Cambridge 9618 · International A Level Computer Science · ~17 min read
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Wireless Networks Overview
Wireless networks transmit data using radio waves rather than physical cables. Devices communicate by sending and receiving radio signals within a specific frequency range. The main wireless networking technologies in Cambridge 9618 are Wi-Fi (WLAN) and Bluetooth.
📶 Wi-Fi (WLAN)
IEEE 802.11 standard family
Range: ~30–100m indoors
Frequency: 2.4 GHz or 5 GHz
High data rates (up to several Gbps)
Connects many devices to a network/internet
Requires a Wireless Access Point (WAP)
Identified by SSID (network name)
🔵 Bluetooth
IEEE 802.15.1 standard
Short range: ~1–10m typically (100m max)
Frequency: 2.4 GHz
Lower data rates (up to ~3 Mbps classic, 2 Mbps BLE)
Personal Area Network (PAN)
Direct device-to-device connection (pairing)
Used for: headphones, keyboards, mice, IoT
Key WLAN Components
WLAN architecture
📱
Wireless devices
Laptops, phones, tablets — contain wireless NICs that communicate via radio waves
📡
WAP
Wireless Access Point — receives wireless signals from devices and forwards to wired network. Also called a wireless router when it includes routing capability.
🔌
Wired backbone
Ethernet switches and cables connecting WAPs to each other and to the internet gateway
🌐
Internet gateway
Router connecting the local network to the internet via the ISP
SSID — Service Set Identifier
The SSID is the name of a wireless network. When a WAP broadcasts its SSID, devices can detect and connect to the network. Key points:
WAPs broadcast their SSID by default so devices can discover the network
SSID hiding: the WAP can be configured to not broadcast its SSID — users must know the name to connect. This is a weak security measure (the SSID can still be discovered by analysing traffic)
Multiple WAPs in a building can share the same SSID — devices connect to the nearest WAP (Extended Service Set / ESS)
A single WAP serving one area = Basic Service Set (BSS)
IEEE 802.11 Wi-Fi Standards
Standard
Common Name
Frequency
Max Speed
Year
802.11b
Wi-Fi 1
2.4 GHz
11 Mbps
1999
802.11g
Wi-Fi 3
2.4 GHz
54 Mbps
2003
802.11n
Wi-Fi 4
2.4/5 GHz
600 Mbps
2009
802.11ac
Wi-Fi 5
5 GHz
3.5 Gbps
2014
802.11ax
Wi-Fi 6
2.4/5/6 GHz
9.6 Gbps
2019
2.4 GHz vs 5 GHz: 2.4 GHz has longer range but slower speeds and more interference (shared with Bluetooth, microwaves). 5 GHz has shorter range but faster speeds and less congestion.
Wireless Security
Wireless networks are vulnerable to eavesdropping (radio signals travel through walls). Several mechanisms protect WLAN security:
🔑
WPA2/WPA3
Wi-Fi Protected Access — encrypts all wireless traffic. WPA3 is the current standard with stronger encryption (AES-256).
📛
SSID Hiding
Stops broadcasting the network name. Weak security — SSID can still be found by sniffing wireless traffic. Not sufficient alone.
🔒
MAC Filtering
Only allows devices with specific MAC addresses to connect. Moderate security — MAC addresses can be spoofed by attackers.
🌐
VPN
Encrypts all traffic between device and VPN server, even on unsecured public Wi-Fi networks.
🚫
Firewall
Filters incoming and outgoing network traffic based on rules. Blocks unauthorised access attempts.
🔐
Strong Password
A complex WPA2/3 passphrase prevents brute-force attacks on the network password.
WEP → WPA → WPA2 → WPA3
Wireless encryption has evolved: WEP (Wired Equivalent Privacy) was the original standard but has severe vulnerabilities — it can be cracked in minutes. WPA replaced it; WPA2 (using AES encryption) is the widely deployed standard. WPA3 is the latest, fixing WPA2's weaknesses including offline dictionary attacks.
Bluetooth
Bluetooth creates a short-range Personal Area Network (PAN) between devices. It uses frequency hopping spread spectrum (FHSS) — rapidly switching between 79 frequencies 1600 times per second — which reduces interference and improves security.
