џWPCL ћџ2BJ|xа АH аа АА X агга ХА6p&А6p&Х аеЮ† а Hр аааУ Уб cмˆ4 PŽТ б FascicleVI.5 Р-Р Rec. Q.541 Ф ФPAGE1У Уб cмˆ4 PŽТ б ЮееЃ† а HH аааб cмˆ4 PŽТ бPAGE2У Уб cмˆ4 PŽТ б Fascicle VI.5 Р-Р Rec. Q.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 Q.541 аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаСр(AСб cмˆ4 PŽТ бDIGITAL EXCHANGE DESIGN OBJECTIVES Р-Р GENERAL аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ б1ТX ТGeneralФ ФЦЦ С СThis Recommendation applies to digital local, combined, transit and international exchanges for telephony in Integrated Digital Networks (IDN) and mixed (analogue/digital) networks, and also to local, combined, transit and international exchanges in an Integrated Services Digital Network (ISDN). The field of application of this Recommendation is more fully defined in Recommendation Q.500. Some objectives only apply to a certain type (or types) of exchange. Where this occurs, the application is defined in the text. Where no such qualification is made, the objective applies to all exchange applications. ‚У У2ТX ТGeneral design objectivesФ ФЦЦ С СThe exchange and/or any associated operations and maintenance systems/centers shall have the capabilities needed to allow the exchange to be operated and administered efficiently while providing service in accordance with an Administration's performance requirements. 2.1Тh  ТУУExchange modifications and growthЦЦ а H аФФС СThe exchange should be capable of having hardware and/or software added or changes made without causing a significant impact on service (see РSРS 4.4, 4.10.2 Р-Р Planned outages). 2.2Тh  ТУУService provisioning and recordsЦЦ ФФС СThere should be efficient means of establishing service, testing, discontinuing service and maintaining accurate records for: Та ТР-РТ№ Тsubscriber lines and services,ЦЦ Та ТР-РТ№ Тinterexchange circuits.ЦЦ а HH а2.3Тh  ТУУTranslations and routing informationЦЦ а H аФФС СThere should be efficient means of establishing, testing and changing call processing information, such as translation and routing information. 2.4Тh  ТУУResource utilizationЦЦ а H аФФС СThere should be efficient means of measuring performance and traffic flows and to arrange equipment configurations as required to insure efficient use of system resources and to provide a good grade of service to all subscribers (e.g., load balancing). 2.5Тh  ТУУPhysical design objectivesЦЦ ФФС СThe exchange shall have a good physical design that provides: Та ТР-РТ№ Тadequate space for maintenance activities,ЦЦ Та ТР-РТ№ Тconformance with environmental requirements,ЦЦ а H аТа ТР-РТ№ Тuniform equipment identification (conforming with the Administration's requirements),ЦЦ а H аТа ТР-РТ№ Тa limited number of uniform power up/down procedures for all component parts of the exchange.ЦЦ а HH ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HСУ У3С  Сб cмˆ4 PŽТ бIntegrated Digital Network design objectivesЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф3.1Тh  ТУУExchange timing distributionЦЦ а H аФФС СThe timing distribution system of an exchange will be derived from a highly reliable exchange clock system. The distribution of timing within а H аthe exchange must be designed so that the exchange will maintain synchronism on 64 kbit/s channel timeslots in a connection through the exchange. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.2С   Сб cмˆ4 PŽТ бУУNetwork synchronizationЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СWithin a synchronized IDN/ISDN, different methods of providing timing between exchanges may be used. An exchange should be able to be synchronized: а H аТа ТТ№ ТС€ Сa)СpСby an incoming digital signal at an interface A (or B, if provided) as defined in Recommendation Q.511; this applies only to signals derived from a Primary Reference Source, as defined in Recommendation G.811;ЦЦ а H аТа ТТ№ ТС€ Сb)СpСdirectly by a Primary Reference Source, using an interface complying with Recommendation G.811;ЦЦ а H аТа ТТ№ ТС€ Сc)СpСoptionally, by an analogue signal at one of the frequencies listed in Recommendation G.811.ЦЦ а HH аС СPlesiochronous operation should also be possible. а H аС СThe clock of the local, combined or transit exchange shall be responsible for maintaining the synchronization in the part of the network associated with that exchange. С СThe timing performance of the clocks in local, combined or transit exchanges should comply with Recommendation G.811. The timing performance of clocks at subscriber premises, at digital PABXs, in digital concentrators, at muldexes, etc., require further study. а H аС СSynchronized national networks may be provided with exchange clocks not having the frequency accuracy required for international interworking. However, when these synchronized networks within national boundaries are required to interwork internationally as part of the international IDN/ISDN, it will be necessary to provide means to operate these national networks to the internationally recommended value of frequency accuracy in Recommendation G.811. