Telephone side gateway and public telephone relay system

Abstract

To reduce a delay generated in performing, via an IP network, relay transfer of a charging control signal to be exchanged between an exchange and a public telephone set.SOLUTION: A telephone side GW 10B includes a charging relay circuit 16A that on the basis of a charging signal transmission interval tk, a delay time td required for charging signal relay transfer, and preceding time transmission start timing Tp of the preceding time charging signal reported from a station side GW 10A, predicts the next time transmission start timing Tn of the preceding time charging signal to be transmitted to an analog line LB and, when the obtained next time transmission start timing Tn comes, transmits, to the analog line LB, a substitution charging signal Ss instead of the next time charging signal Sn to be relay-transferred from the station side GW 10A.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a relay and forwarding technique for relaying and forwarding, via an IP line and an IP network, a billing control signal exchanged between an exchange and a public telephone via an analog line. [Background technology]

[0002] Generally, when a public telephone charges a telephone call fee from the coins or prepaid card inserted by the user, the public telephone charges the user based on a charging signal (collection signal) sent from the exchange, and transmits a coin collection completion signal indicating the completion of the charging operation to the exchange. The exchange then collects the telephone call fee for each collection period, such as one month, based on the coin collection completion signal. For a long time, exchanges and public telephones were connected via analog lines that make up the Public Switched Telephone Network (PSTN), i.e., outdoor wiring consisting of two-wire metallic cables. For this reason, the billing control signals for controlling these billing operations are transmitted using the time-varying line voltage of the analog lines (voltage pulses and sine waves).

[0003] On the other hand, due to the aging and discontinuation of switching equipment, there are plans to gradually migrate the telephone network connecting exchanges and public telephones from the public switched telephone network to an IP network (see, for example, Reference 1). This plan calls for changing the outdoor wiring used to connect exchanges and public telephones from analog lines to IP lines using optical cables. In this case, in order to continue using the existing exchange and public telephones, a gateway (GW) that relays between the analog signals of the analog lines and the packets of the IP lines is required. Therefore, this plan considers a public telephone relay system that connects the central office GW between the central office analog lines and the IP lines, and the telephone GW between the telephone telephone analog lines and the IP lines, relaying and forwarding voice and billing control signals via the IP network. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Akiyuki Yamakawa, INTERNET Watch News, "NTT to migrate fixed-line telephones from PSTN to IP network around 2025, reducing the burden on users while keeping telephone sets and analog lines intact", 2015 / 11 / 6, Impress Corporation, [Searched 2023 / 7 / 7], Internet<URL:https: / / internet.watch.impress.co.jp / docs / news / 729373.html> Summary of the Invention [Problem to be solved by the invention]

[0005] SLIC (Subscriber Loop Interface Circuit) and DAA (Data Access Arrangement) are widely used as the main interfaces for terminating analog lines using two-wire metallic cables. SLIC and DAA have the function of converting between analog voice on analog lines and voice packets on IP lines, and also the function of converting between call control signals on analog lines and call control packets on IP lines. However, the function of SLIC and DAA to convert between call control signals and call control packets is intended for use with general analog lines for subscribers, and the billing signal unique to public telephones, which is only used with analog lines for public telephones, is delayed, and the coin collection completion signal cannot be converted. For this reason, it is necessary to provide a relay circuit configuration for the billing signal and the coin collection completion signal separately from the relay circuit configuration for the call control signal.

[0006] Since the call control signal and billing control signal sent to the analog line are composed of voltage pulses as described above, it is possible to use a known voltage change detection method for detecting changes in the line voltage of the analog line to notify changes in the line state in packets. When determining changes in the line voltage of the analog line, such a voltage change detection method requires a monitoring period of a certain length to confirm that the change in the line voltage has been completed. For this reason, when such a voltage change detection method is used, relay transfer of the billing control signal is significantly delayed, resulting in the problem that the exchange cannot correctly recognize the billing operation of the public telephone.

[0007] The present invention is intended to solve these problems, and aims to provide a relay and forwarding technology that can reduce the delay that occurs when billing control signals exchanged between a switching center and a public telephone are relayed and forwarded via an IP network. [Means for solving the problem]

[0008] In order to achieve the above object, the telephone side gateway of the present invention comprises a central office gateway connected to an exchange via a central office analog line and connected to an IP network, and a telephone side gateway connected to a public telephone via a telephone side analog line and connected to the IP network, the central office gateway and the telephone side gateway being used in a public telephone relay system in which the central office gateway and the telephone side gateway relay analog voice, call control signal, and charging signal of the central office analog line and analog voice, call control signal, and coin collection completion signal of the telephone side analog line to each other via the IP network, the central office gateway and the telephone side gateway being used in a public telephone relay system in which the central office gateway and the telephone side gateway relay analog voice, call control signal, and coin collection completion signal of the telephone side analog line to each other via the IP network, the central office gateway comprising a charging relay circuit configured to predict the next start timing of transmission of a next charging signal to be transmitted to the telephone side analog line based on the transmission interval of the charging signal, the transfer time required for relaying the charging signal, and the previous start timing of transmission of the previous charging signal notified by the central office gateway, and to transmit a substitute signal in place of the next charging signal relayed from the central office gateway to the telephone side analog line when the obtained next start timing of transmission arrives.

[0009] In addition, one configuration example of the telephone side gateway according to the present invention is configured so that if the beginning of the next charging signal is not detected before a predetermined detection time has elapsed from the start of transmission of the alternative charging signal, the charging relay circuit immediately stops transmitting the alternative charging signal.

[0010] In addition, one configuration example of the telephone side gateway according to the present invention is configured so that the transfer time includes the transfer time required for relaying and transferring the billing signal and the transfer time required for relaying and transferring the coin storage completion signal.

