Computer Networks · TEE · papers
Q1(c) · Round-robin scheduling
2023-01-27 · AI-only Sem V
Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.
Q1(c). Set 1 contains packets 1,4,6; set 2 contains 2,3,5,7. Packet 1 arrives before t=0; 2,3,4 arrive during (0,1); 5 during (2,3); 6,7 during (3,4). Each packet takes one slot, starting at a slot boundary after arrival. Round-robin begins with set 1 and uses FIFO within a set. Give departures at t=1 through 7 and justify. [5 marks]
Answer
Given
Arrival groups in the question; one-unit service; slot-boundary starts; FIFO inside each queue.
To find
Departure order at t=1 through7.
Formula and why
At each slot start, consider only packets that have already arrived.
Round robin alternates nonempty queues, skipping an empty queue.
Solution
Step 1. Apply the queue rule at each boundary
| Service interval | Departure packet | Reason |
|---|---|---|
| [0,1) | 1 | Only packet1 has arrived. |
| [1,2) | 2 | Use set2: oldest is2. |
| [2,3) | 4 | Use set1: oldest is4. |
| [3,4) | 3 | Use set2: oldest is3. |
| [4,5) | 6 | Use set1:6 has arrived. |
| [5,6) | 5 | Use set2:oldest is5. |
| [6,7) | 7 | Set1 empty; set2 supplies7. |
Step 2. Write the required ordered digits
1 2 4 3 6 5 7