KR20010064747A - Method of estimation node-selection and investment cost in broadband subscriber line - Google Patents

Abstract

PURPOSE: A method for designing and analyzing a broadband subscriber network is provided to select a service possible telephone office and nodes connected by layers using the amount of data traffic by telephone offices and the information of the shortest route, to compute node connection information, estimated traffic information and transport information for the selected telephone office and to estimate the expenses. CONSTITUTION: A simulation device is initialized through the input of databases to design a broadband subscriber network(201). After the initialization, various user input items are inputted(202). If an analysis execution basis setup method is set up on the basis of demand(203), an average monthly data traffic database is updated into a demand database(204). Traffic demand distribution, transport information and cost information, depending on node selection and traffic rates by layers, is calculated using the other input items, except updated data information, demand data information and the analysis execution basis setup method(205). An output result is recalculated through user updating(206).

Description

Method of estimation node-selection and investment cost in broadband subscriber line}

The present invention relates to a method for design analysis of a broadband subscriber network such as an asymmetric digital subscriber line (ADSL) network in a general computing environment. Using the shortest distance information, the serviceable telephone station and nodes connected to each level (DSLAM, Edge, Core) are selected.The node connection information, estimated traffic information, transmission information (line class, line demand, And a computer-readable recording medium having recorded thereon a program for realizing the method.

The conventional network design method has been developed based on the telephone network. The use of this design method in ADSL, a new communication service that is sensitive to traffic types, regional demands, and distance factors, has the following limitations.

First, the existing phone traffic is very different from the circuit share of the ADSL traffic. In this regard, the characteristics of telephone traffic are intermittent data transmission, whereas ADSL traffic continuously transmits a large amount of data.

Second, due to the large number of information and stable network conditions for national telephone subscriber demand for a long time, the current telephone network has detailed demand by country, region and headquarters. However, in the case of ADSL, this information is not yet analyzed.

Third, the telephone network has already been stabilized technically and is installed within the standard allowable distance from the subscriber's nearest telephone station, but ADSL is technically limited in distance (within 5 km) so that all subscribers cannot use it in the current network. Do.

In the case of a small number of developed countries in the excluded countries, there is a network design simulation system for ADSL and other new services.

However, these systems are not only very expensive, but also inconvenient to pay additional consulting fees in some cases. In addition, in most cases, it is necessary to continuously pay a large fee for system training and system upgrades, and it takes a long time for a user to learn how to use the system of such an excluded country and apply it to a business.

Therefore, it is essential to establish a design method that takes into account the specificity of the features of the ADSL service, and at the same time, a new network design method having an important meaning only for the ADSL service that analyzes selected nodes, node connection information, expected traffic information, and transmission information. Required.

The present invention, which is designed to meet the above requirements, provides a service using data traffic volume of each telephone station, shortest distance information between a local station and a long-distance station, etc. when considering an asymmetric digital subscriber line (ADSL) network in a general computing environment. Selects possible telephone stations and nodes connected to each level (DSLAM, Edge, Core), and calculates node connection information, estimated traffic information, and transmission information (line class, line demand, line cost, etc.) for the selected telephone station. It is an object of the present invention to provide a method of designing and analyzing a broadband subscriber network for estimating the cost and a computer-readable recording medium recording a program for realizing the method.

1 is an exemplary configuration diagram of a hardware system to which the present invention is applied.

2 is a flow chart of an embodiment of a design analysis method of a broadband subscriber network according to the present invention;

3 is a flowchart illustrating an embodiment of a process of selecting a first-tier telephone station, node connection, expected traffic, and transmission information according to the present invention;

4 is a flowchart illustrating a process of selecting a second rank "DSLAM" and calculating node connection, expected traffic, and transmission information according to the present invention.

5 is a flowchart illustrating an embodiment of a process for calculating a three-tier "Edge" and calculating node connection, expected traffic, and transmission information according to the present invention.

Figure 6a and 6b is a flow diagram illustrating an embodiment of the process of calculating the four-tier "Core" selection and node connection, expected traffic, transmission information according to the present invention.