[0011] The public telephone relay system according to the present invention comprises a central office gateway connected to an exchange via a central office analog line and connected to an IP network, and a telephone side gateway connected to a public telephone via a telephone side analog line and connected to the IP network, the central office gateway and the telephone side gateway relaying analog voice, call control signal, and charging signal of the central office analog line and analog voice, call control signal, and coin collection completion signal of the telephone side analog line to each other via the IP network, the telephone side gateway comprising a charging relay circuit configured to predict the next start timing of sending a next charging signal to be sent to the telephone side analog line based on the sending interval of the charging signal, the transfer time required for relaying the charging signal, and the previous start timing of sending the previous charging signal notified by the central office gateway, and when the obtained next start timing of sending arrives, to send a substitute charging signal in place of the next charging signal relayed from the central office gateway to the telephone side analog line. Effect of the Invention

[0012] According to the present invention, it is possible to reduce delays that occur when billing control signals exchanged between a switching center and a public telephone are relayed through an IP network. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a block diagram showing a configuration of a public telephone relay system according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing the configuration of the station side gateway. [Diagram 3] FIG. 3 is a block diagram showing the configuration of the telephone-side gateway. [Figure 4] FIG. 4 is a waveform diagram showing a part of the billing signal. [Diagram 5] FIG. 5 is a waveform diagram showing a coin storage completion signal. [Figure 6]FIG. 6 is a timing chart showing the exchange of billing control signals according to the first embodiment. [Figure 7] FIG. 7 is a timing chart showing the operation of predicting the sending timing. [Figure 8] FIG. 8 is a timing chart showing the exchange of billing control signals according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Next, an embodiment of the present invention will be described with reference to the drawings. [First embodiment] First, a public telephone relay system according to a first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the public telephone relay system 1 according to the present embodiment is a system in which a switching center 20A and a public telephone 20B relay and transfer voice signals, call control signals, and billing control signals exchanged between them via a central office analog line LA and a telephone analog line LB, via an IP network NW such as the Internet.

[0015] [Public telephone relay system] The public telephone relay system 1 mainly comprises a station-side gateway 10A connected to an exchange 20A via a station-side analog line LA using a two-wire metallic cable, and connected to an IP network NW via a station-side IP line WA using an optical cable, and a telephone-side gateway 10B connected to a public telephone 20B via a telephone-side analog line LB using a two-wire metallic cable, and connected to the IP network NW via a telephone-side IP line WB using an optical cable.

[0016] [Central station gateway] As shown in FIG. 2, the office-side gateway (hereinafter referred to as the office-side GW) 10A has, as its main circuit configuration, an IP line I / F circuit 11A, a data access arrangement (hereinafter referred to as DAA) 12A, a signal processing circuit 13A, and a control circuit 14A.

[0017] [IP line I / F circuit] The IP line I / F circuit 11A is connected to the IP network NW via the IP line WA, and is configured to convert the voice packets, call control packets, accounting control packets, and transmission interval packets output from the control circuit 14A into optical signals and transmit them to the IP line WA, and to convert the optical signals received from the IP line WA into voice packets, call control packets, and accounting control packets and output them to the control circuit 14 A. In the present invention, a packet that stores the state of the accounting control signal is called an accounting control packet, and a packet that stores the transmission interval of the accounting signal is called a transmission interval packet.

[0018] [DAA] The DAA 12A is connected to the exchange 20A via an analog line LA, and is configured to convert voice data and call control data output from the control circuit 14A into voice signals and call control signals and transmit them to the analog line LA, and to convert voice signals and call control signals received from the analog line LA into voice data and call control data and output them to the control circuit 14A.

[0019] [Signal processing circuit] The signal processing circuit 13A is connected to the exchange 20A via an analog line LA, detects the state of the billing signal based on the line voltage value detected from the analog line LA, converts it into billing control data and outputs it to the control circuit 14A, sends a coin storage completion signal to the analog line LA based on the billing control data output from the control circuit 14A, measures the transmission interval of the billing signal sent from the exchange 20A to the analog line LA, and is configured to output transmission interval data indicating the obtained transmission interval to the control circuit 14A.

[0020] [Control circuit] The control circuit 14A has a CPU and its peripheral circuits, and is configured to perform relay processing of voice data, call control data, billing control data, and transmission interval data by the CPU working in cooperation with a program stored in a memory circuit (not shown).

[0021] Specifically, the control circuit 14A is configured to convert voice packets and call control packets input from the IP line I / F circuit 11A into voice data and call control data and output them to the DAA 12A, convert voice data and call control data input from the DAA 12A into voice packets and call control packets and output them to the IP line I / F circuit 11A, convert billing control packets input from the IP line I / F circuit 11A into billing control data and output them to the signal processing circuit 13A, convert billing control data input from the signal processing circuit 13A into billing control packets and output them to the DAA 12A, and convert transmission interval data input from the signal processing circuit 13A into transmission interval packets and output them to the IP line I / F circuit 11A.

[0022] [Call relay circuit] In the present invention, the cross-sectional circuit section of the station side GW 10A, which is composed of the IP line I / F circuit 11A, the DAA 12A, and a part of the control circuit 14A and relays the voice signals and call control signals used in the call, is conveniently referred to as the call relay circuit 15A. The call relay circuit 15A is configured to relay and transfer the analog voice and call control signals of the analog line LA and the voice packets and call control packets of the IP network NW to each other.

[0023] [Billing relay circuit] Of the central office side GW10A, the cross-sectional circuit section consisting of the IP line I / F circuit 11A, the signal processing circuit 13A, and a part of the control circuit 14A, which relays the charging control signal used for charging operation, is conveniently referred to as the charging relay circuit 16A. The charging relay circuit 16A is configured to detect the charging signal from the line voltage value of the analog line LA, convert it into charging data, store it in a charging control packet, notify the telephone side GW10B via the IP network NW, obtain the charging data from the charging control packet notified from the telephone side GW10B via the IP network NW, and send a coin collection completion signal to the analog line LB.

[0024] [Telephone side gateway] As shown in Fig. 3, telephone side gateway (hereafter referred to as telephone side GW) 10B mainly comprises an IP line I / F circuit 11B, a subscriber loop I / F circuit (hereafter referred to as SLIC: Subscriber Loop Interface Circuit) 12B, a signal processing circuit 13B, and a control circuit 14B. Of these circuits, the IP line I / F circuit 11B, the SLIC 12B, and a part of the control circuit 14B constitute a call relay circuit 15B that relays voice signals and call control signals used in calls, and the IP line I / F circuit 11B, the signal processing circuit 13B, and a part of the control circuit 14B constitute an accounting relay circuit 16B that relays accounting control signals used in accounting operations.

