JP2009027547A - Failure detecting method, failure detecting system and failure detecting program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide high-reliability voice communication by speedily detecting a failure of a network device by a simple configuration in order to avoid an influence upon voice communication caused by incurring the failure in the network device. <P>SOLUTION: The failure detection system which is adapted to detect a failure that occurs in each of network devices on a voice communication network comprises a call control means; a speech history information generating means for receiving speech information relating to speeches between a plurality of telephone terminals from each of network devices to which a speech channel between the plurality of telephone terminals is allocated by the call control means to generate speech history information; a speech history information holding means for holding the speech history information; and a failure detecting means which refers to the speech history information holding means to detect a failure of a network device on the basis of the speech history information for each network device to which the speech channel is allocated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a failure detection method, a failure detection system, and a failure detection program, and can be applied to, for example, a method, system, and program for detecting a failure or failure in a network device that realizes voice communication.

  In recent years, voice communication technology (so-called IP telephone) using a network communication network has been rapidly spread. The services provided by this IP phone include, for example, basic phone service (phone call incoming / outgoing service) and various additional services. The reliability required for IP phones is the conventional fixed phone (eg, analog phone, ISDN, etc.) ) Is required to be as reliable as.

  Therefore, in order to realize highly reliable voice communication, when a failure occurs in a network device on the voice communication network, it is desired to quickly detect the failure and take an appropriate and prompt response.

  Hereinafter, a failure detection method when a failure occurs in a network device (communication device) on a conventional voice communication network will be described with reference to the drawings.

  On the VoIP network shown in FIG. 2, the call control server 2 mainly performs a relay between the class 5 call control server (CA) 21 that directly accommodates the user terminal 7 and the existing public telephone network (PSTN). 4, a call control server (CA) 22, a database (DB) 23 for managing subscriber and system / node data, and a management unit 24.

  Main VoIP devices other than the call control server 2 include, for example, an access gateway (AGW) 4 that performs access control for subscribers, a signaling gateway (SGW) 5 that performs exchange of call control signals with the PSTN network, and a PSTN network. The VoIP devices 4 to 6 are generally placed under the monitoring of call control servers (CA) 21 and 22.

  Conventionally, the call control servers (CA) 21 and 22 monitor the VoIP devices 4 to 6, and even when a failure cannot be detected by the VoIP device itself, a response to the control signal from the call control servers (CA) 21 and 22 , The call control servers (CA) 21 and 22 detect a failure of the VoIP devices 4 to 6.

  For example, in FIG. 3, it is assumed that a failure occurs in the signaling gateway (SGW) 5 and the failure cannot be detected in the signaling gateway (SGW) 5 itself.

  In this case, as a conventional failure detection method, first, as shown in FIG. 3, the call control server (CA) 22 transmits some control signal to the signaling gateway (SGW) 5 (step S1).

  On the other hand, the signaling gateway (SGW) 5 cannot respond to the control signal from the call control server (CA) 22 because a failure has occurred, and cannot return a response signal (step S2). ).

  Then, the call control server (CA) 22 determines the failure of the signaling gateway (SGW) 5 by not being able to confirm the reply of the response signal from the signaling gateway (SGW) 5 within a predetermined time, and maintains that fact. The terminal 9 is notified (step S3). Thereby, the maintenance person recognizes the failure of the signaling gateway (SGW) 5 and takes a predetermined measure.

  Japanese Patent Application Laid-Open No. 2004-228561 describes a technique related to detecting a failure of a network device on a conventional network and countermeasures for the failure described above.

Japanese Patent Laid-Open No. 2003-110741

  As described above, according to a failure detection method for a network device (so-called VoIP device) on a conventional voice communication network, the call control servers (CA) 21 and 22 return control signals from the VoIP devices 4 to 6 and the like. The failure of the VoIP devices 4 to 6 can be detected based on the above.

  However, unlike the control signal, the audio signal (RTP) between the user terminal 7 and the user terminal 8 is exchanged without passing through the call control servers (CA) 21 and 22, and as shown in FIG. This is performed in the route of terminal 7 ⇔ AGW 4 ⇔ MG 6 ⇔ PSTN ⇔ user terminal 8.

  Therefore, when a failure that cannot be recognized by the VoIP device itself occurs, for example, a voice call failure such as inability to hear a one-way voice may occur, and a problem may arise in that highly reliable voice communication cannot be provided.

