GB2465833A - An apparatus for communicating between an alarm device and an alarm gateway over the Public Switched Telephone Network. - Google Patents

Abstract

A method and apparatus for providing for communication over a public switched telephone network (PSTN) 30, between an alarm device 20 and a remote device such as an alarm gateway 50, polling server 60 or alarm receiving centre 40. The alarm device 20 is of the type which communicates using the dual tone multi-frequency fast format (DTMF FF) protocol. An interface device 10 provides for such communication by communicating with the alarm device 20 using a DTMF FF protocol, and communicating with the remote device using a modified DTMF FF protocol, so as to overcome problems when communicating over a PSTN telephone network 30.

Description

ELECTRONIC DEVICE

Technical Field

The present invention relates to a method and an apparatus for providing for communication over a PSTN, to an alarm gateway arranged to communicate with an interface device via a PSTN, and to a polling server arranged to communicate with an interface device via a PSTN.

Background

Alarm devices are used in domestic, commercial and other premises to signal an alert indicative of an alarm condition being met, such as, for example, an intruder entering the premises. Upon such an alert being signalled, alarm devices send an alarm message to a remote device. Some existing alarm devices are connected to and form part of an alarm network over which the alarm device can communicate with a remote device, such as an Alarm Receiving Centre (ARC). Some existing devices use the Public Switched Telephone Network (PSTN) to send the alarm messages to the remote ARC which is connected to the alarm unit via the PSTN. The ARC then takes appropriate action, such as informing a predetermined responsible person, or the police, that an alarm message has been received. The cause of the alert can then be investigated.

The manner in which some existing alarm devices communicate over the PSTN is the Dual Tone Multi-Frequency Fast Format (DTMF FF) Protocol, as defined in draft IEC Publication 839: Alarm Systems, Part 8: DTMF Protocol for use in digital communicator alarm transmission systems at interfaces with the PSTN, document reference IECITC79/WG5/17D and BSIA Form 255.

Briefly, this protocol can be described as adhering to the following steps: first, an alarm device dials the telephone number of the remote device using Dual Tone Multi-Frequency (DTMF) tone-pairs. The alarm device then waits to receive an acknowledgement signal from the PSTN, the acknowledgement signal indicating that the dialled telephone number has been correctly received. Upon receiving this acknowledgement signal, the alarm device sends a string of up to 23 DTMF tone-pairs to the remote device, and then repeats this string a second time. The remote device compares the two DTMF strings and, if they match, the remote device sends a further acknowledgement signal to the alarm device. This further acknowledgement is usually referred to as a "Kiss-Off'. After sending the two strings of DTMF tone-pairs, the alarm device awaits the reception of the Kiss-Off acknowledgement signal.

If, after a predetermined time-out period (usually 400 to 600 ms) the Kiss-Off acknowledgement signal is not received by the alarm device then the alarm device sends the DTMF tone-pair string a third time. The remote device then has the opportunity to compare the second and third DTMF strings sent by the alarm device to determine whether or not they match. If there is a match then the remote device sends the Kiss-Off acknowledgement signal to the alarm device. If, after a further predetermined time-out period, the Kiss-Off acknowledgement signal is not received at the alarm device, the alarm device sends the DTMF string a fourth and final time to the remote device. The remote device then has a final opportunity to match consecutive pairs of DTMF strings and, if appropriate, to send the Kiss-Off acknowledgement signal to the alarm device. This arrangement provides for error checking and correct reception of the DTMF pairs at the remote device, and provides for confirmation at the alarm device that the remote device has correctly received the DTMF string.

Any practical communications network exhibits an end-to-end transmission delay, defined as the time taken for data sent into the network at its connection with the data source to travel through the network and arrive at the destination (e.g. the remote device) on the other side of the network. For legacy PSTNs, and such as for example the UK telephone network infrastructure in use during the latter half of the 20th century, referred as "2OCN", the end-to-end transmission delay of such a PSTN was essentially predictable and could be guaranteed to be below a defined limit in terms of a number of milliseconds, typically about 2Oms. Furthermore, a remote device, such as an ARC, exhibits an internal processing delay, defined as the time taken from the DTMF string being received by the remote device to the remote device sending the Kiss-Off acknowledgement signal. Some existing remote devices have an internal -processing delay of up to 250ms. Accordingly, the predetermined time-out delays designed into the DTMF FF Protocol (within which the Kiss-Off acknowledgement signal must be received by the alarm device if the alarm device is not to retransmit the DTMF string a third, or fourth time) should be set longer than a combined response delay (defined as twice the maximum end-to-end transmission delay through the legacy PSTN, plus the expected maximum internal processing delay of the remote device). This being the case, once the predetermined time-out delay has expired, it is known that no Kiss-Off signal will subsequently be received by the alarm device.

At the present time, at least in the UK, the PSTN infrastructure is being upgraded from the legacy PSTN referred to as 2OCN to a new infrastructure based upon packet switching and referred to as "21CN", or 21st century network. Because the new network infrastructure uses packets, similar to Internet infrastructure, the end-to-end network delay is no longer predictable as was the case for the legacy PSTN. In particular, it is not possible to place a definite maximum limit on the end-to-end network delay between an alarm device and an ARC connected via the new 21 CN PSTN. A problem resulting from this is that devices using the DTMF FF Protocol to communicate can fail to communicate properly: a failure mode arises when the combined response delay is close to the predetermined time-out delay at the alarm device. Thus, either an end-to-end network delay or a remote device internal processing delay which is too long can cause the failure mode to occur. In such a failure mode, the Kiss-Off acknowledgement signal may have been sent by the ARC, but due to a long combined response delay before the Kiss-Off acknowledgement signal arrives at the alarm device, the predetermined time-out period expires at the alarm device causing the alarm device to retransmit the DTMF string at substantially the same time that the Kiss-Off acknowledgement signal would otherwise arrive at the alarm device. Since the telephone line is a single duplex connection, the incoming Kiss-Off acknowledgement signal and the outgoing DTMF string retransmission interfere with each other and it is likely that the Kiss-Off acknowledgement signal will not be received at the alarm device. Meanwhile, the ARC has completed its operations and is no longer listening for further DTMIF strings and will therefore not send any further Kiss-Off acknowledgement signals. Thus, the alarm device never receives a Kiss-Off acknowledgement signal.

There is a very large installed base of existing alarm devices which use the DTMF FF protocol to communicate. It is thought that many of these existing alarm devices will fail when the PSTN infrastructure is upgraded to the newer 21 CN architecture. In order to change all of the existing units it is estimated that it would take the existing maintenance workforce around 2 years to.complete the task, even if they did nothing else. A solution to this problem is therefore required.

Summary

According to a first aspect of the present invention there is provided a method of operating an interface device to provide for communication between an alarm device and a remote receiving device over a PSTN having unpredictable end-to-end transmission delays, the alarm device and the remote receiving device arranged to communicate with each other in accordance with the DTMF Fast Format protocol, the method comprising: a) the interface device receiving from the alarm device at least one of two DTMF strings indicative of information to be transmitted from the alarm device to the remote receiving device in accordance with the DTMF Fast Format protocol; b) in response to receiving the at least one string, the interface device sending the at least one string over the network to the remote device; c) in response to receiving the at least one string, the interface device sending to the alarm device a signal indicative of the two strings having been received in accordance with the DTMF Fast Format protocol, without waiting for such a signal from the remote receiving device.

