QUESTION 3 ITOTAL MARKS: 25] Q 3(a) Describe the following scheduling policies a
ID: 3920747 • Letter: Q
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QUESTION 3 ITOTAL MARKS: 25] Q 3(a) Describe the following scheduling policies and suggest a scenario in which each might be used [12 Marks] FIFO Round Robin Weighted Fair Queuing Priority (3 marks each) [13 Marks] Q 3(b) Consider Figure 3(b) showing packet audio transmissions and reception times i) Compute the estimated delay for packets 2 through 8, using a weighted moving average with u 0.1. (5 marks) i) Compute the estimated deviation of the delay from the estimated average for packets 2 through 8, a weighted moving average with u 0.1. (5 marks) i) Suppose at the end of a talkspurt, you had calculated the values as in parts 3(b) i) and 3(b) ii). Describe how you would use these values to estimate the playout delay for the next talkspurt. (3 marks) Packets Packets generated Packets --' received time 8 Figure 3(b) End of Question 3]Explanation / Answer
According to the chegg guidelines if multiple questions are posted, on;ly first questions has to be answered completely. so here is the answer for (a)
FIFO
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1. Stands for First In First Out
2. It is simple, easy and useful
3. It is basically about priority serving for the ones that comes first in the queue.
4. To create this scheduling you need to use data structures like queue and when the process is completed dequeue the process which was in the front of the queue and give priority to the next process in the queue.
5. This technique can be used in small system that do not give importance to the input and output.
Scenario : Consider a queue in cinema hall or a checkout line in the store. Here the person standing first in the queue (First In) is dealt and relieved from the queue (First Out).
Round Robin
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1. It is a preemptive process.
2. Each process has quantum that is every process has a fixed time to execute.
3. When the process completes it's execution , it is preempted and chance is given to other process to execute.
4. To save the states of preempted processes it uses context switching.
5. Task with same priority is scheduled with round robin.
Scenario : Consider world famous FIFA play where all the players meet all other players in turn (all-play-all tournament). Here each contestantsplays every other contestants.
Weighted Fair Queuing
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1. It is a network scheduler algorithm.
2. Generalised Processor Sharing strategy is implemented.
3. It is also known as packet by packet GPS.
4. Sharing process within one packet transimision time span regardless of incoming request.
5. Queue size can be modified but if it is too small it becomes conjested and if too large becomes non utlised.
Scenario : In CDMA spread spectrum cellular networks, the required energy can be the cost and in the channel allocation in dynamic system, number of near by base station can be the cost which can't use the same frequency channel.
Priority
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1. Scheduling the process according to the priority.
2. It chooses the task as per the priority assigned to each and every process.
3. Process having the highest priority is served first and process with same priority is served based on First Come First Serve (FCFS) or round robin.
4. Assigning priorities can be static or dynamic. Static preference can be given during creation of the process/ task and dynamic preference can be based on the behaviour of the task.
5. It can be wither preemptive or non preemptive.
Scenario : Shortest job first where the task with less execution time is executed first to reduce the average waiting time for the other process awaiting execution.
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