Simulation Implementation

Simulation Implementation Using high-level languages

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?

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

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

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

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)?

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

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”

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

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

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

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

What? Me Simulate? • Paper by Dr. Halverson

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

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

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

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

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

ENTER-QUEUE • Add customer to queue • Update queue statistics

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

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

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

Simulation Implementation