Networks

:::info Board Coverage AQA Paper 2 | Edexcel Paper 2 | OCR J277 Paper 2 | WJEC Unit 2 :::

1. Types of Networks

1.1 LAN and WAN

Feature	LAN (Local Area Network)	WAN (Wide Area Network)
Coverage	Small area (building, school, home)	Large area (cities, countries, global)
Ownership	Owned by the organisation	Owned by multiple organisations/ISPs
Speed	Fast (100 Mbps — 10 Gbps)	Slower than LAN
Cost	Low setup and maintenance	High setup and maintenance

The Internet is the largest WAN in the world, connecting billions of devices globally.

WLAN (Wireless LAN): A LAN that uses wireless connections (Wi-Fi) instead of cables. Common in Homes and schools.

PAN (Personal Area Network): Covers a very small area (a few metres). Bluetooth connections Between a phone and headphones are an example.

1.2 Client-Server vs Peer-to-Peer

Client-Server:

A central server provides resources and services to client computers
The server manages security, backups, and data
Advantages: centralised management, better security, easy backups
Disadvantages: server is a single point of failure, more expensive

Peer-to-Peer (P2P):

All computers are equal; each can share resources directly with others
No central server
Advantages: cheaper, no single point of failure
Disadvantages: harder to manage, weaker security, no central backup

Client-server vs P2P comparison:

Feature	Client-Server	Peer-to-Peer
Central device	Yes (server)	No
Cost	Higher	Lower
Security	Centralised, stronger	Decentralised, weaker
Backup	Centralised	Each user responsible
Scalability	Easier to scale	Difficult at large scale
Failure impact	Server failure affects all	Only affected peer goes down
Best for	Businesses, schools	Small home networks

1.3 Network Topologies

A network topology describes the physical or logical arrangement of devices in a network.

Star topology:

All devices connect to a central switch or hub
If the central device fails, the network fails
If one cable fails, only that device is affected
Easy to add or remove devices
Most common topology in modern networks

Mesh topology:

Every device is connected to every other device (full mesh) or to multiple devices (partial mesh)
Very reliable (multiple paths for data)
Expensive (many cables)
Complex to set up
Used in critical systems where reliability is essential

Bus topology:

All devices connected to a single backbone cable
Cheap and simple
If the backbone cable fails, the entire network fails
Performance degrades with many devices (collisions)
Rarely used in modern networks

Ring topology:

Devices connected in a circular loop
Data travels in one direction
If one device or cable fails, the entire network fails
Rarely used (modern ring networks use dual rings for redundancy)

1.4 Comparing Topologies

Feature	Star	Mesh	Bus	Ring
Cost	Low	High	Very low	Low
Reliability	Medium	Very high	Low	Low
Scalability	Good	Poor	Poor	Poor
Fault tolerance	Good	Excellent	Poor	Poor
Cable required	One per device	Many	One backbone	One ring
Common use	LANs	Critical systems	Legacy	Legacy

Worked Example. A school has 30 computers in a computer lab. Recommend a topology and justify Your answer.

A star topology is most appropriate. Each computer connects to a central switch via its own cable. If one cable fails, only that computer is affected. It is easy to add or remove computers. The Switch manages traffic efficiently, avoiding collisions.

1.5 Network Models in Practice

Worked Example. A small office has 5 computers, a printer, and a router connected to the Internet. Draw and describe the network topology.

All devices connect to a central switch (star topology). The switch connects to the router, which Connects to the Internet via the ISP. The printer may be connected directly to the switch or shared Through one of the computers. This is a LAN with a star topology connected to a WAN (the Internet).

