LectureNote 04 Flashcards
What is a queuing system?
A discrete-event model that uses random numbers to represent the arrival and duration of events.
Queuing systems consist of servers and queues of objects to be served, typically following a first-in, first-out structure.
What is the objective of a queuing system?
To utilize the servers as fully as possible while keeping the wait time within a reasonable limit.
What are the components of a queuing system?
- Arrivals: Entities arriving at the system (e.g., customers, data packets)
- Queue: Waiting line where entities may wait for service
- Servers: Resources providing the service (e.g., machines, workers)
- Service: Process by which entities receive attention or processing
- Departure: Entities leave the system after service.
How does queuing theory help in simulation?
It allows for careful analysis and optimization of waiting lines through features such as arrival frequency, service times, and queue capacity.
What can queuing theory predict for businesses?
- Processing times of customer requests
- The number of people who have to wait in line
- The number of rejected or lost customers in a queue
- The utilization of resources that handle customer requests.
What is the purpose of queue modeling?
To discover a balance between waiting times and resource utilization.
What are the six characteristics of queueing systems in Kendall’s notation?
- A: Arrival process
- S: Service process
- c: Number of servers
- K: Capacity of the queue
- N: Population size
- D: Queueing discipline.
What does the parameter ‘A’ in Kendall’s notation represent?
The arrival process, representing the frequency of new requests arriving in the system.
What does the parameter ‘S’ in Kendall’s notation represent?
The service process, which denotes the amount of time necessary to service a request.
What does the parameter ‘c’ in Kendall’s notation indicate?
The number of servers who handle requests in the system.
What does the parameter ‘K’ in Kendall’s notation refer to?
The capacity of the queue, indicating how many requests can be taken by the system.
What does the parameter ‘N’ in Kendall’s notation signify?
The population size from which customers arrive, often assumed to be infinite.
What does the parameter ‘D’ in Kendall’s notation determine?
The queueing discipline, which dictates how requests are handled and prioritized by the servers.
What is the First-Come, First-Served (FCFS) scheduling process?
A scheduling method where the process requesting CPU first gets it first, managed with a FIFO queue.
What is the average waiting time for processes in FCFS scheduling?
Calculated by taking the sum of individual waiting times divided by the number of processes.
What is Shortest-Job-First (SJF) scheduling?
A scheduling method that associates each process with the length of its next CPU burst and schedules the process with the shortest time.
What is a key challenge of implementing SJF scheduling?
It is impossible to implement perfectly because it requires knowledge of the length of the next CPU request.
What is the formula to predict the time a process will use on its next schedule in SJF?
t(n+1) = w * t(n) + (1 - w) * T(n), where: t(n+1) is time of next burst, t(n) is time of current burst, T(n) is average of all previous bursts, w is a weighting factor.
What does SJF stand for?
Shortest-Job-First
What is the formula for predicting the time of the next process in SJF scheduling?
t(n+1) = w * t(n) + (1 - w) * T(n)
In the formula t(n+1) = w * t(n) + (1 - w) * T(n), what does t(n+1) represent?
Time of next burst
In the formula t(n+1) = w * t(n) + (1 - w) * T(n), what does T(n) represent?
Average of all previous bursts
In SJF scheduling, what is the average waiting time calculated for the processes P1, P2, P3, and P4?
7
What is the burst time of process P4 in the SJF example?
3
What is the average waiting time for the preemptive SJF example?
6.5 milliseconds
In Priority Scheduling, what is associated with each process?
A priority number (integer)
True or False: In Priority Scheduling, the CPU is allocated to the process with the lowest priority number.
False
In Priority Scheduling, what does SJF represent?
Shortest-Job-First scheduling where priority is the inverse of predicted next CPU burst time
What is the average waiting time calculated in the example of Priority Scheduling?
8.2 msec
What does Round Robin (RR) scheduling entail?
Each process gets a small unit of CPU time (time quantum q)
What happens when a process exceeds its time quantum in Round Robin scheduling?
The process is preempted and added to the end of the ready queue
What is the typical range for time quantum in Round Robin scheduling?
10-100 milliseconds
In the example of RR with a time quantum of 4, what is the burst time of process P1?
24
True or False: Round Robin scheduling typically has a lower average turnaround time than SJF.
False
List some notable industries where queueing theory has found application.
- Healthcare
- Banking
- Traffic management
- Manufacturing
- Transportation and logistics
- Call centers
- Telecommunications and computer systems
- Customer Service
What does the symbol λ denote in queuing theory?
The arrival rate (number of arrivals per second)
What does the symbol Ts represent in queuing theory?
The mean service time for each arrival excluding the waiting time in the queue
What is the mean waiting time of all items denoted by in queuing theory?
Tw
What characterizes a Single Server Queue?
It has a single server providing service to connected devices or items
In a Multi Server Queue, what happens when an item requests a server and none are available?
The queue begins to start until a server is free
What is the maximum input rate in a Multi Server Queue represented by?
λmax = N/Ts
What is the purpose of a time-sharing system?
To allow multiple users to share system resources simultaneously
What is an example of a time-sharing simulation system?
SimOS
What is the focus of the SimOS simulation system?
To study complex computer hardware designs, analyze application performance, and study operating systems
Differentiate between Balking and Reneging in queuing theory.
Balking occurs when a customer decides not to enter a queue due to long wait times, while Reneging occurs when a customer leaves the queue after waiting for some time.