Step (c) may include the step of the interface device sending the signal in response to receiving both of the two strings.

In the method above, the alarm device may be, for example, a fire alarm unit, an intruder alarm unit, a personal alarm unit.

In the method above, the at least one string in step (b) may be sent twice over the network to the remote device. It may be sent twice only.

In the method above, the remote device may be an ARC, an alarm gateway, an administration server or a polling server. The alarm gateway andlor the polling server may be as defined herein below.

In the method above, when the remote device is an ARC, the interface device communicates with the remote device using a robust variant of the DTMF Fast Format protocol, the ARC being arranged to communicate using the DTMF Fast Format protocol.

In the method above, when the remote device is an alarm gateway the interface device communicates with the remote device by a modem connection or using a robust variant of DTMF Fast Format protocol. The modem connection preferably runs at about 300 signal transitions per second.

In the method above, before the step of sending the at least one string over the network to the remote device, a step of opening a communications link over the network between the interface device and the remote device may be performed.

In the method above, when the remote device is arranged to conmiunicate using DTMF Fast Format protocol, after the step of sending the at least one string over the network to the remote device, if a signal indicative that the at least one string has been received by the remote device is not received within a predetermined period of time, the signal, then the communications link may be closed, and subsequently the steps of opening a communications link and sending the at least one string over the network to the remote device may be repeated. Preferably the predetermined period of time is about 1 second.

In the method above, the step of receiving from the alann device at least one of the two DTMF strings may be preceded by the step of receiving from the alarm device a first telephone number uniquely identifying a device connected to the PSTN.

In the method above, the step of opening a communications link may incorporate the step of sending a second telephone number over the PSTN, the second telephone number uniquely identifying a device connected to the PSTN with which the communications link is to be established.

The method above may further incorporate the steps of storing data in a memory of the interface device, the stored data including one, any combination, or all of: a pattern telephone number for comparison with each first telephone number received from the alarm device, at least one mapping telephone number for selective sending over the PSTN, a polling telephone number for selectively sending over the PSTN, an administration telephone number for selectively sending over the PSTN, and log data, each telephone number uniquely identifying a device connected to the PSTN.

In the method above, the polling telephone number andlor the mapping telephone number may be a toll-free telephone number.

The method may further comprise a step of comparing the pattern telephone number with the first telephone number, and selectively causing the second telephone number to be one of the first telephone number and the at least one mapping telephone number, one of the at least one mapping telephone numbers being selected when the first telephone number is determined to match the pattern telephone number, and the first telephone number being selected when the first telephone number is determined not to match the pattern telephone number.

In the method above, each mapping telephone number may be the same as the pattern telephone number, or may be different from the pattern telephone number.

In the method above, the step of sending the at least one string to the remote device may include sending the at least one string to one or more remote devices, wherein the second telephone number may be modified using a rule or by recalling one or more mapping telephone numbers, so as to uniquely identify one or more remote devices.

Each pattern telephone number may have a plurality of different mapping telephone numbers associated therewith.

In the method above, the at least one string may contain an identification code identifying the alarm device and the identification code may be modified by the interface device before it is sent therefrom. The modification may be by a rule or a memory look-up table, the modification depending on which of multiple remote devices the at least one string is sent to, before the at least one string is sent over the PSTN to the remote device.

The method may also comprise the step of the interface device periodically sending a polling message from the interface device to a polling server, the second telephone number selected to be the polling telephone number, the polling server uniquely identified by the polling telephone number, the polling message indicating to the polling server that the alarm unit is operating correctly.

The method may also incorporate the step of sending additional polling messages to the polling server, the additional polling messages including an open message indicating that a premises has been unlocked, andlor a close message indicating that the premises has been locked.

The method may incorporate steps to operate a static polling policy, wherein polling messages are periodically sent to the polling server with a predetermined polling time interval.

The method may incorporate steps to operate a dynamic polling policy wherein polling messages are sent to the polling server with a frequency influenced by whether or not an additional polling message has been sent during a predetermined polling time period.

The method may incorporate the step of the interface device operating an electrical switch to normally connect a user device to the PSTN when the first telephone number is determined not to match the pattern telephone number; and to disconnect the user device from the PSTN when the first telephone number is determined to match the pattern telephone number. The user device may be, for example, a telephone or a fax machine.

In the method above, after the step of sending the at least one string over the network to the remote device, the method may further comprise the steps of the interface device monitoring for reception of, and/or receiving from, the remote device a signal indicative that an administration operation should be performed. If such a signal is received the method may include the step of the interface device opening a communications link to an administration server. This may be by sending an administration telephone number uniquely identifying an administration server connected to the PSTN, thereby opening a communications link to the administration server.

In the method above, after the step of opening a communications link to the administration server, the method may further comprise the steps of the interface device receiving configuration data from the administration server and storing the configuration data in memory of the interface device, and/or sending logged information stored in the memory to the administration server.

In the method above, the logged information may include records of failed polling attempts.

According to a second aspect of the present invention there is provided an interface device for providing for communication over a PSTN, between an alarm device and a remote receiving device, the alarm device and remote receiving device-arranged to communicate in accordance with the DTMF Fast Format protocol, the combined response delay of the PSTN and the remote device being unpredictable, the interface device arranged: a) to receive from the alarm device at least one of two DTMF strings indicative of information to be transmitted from the alarm device to the remote receiving device in accordance with the DTMF FF protocol; b) in response to receiving the at least one string, to send the at least one string over the network to the remote device; c) in response to receiving the at least one string, to send to the alarm device a signal indicative of the two strings having been received in accordance with the DTMF Fast Format protocol, without waiting for such a signal from the remote receiving device.

The device may arrange to carry out the method of the first aspect of this invention.

The device may derive its power source from the alarm unit. The power supply Voltage is preferably in the range of about 9V to about 30V.

The device may be provided as a unit that can be fitted so as to receive communications from a pre-installed alarm device and so as to be connected to a pre-installed PSTN line. In other words, the device may be arranged for retro-fitting between an existing alarm device and its PSTN connection. In this way, an alarm device designed for use on the 2OCN network may communicate over the 2OCN or 21 CN network, via the interface device.

Many existing alarm devices have no facility for periodically informing an ARC, possibly via an intermediate network entity, that the alarm device and its connection to the PSTN are operating correctly. Such a periodic confirmation that the alarm device is operating correctly and is properly connected to the PSTN is desirable since it is possible that an alarm device could fail at any time for a number of reasons, such as, for example, the power being removed deliberately by a would-be intruder, the connection to the PSTN being deliberately cut, or simply due to a malfunction. Some existing devices have this capability, in which case a further problem can arise whereby if the messages confirming that the alarm device is operational, known as polling messages, are not received by the ARC, then an alarm may be raised. This is intentional, since the lack of reception of polling messages could indicate that the alarm device is malfunctioning. However, sometimes the apparent failure is due to a failure in the PSTN, not in the alarm device. In these cases, a false alarm may be received. Such a false alarm can be expensive or inconvenient to deal with since it may involve for example the police being called. Therefore, a method of enhancing the handling of polling message failure is desirable.

