Computer Networks & Internet
LAN/WAN, Protocols & Internet Services
Network Types
Classified by geographic coverage
| Type | Full Name | Coverage | Speed | Example |
|---|---|---|---|---|
| PAN | Personal Area Network | Few metres (personal devices) | Low | Bluetooth headset, smartwatch pairing |
| LAN | Local Area Network | Building / campus (up to 1 km) | High (1 Gbps+) | Office network, school lab, home WiFi |
| MAN | Metropolitan Area Network | City / town (10–100 km) | Medium-High | City-wide cable TV, university campuses |
| WAN | Wide Area Network | Countries / worldwide | Variable | The Internet, banking networks, VPN |
Intranet
A private network that uses internet technologies (TCP/IP, web browsers, HTTP) but is accessible only within an organisation. Used for internal communication, file sharing, HR portals, and internal websites. Employees access it from the office or via VPN.
Internet
A global public WAN connecting billions of devices worldwide. Uses the TCP/IP protocol suite. No single organisation owns it — it is maintained cooperatively by ISPs, governments, and organisations through agreed standards.
LAN Advantages
High speed, low cost, easy resource sharing (printers, files), easy to manage and maintain.
WAN Challenges
High cost to maintain, security risks (data travels through public infrastructure), slower than LAN.
Network Topologies
Physical and logical arrangement of devices
Bus Topology
All devices share a single communication line (backbone). A signal travels the entire bus; each device checks if the message is for it.
✓ Simple, cheap to install
✗ If backbone fails, entire network fails; performance degrades with more devices
Star Topology
All devices connect to a central hub or switch. All communication passes through the center.
✓ Easy to add/remove devices; one failure doesn't affect others
✗ Central hub = single point of failure; more cable needed
Ring Topology
Devices connected in a closed loop. Data travels in one direction (or both in dual ring). Each device acts as a repeater.
✓ No collision; predictable performance
✗ One device failure breaks the ring; difficult to troubleshoot
Mesh Topology
Every device has a direct link to every other device. n devices → n(n-1)/2 links.
✓ Maximum fault tolerance; no single point of failure
✗ Very expensive; complex wiring; impractical for large networks
Hybrid topology combines two or more topologies. Most real networks are hybrids: e.g., Star-Bus (multiple star networks connected via a common bus) or Star-Ring. Real enterprise networks use star topology within floors and mesh between buildings.
Transmission Media
Physical and wireless channels that carry data
Guided (Wired) Media
| Type | Description | Speed | Example Use |
|---|---|---|---|
| Twisted Pair Cable (UTP/STP) | Two insulated copper wires twisted together to reduce interference. Most common for LAN. | 10 Mbps – 10 Gbps | Ethernet LAN (Cat5e, Cat6), telephone lines |
| Coaxial Cable | Central copper conductor surrounded by insulation and a metal shield. More interference-resistant than twisted pair. | Up to 10 Gbps | Cable TV, older Ethernet networks |
| Fibre Optic Cable | Transmits data as pulses of light through glass or plastic fibres. Fastest, most expensive, immune to EMI. | Up to 100 Tbps | Internet backbone, long-distance, hospital networks |
Unguided (Wireless) Media
Radio Waves
Low-frequency waves that can pass through walls. Used for WiFi, AM/FM radio, and Bluetooth.
eg: WiFi (2.4 GHz, 5 GHz), Bluetooth
Microwave
High-frequency, line-of-sight transmission over long distances. Requires antenna towers placed within 50 km.
eg: Point-to-point links, satellite communication
Infrared
Very short range, requires clear line of sight. Cannot pass through walls. Used for close-range device control.