  Therefore, in order to avoid the above problems from affecting voice communication over a long period of time, it is possible to quickly detect a failure of a network device on the network with a simple configuration, and to perform highly reliable voice communication. There is a need for a failure detection method, a failure detection system, and a failure detection program.

  In order to solve this problem, a failure detection system according to a first aspect of the present invention is a failure detection system that detects a failure that occurs in each network device in a voice communication network that includes a plurality of network devices. 1) Call control means for performing call control between a plurality of telephone terminals; and (2) Calls between a plurality of telephone terminals from each of network devices to which call lines between the plurality of telephone terminals are assigned by the call control means. Call history information generating means for receiving such call information and generating call history information based on the call information; (3) call history information holding means for holding call history information received from the call history information generating means; (4 ) Refer to the call history information holding means, and based on the call history information for each network device to which the call line is allocated, Characterized in that it comprises a fault detection means for output.

  A failure detection method according to a second aspect of the present invention is a failure detection method for detecting a failure that occurs in each network device in a voice communication network configured by including a plurality of network devices. A call control step for performing call control between the telephone terminals, and (2) a call history information generating means, from each of the network devices to which the call lines between the plurality of telephone terminals are assigned by the call control means. A call history information generating step of receiving call information related to a call between the two and generating call history information based on the call information; and (3) the call history information holding means receives the call history information received from the call history information generating means. A call history information holding step to hold, and (4) the failure detection means refers to the call history information holding means, and performs call execution for each network device to which a call line is assigned. Based on the information, characterized in that it comprises a failure detecting step of detecting a failure in the network device.

  According to a third aspect of the present invention, there is provided a failure detection program for detecting a failure occurring in each network device in a voice communication network configured by including a plurality of network devices. Call control means for performing call control between terminals, (2) receiving call information related to a call between a plurality of telephone terminals from each of network devices to which a call line between the plurality of telephone terminals is assigned by the call control means; Call history information generating means for generating call history information based on the call information, (3) Call history information holding means for holding call history information received from the call history information generating means, and (4) Call history information holding means And detecting a failure of the network device based on the call history information for each network device to which the call line is assigned. Is characterized in that the function as harm detecting means.

  According to the failure detection method, the failure detection system, and the failure detection program of the present invention, in order to avoid a failure due to a failure occurring in a network device from affecting voice communication over a long period of time, A device failure can be detected quickly with a simple configuration, and highly reliable voice communication can be provided.

(A) First Embodiment Hereinafter, a first embodiment of a failure detection method, a failure detection system, and a failure detection program according to the present invention will be described with reference to the drawings.

  In the first embodiment, a case where the present invention is applied to a call control server that performs call control on a network to which an IP network and an existing public telephone network (PSTN) can be connected will be described as an example.

(A-1) Configuration of First Embodiment FIG. 1 is a configuration diagram showing a configuration of a voice communication network according to the first embodiment. In FIG. 1, a voice communication network 10 according to the first embodiment is a network in which an IP network (hereinafter also referred to as a VoIP network) and a PSTN can be connected.

  The voice communication network 10 of the first embodiment includes a call control server 1, an access gateway (AGW) 4, a signaling gateway (SGW) 5, a media gateway (MG) 6, and a user terminal 7 on a VoIP network. Have at least. Further, the network 10 includes at least a user terminal 8 on the PSTN.

  The call control server 1 performs call control between user terminals 7 and 8 that desire voice communication. The call control server 1 mainly includes at least a call control server (CA) 11, a call control server (CA) 12, a database (DB) 13, and a management unit 14 as function components of call control. In addition, the call control server 1 can distribute and arrange these function components 11 to 14 on the VoIP network as long as the function components 11 to 14 can cooperate with each other. FIG. 1 shows a case where these function components 11 to 14 are distributed on the VoIP network.

  The call control servers (CA) 11 and 12 are call agents that realize a soft switch. For example, correspondence processing between a telephone number and an IP address, cooperation control processing between an IP network and a PSTN, and control such as call and signaling Processing is performed.

  The call control server (CA) 11 is a class 5 call control server (CA) that directly accommodates user terminals 7 on the VoIP network. The call control server (CA) 12 is a class 4 call control server (CA) that performs relay processing with the PSTN.