2. Network Hardware

2.1 Key Devices

Device	Function
Router	Connects different networks together; directs data packets to their destination; assigns IP addresses (DHCP)
Switch	Connects devices within a LAN; directs data to the correct device using MAC addresses
Hub	Connects devices in a LAN; broadcasts data to ALL connected devices (less efficient than a switch)
Network interface card (NIC)	Allows a device to connect to a network; has a unique MAC address
Wireless access point (WAP)	Allows wireless devices to connect to a wired network
Bridge	Connects two segments of a LAN, filtering traffic
Repeater	Amplifies signals to extend the range of a network

2.2 Switch vs Hub

A hub broadcasts incoming data to ALL ports. This is inefficient and causes collisions because Every device receives every message, even if it was not the intended recipient.

A switch learns which device is connected to each port and directs data only to the intended Recipient. This is more efficient and reduces collisions.

Analogy. A hub is like a person shouting a message in a crowded room — everyone hears it. A Switch is like a person handing a sealed envelope directly to the intended recipient.

Worked Example. Computer A sends a message to Computer B on a network with a hub. What happens?

The hub receives the message and broadcasts it to ALL ports. Computers C, D, and E also receive the Message, even though it was only intended for Computer B. Each computer checks the destination MAC Address and discards the message if it does not match. This wastes bandwidth on all devices.

2.3 Router vs Switch

A switch connects devices within a single LAN and forwards frames based on MAC addresses.

A router connects different networks (e.g., a LAN to the Internet) and forwards packets based on IP addresses. Routers can also perform NAT (Network Address Translation), allowing multiple devices On a LAN to share a single public IP address.

Device comparison by OSI layer:

Device	OSI Layer	Address Used	Connects
Hub	Physical (1)	None	Devices within a LAN
Switch	Data Link (2)	MAC address	Devices within a LAN
Router	Network (3)	IP address	Different networks

3. Network Models

3.1 The TCP/IP Model

The TCP/IP model has four layers:

Layer	Function	Examples
Application	Provides services to user applications	HTTP, FTP, SMTP, DNS
Transport	Ensures reliable delivery of data	TCP, UDP
Internet (Network)	Routes data packets across networks	IP, routing protocols
Link (Network Access)	Handles physical transmission of data	Ethernet, Wi-Fi, MAC addressing

3.2 The OSI Model (Higher Tier)

The OSI (Open Systems Interconnection) model has seven layers:

Layer	Name	Function	Examples
7	Application	User interface, applications	HTTP, FTP, DNS
6	Presentation	Data formatting, encryption	SSL/TLS, JPEG, ASCII
5	Session	Session management	NetBIOS
4	Transport	End-to-end delivery	TCP, UDP
3	Network	Routing and addressing	IP, ICMP, ARP
2	Data Link	Node-to-node delivery, MAC	Ethernet, Wi-Fi
1	Physical	Electrical signals, bits	Cables, hubs

Mnemonic: “All People Seem To Need Data Processing” (Application, Presentation, Session, Transport, Network, Data Link, Physical).

TCP/IP vs OSI: The TCP/IP model is the practical model used on the Internet. The OSI model is a Theoretical reference model. TCP/IP’s Application layer combines OSI layers 5, 6, and 7. TCP/IP’s Link layer combines OSI layers 1 and 2.

3.3 The Four-Layer Model in Action

Example: Sending an email using SMTP over TCP/IP.

Application layer: SMTP protocol prepares the email message.
Transport layer: TCP breaks the message into segments and adds sequence numbers and error-checking.
Internet layer: IP adds source and destination IP addresses, creating packets.
Link layer: Ethernet/Wi-Fi adds MAC addresses and transmits the data as frames.

Encapsulation. At each layer, data is wrapped (encapsulated) with a header. At the receiving End, each layer removes (decapsulates) its header before passing data up. The application receives Only the original message.

Encapsulation sequence:

$\mathrm{Data \xrightarrow{\mathrm{Transport} \mathrm{Segment \xrightarrow{\mathrm{Internet} \mathrm{Packet \xrightarrow{\mathrm{Link} \mathrm{Frame$

Decapsulation at receiver: Frame $\to$ Packet $\to$ Segment $\to$ Data.

