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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
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
+
inbound PSTN CUR
Call usage rates
+
outbound PSTN CUR
Example
1.
Issue 3.4.1 June 2005
149
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