KR100812946B1 - System and Method for Managing Quality of Service in Mobile Communication Network - Google Patents

Abstract

The present invention detects a packet passing along a network link in a mobile communication network, calculates a quality indicator (QI), and uses the statistical value of the calculated quality indicator as a reference value for determining whether there is an abnormality in service quality. The present invention relates to a service quality management system and method in a mobile communication network that calculates and manages a service quality based on this.

In the mobile communication network of the present invention, a service quality management system includes a DB server for collecting, storing, and managing quality indicator (QI) data calculated from data detected from packets passing along a network link of a mobile communication network; And a QoS server extracting sample data from the service quality indicator data stored in the DB server and performing statistical analysis on the extracted sample data to calculate a service quality indicator reference value which is a failure determination criterion of the mobile communication service. It is configured to include a technical feature.

Description

System and Method for Managing Quality of Service in Mobile Communication Network

1 is a block diagram of a service quality management system according to an embodiment of the present invention;

2 is a block diagram of the probing equipment of FIG.

3 is a configuration diagram of a QoS server of FIG. 1;

4 is a flowchart illustrating a QI calculation process of a service quality management method according to an embodiment of the present invention;

5 is a flowchart illustrating a failure process of a service quality management method according to an embodiment of the present invention.

<Description of Symbols for Main Parts of Drawings>

100: service quality management system

110: probing equipment

111: packet copy unit

112: data detection unit

113: QI calculation unit

120: QoS Viewer

130: QoS server

131: sampling unit

132: statistical processing unit

133: normalization unit

134: fault setting unit

135: QI reference value calculation unit

136: QI reference value storage unit

137: QI collector

138: disability judgment unit

139: disability information reporting unit

140: DB server

141: QI Database

The present invention relates to a service quality management system and method in a mobile communication network, and more particularly, to detect a packet passing along a network link, to calculate a quality indicator (QI), and to perform a statistical analysis of the calculated quality indicator. The present invention relates to a service quality management system and method in a mobile communication network which calculates a reference value, which is a standard for determining whether there is an abnormality in service quality, and manages the service quality based on this.

Today's networks that provide multimedia services are suffering from frequent bottlenecks and congestion due to the explosive increase in Internet usage and traffic, which is causing serious problems in reducing the quality of network services. In addition, indiscriminate service congestion caused by the emergence of various web-based applications does not guarantee stable services for core tasks.

As network utilization increases, the demand for a stable network service foundation is further heightened, and service operators are in urgent need of efficient traffic control and bandwidth management for optimal network operation and management.

For efficient traffic control and bandwidth management, it is necessary to continuously monitor the network network for quality evaluation of the network and data, and to calculate and analyze quality indicators according to the quality evaluation. There is no systematic way for this.

Accordingly, the present invention is to solve all the disadvantages and problems of the prior art as described above, and comprehensively analyzes all sections of a mobile communication network link providing a voice service and a wireless Internet data service, and objectively determines the quality of service. It is an object of the present invention to provide a service quality management system and method in a mobile communication network that can establish a standard that can manage and diagnose the quality of service through the mobile communication network.

The object of the present invention is a DB server for collecting, storing and managing Quality Indicator (QI) data calculated from data detected from packets passing along a network link of a mobile communication network; And a QoS server extracting sample data from the service quality indicator data stored in the DB server and performing statistical analysis on the extracted sample data to calculate a service quality indicator reference value which is a failure determination criterion of the mobile communication service. It is achieved by a service quality management system in a mobile communication network comprising a.

In addition, the above object of the present invention (A) Quality Indicator (QI) data calculated from the data detected in the packet passing along the network link of the mobile communication network QoS server for managing the service quality failure of the mobile communication network Extracting, as a sample, service quality indicator data for a predetermined period of time from the service quality indicator data stored in a DB server for storing the data; (B) the QoS server performing statistical analysis of the extracted sample data to calculate and store a service quality index reference value which is a failure determination criterion of a mobile communication service; Including a, it is achieved by the service quality management method in the mobile communication network to make the determination of the failure of the service based on the service quality indicator reference value.

Details of the above object and technical configuration of the present invention and the resulting effects thereof will be more clearly understood from the following detailed description based on the accompanying drawings.

