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Worked Examples

Step-by-step solutions for protocols and connections

How to Use These Examples

Study each worked example carefully. Follow the step-by-step reasoning, then try the practice problems to test your understanding.

Example 1: Choosing Wired vs Wireless

Problem

A small business is setting up a new office with the following needs:

  • 5 desktop computers at fixed desks
  • 3 laptops that move between meeting rooms
  • 1 network printer in the corner
  • A server that stores important business files

Recommend the best connection type for each device and justify your choices.

Solution

Step 1: Identify device requirements

Consider each device's needs:

  • Desktop computers: Fixed location, need reliable connection
  • Laptops: Need mobility between rooms
  • Printer: Fixed location, moderate usage
  • Server: Fixed, critical device, needs maximum reliability and speed

Step 2: Apply wired vs wireless criteria

Device Recommended Justification
Desktop computers (5) Wired (Ethernet) Fixed location, faster and more reliable than WiFi
Laptops (3) Wireless (WiFi) Need to move between meeting rooms; mobility essential
Printer Either (WiFi acceptable) Fixed location but WiFi is convenient; print jobs don't need ultra-high speed
Server Wired (Ethernet) Critical device needs maximum speed, reliability, and security

Step 3: Final recommendation

Use wired connections for: All 5 desktops and the server (7 Ethernet ports needed)

Use wireless connections for: All 3 laptops and optionally the printer

Equipment needed: A network switch with at least 8 ports, a wireless access point (WAP) for WiFi coverage

Example 2: Identifying Valid IP Addresses

Problem

Which of the following are valid IPv4 addresses? Explain why each is valid or invalid.

  1. 192.168.1.1
  2. 256.100.50.1
  3. 10.0.0.255
  4. 172.16.0
  5. 192.168.1.1.5

Solution

Step 1: Recall IPv4 format rules

  • Exactly 4 numbers (octets) separated by dots
  • Each number must be between 0 and 255 (inclusive)
  • No extra dots or numbers

Step 2: Check each address

Address Valid? Reason
192.168.1.1 Valid 4 numbers, all between 0-255
256.100.50.1 Invalid 256 is too high - maximum is 255
10.0.0.255 Valid 4 numbers, all between 0-255 (0 and 255 are allowed)
172.16.0 Invalid Only 3 numbers - needs exactly 4
192.168.1.1.5 Invalid 5 numbers - has one too many

Final Answer

Valid addresses: (a) 192.168.1.1 and (c) 10.0.0.255

Invalid addresses: (b), (d), (e)

Example 3: Selecting the Right Protocol

Problem

Match each task to the most appropriate protocol and explain why:

  1. Browsing a shopping website
  2. Uploading files to a web server
  3. Logging into online banking
  4. Sending an email to a colleague
  5. Checking email on multiple devices

Protocols: HTTP, HTTPS, FTP, SMTP, IMAP, POP3

Solution

Step 1: Recall protocol purposes

  • HTTP: Transfer web pages (no encryption)
  • HTTPS: Transfer web pages securely (encrypted)
  • FTP: Transfer files to/from servers
  • SMTP: Send emails
  • IMAP: Receive emails with sync across devices
  • POP3: Download emails to one device

Step 2: Match each task

Task Protocol Reasoning
1. Browsing a shopping website HTTPS Shopping involves personal data; needs encryption
2. Uploading files to web server FTP Designed specifically for file transfers
3. Logging into online banking HTTPS Financial data must be encrypted; HTTP would be insecure
4. Sending an email SMTP SMTP is the protocol for outgoing email
5. Checking email on multiple devices IMAP IMAP syncs across devices; POP3 would cause issues

Example 4: Understanding MAC Addresses

Problem

A network administrator sees these two MAC addresses on the network:

  • Device A: 00:1A:2B:3C:4D:5E
  • Device B: 00:1A:2B:7F:8A:9B

What can you deduce about these devices?

Solution

Step 1: Recall MAC address structure

A MAC address has two parts:

  • First 3 pairs (OUI): Identifies the manufacturer
  • Last 3 pairs: Unique device identifier

Step 2: Analyse the addresses

Device A:

00:1A:2B:3C:4D:5E

Device B:

00:1A:2B:7F:8A:9B

Step 3: Draw conclusions

Same manufacturer: Both devices have the OUI 00:1A:2B, meaning they were made by the same company.

Different devices: The device IDs are different, so they are two separate physical devices.

Possible scenario: Two laptops or network cards from the same manufacturer (e.g., both Dell, or both Intel NICs).

Example 5: Understanding the TCP/IP Layers

Problem

A user opens their web browser and types https://www.example.com. Describe what happens at each layer of the TCP/IP model.

Solution

Step 1: Identify the layers (top to bottom)

  1. Application Layer
  2. Transport Layer
  3. Internet Layer
  4. Network Access Layer

Step 2: Describe each layer's role

Layer 4: Application Layer
  • Browser uses HTTPS protocol to request the web page
  • DNS is used to convert www.example.com to an IP address
  • Creates an HTTP request: "GET / HTTP/1.1"
Layer 3: Transport Layer
  • TCP breaks the data into segments
  • Adds port numbers (port 443 for HTTPS)
  • Ensures reliable delivery with acknowledgements
Layer 2: Internet Layer
  • IP adds source and destination IP addresses
  • Creates packets that can be routed across networks
  • Determines the path to the destination
Layer 1: Network Access Layer
  • Adds MAC addresses for local delivery
  • Converts data to electrical signals (Ethernet) or radio waves (WiFi)
  • Physically transmits the data

Step 3: Summary

Each layer adds its own information (headers) as data moves down. The receiving server reverses the process, moving up through layers to deliver the web page to the browser.

Example 6: Encryption and Security

Problem

A school is setting up a new WiFi network. The head teacher asks: "Why do we need to encrypt the WiFi? What's the worst that could happen?"

Explain the importance of WiFi encryption.

Solution

Step 1: Explain how unencrypted WiFi works

  • WiFi signals are radio waves that travel through the air
  • Without encryption, anyone within range can capture these signals
  • Special software can read the data being transmitted

Step 2: Identify the risks

Risks of Unencrypted WiFi:
  • Data interception: Login details, emails, and documents could be captured
  • Student data breach: Personal student information could be stolen
  • Unauthorised access: Anyone could connect to the network
  • Bandwidth theft: Nearby residents could use the school's internet
  • Legal liability: Illegal activities could be traced back to the school

Step 3: Explain how encryption helps

WiFi encryption (WPA2/WPA3):

  • Scrambles all data so it can't be read without the password
  • Only authorised users with the password can connect
  • Each connection uses a unique encryption key
  • Protects student and staff data in transit

Recommendation: Use WPA3 encryption with a strong password. Consider separate networks for staff, students, and guests.

Practice Problems

Try these problems on your own before revealing the answers.

Practice 1

A doctor's surgery needs to set up computers for:

  • Reception desk (handles patient check-in)
  • Doctor's consulting room (accesses patient records)
  • Waiting room tablet (patients fill in forms)

Recommend wired or wireless for each and explain why.

Practice 2

Which of these are valid MAC addresses?

  1. 00:1A:2B:3C:4D:5E
  2. 00:1A:2B:3C:4D
  3. 00:1A:2B:3C:4D:5E:6F
  4. GG:1A:2B:3C:4D:5E

Practice 3

Explain why a company might use both HTTP and HTTPS on their website.

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