GB2332592A

GB2332592A - Telephone line monitoring

Info

Publication number: GB2332592A
Application number: GB9726650A
Authority: GB
Inventors: Stewart Leeper
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1997-12-17
Filing date: 1997-12-17
Publication date: 1999-06-23
Also published as: GB9726650D0

Abstract

A telephone (11) sends characterization tones to a telephone exchange (10) to determine the integrity of the coupling between the telephone (11) and the exchange (10). If the coupling is disturbed, an error indication is displayed.

Description

2332592 TELEPHONE OPERATING METHOD

Background of the Invention

The present invention relates, in general, to telephones, and more particularly to a telephone operating method.

The ever increasing need for security has increased the need to provide better security for telephones and especially for pay telephones. Telephone conversations can be monitored by coupling electronic devices to telephone lines that interconnect the telephone to a telephone central office or exchange. Additionally, public telephones can be damaged due to vandals or theft of telephone elements such as the receiver. Typically, telephones do not have any security measures that detect or inform users of such security violations.

Accordingly, it is desirable to have a method of operating a telephone that can detect electronic devices that are coupled to the telephone line, that provides data security for the conversations conducted over the telephone, and that alerts users to security violations.

Brief Description of the Drawings

FIG. 1 schematically illustrates a block diagram of a portion of a telephone system in accordance with the present invention; FIG. 2 is a flow chart illustrating some of the operations of the telephone system shown in FIG. 1 in accordance with the present invention; 25 and FIG. 3 is a continuation of the flow chart of FIG. 2 in accordance with the present invention.

Detailed Description of the Drawings

FIG. 1 is a block diagram illustrating a portion of a telephone system that includes a telephone central office or telephone exchange 10 that is coupled to a telephone or phone 11. Phone 11 and exchange 10 are coupled via telephone lines or telephone wires 21 and 22, or other interconnecting medium 35 such as fiber optic links. Phone 11 and exchange 10 have a security protocol that facilitates detecting security breaches that may result in other parties over hearing conversations conducted on phone 11 or other security breaches such as the theft of portions of phone 11.

Phone 11 has a receiver 14 that functions as the receiver of any ordinary telephone. Phone 11 may also include a display 36 in order to provide visual messages to a user of phone 11, and a card reader 37. Phone 11 also has a controller 12 that is utilized to control the flow of voice messages and security protocols between phone 11 and exchange 10.

Controller 12 has a storage area 13 used for maintaining information and codes that facilitate providing the security. Storage area 13 typically contains a phone identification or phone ID that is used for encrypting information or voice before phone 11 transmits the information or voice to exchange 10. As will be seen hereinafter, exchange 10 receives the phone ID and compares it to a phone ID stored within exchange 10. Area 13 also contains characterization tone information that is used to transmit characterization tones to exchange 10 allowing exchange 10 to determine the integrity of the coupling between phone 11 and exchange 10. Exchange amplitude and exchange phase factors are also stored within storage area 13 and are derived from characterization tones transmitted from exchange 10 to phone 11 as will be seen hereinafter. An exchange ID is stored in storage area 13 and is used to decrypt encrypted information transmitted from exchange 10 to phone 11. Typically, controller 12 is a digital signal processor (DSP) and the encryption and decryption functions are performed by software within the DSP. The use of encryption algorithms by DSPs to encrypt and decrypt information is well known to those skilled in the art.

An analog-to-digital converter 16 receives analog information from receiver 14 and converts it to a digital format so that controller 12 may manipulate and transmit the information in digital form. A modulator 18 receives a serial digital data stream from controller 12 and converts it to an analog signal that is transmitted over wires 21 to exchange 10. Similarly, exchange 10 has a modulator 27 that is used to modulate and transmit information to phone 11. Phone 11 receives the information from exchange 10 in a serial stream and demodulates the information tO digital form with a demodulator 19. Demodulator 19 presents the serial digital data to controller 12 and controller 12 performs decryption and other functions, as will be seen hereinafter. After processing the information, controller 12 presents the serial digital data to a digital-to-analog converter 17 that converts the digital information to analog and drives receiver 14 with the analog information.

