ITU-T E 420-1993 CHECKING THE QUALITY OF THE INTERNATIONAL TELEPHONE SERVICE C GENERAL CONSIDERATIONS《检验国际电话业务的质量 一般考虑》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 % TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU4%,%0(/.%G0G0.%47/2+G0G0!.$G0G0)3$.15!,)49G0G0/ they reflect the quality of:i) providing the customer with the ability to use the desired services;ii) furnishing a desired level of service for:_ connection es

2、tablishment,_ connection retention,_ connection quality,_ billing integrity.These main parameters can be supervised by quality of service indicators (e.g. efficiency rate, call cut-off rate,etc.).Objectives can be set for these indicators and can be revised at regular intervals.When a deterioration

3、of these supervision indicators is detected, or when an improvement programme isstarted, more data must be collected by measurements to permit a more detailed analysis in order to locate theimpairment causes which lie behind the observed problem areas.2 Methods of measuring the quality of service2.1

4、 The following methods of measuring the quality of service are described:1) service observations by external means;2) test call (simulated traffic);3) customer interviews;4) internal automatic observations.2.2 Administrations are recommended to draw up a programme for observations and tests designed

5、 for assessmentof circuits and equipment, supervision of operators and evaluation of the quality of service given to subscribers. Itwould be desirable if telephone Administrations were to exchange statistics on quality of service.2.3 Table 1/E.422 relates to the manual and semi-automatic observation

6、s of the quality of international automaticand/or semi-automatic service. It provides in particular a check of the percentage of unsuccessful calls due to technicalfaults (equipment shortages or failures).Table 2/E.422 relates the same information as Table 1/E.422 but does not include information wh

7、ich can onlybe obtained by operators listening in (automatic observation)._1)Such tables can be found in the handbook cited in 1.2 Fascicle II.3 - Rec. E.420Table 1/E.423 relates to observations on traffic set up by operators. It provides, in manual and semi-automaticservice, a means of determining

8、the efficiency of international circuits, of assessing the work of operators and thequality of transmission.Table 2/E.423 summarizes observations of the time-to-answer by operators. The table is compiled by automaticmeans.Table 1/E.424 is used to record the results of test calls undertaken especiall

9、y when the observations shown inTable 1/E.422 make it clear that the percentage of faults is too high.The use of customer interviews as a method of measuring telephone service quality is the subject ofRecommendation E.125 which is particularly concerned with the determination of sources of user diff

10、iculty which mayarise when making an international automatic telephone call.Recommendation E.426 contains a general guide to the expected percentage of effective international callattempts.Table 1/E.427 may be used to supplement the information contained in Table 1/E.422 when the observationsshown i

11、n that table make it clear that the percentage of faults due to customer difficulties is too high or the outcome ofthe application of Recommendation E.125 demonstrates the need for additional information.Recommendation E.425 describes the data that might be taken from the switching centres with resp

12、ect toquality of service, and the exchange of that data.2.4 Paying attention to the quality of service of the incoming traffic stream is of major importance, since theincoming Administration is in a better position to improve the situation.In the past less attention has been paid by several Administ

13、rations to the quality of service (QOS) on incomingcalls than on outgoing calls. This situation should not persist in the future.Therefore, in addition to the measurement of QOS of the outgoing traffic stream which is described in thisseries of Recommendations, Administrations are strongly advised t

14、o observe the incoming traffic stream with the aimto improve the QOS.3 Other sources of information on the quality of serviceThe following sources are useful to consider when trying to improve the quality of service: subscriber complaints (see Annex B); other Administrations or organizations such as

15、 INTELSAT (SPADE reports); operators contacting maintenance staff for direct action; operators giving information on QOS: if operator traffic is significant one might consider organizing theflow of this type of information by establishing “trouble codes“, e.g. echo, no tone, no answer, etc.; reports

16、 from “national“ switching centres: the QOS as experienced by the subscriber does not only dependon the international network and the network of the country of destination but also on the national networkof the country of origin; user organizations/large companies: asxlarge companies have much to ga

17、in from an improved QOS theymight be willing to cooperate with Administrations; holding time versus conversation time measurements; average conversation time; traffic measurements; transmission measurements.Fascicle II.3 - Rec. E.420 3ANNEX A(to Recommendation E.420)A possible approach to integrate

18、activities measuringthe quality of service into an overall problem-investigating processThe flowcharts of the resource allocation process and a typical problem identification procedure are given inFigures A-1/E.420 and A-2/E.420. The numbers 1) through 10) in the figures correspond to the processes

19、describedbelow.1) The exception threshold is set to detect possible isolated destinations. It is up to the individualAdministration to set the value.2) A destination could be regarded as being under isolated condition when the bid frequency is significantenough to show that there is some demand to t

