Public telephone relay system and gateway

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 station side GW 10A sequentially samples line voltage values of an analog line LA and stores them in packets, notifies a telephone set side GW 10B via an IP network NW, acquires sinusoidal signal data from packets received from the telephone set side GW 10B via the IP network NW, and outputs a sinusoidal signal to the analog line LA so as to be equal to a coin completion signal. The telephone set side GW 10B sequentially samples sinusoidal signals of an analog line LB and stores them in packets, notifies the station side GW 10A via the IP network NW, acquires the line voltage values from the packets received from the station side GW 10A via the IP network NW, and sequentially controls line voltage values of the analog line LB so as to be equal to the line voltage values.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 network, billing control signals exchanged between an exchange and a public telephone. [Background technology]

[0002] Generally, when a public telephone charges a telephone call fee from a coin or prepaid card inserted by a 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 coin collection 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 system 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 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 the change in the line state in a packet. When determining a change 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, the 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 signals exchanged between a switching center and a public telephone are relayed via an IP network. [Means for solving the problem]

[0008] In order to achieve the above object, the public telephone relay system of the present invention comprises a station-side gateway connected to an exchange via a station-side analog line and also connected to an IP network, and a telephone-side gateway connected to a public telephone via a telephone-side analog line and also connected to the IP network, the station-side gateway having a call relay circuit for relaying and transferring analog voice and call control signals of the station-side analog line and voice packets and call control packets of the IP network to each other, and a line voltage value of the station-side analog line is successively sampled, stored in a packet, notified to the telephone-side gateway via the IP network, and a signal output from the packet notified from the telephone-side gateway via the IP network. and a billing relay circuit that acquires coin storage completion signal data from the telephone side analog line and outputs a sine wave signal to the station side analog line so that the signal becomes equal to the coin storage completion signal, and the telephone side gateway comprises a call relay circuit that relays analog voice and call control signals of the telephone side analog line and voice packets and call control packets of the IP network to each other, and a billing relay circuit that sequentially samples the coin storage completion signal of the telephone side analog line, stores it in a packet, notifies the station side gateway via the IP network, acquires the line voltage value from the packet notified from the station side gateway via the IP network, and sequentially controls the line voltage value of the telephone side analog line so that it becomes equal to the line voltage value.

[0009] The gateway according to the present invention comprises a gateway constituting a telephone side gateway used in the above-mentioned public telephone relay system. Effect of the Invention

[0010] According to the present invention, it is possible to relay and transfer an accounting control signal exchanged between an exchange and a public telephone via an analog line via an IP line and further via an IP network. [Brief description of the drawings]

[0011] [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 the 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Next, an embodiment of the present invention will be described with reference to the drawings. [Public telephone relay system] First, the public telephone relay system according to the present embodiment will be described with reference to 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.

[0013] The public telephone relay system 10 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.

[0014] [Central station gateway] As shown in Fig. 2, the central office gateway (hereafter, central office GW) 10A mainly comprises an IP line I / F circuit 11A, a data access circuit (hereafter, DAA: data access arrangement) 12A, a signal processing circuit 13A, and a control circuit 14A. Of these circuits, the IP line I / F circuit 11A, the DAA 12A, and a part of the control circuit 14A constitute a call relay circuit 15A that relays voice signals and call control signals used in calls, and the IP line I / F circuit 11A, the signal processing circuit 13A, and a part of the control circuit 14A constitute an accounting relay circuit 16A that relays accounting control signals used in accounting operations.

[0015] [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 voice packets, call control packets, and voltage packets output from the control circuit 14A into optical signals and transmit them to the IP line WA, and convert optical signals received from the IP line WA into voice packets, call control packets, and coin storage completion signal packets and output them to the control circuit 14A. In the present invention, a packet in which a line voltage value is stored is called a voltage packet, and a packet in which a coin storage completion signal is stored is called a coin storage completion signal packet.

[0016] [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.

[0017] [Signal processing circuit] The signal processing circuit 13A is connected to the exchange 20A via an analog line LA, and is configured to output a coin storage completion signal to the analog line LA based on the coin storage completion signal data sequentially output from the control circuit 14A, convert the line voltage values ​​sequentially sampled from the analog line LA into voltage data, and output it to the control circuit 14A.

[0018] [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, voltage data, and coin storage completion signal data by the CPU working in cooperation with a program stored in a memory circuit (not shown). 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 coin storage completion signal packets input from the IP line I / F circuit 11A into coin storage completion signal data and output them to the signal processing circuit 13A, and convert voltage data input from the signal processing circuit 13A into voltage packets and output them to the IP line I / F circuit 11A.

[0019] [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.