[0025] [IP line I / F circuit] The IP line I / F circuit 11B is connected to the IP network NW via the IP line WB, and is configured to convert the voice packets, call control packets, and billing control packets output from the control circuit 14B into optical signals and transmit them to the IP line WB, and to convert the optical signals received from the IP line WB into voice packets, call control packets, billing control packets, and transmission interval packets and output them to the control circuit 14B.

[0026] [SLIC] SLIC 12B is connected to public telephone 20B via analog line LB, and is configured to convert voice data and call control data output from control circuit 14B into voice signals and call control signals and transmit them to analog line LB, and to convert voice signals and call control signals received from analog line LB into voice data and call control data and output them to control circuit 14B.

[0027] [Signal processing circuit] The signal processing circuit 13B is connected to the public telephone 20B via an analog line LB, and is configured to output a billing signal to the analog line LB based on billing control data output from the control circuit 14B, detect a coin storage completion signal based on a sine wave signal detected from the analog line LB, convert it into billing control data, and output it to the control circuit 14A.

[0028] [Control circuit] The control circuit 14B has a CPU and its peripheral circuits, and is configured to perform relay processing of voice data, call control data, billing control data, and transmission interval data by the CPU working in cooperation with a program stored in a memory circuit (not shown).

[0029] Specifically, the control circuit 14B is configured to convert voice packets and call control packets input from the IP line I / F circuit 11B into voice data and call control data and output them to the SLIC 12B, to convert voice data and call control data input from the SLIC 12B into voice packets and call control packets and output them to the IP line I / F circuit 11B, to convert billing control packets input from the IP line I / F circuit 11B into billing control data and output them to the signal processing circuit 13B, and to convert billing control data input from the signal processing circuit 13B into billing control packets and output them to the IP line I / F circuit 11B.

[0030] The control circuit 14B also acquires the transmission interval of the charging signal from the transmission interval packet input from the IP line I / F circuit 11B, and predicts the next transmission start timing Tn indicating the transmission start timing of the next charging signal Sn to be transmitted to the analog line LB based on this transmission interval, the transfer time required for relaying and transferring the charging signal, and the previous transmission start timing Tp indicating the transmission start timing of the previous charging signal Sp notified by the station-side GW 10A.When the obtained next transmission start timing Tn arrives, the control circuit 14B is configured to sequentially output, to the signal processing circuit 13B, charging control data indicating a substitute charging signal Ss in place of the next charging signal Sn notified by the station-side GW 10A.

[0031] [Call relay circuit] In the present invention, the cross-sectional circuit section of the telephone side GW 10B, which is composed of the IP line I / F circuit 11B, the SLIC 12B, and a part of the control circuit 14B and relays the voice signal and the call control signal used in the call, is conveniently called the call relay circuit 15B. The call relay circuit 15B is configured to relay and transfer the analog voice and the call control signal of the analog line LB and the voice packet and the call control packet of the IP network NW to each other.

[0032] [Billing relay circuit] In the present invention, the cross-sectional circuit section of the telephone side GW10B, which is composed of the IP line I / F circuit 11B, the signal processing circuit 13B, and a part of the control circuit 14B, and which relays the charging control signal used for charging operation, is conveniently referred to as the charging relay circuit 16B. The charging relay circuit 16B is configured to detect a coin storage completion signal from the line voltage value of the analog line LB, convert it into storage completion data, store it in a charging control packet, notify the station side GW10A via the IP network NW, obtain the charging control data from the charging control packet notified from the station side GW10A via the IP network NW, and send the charging signal to the analog line LB.

[0033] [Charge control signal] Next, the accounting control signals for controlling the accounting operation in the public telephone 20B, that is, the accounting signal and the coin storage completion signal, will be described with reference to FIG. 4 and FIG. The accounting signal is a control signal for instructing the public telephone 20B to perform accounting from the exchange 20A. This accounting signal is sent from the exchange 20A to the public telephone 20B when a call to the public telephone 20B via the exchange 20A is started, for example, when the other party answers the call. After the call is established, the accounting signal is also sent from the exchange 20A to the public telephone 20B for each call time equivalent to a unit fee.

[0034] The coin collection completion signal is a control signal from the public telephone 20B to the exchange 20A to notify the completion of billing by coin. When the public telephone 20B receives the billing signal, it collects the unit fee with the coin inserted by the user and then returns the coin collection completion signal to the exchange 20A.

[0035] As shown in Figure 4, the charging signal is composed of the time variation of the line voltage of the analog line, i.e., voltage pulses. There are three types of DC line voltages used in the charging signal, each of which is associated with a line state. For example, the voltage state Vn indicates a normal state N, the voltage state VB indicates a break state B, and the voltage state Vr indicates a reverse state R. The voltage state VB is no line potential difference, Vn is a positive voltage state (Vn>Vr), and Vr is a negative (reverse) voltage state (Vr <Vn)。

[0036] In one example of a billing signal, the state of the analog line first changes from a normal state N (voltage state Vn) to a break state B (voltage state VB), and after the break state B is held for a period t1, it changes to a reverse state R (voltage state Vr). After this reverse state R is held for a period t2, it returns to the break state B (voltage state VB), and after the break state B is held for a period t3, it returns to the normal state N (voltage state Vn). The lengths of these periods t1, t2, and t3 are set to 0.40 to 0.60 sec, 0.40 to 1.80 sec, and 0.05 to 0.10 sec, respectively, and the length of the period t of the entire billing signal is set to 0.85 to 2.50 sec.

[0037] On the other hand, the coin collection completion signal consists of a 16 kHz burst signal, as shown in Fig. 5, and is superimposed on the DC line voltage of the analog lines LA and LB at that time. The public telephone 20B starts the accounting operation when it is confirmed that the accounting signal from the switching center 20A has changed from the break state B (period t1) to the reverse state R (period t2) shown in Fig. 4, and returns the coin collection completion signal upon completion of the accounting operation. Therefore, under normal timing, the coin collection completion signal is superimposed on the DC line voltage of the accounting signal during period t2 when the reverse state R is maintained.

