JP2007129656A - Private branch exchange - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly reliable VoIP-compliant IP-PBX system by not using special equipments for monitoring but using only standard equipments providing VoIP without imposing the load of cost and maintenance work on a user and a maintenance person. <P>SOLUTION: A star monitoring with a main body controller A1 as a center and an end-to-end monitoring considered with terminals C1-C7 (the users who use the terminals) as a center are simultaneously performed in the network of respective sections among the main body controller constituting the IP-PBX, terminal controllers B1-B6, and the terminals. Then voice quality of a call is periodically collected only with the use of the standard equipment constituting the IP-PBX. When a detour destination is selected, the unused terminal at a base being the same as that of the terminal during calling is retrieved from the database of the main body controller. The voice quality between the terminal controller and the terminal is previously confirmed. When there is no problem in the voice quality of a detour route, detouring is performed in the network. When the problem still exists, routing is performed through a public network. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  According to the present invention, it is possible to use standard equipment to understand various failures of a private branch exchange, in particular, an IP network used for providing VoIP, and to select a detour when a failure occurs. It relates to private branch exchanges.

  Patent Document 1 describes a technology for positioning a GW device as the end of a network and monitoring VoIP voice quality between GW devices (end-to-end) in an environment where an IP phone is used using an IP network. Has been. Specifically, a threshold value such as a delay of a voice packet positioned as a failure is set in advance in each GW device, and when the threshold value is exceeded, a SNMP (Simple Network Management Protocol) manager is notified, and the SNMP manager Recognizes in which section of the network the voice quality is degraded.

  Further, as another operation, it is possible to periodically collect information on voice quality from the SNMP manager by polling processing and recognize the state of voice packets passing through the GW device in real time. Create an IP network topology from the information obtained by this operation, change the routing information of the IP network (bypass in the IP network), increase the transmission speed by changing the bandwidth (bandwidth control), Regulation (call control) is performed. Also, by installing another measuring device and analysis device under each GW device, voice packets can be generated on a trial basis and end-to-end voice quality in each section can be investigated. Furthermore, in accordance with the quality of the network to which the GW device is connected, a strict value can be set individually for the high quality network and a loose value can be set individually for the low quality network.

  On the other hand, in the Internet telephone system and the detour generation method described in Patent Document 2, when a failure of a WAN line is detected in an IP network, the information is collected in a network monitoring server, and the call is based on the information. By using the control management server and the GW device, the IP telephone call can be diverted to the public network by PPP (point-to-point protocol) connection, and the network management server can be relayed to connect the call. PPP is used by connecting a plurality of calls to a single public line to effectively use a public line for a detour, and by voice compression, one public line is 64 Kbps. , Up to 8 Kbps / G. 729 can be used to connect eight calls.

  The system is composed of a single network management server, a plurality of call control management servers, GW devices, and IP telephone terminals used by users, and the call control management servers are distributed and installed in each network. The network management server includes an IP network I / F and a public network I / F, and each GW apparatus has an IP network I / F and a public network I / F.

JP 2002-271392 A JP 2003-219027 A

  However, the technique described in Patent Document 1 requires a dedicated server for monitoring the IP network, and in order to measure voice quality between end-to-end, a dedicated measuring device is provided for each endpoint (all It is necessary to install the equipment under the control of the GW equipment, and the equipment for analysis must be installed. Therefore, when monitoring the IP network, the burden on the user and maintenance personnel is low in terms of cost and equipment maintenance work. There was a problem of being big.

  Also, if there is a problem with the state of the generated call, it can be bypassed, but it has not been verified beforehand whether there is a problem. Of course, it can be assumed that a voice quality measurement-specific measuring instrument is installed at each endpoint, an analysis device is installed, and the functions described in this document can be linked in advance. However, it is necessary to always connect these test devices, and there is a problem that a considerable burden is generated in terms of cost and maintenance work.

  Further, since a failure between the IP phone and the GW device, a delay in the GW device, a failure of the GW device itself, and the like are not detected, the GW device detects a decrease in voice quality felt by the end user using the IP phone. There was a problem that may not have.

  In addition, the IP network is detoured depending on the detected voice quality degradation point, but if a failure of the GW device itself or a failure of the backbone network occurs, the IP phone cannot be used. In the technology, depending on the type of failure that occurred, it could not be bypassed, and it could not be said to be truly reliable.

