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In telecommunication engineering, and in particular teletraffic engineering, the quality of voice service is specified by two measures: the grade of service (GoS) and the quality of service (QoS). Grade of service is the probability of a call in a circuit ''group'' being blocked or delayed for more than a specified interval, expressed as a vulgar fraction or decimal fraction. This is always with reference to the busy hour when the traffic intensity is the greatest. Grade of service may be viewed independently from the perspective of incoming versus outgoing calls, and is not necessarily equal in each direction or between different source-destination pairs. On the other hand, the quality of service which a ''single'' circuit is designed or conditioned to provide, e.g. voice grade or program grade is called the quality of service. Quality criteria for such circuits may include equalization for amplitude over a specified band of frequencies, or in the case of digital data transported via analogue circuits, may include equalization for phase. Criteria for mobile quality of service in cellular telephone circuits include the probability of abnormal termination of the call. ==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.〔Kennedy I., Lost Call Theory, Lecture Notes, ELEN5007 – Teletraffic Engineering, School of Electrical and Information Engineering, University of the Witwatersrand, 2005〕 The Grade of Service is one aspect of the quality a customer can expect to experience when making a telephone call.〔Peuhkuri M., IP Quality of Service, Helsinki University of Technology, Laboratory of Telecommunications Technology, 1999.〕 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.〔Farr R.E., Telecommunications Traffic, Tariffs and Costs – An Introduction For Managers, Peter Peregrinus, 1988.〕 For a Lost Call system, the Grade of Service can be measured using ''Equation 1''.〔Flood, J.E., Telecommunications Switching, Traffic and Networks, Chapter 4: Telecommunications Traffic, New York: Prentice-Hall, 1998.〕 : For a delayed call system, the Grade of Service is measured using three separate terms:〔 *The mean delay – Describes the average time a user spends waiting for a connection if their call is delayed. *The mean delay – 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「grade of service」の詳細全文を読む スポンサード リンク
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