Furthermore, even those existing devices which have the facility to send periodic polling messages to an ARC, can encounter problems in sending the polling messages to the ARC. These problems occur for the same reasons as previously described in connection with the sending of alarm messages by existing alarm devices over a 2ICN PSTN, i.e. due to the experienced unpredictable response delay. Loss of polling messages can be problematic since it is then uncertain whether or not the alarm device and its connection to the PSTN are operating correctly.

In a third aspect of this invention, there is provided a method of operating an interface device to provide increased functionality to an alarm device that is arranged to communicate over a PSTN, the method including the steps of the interface device: a) receiving from the alarm device a signal indicative of a first telephone number to be sent over the PSTNso as to establish a communications link with a remote location identified by that first telephone number, andlor receiving a first identification number identifying the alarm device; b) comparing the first telephone number with a pattern telephone number; c) retrieving or generating a mapping telephone number in the event that the first and pattern telephone numbers match, and/or retrieving or generating a mapping identification number is the event that the first and pattern telephone numbers match; and d) sending the mapping telephone number over the PSTNso as to establish a communications link with a remote location identified by that mapping telephone number andlor sending the mapping identification number over the PSTN to identify the alarm device.

In this way the interface device may be fitted to a pre-existing or "legacy" alarm device and divert calls attempted by the alarm device to different telephone numbers.

Thus, polling messages that would be sent by the legacy device to, for example, an ARC may be re-directed and handled at another location.

Step (b) may include the interface device comparing the first telephone number with one or more of a plurality of pattern telephone numbers, each pattern telephone number corresponding to a respective one or a plurality of mapping telephone numbers, until a matching pattern telephone number is found; step (d) may include sending over the PSTN the mapping telephone number that corresponds to the matching pattern telephone number.

The method may include the further step of the interface device receiving from a remote device updated pattern andlor mapping telephone numbers. The remote device may be an administration server.

In a fourth aspect of this invention, there is provided an interface device arranged to carry out the method of the third aspect.

In a fifth aspect of this invention, there is provided a method of operating an interface device to provide increased functionality to an alarm device arranged to communicate over a PSTN, the interface device arranged for connection between the alarm device and the PSTN, and the method including the step of the interface device: a) periodically sending over the PS1'N to a remote receiving device a polling message indicative of the interface device being operable.

In a sixth aspect of this invention, there is provided an interface device arranged to carry out the method of the fifth aspect.

The interface device may be arranged to be powered from the alarm device. In this way, a loss of power to the alarm device will result in a loss of power to the interface device and hence to an at least temporary pause in the sending of the periodic polling message, thereby alerting the remote receiving device to a problem in at least one of the interface device and the alarm device.

In a seventh aspect of the present invention there is provided a method of operating an alarm gateway, the method including the steps of: a) the alarm gateway receiving information over a PSTN from an interface device which is in communication with an alarm device, the information including at least oneof: periodic polling messages indicative of the interface device being operable, and an alarm message from the alarm device; and b) the alarm gateway sending to a user of the interface device a message indicative that the information has been received at the alarm gateway.

Step (b) may include the alarm gateway sending the message by SMS messaging over a mobile telephone network, such as GPRS and/or GSM.

In an eighth aspect of this invention, there is provided an alarm gateway arranged to carry out the method of the seventh aspect.

In a ninth aspect of the present invention there is provided a polling server arranged to communicate with an interface device via a PSTN, and which is arranged to monitor for periodic reception of a polling message from the interface device, and if a polling message is not received for a predetermined duration of time the polling server may send a polling failure message to an ARC or to a user, via cable, radio, PSTN, optical or other suitable means, and preferably in which polling failure messages can be sent to a user via a GSM or GPRS radio network SMS message.

The optional features of each aspect may also be optional features of each other aspect. The essential features of each aspect may also be optional features of each other aspect.

In a further aspect, there is provided a computer program including code portions executable by processing means of an alarm device as defined in any aspect above to cause that device to carry out a method as defined in any aspect above.

In a still further aspect, there is provided a record carrier carrying thereon or therein a record of the computer program. The record carrier may be physical storage means, such as solid state, magnetic or optical storage means. The solid state storage means may include, for example, flash memory, ROM, EPROM or EEPROM. The optical storage means may include an optical storage disk such as, for example, a CD-ROM or DVD-ROM. The record carrier may be a signal such as, for example, a radio or electrical signal.

Short Description of the Drawings

Specific embodiments of the invention are now described below by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an alarm signalling system in which devices and methods that embody the present invention operate.

Figure 2 is a schematic block diagram of an embodiment of the present invention for use with an alarm device.

Figure 3 is a block diagram of an embodiment of the present invention for use with an alarm device having a data uploading and/or downloading capability.

Figure 4 is a diagram of signalling between an alarm device and the interface device of the present invention, and between the interface device of the present invention and an ARC.

Specific Description of Certain Exemplary Embodiments Referring to Fig. 1, in overview, a first embodiment of the present invention comprises an interface unit (10) which is arranged for operation in an alarm signalling system (1), the alarm signalling system (1) comprising at least part of a Public Switched Telephone Network (PSTN) (30), at least one ARC (40), the interface device (10) and an alarm device (20). For simplicity, only a single interface device (10) and alarm device (20) are shown in Fig. 1. However, it will be understood that such an alarm signalling system would include many of such devices. The alarm device (20) is arranged to send alarm messages indicative of an alarm alert at a user's premises at which the interface device (10) and the alarm device (20) are installed (not shown) to an ARC, via a communication connection provided by the PSTN. The interface device (10) is interposed between the alarm device (20) and the PSTN (30) and is arranged to provide for communication between the alarm device (20) and the PSTN (30). The interface device (10) has communication ports for connection to the alarm device (20) (which is for example a digital alarm control panel such as, for example, a device which receives inputs from several motion detectors and upon receiving an input indicating an alarm condition has been met, sends an alarm message via the PSTN to an ARC) and to the PSTN (30). The connection between the interface device (10) and the alarm device is by a short cable (5), of a metre or so in length, but in any case long enough to connect the two devices which are usually situated close to each other in a single room. The communication ports are compatible with commonly used PSTN equipment such as telephones and fax machines.

Accordingly, both the alarm device (20) and the ARC (40) are connected to the PSTN (the alarm device (20) is connected to the PSTN indirectly via the interface device).

As will be understood, the PSTN is arranged to selectively connect together for communication devices connected to the PSTN, the selection being controlled by a telephone number which the PSTN is arranged to receive from any of the connected devices (for example, the interface device). The telephone number uniquely identifies another connected device (for example, the ARC). The alarm signalling system (1) is thereby arranged to selectively couple each alarm device (20) in communication with at least one ARC (40).

In the embodiment shown in Fig. 1, the alarm signalling system (1) additionally comprises an alarm gateway (50) which is connected to the PSTN (30) by a telephone line (35) and to an alarm service network (90). The alarm gateway (50) is operable to forward alarm-related messages, receivable from the alarm device (20) via the interface device (10) over the PSTN (30), to the alarm service network (90). Alarm-related messages include alarm messages indicative of an alarm condition having been met and polling messages indicative of the alarm device (20) being operative (some alarm devices periodically send a "polling message" to a remotely situated device which monitors for polling messages and infers a malfunction of the alarm device if polling messages are not regularly received). An example of such an alarm gateway (50) is the GEMINI GATEWAY (TM) maintained by CSL (DUALCOM) LIMITED.

