CWS CWS 802.11 Standards and Protocols 5 — Questions and Answers
Question 1: What is the role of the Distribution System (DS) in 802.11 architecture?
- Encrypts frames between the STA and the AP
- Interconnects multiple BSSs to form an Extended Service Set (ESS) (Correct answer)
- Manages the contention window for channel access
- Provides IP address assignment to wireless clients
Correct answer: Interconnects multiple BSSs to form an Extended Service Set (ESS)
The Distribution System interconnects APs and bridges 802.11 frames to the wired backbone, allowing multiple BSSs to form a single ESS with seamless Layer 2 connectivity.
Question 2: Which 802.11 feature allows an AP to steer a dual-band capable client from 2.4 GHz to 5 GHz?
- TPC (Transmit Power Control)
- BST (Band Steering Technology)
- BSS Transition Management (802.11v) (Correct answer)
- DFS (Dynamic Frequency Selection)
Correct answer: BSS Transition Management (802.11v)
802.11v BSS Transition Management lets APs send suggestions or requests to clients to transition to a different BSS, which can include steering to a less congested or higher-frequency band.
Question 3: What is the maximum theoretical throughput of 802.11g?
- 11 Mbps
- 22 Mbps
- 54 Mbps (Correct answer)
- 72 Mbps
Correct answer: 54 Mbps
802.11g achieves a maximum PHY rate of 54 Mbps using OFDM in the 2.4 GHz band, matching the speed of 802.11a in the 5 GHz band.
Question 4: Which channel access method is mandatory for all 802.11 STAs and serves as the baseline for medium contention?
- PCF (Point Coordination Function)
- HCF (Hybrid Coordination Function)
- DCF (Distributed Coordination Function) (Correct answer)
- EDCA (Enhanced Distributed Channel Access)
Correct answer: DCF (Distributed Coordination Function)
DCF is the mandatory baseline medium access method based on CSMA/CA with random backoff, required for all 802.11 compliant stations.
Question 5: What does a STA do when it detects a 'hidden node' problem cannot be solved passively?
- Increases its transmit power to overcome the hidden node
- Enables RTS/CTS handshake to reserve the medium before transmitting (Correct answer)
- Switches to a non-overlapping channel automatically
- Sends a de-auth frame to the conflicting station
Correct answer: Enables RTS/CTS handshake to reserve the medium before transmitting
RTS/CTS allows a transmitting station to reserve the medium; the CTS frame is heard by stations that cannot hear the original sender, preventing collisions.
Question 6: Which element in a 802.11 Beacon frame tells clients the interval at which Beacons are transmitted?
- Capability Information field
- DTIM Count field
- Beacon Interval field (Correct answer)
- TIM (Traffic Indication Map) element
Correct answer: Beacon Interval field
The Beacon Interval field specifies the time between successive Beacon transmissions in units of Time Units (TUs), where 1 TU = 1024 microseconds.
Question 7: In 802.11ax, what does 'Target Wake Time' (TWT) primarily accomplish?
- Sets the time an AP must wake to process management frames
- Negotiates scheduled wake intervals so IoT/battery devices sleep longer and reduce channel contention (Correct answer)
- Defines the wakeup latency after a DTIM beacon for power-save clients
- Specifies the deadline for a TXOP burst to complete
Correct answer: Negotiates scheduled wake intervals so IoT/battery devices sleep longer and reduce channel contention
TWT allows an AP and client to negotiate specific times for the client to wake and communicate, dramatically improving battery life for IoT devices and reducing simultaneous channel contention.
CWS CWS 802.11 Standards and Protocols 5
What is the role of the Distribution System (DS) in 802.11 architecture?