TELEPHONE CALLBACK DETECTOR

Abstract: A callback system detector (300) is connected between a toll trunk (200) and a local switched telephone network (100) for detecting and discouraging operation of a toll callback system wherein incoming calls on the toll trunk line are employed as a gateway for a user of the switched telephone network (100) to place calls within a remote telephone network and thus avoid tariffs charged by the local network (100) for outgoing calls to the remote network. The callback system detector is configured to determine the presence, within an incoming call on the toll trunk (200), of a condition indicative of operation of such a callback system. Such a condition may be defined as incoming dial or ringing tones on the toll trunk, or as outgoing dual-tone multi-frequency (DTMF) tones on the toll trunk. In order to allow such tones to be transmitted in the normal course of a call that may legitimately employ such tones, operation of the callback detector may advantageously be limited to a predetermined time period defining an initial call interval. The callback detector (300) may be configured to disrupt communication within the call upon detection of the condition, or further may be configured to cause disconnection of the call or assessment of a billing charge to the local recipient of the call.

Description: TELEPHONE CALLBACK DETECTOR Background of the Invention In some regions, there can be a wide disparity in international telephone rates and the applicable rate often depends on the country from which a call originates. International settlement rates between long distance carriers are sometimes set such that is can be significantly less expensive to place a call into Country A from Country B than to place a call into Country B from Country A. When such a rate disparity exists, a person in Country A, for example, can arrange for a service in Country B to call him, and then allow him to dial a call through Country B's telephone network to his desired destination. The caller in Country A then pays the lower rate for a call originating in Country B and avoids the higher rate that would apply if he had placed a normal long distance call from Country A. In another scenario, it could be less expensive to place a call between Countries A and C by establishing two simultaneous calls, one from Country B into Country A, as described above, and another from Country B into Country C. Those two calls could then be interconnected within Country B to effect an international connection between Countries A and C, but at the lower rate available in Country B. In some countries, the use of such "callback" services is illegal or is at least a drain on the revenues of the international long distance carrier in the higher rate country. Therefore, it would be desirable to detect such calling patterns and either block the call or apply a suitable surcharge to the caller from the higher rate country so as to discourage such techniques. Summary of the Invention The above-described problems associated with the current state of the art in international telecommunications are resolved to a large extent by a callback detection system in accordance with the present invention. A switched telephone system has an international trunk line for carrying voice signals to another country and a signaling channel associated with the trunk line. A signaling monitor is connected to the signaling channel for monitoring signals on the channel and detecting signals that are being transmitted from a location at a remote end of the international trunk line. The signaling monitor provides a remote-call indication signal when such a condition is detected. A callback detector is operatively connected to the international trunk line. The callback detector is also connected to the signaling monitor for receiving the remote-call indication signal. When the callback detector receives a remote-call indication signal it begins to monitor a corresponding channel on the trunk line for a signal that is indicative of a call emanating from a callback service. When such a signal is detected, the callback detector either blocks the call or sends a callback indication signal to the central switching system or billing system of the telecommunications company for appropriate action. Such action would include blocking the call or applying an appropriate surcharge to the account of the caller. Detailed Description Referring now to Figure 1 there is shown a telecommunications network 100 in a first country (Country A) which has international trunk lines 200 connected thereto for transmitting calls to and receiving calls from another country (Country B). Associated with the international trunk lines 200 is a signaling channel 600. The signaling channel 600 is embodied as a standard or non-standard signaling channel, such as, but not limited to, international signaling system 5, 6, or 7. The international trunk lines are connected through a callback detector 300 and the signaling channel 600 is connected through a signaling monitor 500. The signaling monitor 500 is preferably incorporated into the switched telephone network 100. The signaling monitor 500 is connected to the callback detector 300 and the callback detector 300 is connected to the switching system or billing system 400 of the international long distance carrier in Country A. The signaling monitor 500 monitors the signaling channel 600 for an incoming call, that is, a call originating from the remote end of the international trunk lines 200. In the present embodiment, the call could originate from Country B which has a lower international long distance rate for calls into Country A relative to the rate for calls into Country B from Country A. When such a call is detected, the signaling monitor 500 communicates that information to the callback detector 300 and identifies the particular channel that is receiving the incoming call. The callback detector then monitors the specified channel for any of the following telltale conditions within a preselected initial period of the call: (1) an incoming dial tone; (2) outgoing dual tone multi-frequency (DTMF) signaling; or (3) an incoming ringing tone. An incoming dial tone would not normally be present on an incoming call. However, it is often used by callback systems to indicate to the subscriber that a call back to the originating can be made. A callback subscriber often uses DTMF signals to signal his desired call destination to the callback system. While subscribers use DTMF signaling to control voice response systems such as voice mail, such signaling is not normally used during the initial period of an incoming call, defined as a predetermined time interval from the commencement of the call. In a "callback" telephone call, an incoming ringing tone from the selected destination telephone indicates to the callback subscriber that the callback call is being attempted. Although it is possible to get an incoming ringing tone on an incoming call under other conditions, such as call re- routing, those conditions would not normally be present during the initial period of the call. When the callback detector 300 detects any of the foregoing conditions, the call is determined to be a "callback" call. At this point, the callback detector 300 may force the termination or disruption of the call by any number of methods, such as interrupting the speech path between the switched network 100 and the international trunks 200. Such interruption may include insertion of idle code in both directions in the speech path or the insertion of an "all trunks busy" or other tone in the speech path. Alternatively, the presence of a callback call can be communicated by the callback detector 300 to the telephone company's switching or billing system 400 so that the call can be disconnected or blocked, or so that an appropriate surcharge can be applied to the subscriber's telephone billing account. Signaling between the callback detector 300, the signaling monitor 500, and the switching or billing system 400 is preferably sent via dedicated connections or within the signaling protocol of the speech channel 200.