  The database 13 is a database that stores subscriber information, system / node data, and the like, and the management unit 14 manages information stored in the database 13.

  The access gateway (AGW) 4 controls access of the subscriber (user terminal 7) to the IP network.

  The signaling gateway (SGW) 5 performs conversion processing between signaling information in the PSTN and a call control signal on the IP network, and exchanges a call control signal between the IP network and the PSTN.

  The media gateway (MG) 6 exchanges voice signals (RTP) between the IP network and the PSTN. That is, the media gateway (MG) 6 packetizes the voice signal from the PSTN and sends it to the IP network, and sends the packet from the IP network as a voice signal to the PSTN.

  The user terminals 7 and 8 are telephone terminals capable of voice communication. The user terminal 8 corresponds to a general telephone. The user terminal 7 includes, for example, an IP telephone terminal (concept including a portable terminal) and an information processing apparatus (for example, a soft phone) such as a personal computer that can execute voice communication software.

  Next, the details of the functional configuration of the call control server 1 of the first embodiment will be described with reference to FIG. FIG. 5 is a functional configuration diagram showing a functional configuration of the call control server 1.

  5, the call control server 1 includes the call control server (CA) 11, the call control server (CA) 12, the database (DB) 13, and the management unit 14, as described above.

  The call control servers (CA) 11 and 12 have call line assignment units 112 and 121. The call line assignment units 112 and 121 determine a gateway for making a call between the user terminal 7 and the user terminal 8, assign a communication line to the gateway, and manage this. When a plurality of calls are established, the call control servers (CA) 11 and 12 allocate and manage communication lines for the gateways of the respective calls.

  The call control servers (CA) 11 and 12 generate call history information such as a call start time and a call end time for each call line after each call is established. Then, the call control servers (CA) 11 and 12 give the call history information for each call line to the database 13 for storage.

  The management unit 14 obtains predetermined call history information 131 based on the call history information from the call control servers (CA) 11 and 12 stored in the database 13 and stores the call history information 131. .

  The management unit 14 also analyzes the presence / absence of a failure in a communication device (for example, the media gateway (MG) 6) on the IP network based on the call history information 131 stored in the database 13. 141. Furthermore, when the call history information analysis unit 141 obtains an analysis result indicating that a communication device failure has occurred, the management unit 14 includes a notification unit 142 that notifies the maintenance terminal 9 to that effect.

  Here, the call history information 131 is information indicating a ratio of a short-time call volume (for example, a call volume having a call time of 60 seconds or less) for each call line. The unit time for defining the short-time call volume can be arbitrarily set.

  FIG. 6 illustrates the call history information 131. In FIG. 6, the horizontal axis indicates the communication device serial number, and the vertical axis indicates the ratio of short-term call volume.

  As shown in FIG. 6, the communication device that is operating normally has a short-time call rate of about 40% to 50%, whereas the communication device in which a failure has occurred (for example, the communication device with the serial number “1344”). ) Shows that the ratio of short-term call volume is a high value exceeding 90%.

  Therefore, the call history information analysis unit 141 of the management unit 14 according to the first embodiment is based on the call history information 131 indicating the ratio of the short-time call volume of each call line, and when the short-time call volume is greater than or equal to the threshold, It is determined that some kind of failure that cannot be detected by the communication device itself has occurred, and when the short-term call volume is less than the threshold value, it is determined to be normal.

  As described above, the reason for detecting the failure of the communication device based on the ratio of the short-term call volume is, for example, that some failure that cannot be detected by the communication device itself occurs, for example, an audio signal such that one-way sound cannot be heard. This is because, when a problem occurs, the user does not make a call for a long time and repeats the call, so that a large number of calls with a short call time occur.

  In the first embodiment, when this characteristic is used and the call history information analysis unit 141 detects a short-term call volume equal to or greater than a threshold, it is assumed that some kind of failure that cannot be detected by the communication device itself has occurred.

(A-2) Operation of First Embodiment Next, a failure detection method by the call control server 1 of the first embodiment will be described with reference to the drawings.

  FIG. 7 shows the overall flow of the failure detection method of the first embodiment. In FIG. 7, a case where a call is made between the user terminal 7 on the IP network and the user terminal 8 on the PSTN will be described as an example.