The alarm service network (90) is a network of X.25 radio links (95) and kilostream X.25 lines (36) and is arranged to route and transmit alarm-related messages. The alarm service network (90) is connected to at least one ARC. The alarm service network (90) is further arranged to selectively forward alarm messages from the alarm gateway (50) to the ARC (40) either by the X.25 radio link (95) or by the kilostream X.25 line (36).

The alarm service network (90) is further connected to and arranged to forward polling messages to a primary polling server (60) and a secondary polling server (62) (in some embodiments, however, there are more or less than two polling servers).

Each pofling server (60, 62) is connected to the alarm service network (90) by a kilostream X.25 line (36), and to a radio network (70) by leased lines. The radio network (70) is a GPRS radio network but in other embodiments is a GSM radio network.

Each polling server (60, 62) is arranged to monitor for polling messages and infer a malfunction of the alarm device andlor its connection (35) to the PSTN (30) if polling messages are not regularly received, and in this case to generate at least one "polling failure message". In some embodiments, each polling server (60, 62) may forward or send other types of messages in addition to or instead of polling failure messages.

Each polling server is connected to and arranged to forward polling failure messages to the radio network (70) for delivery to a mobile telephone (80) of the user via radio link (75).

Each polling server is further arranged to forward polling failure messages to the alarm service network (90) for forwarding polling failure messages to an ARC (40), selectively via the radio link (95) or via the kilostream X.25 line (36), the selection made depending on a stored user preference.

Referring to Fig. 2, in overview the interface device (10) comprises a microprocessor (201) having memory (202, 203), power supply components (240, 245), interface components for connection to an alarm device (200, 204, 205, 206, 207, 208, 209) and interface components for connection to a PSTN (210, 211, 212, 213, 214, 215, 216, 217,218,220).

As shown in Fig. 2, the memory (202, 203) includes flash memory and non-volatile memory, the microprocessor (201) including the flash memory (202) and being connected to the non-volatile memory (203). The microprocessor is also connected to an admin call switch (250) with which a user can provide input, LED indicators (260) which provide output to a user, and is connected to a clock (270) which provides time information to the microprocessor (201).

The power supply components will now be described. An external power supply (242) connects to the interface device (10) at power supply port (241) which is connected to power supply circuitry (245) and to DC Voltage detector (240). The power supply circuitry (245) is arranged to receive power from the power supply port (241) and to provide a regulated power supply output which is connected to the remainder of the circuitry so as to be able to supply power. The DC Voltage detector (240) is arranged to monitor the power supply voltage and provide an output which is connected to the microprocessor (201), capable of informing the microprocessor (201) if the power supply input Voltage is outside of a predetermined Voltage range. The interface device (10) is arranged to operate from a supply Voltage in the range of Voltages normally supplied by an alarm device, for example 9 to 30 Volts.

The interface components will now be described. The interface device (10) is arranged to connect to an alarm device (20) via an alarm device port (200). The alarm device port (200) is connectable to an alarm device (20) and is connected to a current sensor (205) which is arranged to sense a current load connectable between the conductors of the alarm device port (200). The current sensor (205) is connected between the alarm device port (200) and a PS1'N interface simulator (204) which is arranged to simulate the interface of a PSTN so as to be indistinguishable, so far as necessary to ensure correct operation, from a PSTN by an alarm device (20). The PSTN interface simulator (204) incorporates a DC Voltage generator (206) for generating a DC Voltage signal component on the alarm device port (200), a dial tone generator (207) arranged to selectively generate a dialling tone under control of the microprocessor (201), a DTMF detection circuit (208) arranged to detect DTMF tone-pairs at the alarm device port (200) send related information to the microprocessor (201), and a handshake and Kiss-Off tone generator (209) arranged to generate handshake and Kiss-Off acknowledgement signals under control of the microprocessor (201).

The interface device (10) is also arranged to connect to the PSTN (30) via PSTN port (210). A user's phone, or fax device (230) can also connect to the PSTN (30) electrically in parallel with the PSTN port (210) of the interface device (10).

The interface device (10) further comprises a PSTN interface (220) for interfacing the microprocessor to a PSTN (30), an on-hook switch (218) for selectively connecting the PSTN interface to the PSTN port (210) and a broadband filter (211) for providing filtering so as to ensure compatibility of the interface device (10) with broadband installations. The microprocessor (201) is connected to the PSTN interface (220) which is also selectively connected to a broadband filter (211) by the on-hook switch (218). The on-hook switch (218) is controllable by the microprocessor (201) and is connected to the PSTN port (210).

The PSTN interface (220) further comprises a DC Voltage detector (213) for detecting the dc Voltage signal component at the PSTN port (210), a dial tone detector (214) for detecting a dial tone signal at the PSTN port (210), a DTMF generator (215) for generating PSTN tone-pairs at the PSTN port (210), a 300 baud modem (216) for sending and receiving data at the PSTN port (210), and a ringing detector (217) for detecting a ringing tone at the PSTN port (210). Each of the aforementioned components (213, 214, 215, 216, 217) comprised in the PSTN interface (220) is connected between the microprocessor (201) and an isolated PSTN interface (212) to provide electrical isolation between the PSTN port (210) connections and the aforementioned components (213, 214, 215, 216, 217).

The interface device (10) is constructed using known electronic device manufacturing techniques such as, for example, the use of printed circuit boards and moulded plastic cases and/or folded metal enclosures. The skilled reader will be familiar with such methods of construction and it is not necessary to elaborate further here. It is worthy of note, however, that many of the elements shown in Fig. 2 are implemented using software running on the microprocessor (201), these functional blocks including the dial tone generator (207), the DTMF detection block (208) the handshake and Kiss-Off tone generator (209), the clock (270), the dial tone detector (214), the DTMF generator (215), the 300 baud modem (216), the ringing detector (217) and other control and monitoring tasks as would be understood to be part of such a system by the skilled reader. The DC Voltage detector (240) and current sensor (205) are implemented either using commonly known analogue circuitry, such as a comparator, but in other embodiments may be implemented using an analogue to digital converter, the output of which would be fed to the microprocessor and the detection performed by software running thereupon. A skilled reader will understand that many combinations of standard electronic design techniques can be used to implement the functional blocks shown in Figs. 2 and 3.

The system shown in Fig. 1 is constructed using elements commonly in use, such as telephone lines (35), telephone exchanges (32), a PSTN (30), a radio network (70) (for example, a GPRS radio network, although other embodiments can use a GSM radio network) and existing ARCs (40). The primary polling server (60), secondary polling server (62) and alarm gateway (50) are constructed using standard server equipment in conjunction with standard interfaces to telephone lines, kilostream X.25 lines, and leased lines.

Prior to operation of the interface device (10), the device (10) installed at a user's site, close to an alarm device (20). During installation, the alarm device (20) and interface device (10) are preferably connected by a relatively short telephone cable (5) (usually less than, for example, one metre in length) attached to the alarm device port (200) of the interface device (10) by an installer, as shown in Fig. 1. The interface device power supply port (241) is preferably attached by the installer to a power supply outlet of the alarm device, although in some installations the power supply port (241) is attached to a separate power supply, depending on the relative convenience thereof.

The interface device (10) is further attached to the PSTN via a telephone cable (35) by the installer. The installer can be a person employed to install alarm related devices or can be an end user.

