Question13 Which concurrent transmissions illustrate an exposed terminal case, where a device unnecessarily defers its transmission because it can hear another device transmitting, even though it could have transmitted without causing a collision at the intended receiver? Select one or more alternatives: W→X while U→V V→X while U→W U→V while X→Y ResetMaximum marks: 2

Question

BlackTom AI · Accepted Answer

The question asks us to identify concurrent transmissions that illustrate an exposed terminal scenario, where a device defers its transmission because it can hear another device transmitting, even though its own transmission would not cause a collision at the intended receiver.
Option A: W→X while U→V
In this setup, device W is transmitting to X while U is transmitting to V. If X is the intended receiver for W and V is the intended receiver for U, we need to consider whether W’s transmission would interfere with U’s at their respective receivers. The exposed terminal condition occurs when a node hears a transmission and defers, believing a collision could occur, even though the other transmission would not actually cause a collision at the receiver. If W’s signal does not interfere with V or if U’s transmission to V does not impair W’s to X, the scenario may reflect an exposed terminal. The key is whether the deferral is unnecessary given the topology. Depending on the network layout, this option can illustrate an exposed terminal if W defers due to sensing U, yet X would still receive W’s frame without collision at X.
Option B: V→X while U→W
Here, V is sending to X and U is sending to W. We must check whether V’s transmission would interfere with U’s at W or with X’s reception, and whether U would overhear V and defer unnecessarily. If V’s signal is heard by U but would not cause a collision at X or W, the node U might unnecessarily defer. However, the specific pairing V→X and U→W often represents a different interaction pattern and may or may not produce an exposed terminal depending on the carrier sensing range and relative positions. The reasoning hinges on who can overhear whom and whether deferral is actually unnecessary at the time.
Option C: U→V while X→Y
In this configuration, U transmits to V while X transmits to Y. If U’s transmission to V is heard by X and causes X to defer, yet X’s transmission to Y would not collide with U’s at Y, this is a classic illustration of an exposed terminal: a node (X) defers because it senses the medium is busy due to a transmission that would not affect its own receiver. This aligns with the exposed-terminal concept where listening causes deferral even though the concurrent transmission would not cause a collision at the intended recipient. Therefore, this scenario is consistent with an exposed terminal behavior.
Option D: ResetMaximum marks: 2
This appears to be a formatting or metadata note rather than a valid transmission pair. It does not describe a radio transmission scenario and should not be considered a candidate for the exposed terminal condition. It lacks a sender–receiver pair and cannot illustrate the physical scenario described in the question.
In summary, the pairs that align with the exposed-terminal idea are those where a node defers due to sensing another transmission, but such a deferral would not lead to a collision at the intended receiver. Among the given options, the combinations that fit this pattern are those where the sensing node would unnecessarily defer while its own transmission would not cause a collision at its own receiver. The first and the third options align with this concept in typical exposed-terminal reasoning, while the second depends on the specific topology and sensing relationships. The fourth option does not represent a valid transmission pair and should be disregarded as not applicable to the question’s scenario.

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