Pairing: devices must authenticate each other before communicating (PIN or passkey)
Piconet: a Bluetooth network of one master device (up to 7 active slaves)
Bluetooth Low Energy (BLE): very low power variant — used in IoT sensors, fitness trackers, beacons
Range typically 10m; Bluetooth 5 extends to ~40m at lower speeds
Wired vs Wireless Comparison
🔌 Wired (Ethernet)
Faster — up to 100 Gbps
More reliable — no signal interference
More secure — physical access required
Lower latency
Less flexible — cables restrict movement
Higher infrastructure cost (cabling)
📶 Wireless (Wi-Fi)
More flexible — devices can move freely
Easy to add devices without cabling
Signals can be intercepted (less secure)
Subject to interference (walls, other devices)
Speed decreases with distance/obstacles
Lower infrastructure cost for large areas
Feature
Wi-Fi (WLAN)
Bluetooth
Standard
IEEE 802.11
IEEE 802.15.1
Range
30–100m+ (indoors)
~1–10m (100m max)
Speed
Up to 9.6 Gbps (Wi-Fi 6)
Up to ~3 Mbps
Network type
LAN/WLAN
PAN
Devices
Many (100s)
Up to 7 active (piconet)
Power
Higher
Lower (BLE especially)
Typical use
Internet access, file sharing
Headphones, keyboards, IoT
Cambridge 9618 exam tip: Know SSID = network name broadcast by WAP; WAP = device that connects wireless clients to wired network; WLAN = wireless LAN using IEEE 802.11; Bluetooth for short-range PAN using pairing. For security: know WPA2/WPA3 encryption, SSID hiding (weak), MAC filtering (moderate). Distinguish 2.4 GHz (longer range, slower, more interference) from 5 GHz (shorter range, faster, less congestion). In the exam, "wireless" questions often test SSID, WAP, and security measures.
⚠️ Common Mistakes
Confusing WAP and router — a WAP only provides wireless access to a wired network; a router also performs IP routing. Many home devices combine both (wireless router)
Saying SSID hiding makes a network secure — it is only a weak measure; the SSID can still be discovered by traffic analysis. WPA2/WPA3 encryption is the primary security measure
Saying Bluetooth and Wi-Fi use different frequencies — both commonly use 2.4 GHz, which is why they can interfere with each other
Forgetting that MAC filtering can be bypassed — MAC addresses can be spoofed (faked) by an attacker who observes valid addresses in wireless traffic
Confusing WEP and WPA — WEP is an old, broken standard; WPA2/WPA3 are the current secure standards
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Worksheet — 3.2.3 Wireless Networking
8 questions · Cambridge 9618 standard
Q1State what is meant by an SSID and explain how it is used when connecting to a wireless network.[3]
✅ Mark scheme
SSID stands for Service Set Identifier [1]; it is the name of a wireless network [1]; it is broadcast by the WAP so that nearby devices can detect and identify the network; a user selects the SSID from a list and enters credentials to connect [1].
Q2Describe the role of a Wireless Access Point (WAP) in a WLAN.[2]
✅ Mark scheme
A WAP receives wireless signals (radio waves) from wireless devices (laptops, phones) [1]; it acts as a bridge between the wireless devices and the wired network infrastructure, forwarding data between them [1]. Accept: provides the access point through which wireless devices connect to the local network and internet.
Q3A school wants to secure its wireless network. State three security measures and for each explain one limitation.[6]
✅ Mark scheme
WPA2/WPA3 encryption — limitation: if the passphrase is weak it can be cracked by brute force [1+1]; SSID hiding — limitation: SSID can still be discovered by analysing wireless traffic; not a strong defence [1+1]; MAC address filtering — limitation: MAC addresses can be spoofed (faked) by an attacker who observes valid addresses in traffic [1+1]. Award 1 per measure + 1 per valid limitation.
Q4Give two differences between Bluetooth and Wi-Fi.[2]
✅ Mark scheme
Any two from: Wi-Fi has a longer range (30–100m) compared to Bluetooth (~10m) [1]; Wi-Fi has much higher data transfer speeds than Bluetooth [1]; Wi-Fi is designed for network/internet access; Bluetooth is for short-range device-to-device (PAN) connections [1]; Wi-Fi supports many simultaneous devices; Bluetooth piconet supports up to 7 active slaves [1].
Q5Explain why using 5 GHz Wi-Fi instead of 2.4 GHz can improve network performance in an office building.[3]
✅ Mark scheme
5 GHz offers higher maximum data transfer speeds than 2.4 GHz [1]; 5 GHz has more available channels and less congestion — fewer devices/neighbouring networks use 5 GHz, so there is less interference [1]; 2.4 GHz is also shared with Bluetooth, microwaves, and other devices which cause interference — 5 GHz avoids this [1]. Note: accept limitation that 5 GHz has shorter range and penetrates walls less well.
