Lesson 1: Your First Model
Operating Parameters and Requirements
In our first lesson, we will model a small call center. The objective of this lesson is to find the appropriate staffing level for a given call volume. We will be modifying the model itself, as well as changing some parameters to reach the objective.
Help desk staff (Level 1 resource) make $15/hr while support staff (Level 2 resource) make $18/hr.
75% of the calls taken can be resolved over the phone within the first 2 minutes. Once the question is answered, the call exits the system. But the remaining 25% of calls are more difficult and require additional research. The research function takes 20 minutes to complete. Following the research, the call must be returned to the customer. This call back takes 3 minutes.
New calls come into the call center every 5 minutes. Management has determined that the average customer with a difficult issue should not wait more than 60 minutes to receive a callback.
Open the Model
Start ProcessModel and open the Lesson 1 – Call Center model package by selecting the Open option from the File menu.
This will open the model in ProcessModel. Make sure you use File / Save As and save the model as another name when saving the changes. Otherwise, you will overwrite your original model.
You should now see the model shown below.
Answer the following questions without simulating the model. Supposing 200 calls arrived:
- How many calls exit without requiring research?
- How long does each simple call take to complete?
- How many calls require research?
- How long does it take to service the difficult calls?
Simulating the Model
To simulate the model, click the Simulation menu and then select the Save & Simulate option.
The upper left region of the simulation window is called the Scoreboard. It shows some key statistics for entities that have completed the process and left the model. The upper right section of the window shows the simulation clock. 30 hours and 23 minutes into the simulation, the 63 completed difficult calls have taken an average of 681.24 minutes to make it through the process. That may be a surprise since the total activity time for the model is only 25 minutes. One of the benefits of simulation is to demonstrate what will happen, rather than what is supposed to happen or what you think will happen.
You can speed up the simulation or slow it down by dragging the scroll bar at the top of the window to the right or left.
The indicator lights above the resources show their activity. Red means the resource is on break or off shift. Blue means the resource is on shift but waiting for work. Green means the resource is currently working on an entity.
The number above and to the left of an activity represents the contents of its input queue. In this case, there are 14 calls waiting to be returned because the activity is currently busy. The number below an activity shows the current contents of a multi-capacity location. The Perform Research activity has a capacity of 10, but since there is only 1 Level 2 resource, only 1 entity can be processed at a time at that location.
View the Output Report
Following the simulation you will be asked if you want to see the results. Click Yes, or after returning to ProcessModel click the output report button .
Click the General Report and then go to the Resources section. You’ll notice that the Level 2 resource was busy 96.7% of the time while the Level 1 resource was only busy 40% of the time.
Click the Entity section. You see that 70 Difficult calls left the model and took an average of 669.69 minutes to do it.
Goto the Activities section. Notice the input queue for the Return Call activity had an Average Contents of 21.76 and an average wait time of 497.37 minutes. That was over 8 hours in that activity before the call was returned. Our manager is not happy!
Solution 1 – Hire More Staff
Close the output report. Then double click on the Level 2 resource and change the Quantity field to 2.
Save this as a new file by clicking the Save As option on the File menu. Save the file as using the name Lesson 1 – Solution 1. Now simulate your model and find the average cycle time for the Difficult calls.
5. How much improvement was there in the cycle time?
6. How did the resource utilization change?
7. Is that utilization change good or bad? Why?
Solution 2 – Change Entity Handling
While there was a dramatic improvement in cycle time, solution 1 will increase the cost. Let’s try another where the Level 2 resource stays with the entity from when they begin research until after they return the call.
Open the original call center model by clicking File and then Open. Select the Lesson 1 – Call Center model. Change the Get and Free connector from Perform Research to Level 2 to a GET.
Also change the Get and Free connector from Level 2 to Return Call to a Free.
Now, instead of the Level 2 resource being freed immediately after the Perform Research work is complete, the resource will travel with the Difficult call through the Return Call activity until the call is complete and has been returned.
Save this new model as Lesson 1 – Solution 2. Simulate the model.
The average cycle time for research calls is 212.27 minutes which is not as good as in Solution 1. However, there wasn’t a cost increase due to adding a level 2 resource. The Perform Research input queue has an average content of 8.28 and an average time of 179.23 minutes.
8. Where is the queue buildup now?
9. What happened to the input queue buildup at Return Call?
Solution 3 – Change Responsibilities
Since the Level 1 resource has some free time, let’s see what happens if we have them return calls instead of the Level 2 resource.
Close any models you have open. Open the Lesson 1 – Call Center model. Click the dashed line connecting the Level 2 resource to the Return Call activity. Press the Delete key on your keyboard. Hover your mouse over the Level 1 resource. Then click and drag your mouse to Return Call.
Rename your model to Lesson 1 – Solution 3 by clicking the Save As option on the File menu.
After simulating this new model, you’ll notice the cycle time for Difficult calls has dropped to 105.35 minutes.
10. What was the Average Contents value for the Perform Research input queue?
11. How long did the average Difficult call wait in the input queue of the Perform Research activity?
12. What was the utilization of each resource?
Solution 4 – Alternate Resource
Another alternative is to cross-train Level 1 workers so they can help to do research when they aren’t busy taking calls. Remember, though, that taking calls is their first priority. So if they are doing research and a call comes in, they need to stop doing their research to take the call.
Open the Lesson 1 – Call Center model. Hover the mouse over the Level 1 resource. Click and drag your mouse to the line connecting Level 2 to Perform Research.
To place priority on taking calls, click the connector between Level 1 and Take Call. Then click the Respond Immediately check box.
Save this file as Lesson 1 – Solution 4. Then simulate the model.
The average cycle time for Difficult calls is now 53.95 minutes. Remember, management wanted that time to be under 60 minutes.
13. What happened to the utilization for Level 1 and Level 2 resources?
14. You have tested several potential solutions. What are some of the benefits of testing potential solutions on the computer vs using the actual system?
Self Teaching Guide
- Your First Model
- Replications and Distributions
- Entity Arrivals
- Attributes, Variables, and Action Logic
- A More Complex Call Center
- Model Building Techniques
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