[0020] [Billing relay circuit] In the present invention, the cross-sectional circuit section of the station side GW10A, which is composed of the IP line I / F circuit 11A, the signal processing circuit 13A, and a part of the control circuit 14A, and which relays the billing control signal used for billing operation, is conveniently referred to as the billing relay circuit 16A. The billing relay circuit 16A is configured to sequentially sample the line voltage value of the analog line LA, store it in a voltage packet, notify the telephone side GW10B via the IP network NW, obtain the coin storage completion signal data from the packet notified from the telephone side GW10B via the IP network NW, and output the coin storage completion signal to the analog line LA so that it is equal to the coin storage completion signal.

[0021] [Telephone side gateway] As shown in FIG. 3, the telephone side gateway (hereinafter referred to as the telephone side GW) 10B has, as its main circuit configuration, an IP line I / F circuit 11B, a subscriber loop I / F circuit (hereinafter referred to as the SLIC: Subscriber Loop Interface Circuit) 12B, a signal processing circuit 13B, and a control circuit 14B.

[0022] [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 coin storage completion signal 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, and voltage packets and output them to the control circuit 14B.

[0023] [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.

[0024] [Signal processing circuit] The signal processing circuit 13B is connected to the public telephone 20B via an analog line LB, and is configured to control the line voltage value of the analog line LB based on the voltage data sequentially output from the control circuit 14B, 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.

[0025] [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, voltage data, and coin storage completion signal data by the CPU working in cooperation with a program stored in a memory circuit (not shown).

[0026] 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, 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, convert voltage packets sequentially input from the IP line I / F circuit 11B into voltage data and output them to the signal processing circuit 13B, and convert coin storage completion signal data sequentially input from the signal processing circuit 13B into coin storage completion signal packets and output them to the IP line I / F circuit 11B.

[0027] [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.

[0028] [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 billing control signal used for billing operation, is conveniently referred to as the billing relay circuit 16B. The billing relay circuit 16B is configured to sequentially sample the coin storage completion signal of the analog line LB, store it in a coin storage completion signal packet, notify the station side GW10A via the IP network NW, obtain the line voltage value from the voltage packet notified from the station side GW10A via the IP network NW, and sequentially control the line voltage value of the analog line LB so that it becomes equal to the line voltage value.

[0029] [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.

[0030] The coin storage 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 storage completion signal to the exchange 20A.

[0031] As shown in Figure 4, the charging signal is composed of the time change in the line voltage of the analog lines LA and LB, 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)。

[0032] In one example of a billing signal, the state of the analog line 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.

[0033] 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. 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 a coin collection completion signal upon completion of the accounting operation. For this reason, the coin collection completion signal is usually superimposed on the DC line voltage of the accounting signal during period t2 when the reverse state R is maintained.

[0034] [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 checks for the arrival of the coin storage completion signal during a waiting period tw of a predetermined length from the start of the reverse state R of the billing signal. If the arrival of the coin storage completion signal is confirmed within the waiting period tw, the exchange 20A determines that the billing operation using coins has been performed at the public telephone 20B, and if the arrival of the coin storage completion signal is not confirmed within the waiting period tw, the exchange 20A determines that the billing operation using a prepaid card has been performed.

[0035] Here, since the analog lines LA and LB are outdoor wiring, noise may be included in the line voltage. In order to accurately detect changes in DC voltage, there is a voltage change detection method that confirms that the voltage remains constant for a predetermined monitoring period tm when the change occurs and that the voltage change is complete. Therefore, when such a well-known voltage change detection method is used to detect billing signals, changes in the line state can be detected with high accuracy. However, for example, when such a voltage change detection method is used in the central office side GW10A and the telephone set side GW10B, it is expected that a delay will occur as shown in Figure 6.

[0036] 6, when the output of the billing signal Sa1 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 office side GW monitors the line voltage value of the analog line LA for the monitoring period tm from time T0, and when it is confirmed that the DC voltage change is complete, it transmits a break notification 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 GW10B receives the break notification 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 Sa1' arrives at the public telephone 20B at time T0', delayed by the monitoring period tm from time T0 and the packet transfer time required by the IP network NW.

[0037] 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 Sb1 returned from the public telephone 20B.

[0038] Therefore, the coin storage completion signal Sb1 that starts to be transmitted from the public telephone 20B at time T5 is significantly delayed from passing through the telephone side GW10B, the IP network NW, and the station side GW10A until it reaches the exchange 20A as the coin storage completion signal Sb1' at time T5', and it will not arrive in time for the waiting period tw from time T1. In such a case, even though the charging operation at the public telephone 20B has been completed, the exchange 20A will not be able to recognize the completion of the charging operation for that coin.

[0039] 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 billing control signals, the present invention does not determine and notify the line status of the analog circuits LA and LB, but instead sequentially samples the line voltages and coin storage completion signals of the analog circuits LA and LB and notifies them to each other between the station side GW10A and the telephone side GW10B, and controls the line voltages and coin storage completion signals of the analog circuits LA and LB based on the notifications.

