CWAP flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- PPDU composition
- A PPDU consists of the PHY preamble, the PHY header (SIG fields), and the PSDU. The PSDU is the MAC frame, also called the MPDU.
- OFDM preamble duration
- The legacy OFDM preamble is 20 microseconds: 8 us short training field, 8 us long training field, and 4 us SIGNAL field carrying rate and length.
- HT-mixed preamble purpose
- The HT-mixed preamble begins with legacy L-STF, L-LTF, and L-SIG so 802.11a/g devices can decode and defer, followed by HT-SIG, HT-STF, and HT-LTFs.
- VHT-SIG-A modulation
- VHT-SIG-A is transmitted with BPSK so that 802.11n devices can decode it and correctly defer for the duration of the VHT PPDU.
- EHT key features
- 802.11be EHT adds U-SIG and EHT-SIG fields, supports 320 MHz channels, 4096-QAM, and up to 16 spatial streams for very high throughput.
- MCS index meaning
- An MCS index specifies a modulation and coding rate combination. Higher indexes carry more bits per symbol but require higher SNR to decode reliably.
- Barker preamble rates
- Legacy DSSS uses a 1 Mbps Barker long preamble; HR-DSSS short preamble runs at 2 Mbps. The PLCP header always uses the preamble rate, not the payload rate.
- MAC header address order
- Address 1 is the receiver, Address 2 the transmitter, Address 3 the BSSID or destination/source, and Address 4 appears only in WDS frames.
- To DS and From DS
- To DS=1, From DS=0 indicates an uplink frame to the AP. To DS=0, From DS=1 indicates a downlink frame. Both set to 1 indicates a WDS link.
- Frame Control field size
- The Frame Control field is 2 bytes and contains protocol version, type, subtype, To DS, From DS, More Fragments, Retry, Power Management, More Data, Protected, and Order.
- QoS Control TID mapping
- The QoS Control field carries a 4-bit TID. TIDs 0-7 map to four access categories: AC_VO, AC_VI, AC_BE, and AC_BK.
- Control frame subtypes
- Common control subtypes are RTS (11), CTS (12), ACK (13), Block ACK Request (8), Block ACK (9), and PS-Poll (10). Control frames carry no frame body.
- FCS behavior
- The 32-bit FCS is a CRC over the whole frame. Frames failing the FCS are silently discarded, which appears in captures as retransmissions or missing acknowledgments.
- Association request contents
- An Association Request carries supported rates, extended supported rates, HT/VHT/HE capabilities, and the RSN information element describing ciphers and authentication key management.
- Client join sequence
- A client joins by probe request and response, authentication, association request and response, then the 4-way EAPOL handshake or 802.1X exchange.
- Beacon interval default
- The default beacon interval is 100 time units, equal to 102.4 milliseconds. The beacon carries the TIM and DTIM used for power-save delivery.
- SIFS values
- SIFS is 10 microseconds for OFDM PHYs (802.11a/g/n/ac/ax) and 16 microseconds for DSSS PHYs. SIFS precedes ACKs, CTS, and fragment bursts.
- RTS/CTS threshold
- RTS/CTS is used when a frame exceeds dot11RTSThreshold, or to mitigate hidden nodes. RTS is 20 bytes and CTS is 14 bytes; both set the NAV.
- Block ACK setup
- An ADDBA Request and Response establish a block ACK agreement. A single Block ACK can then acknowledge up to 64 MPDUs within the agreed window.
- Fast transition 802.11r
- 802.11r fast transition lets a client reassociate with a new AP using a pre-derived key, avoiding a full 802.1X or 4-way handshake during roaming.
- Passive versus active scanning
- Passive scanning listens for beacons on each channel. Active scanning sends probe requests and waits up to MinChannelTime or MaxChannelTime per channel.
- 2.4 GHz non-overlapping channels
- In 2.4 GHz, channels 1, 6, and 11 are the standard non-overlapping set, since each 22 MHz wide channel is spaced 5 MHz apart.
- Noise floor assessment
- A noise floor near -95 dBm is excellent and -85 dBm is marginal. An SNR of 25 dB or more is needed for the highest MCS values.
- Co-channel interference
- Co-channel interference appears as a raised noise floor beneath the AP signal, because another 802.11 network occupies the same channel.
- Adjacent-channel interference
- Adjacent-channel interference shows energy spilling from a neighboring channel, typically causing retries without a raised noise floor directly under the AP signal.
- DFS channel move time
- On detecting radar, an AP must vacate the channel within 10 seconds and must not transmit on that channel for 60 seconds.
- Common 2.4 GHz interferers
- Microwave ovens sweep the 2.4 GHz band, Bluetooth hops across it, and cordless phones and video cameras also emit energy that raises the noise floor.
- Spectrum waterfall display
- A waterfall plots frequency against time and colors by amplitude, making intermittent emitters such as microwaves or Bluetooth easy to identify.
- Channel utilization threshold
- Sustained 802.11 channel utilization above roughly 50 to 60 percent indicates congestion; determine whether airtime is consumed by 802.11 or non-802.11 sources.
- Monitor mode capture
- Monitor mode captures all over-the-air frames, including management and control frames, while a normal client adapter sees only frames addressed to it.
- EAPOL handshake messages
- The 4-way handshake exchanges EAPOL message 1 (ANonce), message 2 (SNonce and MIC), message 3 (GTK and MIC), and message 4 (acknowledgment).
- Deauthentication reason codes
- Common reason codes include 1 unspecified, 2 previous authentication invalid, 3 station leaving, 4 inactivity, and 15 four-way handshake timeout.