1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 - TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU-!).4%.!.#% ).4%2.!4)/.!,G0G0,%!3%$G0G0#)2#5)43!33%33-%.4G0G0/ national purposes.3.2 International purposesThe assessment procedure is used for international purposes when two Administrations wish to assess t
2、ogetherthe performance of individual international leased circuits (or a group of circuits) as a whole for special investigations,for dealing with customers complaints or similar situations.For such assessments it is necessary, as far as practicable, to gather simultaneously all available informatio
3、n onthe performance of the circuit(s) from the Administrations involved. Thus, the stations with control responsibilities(Recommendations M.1012 and M.1013) play an essential role._1)In this Recommendation only full-time, point-to-point international leased circuits (as defined in Recommendation M.1
4、010 andspecified in Recommendations M.1020, M.1025 and M.1040) are considered. The service availability performance of part-time,wide-band, multi-terminal, tec. international leased circuits requires further study.2 Fascicle IV.2 - Rec. M.1016Note This approach should be followed when investigations
5、 of the service availability performance ofinternational leased circuits is undertaken by CCITT, as may be required from time-to-time.3.3 National purposesThe assessment procedure is used for national purposes when an individual Administration wishes to provideitself with information for its own int
6、ernal purposes on the performance of the international leased circuits it operates,for example, to identify adverse trends in performance, or to check the effectiveness of its maintenance procedures. Suchevaluations of international leased circuit performance may be based on information already avai
7、lable to theAdministration (without the need to gather information from other Administrations), and may be carried out for allcircuits whether or not the Administration provides the control station.Note Assessments of the type mentioned in 3.1 and 3.2 above in no way change the intent that controlst
8、ations be informed of all faults detected by a sub-control station see Recommendation M.1013.4 Description of the assessment procedure4.1 Collection of basic dataThree fundamental conditions must be taken into account when collecting basic data for assessing the serviceavailability performance of in
9、ternational leased circuits:a) faults, as reported by the customer and confirmed by tests and investigations carried out by theAdministrations;b) impairments to normal service, as reported by the customer, where the customer chooses to continue touse the circuit in a degraded condition;c) planned in
10、terruptions to service to enable, for example, permanent repair work to be carried out,maintenance routines to be performed, etc. (see Recommendation M.490 3).In determining if and how downtime is to be included in the assessment procedure, the following principlesshould be applied: if tests or inve
11、stigations reveal that a fault or impairment exists (or has existed), downtime will be takeninto account; if no fault or impairment is ever observed by the Administration, no downtime will be taken into account; the time the Administration returns service to the customer (or the first attempt to do
12、so) is taken as theend of downtime; only those planned interruptions which unacceptably disrupt the customers service will be taken intoaccount.Note Where the bandwidth of the circuit is divided to provide for simultaneous multiple transmission ofdifferent services (for example, simultaneous speech
13、plus data), only those faults which affect the entire circuit andpartial faults which require the entire circuit to be taken out of service for fault finding and repair should be taken intoaccount in the assessment procedure.These principles are embodied in Tables A-1/M.1016 and A-2/M.1016, which de
14、fine those conditions wheredowntime should be taken into account, and the start and end of downtime, for customer reported faults and plannedinterruptions of service respectively.In certain circumstances the assistance of the customer or access to his premises is necessary to locate/clear afault or
15、an impairment to service. Where the customer denies such assistance, or denies access to his premises, the extradowntime which may result should be excluded from the assessment of performance.Fascicle IV.2 - Rec. M.1016 34.2 Basic dataThe basic data required in connection with the assessment procedu
16、re are: the number of international leased circuits involved. Guidance on how to determine this number is givenin Annex B; the designation of each circuit involved, as agreed between Administrations in accordance withRecommendation M.140 4; for each involved circuit, the number of faults and unaccep
17、table planned interruptions of service withinthe observation period (refer to Annex A); for each fault and planned interruption of service:i) the start of downtime (in UTC)2)ii) the end of downtime (in UTC)iii) the duration of downtime; the address(es) of involved Administrations and, ideally, the n