4. Network Protocols

4.1 Key Protocols

Protocol	Layer	Purpose
TCP	Transport	Reliable, connection-oriented data transfer; breaks data into segments; checks for errors
UDP	Transport	Fast, connectionless data transfer; no error checking; used for streaming
IP	Internet	Addresses and routes packets across networks
HTTP	Application	Transfers web pages (port 80)
HTTPS	Application	Secure version of HTTP (port 443); uses encryption
FTP	Application	Transfers files between client and server (ports 20/21)
SMTP	Application	Sends email (port 25)
POP3/IMAP	Application	Receives email (port 110/143)
DNS	Application	Resolves domain names to IP addresses (port 53)
DHCP	Application	Assigns IP addresses automatically (port 67/68)

4.2 TCP vs UDP

Feature	TCP	UDP
Connection	Connection-oriented (handshake)	Connectionless
Reliability	Guaranteed delivery, error checking	Best effort, no guarantees
Speed	Slower	Faster
Order	Data arrives in order	Data may arrive out of order
Use cases	Web browsing, email, file transfer	Streaming, gaming, VoIP

TCP three-way handshake:

Client sends SYN (synchronise) to server
Server responds with SYN-ACK (acknowledge)
Client sends ACK — connection established

Why the handshake? The handshake ensures both sides are ready to communicate and agree on Initial sequence numbers. Without it, data could be sent before the receiver is ready, causing Packet loss.

When to use UDP. UDP is appropriate when speed matters more than reliability. A few lost packets In a video stream are barely noticeable (a momentary glitch), but waiting for retransmission would Cause visible lag. Similarly, in online gaming, a stale position update is useless — the game needs The most recent data, not old reliable data.

4.3 Protocol Port Numbers

Well-known ports are standardised so that services can be found at predictable addresses.

Port	Protocol	Purpose
20/21	FTP	File transfer
22	SSH	Secure shell
25	SMTP	Email sending
53	DNS	Domain names
80	HTTP	Web pages
110	POP3	Email receiving
143	IMAP	Email receiving
443	HTTPS	Secure web pages
993	IMAPS	Secure IMAP

5. IP Addressing

5.1 IPv4 Addresses

An IPv4 address is a 32-bit number, written as four decimal numbers separated by dots:

$\mathrm{Example: 192.168.1.1$

Each number ranges from 0 to 255 (8 bits each, total 32 bits).

Total possible IPv4 addresses: $2^{32} = 4,294,967,296$ (approximately 4.3 billion).

Worked Example. Convert the IP address 192.168.1.1 to binary.

$192 = 11000000$$168 = 10101000$$1 = 00000001$$1 = 00000001$ .

$192.168.1.1 = 11000000.10101000.00000001.00000001$ .

5.2 IPv6 Addresses (Higher Tier)

An IPv6 address is a 128-bit number, written as eight groups of hexadecimal:

$\mathrm{Example: 2001:0db8:85a3:0000:0000:8a2e:0370:7334$

Total possible IPv6 addresses: $2^{128} \approx 3.4 \times 10^{38}$ .

Why IPv6? IPv4 addresses have been exhausted due to the growth of the Internet. IPv6 provides a Vastly larger address space, ensuring enough addresses for the foreseeable future.

IPv6 address shortening rules:

Leading zeros within each group can be omitted: 0001 becomes 1``0db8 becomes db8.
Consecutive groups of all zeros can be replaced with :: (only once per address).

Example: 2001:0db8:0000:0000:0000:0000:0000:0001 becomes 2001:db8::1.

5.3 MAC Addresses

A MAC (Media Access Control) address is a 48-bit unique identifier assigned to a network Interface card by the manufacturer. It is written as six pairs of hexadecimal digits:

$\mathrm{Example: 00:1A:2B:3C:4D:5E$

Difference between IP and MAC addresses:

Feature	IP Address	MAC Address
Assigned by	Network (DHCP or manually)	Manufacturer (permanent)
Changes?	Yes (can change)	No (fixed to hardware)
Used for	Routing across networks	Identifying devices on a local network
Layer	Internet layer	Link layer
Length	32 bits (IPv4)	48 bits

Analogy. An IP address is like a postal address (it changes when you move). A MAC address is Like a National Insurance number (it is permanently assigned to you).