  On the other hand, in the technique described in Patent Document 2, it is necessary to install a call control management server for the GW device that monitors the state of the WAN line, and a considerable number of units are required to construct a large-scale VoIP network. A server is required, and there is a problem that the burden on the user and maintenance personnel is heavy in terms of cost and equipment maintenance work.

  In addition, since the public line is effectively used, the public line is centrally accommodated in the GW device, and when the GW device itself has a failure, both the IP network and the public network are used. There is a problem that IP telephone cannot be used and various obstacles cannot be dealt with.

  In addition, it is necessary to monitor the faulty WAN line of the IP network to determine execution of detours, and not detect processing capacity over in the GW device due to compression / combining or traffic, delay between the GW device and the IP phone, etc. Also, it is considered that the criteria that the GW device detects as a failure of the WAN line cannot detect the cause of voice packet quality degradation (a slight delay that causes echo noise), so the end user using the IP phone feels There has been a problem that the network monitoring server may not be able to detect a drop in voice quality.

  Therefore, the present invention uses only standard equipment that provides VoIP, does not give users and maintenance personnel the cost and burden of maintenance work, does not require monitoring equipment, clients, and servers. An object of the present invention is to provide a highly reliable VoIP compatible IP-PBX system.

  In addition, the present invention treats an IP phone as the end of a voice service so as not to cause a difference in recognition between the failure detection function and the end user using the IP phone, and monitors VoIP-compatible IP- An object of the present invention is to provide a PBX system, and further, does not require a dedicated device for monitoring voice quality, and does not waste a limited IP address by a monitoring device.

  In order to achieve the above object, the present invention is a private branch exchange that is connected to a network under an Internet protocol environment and performs call connection processing between terminals, and performs processing including call control and monitoring of peripheral devices, A main body control device that is made redundant in an active system and a standby system, and a main body control device that is connected to the main body control device and the terminal and performs processing including conversion of voice packets, the main body control device, A health check packet is transmitted to the terminal control device, and when there is no response from the terminal control device to the health check packet, it is determined as abnormal, and when there is a response, the main body control device and the terminal control device are determined. A normal number between the active main body control device and the terminal control device, and the standby main body control device and the terminal control device. Comparing the normal number between, characterized in that to operate the normally large number of systems to a new operating system.

  According to the present invention, when a failure is detected between the terminal controller and the terminal controller that performs processing including conversion of voice packets, the private branch exchange is switched to the active system having a large number of normals. Therefore, it is possible to provide a highly reliable private branch exchange and a VoIP compatible IP-PBX system.

  In the private branch exchange, the main body control device transmits a health check packet to the terminal, determines that there is no response to the health check packet from the terminal, and determines that the number of abnormalities exceeds a predetermined number. Can disconnect the terminal.

  In the private branch exchange, the main body control device notifies the terminal control device of the address of the terminal, and the terminal control device notifies the terminal of the health based on an instruction from the main body control device. The main body control device periodically transmits a health check packet to the terminal control device to collect the terminal information, and the number of times that the state of the terminal is determined to be abnormal is predetermined. When the number of times is exceeded, the terminal can be disconnected.

  Further, in the private branch exchange, when two of the terminals are in a call state, the voice packets transmitted / received by both terminals are counted, and the main body controller periodically counts the count values of both terminals. Can be monitored and the voice quality of the terminal can be monitored, without using a monitoring device, client and server, and using only a standard device that provides VoIP, a reliable VoIP A corresponding IP-PBX system can be provided.

  Further, in the private branch exchange, when two of the terminals are in a call state and the main body control device monitors the voice quality of the terminals and determines that the voice quality is degraded, the terminal And two uncommitted terminals installed at the same base, respectively, and search for and select a terminal control device in which a health check is normally performed, and the selected terminal and the selected terminal. When a test call is performed between the terminal control devices, and the test call is normal, the unspeaked terminal is selected instead of the two terminals whose voice quality is deteriorated. By connecting to the terminal control device and turning back between the terminal control devices, the detour processing in the network can be performed. This eliminates the need for a dedicated device to monitor the voice quality, collects all the dissatisfaction with the voice quality felt by the user, and always provides high voice quality by processing such as detours, and has a finite IP The address is not wasted on the monitoring device. In addition, since only the standard devices that make up the IP-PBX are used to check the detour route in advance, the sound quality of the route to be selected during detouring can be checked in advance without using a dedicated measurement device. Is possible.

