This presentation introduces discrete-event simulation software. It discusses what discrete-event simulation is, how it models systems as sequences of events over time. It covers the basic constructs like entities, resources, control elements and operations. It explains how simulation execution advances by processing the next event. It discusses entity states like active, ready, time-delayed and conditional-delayed. It also summarizes different implementations in discrete-event modeling languages and tools like Arena and AutoMod.

1. Welcome
To
My Presentation

2. Presentation on
How discrete-event simulation software works and
why it matters

3. What is discrete-event simulation ?
A discrete-event simulation (DES) models is the operation of a system as a discrete sequence of events
in time. Each event occurs at a particular instant in time and marks a change of state in the system.
Between consecutive events, no change in the system is assumed to occur; thus the simulation can
directly jump in time from one event to the next.

4. Nature of Discrete-Event Simulation
 Event time: discrete; state: usually discrete
 Transaction-flow world view: discrete units of traffic that move from point to point while competing for scarce
resources
 Two or more events often have to be manipulated at the same time point. How to order them?
m1
m2
l

5. Discrete-Event Modeling Languages
 There are different implementations, which aim to provide convenience for modelers.
 Arena for example, provides graphical user interface for the users to input the simulation model.

6. Basic Simulation Constructs
Topics includes -
 Entity – a unit of traffic
 Resources – service machine
 Control Elements – support delay or logical alternatives
 Operations - an action for an entity

7. Model Execution
 The simulation advances with the
simulation clock, which advances
when an event happens
 Carry out all possible actions at the
current simulated time -> advance the
simulated clock;
 and repeat;
initialize event list
get next (nearest future)
event from event list
time = event time
process event
(change state values, add/delete
future events from event list
update statistics
done?

8. Entity States
 Active State: current moving state
 Ready State: ready but wait due to limited resource
 Time-Delayed State: entity waiting for a known future time so they can enter ready state
 Condition-Delayed State: remove automatically when conditions permit
 Dormant State: modelers set it

9. Entity Management Structure
 Active State – kept in a list
 Ready State – in current event list
 Time-Delayed State – in future event list
 Conditional-Delayed State – delay list
 Dormant State – user-managed list
 All these lists are used to store data and provide easy access to their elements

10. Different Implementation in Tools
 The paper together with its WSC96’ version gives 6 representative implementations.
Two examples here -
 AutoMod, version 9 (Phillips 1997)
 Siman, the core of Arena

11. AutoMod Language
Generic Term AutoMod Equivalent
External Entity Load
Internal Entity Logical Load
Resource Resource; Queue; Block
Control Element Counter;
Process Traffic Limit
Operation Action
Current Events List Current Event List
Future Events List Future Event List
Delay List Delay List;
Condition Delay List;
Load Ready List
User-Managed List Order List

12. Why It Matters
 Trying to re-capture a resource immediately
 The first in line is still delayed
 Yielding control
 Conditions involving the clock
 Mix Mode Waiting

13. Group Members
 Rawnat Jahan Anika [183 019 042]
 Subho Mrong [163 019 042]

14. Thank You!