The GATE Grind

GATE 2014 CS (CS1) – Question 38

Computer Networks · Data Link Layer: Error Detection, Medium Access Control, Flow Control · 2 marks · Numerical answer

Selective-repeat sliding-window frames are 1 KB over a 1.5 Mbps link with one-way latency 50 ms. For link utilization 60%, find minimum sequence-number field size (bits).

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: 5 to 5

Explanation

A1KB frame takes approximately5.33ms using1000bytes, while round-trip propagation is100ms. Utilisation W/(1+2a)≥0.6 requires W≥12frames(also12using1024bytes). Selective repeat needs a sequence space at least2W=24. Therefore ceil(log₂24)=**5bits**.