Voice Usage Forecast

A voice usage forecast involves an estimation of the amount of voice traffic
generated by the average voice user. Ideally this should also be provided on
a monthly basis. The voice profile should include the distribution of traffic
in terms of mobile-to-land, land-to-mobile, mobile-to-mobile, and mobile-tovoice
mail. For the mobile-to-land aspect, there should also be a breakdown
of what percentage is local and what percentage is long distance. Ideally,
the voice usage profile information should include the average number of
calls per subscriber in the busy hour and the mean holding time (MHT) per
call. Quite often, however, marketing organizations are likely to simply provide
information in terms of minutes of use (MoUs) per subscriber per
month. In that case, it is up to the engineering organization to derive the
busy-hour usage. The following is an example of how this can be done.

Example: Average user has 400 MoUs per month.
Assume for example that 90 percent of traffic occurs during work days
(that is, only 10 percent on weekends).
Assume 21 work days per month.
Assume that in a given day, 10 percent of voice traffic occurs during the
busy hour.
Then the average busy-hour usage (in MoUs) per subscriber is given by
Thus, in our example, we get 400
0.9
0.10/21  1.71 MoU/sub/busy
hour.
Dividing by 60 gives the number of Erlangs  0.0286 in our example 
28.6 milliErlangs.
If we multiply this number by the total number of subscribers, then we
can determine the total busy-hour Erlang demand, which is a critical network
dimensioning factor. What we also need, however, is the total number
of call attempts as some network elements are limited more by the processing
effort involved in call establishment rather than the total throughput.
If we assume that most calls are completed (which is often the case in
today’s world of voice mail), then determining the number of busy-hour call
attempts (BHCAs) is done by the following formula:
If in our example we assume a MHT of 120 seconds, then we get a persubscriber
BHCA of
Thus, the average subscriber makes 0.86 call attempts in the busy hour.