In operation, the interface device (10) acts to receive information regarding alarms, status andlor test messages from the alarm device (20), and forwards this information to either an ARC (40) or an alarm gateway (50) via a PSTN (30). The information is sent from the alarm device (20) to the interface device (10) via the short telephone cable (5). The information travels from the interface device (10) to the PSTN (30) via a telephone line (35). The information travels through the PSTN (30), which is either of the 2OCN PSTN infrastructure type, or the newer 21 CN PSTN infrastructure type.

2ICN PSTNs have an unpredictable end-to-end network delay across them. The information emerging on the far side of the PSTN (30) is sent via a telephone line (35) to a device connected to said telephone line, such as an ARC (40), or to an alarm gateway (50), depending on the telephone number sent to the PSTN (30) by the interface device (10) (as is described in more detail below). In the case of the ARC (40) being the destination for the information, and the information being an alarm message, the ARC (10) notes the alarm and informs an appropriate responsible person who is then able to investigate the premises at which the interface device (10) and alarm device (20) are installed. In the case of the alarm gateway (50) being the destination for the information, the alarm gateway forwards the information via an X.25 line (37) to the alarm service network (90). The alarm service network (90) can then send the information either by radio link (95) to the ARC (40) or by kilostream X.25 line (36) to the ARC (40). As before, the ARC can then inform the appropriate responsible person in order that they may take action. The interface device (10) communicates either directly with the ARC (40) or with the alarm gateway (50), depending on a stored user preference in the memory (202,203) of the interface device (10). When the interface device (10) communicates directly with the ARC (40), communication is by DTMF FF. When the interface device (10) communicates with the alarm gateway (50), communication is by 300 baud modem connection. In other embodiments, communication can be by DTMF FF or by modem connection (not limited to 300 baud speeds) when communicating with either the ARC (40) directly or to the alarm gateway (50).

As shown in Fig. 2, in operation, the PSTN interface simulator (204) and associated components (206, 207, 208, 209) simulate a PSTN interface to the alarm device (20).

Similarly, the PSTN interface (220) and associated blocks (212, 213, 214, 215, 216, 217) present an interface to the PSI'N at the PSTN port (210). A broadband filter (211) provides filtering for broadband compatibility.

In order to communicate in a robust manner with the ARC (40) via the PSTN (30), the interface device (10) is arranged to implement a modified, robust variant of DTMF FF protocol. In a preferred embodiment, shortly before the alarm device (20) begins to send information, it firstly connects an electrical load between the conductors (wires) of the short cable (5), the cable (5) connecting the alarm device (20) to the alarm device port (200) of the interface device (10). The current sensor (205) of the interface device (10), as shown in Fig. 2, detects the current drawn by this load and alerts the microprocessor (201) that the alarm device is about to begin communication. This alert can be used to, for example, switch on certain parts of the circuitry of the interface device (10) (thereby allowing implementation of a power saving strategy), or to cause a log entry to be entered into a log stored in the non volatile memory (203) of the microprocessor (201).

The interface device (10) then awaits reception of a first telephone number (450) from the alarm device (20). The alarm device (20) sends the first telephone number (450) to the interface device (10) and then awaits an acknowledgement signal (453) from the interface device (10). Upon reception by the interface device (10) of the first telephone number (450), the interface device (10) sends a second telephone number (451) to the PSTN (30), thereby opening a communications link with a remote device identified by that second telephone number. The remote device can be an ARC (40) or an alarm gateway (50). The second telephone number (451) is selectively either the same as the first telephone number (450), or is derived from the contents of the microprocessor non-volatile memory (203) or flash memory (202) in a manner described later in this application, based upon a predetermined user preference stored in memory (202, 203). The interface device (10) then awaits the reception of an acknowledgement (452) from the remote device. When the interface device receives the acknowledgement (452) from the remote device, the interface device (10) sends another acknowledgement (453) to the alarm device (20). This completes the stage of sending a telephone number from the alarm device (20), via the interface device (10) and to the PSTN (30), thereby uniquely addressing the remote device.

Upon reception by the alarm device (20) of the acknowledgement (453), the alarm device sends a string of DTMIF tone-pairs (454), in accordance with the DTMF FF protocol, to the interface device which is awaiting the string. This first string of DTIV[F tone-pairs (454) is closely followed by the alarm device (20) sending a second identical string of DTMF tone-pairs (456) to the interface device (10), in accordance with the DTMF FF protocol. The interface device (10) then sends a "Kiss-Off' acknowledgement signal (458) as an acknowledgement to the alarm device (20) that the two DTMF strings have been correctly received by the interface device (10). In other embodiments, the interface device can send the Kiss-Off acknowledgement signal to the alarm device after having received a greater number or a lesser number of identical DTMF strings from the alarm device (20) than two.

After the first DTMF string (454) has been received by the interface device (10) from the alarm device (20), the interface device (10) sends a first copy (456) of the first DTMF string (454) to the remote device over the PSTN (30). The interface device (10) closely follows this action by sending a second copy (457) of the DTMF string (454) to the remote device over the PSTN (30). The interface device (10) then awaits reception of a "Kiss-Off' acknowledgement signal from the remote device over the PSTN (30) which indicates to the interface device (10) that the remote device has correctly received the first (455) and second copies (457) of the DTMF string (454).

The remote device verifies correct reception of the DTMF strings by comparing the first and second copies (455,457) for an exact match, and sends a Kiss-Off acknowledgement signal to the interface device (10) if there is a match. (In other embodiments, the interface device (10) may wait until it has received the second DTMF string from the alarm device (20) before sending the first copy (455) of the first DTMF string (454) to the remote device over the PSTN (30).) When the remote device is an ARC, the first and second copies (455, 457) are sent using DTMF FF protocol. When the remote device is the alarm gateway (50), the first and second copies (455, 457) are sent using the modem (216). The remote device is selectable based upon stored user preferences in the memory (202, 203) and is preferably the alarm gateway (50). In some embodiments, if a connection with the alarm gateway (50) fails, the interface device reverts to the remote device being the ARC (40).

If the Kiss-Off acknowledgement (459) is received from the remote device over the PSTN (30) within a predetermined time-out period (which is about 1 second) then the interface device (10) closes the communications link with the remote device over the PSTN (30) (which the interface device (10) previously caused to be opened by the action of sending the second telephone number (451) over the PSTN). This concludes the normal operating protocol in the absence of any errors.

If, however, the interface device (10) does not receive a Kiss-Off acknowledgement signal (459) from the remote device over the PSTN (30) within the predetermined time-out period, the interface device closes the communications link with the remote device over the PSTN (30), and subsequently repeats the steps of sending the second telephone number (451) over the PSTN (30) (and thereby opening a communications link with the remote device over the PSTN); waiting to receive an acknowledgement (452) from the remote device that the second telephone number has been correctly received; sending the first and second copies of the DTMF string (455, 457); and awaiting the reception of the Kiss-Off acknowledgement signal (459) from the remote device over the PSTN (30).

