All 802.11 Standards — Full Comparison Table
| Standard | Wi-Fi Name | Year | Frequency | Max Speed | Range (indoor) | Key Feature |
|---|---|---|---|---|---|---|
| 802.11a | Wi-Fi 1 | 1999 | 5 GHz | 54 Mbps | ~35 m | First 5 GHz standard — less interference, shorter range |
| 802.11b | Wi-Fi 2 | 1999 | 2.4 GHz | 11 Mbps | ~35 m | First widely adopted WiFi — cheapest, most compatible |
| 802.11g | Wi-Fi 3 | 2003 | 2.4 GHz | 54 Mbps | ~38 m | Same speed as 802.11a but on 2.4 GHz — backward compatible with b |
| 802.11n | Wi-Fi 4 | 2009 | 2.4 GHz 5 GHz | 600 Mbps | ~70 m | First dual-band — introduced MIMO (multiple antennas) |
| 802.11ac | Wi-Fi 5 | 2013 | 5 GHz only | 3.5 Gbps | ~35 m | MU-MIMO, wider channels (80/160 MHz), beamforming |
| 802.11ax | Wi-Fi 6 / 6E | 2019/2021 | 2.4 5 6 GHz | 9.6 Gbps | ~30 m | OFDMA, BSS Colouring, TWT — designed for dense environments |
2.4 GHz vs 5 GHz vs 6 GHz — Which Band to Use
The frequency band is the most important trade-off in wireless networking. Each band has distinct characteristics that determine when it's the right choice. This is one of the most tested concepts on both A+ and Network+.
Works with older devices (b/g/n)
Longer signal propagation
Crowded — microwaves, Bluetooth, neighbours
Lower max speeds
Less interference and congestion
Much higher speeds (ac/ax)
Doesn't penetrate obstacles as well
Not compatible with a/b/g only devices
59 additional 20 MHz channels
No legacy device interference
Requires Wi-Fi 6E capable devices
Limited device support currently
Scenario: Users in an open office with many wireless devices experience slow speeds and frequent disconnects despite strong signal. What is the most likely cause, and what should the administrator change?
Answer: Channel congestion on 2.4 GHz. Switch devices to 5 GHz or configure the AP to use a less congested 2.4 GHz channel (1, 6, or 11). The key phrase in the scenario is "many devices" — this signals congestion, not signal strength (which would be described as weak signal or range issues).
Non-Overlapping Channels — Why This Matters
WiFi channels are subdivisions of the frequency band. When two access points use overlapping channels, their signals interfere with each other — degrading performance for both. Using non-overlapping channels in areas with multiple APs is essential for a well-designed wireless network.
2.4 GHz Channel Layout (US)
5 GHz Channels
5 GHz has 23+ non-overlapping 20 MHz channels (and fewer when using wider 40/80/160 MHz channels). This is why 5 GHz handles dense environments so much better — more APs can operate simultaneously without interfering with each other. Channel selection on 5 GHz is less critical than on 2.4 GHz but still important in high-density deployments.
MIMO and MU-MIMO — What the Abbreviations Mean
MIMO (Multiple Input, Multiple Output) was introduced with 802.11n. Instead of a single antenna transmitting and receiving, MIMO uses multiple antennas to send multiple data streams simultaneously — dramatically increasing throughput. An 802.11n access point with 4×4 MIMO (4 transmit, 4 receive antennas) can theoretically transmit four independent data streams at once. The 600 Mbps theoretical maximum of 802.11n comes from MIMO combined with wider 40 MHz channels.
MU-MIMO (Multi-User MIMO), introduced with 802.11ac Wave 2, extends MIMO to serve multiple clients simultaneously. With single-user MIMO (SU-MIMO), the AP talks to one device at a time and takes turns. With MU-MIMO, the AP can transmit to multiple devices at the same time using spatial streams. 802.11ac supports 4-user MU-MIMO (downlink only); 802.11ax extends this to 8-user MU-MIMO in both directions (uplink and downlink).
