GB2300993A - Telephone modem - Google Patents

Abstract

A telephone handset 11 and a modem system 13 are connected in parallel to a standard PSTN line 10. The modem system identifies predetermined incoming numbers and responds to those by enabling a digital data device such as a data logger 14 for automatic data transfer. Other numbers are ignored by the modem device, and cause the handset to ring for manual answering. If the incoming call includes a CLI signal, that precedes the ring signal. In the modem system, a CLI demodulator 21 extracts the calling number, and a microprocessor 22 compares it against a list of stored number in memory 26. If it matches, the microprocessor enables a PSTN modem 25 to establish communication between line 10 and the data logger immediately, ie before the ring signals which normally follows the CLI signal can appear. If there is no match, modem 25 remains unenergized, and the normal ring signals appear and pass to the handset also on line 10, to cause it to ring in the usual way.

Description

Telephorle Modem The present invention relates to telephone modems.

A telephone modem is e device which couples a computer to a telephone line, modulating digital signals from the computer into a form which is compatible with the telephone system and demoduleting such modulated signals received from the telephone system back into e digital form. (The computer may here be any digital device for hendling data, eg e date logger.) Such a device carries out various control functions in addition to the specific modulation and demodulation of signals between digital and tone form.

We will use the term "modem system" for the complete device, "modem" alone for specific modulator/demodulator units therein, and "modem device" for the modem system excluding the modem device.

There are many situations in which it is desirable to have a (telephone) modem system and some additional device (typically an ordinary telephone handset) both connected to a common telephone line. Our earlier patent application GB 2 258 788 A discusses such situations. That patent specification is concerned specifically with situations in which there is a system with a digital data device and a domestic handset both connected to a telephone line, and the digital data device is likely to be rung up by some remote unit for automatic data exchange (typically downloading of data from the digital data device to the remote unit) at quiet times, typically during the night. (The digital data device there is regarded as including a modem device or system for coupling to the telephone line.) The problem addressed by that patent specification is that for the remote device to ring up, a ring signal has to be sent, and this will be received by the handset as well as by the digital data device. This is liable to result in unnecessary disturbance to the operator et highly inconvenient times of day (or more usually night). The solution proposed there is to provide means for temporarily inhibiting the ring signal to the handset, so that the digital data device is given the opportunity to respond to the ring signal; the handset only rings if the digital data device fails to respond to the ring signal.

That arrangement hes a significant disadvantage. Since the digital data device will respond to ring signals before the handset rings, the handset user will never be able to receive calls. To overcome this, it is necessary to disable the digital data device during periods when the handset user wants to be able to receive incoming calls. This makes the system more complicated, and greatly limits its flexibility.

We have now realized that with recent developments in the public telephone system, a different and better way of dealing with the situation is feasible.

According to the invention there is provided a telephone modem device for controlling a modem for converting between digital signals and telephone signals, the device comprising CLI signal receiving means for receiving CLI (calling line identification) messages on the telephone line, number recognition means for recognizing predetermined calling numbers, and enabling means for thereupon enabling the modem.

A digital data signalling system operating over standard telephone lines has been introduced by Bellcore in the USA. That system is termed CLASS (Custom Celling Local Area Signalling System), and is used primarily for CLI. In that system, when a telephone is called, a message including a digital information block is sent between the first and second ring bursts; the digital information block includes an identification of the calling number.

BT (British Telecom) are introducing data communication systems which operate over standard telephone lines and are, broadly, modified and generalized versions of the CLASS system. BT are in fact introducing two services, CLI (or CLIP) - calling line identification (or calling line identification presentation), and a No-Ring service. These services perform different functions, but their protocols are closely related. The BT CLI service is described, for example, in their SINs (Suppliers Information Notes) 227 and 242, and their No-Ring service is outlined in their MIU Specification document 7508\TECH\NOTE\002- 1 and a 4page hend-out note "Proposed Meter Interface Unit (MIU) Network Interface Protocol)" distributed by them in connection with a seminar held by them at Martlesham Heath on the 12th August 1993.

The BT CLI service involves sending a CLI message including a CLI data block as part of a normal call, in which the first ring signal of the call is preceded by the CLI message. The data block in this CLI message can be detected and decoded by suitable equipment, end the calling number displayed to the operator who responds to the call. One difference between this system and the Bellcore CLASS system is in the position of the CLI message relative to the ring signals. In the Bellcore system, the CLI message follows the first ring signal, which means that if the receiver is picked up very quickly, the call may be answered before the message has been fully received; picking up the receiver may inhibit or interfere with reception of the message. The BT system obviates this denger by sending the CL1 message immediately before the first ring signal.

The No-Ring service involves sending a message which is stand-alone (ie not associated with a normal call involving ring signals). This is primarily intended for on-hook calls (ie calls in which the receiver is not lifted off its hook), although it may perhaps also operate in off-hook (receiver lifted) conditions as well. No-Ring signals will be received by MIU (Meter Interface Unit) modules; en MIU module will be connected to the telephone line in parallel with a normal telephone handset or other telephone unit (eg fax machine). The No-Ring service is intended principally for remote reading of gas, electricity, and water meters, though it can be used for more general telemetry. Once the No-Ring connection has been established, data can be transmitted down the telephone line from the MIU module.

