Computer Networks · TEE · papers
Q1(c) · Priority scheduling
2022-11-16 · AI-only Sem V
Exact historical variant. Current-syllabus questions solved; excluded topics and source limitations stated.
Q1(c). Packets arrive as shown: packet 1 before t=0; packets 2,3,4 during (0,1), in that order; packet 5 during (2,3); packets 6,7 during (3,4), in that order. One packet takes one slot and starts only at the next slot boundary after arrival. Packets 2,3,5,7 have priority over 1,4,6; use FIFO within each priority class. Give and justify departures at t=1,2,3,4,5,6,7 as seven ordered digits. [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.
Strict priority chooses the high queue whenever it is nonempty. A running packet is not preempted.
Solution
Step 1. Apply the queue rule at each boundary
| Service interval | Departure packet | Reason |
|---|---|---|
| [0,1) | 1 | Only1 is available. |
| [1,2) | 2 | High-priority2 is oldest. |
| [2,3) | 3 | High-priority3 precedes low-priority4. |
| [3,4) | 5 | High-priority5 has arrived. |
| [4,5) | 7 | High-priority7 precedes low-priority4 and6. |
| [5,6) | 4 | No high-priority packet remains; send oldest low4. |
| [6,7) | 6 | Send remaining low6. |
Step 2. Write the required ordered digits
1 2 3 5 7 4 6