Call usage rates
Alternatively, 100 Erlangs of total station usage could also hypothetically correspond to 35 Erlangs of intercom call usage, 10 Erlangs of inbound PSTN usage, and 20 Erlangs of outbound PSTN usage. Using the procedure from the preceding example to verify this:
●Intercom station usage = 70 Erlangs (2 Avaya stations per call x 35 Erlangs of intercom call usage)
●Inbound station usage = 10 Erlangs (1 Avaya station per call x 10 Erlangs of inbound call usage)
●Outbound station usage = 20 Erlangs (1 Avaya station per call x 20 Erlangs of outbound call usage)
The 70 Erlangs that are associated with intercom calls, plus the 10 Erlangs that are associated with inbound calls, plus the 20 Erlangs that are associated with outbound calls total 100 Erlangs of station usage.
However, suppose that once again the station usage is 100 Erlangs. Assuming that there is no tandem traffic, this cannot correspond to 10 Erlangs of intercom call usage, 20 Erlangs of inbound PSTN usage, and 30 Erlangs of outbound PSTN usage.
●Intercom station usage = 20 Erlangs (2 Avaya stations per call x 10 Erlangs of intercom call usage)
●Inbound station usage = 20 Erlangs (1 Avaya station per call x 20 Erlangs of inbound call usage)
●Outbound station usage = 30 Erlangs (1 Avaya station per call x 30 Erlangs of outbound call usage)
The 20 Erlangs that are associated with intercom calls, plus the 20 Erlangs that are associated with inbound calls, plus the 30 Erlangs that are associated with outbound calls total 70 Erlangs, leaving 30 Erlangs of unaccounted station usage. This is a sign that the parsing of call traffic into intercom, inbound, and outbound might have been done erroneously. One possible explanation for the extra 30 Erlangs of station usage is adjunct traffic, such as stations that are connected to voice mail, providing that 30 Erlangs of voice mail calls makes sense in the model.
The bottom line is, regardless of what model is used to parse call traffic into its various components, one must be able to reconcile the overall station usage with the overall call usage. Specifically, if there is no tandem traffic, the following relationship must hold:
SUR = (2 ⋅ intercom CUR) + inbound PSTN CUR + outbound PSTN CUR
Having established that point, several examples describe some methods for populating the COI matrix. For the sake of continuity, all of the examples are built upon Example 1: Station usage.
Issue 6 January 2008 185