5.4 Private vs Public IP Addresses

Private IP ranges (not routable on the public Internet):

10.0.0.0 to 10.255.255.255
172.16.0.0 to 172.31.255.255
192.168.0.0 to 192.168.255.255

Devices on a home LAN use private IP addresses. The router uses NAT (Network Address Translation) to map private addresses to a single public IP address when communicating with the Internet.

Worked Example. A home network has devices with IP addresses 192.168.1.2, 192.168.1.3, and 192.168.1.4. The router’s public IP is 203.0.113.5. When device 192.168.1.2 sends a request to a web Server, NAT translates the source address from 192.168.1.2 to 203.0.113.5. When the response Arrives, NAT translates the destination back to 192.168.1.2.

6. Network Security

6.1 Threats

Threat	Description
Malware	Malicious software (viruses, worms, trojans, ransomware, spyware)
Phishing	Fraudulent emails or websites that trick users into revealing personal information
Social engineering	Manipulating people into breaking security procedures
Brute force attacks	Trying every possible password to gain access
Denial of service (DoS)	Overwhelming a server with traffic to make it unavailable
Interception	Eavesdropping on network communications
Data theft	Unauthorised access to or copying of data

Types of malware in detail:

Virus: Attaches to a legitimate program and replicates when the program runs. Requires a host file to spread.
Worm: Self-replicating malware that spreads over networks without requiring a host file or user action.
Trojan: Malware disguised as legitimate software. Does not self-replicate. Named after the Trojan horse of Greek mythology.
Ransomware: Encrypts the victim’s files and demands payment ( in cryptocurrency) for the decryption key.
Spyware: Secretly monitors the user’s activity, collecting passwords, browsing history, and personal data.

6.2 Prevention Methods

Method	Description
Firewall	Hardware or software that monitors and filters network traffic based on rules
Encryption	Converting data into a coded form that can only be read with the correct key
Strong passwords	Long, complex passwords that are difficult to guess
Antivirus software	Detects and removes malware
Two-factor authentication (2FA)	Requires two forms of identification to log in
User access levels	Limiting what each user can access based on their role
Physical security	Locks, security guards, CCTV
Penetration testing	Simulated attacks to find vulnerabilities
Software updates	Installing patches to fix known security vulnerabilities

6.3 Encryption

Symmetric encryption: The same key is used to encrypt and decrypt data. Fast but requires secure Key exchange. Example: AES.

Asymmetric encryption: A public key encrypts data; a private key decrypts it. Slower but more Secure (no need to exchange keys). Example: RSA.

How HTTPS uses both:

Browser requests the server’s public key (from its digital certificate)
Browser generates a random session key and encrypts it with the server’s public key
Server decrypts the session key with its private key
Both sides now share the session key and use symmetric encryption (AES) for fast data transfer

SSL/TLS: Used to secure web traffic (HTTPS). The browser and server establish a secure Connection using asymmetric encryption, then switch to symmetric encryption for speed.

Hashing: A one-way function that converts data into a fixed-length hash. Used for storing Passwords. Even a small change in input produces a completely different hash.

Worked Example (Higher Tier). Explain how a man-in-the-middle attack works and how HTTPS Prevents it.

In a MITM attack, an attacker intercepts communication between two parties. Without HTTPS, the Attacker can read and modify all data. With HTTPS, the browser verifies the server’s digital Certificate against a trusted certificate authority (CA). The attacker cannot forge a valid Certificate, so the browser warns the user. The encrypted connection ensures the attacker cannot Read or modify the data even if they intercept it.

7. The Internet and the World Wide Web

7.1 Key Distinctions

The Internet is the global network of interconnected computers and cables.