18、ame and telephone number of anappropriate contact person within each Administration.The additional information specified in 5 below is also considered as basic data for the assessmentprocedure.4.3 Observation periodFor the purpose envisaged in 3.2 above, the observation period should be three calend
19、ar months. Forpractical reasons it is advisable that the observation period start at 00.00 UTC on the first day of a quarter of the year,and end at 24.00 UTC on the last day of that quarter.For the purpose envisaged in 3.3 above, Administrations are free to select an observation period which suitsth
20、eir needs.4.4 Exchange of information between terminal AdministrationsAt the end of the observation period, the basic data is recorded on forms, examples of which are shown inAppendices I and II to this Recommendation. Examples of completed forms are given in Appendices III and IV to thisRecommendat
21、ion. Appendices I and III relate to information supplied by the control station, while Appendices II and IVrelate to the sub-control station. Forms, completed with information from the sub-control station should be sent to theAdministration which has control station responsibility.4.5 Elaboration of
22、 resultsIt is the responsibility of the Administration providing the control station to combine the information suppliedby the control and sub-control stations. In practice it is found that this information is often different, and the followingrules should be used to handle such differences:a) if a
23、fault (or unacceptable planned interruption) is reported by both control and sub-control stations, thenthe start of downtime is the earliest time indicated by the control or sub-control station and the end ofdowntime is that recorded by the control station;b) if a fault (or unacceptable planned inte
24、rruption) is reported by only one of the stations, then such a fault isdeemed to have occurred and the corresponding downtime is taken into account.For rules used for combining the additional information specified in 5 below, reference is made to Annex C._2)UTC = Coordinated universal time (UTC is e
25、qual to GMT, but replaces it; see Recommendation B.11 5).4 Fascicle IV.2 - Rec. M.10164.6 Presentation of service availability performance informationThe methods of calculating and presenting service availability performance information for international leasedcircuits are given in detail in Annex B
26、.When service availability performance information is to be supplied to other Administrations, and whenmaking international comparisons, the following parameters should be presented:a) number of circuits involved in the assessment. (Where this is less than the total number of circuits inservice, the
27、 number of circuits in service should also be supplied),b) mean downtime per circuit,c) mean number of faults per circuit,d) mean time to failure (MTTF),e) percentage of circuits for which no downtime was recorded,f) mean time to restore service (MTRS).In addition, and at the discretion of Administr
28、ations, the following parameters may also be presented:g) long-term mean downtime per circuit (over at least four consecutive observation periods),h) percentage of circuits with downtime less than the mean,i) downtime per circuit not exceeded by 95% of the circuits.For items a) to i) above, referenc
29、e is made to Annex B.4.7 Treatment of events which distort service availability performance figuresService availability performance figures for international leased circuits can be significantly influenced (ortheir meaningfulness destroyed) by catastrophic events, for example, destruction of facilit
30、ies by hurricane or earthquake.In view of this, the following procedure should be adopted:Events which, based on previous experience, have noticeably influenced the performance figures should not beexcluded. However, in this case, a second calculation should be made to present the performance figure
31、s with thecatastrophic event(s) excluded.This procedure attempts to maximize the possibility of all events being included in the performance figures insome manner.5 Considerations for comparing service availability performance information internationally5.1 Administrations are encouraged to exchange
32、 service availability performance information on internationalleased circuits on a regular basis.5.2 In order to assist the interpretation of service availability performance information, particularly whenexchanged between Administrations, relevant additional information should also be supplied. Suc
33、h additionalinformation should cover the following aspects:a) priority maintenance attention to international leased circuits;b) duplicated circuit sections;c) fault clearance service;d) transmission limits which define whether or not a fault exists;e) information to customers about planned interrup
