Grade of Service (or GOS) is the probability of a subscriber finding
Congestion. Congestion means that all circuits are busy and no
Switch path is available. Thus, a higher GOS means poor Service.
A GOS 0.01 means 1 out of every 100 call is lost(or rejected) due
to congestion on circuits.
X = (( Traffic in Erlangs)^ n) / n!
SIGMA Y = (( Traffic in Erlangs)^ k) / k! ; k = 0 to k=n
GOS = X / SIGMA Y
Where n = Total no. of Circuits (or channels) avaible.