GB2173973A

GB2173973A - Telephone switching systems

Info

Publication number: GB2173973A
Application number: GB08509554A
Authority: GB
Inventors: Douglas William Barry
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-04-15
Filing date: 1985-04-15
Publication date: 1986-10-22
Also published as: GB8509554D0; GB2173973B

Abstract

A telephone switching system provides dial tone to connected telephones when they go off-hook. Digits dialled are interpreted as a wanted external number. In this way the system resembles a direct exchange line in operation. By signalling a switchook flash instead of a dialled digit, the telephone can request special features such as internal calls or abbreviated dialling, if the switchook flash is signalled during an external call, the special features could include enquiry and transfer, or multi-party conference connections. The system operation is convenient when most calls are outgoing rather than internal, and also for casual users, who do not need to be aware that a switching system is in use. A distinctive dial tone, given in response to the switchook flash, can also be given to warn telephone users if the external line is unavailable. <IMAGE>

Description

SPECIFICATION Telephone switching system This invention relates to a telephone switching system, used to connect a number of telephones to each other, and also able to be connected to a public switched telephone network, to a PABX, orto a private network.

Many telephone switching systems use special telephones with buttons or keys which are not used to indicate digits 1 to 0, but which are used for access to special features. Such systems include key systems, and PABX's with recall button telephones.

This invention does not require the use of such telephones, as it provides access to special features by means of a timed disconnection pulse. Such a pulse is known as a switchook "flash", and can be given manually from a conventional telephone. The timing limits for detection of such a pulse are typically 300ms to is.

In the operation of a direct exchange line telephone, dial tone is received when the telephone goes off-hook. Digits dialled towards the exchange then correspond to a wanted external number. In the operation of a PABX, dial tone is also given when the telephone goes off-hook, but a digit has to be dialled to indicate that an exchange line call is required. Only after a second tone do the digits dialled correspond to a wanted external number.

According to the present invention, digits dialled after a first dial tone do correspond to a wanted external number. In this way the switching system resembles a direct exchange line in operation rather than a PABX. This procedure is convenient when most calls are outgoing rather than internal, and also for casual users, who do not need to be aware that a switching system is in use.

To obtain special features, the switchook flash is given in response to dial tone, or at any other time if allowed for in the sequence of operations of the system. In this event, a second tone, which is readily distinguishable from the first dial tone, is given by the system, and digits 1 to 0 may then have alternative interpretations to initiate special features, such as abbreviated dialling or internal connections.

A specific embodiment of the invention will now be described by way of example, with reference to the accompanying figure 1.

The sequence of operations of the system is determined by programming in the System Controller 10. If the system is connected to the PSTN, to a PBX, or to a private network, a Line Termination Circuit 1, and Outpulsing Circuit 2, are provided, using well-known art. A Detector Circuit 5 monitors the state of line, providing signals for the System Controller 10 when an incoming call is detected, and also to indicate the presence or absence of line feeding voltage which confirms the line is connected and working. Several Extension Line Circuits 4 are provided, to each of which one or more telephones are connected, either directly or in an extension plan. An off-hook condition from a telephone connected to an Extension Line Circuit 4 is detected by the Scanner Circuit 8, using wellknown art.The System Controller 10 then causes a diai tone, which may resemble the dial tone of the external network or PBX, to be connected from the Ringing And Tone Generator 7 to the Extension Line Circuit 4, either via the Switch Matrix 3 or by other well-known means.

In response to this dial tone, the telephone connected to the Extension Line Circuit 4 may signal a series of decimal digits; which are detected by the Scanner Circuit 8. This series of digits conveys to the System Controller 10 a wanted outgoing number to be outpulsed to the external network or PBX. The System Controller 10 initiates an external connection in response to the detection by the Scanner Circuit 8 that the signal from the telephone begins with a loop break impulse corresponding to a decimal digit rather than a loop break of 300ms to is, which is considered to be a switchook flash. The external connection is established under the direction of the System Controller 10, between the Extension Line Circuit 4 and the Line Termination Circuit 1 by means of the Switch Matrix 3.The wanted outgoing digits are sent from the Outpulsing Circuit 2 after a brief delay whilst the external line is seized by the Line Termination Circuit 1, and dial tone from the external line is detected in the Detector Circuit 5 or else the dial tone is assumed to have been received after a short timeout programmed into the System Controller 10 and determined by use df the Timer 11.

In the present invention, in response to the system dial tone given to the Extension Line Circuit 4 from the Ringing And Tone Generator 7 as described above, the telephone may signal a switchookflash instead of a decimal digit. When detected by the Scanner Circuit 8 this conveys to the System Controller 10 a request for special facilities.