First, FIG. 1 is a configuration diagram of a service quality management system according to an embodiment of the present invention, FIG. 2 is a configuration diagram of probing equipment of FIG. 1, and FIG. 3 is a configuration diagram of a QoS server of FIG.

As shown in FIG. 1, the service quality management system 100 of the present invention includes a probing equipment 110, a QoS viewer 120, a QoS server 130, and a QI DB 141 existing on a network. It is composed of a DB server 140.

In order to objectively and systematically evaluate the multimedia quality of service, the probing equipment 110 uses an electrical scheme to transmit and receive packets (control signals and user data), that is, packets transmitted and received between the mobile communication terminal and the mobile communication network, along the network link of the mobile communication network. Copying in real time through the packet, and calculates the quality indicator (hereinafter referred to as 'QI') from the packet and stores it in the DB server 140, as shown in FIG. As described above, the packet copying unit 111 includes a packet copying unit 111, a data detecting unit 112, and a QI calculating unit 113.

The packet copying unit 111 copies a packet passing along a network link of a mobile communication network in real time, and the data detecting unit 112 performs QI measurement through a specific packet filtering rule set for QI measurement from the copied packet. The data is detected and transferred to the QI calculator 113. Here, the packet filtering rule refers to a rule for extracting only information necessary for QI measurement from a packet including a plurality of information.

The QI calculator 113 calculates a QI using data transmitted from the data detector 112 and transmits the QI to the DB server 140.

Next, the QoS viewer 120 graphically processes the service quality information of each user into an easy-to-understand form so that the operator can easily monitor the service quality information and provides the GUI in the form of a graphical user interface (GUI).

The DB server 140 stores and manages the QI data transmitted from the QI calculating unit 113 in the QI DB 141, and determines the failure criteria in order to manage the quality of service stored in the QI DB 141. To the QoS server 130 to establish a failure status determination and the like.

QoS server 130 manages the operation of one or more probing equipment 110, extracts sample data from the QI data stored in the DB server 140, performs a statistical analysis of the extracted sample data of the mobile communication service Comparing the calculated first QI reference value with the QI stored in the DB server 140 to determine whether there is a failure, and transmitting failure occurrence information to an operator terminal. Perform the second role.

In order to perform the first role, the QoS server 130 may include a sampling unit 131, a statistical processing unit 132, a normalization unit 133, a failure stage setting unit 134, and the like. QI reference value calculation unit 135, and QI reference value storage unit 136, and includes a QI collection unit 137, a failure determination unit 138, a failure information reporting unit 139 to perform the second role. All.

The sampling unit 131 extracts collected data for a predetermined period of the QI data stored in the DB server 140 as a sample and provides the sample to the statistical processing unit 132.

The statistical processing unit 132 calculates basic statistical data such as probability distribution, mean, and standard deviation of the extracted sample QI data, and provides the basic statistical data to the normalization unit 133, and the normalization unit 133 uses the basic statistical data. The QI data is normalized to a standard normal distribution, and a random variable following the standard normal distribution is calculated. Since the statistical processing unit 132 and the normalization unit 133 vary in information such as 'time', 'throughput', and 'success rate', which can be an indicator of service quality in a mobile communication network, the unit of such various information is common. Required to calibrate in phosphorus units.

번째 QI 평균이

보다 작거나 같은 확률은 다음 수학식 1과 같다.Meanwhile, the statistical processing unit 132 or the sampling unit 131 determines an appropriate period for the basic statistical data and the number of sample data or according to predetermined information. According to the Central Limit Theorem, an important theory of statistics, if the QI is measured during a sufficient collection period (typically more than 20 samples), then the distribution of the mean of the QI sample should follow the Normal Distribution. According to the normal distribution,

Second QI mean

The probability less than or equal to is equal to the following Equation 1.

는 프로빙 장비(110)에서 수집한

번째 QI를 나타내는 확률변수를,

는

의 모평균을,

는 모분산을 의미한다. 특정 QI의 모평균과 모분산을 구하는 것은 현실적으로 용이하지 않으므로, 본 발명에서는 QI DB(141)에 일정기간 누적된 품질지표 데이터를 이용하여 평균(

)과 분산(

)을 계산한 후, 이를 모평균과 모분산으로 대체하는 방법을 채택한다. 여기서, 상기 일정 기간은 시스템에서 구할 수 있는 최대 기간으로 정하는 것이 바람직하다.In Equation 1,

Collected from the probing equipment 110

The random variable representing the fourth QI,

Is

The mean of,

Means the variance. Since it is not practically easy to obtain a population mean and a variance of a specific QI, in the present invention, the average (

) And variance (

), And then replace it with the population mean and population variance. Here, the predetermined period is preferably set to the maximum period that can be obtained from the system.