* Explanation of symbols for the main parts of the drawings

11: central processing unit 12: main memory unit

13; Secondary storage device 14: input device

15: display device

In order to achieve the above object, the present invention provides a method for designing a broadband subscriber network such as an asymmetric digital subscriber line (ADSL) network in a computing system. Initialize the simulation device by inputting monthly data traffic volume, shortest distance information between city station and long-distance station), and set analysis performance standard, execution method, node selection criteria for each level, traffic ratio for each level, and top level A first step of performing a setup procedure for selecting nodes for each level by receiving a headquarter name and a transmission cost where a core should exist; A second step of updating the data traffic volume database initialized according to the demand information of the analysis performance criterion setting function during the input with demand data information; And a third step of calculating traffic / demand distribution, transmission information, and cost information according to the selection of stations for each level and the traffic ratio of each level.

In addition, the present invention initializes a simulation apparatus by inputting a database (average monthly data traffic amount, shortest distance information between a local station and a foreign country) for designing a broadband subscriber network to a computing system having a processor, and performing analysis. Set-up procedure for setting node by each level by inputting standard setting function, execution method setting function, node selection criteria by each level, traffic ratio by each level, headquarters where top level core should exist, and transmission cost Function to perform; Updating the data traffic volume database initialized according to the demand information of the analysis performance criterion setting function during the input with demand data information; And a computer-readable recording medium having recorded a program for realizing a function for calculating traffic / demand distribution, transmission information, and cost information according to the selection of stations by each level and the traffic ratio of each level.

The present invention is a database of the data traffic volume of each telephone station, the shortest distance information between the local and local stations, etc., which are considered in ADSL network planning, and the serviceable telephone station and the nodes connected to each level (DSLAM, Edge, Core) are used. It calculates the node connection information, estimated traffic information, transmission information (line class, line demand, line cost, etc.) for the selected telephone station, and estimates the cost accordingly, so that it can be learned without deep knowledge of ADSL network. And design and analysis results that can be used and easily applied to business reality are derived.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exemplary configuration diagram of a general hardware system.

As shown in FIG. 1, a general hardware system includes a central processing unit 11, a main memory device 12 connected to the central processing device 11, and an auxiliary memory device 13 connected to the main memory device 12. And an input device 14 and a display device 15 connected to the central processing unit.

Here, the hardware system stores a central processing unit 11, a program executed in the central processing unit 11, which controls and manages the overall operation of the computer, and stores various data used during or during the execution of a task. And a main memory device 12, an auxiliary memory device 13, and input / output devices 14 and 15 for inputting and outputting data to and from a user.

The auxiliary memory device 13 stores a large amount of data, and the input / output devices 14 and 15 include a general keyboard, a display device, a printer, and the like.

However, since the computer hardware environment having the configuration as described above is only a technique well known in the art, detailed description thereof will be omitted herein. However, it is installed in the main memory device 11 and uses the data traffic volume of each telephone station to be considered in planning ADSL network, the shortest distance information between the local and intercity stations, etc., and the nodes connected to each level (DSLAM, Edge, Core) ), Calculate the node connection information, estimated traffic information, transmission information (line class, line demand, line cost, etc.) for the selected telephone company, and explain in detail the process of estimating the cost accordingly. do.

In the analysis of ADSL network design, the simulation device is initialized by inputting the database (data traffic volume, shortest distance information between local and overseas stations) for the design, and the method of setting analysis performance criteria, method of execution method, and each level It performs setup procedure to select nodes by each node by inputting node selection criteria by each node, traffic ratio by each level, headquarters where the highest level core should exist, and transmission cost.

Thereafter, the data traffic volume database initialized according to the demand information of the analysis performing criteria setting method during the input is updated with demand data information as necessary.

Next, traffic / demand distribution, transmission information, and cost information are calculated according to node selection for each level and traffic ratio for each level.

The result is displayed and printed in MS database, Excel, text, HyperText Markup Language (HTML), chart, and heterogeneous database, and the result can be recalculated through user update.

2 is a flowchart illustrating a method for designing and analyzing a broadband subscriber network according to the present invention, and shows a procedure for node selection, traffic and transmission information calculation in an ADSL network.

As shown in FIG. 2, the method for design analysis of a broadband subscriber network, particularly an ADSL network, according to the present invention, first undergoes an initialization process of receiving a database to be simulated. It is an Access relational database, which defines and inputs the monthly average data traffic volume of 420 telephone stations across the country, the shortest distance matrix between telephone stations by headquarters, and the distance matrix between existing tolls currently existing by headquarters (201).

