I often had to explain in simple terms the concepts of Busy Hour and Busy Day to non-technical colleagues while working on network capacity planning. Eventually I decided to come up with a simple illustration that helped me a lot to clarify the concept. This is what I am sharing today.
The Network Busy Hour (NBH) in a day is the 60min period of time when the entire network carries the highest amount of traffic. There is a voice and a data busy hour, which are not necesarily happening at the same time, and during which the total carried traffic is measured in Erlang or Bytes, respectively. The NBH is usually happening in the evening. In the example below, it is between 22:00 and 22:59 for both voice and data traffic.
To quantify how important is the Busy Hour with respect to the total network traffic of the day, we usually calculate the Number of Busy Hours per Day. This number answers to the question “To how many times my BH traffic corresponds to my entire daily traffic ?” as illustrated below:
This number varies in theory between 1 (all traffic of the day happens in one single hour – the operator nightmare) and 24 (all traffic during the day is perfectly spread and constant every hour – the operator dream).
The same approach applies to days of the month: the daily traffic is not the same every day of the month. There are usually peaks during end of weeks and weekends, and often higher traffic at the beginning of the month (after pay day when people have money to spend).
It is important to calculate the Busy Days per Month when planning Network Capacity as commercial inputs in terms of traffic are usually given as monthly traffic. Just dividing the monthly traffic by 30 days will underestimate the peak traffic per day and then the busy hour traffic that will be used for dimensioning purposes.
So overall if you consider the 2 illustrations above, with 8 Busy Hour per Day and 20 Busy Days per Month, you can calculate that you will have an equivalent of 160 Busy Hour per Month which will allow you converting a commercial traffic forecast into a Busy Hour traffic, which will serve as a basis for capacity planning.
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