The advantages of the above method of operation over legacy alarm devices (20) which use the DTMF FF protocol include the following: Firstly, because the interface device (10) sends a Kiss-Off acknowledgement signal to the alarm device (20) without waiting for reception of a Kiss-Off acknowledgement signal (459) from the remote device (for example, an ARC), the interface device (10) is able to wait for an extended time-out period when awaiting the Kiss-Off acknowledgement (459) from the remote device, without causing an expiry of the predetermined time-out period in the alarm device (20) for reception of the Kiss-Off acknowledgement signal at the alarm device (20). Such a time-out in the alarm device could otherwise occur, and cause incorrect communication when the PSTN is of the 21CN network infrastructure type or when the remote device has a relatively long internal processing delay. Furthermore, resulting from the extended interface device time-out period, there is a relatively low likelihood of time-out expiry in the interface device (10) when the interface device is awaiting reception of a Kiss-Off acknowledgement signal from the remote device via a 21CN PSTN (30) having an unpredictable end-to-end transmission delay, or from a remote device having a relatively long internal processing delay. This is the case even when, for example, the network end-to-end delay is of the order of 2 x l5Oms and the remote device internal processing delay is of the order of 250ms. This facilitates correct communication between the interface device (10) and the remote device, and thereby facilitates communication between the alarm device (20) and the remote device via the interface device (20).

Secondly, because in a preferred embodiment the interface device (10) transmits only two copies of the DTMF string (455, 457) to the remote device over the PSTN (30) before beginning the time-out period, and the interface device closes the communications link with the remote device before retrying in the event that a Kiss-Off acknowledgement (459) does not arrive at the interface device (10) before the predetermined time-out period expires, one of the problems identified herein above as affecting existing alarm devices is addressed. It will be recalled that one such problem arose because existing alarm devices would re-transmit a third or fourth copy of the DTMF string if the predetermined time-out period expired without the Kiss-Off acknowledgement (459) having been received, and this lead to the possibility of the Kiss-Off acknowledgement (459) arriving substantially coincidentally with or overlapping with the third or fourth copy of the DTMF string transmitted by the interface device (10), leading to loss of the Kiss-Off acknowledgement (459). This failure mode is avoided with embodiments of the present invention. Such embodiments thus facilitate reliable communication with a remote device having long internal processing delays, or via a network having a long or unpredictable end-to-end transmission delay.

The interface device (10) also incorporates the ability to check the telephone number (450) received from the alarm device (20) (hereinafter, the "first telephone number"), and if it matches a pattern telephone number stored in the non-volatile memory (203) or flash memory (202) with which a mapping telephone is associated, the interface device selectively substitutes the associated mapping telephone number (also stored in memory) for the first telephone number (450) when sending the telephone number (451) (hereinafter the "second telephone number") from the interface device (10) to the PSTN), depending on predetermined user preferences stored in memory (202, 203). The interface device (10) can thereby cause messages sent by the alarm device (20) to be re-directed to an ARC (30) or another remote device, such as an alarm gateway (50).

Additionally, the contents of the non-volatile memory (203) and/or flash memory (202) in the interface device, such as the pattern and/or mapping telephone numbers, can be updated remotely via the PSTN coimection. This facility allows the second telephone number dialled by the alarm device (20) to be selectively mapped to a remotely updateable mapping telephone number held in the memory of the interface device (10).

Remote updating operates as follows. When the interface device (10) receives an update instruction from a remote device (for example, from a polling server via the alarm gateway, or from the alarm gateway) indicating that a remote update procedure should be carried out, the interface device (10) closes the communication link with. the remote device and then dials a connection with an administration server. The update instruction is preferably a modified Kiss-Off acknowledgement at the end of a 300 baud conmiunication session. In this embodiment, the administration server is the alarm gateway (50), although in other embodiments the administration server can be a separate server accessed via the alarm gateway or can be another device connected to the PSTN. The administration server is then able to update the contents of the interface device (10) memory (202, 203) by sending messages to the interface device (10).

During a communications session with the administration server, the contents of the memory (202, 203) can selectively be updated with new values, including those for the pattern telephone number, the mapping telephone number, a polling telephone number and any other parameters which may be required to be remotely updated, depending on the preferences of an administration server operator.

An admin call switch (250) can be pressed by a user in order to cause the interface device (10) to call an administration server, which can be the alarm gateway (50), as previously described.

A clock (270) provides time and date information which can be selectively entered in a log stored in the microprocessor memory (202, 203), depending on stored user preferences. The contents of the log can selectively, based upon stored user preferences, be uploaded to the administration server when instructed by either the pressing of the admin call switch (250), or the reception of the update instruction. The interface device (10) is also arranged to upload the contents of the log to the administration server at periodic time intervals as measured by the clock (270), and when the memory which is used to store the log becomes full.

In operation, a power supply (245) regulates the incoming power supply Voltage and supplies power to the components. A DC Voltage detector (240) monitors the external power supply Voltage and report to the microprocessor if the power supply Voltage goes out of a defined range. Such "out of range" events from the DC Voltage Detector are also recorded in the log stored in the microprocessor memory (202, 203) and can selectively (based upon stored user preferences) initiate the sending of a message by the interface device (10) to the ARC or to the alarm gateway.

Resulting from the ability to remotely update the pattern telephone number and the mapping telephone number, legacy alarm devices (20) (which may not have the ability to be remotely updated and may only have the ability to dial a fixed telephone number to access the ARC) are provided with a mechanism whereby the number which is dialled for accessing the ARC (40) can be remotely updated. Although the legacy alarm device (20) continues to dial a fixed telephone number to access the ARC, the interface device (10) is able to map this fixed telephone number to the mapping telephone number stored in memory (202, 203). As previously described, this mapping telephone number can be remotely updated, thus the ability to remotely update the telephone number which is dialled when a legacy alarm device (20) tries to access the ARC is provided.

The way that mapping works, in operation, for the embodiment shown in Fig. 2 is as follows. A legacy alarm device (20) typically calls a fixed number which it contains for accessing the ARC (40). This number can be programmed (either during manufacture or during operation using theremote updating mechanism) into the interface device (10) as the pattern telephone number stored in the microprocessor memory (202, 203). When the alarm device (20) starts to dial, it connects an electrical load across the two wires of the telephone cable (5) which links the alarm device (20) and the interface device (10). This causes the current sensor (205) to detect the load, and to inform the microprocessor (201). The interface device (10) then monitors the DTMF tone-pairs arriving on the alarm device port (200) and decodes from these the first telephone number (450) dialled by the alarm device (20). The interface device (10) compares this first telephone number (450) with the pattern telephone number and, if the two numbers match, the interface device (10) begins the sequence of operations shown on the right hand side of Fig. 4, and sends the mapping telephone number stored in the memory (202,203) as the second telephone number (451) instead of the first telephone number (450).

Additionally, when the first telephone number (450) matches the pattern telephone number, the interface device (10) can selectively (based upon stored user preferences) substitute a mapping identification number stored in memory (202, 203) for an identification number received from the alarm device (20) as part of the DTMF strings (454, 456). The interface device thus selectively sends the mapping identification number to the remote device instead of the identification number received from the alarm device (20).

The mapping telephone number can be programmed to be the same as the telephone number dialled by the alarm device (20), or the mapping telephone number can programmed to be different. The mappingtelephone number can thereby selectively address a different ARC (40) than that dialled by the alarm device (20), or can address the alarm gateway (50). Preferably, the mapping telephone number is used to address the alarm gateway (50) which is arranged to pass alarm related messages to a further remote device connected to it, such as for example an ARC (50). In operation, the alarm gateway (50) forwards alarm related messages to the further remote device, via the alarm service network (90) and a radio link (95) andlor a cabled connection such as a kilostream X.25 line (36). Alternatively or additionally in other embodiments the alarm gateway (50) is arranged to pass the alarm message to a responsible user via suitable means such as by a GPRS or GSM radio network, and mobile telephone SMS messaging.