  Further, in the private branch exchange, a test call is made to an uncalled terminal installed at the same site, and if the test call is not normal, an uncalled terminal is further passed through the public network. The detouring process can be performed by making a test call.

  As described above, according to the present invention, a standard device that provides a VoIP without using a monitoring device, a client, or a server without incurring cost and a burden of maintenance work to a user or maintenance personnel. It is possible to provide a highly reliable VoIP compatible IP-PBX system using only the network.

  FIG. 1 shows a system including an embodiment of a private branch exchange (hereinafter referred to as “IP-PBX”) according to the present invention. This IP-PBX system includes a main CPU that is made redundant with an active system and a standby system. (Main body control device, A1), IP terminal control devices (B1 to B6), network devices (D1 to D10) constituting the IP network, and IP terminals (C1 to C4: Phone, C5 to C7: TRK (Trunk)).

  An IP terminal having a TRK I / F is positioned as a GW (gateway) that connects an IP network and a public network. An IP terminal having a telephone I / F is positioned as a telephone that can communicate with an IP network.

  As shown in FIG. 2, the main body CPU (A1) made redundant with the active system and the standby system has a CPU (a1), a storage medium (a2), a memory (a3), and a TDM (Time Division Multiplex: The same dedicated hardware (a4), basic OS unit (a5), call processing unit (a6) as used in the conventional PBX for providing time division multiplexing (I / F), and monitoring General extension, leased line, and public line connected to the processing unit (a7), the external device management unit (a8) that manages the I / F of the charging device / maintenance terminal, and the main body CPU (A1) with dedicated hardware The circuit management unit (a9) manages I / Fs of various circuits such as lines, and the transmission / reception processing unit (a10) communicates with peripheral devices. Of these, the detailed configuration of the same dedicated hardware as that of the conventional PBX is not directly related to the present invention, and the description thereof will be omitted.

  As shown in FIG. 3, the IP terminal control devices B1 to B6 include a CPU (b1), a storage medium (b2), a memory (b3), a basic OS unit (b4), and a main body CPU (A1). A main body CPU communication unit (b5) that manages the I / F, an IP terminal management unit (b6) that controls the IP terminal, and a voice management unit (TDM and IP packet voice conversion and voice compression / decompression processing) b7) and a transmission / reception processing unit (b8) that communicates with the IP terminal / main body CPU (A1).

  As shown in FIG. 4, the IP terminals C1 to C7 include a CPU (c1), a storage medium (c2), a memory (c3), and dedicated hardware (c4) for performing I / F of the telephone / TRK. And an IP terminal control unit communication unit (c6) that manages the I / F between the basic OS unit (c5) and the IP terminal control unit, and a voice that performs IP packet and TDM voice conversion and voice compression / decompression processing It comprises a management unit (c7), a transmission / reception processing unit (c8) that communicates with the IP terminal control device / main body CPU (A1), and a module (c9) that performs the basic functions of the telephone / TRK. Note that the configuration of dedicated software and hardware for operating as a general telephone is not directly related to the present invention, and thus the description thereof is omitted.

  Next, refer to the explanatory diagrams of FIGS. 5 to 6, the flowcharts of FIGS. 7 to 12, the packet formats used for the monitoring of FIGS. 13 to 14, and the database configuration diagrams of FIGS. The operation of the IP-PBX system having the above configuration will be described.

  First, the operation of the network monitoring process of the present invention will be described with reference to FIGS. 5, 7 to 10, the packet formats of FIGS. 13 to 14, and the databases of FIGS. 15 to 19.

  In the IP-PBX system, the IP network, and the public network constructed with the configuration of FIG. 5, the main system CPU (A1) of the active / standby system is connected to the IP terminal control devices B1 to B6 and the IP terminals C1 to C7. Health check is performed. This health check is expressed as a “star-type” health check in the present invention because the health check is performed from the IP-PBX installed in the center to the peripheral device (IP terminal control device, IP terminal). .

  First, the health check process between the main body CPU (A1) and the IP terminal control devices B1 to B6 will be described with reference to FIG.

  The registration information of the IP terminal control device is read from the database, a health check packet is created and transmitted to the IP terminal control device (S11). The database referred to at this time is an IP address in the database of FIG. The format of the packet to be transmitted is shown in FIG.

  Among these, the data number of the data requested for the health check is set in the request data type in the direction from the main body CPU to the IP terminal control device (left side). In response to the request, the IP terminal device side creates reply data. The format of FIG. 13 is described in a state where all data is requested. Similarly, in the request data type (terminal data), data necessary for performing an IP terminal health check from the IP terminal control device is set.

  For the packet (right side) returned from the IP terminal control device to the main body CPU, the number of times and time related to transmission / reception in each section are set. Also, data related to warning sound transmission is set. This warning sound means that when the IP terminal has not received a voice packet (RTP) for a certain period of time (set at the time of initial data registration of the IP terminal) (the receiving side is silent), There is a process of making a warning sound to the public network side, and the IP terminal control device collects from the IP terminal whether or not the execution has been performed and operates to notify the main body CPU of the result. Since this warning sound is not directly related to the operation of the present invention, detailed description thereof is omitted.

  As a result of the transmission of the health check packet, it is confirmed whether there is a reply (S12). If there is a normal reply, the result is stored in the database of FIG. 17 and the next apparatus is checked (S13). If there is no reply, the number of abnormalities is confirmed (S14). If the set value recognized as a failure recorded in the database in FIG. 15 is not reached, the result (counting up the number of abnormalities) is displayed. The data is stored in the database 17 and the next apparatus is checked (S13).

  If the number of abnormalities exceeds the set value, the result (abnormality) is stored in the database of FIG. 17, and the number of normal devices of the main CPU operating system and the standby system is compared (S15 and S16). ). As a result, when the number of the current operating system is smaller (the number of the standby system is larger), the operation system of the main body CPU is switched (S17). On the other hand, when there are more normal devices in the current operational system, the IP terminal control apparatus is disconnected without switching the operational system (S18).

  Next, the health check process between the main body CPU (A1) and the IP terminals C1 to C7 will be described with reference to FIG.

First, the registration information of the IP terminal is read from the database, and the health check packet (P
ING) and send it to the IP terminal (S21). The database referred to at this time is an IP address in the database of FIG. As a result of the transmission, if there is a normal response, the result is stored in the database of FIG. 18, and the next terminal is checked (S23). If there is no response, the number of abnormalities is confirmed (S24). If the set value recognized as a failure recorded in the database of FIG. 16 is not reached, the result (counting up the number of abnormalities) is displayed. 18 is stored in the database and the next terminal is checked (S23). If the number of abnormalities exceeds the set value, the result (abnormality) is stored in the database of FIG. 18, and the IP terminal is disconnected (S25).

  Next, the health check process between the IP terminal control devices B1 to B6 and the IP terminals C1 to C7 will be described with reference to FIG.

  First, the main body CPU notifies the IP terminal control device of the IP address of the IP terminal. The I / F used for the notification uses a health check packet between the main body CPU and the IP terminal control device. The packet format is as shown in FIG. Among them, the IP address of the terminal is included in the request data (terminal data type) in the direction of the main body CPU → IP terminal control device (left side). The IP terminal control device transmits a PING to the IP terminal based on an instruction from the main body CPU (S32). The main body CPU periodically collects information on the IP terminal by using health check packets to the IP terminal control device (S33).

  If there is no reply from the IP terminal control device as a result of the above operation, the health check NG process of the IP terminal control device (to S12 in FIG. 7) is performed (S35). If there is a reply, the contents of the packet are confirmed (S36 / S37). If the state of the IP terminal is normal, the result (normal) is stored in the database of FIG. 18, and the process proceeds to the next process (S38). ). If the result is abnormal, the number of abnormalities is confirmed (S39). If the result is less than the set value recognized as a failure recorded in the database of FIG. 16, the result (counting up the number of abnormalities) is displayed. 18 is stored in the database, and the next terminal is checked (S38). If the number of abnormalities exceeds the set value, the result (abnormality) is stored in the database of FIG. 18, and the IP terminal is disconnected (S3a).

  Next, voice quality information collection processing between IP terminals and IP terminals or between IP terminals and IP terminal control devices will be described. This monitoring process is expressed as “end-to-end type” with respect to the “star type” described above. This is because each IP terminal located closest to the user is positioned as an end point of the IP network, and each IP terminal monitors voice quality for each call. The processing sequence of this processing is as shown in FIG.

  In the same figure, an entire processing sequence when IP terminals (telephones) communicate with each other is described. The processing newly added according to the present invention is processing within a dotted line. The IP terminal (telephone) is placed in a call state by making a call from an empty (unused) state, determining the other party, and responding by the other party's IP terminal (telephone). Since the processing so far is the same as the existing technology, the description is omitted. According to the present invention, when an IP terminal enters a call state, both IP terminals start counting of transmission / reception voice packets (RTP). The main body CPU periodically collects data of the results monitored and collected by the sender and receiver IP terminals (S41 and S42).

  This process is performed separately from the health check between the main body CPU and the IP terminal. The format of the packet used in the I / F of this process is as shown in FIG. In this, the type of request data (RTP data) is set in the direction from the main body CPU to the IP terminal (left side), and the IP terminal operates to send back the request data. RTP data returned in the direction from the IP terminal to the main body CPU (right side) is described. The set data includes the start time / end time of the call (when the call has been completed), codec / payload information, and RTP transmission / reception / reception loss count. In addition, the thing exceeding the jitter buffer set to the IP terminal is treated as a loss. The main body CPU monitors the voice quality of the IP terminal using this packet (S41 to S43).

  Next, using the information obtained from the database of FIGS. 17 and 18 collected by the above processing and the association information of each IP terminal and base ID recorded in the database of FIG. A process for diverting a call that is present will be described with reference to FIGS.

  First, IP terminal A (telephone) and IP terminal B (telephone) are directly connected using an IP network to provide voice. When the voice quality information (RTP data) collected in this state was confirmed (S51 and S52), a decrease in voice quality could be confirmed. If there is no problem with the voice quality, the call state is continued as it is (S53).

  The main body CPU, which has confirmed the voice quality degradation, extracts two IP terminals installed at the same site as the IP terminal A / B from the unused ones from the database of FIG. In this description, the IP terminal C / D is extracted. Further, the main body CPU searches for and selects an IP terminal control apparatus that has a normal health check with the IP terminal C / D. The main body CPU instructs each of the IP terminal C-IP terminal control device and the IP terminal D-IP terminal control device to make a test call (voice data is transmitted as test data from both directions). . For the codec and payload used at this time, the same setting values as those used in the call between the IP terminals A / B are used (S54).

  The main body CPU collects and monitors the voice quality of the telephone call that is being tested in a sequence similar to the processing sequence of FIG. 10 (S55 to S58). The collected results are confirmed (S59 and S5a). If there is no problem, IP terminal A is connected to IP terminal C instead of IP terminal C, and IP terminal B is connected to IP terminal control apparatus instead of IP terminal D (S5c). Then, the detour processing in the IP network is performed by connecting the IP terminal control devices so as to be folded back. If a voice quality drop is confirmed even in the tested call (S5b), it is confirmed whether there is another IP terminal control device that can be connected to the IP terminal C / D (S5d / S5e). . If another IP terminal control device can search, the process returns to S51 on the previous page, and the voice quality test is performed again.

  This test is performed until a normal route is found in the IP network in this way, but it is confirmed by the voice quality monitoring process in FIG. 10 that the voice quality between the IP terminal A and the IP terminal B has been improved on the way. If it is possible, the process is automatically interrupted by the confirmation in S51. In such processing, when it is determined that it is not possible to reliably provide a voice with good voice quality through the detour route in the IP network (FIG. 12: S5f), the public network detour processing is entered as the final processing.

  This process extracts the IP terminal E (TRK) at the same site as the IP terminal A (telephone) and the IP terminal F (TRK) at the same site as the IP terminal B (telephone). Are processed so that IP terminal B and IP terminal F are connected to each other on the IP network. This process is possible because IP terminal A automatically operates to transfer to the telephone number (dial-in number) of the public network of IP terminal F and the number (additional dial-in number) of IP terminal B. It is said. Since this process is a technique that is standardly described in the conventional PBX technique, the details are omitted.

  According to the present invention for performing the above processing, when confirming a decrease in voice quality of the IP terminal used by the user, no special device is required, and no operation is performed by the user. By automatically detouring to a path that can provide stable voice quality, IP-PBX that can provide highly reliable voice with high quality is realized.