Q6A business has offices spread across a large building and uses multiple WAPs all sharing the same SSID. What networking concept does this implement and what is its benefit?[2]
✅ Mark scheme
Extended Service Set (ESS) [1]; the benefit is that a device can roam seamlessly around the building, automatically connecting to the nearest/strongest WAP without the user needing to manually reconnect or change network settings [1]. Accept: allows wireless coverage across a large area that a single WAP could not cover.
Q7Explain what SSID, WEP, WPA, and MAC address filtering are in the context of wireless networking. For each, state whether it relates to identification, authentication, or access control, and identify one weakness of WEP compared to WPA.[5]
✅ Mark scheme
SSID (Service Set Identifier): the name of a wireless network — identification [1]; WEP (Wired Equivalent Privacy): an encryption protocol for wireless — authentication/security [1]; WPA (Wi-Fi Protected Access): a stronger encryption standard replacing WEP — authentication/security [1]; MAC address filtering: only devices whose MAC address is on an approved list can join — access control [1]; Weakness of WEP: uses a static encryption key that can be cracked by capturing enough packets; WPA uses dynamic keys (TKIP/AES) which change per session, making it significantly harder to crack [1].
Q8Explain why wireless networks are considered less secure than wired networks. Describe three specific security risks associated with wireless networking and, for each, state one mitigation measure.[6]
✅ Mark scheme
Wireless signals are broadcast through the air and can be intercepted by anyone within range, unlike wired connections that require physical access [1]; Risk 1: eavesdropping / packet sniffing — an attacker captures wireless packets; mitigation: enable WPA2/WPA3 encryption so data is unreadable without the key [1]; Risk 2: unauthorised access — an attacker connects to the network without permission; mitigation: use a strong WPA2 passphrase and MAC address filtering [1]; Risk 3: evil twin / rogue access point — attacker sets up a fake AP with the same SSID to intercept traffic; mitigation: educate users to verify certificate/SSID and use VPN over untrusted networks [1]; Award max 6.
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Mini Test — 3.2.3 Wireless Networking
10 questions · 10 marks · 10 minutes
⏱ 10:00
Section A — Multiple Choice [5 marks]
Q1What does SSID stand for?
Q2Which wireless security standard is currently considered most secure?
Q3Bluetooth creates which type of network?
Q4A WAP broadcasts its SSID. An administrator disables SSID broadcasting. What is the main limitation of this security approach?
Q5Which IEEE standard defines Wi-Fi?
Section B — Short Answer [5 marks]
Q6State two advantages of wireless networking over wired networking.
Mark schemeAny two from: devices can move freely without being restricted by cables [1]; easier and cheaper to add devices to the network (no cabling required) [1]; suitable for places where cables are impractical (e.g. historic buildings, large open spaces) [1].
Q7Explain why MAC address filtering is not a fully secure method of protecting a wireless network.
Mark schemeMAC address filtering allows only devices with specific MAC addresses to connect [1]; however, an attacker can use wireless traffic analysis to discover the MAC address of a legitimate device and then spoof (fake) their own device's MAC address to match — bypassing the filter [1].
Q8Describe one advantage of 5 GHz Wi-Fi over 2.4 GHz and one advantage of 2.4 GHz over 5 GHz.
Mark schemeAdvantage of 5 GHz: higher speeds and less interference/congestion — fewer devices share this band and it does not clash with Bluetooth/microwaves [1]; Advantage of 2.4 GHz: longer range and better wall penetration — lower frequency waves travel further and pass through solid objects more easily [1].
Q9State what Bluetooth pairing is and why it is needed.
Mark schemePairing is the process by which two Bluetooth devices authenticate each other (typically by exchanging a PIN or passkey) [1]; it is needed to ensure that only trusted, authorised devices can communicate — preventing unauthorised devices from connecting and intercepting data [1].
Q10A large hotel installs 20 WAPs all broadcasting the same SSID. What is this network structure called and what benefit does it provide to guests?
Mark schemeExtended Service Set (ESS) [1]; guests can roam anywhere in the hotel and their device automatically connects to the nearest/strongest WAP without needing to reconnect manually or change network settings — seamless roaming [1].