eg: TV remote controls, IrDA device pairing
Transmission Modes
Direction of data flow between devices
| Mode | Direction | Description | Example |
|---|---|---|---|
| Simplex | One-way only | Data flows in only one direction. The sender can never receive; the receiver can never send. | TV broadcast, keyboard to CPU, radio |
| Half-Duplex | Both ways, but not simultaneously | Either party can send or receive, but not at the same time. One must wait for the other to finish. | Walkie-talkie, CB radio, old WiFi networks |
| Full-Duplex | Both ways simultaneously | Both parties can send and receive data at the same time. Most efficient use of bandwidth. | Telephone call, modern Ethernet, video call (Zoom) |
Network Devices
Hardware that builds and connects networks
| Device | OSI Layer | Function | Key Difference |
|---|---|---|---|
| NIC (Network Interface Card) | Layer 2 | Provides physical connection to network. Has a unique MAC address. | Every networked device has one — the hardware identity on the network |
| Hub | Layer 1 | Broadcasts incoming data to ALL connected ports. Dumb device. | No intelligence; creates collision domain; largely obsolete |
| Switch | Layer 2 | Sends data only to the specific destination MAC address port. Smart hub. | Reduces collisions; each port is its own collision domain |
| Router | Layer 3 | Connects different networks; routes packets using IP addresses. | The device that connects your home network to the Internet |
| Modem | Layer 1-2 | Modulates/demodulates signal for transmission over telephone/cable lines. | Converts digital data to analog signal and back |
| Access Point (AP) | Layer 2 | Extends wired network to wireless (WiFi) devices. | Not the same as a router; only provides wireless access |
| Firewall | Layer 3-7 | Monitors and filters network traffic based on security rules. | Can be hardware or software; first line of network defense |
OSI Model & TCP/IP
Standardized frameworks for network communication
| Layer # | OSI Layer | Function | Protocols/Examples |
|---|---|---|---|
| 7 | Application | Provides network services directly to end-user applications | HTTP, HTTPS, FTP, SMTP, DNS, Telnet |
| 6 | Presentation | Data translation, encryption, compression | SSL/TLS, JPEG, MPEG, ASCII conversion |
| 5 | Session | Establishes, manages, and terminates sessions between applications | NetBIOS, RPC, SQL sessions |
| 4 | Transport | End-to-end delivery, error recovery, flow control, segmentation | TCP (reliable), UDP (fast/unreliable) |
| 3 | Network | Logical addressing (IP), routing between networks | IP, ICMP, routing (RIP, OSPF) |
| 2 | Data Link | Physical addressing (MAC), frame creation, error detection | Ethernet, WiFi (802.11), ARP |
| 1 | Physical | Transmits raw bits over physical medium | Cables, hubs, repeaters, NICs |
OSI vs TCP/IP
OSI has 7 layers (theoretical model). TCP/IP has 4 layers: Application (= OSI 5+6+7), Transport (= OSI 4), Internet (= OSI 3), Network Access (= OSI 1+2). TCP/IP is what the Internet actually uses.
Mnemonic for OSI layers (top to bottom)
"All People Seem To Need Data Processing"
A=Application · P=Presentation · S=Session · T=Transport · N=Network · D=Data Link · P=Physical
Key Network Protocols
Rules that govern network communication
| Protocol | Full Name | Port | Purpose |
|---|---|---|---|
| HTTP | HyperText Transfer Protocol | 80 | Web page request/response (unencrypted) |
| HTTPS | HTTP Secure | 443 | Encrypted web communication using TLS/SSL |
| FTP | File Transfer Protocol | 21 | Transfer files between client and server |
| SMTP | Simple Mail Transfer Protocol | 25 | Send email from client to mail server |
| POP3 | Post Office Protocol v3 | 110 | Download email from server (deletes from server) |
| IMAP | Internet Message Access Protocol | 143 | Access email on server (keeps on server) |
| DNS | Domain Name System | 53 | Translate domain names → IP addresses |
| DHCP | Dynamic Host Configuration Protocol | 67/68 | Automatically assign IP addresses to devices |
| TCP | Transmission Control Protocol | varies | Reliable, ordered, error-checked delivery |
| UDP | User Datagram Protocol | varies | Fast, connectionless, no error recovery (video, gaming) |
Internet Services
What the Internet enables and how it works
World Wide Web (WWW)
System of interlinked web pages (HTML documents) accessed through browsers. Uses HTTP/HTTPS. The web is just one service ON the Internet — not the whole Internet.
