1 Simulation Implementation Using high-level languages

2 Implementation of a Single- Server Queuing System Two Main Entities SERVER: Busy= 0/1 QUEUE: Qsize= # Two Critical Events – for customers Arrival Complete Service (Depart) How do these entities interact? Initialization? How are each of the variables affected? How should simulation terminate?

3 Snapshot or System Image State of the system at a given time State variables Queue Future Events List (FEL)

4 Generating Future Events Bootstrapping: a method for generating an arrival stream on an “as you go” basis As opposed to generating all events at once a.k.a. on-the-fly

5 Generating Future Events Process 1. Generate initial arrival; when it is removed from FEL generate new interarrival time - add to clock for arrival time- place next arrival on FEL 2. When item is placed in service, generate service time - add to clock – place completion event on FEL

6 DATA Structures Future Events List (FEL) Queue (1 or more) What information is required for each one? What information is not required but might be convenient? When and how are insertions & deletions made? When are various units of information generated (calculated)?

7 Queue Standard FIFO Customer identification Time entered queue Arrival time Type of service being requested (if more than one)

8 Future Events List Array implementation Each row represents a specific event Customer ID (identification number) Time of occurrence Search for smallest time to get the “next event”

9 Future Events List Linked List ordered by time of occurrence Event Type Time of Occurrence Identification of customer

10 Generating Arrivals Initialize at a fixed time or time zero One for each type of arrival Subsequent arrivals are generated as arrival is removed Remove arrival- generate IAT- add to current time (clock) - put on FEL At any time, there should only be one arrival of any given type

11 Generating Departures Complete Service Generated when customer enters the service that will cause the departure Not necessarily upon arrival, not if enter queue, only when enter service Enter service (from queue or from arrival) - generate service time - add to current time (clock) - put on FEL

12 Generating Events Terminate Event Only one: placed on FEL at initialization Snapshot Event (Status Report) Initialize 1 st one Remove from FEL- add time unit - return to FEL

13 What? Me Simulate? Paper by Dr. Halverson

14 Generation of Events Initialization of FEL One arrival (of each type) Snapshot Stop event Generation of Arrival When removed from FEL, generate next arrival

15 MAIN Initialize FEL, statistical variables, clock Remove next-event from FEL While not stop-event Clock = next-event.time Case next-event of Arrival: produce next arrival call ARRIVE Departure: call DEPART Snapshop: call SNAPSHOT Remove next-event from FEL Stop-simulation: call STATS; call OUTPUT

16 ARRIVE If server_status = busy Then call ENTER-QUEUE Else call ENTER-SERVICE

17 DEPART If queue = empty Then server_status= free Else call REMOVE-FROM-QUEUE

18 ENTER-SERVICE server_status = busy Generate departure event Update service stats

19 ENTER-QUEUE Add customer to queue Update queue statistics

20 REMOVE-FROM-QUEUE Update queue and statistics Call ENTER-SERVICE

21 STATS Compute final averages, totals, etc. IAT, Service time, Utilization Queue length, max, min, average Number arrivals, departures Wait time, Time in system

SNAPSHOT Generate next Snapshot event, place in FEL Print State variables Print Queue Print FEL 22

23 OUTPUT Print results

PROJECT #1 Must follow the guidelines presented in class for the form of your program. Must use object oriented approach Print out of Code due in 1 week 24