[0040] [Operation of the public telephone relay system] Next, the operation of the public telephone relay system 1 according to this embodiment will be described. 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.

[0041] First, the operation of relaying the line voltage value of the analog line LA to the analog line LB will be described with reference to Figs. In the office side 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 a voltage packet and outputs it to the IP line I / F circuit 11A. The IP line I / F circuit 11A converts the voltage packet output from the control circuit 14A into an optical signal and transmits it to the IP line WA.

[0042] In the telephone GW 10B, the IP line I / F circuit 11B converts the optical signal received from the IP line WB into a voltage packet and outputs it to the control circuit 14B. The control circuit 14B converts the voltage 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.

[0043] 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, since there is no need to judge the line state, i.e., to confirm that the change in the line voltage value has been completed, the monitoring period tm required to confirm the completion of the voltage change can be omitted.

[0044] Next, an operation of relaying a coin storage completion signal on the analog line LB to the analog line LA will be described with reference to Figs. In the telephone side GW10B, the signal processing circuit 13B converts the coin storage completion signal sequentially sampled from the analog line LB into coin storage completion signal data and outputs it to the control circuit 14B. The control circuit 14B converts the coin storage completion signal data input from the signal processing circuit 13B into a coin storage completion signal packet and outputs it to the IP line I / F circuit 11B. The IP line I / F circuit 11B converts the coin storage completion signal packet output from the control circuit 14B into an optical signal and transmits it to the IP line WB.

[0045] In the station side GW10A, the IP line I / F circuit 11A converts the optical signal received from the IP line WA into a coin storage completion signal packet and outputs it to the control circuit 14A. The control circuit 14A converts the coin storage completion signal packets sequentially input from the IP line I / F circuit 11A into coin storage completion signal data and outputs it to the signal processing circuit 13A. The signal processing circuit 13A controls the coin storage completion signal to be output to the analog line LA based on the coin storage completion signal data sequentially output from the control circuit 14A.

[0046] As a result, the coin storage completion signal on the analog line LB is notified from the telephone side GW10B to the station side GW10A via the IP network NW, and the coin storage completion signal output to the analog line LA is controlled, so that a coin storage completion signal equal to that on the analog line LB is output to the analog line LA. At this time, the signal processing circuit 13B does not judge the line state of the analog line LB, but only sequentially samples the coin storage completion signal of the analog line LB. Therefore, since there is no need to judge the coin storage completion signal state, i.e., to confirm that the change of the coin storage completion signal has been completed, the monitoring period tm required to confirm the completion of the change of the coin storage completion signal can be omitted.

[0047] The line voltage values ​​in the signal processing circuits 13A and 13B must be sampled at intervals that allow accurate reproduction of the billing signal and the coin storage completion signal. For example, in the billing signal shown in FIG. 4, the period t3 indicating the break state B is 0.05 sec. Also, the coin storage completion signal shown in FIG. 5 is 16 kHz, and the half-period pulse length is 31.25 μsec. Therefore, sampling should be performed at intervals that allow accurate reproduction of voltage pulses of these time lengths. Note that noise contained in the line voltage is also relayed between the analog lines LA and LB, but the exchange 20A and the public telephone 20B are originally connected to outdoor wiring made of metallic cable, and have resistance to such noise, so the effect of noise relay is not a problem.

[0048] Next, the relay operation of the billing signal and the coin storage completion signal will be described with reference to FIG. When the output of the billing signal Sa5 is started from the exchange 20A at time T50, 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 sequentially samples the line voltage value of the analog line LA, and transmits the change of the line state to the break state B in a voltage packet to the telephone set side GW 10B. The telephone side GW 10B controls the line voltage value of the analog line LB based on the line voltage value notified by the station side GW 10A in a voltage packet via the IP network NW.

[0049] Therefore, 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'. Similarly, the change to the reverse state R at time T51, the change to the reverse state R at time T52, and the change to the normal state N at time T53 are reproduced as a change of the analog line LB to the reverse state R at time T51', a change to the break state B at time T52', and a change to the normal state N at time T53', respectively. As a result, the billing signal Sa5 sent from the exchange 20A from time T50 to time T53 is relayed to the public telephone 20B as the billing signal Sa5' from time T50' to time T53'.

[0050] 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 upon completion of the billing operation, sends a coin storage completion signal Sb5 to the analog line LB from time T55 to time T56. The telephone side GW 10B sequentially samples the line voltage value of the analog line LB, and sequentially transmits the coin storage completion signal to the station side GW 10A in a coin storage completion signal packet.