The World Wide Web (WWW) is a collection of web pages accessed over the Internet using HTTP/HTTPS.

The Web is a service that runs ON the Internet. The Internet existed before the Web (since 1969 as ARPANET). The Web was invented by Tim Berners-Lee in 1989. Other services that run on the Internet Include email (SMTP), file transfer (FTP), and VoIP.

7.2 How the Web Works

A user enters a URL (e.g. Https://www.example.com) in a browser
The DNS (Domain Name System) translates the domain name into an IP address
The browser sends an HTTP request to the web server at that IP address
The server processes the request and sends back HTML, CSS, and JavaScript files
The browser renders the page for the user

DNS resolution in detail:

Browser checks its own cache
Operating system checks its DNS cache
Query sent to the recursive DNS resolver ( the ISP’s DNS server)
If not cached, the resolver queries the root name server (returns the TLD server for .com)
The TLD server returns the authoritative name server for example.com
The authoritative server returns the IP address
The result is cached at each level for future queries

7.3 Search Engines

A search engine (e.g. Google) uses automated programs called web crawlers (or spiders) to:

Crawl: Follow links from page to page, discovering new pages
Index: Store and organise information about each page
Search: When a user enters a query, the search engine ranks matching pages by relevance

Page ranking algorithms consider:

Keywords in the page content and title
Number and quality of links pointing to the page
Page popularity and user engagement
Page loading speed and mobile-friendliness

8. Data Transmission

8.1 Packet Switching

Data is broken into small packets for transmission across a network. Each packet contains:

The data being sent
A header (source address, destination address, sequence number, error checking)
A trailer (error checking)

Advantages of packet switching:

No dedicated route needed (packets can take different paths)
If a packet is lost, only that packet needs to be resent
Multiple users can share the same network
Resilient to failures (packets can be rerouted around broken links)

Packet switching vs circuit switching:

Feature	Packet Switching	Circuit Switching
Connection	No dedicated connection	Dedicated connection
Resource usage	Efficient (shared)	Wasteful (reserved)
Reliability	Packets can take different paths	Fixed route
Example	The Internet	Traditional telephone network

8.2 Transmission Media

Medium	Type	Speed	Distance	Security
Copper cable (twisted pair)	Guided	Medium	Short	Low (can be tapped)
Fibre optic cable	Guided	Very fast	Long	High
Wi-Fi (radio waves)	Unguided	Fast	Short	Low (interceptable)
Microwave	Unguided	Fast	Medium-Long	Medium
Satellite	Unguided	Variable	Very long	Medium

Fibre optic vs copper:

Fibre optic carries data as light pulses through glass fibres. Much faster (can carry terabits per second), immune to electromagnetic interference, and harder to tap.
Copper carries data as electrical signals. Cheaper and easier to install, but slower and susceptible to interference.

8.3 Encryption for Data Transmission

All data sent over public networks should be encrypted. HTTPS uses TLS (Transport Layer Security) to Encrypt web traffic, preventing interception.

Certificate authorities (CAs). When you visit an HTTPS site, the server presents a digital Certificate issued by a trusted CA. The browser verifies this certificate to ensure it is Communicating with the genuine server and not an impostor. This prevents man-in-the-middle attacks.

1.6 Network Models in Practice

Worked Example. A small office has 5 computers, a printer, and a router connected to the Internet. Describe the network topology.

Worked Example. A school has two buildings, each with 20 computers connected by switches. The two Buildings are connected by a fibre optic cable. Describe the topology.

Each building has a LAN with a star topology. The buildings are connected by the fibre optic cable, Forming a WAN. Each building has its own switch, and the switches are connected to a router that Manages inter-building traffic.