On the other hand, since the normal distribution probability value of Equation 1 should be calculated directly through integration, the calculation is complicated and time consuming, and according to the present invention, the normalization unit 133 has a mean of 0 and a standard deviation of 1, which is 'standard'. A method of converting the data into a normal distribution 'is adopted.

번째 품질 지표의 확률변수(

)를 '표준 정규 분포'의 확 률변수(

)로 변환시키는 공식이다. 즉, 일정기간 이상 누적된 평균(

), 표준편차(

) 및

를 다음 수학식 2에 대입하면, 표준 정규 분포의 확률변수(

)을 계산할 수 있으며, 이때 변환된

는 표준 정규 분포를 따른다. Equation 2 is

Random variables of the first quality indicator (

) Is the probability variable (

) That is, the average accumulated over a period of time (

), Standard Deviation(

) And

If you substitute in Equation 2, the random variable of the standard normal distribution (

), Where the converted

Follows a standard normal distribution.

번째 QI를 변환한 확률변수값(

)이

보다 작거나 같은 확률을 구하는 식을 나타낸 것이며, 수학식 3은 확률 분포 함수표를 참조하면 쉽게 구할 수 있다.Equation 3 is a standard normal distribution function,

Random variable that transforms the first QI (

)this

Equation for obtaining the less than or equal probability is shown, and Equation 3 can be easily obtained by referring to the probability distribution function table.

Next, the fault stage setting unit 134 sets one or more fault stages and the probability of occurrence of each fault stage based on the calculated data of the normalization unit 133.

In this case, the failure stage setting unit 134 prepares a critical failure stage, which means that the system operation is not possible, and a major failure stage and system failure preparation, which means that some failure occurs in the system. It can be set by dividing it into minor fault stage, which means that it is required.

After the failure step setting unit 134 defines the failure step, it sets the probability that the step occurs. That is, for each stage, it defines the probability of generating a minor stage (p_mi), the probability of a major stage (p_ma), and the probability of a critical stage (p_cr), which are based on the system configuration, collected data, and management policy. Can be determined.

For example, as a result of analyzing the configuration and fault data of the equipment, if the critical stage occurs in about 1 in 1000 cases, set p_cr to 0.1%. In addition, the ratio of failure stages may be determined according to the management policy such as the targets targeted by the organization, and p_cr is set at 0.1%, p_ma is 0.5%, and p_mi is set at 1%. Set it to On the other hand, the occurrence probability for each failure stage is used as an input parameter when determining the reference value for determining whether the QI abnormality.

The QI reference value calculating unit 135 is based on the calculation data of the statistical processing unit 132 and the normalization unit 133, and the setting information of the disability step setting unit 134, for each disability step serving as a criterion for determining whether there is a failure. By calculating the QI reference value and storing it in the QI reference value storage unit 136, a failure determination criterion is established.

로 변환하고, 표준 정규 분포의 확률변수값을 구하는 상기 수학식 2에, 상기 통계 처리부에 의해 산출된 QI의 평균값

및 표준편차값

과, 상기 변환된 확률변수값

를 대입하여, 각 장애단계별 QI 기준치

를 산출할 수 있다.At this time, the QI reference value calculating unit 135 uses the standard normal distribution table to determine the probability value of each occurrence of the disability step set by the disability level setting unit 134 using a standard normal distribution table.

The average value of the QI calculated by the statistical processing unit in Equation (2) for converting to

And standard deviation

And the transformed random variable value

QI threshold for each disability level by substituting

Can be calculated.

는 수학식 3에서 계산되는 확률값과 장애단계별 발생 확률이 일치하는 지점의 값으로 계산할 수 있다. 수학식 4는 수학식 3의 역함수로, 장애단계별 발생확률(p)에 해당되는 표준 정규 분포표 상의 확률변수값

를 산출하는 식이다.In other words, random variable value

May be calculated as a value of a point where the probability value calculated in Equation 3 and the occurrence probability for each disability step coincide. Equation 4 is an inverse function of Equation 3, and the value of the random variable in the standard normal distribution table corresponding to the probability of occurrence of each stage of disability (p)

Is an expression that calculates.