A control unit or microcontroller (MCU) 23 receives error information and other information to be displayed to a telephone user and presents the information to display 36. MCU 23 also receives information from card reader 37 and presents the information to controller 12 so that controller 12 may transmit the information to exchange 10.

Exchange 10 has a line card or controller 31 that is similar to and functions in a similar manner as controller 12. Controller 31 typically is one of many controllers in a large telephone exchange, typically called line cards, that are connected to a bus that is controlled by another processor (not shown).

Large telephone exchanges having line cards interconnected to a bus and controlled by an external processor is a configuration that is well know to those skilled in the art. Controller 31 has a storage area 32 that fimctions similarly to area 13. Controller 31 receives serialized digital information from a demodulator 26 which in turn receives the modulated information transmitted by phone 11. After processing the information, a digital-to- analog converter 28 receives digital information from controller 31 and presents the information to a bus (not shown) to which controller 31 is attached. Similarly, controller 31 receives digital information from an analog-to-digital converter 29 that receives analog information from the external bus. Controller 31 transmits serialized data in digital form to a modulator 27 which modulates the digital information and transmits it to phone 11.

Modulators 18 and 27 modulate the digital information in one of many well known modulation techniques such as Global System for Mobile communication (GSM), European Telecom Standards Institute (ETSI) specification such as ETSI G729A, or other well know modulation techniques.

The information exchanged between phone 11 and exchange 10 typically is in a packet form and each packet is spaced at periodic intervals.

In one embodiment, each packet contains information in the following order:

encrypted voice information, encrypted payment data (credit information from pay phone 11 35to exchange 10 or debit information from exchange 10 to phone 11), and characterization tone.

Phone 11 and exchange 10 each create a characterization tone that is transmitted to the other unit in order to characterize the coupling between phone 11 and exchange 10, and to detect changes in the coupling. Any change in the coupling characteristics may indicate the phone coupling is being monitored. Typically, each characterization tone is acombination of frequencies, for example signals at ten kilohertz and twenty kilohertz, that are be transmitted from phone 11 to exchange 10. controllers 12 and 31 generate the characterization tone fom the stored digital word or words that represent the frequency or frequencies to be transmitted (as illustrated by the TONES word shown in controllers 12 and 31). Each word represents a frequency to be transmitted as the characterization tone. Techniques for using a DSP to generate a frequency from a stored digital word are well known in the art.

Upon receiving the characterization tone, controllers 12 and 31 determine the corresponding amplitude factor by comparing the amplitude of the received characterization tone to the known amplitude utilized to transmit the characterization tone thereby determining the amplitude loss in the coupling between phone 11 and exchange 10. controllers 12 and 31 also measure the phase of each characterization tone and determines the phase shift that occurred during transmission of the characterization tone. The amount of phase shift represents the phase factor. Techniques for determining amplitude and phase shift of a received signal are well know to those skilled in the art, including routines or algorithms utilized by a DSP to determine such information.

Upon installation, phone 11 sends an initial characterization tone to exchange 10. Exchange 10 receives the characterization tone and determines both the amplitude of the received signal and the phase shift of the received signal in order to determine a phone amplitude factor and a phone phase factor. The amplitude and phase factors are stored in controller 31. During phone operation or while phone 11 is idle, phone 11 again transmits the characterization tones. The characterization data developed by exchange 10 from the received tones is compared to the original characterization data or factors in order to determine the integrity of the coupling between phone 11 and exchange 10. Thereafter, during the operation of phone 11, phone 11 transmits characterization tones with each packet of information sent from phone 11 to exchange 10. Exchange 10 determines a new or received phone amplitude factor and new or received phone phase factor. The received factors are compared to the stored phone amplitude and phone phase factors. If the received amplitude and phase factors do not match the stored values of the phone amplitude and phone phase factors, exchange 10 sends an error indication to phone 11. If wires 21 and 22 have been disturbed either by tapping of the phone lines or destruction, the received phone amplitude factor and received phone phase factor typically will not match the originally transmitted and stored phone amplitude and phone phase factors.

Similarly, Pxchange 10 transmits a characterization tone to phone 11 so that phone 11 may determine the integrity of the coupling between phone 11 and exchange 10 and generate error conditions when the received exchange amplitude factor and received exchange phase factors do not match the stored values.

