What cause of hidden nodes within a BSS would be more likely lead to an increase in collisions and retries?

Question

Options

• AData frames too large for the physical environment
• BClient stations broadcasting with too much power
• CAccess points broadcasting with too little power
• DLarge 802.11 cells with physically distributed stations

• A
  14% (6)
• B
  7% (3)
• C
  49% (21)
• D
  30% (13)

Explanation

Option C is correct because when an AP transmits with insufficient power, its signal doesn't reliably reach all client stations in the BSS. Clients may still successfully transmit to the AP (uplink) using their own power, but they cannot hear the AP's ACKs, CTS frames, or other management traffic (downlink). Without those AP transmissions to update their Network Allocation Vector (NAV), distant clients have no way to detect that the medium is busy, so two clients can simultaneously transmit to the AP - the textbook hidden node collision.

Why the distractors are wrong:

• A (large frames): Frame size affects how long a collision lasts, not whether stations can detect each other. This doesn't create hidden nodes.
• B (clients with too much power): More client TX power actually reduces the hidden node problem - stations are more likely to hear each other and defer transmission.
• D (large cells with distributed stations): This describes the environment where hidden nodes appear, not a root cause. A large cell with a properly powered AP can still coordinate medium access via RTS/CTS; it's the AP's inadequate power that breaks that coordination.

Memory tip: Think of the AP as a traffic light. If the light (AP) is too dim (low TX power), drivers (clients) far away can't see it, so two drivers from opposite directions both think it's safe to go - crash (collision). The clients can see the intersection (reach the AP) but can't coordinate because the signal controlling them is too weak.

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