The Principle of Grading (Grade of Service)

The Principle of Grading (Grade of Service) Points : the principle of grading (grade of service) The effectiveness of telephone corporation must be such that, it has to give the best service to its subscribers, i.e., the number of switching equipment must be such that no call should fail to expand.

At times during busy hour, the telephone traffic amplify to highest. To cope by this the company has to give the required switch equipment which are extremely luxurious. These equipment will be in use just for a partial period of time and will stay idle for rest of the day. So the cost of installation will increase very much. This cost must be made sensible through losing a small part of traffic. So in practice, a definite percentage of subscribers fail to get a connection due to non-availability of switching equipment. The possibility that a definite percentage of subscribers will not be able to create a call is call the grade of service.

The on the whole grade of service, which consists of the individual grades of service in different stages of the exchange, is find out by the possibility of failing to make a connection among the two parties. The overall grade of service during the busy hour can be use to calculate the number of switching equipment and circuits.

The greater part of the on the whole loss is allowable in those sections, which have the maximum annual costs. The costs of the junction circuits, i.e., connection among exchanges, will be higher than those of the selector stages in the exchange. So it is more inexpensive to tolerate a lower grade of service, i.e., higher losses, in the junction circuits. Thus different selector stages are generally calculated with a grade of service of 0.001 to 0.01(1 call per 1000 to I call per 100), whereas for junctions (both local and long distance circuits) a grade of service of 0.005 to 0.05(5 calls per 1000 to 5 calls per 100) is adopted. The local calls will thus have best grade of service because only selector stages are’ involved.

The overall grade of service per connection can have a value of 0.06 to 0.07 with no considerably reducing the service to subscribers. This is due to the fact that there are chances a call is not done for other reasons, e.g., the called party being engaged or not available.

The least amount grade of service will occur only in the busy hour, so that in most cases, the actual grade of service will be improved.