When the initialization process is completed as described above, various user inputs are received (202).

Detailed input of this process is to set up the analysis performance standard (traffic or demand based, but when the demand base is set, enter the national or headquarters demand), how to set the performance method (all headquarters with the same selection rate or headquarters) Enter the different selection rate for each level, and select the node selection criteria for each level (Enter the minimum allowable monthly average traffic and the average monthly used traffic per person in case of 1st-level telephone company, and allowable minimum capacity in case of 2nd-level DSLAM, 3rd-edge Edge and 4th-level Core) In this case, the standard can be set or unset, and the minimum capacity allowed when setting), the traffic ratio for each level (enter the percentage of traffic going to the lower level, the same level, and the higher level), and the top level (Core) must exist. (The headquarters of the 10 headquarters where the core will be installed), and the transmission cost (the unit price per line or Mbps).

Subsequently, if the analysis performance standard setting method is set based on demand (203), the demand for each telephone station is calculated by multiplying the ratio of the monthly average data traffic volume of the telephone company which is defined by the demand of the national or headquarters, and the average monthly data traffic volume data. The base is updated with the demand database (204). Afterwards, all calculations use the demand database, not the data traffic database.

Next, except for the updated traffic data information or demand data information and the method of setting the analysis performance criteria, the traffic / demand distribution, transmission information, and cost information according to the selection of nodes for each level and the traffic ratio for each level are used. Calculate (205).

The result is displayed and printed in MS database, Excel, text, HTML, chart, and heterogeneous database, and the result can be recalculated through user update (206).

3 is a flowchart illustrating a process of selecting a first-tier telephone station, node connection, expected traffic, and transmission information calculation process according to the present invention, and repeatedly executing the number of national telephone stations (420 countries).

As shown in FIG. 3, the first-tier telephone station selection, node connection, expected traffic, and transmission information calculation process according to the present invention is performed by selecting the first-tier telephone station selection criterion among the node selection criteria for each rank in step "202". If the allowed monthly average traffic is more than or equal to the traffic volume of each telephone station, it is determined as a station capable of receiving ADSL service (301) and goes to the module 304 for traffic calculation.

Otherwise, if the previous year has already been selected as a station capable of receiving ADSL services and is recorded in the output database, that is, the telephone station has already determined that related equipment and costs have occurred since ADSL service demand has occurred before (302). Even if the selection criteria are not met, the traffic is regarded as a serviceable telephone station (304). If not, the next telephone station information is read (303).

Then, to calculate the traffic for the first selected telephone station, the input, internal, upper traffic is calculated (304) according to the traffic ratio for each level previously input in step 202, input line level, input circuit. The number of bows, internal line and internal lines is also calculated (305), where the input of the primary rank telephone station and the internal line are limited to DS1 (less than 1.544 Mbps).

Next, the upper traffic may be DS1 or DS3 (1.544 Mbps to 45 Mbps), which determines the upper traffic amount (306) and determines the circuit level and the number of circuits (307 and 308).

The line cost is calculated using the calculated number of lines or traffic and the transmission cost previously input in step 202.

Thereafter, the telephone station determined as the primary rank and its related traffic, line class, number of lines, and cost-related information are further updated in the output database (310) and moved to the record with the next telephone station information (303).

FIG. 4 is a flowchart illustrating a process of selecting a second rank "DSLAM" and calculating node connection, expected traffic, and transmission information according to the present invention, and repeatedly executing the number of national call rights (144 call rights).

As shown in FIG. 4, the second-order "DSLAM" selection, node connection, expected traffic, and transmission information calculation process according to the present invention first select the DSLAM having the largest traffic volume among the telephone stations in the same coverage area (401), If the sum of the telephone station traffic capacities selected in the previous step in the same coverage area is greater than or equal to the allowable minimum capacity of the second-tier DSLAM among the node selection criteria for each of the ranks in step "202" (402), the number of DSLAMs is increased by one (404). Allows you to install multiple DSLAMs on selected DSLAM nodes. If not, the output database is searched if it is already selected as a DSLAM node in the previous year (403).

As a result of the search, if it is not the DSLAM of the previous year, the next call right information is read (413).