In a further embodiment as shown in Fig. 3, the alarm device (20) incorporates a panel (320) and an alarm controller (330), the alarm controller having a data upload and/or download facility. When the interface device (10) is used with an alarm device incorporating an alarm controller having upload and/or download capability, additional components are included in the interface device (10). The additional components include a first switch (350) connected between the alarm device port (200) and the PSTN port (210). In Fig. 3, the first switch (350) is shown specifically as connecting between the PSTN Interface Simulator (204) terminal nearest the alarm device port (200), and the broadband filter (211) terminal nearest the on-hook switch (218).

Also, as shown in Fig. 3, the interface device (10) also has a user port (300). A user telephone, or fax machine (310), for example, can be connected at user port (300).

User port (300) is connected to PSTN port (210) by a second switch (340). Both the first and second switches (350, 340) are controllable by the microprocessor (201).

In the embodiment shown in Fig. 3, in operation, the alarm device (20) has the ability to upload and/or download data and therefore requires the ability to communicate with devices other than the ARC and possibly to communicate using protocols other than DTFM FF. If the telephone number dialled by the alarm device (20) matches the pattern telephone number stored in the microprocessor memory (202,203), then it follows that the alarm device (20) will use DTMF FF protocol for the communication since the pattern telephone number is always that of a device which communicates using DTMF FF protocol, for example an ARC. If the telephone number dialled by the alarm device (20) does not match the pattern telephone number, it is not known that the alarm unit will communicate using DTMF FF protocol. Since the microprocessor (201) of the interface unit (10) does not know how to communicate using protocols other then DTMF FF, the microprocessor (201) and its associated DTMF interfaces (204, 220) must be bypassed. The embodiment shown in Fig. 3 additionally has the ability to switch telephone calls originating from the alarm device (20) through the interface device (10), bypassing the microprocessor (201) and its associated PSTN simulator (204) and PSTN interface (220). This is accomplished by the first switch (350).

The embodiment shown in Fig. 3 operates as follows. When the alarm device (20) starts to dial, it connects an electrical load across the two wires of the telephone cable (5) linking the alarm device (20) and the interface device (10). This causes the current sensor (205) to detect the load and to inform the microprocessor (201). The interface device (10) then monitors the DTMF tone-pairs arriving on the alarm device port (200) and decodes from these the first telephone number (450) dialled by the alarm device (20). The interface device (10) compares this first telephone number (450) with the pattern telephone number and if they match, the interface device (10) disconnects the alarm device (20) from the PSTN port (210) by opening the first switch (350). This cancels the communication link partially set up through the PSTN (30) by the alarm device (20). The on-hook switch (218) is then closed and the interface device (10) begins the sequence of operations shown on the right hand side of Fig. 4, as previously described, and sençls the mapping telephone number stored in the memory (202,203) as the second telephone number (451) to the PSTN (30). This opens a new communications link from the interface device to the remote device via the PSTN (30) using the mapping telephone number instead of the first telephone number (450) dialled by the alarm device. If there is no match, the interface device (10) takes no further action in respect of the communications link which the alarm device (20) is attempting to open, and the interface device maintains the first switch (350) in the closed position, thereby allowing the alarm device (20) to continue its communication session via the PSTN (30).

A user's telephone, or fax (for example), can be connected to the user port (300). In operation, the user port (300) is normally ôonnected to the PSTN (30) via the second switch (340). If the alarm unit (20) or the interface device (10) need to use the telephone line (35) to the PSTN (30) then the second switch (340) is opened so as to give priority to the alarm device (20) which is connectable to the PSTN (under control of the microprocessor) via the first switch (350) or to the interface device (10) which is connectable (under control of the microprocessor) to the PSTN via the on-hook switch (218).

The interface device is additionally able, in some embodiments, to send periodic "polling" messages to a polling server using the modem link via the PSTN (30) and the alarm gateway (50). The alarm gateway (50) is allocated one or more telephone numbers on the PSTN (30) that identify the alarm gateway (50) and can be used to establish a communications link therewith. In a preferred embodiment, the modem link runs at a line speed of about 300 baud (or 300 signal transitions per second). A relatively low line speed is used to increase reliability. The interface device (10) uses its clock (270) to determine when to send polling messages. The polling messages are routed by the alarm gateway (50) via an alarm service network (90) to one of a primary and a secondary polling server (60, 62). The polling server (60, 62) which is designated to receive the polling messages, monitors for the periodic reception of the polling messages, and flags a polling failure if a polling message is not received for a defined period of time. This period of time, and the periodicity of the sending of polling messages, can be adjusted according to the relative importance of maintaining security at the site being monitored for alarm-related alerts. The polling server (60, 62) handles the monitoring of polling messages, therefore the ARC (40) does not have to monitor polling messages. The number of calls handled by the ARC (40) is thereby reduced.

The interface device (10) is preferably supplied with power by the alarm device (20).

This is so that if the power supply to the alarm device (20) fails, the interface device is no longer able to send polling messages to the polling server, which would otherwise indicate incorrectly that the alarm unit is functioning correctly. In some embodiments, the interface device sends polling messages to the polling server (60, 62) via the PSTN (30), alarm gateway (50) and alarm service network (90) only when it has received any type of message (for example, a status message) from the alarm device (20) within a predetermined period of time. This feature can be selectable by a stored user preference.

If a polling failure is detected, a polling failure message is selectively sent (depending on user preferences) by the polling server (60, 61) to the ARC (50) via the alarm service network (90), and/or to a responsible user via a radio network (70) and mobile telephone (80). The polling failure message can be sent in the form of, for example, an SMS text message. It can be cheaper and more convenient to send polling failure messages to a responsible user, rather than directly to an ARC, since the responsible user may be able at low cost and/or low inconvenience to determine if the polling failure alarm is a false alarm or not. Alternatively, polling failure messages can selectively (depending on user preferences) be sent to an ARC (50). The ARC can then notify a responsible user and/or, for example, the police service.

The alarm device can be a fire alarm unit, a commercial or domestic intruder alarm unit, a personal alarm unit.

Features of the embodiments described and shown in the Figures can be combined in any combination, as would be understood by the skilled reader as being practicable The scope of the invention is not intended to be limited to any particular described embodiment but instead is defined by the attached claims.