34、tions to service.Annex C specifies the above information in greater detail, while Appendices III and IV show how theinformation is to be exchanged between Administrations.5.3 Detailed maintenance procedures and the methods by which Administrations confirm the existence of faults oninternational leas
35、ed circuits are different. Such differences may lead to differences in the service availabilityperformance results obtained by Administrations.Fascicle IV.2 - Rec. M.1016 5ANNEX A(to Recommendation M.1016)Rules for determining the number of faults and the downtimeto be taken into account in assessme
36、nts of the serviceavailability performance of international leased circuitsA.1 Detailed principles for the determination of the number of faults and impairments affecting service availabilityperformance, and their resulting downtime, are given in Table A-1/M.1016.d01-scTABLE A-1/M.1016.D016 Fascicle
37、 IV.2 - Rec. M.1016A.2 Principles to determine the downtime due to planned interruptions of service are given in Table A-2/M.1016.d02-scTABLE 2/M.1016.D02A.3 If a circuit is in a downstate at the beginning of the observation period, the fault or planned interruption ofservice causing the downstate i
38、s not taken into consideration. However, downtime is deemed to start at the beginning ofthe observation period.A.4 If a circuit is in a downstate at the end of the observation period, the fault or planned interruption of servicecausing the downstate is taken into consideration. The downstate is deem
39、ed to end at the end of the observation period.ANNEX B(to Recommendation M.1016)Presentation of service availability performanceinformation for international leased circuitsNote This annex contains additional explanations and rules of calculation for the performance parametersspecified in 4.6. B.1 t
40、o B.9 below relate to items a) to i) in 4.6 respectively.B.1 Determination of the number of circuits involved in the assessmentThe calculation of service availability performance figures for international leased circuits requires that theexact number of circuits, n involved in the assessment be dete
41、rmined.Fascicle IV.2 - Rec. M.1016 7For the assessment purposes envisaged in 3.1, only those circuits existing throughout the observation periodshould be considered. Thus, circuits provided or ceased within an observation period should be ignored.For the purpose envisaged in 3.2, the number of circu
42、its existing at the end of the observation period can beused in the calculation of service availability performance figures.For both the purposes mentioned above, all full-time, point-to-point international leased circuits should beincluded in the assessment. However, should the effort and cost of t
43、his approach be too great, Administrations may use arandomly selected sample of circuits of suitable size.B.2 Mean downtime per circuitMean downtime per circuit should be calculated using the following formula:Mean downtime per circuit (DT) = 1n Downtime in observation periodwheren is the number of
44、circuits involved (cf. B.1)downtime is in hoursDTis in hours.B.3 Mean number of faults per circuitThe mean number of faults per circuit should be calculated using the following formula:Mean number of faults per circuit = 1n Faultswheren is the number of circuits involved (cf. B.1).B.4 Mean time to f
45、ailureMean time to failure (MTTF) should be calculated using the following formula:MTTF = (n observation period) ( Downtime)Events that contribute to downtimewheren is the number of circuits involved (cf. B.1)MTTF is in daysObservation period is in daysDowntime is in daysNote The right hand side of
46、the equation above is sometimes called mean time between failures (MTBF).B.5 Percentage of circuits for which no downtime was recordedPercentage of circuits for which no downtime was recorded =Number of circuits with no downtimen 100wheren is the number of circuits involved (cf. B.1)This percentage
47、corresponds to the point marked “y1” in Figure B-1/M.1016.8 Fascicle IV.2 - Rec. M.1016B.6 Mean time to restore serviceMean time to restore service (MTRS) should be calculated using the following formula:MTRS = Downtime Events that contribute to downtimewhereDowntime is in hoursMTRS is in hoursB.7 L
48、ong-term mean downtime per circuitLong-term mean downtime per circuit should be calculated on the basis of the results of at least fourconsecutive observation periods, weighted for the number of circuits involved, from the following formula:(In the case of 4 observation periods)Long-term mean downti
49、me per circuit (DT)= i = 14(ni DTi)i = 14niwhereniand DTiare the values corresponding to each observation periodDTiis in hoursDTis in hoursB.8 Percentage of circuits with downtime less than the mean value (DT)The percentage of circuits with a total downtime less than the mean downtime per circuit (DT) should bedetermined, for example, by preparing a cumulative frequency distribution graph as shown in Figure B-1/M.1016. (Therequired percentage of circuits is shown by point “y2”
