џWPCL ћџ2BJ|xа АH аа АА X агга ХА6p&А6p&Х аеЮ† а Hр аааУ Уб cмˆ4 PŽТ б Fascicle II.3 Р-Р Rec. E.541 Ф ФPAGE1У Уб cмˆ4 PŽТ б ЮееЃ† а HH аааб cмˆ4 PŽТ бPAGE4У Уб cмˆ4 PŽТ б Fascicle II.3 Р-Р Rec. E.541 Ѓеа H№ ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаа X  аб cмˆ4 PŽТ бAll drawings appearing in this Recommendation have been done in Autocad. ‚У УRecommendation E.541 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр(<Сб cмˆ4 PŽТ бOVERALL б cмˆ4 PŽТ бGRADE OF SERVICE FOR INTERNATIONAL CONNECTIONS Ср(JС(SUBSCRIBERР-РTOР-РSUBSCRIBER) аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б1ТX ТIntroductionФ ФЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.1С   СThe overall grade of service (subscriberР-РtoР-Рsubscriber) on international connections Р-Р relating only to the phenomena of congestionй7€ congestionб cмˆ4 PŽТ б7й in the entire network as a result of the traffic flow Р-Р depends on a number of different factors, such as the routing arrangements in the national and international parts of the connection, congestion allowed per switching stage, the methods used to measure traffic and compute the traffic base, and the time differences between the busy hoursйS time differences between the busy hoursб cмˆ4 PŽТ бSй of the various links involved in the connection. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.2С  СThe most satisfactory way in which this grade of service could be described would be to give its distribution. The design average grade of service during the busy hour of the complete connection would be the most useful single parameter. However, until such time as continuous traffic measurements are carried out during the busy season in all parts of the network on a routine basis, it is not possible to compute this average grade of service. Therefore, at this stage it cannot be used as a criterion for the dimensioning of the network. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа1.3С   СThe only practical way of ensuring an acceptable overall grade of service on international calls is to specify an upper limit on the design loss probabilityй< loss probabilityб cмˆ4 PŽТ б<й per connecting link in the national network as is done for the links in the international network (see Recommendation E.540). аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа‚У У2ТX ТGeneral considerationsЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа2.1С   СSince the success of the international automatic serviceй( international automatic service(йб cмˆ4 PŽТ б is highly dependent on the grade of service of all links involved in the connection from subscriberР-РtoР-Рsubscriber, it is desirable that the originating and terminating national network involved in the connection has grade of service standardsйjб cмˆ4 PŽТ б grade of service standardsб cмˆ4 PŽТ бjй comparable with those of the international network. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа2.2С  СIt is especially important that the links in the country of destination should have a good grade of service for handling the traffic, since high congestion in the terminating national network could have serious effects on the international networkйeб cмˆ4 PŽТ б international networkб cмˆ4 PŽТ бeй. High congestion in the network of the country of destination causes added retrials with consequent increased loading on common switching devices as well as increased occupation of the routes with ineffective calls. ‚б cмˆ4 PŽТ бУ У3ТX ТDesign objectivesФ ФЦЦ 3.1С  СIt is recommended that the links in the national network should be designed for a loss probabilityб cмˆ4 PŽТ бУУ1жОIа H ааа1)ФФб cмˆ4 PŽТ бThe loss probability mentioned refers to busy hour traffic values as defined in Recommendation E.500. Ож)б cмˆ4 PŽТ бФФ not exceeding 1 per cent per link in the final choice route during its applicable busy hour. It is recognized, however, that in some countries additional congestion is permitted for the internal switching stages of the transit exchangesй= transit exchangesб cмˆ4 PŽТ б=й. It is also recognized that, where this recommended grade of service is not provided for the national service, it may not be economically feasible to provide it for international relations. 3.2С  СThe maximum number of links in tandem used by an international connection is defined by Recommendation E.171 [1]. 3.3С  СAlthough the worst overall grade of service would be approximated by the sum of loss probabilities for individual links connected in tandem, on most calls the overall grade of service will be significantly better.‚У У Та Т4СpСб cмˆ4 PŽТ бMaximum traffic loadingЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф4.1С   СAn acceptable automatic service on a final circuit group is difficult to maintain if the traffic loadingй; traffic loadingб cмˆ4 PŽТ б;й on the group exceeds a level corresponding to a calculated Erlang grade of service of 10 per cent. Beyond this traffic loading, service on the route may rapidly deteriorate. This condition will be accentuated under the cumulative effect of repeat attempt calls if these should occur. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа4.2С  СThe curves of Figure 1/E.541 indicate the proportionate reduction in circuits that may be tolerated for a short period, 15 minutes for example, under normal busyР-Рhour conditions, on a fullР-Рavailability circuit group dimensioned for 1 per cent Erlang loss, in accordance with the above traffic overload criterion. Table 1/E.541 gives the figures used to plot the curves. ‚Ср KСб cмˆ4 PŽТ бFigure 1/E.541 Љ CCITT 48110 б cмˆ4 PŽТ б Ср SСб cмˆ4 PŽТ бTABLE 1/E.541 а H аУ УPercentage reduction in the number of circuits if the calculated Erlang grade of service is not to exceed 10 %Ф Ф б cмˆ4 PŽТ бвЦ‚HИ Ј xЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P И џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаааб cмˆ4 PŽТ б Ср >СIf originally operating at 1 % congestion, % reduction Ср CСin circuits allowed to yield 10 % congestion а Ј ј ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P И Ј џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа Ј ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡СрSСб cмˆ4 PŽТ бNumber of circuits аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЈ hа8АџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСрUСRandom traffic СрPС(peakedness factor = 1.0) аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЈ `ШИ ˜xџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСрQСPeakedness factor = 2.5 а ј ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ`ШИ ˜xџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџpи P И џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр.ШoСб cмˆ4 PŽТ б5 Ср.ШmС37.7 Ср.ШoСР-Р а ј аб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡Ср.ШnСб cмˆ4 PŽТ б10 Ср.ШmС32.3 Ср.ШmС40.2 а ј аб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡Ср.ШnСб cмˆ4 PŽТ б20 Ср.ШmС27.2 Ср.ШmС33.3 а ј аб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡Ср.ШnСб cмˆ4 PŽТ б30 Ср.ШmС24.8 Ср.ШmС30.1 а ј аб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡Ср.ШnСб cмˆ4 PŽТ б50 Ср.ШmС21.7 Ср.ШmС26.5 а ј аб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡Ср.ШnСб cмˆ4 PŽТ б100 Ср.ШmС18.3 Ср.ШmС22.4 а ј аб cмˆ4 PŽТ бˆа ј аб cмˆ4 PŽТ бвЦƒHИ Ј xЦв‡Ср.ШnСб cмˆ4 PŽТ б150 Ср.ШmС16.7 Ср.ШmС19.7 а ј аб cмˆ4 PŽТ бˆа Hx ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬа4.3С   СThe curves of Figure 1/E.541 are intended merely as a guide. If the breakdown occurs during an exceptionally busy hour, the permissible proportionate reduction will be less. Conversely, if the breakdown occurs during an hour of light traffic, a higher proportionate reduction in circuits could be tolerated. A higher reduction might also be acceptable after an appropriate oral announcement has been introduced. In the general case, a knowledge of the circuit occupancy will enable an estimate to be made of the prevailing Erlang loss figure with the reduced number of circuitsй> number of circuitsб cмˆ4 PŽТ б>й. С  СThe permissible reduction in the case of large groups should not be аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаexceeded; otherwise very serious congestion can result from repeated attemptsй= repeated attemptsб cмˆ4 PŽТ б=й. ‚У У5ТX ТGeneral notesФ ФЦЦ С СУУNote 1ФФ Р-Р Teletraffic implications for international switching and operational procedures under failure of a transmission facility are discussed in Supplement No. 5 of this fascicle. С СУУNote 2ФФ Р-Р Alternative routingй>Alternative routingб cмˆ4 PŽТ б>й in the national and in the international networks provides on average a grade of service that is better than that provided in the theoretical final route. С СУУNote 3ФФ Р-Р NonР-Рcoincidence of traffic peaks in the national and international networks will provide reduction in the overall grade of service compared with the sum of the design grade of service values per link. С СУУNote 4ФФ Р-Р Time differences will also improve the resulting grade of service. С СУУNote 5ФФ Р-Р The methods of measuring and calculating the traffic base for provisioning purposes in the national networks may be different in various countries and differ from the methods for the international network given in Recommendation E.500. This means that the national traffic values are not always comparable among themselves or with the values of the international network. Each Administration must estimate how its design traffic level compares with that recommended for the international network. С СУУNote 6ФФ Р-Р The design grade of service value of each link will only apply if the traffic at each switching stage is equal to the forecast. In practice, such a situation will seldom occur. Furthermore, the planning procedure normally is such that the specified grade of service should not be exceeded until the end of the planning period. In a growing network, this means that the circuit groups during almost the whole planning period give a better service than the specified critical standard. С СIn conclusion, the overall grade of service depends on the accuracy of forecasts made and the planning procedure used, i.e. it depends on the interval between plant additions and on the specific traffic value in future to which the grade of service is related. ‚У УС СReferenceФ Ф [1]Тh  ТCCITT RecommendationУУ International routing planФФ, Rec. E.171.ЦЦ