The System Controller 10 connects a second tone to the Extension Line Circuit 4. This tone is readily distinguishable from the previous dial tone. In response to this second tone, the telephone connected to the Extension Line Circuit 4 may signal one or more decimal digits which are now interpreted by the System Controller 10 as a special pre-programmed feature request. For example in a system with only a few extensions, the digit 1 may indicate a request for an internal connection to extension line 1, whereas with more extensions more than one digit may be required for an internal call. Because all connections through the system are set up using the Switch Matrix 3, the System Controller 10 can arrange that a connection between two Extension Line Circuits 4 can have privacy against overhearing from a third Extension Line Circuit 4.Alternatively a different sequence of digits and switchook signals could indicate a request for a multi-line conference, in which three or more Extension Line Circuits 4 are connected via the Switch Matrix 3 in such a way that mutual conversation and hearing is possible.

As a further example of digit interpretation, the digit 0 may indicate a request to repeat a call attempt to the external line, using the last digit sequence previously outpulsed. Other digit combinations may invoke a call attempt to the external line using a digit sequence previously stored by the System Controller 10. Further digit combinations may control the storage of digit sequences for outpulsing, or any other call feature programmed into the System Controller 10.

The connection of such calls through the Switch Matrix 3, the establishment of transmission paths, the clearing down of calls upon completion, and the handling of calls incoming from the external network or PBX by sending alerting signals from the Ringing And Tone Generator 7 to the Extension Line Circuit 4, are all done using well-known art. In this example, the system includes Switch Drivers 6, Relay Drivers 9, Timers 11, and a Power Supply 12 to enable these functions to be completed.

An additional feature of the system is that the Extension Line Circuit 4 and Scanner Circuit 8 remain alert to the condition of the users telephone at all times. The signal of a switchookflash may be given at any time, for example whilst the telephone is already connected in an internal or external call. In response to the detection of switchook flash by the Scanner Circuit 8, the System Controller 10 will place the existing connection on "hold" and give the said second tone to the Extension Line Circuit 4, using the Switch Matrix 3 and the various drivers as necessary.In response to the second dial tone, the telephone connected to the Extension Line Circuit 4 may signal one or more decimal digits which will be detected by the Scanner Circuit 8 and which will carry to the System Controller 10 a wanted special facility such as an enquiry call to another extension, possibly to be followed by a call transfer or a conference connection. The exact significance and sequence of the dialled digits, together with any further switchook signals, is a matter of system implementation choice in the programming of the System Controller 10. Each of the wanted special facilities is implemented using the Switch Matrix 3 in cooperation as necessary with the other parts of the system already described.

A further embodiment of the invention is shown dotted in Figure 1. This shows a Multi-Frequency (MF) Signal Detector 13 which enables the extension lines to use telephones with MF sending of digits, instead of decadic impulse signalling. The mechanism of the switchook flash is still used to indicate a change of digit interpretation from wanted external number to special feature. The Outpulsing Circuit 2 may send MF or decadic impulsing digits whichever is appropriate to the external network of PBX.

In a further embodiment of the inyention, using Figure 1,the detection of an absence of external line feeding voltage by the Detector Circuit 5 causes the System Controller 10 to give the said second tone when a telephone connected to the Extension Line Circuit 4 goes off-hook. If the telephone user is not aware that the external line is disconnected, or unavailable, then the second tone acts as a warning indication. If the user is already aware that the external line is unavailable, he may proceed directly to request any of the special features of the system not related to external calls, such as an internal call or conference connection.

In a further embodiment of the invention, the system may have more than one external line. The system operation is otherwise the same as for a single line system.

Claims

1. A telephone switching system, able to interworkover one or more connections with a public switched telephone network, a PABX, or a private network, and able to be used with loopdisconnect or multi-frequency impulsing telephones having no special signalling features or buttons other than decimal digits 1 to 0 and the on/off switchook, able to provide privacy from overhearing between telephones, and in which system any sequence of digits dialled from a telephone in response to dial tone corresponds to a wanted external number whereas a break pulse of short duration typically 300ms to 1s, known as a switchookflash from a telephone indicates that an external number is not required and causes the system to supply a different dial tone, in response to which certain sequences of dialled digits now may correspond to a wanted internal number or a wanted special feature of the system, for example, abbreviated dialling of an external call.

2. A system as in claim 1, in which the absence of electrical conditions indicating connection to an external network can be detected, and in which the operation is thereupon modified to provide the said different dial tone and said different digit sequence interpretation to any telephone which subsequently goes off-hook, and in which system such special features as may usefully be provided, for example internal calls, are still available to the telephone despite the absence or failure of the said external network or PABX connection.

3. A system as in claims 1 or 2 in which the signal of a switchookflash from a telephone may be given at other times than in response to dial tone, for example at a time when the telephone is already connected in an internal or external call, and in which system the operational response is to provide the said different dial tone and said different digit sequence interpretation enabling a special feature of the system to be invoked, for example the establishment of an enquiry or transfer connection to another telephone.