2. Network Hardware

2.1 Key Devices

Device	Function
Router	Connects different networks together; directs data packets to their destination; assigns IP addresses (DHCP)
Switch	Connects devices within a LAN; directs data to the correct device using MAC addresses
Hub	Connects devices in a LAN; broadcasts data to ALL connected devices (less efficient than a switch)
Network interface card (NIC)	Allows a device to connect to a network; has a unique MAC address
Wireless access point (WAP)	Allows wireless devices to connect to a wired network
Bridge	Connects two segments of a LAN, filtering traffic
Repeater	Amplifies signals to extend the range of a network

2.2 Switch vs Hub

A hub broadcasts incoming data to ALL ports. This is inefficient and causes collisions because Every device receives every message, even if it was not the intended recipient.

A switch learns which device is connected to each port and directs data only to the intended Recipient. This is more efficient and reduces collisions.

Analogy. A hub is like a person shouting a message in a crowded room — everyone hears it. A Switch is like a person handing a sealed envelope directly to the intended recipient.

Worked Example. Computer A sends a message to Computer B on a network with a hub. What happens?

2.3 Router vs Switch

A switch connects devices within a single LAN and forwards frames based on MAC addresses.

Device comparison by OSI layer:

Device	OSI Layer	Address Used	Connects
Hub	Physical (1)	None	Devices within a LAN
Switch	Data Link (2)	MAC address	Devices within a LAN
Router	Network (3)	IP address	Different networks

2.4 MAC Addresses in Detail

A MAC address is a 48-bit unique identifier assigned to a NIC by the manufacturer. It is written as Six pairs of hexadecimal digits: 00:1A:2B:3C:4D:5E.

The first 24 bits (3 bytes) identify the manufacturer (OUI — Organisationally Unique Identifier). The last 24 bits identify the specific device.

Worked Example. Why do switches use MAC addresses instead of IP addresses?

Switches operate at layer 2 (Data Link) of the OSI model, which deals with local network delivery Using MAC addresses. IP addresses are used at layer 3 (Network) for routing between networks.

2.5 Transmission Media in Detail

Copper cable (twisted pair):

Uses electrical signals
Category 5e (Cat5e) supports up to 1 Gbps
Category 6 (Cat6) supports up to 10 Gbps over short distances
Maximum distance: 100 metres (without repeaters)

Fibre optic cable:

Uses light pulses through glass or plastic fibres
Speeds up to 100 Gbps or more
Immune to electromagnetic interference
Can span several kilometres without repeaters
More expensive to install but lower maintenance costs

Worked Example. A school needs to connect two buildings 500 metres apart. Which transmission Medium should they use and why?

Fibre optic cable. Copper (twisted pair) has a maximum reliable distance of 100 metres. Fibre optic Can span the 500 metres without repeaters and provides higher bandwidth for future growth.

8. Data Transmission

8.1 Packet Switching

Data is broken into small packets for transmission across a network. Each packet contains:

The data being sent
A header (source address, destination address, sequence number, error checking)
A trailer (error checking)

Advantages of packet switching:

No dedicated route needed (packets can take different paths)
If a packet is lost, only that packet needs to be resent
Multiple users can share the same network
Resilient to failures (packets can be rerouted around broken links)

Packet switching vs circuit switching:

Feature	Packet Switching	Circuit Switching
Connection	No dedicated connection	Dedicated connection
Resource usage	Efficient (shared)	Wasteful (reserved)
Reliability	Packets can take different paths	Fixed route
Example	The Internet	Traditional telephone network

8.2 Error Detection

Parity check: An extra bit added to make the number of 1s even (even parity) or odd (odd Parity).

Checksum: A value calculated from the data and sent with it. The receiver recalculates and Compares.

Worked Example. Calculate the parity bit for 1011011 using even parity.

Number of 1s = 5 (odd). Parity bit = 1 (to make total even). Transmitted: 11011011.

8.3 Encryption for Data Transmission

All data sent over public networks should be encrypted. HTTPS uses TLS (Transport Layer Security) to Encrypt web traffic, preventing interception.

