★ Grade of Service is a probability of a cell in a circuit group which is blocked / delayed for more than a specified interval.

★ GoS is expressed as a vulgar fraction / decimal fraction.

★ It is with reference to the busy hour at the time of greatest intensity of the traffic.

★ GoS may be viewed independently from the perspective of incoming vs outgoing calls.

★ The GoS is not essentially equal between source to destination pairs.