Core Concepts and Terminology
The vocabulary the exam assumes
AWCC uses RF and 802.11 terms precisely, and items often hinge on one unit or one acronym. Build fluency in the following before anything else.
Units and link budget
- dBm is an absolute power; dBi and dBd describe antenna gain; dB is a relative change.
- +3 dB doubles power, +10 dB is ten times, −3 dB halves it. Chain them instead of memorizing tables.
- EIRP = transmit power + antenna gain − cable/connector loss. Regulatory limits apply to EIRP, not to radio output alone.
- SNR = received signal − noise floor. A −67 dBm signal over a −92 dBm floor is 25 dB SNR.
Identifiers and mobility
An SSID is the network name; a BSSID is one radio's MAC; an ESS is the set of BSSs sharing an SSID. Roaming is client-decided. 802.11k supplies neighbor reports, 802.11v carries BSS transition requests, and 802.11r pre-authenticates so the 4-way handshake is shortened.
PHY generations
802.11n introduced MIMO and 40 MHz; 802.11ac is 5 GHz only with wider channels and MU-MIMO downstream; 802.11ax adds OFDMA, uplink MU-MIMO, and BSS coloring for dense deployments. Higher MCS needs better SNR - widening a channel lowers per-subcarrier power and often lowers the usable MCS.
Worked example
An AP transmits 18 dBm into a 4 dBi antenna through 1.5 dB of cable loss. EIRP = 18 + 4 − 1.5 = 20.5 dBm. If the client hears −67 dBm and the floor is −92 dBm, SNR is 25 dB - enough for 256-QAM but not for the highest 1024-QAM rates, so the design should not promise 802.11ax peak throughput at the cell edge.
Traps that cost marks
Confusing dBm with dBi; treating a doubled channel width as doubled throughput; equating strong RSSI with good SNR in a noisy environment; assuming the infrastructure controls roaming.