Define the term Grade of Service.
Grade of Service: In loss systems, the traffic carried through the network is usually lower than the actual traffic offered to the network through the subscribers. Therefore, the overload traffic is rejected and therefore this is not carried by the network. A amount of traffic discarded by the network is an index of the quality of the service offered through the network and is known as grade of service (GOS) and is defined by the ratio of lost traffic to offered traffic. So, offered traffic is the product of the average number of calls generated through the users and the average holding time per call. GOS is specified with
GOS = A-A0 / A0
Here A= offered traffic A0 = carried traffic A-A0= lost traffic.