Editing Grade of service (section)

==What is Grade of Service and how is it measured?==
When a user attempts to make a telephone call, the routing equipment handling the call has to determine whether to accept the call, reroute the call to alternative equipment, or reject the call entirely. Rejected calls occur as a result of heavy traffic loads (congestion) on the system and can result in the call either being delayed or lost. If a call is delayed, the user simply has to wait for the traffic to decrease, however if a call is lost then it is removed from the system.<ref name="kennedy">Kennedy I., Lost Call Theory, Lecture Notes, ELEN5007 &ndash; Teletraffic Engineering, School of Electrical and Information Engineering, University of the Witwatersrand, 2005</ref>

The Grade of Service is one aspect of the [[quality of service|quality]] a customer can expect to experience when making a telephone call.<ref name="peuhkuri">Peuhkuri M., IP Quality of Service, Helsinki University of Technology, Laboratory of Telecommunications Technology, 1999.</ref> In a Loss System, the Grade of Service is described as that proportion of calls that are lost due to congestion in the busy hour.<ref name="farr">Farr R.E., Telecommunications Traffic, Tariffs and Costs &ndash; An Introduction For Managers, Peter Peregrinus, 1988.</ref> 
For a Lost Call system, the Grade of Service can be measured using ''Equation 1''.<ref name="flood">Flood, J.E., Telecommunications Switching, Traffic and Networks, Chapter 4: Telecommunications Traffic, New York: Prentice-Hall, 1998.</ref>

:<math>\mbox{Grade of Service}=\frac{\mbox{number of blocked calls}}{\mbox{total offered calls}}\qquad(1)</math>

For a delayed call system, the Grade of Service is measured using three separate terms:<ref name="kennedy" />

*The mean delay <math>t_d</math> &ndash; Describes the average time a user spends waiting for a connection if their call is delayed.
*The mean delay <math>t_o</math> &ndash; Describes the average time a user spends waiting for a connection whether or not their call is delayed.
*The probability that a user may be delayed longer than time ''t'' while waiting for a connection. Time ''t'' is chosen by the telecommunications service provider so that they can measure whether their services conform to a set Grade of Service.
* Where and when is Grade of Service measured?
The Grade of Service can be measured using different sections of a network. When a call is routed from one end to another, it will pass through several exchanges. If the Grade of Service is calculated based on the number of calls rejected by the final circuit group, then the Grade of Service is determined by the final circuit group blocking criteria. If the Grade of Service is calculated based on the number of rejected calls between exchanges, then the Grade of Service is determined by the exchange-to-exchange blocking criteria.<ref name="kennedy" />

The Grade of Service should be calculated using both the access networks and the core networks as it is these networks that allow a user to complete an end-to-end connection.<ref name="flood" /> Furthermore, the Grade of Service should be calculated from the average of the busy hour traffic intensities of the 30 busiest traffic days of the year. This will cater for most scenarios as the traffic intensity will seldom exceed the reference level.

The grade of service is a measure of the ability of a user to access a trunk system during the busiest hour. The busy is based upon customer demand at the busiest hour during a week month or year.