The relationship between demand for each Service (and the output of each Transformation) and the capacity of each Resource that is used by the Service is described by the Basis and Supply Ratio.
Basis
Describes which measure of Service demand governs the installation of resources in a Function. For a Service, the Basis determines whether it is the number of Connections, Average Connections, Traffic, Busy Hour Traffic, Revenue, Annual Traffic, Annual Revenue or New Connections that determines the amount of Function capacity used. For a Transformation, the basis is always the Output of the Transformation.
Mapping
Describes whether a Resource is required by a Service or Transformation. If several Resources are grouped together in a Function, then the set of Mappings define in each year how Resources should provide any additional capacity in the Function required to meet demand from a Service or Transformation. Changes in the Mappings over time can be used to represent technological advances and to control the corresponding rate of introduction.
Mappings are typically defined as Interpolated Series data – see 10.3.33 Time-series inputs – and the series for all Resources in a Function are displayed as successive rows in the Mappings dialog for a given Service or Transformation. Incremental demand is required from the various Resources according to the respective Mappings which, in any year, must either sum to 1, in order to ensure that sufficient Resource capacity is provided to meet demand; or zero, if the Service or Transformation does not require this Function.
For an isolated Resource (i.e., one not in a Function), a constant 1.0 Mapping is all that is required to indicate that this Resource is required by a Service or Transformation.
Note: Resource Requirements can be defined directly by dragging between the respective icons – see 4.4.8 Connecting elements.
For example, consider a scenario where analogue equipment is used to provide capacity up until year 4, but digital equipment is used to provide the required additional capacity from year 5 onwards, as shown below.
Figure 1: The Mappings dialog
If you look at a graph of the result of this allocation of Resources, you can see that up to year 4, all demand is met by analogue equipment. After this, all incremental demand is met by capacity of digital equipment. The analogue equipment continues to be used by the existing demand which installed it, and is only replaced by capacity of digital equipment when it reaches the end of its physical lifetime; but no new demand is allocated to analogue equipment after year 4.
Figure 2: Transition from Capacity of one Resource to another
Supply Ratio
Describes the amount of Resource capacity used by each unit of demand. A value of 1 means that each unit of demand – whether Connection, Traffic, Busy Hour Traffic or Transformation Output – uses one unit of Resource capacity.
A Supply Ratio of 0.05 would be appropriate if only 5% of total demand actually used a particular Resource; for example if only 5% of Busy Hour Traffic was international and hence used an international transmission Resource.
If several Resources are grouped together in a Function, then care should be taken to ensure a consistent interpretation of the Supply Ratio. For example, one unit of a Resource with a Supply Ratio of 1.0 would be regarded as equivalent in capacity to two units of a Resource with a Supply Ratio of 2.0.
The Supply Ratio provides significant flexibility when relating demand from multiple Services to the capacity of a single Resource or Function.
Churn Proportion
By default, demand that has been allocated to a Resource will continue to use it until the Resource reaches the end of its physical lifetime. However, by defining a Churn Proportion, you can specify a proportion of that demand which will cease to use that Resource at the beginning of a year and be treated as incremental demand, for which capacity is required, and re-allocated according to the current Mappings.
This mechanism allows you to accelerate the process of introducing a new Resource, as demand that is using the original Resource is moved over to the new Resource sooner than physically necessary. Any units of the original Resource that become redundant as a result of this process can be removed from the network before the end of their physical lifetime if so desired – see 10.3.24 Resource decommissioning.