In a bus arbitration scheme, which approach guarantees fair access by cycling through nodes?

In a bus arbitration scheme, which approach guarantees fair access by cycling through nodes?

• A. First-come-first-served scheduling.
• B. Fixed priority scheme.
• C. Round-robin assigns access in a rotating order to ensure fairness.
• D. Token-passing scheme.

Answer: (C)

Round-robin arbitration ensures fair access by cycling through nodes in a fixed, rotating order. Each time the bus becomes available, control is granted to the next node in line, and the pointer wraps around after the last node. This creates equal time slices for everyone and guarantees that no single node can monopolize the bus, because every node gets its turn in a predictable sequence. First-come-first-served can let a bursty node grab multiple opportunities in a row, leading to unfair access for others. A fixed priority scheme favors higher-priority nodes, which can starve lower-priority ones. Token-passing is another fairness mechanism, but it relies on possession of a token rather than a simple rotating order; the round-robin description specifically captures the idea of cycling through all nodes.

Round-robin arbitration ensures fair access by cycling through nodes in a fixed, rotating order. Each time the bus becomes available, control is granted to the next node in line, and the pointer wraps around after the last node. This creates equal time slices for everyone and guarantees that no single node can monopolize the bus, because every node gets its turn in a predictable sequence.

First-come-first-served can let a bursty node grab multiple opportunities in a row, leading to unfair access for others. A fixed priority scheme favors higher-priority nodes, which can starve lower-priority ones. Token-passing is another fairness mechanism, but it relies on possession of a token rather than a simple rotating order; the round-robin description specifically captures the idea of cycling through all nodes.