As a result of the search, if it is found that the DSLAM in the previous year, it is regarded as the DSLAM node that can be serviced currently, and the DSLAM node is increased even though the selection criteria is lowered by one (404).

Next, the input traffic of the DSLAM is calculated by summing all the upper traffics of the telephone stations selected in the previous step and calculating the internal, upper, and lower parts according to respective traffic ratios (405). Therefore, if the traffic volume is greater than 0 and less than or equal to 1.544 Mbps, calculate the line level to DS1 level (406,407), if it is greater than 1.544 Mbps and less than 45 Mbps to DS3 level (408,409), and if it is more than 45 Mbps to STM1 level, The number of lines is calculated according to the capacity (408, 410).

Thereafter, the transmission cost is calculated using the number of lines or the traffic volume generated in the process to calculate the transmission cost (411).

After all calculations have been made, the output database is further updated (412) and moved to the next currency zone (413).

FIG. 5 is a flowchart illustrating a process of selecting a three-tier "Edge" and calculating node connection, expected traffic, and transmission information according to the present invention, which is repeatedly executed by the number of national headquarters (10 countries).

As shown in FIG. 5, the three-tier "Edge" selection, node connection, expected traffic, and transmission information calculation process according to the present invention may be performed by first calculating the number of DSLAMs selected by the second-tier DSLAM selection method. The number of edges required in the headquarters is determined by multiplying the input selectivity by the method of setting the method of performing the step and performing a rounding operation (501).

Thereafter, the DSLAM is selected in the order of the traffic volume as large as the number of edges calculated above (502), which may be the edges existing at the same location as the DSLAM.

If the selected DSLAMs are the same as the nodes already selected as edge nodes in the previous year, and if any of the existing edge nodes are missing (503), the selected edges of the previous year are subtracted from the smallest amount of traffic among the DSLAMs by the number of previously selected edges. (505). This means that the selected edges will continue to be used without being removed.

Next, it is determined that the position of the DSLAM selected in the above process is the same as the edge position in the headquarters and connects all of the DSLAM and the edge in the same place (504).

If there is a DSLAM not connected to the edge in the above process (506), the edge of the nearest distance among the selected edges is selected (508) by referring to the shortest distance information database between the telephone offices in the headquarters. Connect the unconnected DSLAM (509).

Otherwise, if you set the edge baseline capacity and the sum of the connected DSLAM traffic is above the edge baseline (507), go to the traffic calculation module, otherwise delete the selected edge and the connected DSLAMs (510) and connect to other preset edges. Recalculate to get it done (508, 509).

Thereafter, the input traffic amount of the edge is inputted by the sum of the upper traffic sums of the connected DSLAMs, and the remaining inner, upper and lower traffics are calculated according to respective traffic ratios (511).

Next, the line class and the number of line selection methods are limited to the lowest DS3 level and the highest STM4 level, and the DS3 level (512,513) is 45 Mbps or less, and the STM1 level (514,515) is 155 Mbps or 622 Mbps or more when the range is 45 Mbps to 155 Mbps. In this case, STM4 class is calculated (516,517), and each line is divided into DS3 class 45Mbps, STM1 class 155Mbps, and STM4 class 622Mbps to obtain the number of necessary lines.

Subsequently, the transmission cost is derived by multiplying the calculated number of circuits by the unit of transmission cost per line or Mbps previously input in step 202, and further updating the result in the output database (519). Next, go to the headquarters to be calculated (520).

6A and 6B are exemplary flowcharts illustrating a process of selecting a four-tier "Core", calculating node connection, expected traffic, and transmission information according to the present invention, and repeatedly executing the number of headquarters (10).

As shown in FIGS. 6A and 6B, the process of selecting the fourth rank "Core" and node connection, expected traffic, and transmission information according to the present invention, if the core should exist first (601), determines the number of edges in the headquarters. The number of cores required in the current headquarters is determined by multiplying the application rate of the "202" step and the rounding operation (602).

Thereafter, the edges are selected in order of increasing traffic volume as the number of cores calculated above (603), which may be cores existing at the same location as the edge.

If the selected cores are the same as the nodes already selected as core nodes in the previous year, and if there is a missing one among the existing core nodes (604), the cores selected in the previous year are subtracted from the smallest amount of traffic among the edges by the number of previously selected cores. (605). This means that the selected cores will continue to be used without being removed.