FIG. 2 and FIG. 3 are flow charts illustrating some of the operating steps of phone 11 and exchange 10. Upon installation of phone 11 and initial application of power, phone 11 sends the phone IID along with a characterization tone to exchange 10, and exchange 10 generates and stores phone characterization factors including the phone amplitude factor, the phone phase factor, and phone ID. Although not shown in FIG. 2, if exchange already has phone characterization factors stored, exchange 10 sends an error indication to phone 11 to indicate that phone 11 may have been tampered with. If exchange 10 did not have phone characterization factors previously stored, then exchange 10 sends the exchange ED along with a characterization tone to phone 11 and phone 11 generates and stores exchange characterization factors including the exchange ID, exchange amplitude factor, and the exchange phase factor and stores these within controller 12. Phone 11 and exchange 10 then wait for either phone 11 to initiate a call to exchange 10 or exchange 10 to initiate a call to phone 11 and begin an operation.

FIG. 2 shows the sequence when phone 11 is idle and not used for a call to exchange 10. Phone 11 sends a packet to exchange 10 that includes a characterization tone. Thereafter exchange 10 generates a received phone characterization factor including a new or received phone amplitude factor and a new or received phone phase factor. The received phone amplitude and phase factors are compared to the stored characterization factor including comparing the received phone amplitude factor to the stored amplitude phone factor and the received phone phase factor to the stored phone phase factor.

If the received factors are different from the stored factors, exchange 10 sets an error message and terminates operation. If the received and stored factors are the same and phone 11 is not in operation, phone 11 continues sending characterization tones.

FIG. 3 is a flow chart illustrating some of the sequences that occur when either exchange 10 is transmitting to phone 11 or phone 11 is transmitting to exchange 10 or both occurring simultaneously. Upon exchange 10 initiating a transmission to phone 11, exchange 10 encrypts the exchange ID, voice data, pay data, and other information and forms a packet to send to phone 11. The packet includes the encrypted information followed by the characterization tone as indicated herein before. Phone 11 receives the packet and demodulates it with demodulator 19. The serial demodulated digital information is presented to controller 12. Controller 12 uses the stored exchange ED as a seed value and decrypts the voice data, exchange ED, and the other data. The received exchanged]ED is compared with the value of the stored exchange ID. If the received and stored ED's are different, phone 11 sets a phone error indicator in display 36. If they are the same, phone 11 generates the received exchange characterization factors from the received characterization tone to form the received exchange amplitude factor and received exchanged phase factor and compares these to the stored characterization factors including the stored exchanged amplitude factor and stored exchange phase factor. If the stored characterization factors are different from the received characterization factors, phone 11 sets an error message in display 36. If the factors are the same, phone 11 sends the digital voice information through converter 17 to receiver 14.

Similar fimctions occur when phone 11 is transmitting or initiates a transmission to exchange 10. Receiver 14 converts speech into analog signals that are supplied to converter 16. Converter 16 changes the analog information to digital words that are provided to controller 12.. Through controller 12, phone 11 forms a packet and characterization tones to send to exchange 10. Phone 11 uses the phone ID as a seed value to encrypt the voice information received from converter 16 along with the phone ID and other data including credit and debit information and encrypts the information in order to create the data packet. Phone 11 sends the data packet along with the characterization tone to modulator 18 which modulates the information, as described hereinbefore, and transmits the information to exchange 10. Exchange 10 receives the modulated information and demodulates it through demodulator 26 to provide the serial digital data stream to controller 31. Controller 31 decrypts the voice data, phone ID, and other data and compares the received phone ID to the stored value of the phone ED. If the stored value and the received value are different, exchange 10 sets an error and terminates transmission with phone 11. If the i)hone ID's are the same, exchange 10 generates a phone characterization factor by generating the received phone amplitude factor and the received phone phase factor. These are compared to the stored phone amplitude factor and the stored phone phase factor. If the stored values and received values are difTerent, exchange 10 sets an error indication and terminates communication with phone 11. If the stored and received values are the same, exchange 10 sends the received digitized voice data through digital-to-analog converter 28 to the remainder of the central exchange. This sequence is repeated as long as phone 11 is transmitting to exchange 10.