)을 이용하면, 서비스 품질의 이상 여부를 판단하는 기준치(

)를 계산할 수 있으며, 다음 수학식 5는 상기 기준치를 산출하는 계산식으로, 수학식 2에 의해 쉽게 도출된다. The random variable value (

), The standard value for determining whether the quality of service is abnormal

), And the following Equation 5 is a formula for calculating the reference value, and is easily derived by Equation 2.

)의 평균이 0.2035초이고, 표준편차가 0.1908에 대 한 값을 사전에 알고 있다고 가정하고, 시스템에서 관리하고 있는 크리티컬 단계의 발생확률(

)을 0.1%로 설정하고 있다고 가정한다.Hereinafter, the QI reference value (critical step) setting and management process described above will be described by way of example. In this example, the QI related to the multimedia service is observed for a long time.

) Is assumed to be 0.2035 seconds and the standard deviation knows the value for 0.1908 in advance, and the probability of occurrence of the critical stage managed by the system (

Assume that you set) to 0.1%.

)을 구할 수 있으며, 상기 확률변수값과, 평균 및 표준 편차를 수학식 5에 대입하면, 크리티컬 단계의 기준치(0.7911초)를 계산할 수 있다.If the occurrence probability (0.1%) is substituted into Equation 4, the critical step random variable value (

), And the reference value (0.7911 seconds) of the critical stage can be calculated by substituting the random variable value, the mean, and the standard deviation into Equation 5.

The reference value of each fault level calculated by the QI reference value calculation unit 135 in the same manner as described above is stored in the QI reference value storage unit 136, and the failure determination unit 138 determines whether the service failure of the mobile communication network occurs. If the QI collected by the QI collecting unit 137 which collects the quality of service indicators from the DB server 140 periodically, that is, the service access time is monitored, and a mobile communication terminal having an access time exceeding 0.7911 seconds is found, This is transmitted to the failure information reporting unit 139, and the failure information reporting unit 139 informs the system operator in various ways that the corresponding service quality corresponds to a critical failure level.

That is, the failure determination unit 138 compares the service quality indicators collected by the QI collection unit 137 with the stored service quality indicator reference value to determine whether a failure occurs, and if it is determined that a failure has occurred, corresponding failure occurrence information. The failure information reporting unit 139 transmits the failure occurrence information output from the failure determining unit 138 to the operator terminal in various ways (telephone, e-mail, SMS, etc.).

Next, the operation of the present invention will be described once again sequentially through FIGS. 4 and 5 as follows.

4 is a flowchart illustrating a QI calculation process of a service quality management method according to an embodiment of the present invention, which illustrates the operation of the probing equipment 110, and FIG. 5 is a service quality management method according to an embodiment of the present invention. As a flowchart illustrating a failure processing process, the operation of the QoS server 130 is illustrated.

As shown in FIG. 4, the probing equipment 110 constituting the service quality management system 100 of the present invention copies a packet passing along a network link of a mobile communication network in real time (S201) and from the copied packet. Data for measuring QI is detected through a specific packet filtering rule set for measuring QI (S202).

Next, the probing equipment 110 calculates a QI using the detected data (S203) and stores it in the DB server 140 (S204).

As described above, the QI stored in the DB server 140 in real time is used to establish a failure criterion by the QoS server 130, and the QI is used to monitor the quality of a service according to the failure criterion. Is used.

That is, as shown in FIG. 5, the QoS server 130 extracts QI data for a predetermined period of time from the data stored in the DB server 140 as a sample in order to manage the quality of service failure of the mobile communication network (S301). .

Next, the QoS server 130 calculates basic statistical data including a probability distribution, an average, and a standard deviation of the extracted QI data (S302), and converts the QI data into a standard normal distribution using the basic statistical data. After normalizing and calculating a random variable following a standard normal distribution (S303), based on previously calculated data, one or more failure stages and occurrence probability for each failure stage are set (S304).

Thereafter, the QoS server 130 calculates and stores a QI reference value for each failure stage, which is a failure determination criterion, based on the data and setting information calculated in the previous processes (S305).