  First, when a call request control signal is given to the call control server 1 from the user terminal 7 or the user terminal 8, the call control server 1 calls the call between the user terminal 7 and the user terminal 8 according to a predetermined call control method. Establish.

  At this time, the call control server (CA) 11 exchanges call control signals related to call control processing with the user terminal 7 via the access gateway (AGW) 4. Further, the call control server (CA) 12 exchanges call control signals related to call control processing with the user terminal 8 via the signaling gateway (SGW) 5.

  The call control method performed by the call control server 1 is not particularly limited and can be widely applied. For example, a method defined in SIP (Session Initiation Protocol) or the like can be applied.

  The call control server (CA) 12 assigns a communication line to the media gateway (MG) 6-1 in order to exchange voice signals between the user terminal 7 and the user terminal 8 (step S11). As a result, the user terminal 7 and the user terminal 8 exchange audio signals through the route of the user terminal 7 ⇔ access gateway (AGW) 4 ⇔ media gateway (MG) 6-1 ⇔ PSTN ⇔ user terminal 8.

  At this time, in the call control server (CA) 12, call history information including a call start time and a call end time is generated by the call history information generation unit 121, and the generated communication history information is given to the database 13 and stored. (Step S12).

  At this time, in the management unit 14, predetermined call history information 131 based on the call history information from the call control servers (CA) 11 and 12 stored in the database 13 is constantly or periodically (that is, in FIG. 6). Information indicating the ratio of the short-time call volume of each communication device illustrated) is generated, and the call history information 131 is used to determine whether or not a failure that cannot be detected by the communication device itself has occurred. .

  FIG. 8 is a flowchart showing the operation of communication device failure detection processing in the management unit 14 and the database 13. The flow shown in FIG. 8 is repeated periodically.

  First, the call history information analysis unit 141 of the management unit 14 acquires the call history information of each communication device stored in the database 13 from the database 13 (step S21), and the short-time call whose call time is a predetermined time or less. The amount is obtained for each communication device (step S22).

  Here, the method for obtaining the call volume is not particularly limited, and existing methods can be widely applied. For example, the traffic volume is obtained by multiplying the average value (average hold time) of the call time (hold time) of each call by the number of calls based on the call history information at the call start time and call end time. Then, the call volume can be obtained by measuring the traffic volume per predetermined time. The short-time call volume can be obtained by a method similar to the above-described call volume calculation method when the call time (holding time) is a predetermined time or less.

  Then, when the short-term call volume is obtained by the call history information analysis unit 141 of the predetermined-time management unit 14, as shown in FIG. 6, the ratio of the short-time call volume to the communication time call within the predetermined time is shown for each communication. Obtained for each device (step S23), and compares the threshold value set in advance with the result of the short-term call volume ratio of each communication device, and analyzes the result of the short-time call volume ratio of each communication device (step S23). S24).

  When the ratio of the short-term call volume is equal to or greater than the threshold, the call history information analysis unit 141 determines that the voice function unit of the communication device is faulty (step S25), and the notification unit 142 Notifies the maintenance terminal 9 to that effect (step S26).

  On the other hand, when the ratio of the short-term call volume is less than the threshold, the call history information analysis unit 141 determines that no abnormality has occurred in the voice function unit of the communication device (step S27), and ends the process. .

  Here, a plurality of threshold values having different values may be set as the preset threshold values. Thus, depending on the ratio of short-term call volume, for example, when a low threshold value is exceeded, a preliminary warning failure notification is performed, and when a large threshold value is exceeded, this warning failure notification is performed. Step-by-step failure notification can be performed. As a result, quicker measures can be taken.

  As described above, the management unit 14 and the database 13 can detect the presence or absence of a failure in each communication device by using the communication history information.

  For example, in FIG. 7, it is assumed that a failure has occurred in the audio function unit of the media gateway (MG) 6-1 that exchanges audio signals between the user terminal 7 and the user terminal 8. Due to this failure, voice communication from the user terminal 7 to the PSTN side (user terminal 8 side) is possible, but voice communication from the user terminal 8 to the VoIP network side (user terminal 7 side) is interrupted. Shall.

  Then, due to a problem between the user terminal 7 and the user terminal 8, the user repeats the call many times, so that a large number of calls with a short talk time can occur.