Claims: That which is claimed is: 1. An apparatus for deterring operation of a callback system operating between a switched telephone network and a toll trunk line having speech channels and a signaling channel, comprising: a signaling monitor connected to the signaling channel of the toll trunk line and configured to provide an indication that an incoming call is being received on a corresponding speech channel of the toll trunk line; a callback detector connected with speech channels of the toll trunk line and responsive to the indication provided by the signaling monitor for detecting, within the corresponding speech channel, a condition indicating operation of the callback system using the speech channel. 2. The apparatus of claim 1 wherein the callback detector is configured to disrupt communication on the speech channel upon detection of said condition. 3. The apparatus of claim 2 wherein said callback detector is configured to interrupt the speech channel by at least one of (i) providing an idle code to the speech channel, (ii) providing a busy signal to the speech channel, and (iii) providing an audible tone to the speech channel. 4. The apparatus of claim 1 wherein said callback detector is configured to detect said condition as at least one of (i) an incoming dial tone on the speech channel, (ii) an incoming ringing tone on the speech channel, and (iii) outgoing DTMF tones on the speech channel. 5. The apparatus of claim 4 wherein said callback detector is configured to detect said condition for a predetermined time period limited to a predetermined initial call interval. 6. The apparatus of claim 1 wherein a switching system is connected with the switched telephone network and wherein said callback detector is connected with said switching system and further configured to provide a signal to the switching system for disconnection of the incoming call upon detecting said condition. 7. The apparatus of claim 6 wherein said callback detector is configured to detect said condition as at least one of (i) an incoming dial tone on the speech channel, (ii) an incoming ringing tone on the speech channel, and (iii) outgoing DTMF tones on the speech channel. 8. The apparatus of claim 7 wherein said callback detector is configured to detect said condition for a predetermined time period limited to a predetermined initial call interval. 9. The apparatus of claim 1 wherein a billing system is connected with the switched telephone network and wherein said callback detector is connected with said billing system and further configured to provided a signal to the billing system for applying a predetermined charge for receiving the incoming call. 10. The apparatus of claim 9 wherein said callback detector is configured to detect said condition as at least one of (i) an incoming dial tone on the speech channel, (ii) an incoming ringing tone on the speech channel, and (iii) outgoing DTMF tones on the speech channel. 11. The apparatus of claim 10 wherein said callback detector is configured to detect said condition for a predetermined time period limited to a predetermined initial call interval. 12. The apparatus of claim 1 wherein said callback detector is configured to detect said condition as at least one of (i) an incoming dial tone on the speech channel, (ii) an incoming ringing tone on the speech channel, and (iii) outgoing DTMF tones on the speech channel. 13. The apparatus of claim 1 wherein said callback detector is configured to detect said condition for a predetermined time period limited to a predetermined initial call interval. 14. A method of deterring operation of a callback system between a toll trunk line and a switched telephone network, comprising the steps of: detecting initiation of an incoming call on a channel of said toll trunk line; monitoring said channel of said toll trunk line for a condition indicative of operation of the callback system; and discouraging subsequent operation of the callback system. 15. The method of claim 14 wherein said monitoring step comprises the step of: determining the presence of said condition as one of (i) an incoming dial tone on the channel, (ii) an incoming ringing tone on the channel, and (iii) outgoing DTMF tones on the channel. 16. The method of claim 15 wherein said determining step is performed for a predetermined time period limited to a predetermined initial call interval. 17. The method of claim 14 wherein said discouraging step comprises at least one of (i) disrupting communication on the channel, (ii) providing an idle code to the channel, (iii) providing a busy signal to the channel, (iv) providing an audible tone to the speech channel, (v) disconnecting the call, and (vi) assessing a billing premium for receipt of the incoming call. 16. An apparatus for connection between a toll trunk and a switched telephone network, comprising: a control input for receiving an identification of an incoming call on the toll trunk; a condition detector for detecting a condition of the incoming call indicative of operation of a callback system; and an output for signaling detection of said condition. 17. The apparatus of claim 16 wherein said condition detector is configured to detect at least one of (i) an incoming dial tone on the toll trunk, (ii) an incoming ringing tone on the toll trunk, and (iii) outgoing DTMF tones on the toll trunk. 18. The apparatus of claim 17 wherein said condition detector is configured to detect said condition for a predetermined time period limited to a predetermined initial call interval. 19. The apparatus of claim 16 further comprising means for disrupting communication on the toll trunk in response to detecting said condition.

Inventors: GRITTON CHARLES, SKENE JEREMY, GRITTON, CHARLES, SKENE, JEREMY
Applicants: TELLABS OPERATIONS INC, TELLABS OPERATIONS, INC.
Application year: 1998
Main classification: H04M1
IPC codes: H04M3, H04M15