Next, it is determined that the position of the edge selected in the above process is the same as the core position in the headquarters, so that the edge and the core are all connected in the same place (606).

If there is an edge that is not connected to the core in the above process (607), the core closest to the distance among the preselected cores is selected (608) by referring to the shortest distance information database between telephone stations in the headquarters (608). Unconnected edges are connected (609).

In addition, if it is determined by determining whether the 4th rank Core criterion is set among the node selection criteria for each rank in step "202", it is checked whether the sum of the upper traffic volume of the edge is greater than or equal to the Core standard capacity (610). If it is less than or equal to the selected Core and the connection Edge is deleted (611) to recalculate to connect to other preset Core (608,609).

On the other hand, if all of the core selection work for the headquarters where the core should exist is completed or not the headquarters existing in the core (612), the out of the headquarters to perform the core selection work for the headquarters in which the remaining core does not exist. The station name is stored (613), and the suburbs closest to the current edge are found with reference to the distance information between the city stations in the headquarters (614).

In addition, the intercity of the nearest center of the headquarters selected by the core is determined by referring to the intercity distance information (615), and the nearest core selected from the found intercity center is found again by referring to the distance information within the headquarters. (616).

Thereafter, the input traffic amount of the core is inputted with the sum of the upper traffics of the connected edges, and the remaining internal, upper and lower traffics are calculated according to the respective traffic ratios (617).

Next, the line class and the number of line selection methods are limited to the lowest DS3 level and the highest STM4 level, and the DS3 level (618,619) below 45Mbps, the STM1 level (620,621) between 45Mbps and 155Mbps, or between 155Mbps and 622Mbps or more. In this case, STM4 class is calculated (622,623), and the number of circuits is divided into DS3 class 45Mbps, STM1 class 155Mbps, and STM4 class 622Mbps to obtain the necessary number of lines.

Subsequently, the transmission cost is derived by multiplying the calculated number of lines by the unit of transmission cost per line or Mbps previously input in step 202, and after further updating the result to the output database (625), the next calculation is performed. Move to headquarters (626).

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains, and the above-described embodiments and accompanying It is not limited to the drawing.

As described above, the present invention not only simplifies the understanding and implementation of logic by eliminating inappropriate existing network design items when designing and analyzing the ADSL network, but also makes it easy to apply to the business reality, and also to provide characteristics of the ADSL network. Selecting nodes based on data traffic characteristics and distance limitation factors, which are important influencing factors, promotes network design in a more rational manner, as well as node connection information, estimated traffic information, and transmission information for selected telephone stations. It can be learned and used without deep knowledge of ADSL network, and it is easy to apply to business reality, and this method can be easily softwareized through existing commercial programs. By minimizing the development cost based on this method, the price competitiveness for similar software in the excluded countries There is an effect that can be easily obtained.

Claims (7)

