GB2137454A

GB2137454A - Handsfree telephone system

Info

Publication number: GB2137454A
Application number: GB08305573A
Authority: GB
Inventors: Joseph Hood Mcneilly; Bjorn Napier Hansen
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1983-03-01
Filing date: 1983-03-01
Publication date: 1984-10-03
Also published as: EP0120324A3; EP0120324A2; GB2137454B; ES8503906A1; ES530193A0; JPS59210760A; BE899041A; AU2505584A; GB8305573D0

Description

SPECIFICATION Handsfree telephone system This invention relates to automatic telephone exchange systems, especially to such systems for use as PABXs.

In such a system, a number oftelephones are interconnected via a common switching network via which connections between those telephones are set up. Some of the telephones in such a system, especially when it is a PABX have handsfree facilities, i.e.

the subscriber's instrument has a microphone and a loudspeaker with an access button (or switch). When such a button is operated the instrument is converted from its normal handset use to the handsfree condition. When in this condition it is usual to provide a gain control circuit in each of the telephones which adjusts the gain for both incoming and for outgoing calls in such a way as to preventthe acoustic feedback and sidetone signals from generating a feedback oscillation in the system. Such an oscillation manifests itself as a rather vexatious howling noise.

An object of the invention is to provide a system in which the handsfree facility is provided in a relatively economical manner.

According to the invention, there is provided an automatic telephone exchange system, which includes a number of telephone subscribers' lines connected to a switching network via which com munication connections are set up, wherein the lines include lines having the handsfree facility available, wherein the provision of the handsfree facility for a call involves the control of the gain provided for the lines involved in that call, wherein the switching net work is centrally controlled, and wherein the handsfree control circuitry', which includes the circuitry for providing the said gain control in respect of calls for which the handsfree facility is provided is centrally located so that when it is free it is available for use for any call for which the handsfree facility is required.

Such a system is especially suited for use in a sys tem in which the control of the handsfree facility is effected using microprocessor-controlled digital hardware. Since the gain control circuitry is central ised a considerable economy is effected since the handsfree facility is unlikelyto be needed by all users at the same time.

Embodiments of the invention will now be described with reference to the accompanying draw ings, in which: Figure 1 is a highly schematic block diagram of a fully digital telephone system embodying the invention.

Figure 2 is a highly schematic block diagram in somewhat more detail of a system such as that of Figure 1 with one central handsfree facility control.

Figure 3 is a diagram similarto Figure 2 for a system similar to that of Figure 2 but with two centralised handsfree facility controls.

Figure 1 shows a digital switching network 1 which serves a number of telephone subscriber's instru ments, some of which, such as 2, 3, have access to the handsfree facility. Each such instrument has a mic rophone and a loudspeaker in addition to the hand r set, and a push button which is operated when access to the handsfree facility is wanted. Each such instru ment also has an indicator, such as a small neon lamp or a light-emitting diode, which by its condition tells the user whether the handsfree facility is available.

As already mentioned, when the handsfree facility is used, the enablement of the appropriate channel, transmit or receive, is effected by controlling the gain in those channels. In the arrangement described herein this uses a centralised handsfree gain control circuit 4 which is seized for use for a call when the handsfree facility is needed. Thus the need for separate gain control arrangements at all subscriber's instruments with access to the facility is obviated.

As will be seen from Figure 2, the digital switching network includes a multi-register unit in which each telephone line is allotted an individual address. The digital codes of each speech channel are written into their respective register addresses. Based on signalling information from two lines A and B to be con nected,the PCM code B is then transferred to channel A and the code A is transferred to channel B under control of the DSN control network 5.

Handsfreefacilityto allow one such call, which may be adequate for a relatively small system, is implemented by the addition of four such memory registers. As will be seen, these registers are for the A-B transmit, B-A transmit, A from B receive and B from A receive. The use of these registers is controlled by the DSN control 5 such that the call is transferred from the registers used for it to the four registers for handsfree operation. These four registers are controlied by the handsfree control facility circuit 4.

In the arrangement of Figure 2, callerA has "dialled station B and has also requested the handsfree facility. The digital codes from stations A and B, A-Tx and B-Tx, are therefore diverted to the special addresses in the RAM included in the switching network. These codes are then processed by the handsfree control facility 4 and transferred therefrom to the registers B-Rx and A-Rx. This processing includes the gain adjustment referred to above. Thus the four registers take the place of the original memory locations A and B originally in use for the call, and their contents are processed in the normal way.

Figure 3 shows a system with two handsfree facility circuits, although more than two such circuits may be provided. In view ofthe foregoing description it is felt that Figure 3 does not need any detailed description.

1. An automatic telephone exchange system, which includes a number of telephone subscribers' lines connected to a switching network via which communication connections are set up, wherein the lines include lines having the handsfree facility available, wherein the provision of the handsfree facility for a call involves the control of the gain provided for the lines involved in that call, wherein the switching network is centrally controlled, and wherein the handsfree control circuitry, which includes the circuitry for providing the said gain control in respect of calls for which the handsfree facility is provided is centrally-located so that when it is free it is available