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС3.3С   Сб cмˆ4 PŽТ бУУSlipЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe design objective controlled slip rate within a synchronized region (see Note) controlled by the exchange should be zero provided that input jitter and wander remain within the limits given in Recommendation G.823 and G.824. С СThe design objective controlled slip rate at a digital exchange in plesiochronous operation (or operating to another synchronized region) shall а H аbe not more than one slip in 70 days in any 64 kbit/s channel, provided that input jitter and wander remain within the limits given in Recommendations G.823 and G.824. а H аС СThe operational performance requirements for the rate of octet slips on an international connection or corresponding bearer channel are covered in Recommendation G.822. С СThe occurrence of a controlled slip should not cause loss of frame alignment. а H аС СУУNoteФФ Р-Р A synchronized region is defined as a geographic entity normally synchronized to a single source and operating plesiochronously with other synchronized regions. It may be a continent, country, part of a country or countries. 3.4Тh  ТУУRelative Time Interval Error (TIE) at the exchange outputЦЦ а H аФФС СRelative Time Interval Error (TIE) at the exchange output is defined as the difference in time delay of a given timing signal when compared to a reference timing signal for a given measurement period (see Recommendation G.811). Та ТС€ HС3.4.1С СУУInterface VУУ1ФФЦЦ а H аФФС СRelative Time Interval Error (TIE) at the exchange output at the interface to the basic access digital section requires further study. Та ТС€ HС3.4.2С СУУInterfaces A, B, VУУ2ФФ, VУУ3ФФ and VУУ4ФФЦЦ а H аФФС СThe relative TIE at the output of the digital interfaces A, B, VУУ2ФФ, VУУ3ФФ and VУУ4ФФ over the period S seconds should not exceed the following limits: Та ТТ№ ТС€ С1)СpС(100 S) ns + 1/8 UI for S < 10.ЦЦ Та ТТ№ ТС€ С2)СpС1000 ns for S 10 (see Figure 4/Q.541).ЦЦ а HH а‚Ср8DСб cмˆ4 PŽТ бFigure 1/Q.541 Љ CCITT 72171 б cмˆ4 PŽТ б а H аС СIn the case of synchronous operation the limits are specified on the assumption of an ideal incoming synchronizing signal (no jitter, no wander and no frequency deviation) on the line delivering the timing information. In the case of asynchronous operation the limits are specified assuming no frequency deviation of the exchange clock, (this is equivalent to taking the output of the exchange clock as the reference timing signal for the relative TIE measurements).д k+дŒа H аС СIt is recognized that the approach of using relative TIE to specify the performance of an exchange in the case of synchronous operation in some implementations (e.g., when mutual synchronization methods are used) requires further study. а H аС СAny internal operation or rearrangement within the synchronization and timing unit or any other cause should not result in a phase discontinuity greater than 1/8 of a Unit Interval (UI) on the outgoing digital signal from the exchange. а H аС СThe limits given in Figure 4/Q.541 may be exceeded in cases of infrequent internal testing or rearrangement operations within the exchange. In such cases, the following conditions should be met: С СThe Relative Time Interval Error (TIE) over any period up to 2б cмˆ4 PŽТ бУУ11ФФб cмˆ4 PŽТ б unit intervals should not exceed 1/8 of a UI. For periods greater than 2б cмˆ4 PŽТ бУУ11ФФб cмˆ4 PŽТ б UI, а H аthe phase variation for each interval of 2б cмˆ4 PŽТ бУУ11ФФб cмˆ4 PŽТ б UI should not exceed 1/8 UI up to a maximum total Relative TIE defined in Recommendation G.811 for long time periods. а H а3.5Тh  ТУУSynchronization requirements when interworking with a digital satellite systemЦЦ ФФС СOn a provisional basis the following should apply: а H аС СThe transfer from the timing of the terrestrial digital network to the timing of the satellite system, if required (plesiochronous operation), will not be performed by the digital exchange. The earth station will be equipped with buffer memories of suitable size to compensate for the time delay variations due to shifts of the satellite from its ideal position (and due to any other phenomena with similar effects) and to meet the slip performance requirements established in CCITT Recommendation G.822. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У4С  Сб cмˆ4 PŽТ бAvailability design objectivesЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ Ф4.1Тh  ТУУGeneralЦЦ ФФС СAvailability is one aspect of the overall quality of service of an exchange. С СAvailability objectives are important factors to be considered in the design of a switching system and may also be used by administrations to judge the performance of a system design and to compare the performance of different system designs. С СAvailability may be determined by collecting and evaluating data from exchanges in operation in accordance with draft Recommendation E.450. Data collection may be facilitated by the use of the Telecommunications Management Network (TMN). а H аС СAvailability may be expressed as the ratio of the accumulated time during which the exchange (or part of it) is capable of proper operation to a time period of statistically significant duration called the mission time. а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHp8А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ Ьа‚Availability (A) = eq \f(accumulated upР-Рtime,mission time) = eq \f(accumulated upР-Рtime,accumulated upР-Рtime + accumulated downР-Рtime) а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СSometimes it is more convenient to use the term unavailability (instead of availability) which is defined as: аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHp8А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ Ьа‚Ср LСUnavailability (U) = 1 Р-Р A. а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe terms used in this section, when they already exist, are in accordance with CCITT Recommendation G.106. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС4.2С   СУУCauses ofб cмˆ4 PŽТ б unavailabilityЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThis Recommendation deals with availability as observed from the exchange termination point of view. Both planned and unplanned outages need to be considered, and both types need to be minimized. Unplanned outages reflect on the inherent reliability of the exchange and are therefore considered separately from planned outages in this Recommendation. а H аС СUnplanned unavailability counts all failures that cause unavailability. Thus hardware failure, software malfunctions and unintentional outages resulting from craftperson activity are to be counted. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС4.3С   Сб cмˆ4 PŽТ бУУIntrinsic and operational unavailabilityЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СIntrinsic unavailability is the unavailability of an exchange (or part of it) due to exchange (or unit) failure itself, excluding the logistic delay time (e.g. travel times, unavailability of spare units, etc.) and planned outages. а H аС СOperational unavailability is the unavailability of an exchange (or part of it) due to exchange (or unit) failure itself, including the logistic delay time (e.g. travel times, unavailability of spare units, etc.). 4.4Тh  ТУУPlanned outagesЦЦ а H аФФС СPlanned outages are those intentionally induced to facilitate exchange growth or hardware and/or software modifications. The impact of these activities on service depends on their duration, the time of day they are introduced and on the particular system design. 4.5Тh  ТУУTotal and partial unavailabilityЦЦ ФФС СExchange unavailability may be either total or partial. Total unavailability affects all terminations, and consequently, all traffic that is offered during the outage is equally affected. A partial outage has an effect only on some terminations. С СFrom the point of view of one termination on an exchange (e.g. a subscriber line termination), the numerical value of mean accumulated downtime (and hence the unavailability) for a specified period of time should not depend on the exchange size or its traffic handling capacity. Similarly, from the point of view of a group of terminations of sizeУУ nФФ, the mean accumulated downtime for a specified period of time,УУ in case they are simultaneously unavailableФФ, should not depend on exchange size. However, for two groups of terminals of differing sizeУУ nФФ andУУ mФФ such thatУУ nФФ is greater thanУУ mФФ (УУnФФ > m), the mean accumulated downtime (and hence the unavailability) forУУ nФФ will be less than the mean accumulated downtime (MADT) or the unavailability forУУ mФФ. С СThus: аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHp8А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ Ьа‚Ср KСMADT(УУnФФ) < MADT(УУmФФ) whereУУ nФФ >УУ mФФ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС Сand аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHp8А"(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџ Ьа‚Ср TСU(УУnФФ) < U(УУmФФ) а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаС СThe lower limit ofУУ mФФ is one termination, and it can be specified as having a mean value ofУУ TФФ minutes per year. 4.6Тh  ТУУStatistical basisЦЦ а H аФФС СAny estimation of unavailability is of necessity a statistical quantity, because outages are presumed to occur randomly and