In a design analysis method of a broadband subscriber network such as an asymmetric digital subscriber line (ADSL) network in a computing system, Initializes the simulation device by inputting the database (average monthly data traffic volume, shortest distance information between local and overseas stations) for the design of the broadband subscriber network, and sets an analysis performance criterion, an execution method, and each level. A first step of performing a setup procedure for selecting nodes for each level by receiving a node selection criterion, a traffic ratio for each level, a headquarters name for which a highest level Core should exist, and a transmission cost; A second step of updating the data traffic volume database initialized according to the demand information of the analysis performance criterion setting function during the input with demand data information; And The third step of calculating the traffic / demand distribution, transmission information, and cost information according to the selection of stations by each level and the traffic ratio by each level Design analysis method of broadband subscriber network comprising a. The method of claim 1, Fourth step to output the result to relational database, Excel, text, hypertext generation language (HTML), chart, heterogeneous database and recalculate the result through user update Design analysis method of broadband subscriber network further comprising a. The method according to claim 1 or 2, The third step, If the minimum allowable monthly average speed (Mbps) of the first rank telephone station selection function and the traffic, cost, and transmission information calculation function is the same or greater than or equal to the traffic volume of each telephone station, it is determined as the primary selecting station to calculate the traffic. A fifth step of going to the module, otherwise reading the next telephone station information; The sixth step of calculating input, internal and upper traffic according to the traffic ratio of each level already input for calculating traffic for the first selected telephone company, and calculating input line level, input line number, internal line level, and internal line number ; And A seventh step of calculating a transmission cost using the calculated number of circuits or traffic volume and a previously input transmission cost; Design analysis method of broadband subscriber network comprising a. The method according to claim 1 or 2, The third step, The second traffic level (DSLAM) selection function and the traffic, cost, and transmission information calculation function is selected as the second traffic level (DSLAM) the largest traffic volume among the telephone stations in the same area, and the sum of the traffic volume of the telephone stations selected at the previous stage in the same area. If the second level (DSLAM) is greater than or equal to the allowable minimum capacity, the second level (DSLAM) is increased by one ("1") in the quantity of the second level (DSLAM) to assign a plurality of second levels (DSLAM) to the selected second level (DSLAM) node. Check the output database to see if it has already been selected as a second-level (DSLAM) node in the previous year, and if it turns out to be a second-level (DSLAM) in the previous year, it is considered a currently serviceable second-level (DSLAM) node. A fifth step of establishing a second rank (DSLAM) node and increasing the second rank (DSLAM) quantity by one ("1"); And If the generated traffic is greater than zero ("0") and less than or equal to the first predetermined value (1.544 Mbps), the first communication standard (DS1 class) is greater than the first predetermined value (1.544 Mbps) and the second predetermined value (45 Mbps). Is less than the second communication standard (DS3 class) and the second predetermined value (45Mbps) is the third communication standard (STM1 class). 6 steps Design analysis method of broadband subscriber network comprising a. The method according to claim 1 or 2, The third step, The number of second levels selected by the third level selection function and the DSLAM selection function among traffic, cost and transmission information calculation functions is multiplied by the selection rate input from the execution method setting function and then rounded up. A fifth step of determining the number of third edges required in the headquarters and selecting the second level DSLAM in order of increasing traffic volume by the calculated third edge number; See if the selected second level DSLAM is the same as the nodes already selected as the third edge node in the previous year, and if any of the existing third level nodes are missing, the selected third level ( A sixth step of subtracting the traffic volume among the second levels DSLAM by the number of edges and inserting third levels selected in the previous year; If you have set the third edge reference capacity and the sum of the traffic volume of the connected second rank (DSLAM) is more than the third threshold, go to the traffic calculation module and if not, the selected third edge and connected agent A seventh step of deleting two levels (DSLAMs) and then recalculating them to connect to other preset third levels (Edge); And Limit the line class and the number of line selection methods to the lowest first communication standard (DS3 class) and the highest second communication standard (STM4 class). 2 The third communication standard (STM1 class) between the predetermined value (45 Mbps) and the third predetermined value (155 Mbps), and the second predetermined value between 155 Mbps and the fourth predetermined value (622 Mbps). Calculated according to communication standard (STM4 class), and the number of lines is 1st communication standard (DS3 class) first predetermined value (45Mbps), third communication standard (STM1 class) third predetermined value (155Mbps), second Eighth step of dividing by the 4th predetermined value (622Mbps) of communication standard (STM4 class) and calculating necessary number of lines Design analysis method of broadband subscriber network comprising a. The method according to claim 1 or 2, The third step, With the 4th core selection function of the headquarters where the 4th core does not exist, the out-of-country country which is the closest among the headquarters where the 4th core is selected is referred to by referring to the intercity distance information. The method of designing and analyzing the broadband subscriber network comprising: finding the closest fourth core selected from the suburbs, referring back to the headquarters distance information. In a computing system having a processor, Initialize the simulation device by inputting the database (average monthly data traffic volume, shortest distance information between local and overseas stations) for the design of broadband subscriber network, and set analysis performance criteria, execution method, and nodes for each level. A function of performing a setup procedure for selecting nodes for each level by receiving a selection criterion, a traffic ratio for each level, a headquarters name for which a top level core should exist, and a transmission cost; Updating the data traffic volume database initialized according to the demand information of the analysis performance criterion setting function during the input with demand data information; And Function to calculate traffic / demand distribution, transmission information, cost information according to station selection by each rank and traffic ratio by each rank A computer-readable recording medium having recorded thereon a program for realizing this.