Claims (34)

1. CLAIMS1. A method of operating an interface device to provide for communication between an alarm device and a remote receiving device over a PSTN having unpredictable end-to-end transmission delays, the alarm device and the remote receiving device arranged to communicate with each other in accordance with the DTMIF Fast Format protocol, the method comprising: a) the interface device receiving from the alarm device at least one of two DTMF strings indicative of information to be transmitted from the alarm device to the remote receiving device in accordance with the DTMF Fast Format protocol; b) in response to receiving the at least one string, the interface device sending the at least one string over the network to the remote device; c) in response to receiving the at least one string, the interface device sending to the alarm device a signal indicative of the two strings having been received in accordance with the DTMF Fast Format protocol, without waiting for such a signal from the remote receiving device.
2. 2. A method according to claim 1, wherein step (c) includes the step of the interface device sending the signal in response to receiving both of the two strings.
3. 3. A method according to claim 1 or claim 2, where the at least one string in step (b) may be sent twice over the network to the remote device; and, optionally, twice only.
4. 4. A method according to any preceding claim, wherein the remote device is an ARC, an alarm gateway, an administration server or a polling server.
5. 5. A method according to any preceding claim wherein, when the remote device is arranged to communicate using DTMF Fast Format protocol, after the step of sending the at least one string over the network to the remote device, if a signal indicative that the at least one string has been received by the remote device is not received within a predetermined period of time, then the communications link is closed, and subsequently the steps of opening a communications link and sending the at least one string over the network to the remote device are repeated.
6. 6. A method according to any preceding claim, wherein the step of receiving from the alarm device at least one of the two DTMF strings is preceded by the step of receiving from the alarm device a first telephone number identifying a device connected to the PSTN.
7. 7. A method according to claim 6, wherein the step of opening a communications link includes the step of sending a second telephone number over the PSTN, the second telephone number identifying another device connected to the PSTN with which the communications link is to be established.
8. 8. A method according to any preceding claim, and further including the step of storing data in a memory of the interface device, the stored data including one, any combination, or all of: a pattern telephone number for comparison with each first telephone number received from the alarm device, at least one mapping telephone number for selectivly sending over the PSTN, a polling telephone number for selectively sending over the PSTN, an administration telephone number for selectively sending over the PSTN, and log data, each telephone number identifying a device connected to the PSTN.
9. 9. A method according to claim 7 and further including the step of the interface device comparing the first telephone number with a pattern telephone number, the pattern telephone number having a mapping telephone number associated therewith, and, in the event that the first telephone number matches the pattern telephone number, causing the second telephone number that is sent over the PSTN to be the mapping telephone number.
10. 10. A method according to claim 10, wherein there are a plurality of pattern telephone numbers, each having associated therewith a, or a respective, mapping telephone number, the method including the interface device comparing the first telephone number with the pattern telephone numbers, and, upon finding a match, causing the second telephone number to be the mapping telephone number associated with the matching pattern telephone number.
11. 11. A method according to any preceding claim, wherein the method also includes the step of the interface device periodically sending a polling message from the interface device to a polling server, the polling message indicating to the polling server that the alarm unit is operating correctly.
12. 12. A method according to claim 11, wherein the method includes the interface device operating a static polling policy, wherein polling messages are periodically sent to the polling server with a predetermined polling time interval.
13. 13. A method according to claim 11, wherein the method includes the interface device carrying out a dynamic polling policy in which polling messages are sent to the polling server with a frequency at least partly dependent on whether or not the interface device has previously transmitted a message during a predetermined period, the device reducing the frequency of polling messages in the event that this is the case.
14. 14. A method according to any preceding claim, wherein the method includes the step of the interface device operating an electrical switch to normally connect a user device to the PSTN when the first telephone number is determined not to match the pattern telephone number; and to disconnect the user device from the PSTN when the first telephone number is determined to match the pattern telephone number.
15. 15. A method according to any preceding claim, wherein, after the step of sending the at least one string over the network to the remote device, the method further includes the steps of the interface device monitoring for reception of, and/or receiving from, the remote device a signal indicative that an administration operation should be performed; and if such a signal is received the interface device opening a communications link to an administration server.
16. 16. A method according to claim 15, wherein, afler the step of opening a communications link to the administration server, the method further includes the steps of the interface device receiving configuration data from the administration server and storing the configuration data in memory of the interface device, and/or sending logged information stored in the memory to the administration server.
17. 17. An interface device for providing for communication over a PSTN, between an alarm device and a remote receiving device, the alarm device and remote receiving device-arranged to communicate in accordance with the DTMF Fast Format protocol, the combined response delay of the PSTN and the remote device being unpredictable, the interface device arranged: a) to receive from the alarm device at least one of two DTMF strings indicative of information to be transmitted from the alarm device to the remote receiving device in accordance with the DTMF FF protocol; b) in response to receiving the at least one string, to send the at least one string over the network to the remote device; c) in response to receiving the at least one string, to send to the alarm device a signal indicative of the two strings having been received in accordance with the DTMF Fast Format protocol, without waiting for such a signal from the remote receiving device.
18. 18. An interface device according to claim 17 and further arranged to carry out a method according to any one of claim 1 to claim 16.
19. 19. An interface device according to claim 17 or claim 18, and arranged to receive electrical power for operation thereof from the alarm device.
20. 20. An interface device according to any one of claim 17 to claim 19, wherein the device is a unit that can be fitted so as to receive communications from a pre-installed alarm device and so as to be connected to a pre-installed PSTN line.
21. 21. In a third aspect of this invention, there is provided a method of operating an interface device to provide increased functionality to an alarm device that is arranged to communicate over a PSTN, the method including the steps of the interface device: a) receiving from the alarm device a signal indicative of a first telephone number to be sent over the PSTN so as to establish a communications link with a remote location identified by that first telephone number, and/or receiving a first identification number identifying the alarm device; b) comparing the first telephone number with a pattern telephone number; c) retrieving or generating a mapping telephone number in the event that the first and pattern telephone numbers match, and/or retrieving or generating a mapping identification number is the event that the first and pattern telephone numbers match; and d) sending the mapping telephone number over the PSTN so as to establish a communications link with a remote location identified by that mapping telephone number and/or sending the mapping identification number over the PSTN to identify the alarm device.
22. 22. A method according to claim 21, wherein step (b) includes the interface device comparing the first telephone number with one or more of a plurality of pattern telephone numbers, each pattern telephone number corresponding to a respective one or a plurality of mapping telephone numbers, until a matching pattern telephone number is found; and step (d) includes sending over the PSTNthe mapping telephone number that corresponds to the matching pattern telephone number.
23. 23. A method according to claim 21 or claim 22, wherein the method includes the further step of the interface device receiving from a remote device updated pattern and/or mapping telephone numbers. The remote device may be an administration server.
24. 24. An interface device arranged to carry out a method according to any one of claim 21 to claim 23.
25. 25. A method of operating an interface device to provide increased functionality to an alarm device arranged to communicate over a PSTN, the interface device arranged for connection between the alarm device and the PSTN, and the method including the step of the interface device: a) periodically sending over the PSTN to a remote receiving device a polling message indicative of the interface device being operable.
26. 26. An interface device arranged to carry out a method according to claim 25.
27. 27. An interface device according to claim 27, wherein the interface device is arranged to be powered from the alarm device.
28. 28. A method of operating an alarm gateway, the method including the steps of: a) the alarm gateway receiving information over a PSTN from an interface device which is in communication with an alarm device, the information including at least one of: periodic polling messages indicative of the interface device being operable, and an alarm message from the alarm device; and b) the alarm gateway sending to a user of the interface device a message indicative that the information has been received at the alarm gateway.
29. 29. A method according to claim 29, wherein step (b) includes the alarm gateway sending the message by SMS messaging over a mobile telephone network, such as GPRS andlor GSM.
30. 30. An alarm gateway arranged to carry out a method according to claim 29.
31. 31. A computer program including code portions executable by processing means of an alarm device according to any preceding claim to cause that device to carry out a method according to any preceding claim.
32. 32. A record carrier carrying thereon or therein a record of a computer program according to claim 31.
33. 33. An interface substantially as described hereinbefore with reference to the accompanying drawings and/or as shown in those drawings.
34. 34. A method substantially as described hereinbefore with reference to the accompanying drawings and/or as shown in those drawings.