The present invention in effect allows utilization of the CLI service to achieve a No-Ring service from specified calling numbers. This can be achieved thanks to the fact that in the BT CLl service, the CLI message is sent before the first ring signal. The time intervals in the CLI service are generally measured in milliseconds, and there is therefore ample time for the calling number to be identified and matched against the predetermined numbers and, on a match, for the modulator/demodulator unit to be enabled. before the first ring signal of the call is sent. Thus before the first ring signal is sent, the call is answered (the off-hook condition is established), so no ring signals at all are in fact sent.

An ordinary telephone handset also connected to the line will therefore remain unenergized.

The present invention is primarily intended for use in a system in which an ordinary telephone handset (or similar device) end a digital data device ere both connected to a telephone line. The modem system of the present invention is included in the digital data device, and is programmed with the numbers of the remote systems to which it is to respond automatically. The modem system will therefore detect calls from those systems and automatically connect the digital data device to those systems without any ringing occurring on the telephone handset.Cells from any other numbers will be disregerded by the modem system and will therefore cause the handset to ring, end can be enswered by using that hendset in the usual way. (Of course, the digital data device can be manually controlled to respond to such non-programmed numbers, following picking up of the handset, if desired.) A modem system embodying the invention will now be described, by way of example, with reference to the drawings, in which: Fig. 1 is a block diagram of a telephone line with a digital data device and a telephone handset coupled thereto; and Fig. 2 is a more detailed block diagram of the modem system.

Fig. 1 shows a BT (PSTN, public switched telephone network) telephone line 10 having a telephone handset 11 and a digital data device 12 coupled to it.

The digital data device 12 consists of a modem system 13 and a data unit 14, which may for example be a data logger as shown.

Fig. 2 shows the modem system 13 in more detail. The line 10 is connected through a line termination 20 to a CLI demodulator 21 which detects the incoming CLI message and feeds it to a microprocessor 22 which is suitably controlled (eg by a program contained in a ROM 23). An incoming telephone call consists of a CLI message followed by a ring signal (unless the latter is aborted, as discussed above and below). The start of a CLI message is signalled by a voltage reversal on the line 10, followed by an idle state tone alert signal. In response to this, the microprocessor sends a signal to a line termination unit 24 to produce a current pulse (a "wetting" pulse) and to present a specific AC impedance to the line 10.

The CLI message continues with a channel seizure signal and then a sequence of data bits. The CLI demodulator 21 recognizes and decodes the data bits, and passes them to the microprocessor 22. These data bits include the calling number, ie the telephone number of the device which has originated the call. The microprocessor captures this calling number and compares it with a set of stored numbers in a RAM 26, which constitutes a stored number memory.

When the CLI message ends, the microprocessor disables the line termination unit 24.

If there is no match, the microprocessor performs no further functions.

The CLI message terminates in due course, and the initiation of the call continues with a sequence of ring signals on line 10. These signals pass to the telephone handset 11, causing it to ring, and the operator can lift the receiver to answer the call in the usual way.

If there is a match between the calling number and one of the numbers stored in the RAM, however, the microprocessor energizes a conventional PSTN modem 25. This acknowledges the call, and the ring signals which would normally follow the CLI message. No ring signals reach the telephone handset 11, which therefore remains silent. The operator is unaware of the incoming call.

The PSTN modem, having been enabled by the microprocessor, then functions as a data channel between the line 10 and the data logger (or other device) 14.

Once the call has been initiated in this way, the modem system 1 3 operates in essentially the same way as standard modem systems. Data transfer and exchange can then proceed between the data logger 14 and the remote calling device, and the call is eventually terminated in the usual way.

Obviously, suitable means (not shown) will normally be provided for entering into the RAM the numbers of the remote locations which are likely to be used to interrogate the digital data device.

In the system shown in Figs. 1 and 2, the PSTN modem 25 is fast enough to establish the coupling betwen the line 10 and the logger 14 before the first ring signal appears on line 10. If the PSTN modem is an existing modem, it may be more convenient for it to be controlled indirectly, by a switch located between it and the line 10, rather than being controlled directly as shown. The modem system will then be divided into two parts: the PSTN modem 25, and the remainder of the modem system (forming the modem device).

Further, in some circumstances, an existing modem may not be able to respond before the first ring signal. In that case, the system can be modified by including a 2-way switch which switches the telephone line 10 to either the handset 11 or the PSTN modem 25.

Claims (8)

Clai ms

1 A telephone modem device for controlling a modem for converting between digital signals and telephone signals, the device comprising CLI signal receiving means for receiving CLI (calling line identification) messages on the telephone line, number recognition means for recognizing predetermined calling numbers, and enabling means for thereupon enabling the modem.

2 A telephone modem device according to claim 1 wherein the number recognition means comprises a microprocessor.

3 A telephone modem device according to either previous claim including means for entering and changing the predetermined calling numbers.

4 A telephone modem device according to any previous claim including a line termination circuit and a CLI demodulator coupling the telephone line to the number recognition means.

5 A telephone modem device according to claim 4 including a line impedance unit coupled to the telephone line in parallel with the line termination circuit and controlled by the number recognition means.

6 A telephone modem device substantially as herein described with reference to the drawings.

7 A telephone modem system comprising a telephone modem device according to any of claims 4 to 6 and a PSTN modem coupled to the telephone line in parallel with the line termination circuit and controlled by the number recognition means.

8 Any novel and inventive feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).