Learning Objectives
By the end of this topic you will be able to:
Describe Wi-Fi standards (802.11) and their frequency bands
Explain CSMA/CA and how it avoids wireless collisions
Describe Bluetooth and its use cases
Explain wireless security: SSID, WPA2/WPA3, MAC filtering
Wi-Fi
Wi-Fi Standards (IEEE 802.11)
Wi-Fi uses the IEEE 802.11 family of standards. Devices communicate via radio waves through a Wireless Access Point (WAP). Key parameters: frequency band, maximum data rate, range.
2.4 GHz Band
Longer range; better penetration through walls. More congested — shared with microwaves, Bluetooth. Slower max speeds. Used by 802.11b/g/n.
5 GHz Band
Higher bandwidth; less congestion. Shorter range; weaker wall penetration. Used by 802.11a/n/ac/ax (Wi-Fi 5/6). Better for HD video streaming in close proximity.
Dual-band routers broadcast on both 2.4 GHz and 5 GHz simultaneously, allowing devices to connect to the most suitable band.
CSMA/CA
CSMA/CA — Collision Avoidance
CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) is used in wireless networks. Unlike wired Ethernet (CSMA/CD), wireless devices cannot detect collisions while transmitting, so they avoid them instead.
1. Sense: the device listens to check if the channel is idle (carrier sense).
2. Wait: if the channel is busy, the device waits a random backoff period before sensing again.
3. Transmit: if the channel is idle, the device transmits. After transmission, the sender waits for an ACK (acknowledgement) from the receiver.
4. Retry: if no ACK is received (collision assumed), the device waits a longer random backoff and retries. Multiple collisions lead to exponentially increasing backoff times.
Wireless Security
Wireless Network Security
SSID (Service Set Identifier): the name of the Wi-Fi network. Hiding the SSID provides minimal security — devices can still detect the network. An SSID is not a security measure on its own.
WPA2 / WPA3: Wi-Fi Protected Access. Encrypts all traffic between the device and WAP using AES. WPA3 is the current standard — stronger against dictionary attacks (uses SAE instead of PSK). WEP is obsolete and easily cracked.
MAC address filtering: the WAP maintains a whitelist of allowed MAC addresses. Devices with unlisted MACs are refused connection. Provides some protection but MAC addresses can be spoofed.
Bluetooth: short-range (typically up to 10m), low-power wireless standard. Used for PANs — headsets, keyboards, file transfer. Uses frequency hopping (2.4 GHz) to reduce interference. Not suitable for high-bandwidth applications.
Common Mistakes
Don't Lose Marks
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Saying CSMA/CA prevents all collisions — it reduces the probability of collisions; it does not eliminate them entirely. Simultaneous transmissions can still occur after both devices sense the channel as idle.
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Saying 5 GHz always has better range — 5 GHz actually has shorter range and weaker wall penetration than 2.4 GHz. Its advantage is higher throughput and less interference, not range.
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Saying MAC filtering is strong security — MAC addresses are broadcast in plaintext and can be trivially spoofed by an attacker. It is a layer of security but should not be relied upon alone. WPA2/WPA3 encryption is the primary security mechanism.