For the exam: MIMO = introduced in 802.11n, increases throughput via multiple antennas. MU-MIMO = introduced in 802.11ac, serves multiple clients simultaneously. The practical question is "which standard first supported multiple simultaneous client connections?" — the answer is 802.11ac with MU-MIMO.
802.11ax — What Makes Wi-Fi 6 Different
Wi-Fi 6 (802.11ax) isn't just faster than 802.11ac — it's architecturally redesigned for high-density environments. Three technologies drive this:
OFDMA (Orthogonal Frequency Division Multiple Access) is the biggest architectural change. Previous WiFi standards allocated an entire channel to a single user during each transmission. OFDMA subdivides channels into smaller subcarriers called Resource Units (RUs) and serves multiple clients simultaneously within a single transmission. This dramatically improves efficiency when many devices are connected — the AP doesn't have to wait for one device to finish before serving another.
BSS Colouring solves the overlapping network problem. When an 802.11ax device detects a signal, it checks a "colour" identifier to determine whether the signal is from its own network or a neighbouring network. If it's from a different network, the device can transmit anyway (if signal levels allow), reducing the dead time caused by deferring to nearby APs. This is particularly valuable in dense apartment buildings or office parks where many independent networks share the same channels.
TWT (Target Wake Time) allows the AP to schedule when devices wake up to send or receive data. IoT devices and battery-powered clients can sleep between scheduled wake times, dramatically extending battery life. This is why 802.11ax is positioned as the standard for IoT deployments — smart home devices can participate in WiFi networks while consuming minimal power.
Wireless Security Standards — WEP, WPA, WPA2, WPA3
Wireless security is separate from the 802.11 physical/MAC layer standards but is heavily tested alongside them. The progression from WEP to WPA3 represents the history of wireless encryption vulnerabilities and their fixes.
Site Surveys — Planning a Wireless Deployment
A wireless site survey assesses the physical environment to plan AP placement, channel selection, and power levels. Two types appear on the exam: a passive survey listens to existing wireless traffic without transmitting — it maps signal strength, identifies neighbouring networks, and documents channel usage. An active survey connects to the wireless network and measures throughput, latency, and packet loss from the client's perspective — it tells you not just that signal is present, but whether it's good enough for the intended use.
Key site survey concepts: heat map — a visual overlay showing signal strength across a floor plan, used to identify coverage gaps and overlap zones. Co-channel interference — when two APs in range of each other use the same channel, causing performance degradation (solution: use different non-overlapping channels). Roaming — the process of a client moving from one AP to another as signal strength changes; poor roaming design causes clients to stay connected to a distant AP with weak signal rather than switching to a closer one.
Wireless Troubleshooting — Common Problems and Causes
Slow speeds despite strong signal: Channel congestion (too many devices or APs on same channel), interference from other 2.4 GHz sources (microwaves, Bluetooth, baby monitors), or wrong frequency band (device connected to 2.4 GHz when 5 GHz is available). Check channel utilisation and frequency band.
Intermittent disconnections: Roaming issues (client not switching APs cleanly), AP overload (too many clients per AP), DHCP lease exhaustion, or RF interference from intermittent sources (a microwave that runs at lunch). Use a wireless analyser to capture the environment over time.
Cannot connect at all: Wrong password or SSID, MAC filtering blocking the device, security protocol mismatch (device only supports WPA but AP requires WPA2), or AP association table full (too many connected clients). Check client's wireless adapter settings against AP configuration.
Range shorter than expected: 5 GHz has shorter range than 2.4 GHz — if a deployment switched from 802.11n (dual-band) to 802.11ac (5 GHz only), devices at the edge of the old coverage area may now struggle. Solutions: add APs, reduce transmit power on APs near the edge to force devices to connect to the nearest AP, or implement a mesh network.