로 변환하고, 표준 정규 분포의 확률변수값을 구하는 수학식 2에, 미리 산출된 서비스 품질 지표의 평균값

및 표준편차값

과, 상기 변환된 확률변수값

를 대입함으로써, 산출되는

값이 된다.In this case, the QI reference value is a probability variable value of a standard normal distribution using a standard normal distribution table as a probability of occurrence of each stage of disability.

The average value of the calculated service quality indicators is calculated by Equation 2, which is obtained by converting

And standard deviation

And the transformed random variable value

By substituting

Value.

After the QI reference value is calculated according to the above process, the QoS server 130 collects the QI periodically or in real time from the DB server 140 to determine whether the service failure of the mobile communication network, the calculated It is determined whether a failure occurs in comparison with the QI reference value, and if it is determined that a failure has occurred, the corresponding failure occurrence information is transmitted to the operator terminal (S306).

As those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features, the embodiments described above are exemplary in all respects and are not intended to be limiting. You must understand. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

Therefore, according to the service quality management system and method in the mobile communication network of the present invention, video telephony service and video-on-demand video are established by comprehensively analyzing all sections of the mobile communication network link and establishing a standard for objectively determining the quality of service. There is an effect that the quality of user experience can be improved by systematically managing and diagnosing the user's quality of experience for multimedia services such as video on demand (VoD).

Claims (17)

As a service quality management system in a mobile communication network, A DB server for collecting, storing, and managing Quality Indicator (QI) data calculated from data detected from packets passing along a network link of a mobile communication network; And A QoS server extracting sample data from the service quality indicator data stored in the DB server and performing statistical analysis on the extracted sample data to calculate a service quality indicator reference value that is a failure determination criterion of a mobile communication service; The QoS server, A sampling unit which extracts, as a sample, service quality index data for a predetermined period of service quality index data stored in the DB server; A statistical processor for calculating basic statistical data including probability distributions, averages, and standard deviations of the extracted service quality indicator data; A normalization unit for normalizing the service quality indicator data to a standard normal distribution using the basic statistical data and calculating a random variable following the standard normal distribution; A fault stage setting unit for setting at least one fault stage and a probability of occurrence of each fault stage based on the calculated data of the normalizer; A QI reference value calculation unit for calculating a service quality index reference value for each disability step, which is a criterion for determining whether a failure is based on calculation data of the statistical processing unit and the normalization unit and setting information of the failure level setting unit; And A QI reference value storage unit for storing a service quality indicator reference value for each disability step calculated by the QI reference value calculation unit; Quality of service management system in a mobile communication network, characterized in that consisting of. delete The method of claim 1, The fault stage setting unit, Critical fault level means that the system cannot be operated, the major fault level means that some faults occur in the system, and minor fault means that preparation for system faults is required. Quality of service management system in a mobile communication network, characterized in that the setting by dividing into steps. The method of claim 1, The QI reference value calculation unit, Probability variable value of the standard normal distribution using the standard normal distribution table for the probability of occurrence of each fault level set by the fault level setting unit.

To find the value of the random variable of the standard normal distribution.

The average value of the service quality indicators calculated by the statistical processing unit