[0051] The central office side GW10A controls the coin collection completion signal outputted through the analog line LA based on the state of the coin collection completion signal notified by the telephone side GW10B via the IP network NW in the form of a sine wave signal packet. Therefore, the coin storage completion signal Sb5 sent from the public telephone 20B from time T55 to time T56 is relayed to the exchange 20A as a coin storage completion signal Sb5' from time T55' to time T56'.

[0052] At this time, the time required for sampling the coin storage completion signal and controlling the output of the coin storage completion signal is negligible in the charging operation. Therefore, the delay time td occurring during relay transfer of the charging signal can be regarded as mainly the packet transfer time tx of the IP network NW, that is, from time T50 to time T50'. It is considered that such a delay occurs similarly when the line voltage changes from the voltage state Vb (break state B) to the voltage state Vr (reverse state R) at time T51, when the line voltage changes from the voltage state Vr (reverse state R) to the voltage state Vb (break state B) at time T52, and further when the line voltage changes from the voltage state Vb (break state B) to the voltage state Vn (normal state N) at time T53. In addition, the coin storage completion signal Sb5 returned from the public telephone 20B is also delayed by the delay time td corresponding to the packet transfer time tx of the IP network NW, that is, from time T55 to time T55'.

[0053] However, these delays are significantly reduced compared to the delay time td in Fig. 6, which includes the monitoring period tm required to determine the change in the line voltage value. Therefore, as shown in Fig. 7, the coin storage completion signal Sb5 that starts to be transmitted from the public telephone 20B at time T55 is relayed to the exchange 20A via the telephone side GW10B, the IP network NW, and the office side GW10A before the waiting period tw from time T51 clocked by the exchange 20A ends. This allows the exchange 20A to correctly recognize that the billing operation at the public telephone 20B has been completed.

[0054] [Advantages of this embodiment] In this manner, this embodiment is configured such that the central office GW10A sequentially samples the line voltage value of the analog line LA, stores it in a packet, notifies the telephone side GW10B via the IP network NW, acquires the coin storage completion signal state from the packet received from the telephone side GW10B via the IP network NW, and sequentially controls the coin storage completion signal on the analog line LA to be equal to this coin storage completion signal. Also, the telephone side GW10B sequentially samples the coin storage completion signal on the analog line LB, stores it in a packet, notifies the central office GW10A via the IP network NW, acquires the line voltage value from the packet received from the central office GW10A via the IP network NW, and sequentially controls the line voltage value on the analog line LB to be equal to the line voltage value.

[0055] This allows the change in the line voltage value of the analog line LA on the central office side to be reproduced as a change in the line voltage value of the analog line LB on the telephone side, and the change in the coin storage completion signal on the analog line LB to be reproduced as a change in the coin storage completion signal output on the analog line LA. The delay in this case is significantly reduced compared to the delay time td including the monitoring period tm required to determine the change in the line voltage value described above. Therefore, the coin storage completion signal that is started to be transmitted from the public telephone 20B is delivered to the exchange 20A via the telephone side GW10B, the IP network NW, and the station side GW10A before the waiting period tw timed by the exchange 20A ends. This allows the exchange 20A to correctly confirm that the billing operation at the public telephone 20B has been completed.

[0056] [Extended embodiment] Although the present invention has been described above with reference to the embodiment, the present invention is not limited to the above embodiment. 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. [Explanation of symbols]

[0057] 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, Sa1, Sa5, Sa1', Sa5'...billing signal, Sb1, Sb5, Sb1', Sb5'...coin collection completion signal, tm...monitoring period, td...delay time, tx...packet transfer time, tk...transmission interval, tw...waiting period, T0, T0', T1, T2, T3, T5, T5', T50, T50', T51, T51', T52, T52', T53, T53', T55, T55', T56, T56'...time.

Claims

1. a station-side gateway connected to a switching center via a station-side analog line and also connected to an IP network; 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, a call relay circuit for relaying and transferring analog voice and call control signals of the station side analog line and voice packets and call control packets of the IP network to each other; a billing relay circuit for sequentially sampling a line voltage value of the analog line on the station side, storing the sampled value in a packet, notifying the telephone side gateway via the IP network, acquiring sine wave signal data from the packet notified from the telephone side gateway via the IP network, and outputting a sine wave signal to the analog line on the station side so as to be equal to a coin storage completion signal, The telephone side gateway a call relay circuit for relaying and transferring analog voice and call control signals on the telephone analog line and voice packets and call control packets on the IP network; a billing relay circuit that sequentially samples a sine wave signal of the analog line on the telephone side, stores the sampled signal in a packet, notifies the station side gateway via the IP network, obtains the line voltage value from the packet notified from the station side gateway via the IP network, and sequentially controls the line voltage value of the analog line on the telephone side to be equal to the line voltage value. A public telephone relay system comprising:

2. 2. A gateway constituting a telephone side gateway used in the public telephone relay system according to claim 1.

Images