Additional Practice Questions

Explain the difference between a bridge and a repeater. When would you use each?
A company has a LAN with 100 devices connected to switches. Explain why replacing the switches with hubs would degrade network performance.
Explain what a MAC address is, how it is assigned, and why it is needed.
Calculate the parity bit for the byte 01101011 using even parity. If bit 3 (from the left) is flipped during transmission, will the parity check detect the error?
Explain why fibre optic cable is preferred over copper cable for connecting buildings that are far apart.
A packet with the following structure is sent: [Source IP: 192.168.1.5] [Dest IP: 10.0.0.1] [Seq: 42] [Data: “Hello”] [Checksum: 0xAB]. Explain the purpose of each field.
Explain what NAT is and why it is necessary for a home network to access the Internet.

Common Pitfalls

Confusing the Internet and the World Wide Web. The Internet is the infrastructure (cables, routers, protocols). The Web is a service (web pages) that runs on it.
Confusing TCP and UDP. TCP is reliable and ordered but slower; UDP is fast but unreliable. Use TCP for file transfers and UDP for live streaming.
Confusing IP addresses and MAC addresses. IP addresses are logical and change; MAC addresses are physical and permanent. IP is used for routing; MAC is used for local delivery.
Thinking a hub and a switch do the same thing. A hub broadcasts to all ports; a switch directs data to the correct port using a MAC address table.
Confusing symmetric and asymmetric encryption. Symmetric uses one key (fast); asymmetric uses a key pair (slower but more secure for key exchange).
Forgetting that firewalls filter traffic based on rules. They are not the same as antivirus software. A firewall blocks unauthorised network traffic; antivirus detects and removes malware.
Confusing packet switching with circuit switching. The Internet uses packet switching; the traditional phone network uses circuit switching.
Forgetting port numbers. Each protocol uses a standard port number. HTTP uses port 80, HTTPS uses port 443. These must be correct for communication to work.

Practice Questions

Compare LANs and WANs, giving an example of each.
Describe the function of a router, a switch, and a NIC.
Explain the difference between a star topology and a mesh topology, including advantages and disadvantages of each.
Describe the four layers of the TCP/IP model and give an example protocol for each layer.
Explain the difference between TCP and UDP, and state when each would be appropriate.
Explain the difference between an IP address and a MAC address.
Describe three methods of protecting a network from security threats.
Explain how a web browser loads a web page when the user enters a URL.
Explain how packet switching works and why it is used for data transmission over the Internet.
Describe the role of a firewall and explain how it differs from antivirus software.
(Higher Tier) Describe the seven layers of the OSI model and explain how the TCP/IP model maps to it.
(Higher Tier) Explain the TCP three-way handshake. Why is it necessary?
(Higher Tier) Explain how asymmetric encryption is used in HTTPS to establish a secure connection. Why is symmetric encryption used for the actual data transfer?
(Higher Tier) Explain the difference between NAT and DHCP. What does each protocol do?
(Higher Tier) Convert the IPv4 address 172.16.254.1 to its 32-bit binary representation.
(Higher Tier) Explain how data is encapsulated as it travels from the application layer down to the link layer. Use sending an email as an example.
(Higher Tier) A company has a LAN with 50 devices. Explain why a switch is preferred over a hub for this network.
(Higher Tier) Explain the concept of a DDoS attack. How does it differ from a standard DoS attack, and what defences are available?

Worked Examples

Example 1:

A typical exam question on Networks requires you to apply your knowledge to an unfamiliar context. Read the question carefully, identify the key concept being tested, and structure your answer using the appropriate terminology.

Example 2:

Multi-step problems in Networks often combine two or more concepts. Break the problem down: identify what you need to find, recall the relevant formula or principle, substitute values, and state your answer with correct units or formatting.

Summary

This topic covers the core concepts of networks, including underlying theory, practical implementation, and key applications.

Key concepts include:

TCP/IP and the OSI model
network topologies
protocols (HTTP, FTP, SMTP)
encryption and security
client-server and peer-to-peer

Understanding these concepts thoroughly is essential for both examinations and practical programming, and requires both theoretical knowledge and hands-on practice.

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