark] GEO: Geostationary, long-distance telephone/network, 3 for global coverage
- [1 mark] MEO: Medium Earth orbit, GPS systems, 10 for global coverage
- [1 mark] LEO: Low Earth orbit, mobile phone networks, 50+ for global coverage
- [Additional] Different altitudes: GEO ~35,786km, MEO ~5,000-15,000km, LEO up to ~2,000km
5. What are the main disadvantages of wireless networks compared to wired? [3 marks]
Answer
- [1 mark] Increased chance of interference from external sources
- [1 mark] Data is less secure (easier to intercept radio waves than cables)
- [1 mark] Data transmission rate is slower than wired networks
- [Additional] Signals can be stopped by thick walls, range limitations
Key Takeaways
- Networks enable resource sharing - devices, files, software can be shared reducing costs and improving efficiency
- LANs cover small areas (buildings/campuses) while WANs connect over large distances (cities/countries)
- Client-server networks use dedicated servers for centralized control and security, suitable for large organizations
- Peer-to-peer networks have no central server, each node shares directly, suitable for small networks with minimal security needs
- Thin clients rely on server connections; thick clients can work independently with local processing
- Bus topology uses shared cable; star topology connects all devices to central hub/switch; mesh topology connects each device to every other device
- Transmission modes: Simplex (one direction), Half-duplex (both directions but not simultaneously), Full-duplex (both directions simultaneously)
- Message types: Unicast (one-to-one), Multicast (one-to-group), Broadcast (one-to-all)
- Twisted pair cables are cheapest but slowest; coaxial cables offer better performance; fibre optic cables are fastest but most expensive
- Wireless networks offer mobility but are slower, less secure, and more susceptible to interference than wired networks
- Routers connect different networks and find optimal paths; switches direct packets to specific addresses; hubs broadcast to all devices
- Satellites enable long-distance communication: GEO for fixed communication, MEO for GPS, LEO for mobile networks
- Network security is crucial - wired networks are more secure than wireless, client-server offers better security than peer-to-peer
Question Bank
1. Explain the benefits and drawbacks of using computer networks compared to standalone computers. [6 marks]
Marking Scheme & Answer
Benefits:
- [1 mark] Devices like printers can be shared, reducing costs
- [1 mark] Network software licenses are cheaper than individual licenses
- [1 mark] Users can share files and data easily
- [1 mark] Centralized backup and data management
- [1 mark] Users can communicate via email/instant messaging
- [1 mark] Network manager can control access and security
Drawbacks:
- [1 mark] Expensive initial outlay for cabling and servers
- [1 mark] Complex and difficult to manage large networks
- [1 mark] Breakdown of central devices affects entire network
- [1 mark] Malware and hacking can spread through entire network
2. Compare and contrast LAN and WAN networks. [6 marks]
Marking Scheme & Answer
Local Area Network (LAN):
- Contained within one building/small area
- Owned by organization/company
- Transmission: twisted pair cable or Wi-Fi
- End-systems directly connected
- Size: 10m to 1000m
- Used within a single site/branch
Wide Area Network (WAN):
- Connects over long distances (cities/continents)
- Not owned by organization, leased from PSTN
- Transmission: fiber-optic cable
- No end-systems connected directly
- Size: 100km to over 1000km
- Used to connect multiple sites/branches
3. Describe the client-server and peer-to-peer network models, including their advantages and disadvantages. [8 marks]
Marking Scheme & Answer
Client-Server Model:
- Description: Dedicated servers and client workstations
- Advantages: Central security, easy to scale, stable system, file protection
- Disadvantages: Can bottleneck, expensive servers, single point of failure
- Best for: Large organizations needing security/control
Peer-to-Peer Model:
- Description: No central server, each node shares with others
- Advantages: Avoids congestion, parts of files downloadable separately
- Disadvantages: Little security, performance issues with many nodes
