Grade of Service (GoS) is a characteristic value for telephone networks that refers to the probability of time delays
exceeding a given delay interval. The Grade of Service can refer to the total connection time
or to specific traffic conditions. Grade of Serviceis independent of incoming and outgoing calls and is not necessarily the same in both directions.
The International Telecommunication Union (ITU) addresses the issue of Grade of Service in several ITU Recommendations. For example, E.540 of 1988 describes the acceptable GoS characteristic for international calls, E.525 of 1992 deals with the way in which networks must be constructed so that they can influence the GoS characteristic, and E.493 of 1996 describes the monitoring of GoS values.