[0038] [Delay in charging control signals] Next, the delay of the billing control signal will be described with reference to FIG. As shown in Fig. 4, in order to correctly determine whether the coin storage completion signal returned from the public telephone 20B is a response to the transmitted billing signal, the exchange 20A waits for a predetermined period of time, tw, from the beginning of the billing signal to confirm the arrival of the coin storage completion signal. If the arrival of the coin storage completion signal is confirmed within the wait period tw, the exchange 20A determines that the billing operation using coins has been performed at the public telephone 20B, and totals the telephone call charges using coins for each totaling period, such as one month.

[0039] Here, since analog lines are outdoor wiring and are susceptible to the effects of noise, a voltage change detection method is used in which the line voltage value remains constant for a specified monitoring period tm, and the change in line state is confirmed when the voltage change is complete. However, if such a well-known voltage change detection method is used by the central office side GW 10A and the telephone side GW 10B, it is expected that a delay will occur as shown in Figure 6.

[0040] 6, when the output of the billing signal S1 is started from the exchange 20A at time T0, the line voltage of the analog line LA changes from the voltage state Vn (normal state N) to the voltage state VB (break state B). The central office side GW 10A monitors the line voltage of the analog line LA for a monitoring period tm from time T0, and when it is confirmed that the DC voltage change is complete, it transmits a break notification Mb, indicating that the line state has changed to the break state B, in a packet to the telephone side GW 10B. When the telephone side GW 10B receives the break notification Mb via the IP network NW, it controls the line voltage of the analog line LB from the voltage state Vn (normal state N) to the voltage state VB (break state B). As a result, the billing signal S1' arrives at the public telephone 20B at time T0', delayed by the monitoring period tm from time T0 and the packet transfer time tx of the IP network NW.

[0041] It is believed that such a delay will occur similarly when the line voltage subsequently changes from voltage state VB (break state B) to voltage state Vr (reverse state R) at time T1, when the line voltage changes from voltage state Vr (reverse state R) to voltage state VB (break state B) at time T2, and when the line voltage changes from voltage state VB (break state B) to voltage state Vn (normal state N) at time T3. It is also believed that a similar delay will occur in the coin storage completion signal S2 returned from the public telephone 20B.

[0042] Therefore, the coin storage completion signal S2 that starts to be transmitted from the public telephone 20B at time T5 passes through the telephone side GW10B, the IP network NW, and the station side GW10A, and reaches the exchange 20A as the coin storage completion signal S2' with a significant delay until time T5', and does not arrive in time for the waiting period tw from time T0. In such a case, even though the charging operation at the public telephone 20B has been completed, the exchange 20A cannot recognize the completion of the charging operation for that coin.

[0043] The main cause of this delay in the billing control signal is the configuration in which the GW10A on the office side and the GW10B on the telephone side detect the billing control signal sent to the analog lines LA, LB and relay it to the IP network NW, and the line status of the analog lines LA, LB is determined by the GW10A on the office side and the GW10B on the telephone side. In order to reduce such delays in charging control signals, the present invention is configured so that the telephone side GW10B predicts the start timing of the transmission of the next charging signal to be sent to the analog line LB, and when the obtained transmission start timing arrives, a substitute charging signal Ss is sent to the analog line LB in place of the next charging signal to be relayed from the station side GW10A.

[0044] [Operation of the first embodiment] Next, the operation of the public telephone relay system 1 according to the first embodiment will be described with reference to Fig. 7. Here, the explanation will be focused on the billing signal and the coin collection completion signal exchanged between the exchange 20A and the public telephone 20B in response to the other party's response. Note that the voice signal and the call control signal exchanged between the exchange 20A and the public telephone 20B are the same as the general well-known configuration and operation using SLIC or DAA, and therefore the explanation will be omitted here.

[0045] [Sending charging signal Sa1] As shown in Fig. 7, when the switching center 20A starts outputting the first charging signal Sa1 in response to the remote party's response at time T10, the line voltage of the analog line LA changes from voltage Vn (normal state N) to voltage VB (break state B). The central office GW 10A monitors the line voltage value of the analog line LA, and when it is confirmed that the DC voltage change is complete, it transmits a break notification Mb indicating that the line state has changed to break state B to the telephone set GW 10B in a packet. The central office GW 10A also starts measuring the transmission interval tk of the charging signals Sa1 and Sa2 from time T10, which is the time of the change to break state B.

[0046] When the telephone GW10B receives the break notification Mb via the IP network NW, it controls the line voltage value of the analog line LB from voltage Vn (normal state N) to voltage VB (break state B). Therefore, the change of the analog line LA to the break state B at time T10 is reproduced as a change of the analog line LB to the break state B at time T10', which is delayed by a delay time td including the monitoring period tm of the line voltage value and the packet transfer time tx of the IP network NW. As a result, the head of the billing signal Sa1' arrives at the public telephone 20B at time T10'. After this, the change of the analog line LA to the reverse state R at time T11 and after is also reproduced as a state change of the analog line LB at a timing delayed by the delay time td in the same manner as described above.

[0047] [Sending coin storage completion signal Sb1] When the state of the analog line LB changes from the normal state N to the break state B and further to the reverse state R, the public telephone 20B starts the billing operation and sends a coin storage completion signal Sb1 to the analog line LB upon completion of the billing operation. The telephone side GW 10B monitors the analog line LB, detects the beginning and end of the coin collection completion signal Sb1 from the public telephone 20B, and notifies the station side GW 10A of each in a packet.

[0048] When the station side GW10A receives notification from the telephone side GW10B via the IP network NW that the beginning of the coin storage completion signal Sb1 has been detected, it starts sending the coin storage completion signal Sb1' to the analog line LA, and when the station side GW10A receives notification from the telephone side GW10B via the IP network NW that the end of the coin storage completion signal Sb1 has been detected, it stops sending the coin storage completion signal Sb1'. The exchange 20A checks for the arrival of the coin storage completion signal Sb1 during the waiting period tw, which is a predetermined length of time from the beginning of the billing signal Sa1, i.e., time T10. In this case, the delay time td occurs in the relay transfer of the billing signal Sa1 and the coin storage completion signal Sb1, as described above, so that the timing at which the coin storage completion signal Sb1' arrives at the exchange 20A is significantly delayed, and the signal does not arrive in time for the waiting period tw.