Electronic Mail (Email)
Send/receive messages over the Internet. Uses SMTP to send, POP3/IMAP to receive. Every email has a header (From, To, Subject) and body.
File Transfer (FTP)
Transfer files between computers. FTP clients (FileZilla) connect to FTP servers. SFTP adds encryption.
VoIP (Voice over IP)
Voice calls over the Internet. Encodes audio as data packets. eg: WhatsApp calls, Skype, Zoom.
E-Commerce
Buying/selling goods and services online. B2B (business-to-business), B2C (business-to-consumer), C2C (Daraz, eBay).
Online Banking / E-Gov
Banking services and government services delivered online. Requires strong security (HTTPS, 2FA, OTP).
Key Internet Concepts
IP Address
Unique numerical address for each device (IPv4: 192.168.1.1; IPv6: 128-bit). Like a postal address for packets.
URL (Uniform Resource Locator)
Web address structure: protocol://domain/path — e.g., https://www.example.com/page.html
DNS
Translates www.google.com → 142.250.80.46. Without DNS you'd need to memorize IP addresses.
Web Browser
Software that fetches HTML/CSS/JS from web servers and renders them visually. Chrome, Firefox, Edge, Safari.
HTTP vs HTTPS
HTTP = unencrypted (visible to attackers). HTTPS = TLS-encrypted. Always use HTTPS for sensitive data.
Bandwidth vs Latency
Bandwidth = how much data per second (Mbps). Latency = delay (ms). High bandwidth ≠ low latency.
Analytical Questions
Unit 5 Summary
Core topics and important exam questions
Core Topics Covered
Network definition, types: PAN, LAN, MAN, WAN
Intranet vs Internet distinction
LAN topologies: Bus, Star, Ring, Mesh
Transmission media: guided (twisted pair, coaxial, fibre) and unguided
Transmission modes: simplex, half-duplex, full-duplex
Network devices: Hub, Switch, Router, Modem, AP
OSI model — 7 layers and functions
TCP/IP model — 4 layers
Key protocols and port numbers
Internet services: WWW, email, FTP, VoIP
Important Exam Questions
Differentiate between LAN, MAN, and WAN. (5 marks)
Explain different network topologies with advantages and disadvantages. (10 marks)
What is the OSI model? Explain all 7 layers. (10 marks)
Differentiate between hub, switch, and router. (5 marks)
Explain the types of transmission media. (5 marks)
What are simplex, half-duplex, and full-duplex modes? (5 marks)
Syllabus Coverage Checklist
Introduction to network, intranet, internet
Types of networks (PAN, LAN, MAN, WAN)
LAN topologies
Transmission media (guided and unguided)
Network devices (hub, switch, router, etc.)
Data communication concepts
Transmission modes (simplex/half-duplex/full-duplex)
OSI and TCP/IP models
Key protocols with port numbers
How to Remember This Unit
OSI: "All People Seem To Need Data Processing"
Application · Presentation · Session · Transport · Network · Data Link · Physical
TCP vs UDP: "TCP = True, UDP = Unknown"
TCP = reliable (confirmed delivery) · UDP = unreliable (no confirmation) but faster
Network devices: "Hub is Humble, Switch is Smart, Router is Royal"
Hub=broadcasts to all · Switch=sends to specific MAC · Router=routes between networks by IP
Network types: "P-L-M-W" (Personal → Local → Metro → Wide)
Scale increases, speed decreases, cost increases as you go PAN → LAN → MAN → WAN
Unit 5 Quiz
1. A network that spans a city or metropolitan area is called a:
2. In which topology does every device connect to every other device directly?
3. The OSI model has ___ layers:
4. Which protocol is used to send email from a client to a mail server?
5. DNS stands for: