Lesson 3: Entity Arrivals


Entities are the things that move through your process. They include things like phone calls, patient’s, customer orders, raw materials, service requests, parts, etc. Entities come into your model through Arrival routes (with double headed arrows).

Close any open models and open Lesson 1 – Call Center. Save this model as Lesson 3. Double click on the arrival route connecting the Call entity to the Take Call activity.


A single Call arrives every 5 minutes. Using a Periodic arrival with a First-time value of 0, the first call arrives immediately as the simulation begins.

Continuous – Entities will enter the model as soon as there is capacity to accept them at the first location (activity or storage) connected to the arrival. If the first activity has an input queue, it is ignored.

Daily Pattern – Entities arrive in a weekly (168 hours) repeating pattern, at times and quantities you specify on a given day of the week. If the start time and end time is different, the entities will arrive in a randomly distributed fashion during that block of time. The Quantity field may be a constant, distribution, or scenario parameter.

Ordered – Entities arrive according to the parameters established in the Order Signal route connected to it. This means a request must be made by an event downstream from the ordered arrival rather than from the arrival itself.

Periodic – Entities arrive at the interval indicated in the Repeat every field, in the quantity specified. Since all simulations start at midnight on Monday morning, that is when the first arrival occurs, unless you specify a value in the First time field in which case the arrival will be delayed by that amount of time. Each field may be a constant, distribution, or scenario parameter.

Scheduled – Entities arrive according to schedule you define using a numbered day (e.g. 1 st Monday, 3 rd Thursday). Each arrival is a one-time occurrence which the system does not repeat. The Quantity field may be a constant, distribution, or scenario parameter.

Daily Pattern Example

Let’s create a daily pattern arrival in which a quantity of 48 entities arrives between 8am and noon, then another 48 arrive between noon and 4pm.

Double click on the arrival route connecting the Call entity to the Take Call activity. Change the arrival Type to Daily Pattern and click Define Pattern. Then click New. In the Start time field enter 8:00 am. In the End time field enter 12:00 pm. In the Quantity field enter 48.

Click New and repeat the process for 12:00 pm to 4:00 pm.

Now copy the Monday pattern to Tuesday through Friday by clicking the Copy day button. Click Tuesday and then click Paste Monday. Repeat for Wednesday through Friday. Then click Close.


Each day, Monday through Friday, is divided into two blocks of 8 am to noon and noon to 4 pm. In each of those 10 blocks, a quantity of 48 calls will arrive, randomly distributed through each block.

Daily pattern arrivals (as well as scheduled arrivals and shifts) use a 24 hour clock. Up to now, we have only been concerned with simulating straight working hours. As you will see shortly, this will impact how you set up your models.

Save this model as Lesson 3 and then simulate it.


  1. What is the average cycle time for Difficult calls?
  2. What is the utilization of the Level 2 resource?
  3. Why has the utilization decreased?
  4. Why did the animation stop during the simulation?
  5. How many days were simulated?
  6. How do you make the simulation run for an entire week?
  7. If you change the arrival, so all 96 entities arrive between 8:00 am, and 8:01 am, Monday through Friday, how does this change the results, and why?

Self Teaching Guide

Getting Started


  1. Your First Model
  2. Replications and Distributions
  3. Entity Arrivals
  4. Routings
  5. Attributes, Variables, and Action Logic
  6. Shifts
  7. A More Complex Call Center
  8. Model Building Techniques

Case Studies

  1. Analysis
  2. Replications
  3. Froedtert Hospital Improves ICU Care
  4. Nuclear Site Cleanup
  5. Restaurant Customer Seating Optimization

Appendix: Answers to Lesson Questions

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