[0049] [Sending charging signal Sa2] When the switching center 20A starts outputting the second charging signal Sa2 at time T20, the central office GW 10A transmits a break notification Mb in a packet to the telephone set GW 10B, similar to the charging signal Sa1. The central office GW 10A also ends the measurement of the charging signal transmission interval tk, which started at time T10, at time T20, which is the time of change to the break state B, and notifies the telephone set GW 10B of the obtained transmission interval tk in a transmission interval packet. The central office GW 10A also starts measuring the transmission interval tk of the charging signals Sa2 and Sa3 again from time T20.

[0050] When the telephone GW10B receives the break notification Mb via the IP network NW, it controls the analog line LB to the break state B in the same way as the billing signal Sa1. Therefore, the change of the analog line LA to the break state B at time T20 is reproduced as a change of the analog line LB to the break state B at time T20', which is delayed by a delay time td including the monitoring period tm and the packet transfer time tx of the IP network NW. As a result, the head of the billing signal Sa2' reaches the public telephone 20B at time T20'. After this, the change of the analog line LA to the reverse state R after time T21 is also reproduced as a change of the analog line LB to the reverse state R at a timing delayed by the delay time td in the same way as described above.

[0051] [Prediction of transmission start timing T30'] In addition, for example, when the telephone side GW10B receives a transmission interval packet following a break notification Mb, it predicts the next transmission start timing T30' of the next billing signal Sa3' to be transmitted to the analog line LB following the previous billing signal Sa2' based on the billing signal transmission interval tk obtained from the transmission interval packet, the delay time td that occurs during relaying and forwarding of the billing signal, and the previous transmission start timing T20' of the previous billing signal Sa2' notified by the station side GW10A in the break notification Mb.

[0052] In general, if the transmission interval is tk, the delay time is td, and the previous transmission start timing indicating the transmission start timing of the previous billing signal Sp is Tp, the next transmission start timing Tn indicating the transmission start timing of the next billing signal Sn can be calculated by the following equation (1). Tn = Tp - tk - td ... (1) When predicting the next transmission start timing T30' described above, the previous billing signal Sp corresponds to the billing signal Sa2', and the previous transmission start timing Tp corresponds to time T20'. The transmission interval tk corresponds to the period from time T10 to time T20, and the delay time td is a preset value, and corresponds to, for example, the period from time T20 to time T20'.

[0053] In this case, the time required for sampling the line voltage value and controlling the line voltage value is negligible in the billing operation. Therefore, the delay time td occurring during relay transfer of the billing signal can be regarded as a time including mainly the monitoring period tm of the line voltage value in the central office side GW 10A and the packet transfer time tx of the IP network NW. Therefore, for example, in the case of the billing signal Sa1, the delay time td corresponds to the time from time T10 to time T10'. This delay time td can be obtained in advance by measurement or calculation and stored in the telephone side GW 10B.

[0054] In addition, when compensating for the delay time of the coin collection completion signal as well as the billing signal, the next transmission start timing Tn can be predicted by including the monitoring period tm of the line voltage value in the telephone side GW10B and the packet transfer time tx of the IP network NW in the delay time td. In this case, if the configuration for checking the completion of the change in the line voltage value is the same in the station side GW10A and the telephone side GW10B, the next transmission start timing Tn can be predicted by setting the delay time td to twice the delay time (round trip) that occurs during the relay transfer of the billing signal (one way).

[0055] The delay time td may be calculated by the telephone GW 10B based on the time T20 notified by the packet. For example, the central office GW 10A obtains the time T20 at which the line voltage value of the analog line LA changes from voltage Vn (normal state N) to voltage VB (break state B) and notifies the telephone GW 10B of this in a transmission interval packet, and the telephone GW 10B can calculate the delay time td based on the difference between the time T20 obtained from the transmission interval packet and the time T20' at which the analog line LB changes to the break state B at the beginning of the charging signal Sa2'.

[0056] [Sending coin storage completion signal Sb2] When the state of the analog line LB changes from the normal state N to the break state B and further to the reverse state R, the public telephone 20B starts the billing operation and sends a coin storage completion signal Sb2 to the analog line LB upon completion of the billing operation. The telephone side GW 10B monitors the analog line LB, detects the beginning and end of the coin collection completion signal Sb2 from the public telephone 20B, and notifies the station side GW 10A of each in a packet.

[0057] When the station side GW10A is notified by the telephone side GW10B via the IP network NW that the beginning of the coin storage completion signal Sb2 has been detected, it starts sending the coin storage completion signal Sb2' to the analog line LA, and when the station side GW10A is notified by the telephone side GW10B via the IP network NW that the end of the coin storage completion signal Sb2 has been detected, it stops sending the coin storage completion signal Sb2'. The exchange 20A checks whether the coin storage completion signal has arrived during the waiting period tw, which is a predetermined length of time from the beginning of the billing signal Sa2, i.e., time T20. In this case, because the relay transfer of the billing signal Sa2 and the coin storage completion signal Sb2 has a delay as described above, the timing at which the coin storage completion signal Sb2' arrives at the exchange 20A is significantly delayed, and the signal does not arrive in time for the waiting period tw.

[0058] [Sending charging signal Sa3] When the switching center 20A starts outputting the third charging signal Sa3 at time T30, the central office GW 10A sends a break notification Mb in a packet to the telephone set GW 10B, similar to the charging signals Sa1 and Sa2. At time T30, which is the time of change to the break state B, the central office GW 10A ends the measurement of the sending interval tk of the charging signals Sa2 and Sa3, which started at time T20, and notifies the telephone set GW 10B of the obtained sending interval tk in a sending interval packet. At time T30, the central office GW 10A starts measuring a new sending interval tk.

[0059] Meanwhile, at approximately the same time as time T30, the telephone GW 10B confirms the arrival of the sending start timing T30' of the charging signal Sa3' predicted based on the sending start timing of the charging signal Sa2', and controls the analog line LB to the break state B. As a result, the charging signal Sa3' is sent from the telephone GW 10B to the public telephone 20B via the analog line LB as a substitute charging signal Ss3' in place of the charging signal Sa3' that is next relayed from the station GW 10A.

