All these parameters relate to the concept of
availability. Essentially, it precedes them, so that for any
of these parameters to even be measured, first the
connection needs to available (Oliveira, 2012).
Therefore, it’s established that the availability concept
ranks as the first concern for even basic quality of
service standards. In this way, it becomes preeminent
to define and quantify it and through a mathematical
calculation of probabilities is how this valuable
statistic is estimated and only by real experimental
measures it can be provided. Initially, it is necessary
to understand that to estimate the availability, it’s
necessary to know that all the devices present in a
network have, individually, a probability of failure.
This failure depends on two main factors that form
what is usually called downtime, the expected
equipment failover and the repair time of technicians.
The first is normally listed on the data-sheet of each
equipment and the second is provided by the company
that supports the operation with technical personnel.
In this manner, the availability is considered to be the
probability, in case of an estimation, that a service, or
a device, is available during a period of time.
Therefore, by subtracting from 1 (100%) the sum of
the Average Expected Downtime of the Device
(AEDD) with the Average Time to Repair the Device
(ATRD) divided it by the Total Period of Time (TPT).
The equation shown below Equation 1 describes the
mathematical calculation employed to describe the
Availability of a Single Network Equipment (ASNE)
given in percentage (Tron, 2014):