And standard deviation

And the transformed random variable value

Service quality indicators for each level of disability

A service quality management system in a mobile communication network, characterized in that for calculating. The method of claim 1, The QoS server, And comparing the calculated service quality indicator reference value with the service quality indicator stored in the DB server to determine whether there is a failure and transmitting the failure occurrence information to an operator terminal. The method of claim 5, The QoS server, A QI collector which periodically collects service quality indicators from the DB server to determine whether a service failure occurs in a mobile communication network; A failure determination unit comparing the service quality index collected by the QI collecting unit with the stored service quality index reference value to determine whether a failure occurs, and outputting corresponding failure occurrence information when it is determined that a failure has occurred; A failure information reporting unit for transmitting failure occurrence information output from the failure determining unit to an operator terminal; Quality of service management system in a mobile communication network, characterized in that consisting of. The method according to any one of claims 1 and 3 to 6, The service quality management system, Probing equipment which copies packets passing along a network link of a mobile communication network in real time, calculates the quality of service indicators from the packets and stores them in the DB server; Quality of service management system in a mobile communication network further comprising. The method of claim 7, wherein The probing equipment, A packet copying unit for copying a packet passing along a network link of a mobile communication network in real time; A data detector for detecting data for measuring a service quality indicator from the copied packet through a specific packet filtering rule set for measuring the quality indicator (QI); A QI calculator configured to calculate the service quality index by using the data detected by the data detector and to store it in the DB server; Quality of service management system in a mobile communication network, characterized in that consisting of. As a quality of service management method in a mobile communication network, (A) The QoS server for managing a service quality failure of a mobile communication network stores the quality indicator (QI) data calculated from data detected in a packet passing along a network link of the mobile communication network. Extracting service quality indicator data for a certain period of time from the service quality indicator data as a sample; (B) calculating basic statistical data including probability distributions, averages, and standard deviations of the extracted service quality indicator data; (C) normalizing the quality of service indicator data to a standard normal distribution using the basic statistical data and calculating a random variable following the standard normal distribution; (D) setting at least one fault stage and a probability of occurrence for each fault stage based on the data calculated in step (C); And (E) Based on the data calculated in the steps (B) and (C) and the information set in the step (D), to calculate and store the service quality index reference value for each failure step that is the criteria for determining whether there is a failure step; The service quality management method of claim 1, wherein the determination of the failure of the service is made based on the service quality indicator reference value. delete The method of claim 9, In the step (D), The QoS server has a critical failure level that means that the system cannot operate the failure step, a major failure step that means that some failure occurs in the system, and a minor failure preparation that requires preparation of the system failure. (Minor) A service quality management method in a mobile communication network, characterized in that set by dividing into failure stages. The method of claim 9, In the step (E), The QoS server uses the standard normal distribution table to determine the probability of occurrence of each failure stage by using the standard variable distribution.

To find the value of the random variable of the standard normal distribution.

In the meantime, the average value of the service quality indicators calculated in step (B)

And standard deviation

And the transformed random variable value

Service quality indicators for each level of disability

The service quality management method in a mobile communication network, characterized in that for calculating. The method of claim 9, After the step (E), (F-1) periodically collecting, by the QoS server, quality of service indicators from the DB server to determine whether a service failure occurs in a mobile communication network; (F-2) It is determined whether a failure occurs by comparing the service quality indicators collected in the step (F-1) with the service quality indicator reference value stored in the step (E). Transmitting to the operator terminal; Service quality management method in a mobile communication network comprising a further. The method of claim 13, After step (E), before step (F-1), (G-1) Quality of service through a specific packet filtering rule set for measuring a quality indicator (QI) from the copied packet by a probing device that copies a packet passing along a network link of a mobile communication network in real time. Detecting data for indicator measurement; (G-2) calculating the service quality index by using the detected data and storing it in the DB server; Service quality management method in a mobile communication network comprising a further. The method according to any one of claims 9 and 11 to 14, Before step (A), (a-1) Quality of service through a specific packet filtering rule set by a probing apparatus for copying a packet passing along a network link of a mobile communication network in real time to measure the quality indicator (QI) from the copied packet. Detecting data for indicator measurement; (a-2) calculating the service quality index by using the detected data and storing the service quality index in the DB server; Service quality management method in a mobile communication network comprising a further. (A) Service quality indicator data for a certain period of time among the service quality indicator data stored in the DB server storing the quality indicator (QI) data calculated from the data detected in the packet passing along the network link of the mobile communication network; Extracting as a sample; (B-1) calculating basic statistical data including probability distributions, averages, and standard deviations of the extracted service quality index data; (B-2) normalizing the service quality indicator data to a standard normal distribution using the basic statistical data and calculating a random variable following the standard normal distribution; (B-3) a function of setting one or more failure stages and occurrence probability for each failure stage based on the data calculated by the function (B-2); And (B-4) Each failure step serving as a criterion for failure based on the data calculated by the functions (B-1) and (B-2) and the information set by the function (B-3) Calculating and storing service quality index reference values for each service; A computer-readable recording medium having recorded thereon a program for executing the program. The method of claim 16, The (B-4) function, The probability of occurrence of each stage of disability using the standard normal distribution table

To find the value of the random variable of the standard normal distribution.

, The average value of the service quality indicators calculated by the function (B-1) above.

And standard deviation

And the transformed random variable value

Service quality indicators for each level of disability

Computer-readable recording medium, characterized in that for calculating the function.

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