[0060] Therefore, the change of analog line LA to the break state B at time T30 is reproduced as a change of analog line LB to the break state B without delay and at approximately the same timing as the state change of analog line LA, just as in the case where the switching center 20A and the public telephone 20B are directly connected by the PSTN, and the head of the substitute charging signal Ss3' reaches the public telephone 20B. After this, the state change of analog line LA from time T31 onwards is also reproduced as a state change of analog line LB without delay and at approximately the same timing as the state change of analog line LA.

[0061] [Prediction of start timing of transmission] In addition, for example, when the telephone side GW10B receives a transmission interval packet following a break notification Mb, it predicts the next transmission start timing of the next billing signal (not shown) to be transmitted to the analog line LB following the previous billing signal Sa3' based on the transmission interval tk of the billing signal obtained from the transmission interval packet, the delay time td that occurs during relaying and forwarding of the billing signal, the previous transmission start timing T30' of the previous billing signal Sa3' notified by the station side GW10A in the break notification Mb, and the above-mentioned equation (1).

[0062] [Sending coin storage completion signal Sb3] When the state of the analog line LB changes from the normal state N to the break state B and further to the reverse state R, the public telephone 20B starts the billing operation and sends a coin storage completion signal Sb3 to the analog line LB upon completion of the billing operation. The telephone side GW 10B monitors the analog line LB, detects the beginning and end of the coin collection completion signal Sb3 from the public telephone 20B, and notifies the station side GW 10A of each in a packet.

[0063] When the station side GW10A is notified by the telephone side GW10B via the IP network NW that the beginning of the coin storage completion signal Sb3 has been detected, it starts sending the coin storage completion signal Sb3' to the analog line LA, and when the station side GW10A is notified by the telephone side GW10B via the IP network NW that the end of the coin storage completion signal Sb3 has been detected, it stops sending the coin storage completion signal Sb3' to the analog line LA. The exchange 20A checks whether the coin storage completion signal has arrived during the waiting period tw, which is a predetermined length of time from the beginning of the charging signal Sa3, i.e., from time T30. In this case, since the delay caused by the relay transfer of the charging signal Sa3 is compensated for, the timing at which the coin storage completion signal Sb2' arrives at the exchange 20A is not significantly delayed, and the signal arrives in time for the waiting period tw.

[0064] Therefore, for charging signals Sa3' and after, the telephone side GW10B predicts the transmission start timing in the same manner as described above, and sends them to the public telephone 20B at approximately the same timing as the charging signal sent from the exchange 20A. Therefore, the coin storage completion signal returned from the public telephone 20B always arrives within the waiting period tw of the exchange 20A. This allows the exchange 20A to correctly recognize the charging operation at the public telephone 20B.

[0065] [How to handle cases where the start timing of transmission is unpredictable] To predict the start timing of transmission, the transmission interval tk of the charging pulse is required. Since the call charge for a public telephone varies depending on the distance of the other party, the call time per unit charge, i.e., the transmission interval tk, also depends on the other party. Therefore, the transmission interval tk of the charging signal actually measured by the central office GW10A must be used to predict the start timing of transmission. 7, the transmission interval tk between the charging signal Sa1 and the charging signal Sa2 is obtained at time T20. Therefore, it is too late to predict the transmission start timing T20, and is used to predict the next transmission start timing T30'.

[0066] In addition, since the first measurable transmission interval tk is the transmission interval between charging signals Sa1 and Sa2, the transmission start timings T10 and T20 cannot be predicted. On the other hand, among the charging signals transmitted from the exchange 20A, there are some that do not require the public telephone 20B to return a coin collection completion signal. Therefore, the billing relay circuit 16A (for example, the control circuit 14A) of the station side GW10A may store the occurrence of non-arrival of the coin storage completion signal at the exchange 20A, such as the coin storage completion signals Sb1' and Sb2', and at the point in time when the exchange 20A sends a billing signal that does not require the return of the coin storage completion signal, the station side GW10A may return a pseudo coin storage completion signal corresponding to the non-arrival to the exchange 20A. This allows the error in the fee tally based on the non-arrival coin storage completion signal at the exchange 20A to be corrected by the pseudo coin storage completion signal.

[0067] Even if the next charging signal Sn is not sent from the exchange 20A, this prediction of the sending start timing is executed, and therefore, in response to the arrival of the predicted next sending start timing Tn, sending of an alternative charging signal Ss from the telephone GW 10B to the public telephone 20B is started. In this case, if the next charging signal Sn is sent from the exchange 20A, a break notification Mb indicating the beginning of the next charging signal Sn will arrive in a packet from the exchange GW 10A to the telephone GW 10B with a delay of the delay time td required for relaying and forwarding the charging signal after the sending of the alternative charging signal Ss.

[0068] Therefore, if the billing relay circuit 16B (e.g., control circuit 14B) of the telephone side GW 10B does not detect the beginning of the next billing signal Sn to be relayed from the station side GW 10A before a predetermined detection time has elapsed since the start of transmission of the alternative billing signal Ss, the billing relay circuit 16B (e.g., control circuit 14B) may immediately stop transmitting the alternative billing signal Ss. As a result, transmission of the alternative charging signal Ss starts, and after the analog line LB changes to the break state B, the transmission of the alternative charging signal Ss stops and the line returns to the reverse state R. This change is judged as a momentary line interruption by the public telephone 20B, so there is no effect on the call or the charging operation, and erroneous charging operations at the public telephone 20B can be avoided.

[0069] [Advantages of the first embodiment] In this manner, in this embodiment, the billing relay circuit 16A of the telephone side GW 10B predicts the next transmission start timing Tn of the next billing signal to be transmitted to the analog line LB based on the billing signal transmission interval tk, the delay time td required for relaying and forwarding the billing signal, and the previous transmission start timing Tp of the previous billing signal notified from the station side GW 10A, and when the obtained next transmission start timing Tn arrives, it transmits a substitute billing signal Ss in place of the next billing signal Sn relayed and forwarded from the station side GW 10A to the analog line LB.