It is a block diagram of the system provided with one Embodiment of IP-PBX concerning this invention. It is a block diagram of main body CPU of IP-PBX shown in FIG. It is a block diagram of the IP terminal control apparatus of IP-PBX shown in FIG. It is a block diagram of the IP terminal of the IP-PBX system shown in FIG. It is explanatory drawing of the network monitoring by IP-PBX concerning this invention. It is explanatory drawing of the call detour by IP-PBX concerning this invention. It is a flowchart of the health check between main body CPU-IP terminal control apparatuses by IP-PBX concerning this invention. It is a flowchart of the health check between main body CPU-IP terminals by IP-PBX concerning this invention. It is a flowchart of the health check between IP terminal control apparatus and IP terminal by IP-PBX concerning this invention. It is a flowchart of the voice quality information collection of the IP terminal by IP-PBX concerning the present invention. It is a flowchart of the alternative route selection of the IP terminal by IP-PBX concerning the present invention. It is a flowchart of the alternative route selection of the IP terminal by IP-PBX concerning the present invention. It is a figure which shows the packet format used for the health check by IP-PBX concerning this invention. It is a figure which shows the packet format used for the audio | voice quality information collection by IP-PBX concerning this invention. It is a figure which shows the IP terminal control apparatus health check relevant data recorded on the database of IP-PBX concerning this invention. It is a figure which shows the IP terminal health check related data recorded on the database of IP-PBX concerning this invention. It is a figure which shows the data currently recorded on the IP terminal control apparatus management memory of IP-PBX concerning this invention. It is a figure which shows the data currently recorded on the IP terminal management memory of IP-PBX concerning this invention. It is a figure which shows base ID currently recorded on the IP terminal management memory of IP-PBX concerning this invention.

Explanation of symbols

A1 IP-PBX main unit CPU (active / spare)
B1-B6 IP terminal controller C1-C4 IP terminal (telephone)
C5 to C7 IP terminal (TRK)
C8 to C9 General telephones D1 to D10 IP network equipment E1 General telephone controller E2 Conventional I / F TRK circuit devices a1 to a10 Functional blocks b1 to b8 constituting the main body CPU Functional blocks c1 to c9 constituting the IP terminal controller Functional blocks S11 to S18 constituting the IP terminal Sequence numbers S21 to S25 of the health check process between the main body CPU and the IP terminal control device Sequence numbers S31 to S3a of the health check process between the main body CPU and the IP terminal Control unit between the IP terminal control device and the IP terminal Health check process sequence numbers S41 to S43 IP terminal voice quality information collection process sequence numbers S51 to S5f Detour path selection process sequence numbers

Claims (6)

A private branch exchange that is connected to a network under an Internet protocol environment and performs call connection processing between terminals,
A main body control device that performs processing including call control and monitoring of peripheral devices and is made redundant in the active system and the standby system;
A terminal control device that is connected to the main body control device and the terminal and performs processing including conversion of voice packets;
The main body control device transmits a health check packet to the terminal control device, determines that there is no response from the terminal control device to the health check packet, and determines that there is a response as normal, and the main body control When a failure is detected between a device and the terminal control device, the normal number between the active main body control device and the terminal control device, the standby main body control device, and the terminal control device The private branch exchange is characterized by comparing the normal number of the system with the normal number and operating the system with a large number of normal numbers as a new operational system.   The main body control device transmits a health check packet to the terminal, determines that the case where the response to the health check packet is not received from the terminal is abnormal, and if the number of abnormalities exceeds a predetermined number, The private branch exchange according to claim 1, wherein the private branch exchange is performed.   The main body control device notifies the terminal control device of the address of the terminal, the terminal control device transmits a health check packet to the terminal based on an instruction from the main body control device, and The main body control device periodically transmits a health check packet to the terminal control device to collect the terminal information, and when the number of times that the state of the terminal is determined to be abnormal is equal to or greater than a predetermined number The private branch exchange according to claim 1 or 2, wherein the terminal is disconnected.   When two of the terminals are in a call state, both terminals count the voice packets transmitted and received, and the main body controller periodically collects the count values of both terminals. The private branch exchange according to claim 1, 2 or 3, wherein voice quality is monitored.   When two terminals out of the terminals are in a call state and the main body control device monitors the voice quality of the terminals and determines that the voice quality is deteriorated, each terminal is installed at the same base as the terminal. In addition to extracting two uncalled terminals, search for and select a terminal control device that has been properly checked for health, and test each of the uncalled terminal and the selected terminal control device. If the test call is normal, instead of the two terminals whose voice quality is reduced, the unspeaked terminal is connected to the selected terminal control device, The private branch exchange according to any one of claims 1 to 4, wherein a detour process in the network is performed by turning back the terminals.   A test call is made to a terminal that is not in a call at the same location, and if the test call is not normal, a test call is further made to a terminal that is not in a call via the public network. The private branch exchange according to claim 5, wherein the detour processing is performed.

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