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Handsfree telephone system This invention relates to automatic telephone exchange systems, especially to such systems for use as PABXs. In such a system, a number oftelephones are interconnected via a common switching network via which connections between those telephones are set up. Some of the telephones in such a system, especially when it is a PABX have handsfree facilities, i.e. the subscriber's instrument has a microphone and a loudspeaker with an access button (or switch). When such a button is operated the instrument is converted from its normal handset use to the handsfree condition. When in this condition it is usual to provide a gain control circuit in each of the telephones which adjusts the gain for both incoming and for outgoing calls in such a way as to preventthe acoustic feedback and sidetone signals from generating a feedback oscillation in the system. Such an oscillation manifests itself as a rather vexatious howling noise. An object of the invention is to provide a system in which the handsfree facility is provided in a relatively economical manner. According to the invention, there is provided an automatic telephone exchange system, which includes a number of telephone subscribers' lines connected to a switching network via which com munication connections are set up, wherein the lines include lines having the handsfree facility available, wherein the provision of the handsfree facility for a call involves the control of the gain provided for the lines involved in that call, wherein the switching net work is centrally controlled, and wherein the handsfree control circuitry', which includes the circuitry for providing the said gain control in respect of calls for which the handsfree facility is provided is centrally located so that when it is free it is available for use for any call for which the handsfree facility is required. Such a system is especially suited for use in a sys tem in which the control of the handsfree facility is effected using microprocessor-controlled digital hardware. Since the gain control circuitry is central ised a considerable economy is effected since the handsfree facility is unlikelyto be needed by all users at the same time. Embodiments of the invention will now be described with reference to the accompanying draw ings, in which: Figure 1 is a highly schematic block diagram of a fully digital telephone system embodying the invention. Figure 2 is a highly schematic block diagram in somewhat more detail of a system such as that of Figure 1 with one central handsfree facility control. Figure 3 is a diagram similarto Figure 2 for a system similar to that of Figure 2 but with two centralised handsfree facility controls. Figure 1 shows a digital switching network 1 which serves a number of telephone subscriber's instru ments, some of which, such as 2, 3, have access to the handsfree facility. Each such instrument has a mic rophone and a loudspeaker in addition to the hand r set, and a push button which is operated when access to the handsfree facility is wanted. Each such instru ment also has an indicator, such as a small neon lamp or a light-emitting diode, which by its condition tells the user whether the handsfree facility is available. As already mentioned, when the handsfree facility is used, the enablement of the appropriate channel, transmit or receive, is effected by controlling the gain in those channels. In the arrangement described herein this uses a centralised handsfree gain control circuit 4 which is seized for use for a call when the handsfree facility is needed. Thus the need for separate gain control arrangements at all subscriber's instruments with access to the facility is obviated. As will be seen from Figure 2, the digital switching network includes a multi-register unit in which each telephone line is allotted an individual address. The digital codes of each speech channel are written into their respective register addresses. Based on signalling information from two lines A and B to be con nected,the PCM code B is then transferred to channel A and the code A is transferred to channel B under control of the DSN control network 5. Handsfreefacilityto allow one such call, which may be adequate for a relatively small system, is implemented by the addition of four such memory registers. As will be seen, these registers are for the A-B transmit, B-A transmit, A from B receive and B from A receive. The use of these registers is controlled by the DSN control 5 such that the call is transferred from the registers used for it to the four registers for handsfree operation. These four registers are controlied by the handsfree control facility circuit 4. In the arrangement of Figure 2, callerA has "dialled station B and has also requested the handsfree facility. The digital codes from stations A and B, A-Tx and B-Tx, are therefore diverted to the special addresses in the RAM included in the switching network. These codes are then processed by the handsfree control facility 4 and transferred therefrom to the registers B-Rx and A-Rx. This processing includes the gain adjustment referred to above. Thus the four registers take the place of the original memory locations A and B originally in use for the call, and their contents are processed in the normal way. Figure 3 shows a system with two handsfree facility circuits, although more than two such circuits may be provided. In view ofthe foregoing description it is felt that Figure 3 does not need any detailed description. CLAIMS

1. An automatic telephone exchange system, which includes a number of telephone subscribers' lines connected to a switching network via which communication connections are set up, wherein the lines include lines having the handsfree facility available, wherein the provision of the handsfree facility for a call involves the control of the gain provided for the lines involved in that call, wherein the switching network is centrally controlled, and wherein the handsfree control circuitry, which includes the circuitry for providing the said gain control in respect of calls for which the handsfree facility is provided is centrally-located so that when it is free it is available for use for any call for which the handsfree facility is required.

2. A system as claimed in claim 1, wherein the switching network is a digital network which is under the control of digital processing means, and wherein the speech to be conveyed is dealt with in a digital form.

3. A system as claimed in claim 2, wherein the digital network includes a random access memory which provides a number of registers each of which is allocated to one of the lines served, wherein when a call is set up in respect of one said lines that line's one of said registers is used, wherein the random access memory also includes further registers for use for the handsfree facility which are taken into use in place of those allocated to a pair of lines when those lines need the handsfree facility, and wherein the further registers give access to the gain control circuitry.

4. A system as claimed in claim 3, wherein two or more handsfree facility control circuits are provided, each of which is served by a set of said further registers.

5. An automatic telephone exchange system, substantially as described with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawing.

New or amended claims:

6. An automatic telephone exchange system, which includes a number of telephone subscribers' lines connected to a switching network via which communication connections are set up, wherein the lines include lines having the handsfree facility available, wherein the provision of the hands free facility for a call involves the control of the gain provided for the lines involved in that call, and wherein the handsfree control circuitry, which includes the circuitry for providing the said gain control in respect of calls for which the handsfree facility is provided, is centrallylocated so that when it is free it is available for use for any call for which the handsfree facility is required.