[0070] As a result, the telephone GW10B compensates for the delay that occurs in relaying the charging signal, and the substitute charging signal Ss can be sent from the telephone GW10B to the public telephone 20B at approximately the same timing as the charging signal sent from the exchange 20A. Therefore, the coin storage completion signal returned from the public telephone 20B is also sent from the office GW10A to the exchange 20A without significant delay. Therefore, even if the charging control signal is relayed via the IP network NW, the exchange 20A can confirm the arrival of the coin storage completion signal within the predetermined waiting period tw, and the exchange 20A can correctly recognize the charging operation at the public telephone 20B.

[0071] [Second embodiment] Next, a public telephone relay system 1 according to a second embodiment of the present invention will be described. In the first embodiment, when relaying and transferring a billing control signal via an IP network NW, the station side GW10A and the telephone side GW10B detect a change in the line voltage value of the analog lines LA and LB using a well-known voltage change detection method, and notify the change in the line state by a packet.

[0072] In this embodiment, the station side GW10A and the telephone side GW10B are configured to sequentially sample the line voltage values ​​of the analog lines LA, LB and notify each other of them via the IP network NW in billing control packets, and sequentially control the line voltage values ​​of the analog lines LA, LB so that they become equal to the line voltage values ​​notified in the billing control packets.

[0073] [Central station gateway] The station side GW10A according to this embodiment is different from the first embodiment in that the IP line I / F circuit 11A, the signal processing circuit 13A, and the control circuit 14A constituting the billing relay circuit 16A are partially different from each other. The other configurations are the same as those of the first embodiment, and detailed description thereof will be omitted here.

[0074] [IP line I / F circuit] The IP line I / F circuit 11A is configured to convert the accounting control packet output from the control circuit 14A into an optical signal and transmit it to the IP line WA, and to convert the optical signal received from the IP line WA into an accounting control packet and output it to the control circuit 14 A. In the present invention, a packet in which a line voltage value is stored is called an accounting control packet.

[0075] [Signal processing circuit] The signal processing circuit 13A is configured to convert the line voltage values ​​sampled sequentially from the analog line LA into voltage data and output it to the control circuit 14A, and to control the coin storage completion signal output on the analog line LA based on the coin storage completion signal data sequentially output from the control circuit 14A.

[0076] [Control circuit] The control circuit 14A is configured to convert the billing control packet input from the IP line I / F circuit 11A into coin storage completion signal data and output it to the signal processing circuit 13A, and to convert the voltage data input from the signal processing circuit 13A into a billing control packet and output it to the IP line I / F circuit 11A.

[0077] [Billing relay circuit] The billing relay circuit 16A is configured to sequentially sample the line voltage value of the analog line LA, store it in a billing control packet, notify the telephone side GW10B via the IP network NW, obtain coin storage completion signal data from the packet notified from the telephone side GW10B via the IP network NW, and sequentially control the coin storage completion signal output on the analog line LA so that it is equal to the coin storage completion signal data.

[0078] [Telephone side gateway] The telephone side GW10B according to this embodiment differs from the first embodiment in that the IP line I / F circuit 11B, the signal processing circuit 13B, and the control circuit 14B constituting the billing relay circuit 16B are partially different from those of the first embodiment. The other configurations are the same as those of the first embodiment, and detailed description thereof will be omitted here.

[0079] [IP line I / F circuit] The IP line I / F circuit 11B is configured to convert the billing control packet output from the control circuit 14B into an optical signal and transmit it to the IP line WB, and to convert the optical signal received from the IP line WB into an billing control packet and output it to the control circuit 14B.

[0080] [Signal processing circuit] The signal processing circuit 13B is configured to convert the coin storage completion signal sequentially sampled from the analog line LB into coin storage completion signal data and output it to the control circuit 14B, and to control the line voltage value of the analog line LB based on the voltage data sequentially output from the control circuit 14B.

[0081] [Billing relay circuit] The billing relay circuit 16B is configured to sequentially sample the coin storage completion signal of the analog line LB, store it in a billing control packet, notify the station side GW 10A via the IP network NW, obtain the line voltage value from the billing control packet notified from the station side GW 10A via the IP network NW, and sequentially control the line voltage value of the analog line LB to be equal to the line voltage value.

[0082] [Operation of the second embodiment] Next, the operation of the public telephone relay system 1 according to the second embodiment will be described with reference to Fig. 8. Here, the explanation will be focused on the billing control signals exchanged between the exchange 20A and the public telephone 20B, i.e., the billing signal and the coin storage completion signal. Note that the voice signals and call control signals exchanged between the exchange 20A and the public telephone 20B are similar to the general well-known configuration and operation using SLIC and DAA, and therefore the explanation will be omitted here.

[0083] [Sending charging signal Sa5] In the central office GW 10A, the signal processing circuit 13A converts the line voltage values ​​successively sampled from the analog line LA into voltage data and outputs it to the control circuit 14A. The control circuit 14A converts the voltage data input from the signal processing circuit 13A into an accounting control packet and outputs it to the IP line I / F circuit 11A. The IP line I / F circuit 11A converts the accounting control packet output from the control circuit 14A into an optical signal and transmits it to the IP line WA.

[0084] In the telephone GW 10B, the IP line I / F circuit 11B converts the optical signal received from the IP line WB into an accounting control packet and outputs it to the control circuit 14B. The control circuit 14B converts the accounting control packets sequentially input from the IP line I / F circuit 11B into voltage data and outputs it to the signal processing circuit 13B. The signal processing circuit 13B controls the line voltage value of the analog line LB based on the voltage data sequentially output from the control circuit 14B.

[0085] As a result, the line voltage value of the analog line LA is notified from the station side GW10A to the telephone side GW10B via the IP network NW, and the line voltage value of the analog line LB is controlled, so that a line voltage equal to that of the analog line LA is output to the analog line LB. At this time, the signal processing circuit 13A does not judge the line state of the analog line LA, but only sequentially samples the line voltage value of the analog line LA. Therefore, it is not necessary to judge the line state, i.e., to confirm that the change in the line voltage value has been completed, and therefore it is possible to save the time required to confirm the completion of the voltage change.