  In this case, when the management unit 14 and the database 13 periodically perform the above-described failure detection process and detect that the short-term call rate of the media gateway (MG) 6-1 is equal to or greater than a threshold, 14 notification unit 142 notifies maintenance terminal 9 that a failure has occurred in the voice function unit of media gateway (MG) 6-1 (step S13).

  Here, the notification to the maintenance terminal 9 includes information including at least failure detection information indicating failure detection of the communication device by the failure detection processing of the first embodiment and identification information of the communication device in which the failure has occurred. Notice. As a result, the maintenance terminal 9 can be notified of the failure detected by the communication device itself and the failure that cannot be detected by the communication device itself as in the first embodiment.

  When the maintenance terminal 9 is notified of the failure occurrence of the media gateway (MG) 6-1, the maintenance person recognizes the failure and calls the call control server (CA) that has assigned a telephone line to the media gateway (MG) 6-1. ) 12, the maintenance terminal 9 notifies that a failure has occurred (step S14).

  When the call control server (CA) 12 receives a notification of the occurrence of a failure from the maintenance terminal 9, the call control server (CA) 12 recognizes the failure of the media gateway (MG) 6-1 and newly replaces the media gateway (MG) 6-1. A telephone line is assigned to the gateway (MG) 6-2, and the media gateway (MG) 6-2 is switched as an alternative device (step S15).

  By doing in this way, since the media gateway (MG) 6-2 connected to the PSTN side can be newly set within a short time from the occurrence of the failure, the call between the user terminal 7 and the user terminal 8 can be performed quickly. Can be normalized.

  Further, the media gateway (MG) 6-1 in which a failure has occurred can be maintained after switching to the new media gateway (MG) 6-2.

(A-3) Effect of First Embodiment As described above, according to the first embodiment, even if a failure occurs due to a failure that the communication device itself on the network cannot detect, the call control server Highly reliable voice communication can be provided by quickly detecting the failure of the communication device using the call history information that 1 always acquires.

  In general, a voice call test is performed by actually making a call by hand and confirming the voice of the other party, but it is unrealistic to repeatedly detect the call to a large number of devices and detect a failure of a communication device on the VoIP network. Is. On the other hand, according to the first embodiment, it is possible to detect a failure of a communication device on the VoIP network without performing a conventional voice call test by hand.

  Furthermore, the collection of call history information is an indispensable function for the call control server 1, and a failure detection function can be realized without incorporating a new function into the call control server 1.

  Furthermore, according to the first embodiment, since the processing from the failure detection to the blockage of the failure generating device can be performed automatically, the service recovery time can be shortened compared to the conventional case.

(B) Second Embodiment Next, a second embodiment of the failure detection method, failure detection system, and failure detection program of the present invention will be described.

  In the first embodiment, the failure detection in the media gateway (MG) connected to the PSTN side has been described. In the second embodiment, a failure in the access gateway (AGW) on the VoIP network is detected.

  Since the configuration of the second embodiment can use the configuration diagrams shown in FIGS. 1 and 5, the description of the configuration of the second embodiment is omitted. Further, since the flow shown in FIG. 8 can also be applied to the failure detection processing using the call history information by the management unit 14 and the database 13, the description of the operation of the second embodiment is also omitted.

  According to the second embodiment, by using the failure detection method described in the first embodiment, the occurrence of a failure in the access gateway (AGW) can also be detected, and the failed access gateway (AGW) is blocked. can do. Thereby, an effect similar to that of the first embodiment can be obtained.

(C) Other Embodiments (C-1) In the first and second embodiments, the failure of the entire communication device (media gateway, access gateway, etc.) on the VoIP network is detected. The failure resource may be narrowed down and the failure location inside the communication device may be specified.

  For example, it is assumed that six audio lines are controlled by one LSI in a certain media gateware (MG). In this case, the media gateware (MG) transmits call history information of a call (six voices) controlled by each LSI to the call control server (CA). Then, the call control server (CA) analyzes the call time (short-time call volume) in units of 6 voices for the call history of one media gateway, and thereby the LSI in the media gateway (MG) apparatus has failed. Can be identified and detected.

(C-2) The various processes of the call control server 1, AGW 4, SGW 5, MG 6 and maintenance terminal 9 described in the first and second embodiments are software processes in which hardware is realized by executing a software program. Is to be made. If possible, it may be realized by hardware configured by an electronic circuit or the like.

