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.540 Ф ФPAGE1У Уб cмˆ4 PŽТ б ЮееЃ† а HH аааб cмˆ4 PŽТ бPAGE1У Уб cмˆ4 PŽТ б Fascicle II.3 Р-Р Rec. E.540 Ѓеа HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаа X  аУ Уб cмˆ4 PŽТ бRecommendation E.540 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр86Сб cмˆ4 PŽТ бOVERALL б cмˆ4 PŽТ бGRADE OF SERVICE OF THE INTERNATIONAL PART OF AN Ср8FСINTERNATIONAL CONNECTION б cмˆ4 PŽТ б1Ф ФС  СThe International Routing PlanйH€ International Routing Planб cмˆ4 PŽТ бHй envisages that international traffic relations may be served by any of the following routing arrangements: аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТh ТС€  СТh Тa)СјСdirect circuitsйdirect circuitsйб cмˆ4 PŽТ б;ЦЦ а Hh ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТа ТТ№ ТС€ Сb)СpСtransit operation involving one or more transit centres for all connections,ЦЦ Та ТТ№ ТС€ Сc)СpСdirect highР-Рusage circuits with overflow via one or more transit centres.ЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бС  СIn principle there would be merit in dimensioning international facilities to provide the same grade of serviceй grade of serviceйб cмˆ4 PŽТ б for all relations, however served. Practical considerations make it advisable to depart from one universal value. У У2Ф ФС  СDirect circuit groupsйdб cмˆ4 PŽТ бDirect circuit groupsб cмˆ4 PŽТ бdй are dimensioned, according to Recommendation E.520 on the basis ofУУ pФФ = 1% loss probabilityй`б cмˆ4 PŽТ б loss probabilityб cмˆ4 PŽТ б`й during the mean busy hourй^б cмˆ4 PŽТ б mean busy hourб cмˆ4 PŽТ б^й. An exception is permitted for small groups of very long international circuits for whichУУ pФФ = 3% loss probability is accepted for six or fewer circuits. As the traffic increases the grade of service improves progressively untilУУ pФФ = 1% loss value is reached for 20 circuits. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаУ У3Ф ФС СFor the relations served exclusively by transit operation the grade of service will deteriorate with the number of transit centresй_б cмˆ4 PŽТ б transit centresб cмˆ4 PŽТ б_й in the connection. Measurements made on congestion in such circumstances suggest that the overall grade of service for up to six links in tandem is less than twice the congestion of any of the six links in the chain. Hence, for a series of routes, each dimensioned forУУ pФФ = 1%, the overall grade of service should seldom exceed 2%. An EastР-РWest type of connection would have the advantage of different busy hours on the various links. Corresponding advantage would not apply to NorthР-РSouth circuits. а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС  СIn the case of relations served by highР-Рusage circuitsйBб cмˆ4 PŽТ б highР-Рusage circuitsBй the overflow trafficб cмˆ4 PŽТ бй overflow trafficйб cмˆ4 PŽТ б will route over at least two links and, hence, will be subject to the same deterioration of service as in the case for transit trafficб cмˆ4 PŽТ бй transit trafficйб cмˆ4 PŽТ б. However, a substantial part of the traffic will be connected over the highР-Рusage circuits and the overall grade of service will approximate that of the relations served solely by direct circuits. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СIt is desirable that at least one highР-Рusage circuit should always be provided between a CT3 and its homing CT1, even though the circuit may not be wholly justified on economic considerations alone. However, such a circuit should not be provided unless there is a measurable amount of traffic which exists, or can be foreseen in the busy hourйYб cмˆ4 PŽТ б busy hourб cмˆ4 PŽТ бYй. The provision of such circuits would improve the transmission as well as the grade of service; these considerations should encourage an increase both in traffic and in the revenueР-Рearning capacity of the circuits provided. С СThe overall grade of service for the international part of a connection is a contributory factor to the overall grade of service from the calling party in one country to the called party in another.