Exercise 4: Forecast demand and equipment installation

For this exercise we shall return to the original WiMAX-DSL model, so please close the results, switch back to the Editor, close WiMAX-DSL03 and re-open the default model WiMAX-DSL02.

Use the <recent-file list> at the foot of the File menu in the Editor!

We start by reviewing the customer assumptions for DSL access.

1. Open the Demand dialog from the DSL access service icon menu.

The demand is specified as a number of Homes, calculated as a penetration into an underlying customer base. In this case the customer base is defined by reference to a separate Market Segment element, DSL market.

2. Move the service Demand dialog to one side (by clicking and dragging in the dialog caption) so that you can see the DSL market and DSL access icons underneath.

Market Segment

3. Open the icon menu for DSL market and select Details.

You will see that the DSL market size is defined by a formula, which takes the value 900 throughout the working model. We will come back to the custom inputs (user data) driving this formula later.

4. Close the Details dialog (but leave the Demand dialog on the screen) and look at the arrow running from DSL market to DSL access.

Linking and unlinking

5. Right-click the arrow and select Unlink from the popup menu which appears. The arrow disappears, the background shading is removed from DSL access, and the Customer Base input field in the Demand dialog changes to say 0.00.
6. Now we are going to restore the link. First click the Connect button on the toolbar. The cursor changes to match the image on the button.
7. Click on DSL market. A connecting line appears, originating from that element. As you move the cursor over potential target elements, each of these is also highlighted.

8. Move the cursor over the DSL access service and click again. The connection is re-instated, and you will see that this is reflected in the Customer Base button in the Demand dialog.

You can also activate the Connect tool by pressing <Ctrl+Q> if you find this easier than clicking the toolbar.

As an alternative to the Connect tool, you can also connect elements by using drag-and-drop while pressing the <Ctrl> key (similar to the metaphor for copying files to a sub-folder in Windows Explorer). This is convenient, but can lead to you accidentally copying elements if you ‘miss’ the target element!

Time series defined by a market segment

9. Look ‘inside’ the Customer Base input field by clicking on the small button to the right of the main cell (or by pressing <Enter> while the cell is selected). You will see that this is another time-series dialog with its own Type menu.
10. Pull down the Type menu and note that (reference to) Market Segment is another parameterisation alongside Constant and Interpolated Series.

So, you can define the Customer Base for a service as one of the usual parameterisations, or as a reference to a separate Market Segment element. This structure is very economical when (in general) multiple services are defined with separate penetrations into a common customer base (market).

Penetration and connections

11. Close the Customer Base dialog and look inside the Penetration input field. This is an S-curve where the values start at zero (to the end of 2006) and then rise to 10% in Y2 and 40% in Y3.

If you graph this S-curve, and show the graph as a table, you will see that the penetration reaches 97% by 2015. So we should expect the demand in connections for the DSL access service to reach 900 * 0.97 Homes, i.e., around 873 Homes. We will check this result at the end of this exercise.

Now we are going to look at how the DSL access service is delivered. The primary network interface is a port … on a line card … on a shelf … in a DSLAM. However, there is no need to model down to individual cards, as they are typically purchased as fully-configured shelves, and this is the basic building block we start with.

DSL shelf

12. Close the previous dialogs and look at the Capacity and Lifetime for the DSL shelf resource. You will see that this has a Capacity of 320 Ports and a Physical Lifetime of 10 years.

Notice that there is a small red triangle in the top right corner of the Capacity Unit field: this note indicator shows that there is a note associated with this cell.

13. Display the note by clicking the button on the dialog menu or by pressing <Alt+N> with the Capacity Unit field selected, or by simply hovering over the the field to display a tooltip containing the note. A note is displayed: 20 ports per card × 16 cards per shelf.

So one unit of this resource supports up to 320 units of demand (Homes).

14. Select Move from the dialog menu and go to the Costs dialog.

You will see a capital cost of EUR5000. This is for the unit, i.e., the whole shelf, not an individual port. (The currency unit is defined in the global Financial Data dialog.)

Requirement

15. Close both dialogs and note the green link between DSL access and DSL shelf. This indicates the Requirement for capacity of the DSL shelf from the DSL access service.
16. Right-click the green link and select Details from the popup menu. Note that the Basis is Connections and the Mapping is 1.0. We will experiment with other bases in later exercises.
17. Close the Requirement dialog and then select Requirements from the icon menu for the DSL access service. This opens the Requirements dialog for the service. You will see a field for each resource defined in the model. Most are light grey, indicating no mapping.

18. Left-click on the small button for DSL shelf. The Requirement dialog is displayed – equivalent to double-clicking the green link between DSL access and DSL Shelf (as in step 16).

19. Experiment with unlinking and re-linking. You will see that linking is equivalent to setting the relevant Mapping to 1.0.

This time we will just press <F5> to run the working model. The Results program will load the results and start with a blank View 1.

Now we are going to learn how to draw graphs ourselves.

Drawing graphs

20. Select Draw… from the Graphs menu. The Draw dialog is displayed. This is a tabbed dialog, the first tab of which is the Elements tab. Select DSL access in the Available list and either double-click or press the button to move it to the Selected list.
21. Switch to the Graphs tab. A list of pre-defined graphs is displayed. Select Connections and press OK to draw the graph. Check the value in the last year. Is it as expected?
22. Repeat this process to draw the following charts for the DSL shelf resource. In each case, think about what the graph means and whether you agree with the results.

• Capacities
• Capital Expenditure
• Depreciation and Amortisation.
• Installed and Incremental Units
• Utilisation Ratio

Note: you can select several graphs at once in the Graphs tab by using <Shift + click> for a contiguous selection or <Ctrl + click> for a non-contiguous selection.

23. If there is time, try going back to the Editor and changing the Physical Lifetime to 5 years. What impact do you expect on the results?
24. Re-run the model to find out!

If you still have the Capacities and Installed and Incremental Units graphs for the DSL shelf resource on the screen, please select Save Workspace from the File menu so that these charts will appear automatically when we move on to the next exercise!