20、he destination (e.g. 20 attempts per day) without or nearlywithout answer.3) The most practical way to find out whether improvements may be possible is “consultation with otherAdministrations“.4) Apply, if possible, network management actions, e.g. alternative routing.5) The destination priority, P,

21、 for each destination is calculated as follows:P BID TABR MABR=2)()whereBID2)is the number of total bids to the destination during a certain period of time (for example,1 month);TABR is the target ABR3)(answer bid ratio) performance which is expected as the result of the service improvement activiti

22、es;MABR is the measured ABR3)to the destination during the same period with BID.The TABR is set for each destination and can be based on the average historic ABR and should be higher than that value.In order to comply with Recommendation E.426, 2.2, the TABR to be used in the formula for P given abo

23、ve should not be lower than the MABR experienced one period earlier.6) In order to comply with 2.4, it is suggested to consider also the total international incoming traffic streamas one of the elements which require QOS improvements. It should be noted that the procedure can be wellapplied to domes

24、tic destinations, for example, on an area code basis, and can be applied on an incomingroute basis.7) Perform detailed analysis: when possible, monitor circuit group performance and do analyses on adestination code basis. It is essential to be aware of “killer trunks“ (though observation of the QOS

25、is notdirectly intended to discover killer trunks).8) Discuss possible improvements with counterpart.9) In Recommendation M.710 (General maintenance organization for the international automatic and semi-automatic service) the basic maintenance elements, their functions and the cooperation between th

26、eelements are described. Recommendation M.1230 (Assessment of the performance of the internationaltelephone network) gives guidance on the relationship between service quality observations, networkperformance assessment and maintenance procedures. It should be noted that the QOS very much dependson

27、the proper operation of maintenance elements and maintenance procedures. Therefore, Administrationsfaced with QOS problems are strongly advised to be attentive to the maintenance Recommendationscontained in Volume IV.10) If this procedure does not lead to a successful conclusion, then an escalation

28、procedure may be required(see Recommendation M.711)._2)Paid minutes or the revenues can be used.3)In case ABR cannot be used, ASR (answer seizure ratio) is considered to be an acceptable substitute. Seizures, TASR and MASRare then applicable.4Fascicle II.3 - Rec. E.420Fascicle II.3 - Rec. E.420 5 6

29、Fascicle II.3 - Rec. E.420ANNEX B(to Recommendation E.420)Utilization of customer complaints to improve the quality ofservice for international trafficIt is possible to use subscriber complaints to control processes if the organization of an Administration providespossibilities for centralized colle

30、ction of these complaints.The collected data can be processed statistically to provide useful indications for the operations andmaintenance staff to correct problems and, in so doing, improve the quality of service.Three aspects are relevant in the processing of the data: the data itself; the statis

31、tical processes; the analysis of complaints.B.1 Data to be collectedThe trouble report of an individual customer may be subjective and unqualified since it is usually made by aperson, who is not well trained for observation of quality of service. Therefore it will be necessary to make sure that thei

32、nformation about the complaint is as reliable as possible and useful for identifying the possible impairment of thenetwork that caused the complaint.Examples (see also the handbook cited in 1): data concerning the subscriber numbers involved (route, destination); data concerning the observations dur

33、ing the unsuccessful call attempt(s), or the disturbed call; time of the observation by the customer.B.2 Statistical processes to improve the reliability of the dataReliable data is obtained by statistical processing of large numbers of complaints (e.g. an average value duringa certain period of tim

34、e). In order to achieve this, the following methods are considered to be useful:1) choose complaints whose possible causes seem to relate to impairments of the network;2) accumulate complaints for a certain period of time, for example, one month or one week, depending on thenumber of complaints;3) c

35、alculate the ratio of complaints statistically from accumulated data, for example, complaint-to-completionratio (CTCR), for the chosen period of time:CTCR = Number of complaintsNumber of effective call attempts100%It is practical to use the CTCR in combination with one or more classification aspects

36、 (see B.3) such as “perdestination“.B.3 Analysis of complaintsIt is necessary to identify the possible impairment of the network causing the complaint and smoothly clear thisimpairment in order to actually improve the quality of service. To accomplish this, the complaint needs to be processedinto da

37、ta useful to network maintenance organizations in localizing the possible impairment. The following methodsare considered useful:1) classifying complaints by category of failure;2) classifying complaints by destination, route (or circuit group) and/or area code;Fascicle II.3 - Rec. E.420 73) time of

38、 day analysis. This may be effective in identifying impairments that may not be apparent whenlooked at on a total day basis;4) highlighting relative changes or trends in the statistical data. These changes are likely to reflect a change ofthe network status and are useful indications along with the values themselves. For example, a rapidincrease in the statistical value (e.g. the ratio of complaints) may reflect a new impairment of the network.Reference1 CCITT Manual Quality of service, network management and network maintenance, ITU, Geneva, 1984.