In an alternate embodiment, controller 12 and controller 31 can generate the characterization factors in parallel with decrypting the data packet and with comparing received ID's to stored ID's. Further, one skilled in the art will realize that a summing junction can be placed between modulator 18 and wire 21 and the characterization tones can be inserted and summed with the modulated data packet instead of controller 12 generating a digital representation of the characterization tones and transmitting them through modulator 18. Similarly, another summing junction can be placed after modulator 27 allowing exchange 10 to send the characterization tones in a similar manner. Additionally it will also be noted that exchange 10 could also be another pay phone or other type of equipment that operates in a similar manner to phone 11 or exchange 10.

By now it should be appreciated that there has been provided a novel way to provide a secure telephone system. Using the phone to determine and 35 store characterization factors within the phone permits the phone to determine the integrity of the communication link between the phone and the telephone exchange. Storing characterization factors in the exchange also allows the exchange to determine the integrity of the communication link. Storing exchange the ID in the phone and continually checking the exchange ID with each transmitted data packet permits the phone to determine that it is connected to a proper telephone exchange and to provide a seed value for decrypting encrypted information. Transmitting only_encrypted information also makes it difficult for someone to capture the information transmitted between the phone and the exchange.

Claims

1. A method of operating a telephone comprising: receiving a first characterization tone at a first telephone; and using the first characterization tone received by the telephone for forming a first received characterization data.

2. The method of claim 1 further including storing the first received characterization data in the first telephone.

3. The method of claim 1 further including comparing thefirst received characterization data to other characterization data stored in the first telephone.

4. The method of claim 3 ffirther including setting an error condition when the first received characterization data does not match the other characterization data.

5. The method of claim 1 wherein forming the first received characterization data includes forming a first received amplitude factor and a first received phase factor.

6. The method of claim 1 further including the first telephone transmitting a second characterization tone to a second telephone.

7. The method of claim 1 further including the first telephone receiving a first encrypted data packet and decrypting the first encrypted data packet.

8. A method of operating a telephone comprising: receiving a first encrypted data packet at the telephone; and decrypting the first encrypted data packet into received voice data.

9. The method of claim 8 further including receiving a characterization tone at the telephone.

10. A telephone security method comprising: providing a telephone exchange; providing a telephone coupled to the telephone exchange; sending a first characterization tone from the telephone exchange to the telephone; determining a first exchange amplitude factor from the first characterization tone wherein the determining the first exchange amplitude factor is performed by the telephone; determining a first exchange phase factor from the first characterization tone wherein the determining the first exchange phase factor is performed by the telephone; sending a second characterization tone from the telephone to the telephone exchange; determ J n J n g a first phone amplitude factor from the second characterization tone wherein the determining the first phone amplitude factor is performed by the telephone exchange; and determining a first phone phase factor from the second characterization tone wherein the determining the first phone phase factor is performed by the telephone exchange.

11. The method of claim 10 further including determining a second exchange amplitude factor and a second exchange phase factor; comparing the first exchange amplitude factor and the first exchange phase factor to the second exchange amplitude factor and the second exchange phase factor; and creating a security warning upon a mismatch from the comparing step.

12. The method of claim 11 wherein creating the security warning includes decoupling the telephone from the telephone exchange.

13. The method of claim 11 wherein creating the security warning includes creating an error indication on the telephone.

14. The method of claim 10 further including sending an exchange ID to the telephone from the telephone exchange; using the exchange ID to decrypt signals sent to the telephone from the telephone exchange; sending a phone ID from the telephone to the telephone exchange; and using the phone ID to decrypt signals sent to the telephone exchange from the telephone.

15. The method of claim 10 wherein sending the first characterization tone includes sending a plurality of frequencies.

16. The method of claim 10 further including using a frequency greater than approximately five Kilo-Hertz for sending the first and second characterization tones.

17. The method of claim 16 further including using a frequency less than approximately five Kilo-Hertz for sending voice or data simultaneously with sending the first and second characterization tones.

18. A method of operating a telephone substantially as hereinbefore 20 described with reference to the accompanying drawings.

19. A telephone security method substantially as hereinbefore described with reference to the accompanying drawings.