(C-3) In the first and second embodiments, the call control server (CA) 11, the call control server (CA) 12, the AGW 4, the SGW 5, and the MG 6 are each distributed and arranged if the cooperation processing is possible. It is also possible to arrange a plurality of functional configurations in a form provided in a physical device or device by any combination thereof.

(C-4) In the first and second embodiments, the case where voice communication is performed between the user terminal connected to the VoIP network and the user terminal connected to the PSTN has been described. According to the second embodiment, For example, the present invention can also be applied to voice communication at least between user terminals connected to the VoIP network.

(C-5) In the first and second embodiments, after the failure is detected, when the call control server (CA) allocates a telephone line to another communication device and performs alternative operation, the call control server (CA) In the above description, the instruction is received from the maintenance terminal. However, the communication line may be switched by receiving a direct notification from the notification unit of the management unit.

It is a block diagram which shows the structure of the voice communication network of 1st Embodiment. It is a block diagram which shows the structure of the conventional voice communication network. It is explanatory drawing explaining the failure detection system in the conventional voice communication network. It is explanatory drawing explaining the subject of the failure detection system in the conventional voice communication network. It is a functional block diagram explaining the functional structure of the call control server of 1st Embodiment. It is a figure which shows the telephone call history information which is the ratio of the short time call volume for each communication apparatus of 1st Embodiment. It is explanatory drawing explaining the flow of the failure generation process of 1st Embodiment. It is a flowchart which shows the failure generation process of 1st Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Call control server, 11 ... Class 5 call control server (CA), 12 ... Class 4 call control server (CA), 13 ... DB (database), 4 ... AGW (access gateway), 5 ... SGW (signaling) Gateway), 6 ... MG (media gateway), 7 and 8 ... user terminal, 10 ... voice communication network.

Claims (6)

In a voice communication network configured to have a plurality of network devices, in a fault detection system for detecting faults occurring in each of the network devices,
Call control means for controlling calls between a plurality of telephone terminals;
Call information related to a call between the plurality of telephone terminals is received from each of the network devices to which a call line between the plurality of telephone terminals is assigned by the call control means, and call history information is obtained based on the call information. Call history information generating means for generating;
Call history information holding means for holding the call history information received from the call history information generating means;
A failure detection means for detecting a failure of the network device based on the call history information for each of the network devices to which the call line is assigned, with reference to the call history information holding means. Fault detection system.   Based on the call history information, the failure detection means obtains short-term call volume ratio information within a predetermined time in each network device to which the call line is allocated, and The failure detection system according to claim 1, wherein a failure of the network device is determined based on a comparison result between the ratio information and one or more threshold values.   The failure detection means analyzes a short-time call volume within a predetermined time in each network device in units of a predetermined voice call, and detects a failure in a voice communication control chip mounted in each network device. The fault detection system according to claim 1, wherein:   When the failure detecting unit detects a failure of the network device, the call control unit newly allocates a communication line between the plurality of telephone terminals to another network device and restores the provision of the voice communication service. The failure detection system according to any one of claims 1 to 3, wherein In a failure detection method for detecting a failure that occurs in each network device in a voice communication network configured to have a plurality of network devices,
A call control step in which call control means performs call control between a plurality of telephone terminals;
Call history information generating means receives call information related to a call between the plurality of telephone terminals from each of the network devices to which call lines between the plurality of telephone terminals are assigned by the call control means, and the call information A call history information generating step for generating call history information based on
A call history information holding step in which the call history information holding means holds the call history information received from the call history information generating means;
A failure detecting step of detecting a failure of the network device on the basis of the call history information for each of the network devices to which the call line is assigned with reference to the call history information holding unit; A fault detection method characterized by the above. In a failure detection program for detecting a failure that occurs in each network device in a voice communication network configured to have a plurality of network devices,
On the computer,
Call control means for controlling calls between a plurality of telephone terminals;
Call information related to a call between the plurality of telephone terminals is received from each of the network devices to which a call line between the plurality of telephone terminals is assigned by the call control means, and call history information is obtained based on the call information. Call history information generating means for generating,
Call history information holding means for holding the call history information received from the call history information generating means;
Referring to the call history information holding means, and functioning as a failure detection means for detecting a failure of the network device based on the call history information for each network device to which the call line is assigned. Fault detection program.

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