WLAN Fundamentals and Standards
Domain 1 tests how 802.11 PHY and MAC choices shape real WLAN behavior, plus the RF arithmetic behind coverage and channel reuse.
PHY and standards
- 802.11a uses 5 GHz OFDM; 802.11b/g use 2.4 GHz; 802.11n adds MIMO on both bands; 802.11ac is 5 GHz only; 802.11ax (Wi-Fi 6) adds OFDMA, MU-MIMO and BSS coloring on 2.4/5/6 GHz.
- Wider channels raise peak rate but consume spectrum: 20/40/80/160 MHz. Higher MCS needs better SNR.
MAC and architecture
802.11 uses CSMA/CA with DIFS, random backoff and ACK. Management frames include beacon, probe request/response, authentication and association; control frames include RTS/CTS and ACK; data frames carry To DS/From DS flags. A BSS is one AP plus clients; an ESS joins BSSs by SSID, while BSSID identifies the radio.
RF arithmetic
EIRP = transmitter power + antenna gain - cable loss. Work in dBm/dBi and add gains; never add dBm to dBm. 3 dB is about double power; 6 dB doubles free-space distance. 2.4 GHz non-overlapping channels are 1, 6 and 11; 5 GHz uses channel numbers such as 36, 40, 44 and 48.
Worked example: an AP transmits 20 dBm into a 5 dBi antenna with 1 dB cable loss, so EIRP = 20 + 5 - 1 = 24 dBm. At the same distance, 5 GHz has about 6.4 dB more free-space loss than 2.4 GHz because 20log(5/2.4) is about 6.4 dB. The 5 GHz cell is therefore smaller unless antenna gain or AP density is increased.
Traps: 802.11ac is not a 2.4 GHz standard; 802.11ax is not 6 GHz-only; channel 6 overlaps channels 4-8; a 54 Mbps PHY rate is not 54 Mbps of user throughput.