[0086] Therefore, as shown in FIG. 8, when the line voltage of the analog line LA changes from voltage Vn (normal state N) to voltage VB (break state B) at time T50 due to the accounting signal Sa5, this change is notified from the station side GW10A to the telephone side GW10B in an accounting control packet, and at time T50' the line voltage value of the analog line LB is controlled from voltage Vn (normal state N) to voltage VB (break state B), and transmission of the accounting signal Sa5' begins. At this time, the change of the analog line LA to the break state B at time T50 is reproduced as a change of the analog line LB to the break state B at time T50', delayed by a delay time td corresponding to the packet transfer time tx of the IP network NW. Therefore, the monitoring period tm for checking the change in the line voltage as described above can be omitted from the delay time td occurring during relay transfer of the billing signal Sa5.

[0087] In this case, the delay time td can be measured by using a measurement packet such as a Ping packet to measure the round-trip time required for a packet between the telephone GW10B and the station GW10A, and the packet transfer time tx, which is half of the measured time, can be used as the delay time td. In addition, when compensating for the delay time of not only the billing signal but also the coin collection completion signal, the packet round-trip time can be used as the delay time td. This makes it possible to easily measure the transfer time with simple processing. These transfer times can be measured in advance and stored in the control circuit 14B of the telephone GW10B.

[0088] [Advantages of the second embodiment] In this manner, in this embodiment, the billing relay circuit 16A of the office side GW10A is configured to sequentially sample the line voltage value of the analog line LA, notify the telephone side GW10B via the IP network NW in a billing control packet, and sequentially control the coin storage completion signal output on the analog line LA so as to be equal to the coin storage completion signal notified from the telephone side GW10B in a billing signal packet via the IP network NW, and the billing relay circuit 16B of the telephone side GW10B is configured to sequentially sample the coin storage completion signal of the analog line LB, notify the office side GW10A via the IP network NW in a billing signal packet, and sequentially control the line voltage value of the analog line LB so as to be equal to the line voltage value notified from the office side GW10A in a billing control packet via the IP network NW.

[0089] In analog lines, the line voltage value may become unstable due to the influence of noise, etc., and it is therefore conceivable that the monitoring period tm for confirming the completion of the change may also vary depending on the stability of the line voltage value. Therefore, such a variation in the monitoring period tm appears as a prediction error in the timing to start sending the billing signal. According to this embodiment, it is possible to eliminate the monitoring period tm for confirming the change in the line voltage as described above from the delay time that occurs during the relay transfer of the billing signal and the coin storage completion signal. Therefore, it is possible to significantly suppress the variation in the monitoring period tm, and significantly reduce the prediction error in the timing to start sending the billing signal.

[0090] [Extended embodiment] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. In addition, the respective embodiments can be implemented in any combination within a range that does not contradict each other. [Explanation of symbols]

[0091] 1...public telephone relay system, 10A...station side gateway (station side GW), 10B...telephone side gateway (telephone side GW), 11A, 11B...IP line I / F circuit, 12A, 12B...subscriber loop I / F circuit (SLIC), 13A, 13B...signal processing circuit, 14A, 14B...control circuit, 15A, 15B...call relay circuit, 16A, 16B...billing relay circuit, 20A...exchange, 20B...public telephone, LA, LB...analog line, WA, WB...IP line, NW...IP network, Sa, Sa1, Sa2, Sa3, Sa5, Sa1', Sa2', Sa3', Sa5'...billing signal , Sb, Sb1, Sb2, Sb3, Sb5, Sb1', Sb2', Sb3', Sb5'... coin collection completion signal, Sp... previous charging signal, Sn... next charging signal, Ss, Ss3'... alternative charging signal, tm... monitoring period, td... delay time, tx... packet transfer time, tk... transmission interval, tw... waiting period, Tp... previous transmission start timing, Tn... next transmission start timing, T0, T0', T1, T2, T3, T5, T5', T10, T10', T11, T11', T20, T20', T21, T21', T30, T30', T31, T31', T50, T50'... time.

Claims

1. A telephone-side gateway used in a public telephone relay system, comprising: a station-side gateway connected to an exchange via a station-side analog line and connected to an IP network; and a telephone-side gateway connected to a public telephone via a telephone-side analog line and connected to the IP network, wherein the station-side gateway and the telephone-side gateway relay and transfer analog voice, call control signals, and billing signals of the station-side analog line and analog voice, call control signals, and coin collection completion signals of the telephone-side analog line to each other via the IP network, a billing relay circuit configured to predict a next transmission start timing of a next billing signal to be transmitted to the analog line on the telephone side based on the transmission interval of the billing signal, the transmission time required for relaying and forwarding the billing signal, and the previous transmission start timing of the previous billing signal notified from the station side gateway, and to transmit a substitute billing signal in place of the next billing signal relayed and forwarded from the station side gateway to the analog line on the telephone side when the obtained next transmission start timing arrives. A telephone side gateway comprising:

2. 2. The telephone side gateway according to claim 1, The telephone side gateway is characterized in that the billing relay circuit is configured to immediately stop sending the alternative billing signal if the beginning of the next billing signal is not detected before a predetermined detection time has elapsed from the start of sending the alternative billing signal.

3. 3. The telephone side gateway according to claim 1, A telephone-side gateway according to claim 1, wherein the transfer time is configured to include a transfer time required for relaying the billing signal and a transfer time required for relaying the coin storage completion signal.

4. A public telephone relay system comprising a station-side gateway connected to an exchange via a station-side analog line and connected to an IP network, and a telephone-side gateway connected to a public telephone via a telephone-side analog line and connected to the IP network, the station-side gateway and the telephone-side gateway relaying and transferring analog voice, call control signals, and billing signals of the station-side analog line and analog voice, call control signals, and coin collection completion signals of the telephone-side analog line to each other via the IP network, The telephone side gateway a billing relay circuit configured to predict a next transmission start timing of a next billing signal to be transmitted to the analog line on the telephone side based on the transmission interval of the billing signal, the transmission time required for relaying and forwarding the billing signal, and the previous transmission start timing of the previous billing signal notified from the station side gateway, and to transmit a substitute billing signal in place of the next billing signal relayed and forwarded from the station side gateway to the analog line on the telephone side when the obtained next transmission start timing arrives. A public telephone relay system comprising:

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