CWAP key terms

A synchronization field transmitted before every PHY frame so receivers can detect the signal, align timing, and train equalizers. Its format and length differ by PHY type, such as legacy, HT, or VHT.

The portion of a PHY frame that carries the data rate, length, and other decoding parameters needed to receive the payload. It is sent at a robust rate so any nearby station can decode it.

The legacy signal field present in every OFDM frame, including HT and VHT frames. It advertises a legacy-compatible rate and length so older devices defer for the correct duration.

A two-symbol signal field in 802.11n frames that conveys MCS, channel width, guard interval, and space-time block coding details. It follows L-SIG and tells HT receivers how to demodulate the payload.

The first VHT signal field, sent in a legacy-decodable manner, carrying channel width, MCS, and grouping information. VHT-SIG-B follows it and is decoded only by VHT-capable receivers.

A signal field unique to 802.11ac frames that carries per-user information such as MCS and coding for multi-user transmissions. Its length varies with channel bandwidth and is not decodable by older devices.

A known OFDM symbol sequence used for channel estimation and fine frequency offset correction. In mixed-mode frames it precedes the HT training fields so legacy devices can still decode the preamble.

An 802.11n preamble format that omits legacy training fields to reduce overhead. It cannot be decoded by 802.11a/g devices, so it is rarely deployed in mixed environments.

Modulation and Coding Scheme, an index that pairs a modulation type with a coding rate and, in MIMO systems, a spatial stream count. Higher indexes carry more data but require better signal quality.

A short silent period between OFDM symbols that prevents inter-symbol interference from delayed multipath copies. 802.11n and later allow a short guard interval to increase throughput.

Orthogonal Frequency Division Multiplexing, a technique that spreads data across many closely spaced subcarriers. It underlies 802.11a/g/n/ac and is more robust to multipath than single-carrier modulation.

Orthogonal Frequency Division Multiple Access, which divides a channel into resource units assigned to different stations in the same transmission. Used by 802.11ax for uplink and downlink efficiency.

A group of subcarriers allocated to one station in an 802.11ax OFDMA transmission. RUs vary in size, and the allocation appears in the SIG fields and trigger frames.

An independent data path transmitted from a separate antenna chain in a MIMO system. Multiple streams multiply throughput but require sufficient channel separation and signal quality.

Multiple-Input Multiple-Output, the use of several transmit and receive antennas to improve throughput or reliability. It enables spatial multiplexing, beamforming, and diversity schemes in 802.11n and later.

Multi-User MIMO, where an access point transmits separate streams to several stations simultaneously using beamforming. Downlink MU-MIMO arrived with 802.11ac, and uplink MU-MIMO with 802.11ax.

Steering a transmitted signal toward a receiver by adjusting phase and amplitude across antennas. It improves range and enables MU-MIMO, and it requires channel sounding feedback.

A calibration exchange in which a beamformer sends a sounding frame and the beamformee returns a compressed channel report. The report lets the transmitter compute steering matrices for beamforming.

Received Signal Strength Indicator, a relative measure of received power reported by a radio. It is vendor-scaled and useful for trend analysis rather than absolute comparison across hardware.

The background energy level in a channel when no desired signal is present, measured in dBm. A raised floor reduces SNR and often indicates interference or a non-Wi-Fi emitter.

Signal-to-Noise Ratio, the difference in dB between the desired signal and the noise floor. It predicts achievable data rates and is a better quality gauge than RSSI alone.

A time-versus-frequency plot showing energy as color or intensity. Analysts use it to identify interferers by their shape, such as frequency-hopping, continuous, or bursty patterns.

The percentage of time an interfering signal occupies the channel. A high duty cycle from a non-Wi-Fi device causes persistent contention and retries even when its peak power is modest.

Co-channel or adjacent-channel energy from other 802.11 networks that forces stations to defer or collide. It appears in a spectrum view as OFDM-shaped bursts aligned with frame transmissions.

Overlap between networks or devices using the same channel, which forces shared airtime and causes collisions. It is distinct from adjacent-channel energy that leaks from neighboring frequencies.

A 32-bit CRC appended to every 802.11 frame that lets the receiver detect bit errors. Failures appear as FCS errors in captures and often point to interference or weak signal.

The first field of the MAC header, containing type, subtype, flags, and protocol version bits. It determines how the rest of the frame is interpreted.

Combined values in the frame control field identifying a frame as management, control, or data and specifying its exact function. Analysts filter captures by these values.

A MAC header field that sets the network allocation vector period for the current exchange or carries an association identifier in some control frames. It drives virtual carrier sense.

Two frame control bits that indicate whether a frame travels to the distribution system, from it, or between access points. They determine which address fields hold source, destination, and BSSID.

A data frame whose header carries receiver, transmitter, and BSSID addresses, used for traffic between a wireless station and the wired side. The address meanings shift with the To DS and From DS bits.

A data frame used in wireless distribution systems that adds source and destination addresses beyond the three standard fields. It appears in WDS links and mesh backhaul captures.

A MAC frame type used for joining, leaving, and maintaining a network, including beacon, probe, authentication, association, and action frames. Most are sent without acknowledgment at the MAC level.

A MAC frame type that assists delivery of data frames, such as RTS, CTS, ACK, and block acknowledgment. These frames are short and carry no payload.

A periodic management frame advertising a BSS, its capabilities, supported rates, and security settings. Capture analysis of beacons reveals channel, interval, and configuration mismatches.

A management frame a station broadcasts or unicasts to discover networks, sometimes naming a specific SSID. The matching probe response carries the same capability details as a beacon.

A request-to-send and clear-to-send handshake that reserves the medium and mitigates hidden-node collisions. The CTS updates nearby stations' NAV, and the exchange adds overhead.

Network Allocation Vector, a timer each station maintains from duration values in overheard frames. While nonzero, the station treats the medium as busy even if it senses no energy.

A control frame that acknowledges many data frames at once using a bitmap of sequence numbers. It reduces overhead in aggregation and appears in HT and later captures.

Aggregated MAC Protocol Data Unit, several MPDUs combined into one PHY transmission with a single preamble. Each subframe keeps its own FCS and is individually acknowledged via block acknowledgment.

A bit in the frame control field marking a frame as a retransmission. High retry counts in a capture indicate collisions, interference, or poor signal quality.

A calibration exchange in which a beamformer sends a sounding frame and the beamformee returns a compressed channel report. The report lets the transmitter compute steering matrices for beamforming.