WLAN Fundamentals and Standards
Domain 1 - WLAN Fundamentals and Standards
This domain tests the RF and protocol foundations behind every Huawei WLAN design: 802.11 standards, frequency bands, channel reuse, medium access, and basic service set concepts. Expect questions that compare standards and ask you to pick a channel or explain a behavior.
Core rules
- 802.11b uses 2.4 GHz DSSS; 802.11a uses 5 GHz OFDM; 802.11g uses 2.4 GHz OFDM. 802.11n adds MIMO and 40 MHz channels on both 2.4 and 5 GHz.
- 802.11ac is 5 GHz only, with up to 160 MHz channels and downlink MU-MIMO. 802.11ax (Wi-Fi 6) operates in 2.4, 5, and 6 GHz, adding OFDMA and uplink MU-MIMO.
- In 2.4 GHz, only channels 1, 6, and 11 are conventionally non-overlapping 20 MHz channels. In 5 GHz, channel numbers are larger and many require DFS.
- 802.11 uses CSMA/CA with positive ACK. RTS/CTS mitigates the hidden-node problem but adds overhead.
- SSID names the network; BSSID is the AP radio MAC; ESS is multiple BSSs under one SSID for roaming.
Worked example
A three-floor office needs three APs per floor on 2.4 GHz. A candidate proposes using channels 1, 2, and 3 on each floor to avoid reuse. That is wrong: channels 1/2/3 overlap almost completely. A better plan is 1, 6, 11 repeated per floor, with 5 GHz enabled and 2.4 GHz transmit power reduced. The reasoning is co-channel interference versus adjacent-channel interference: reuse the same three channels far apart rather than pack overlapping channels close together.
Traps
Do not assume 802.11ac works at 2.4 GHz. Do not treat a 40 MHz channel in 2.4 GHz as free-it consumes most of the band. Data rate is not user throughput. CSMA/CA is not CSMA/CD.