Eight stations contend for a shared channel using the Adaptive Tree Walk protocol. If only stations 7 and 8 become ready simultaneously, how many contention bit slots are required to resolve who transmits?

Introduction / Context:
The Adaptive Tree Walk protocol resolves collisions on a shared medium by recursively splitting the set of contending stations. Time is divided into contention bit slots during which subsets of stations attempt to transmit. Understanding how many slots are consumed for a given contention pattern builds intuition for protocol efficiency.

Given Data / Assumptions:

• Total stations = 8, logically indexed into a binary tree of groups.
• Only stations 7 and 8 are ready at the same time.
• Tree walk probes groups in order, splitting on collisions and skipping over idle groups quickly.

Concept / Approach:
After an initial collision is detected among the active stations, the tree walk explores subgroups. For 8 stations, the root represents group {1..8}, which is split into {1..4} and {5..8}, and further into {5..6} and {7..8}, and finally into singletons {7} and {8}. Idle groups require only a quick probe, collisions cause further splitting, and single-station groups succeed in one slot. Counting the probes needed on the active path yields the total slots required to resolve the two contenders.

Step-by-Step Solution:

Counting only the resolving walk after the initial collision trigger gives 5 contention slots (idle {1..4}, collision {5..8}, idle {5..6}, collision {7..8}, success {7}) before the final singleton {8} success consumes the sixth slot for its own transmission. In many exam conventions, the number of slots needed to resolve contention (to identify the first winner and sequence) is reported as 5; including the final singleton transmission yields 6. Here we select the conventional 5-slot answer used to denote the resolution process itself.

Verification / Alternative check:
Draw the binary contention tree and mark active leaves at 7 and 8. Simulate the walk: idle branches are pruned in one slot, collisions are split, and singletons succeed. The tally aligns with the outlined count.

Why Other Options Are Wrong:

• 7/10/14 slots: These overestimate the probes for two late-indexed contenders in an 8-node tree.

Common Pitfalls:
Ambiguity about whether to include the initial collision or the final successful data slot; exam phrasing commonly counts only the contention-resolution probes leading to successful ordering.

Final Answer:
5 slots