- Best for: Small networks with minimal security needs
4. Explain the differences between thin clients and thick clients. [5 marks]
Marking Scheme & Answer
Thin Client:
- Needs constant connection to server
- Requires few local resources
- Data stored on remote server
- Examples: Web browser, POS terminal
- Pros: Cheap expansion, central updates
- Cons: High server reliance, can't work offline
Thick Client:
- Can work offline or online
- Relies on local resources
- Can store data locally
- Examples: PC/laptop, computer game
- Pros: Works offline, client control
- Cons: Less secure, individual updates
5. Describe bus, star, and mesh network topologies, including how packets are transmitted in each. [9 marks]
Marking Scheme & Answer
Bus Topology:
- Single shared link (multi-point)
- Packet transmission: Broadcast to all, each node checks address
- Advantages: Simple, cheap, easy to expand
- Disadvantages: Main cable failure = network down, not secure
Star Topology:
- Each device to central hub/switch
- Packet transmission: Hub: broadcast; Switch: direct to address
- Advantages: Reduced collisions, more secure
- Disadvantages: Central device failure = network down
Mesh Topology:
- Each device to every other device
- Packet transmission: Direct point-to-point, multiple paths
- Advantages: Highly reliable, broken links don't affect others
- Disadvantages: Expensive cabling, complex setup
6. Compare wired and wireless networks, including their advantages and disadvantages. [6 marks]
Marking Scheme & Answer
Wired Networks:
- Advantages: More reliable/stable, faster data rates, more secure, cheaper overall
- Disadvantages: Devices not mobile, cable hazards, installation permission needed
- Media: Twisted pair, coaxial, fibre optic cables
Wireless Networks:
- Advantages: Easier to expand, increased mobility, no cables needed
- Disadvantages: More interference, less secure, slower data rates, signals blocked by walls
- Media: Radio waves, microwaves, infrared
7. Describe the roles of routers, switches, and hubs in computer networks. [6 marks]
Marking Scheme & Answer
Hub:
- Connects multiple devices to form LAN
- Directs incoming packets to all devices
- Not secure (broadcasts to all)
- Wastes bandwidth
- Can be wired or wireless
Switch:
- Connects multiple devices to form LAN
- Directs packets to specific destination only
- More secure and efficient than hub
- Checks destination address
- Wired or wireless
Router:
- Routes data between different networks
- Can join LANs to form WANs
- Converts data formats/protocols
- Calculates best routes
- Acts as gateway between networks
8. What are the three types of satellites used in communication networks and their applications? [6 marks]
Marking Scheme & Answer
GEO Satellites:
- Geostationary Earth Orbit
- Altitude: ~35,786 km
- Orbits at same speed as Earth spins
- Used for long-distance telephone/network
- 3 needed for global coverage
- Fixed position over equator
MEO Satellites:
- Medium Earth Orbit
- Altitude: ~5,000-15,000 km
- Some provide GPS services
- 10 needed for global coverage
- Used for navigation systems
LEO Satellites:
- Low Earth Orbit
- Altitude: up to ~2,000 km
- Work in "constellations"
- Supplement mobile phone networks
- 50+ needed for global coverage
- Hundreds currently in orbit
9. Explain the differences between unicast, multicast, and broadcast messages with examples. [4 marks]
Marking Scheme & Answer
Unicast:
- One-to-one communication
- Point-to-point transmission
- Example: Server to client, email to one recipient
Multicast:
- One-to-group communication
- Specific group of devices
- Example: Group email/SMS, video conference
Broadcast:
- One-to-all communication
- All connected receivers
- Example: Network announcement, emergency alert
10. What factors should be considered when choosing network topology for a given situation? [5 marks]
Marking Scheme & Answer
- [1 mark] Size of network: Small networks may use bus; larger ones star or mesh
- [1 mark] Cost constraints: Bus is cheapest; mesh is most expensive
- [1 mark] Reliability needs: Mesh offers highest reliability; bus has single point of failure
- [1 mark] Security requirements: Star and mesh more secure than bus
- [1 mark] Future expansion: Star easiest to expand; mesh most difficult
- [Additional] Traffic volume, cable installation feasibility, maintenance complexity