Which medium access control (MAC) technique is specifically designed for bus or tree topologies, using a token that is passed logically among stations on the shared medium?

Introduction / Context: Medium access control determines how multiple stations share a common transmission medium without talking over each other. Different physical topologies often inspired distinct MAC strategies—rings, buses, and trees each posed unique coordination challenges.

Given Data / Assumptions:

• Physical topology considered: bus/tree (e.g., coaxial bus or a logical tree).
• We need a MAC technique tailored to that topology.
• Token-based coordination vs contention (CSMA) are classic alternatives.

Concept / Approach: Token Bus (IEEE 802.4) implements a logical ring over a physical bus or tree. A token circulates among stations in a predefined logical order; only the token holder transmits. This prevents collisions while retaining the cabling simplicity of a bus/tree. Token Ring, by contrast, assumes a physical (or concentrator-based) ring. CSMA (as in classic Ethernet) is contention-based rather than token-controlled.

Step-by-Step Solution: Match topology: bus/tree → look for a MAC that overlays a logical ring on a bus.Token Bus fits: token passing without physical ring cabling.Conclude Token Bus is the intended MAC technique.

Verification / Alternative check: Historical standards: IEEE 802.4 explicitly targeted industrial environments with bus cabling, providing deterministic access via token passing.

Why Other Options Are Wrong: Token Ring: Designed for ring topology; not bus/tree.

CSMA: Contention-based; may be used on bus but is not the token-based method asked for.

MAC (generic): Not a specific technique.

None of the above: Incorrect because Token Bus exists and matches.

Common Pitfalls: Equating “bus = CSMA only.” While CSMA dominated Ethernet, token bus was specifically defined for bus/tree with deterministic access.

Final Answer: Token Bus