they are of random duration. Therefore, availability measurements are significant when made over a statistically significant number of exchanges. It follows then, that a single exchange may exceed the unavailability objectives. Further, to be statistically significant the mission time must be adequate in order to have sufficient collected data. The accuracy of the result is dependent on the amount of collected data. 4.7Тh  ТУУRelevant failure eventsЦЦ а H аФФС СDifferent types of failure events may occur in an exchange. In order to evaluate the unavailability of an exchange (or part of it) only those а H аevents having an adverse effect on the exchange's ability to process calls as required should be taken into account. A failure event which is short in duration а H аand results only in call delay rather than in a call denial can be disregarded. 4.8Тh  ТУУAvailability independenceЦЦ а H аФФС СThe design objectives for the unavailability of a single termination or any group of terminations of sizeУУ nФФ are independent of exchange size or internal structure. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС4.9С   Сб cмˆ4 PŽТ бУУIntrinsic downtime and unavailability objectivesЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СThe recommended measure for use in determiningУУ intrinsic unavailabilityФФ is mean accumulated intrinsic down time (MAIDT) for individual or groups of terminations, for a given mission time, typically one year. С СFor one termination: ‚Ср JСMAIDT(1) РCР 30 minutes per year. С СFor an exchange termination group of sizeУУ nФФ: ‚Ср IСMAIDT(УУnФФ) < MAIDT(УУmФФ) whereУУ nФФ >УУ mФФ. а H аС СThis reflects the consequences (e.g. traffic congestion, social annoyance, etc.), of the simultaneous outage of a large number of terminations. С СThe above expression is a statement of principle and means that units serving larger group sizes shall have lower MAIDT. 4.10Т№  ТУУOperational unavailability objectivesЦЦ аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HСФФ4.10.1С јСб cмˆ4 PŽТ бУУLogistic delay timeЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФФС СDue to differing national conditions, logistic delay times may vary from country to country and therefore may not be subject to international Recommendation. а H аС СNevertheless, for design guidance, an indication of the Administration's logistic delays is considered desirable to establish overall operational performance objectives. It is left for the operating Administration to determine how it should be accounted for in the determination of operational unavailability. Та ТС€ HС4.10.2С СУУPlanned outagesЦЦ а H аФФС СPlanned outages are to be minimized to the greatest extent practicable. They should be scheduled so as to have least impact on service practicable. 4.11Т№  ТУУInitial exchange availability performanceЦЦ а H аФФС СA system rarely meets all longР-Рterm design objectives when first placed into service. The objectives contained in this Recommendation may therefore not be fulfilled for a limited period of time after the newly designed switched system has been put into service; this period of time should be minimized to the greatest extent practicable. аЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџH јP Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаТX  ТТX јТС€  СС€ HС‚У У5С  Сб cмˆ4 PŽТ бHardware reliability design objectivesЦЦ а H ааЬџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџHpи P Ј XА`ИhР!(#џџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџџЬаб cмˆ4 PŽТ бФ ФС СA bound on the rate of hardware failures is recommended. It includes all types of hardware failures and the failures counted are independent of whether or not there is a resulting service degradation. а H аС СAn acceptable hardware failure rate for an exchange is a function of the exchange size and the types of terminations. а H аС СThe following formula can be used to verify that the maximum failure rate does not exceed the Administration's requirements: ‚Ср IСeq УУFФФУУб cмˆ4 PŽТ бmaxб cмˆ4 PŽТ бФФ = CУУб cмˆ4 PŽТ б0б cмˆ4 PŽТ бФФ +УУ ФФ\i\su(i=1,УУnФФ,) УУCУУб cмˆ4 PŽТ бiб cмˆ4 PŽТ бФФTУУб cмˆ4 PŽТ бiФФФФб cмˆ4 PŽТ б where: а H аТа ТТ№ ТС€ СУУFФФУУmaxФФСи Сthe maximum acceptable number of hardware failures per unit of time;ЦЦ Та ТТ№ ТС€ СУУTУУiФФФФСpСthe number of terminations of typeУУ iФФ;ЦЦ Та ТТ№ ТС€ СУУnФФСpСthe number of distinct types of terminations;ЦЦ а H аТа ТТ№ ТС€ СCУУ0ФФСpСto be determined taking into account all failures which are independent of exchange size;ЦЦ а H аТа ТТ№ ТС€ СУУCУУiФФФФСpСcoefficients for terminations of typeУУ iФФ, reflecting the number of failures associated with individual terminations of that type. Different hardware used with different types of terminations may result in different values forУУ CУУiФФФФ.ЦЦ С  СЦЦ Та ТЦЦ Та Т