GB2200015A - Pabx - Google Patents

Abstract

An electronic PABX (3) of the older type has an add-on unit, called an emulator, which enables subscriber features not normally available to incoming calls from a modern PABX to be provided. The emulator includes a scanner (5) which scans those lines to check their condition/status. The results of these checks, are placed in a memory (4), and this information is compared with incoming call requests. The result of the comparison causes the appropriate signals for call set to be sent to the PABX (3) via another sender/receiver (7) if that call can be set up with the wanted feature. <IMAGE>

Description

PABX This invention relates to PABXs, and to equipment for use therein.

The most up-to-date digital PABXs have features not available to some of the older electronic PABXs, and also not available to even older eletro-mechanical PABXs.

These newer exchanges need to inter-work with the older PABX types, and though this is limited in performance it is effected over conventional analogue tie lines. In such cases it is not possible to provide "feature transfer" over the network.

One of the features which is provided by the newer types of PABX is DPNSS, which means Digital Private Network Signalling System, and it enables corporate networks to be built up, linked by high speed digital links. DPNSS is a common channel signalling system for use in digital private networks. In its simplest form it provides base call set-up between the modern types of digital exchange. However, it also provides advanced features such as brokers' call, call forwarding, call forward busy, call forward no answer, call transfer, camp on busy, do not disturb, extension-controlled conference, hot line, last number redial, and music on hold. In such a case it is most complex to provide "feature transfer" over the network.

An object of the present invention is to provide equipment whereby such features when provided on older PABXs can be available for calls incoming from newer types of PABXs having DPNSS.

According to the invention there is provided an add-on equipment assembly, for use in association with an automatic telephone exchange to provide additional subscriber features for the lines served by that exchange, which assembly includes first memory means in which details of the features to be provided for said lines are stored, a line scanner to scan the lines of an associated exchange to be afforded said facilities for the assessment of the current condition of those lines, further memory means wherein the results of said scanning are recorded, and control means responsive, when the assembly is in use, to request in respect of an incoming call for a said feature to implement the feature for that call if the condition of the line involved in that call permits the implementation of the feature.

According to the invention there is also provided a PABX, which includes as an add-on unit, a features emulator for providing the PABX with additional features for the use of calls incoming to the PABX, in which the PABX includes a line scanner which scans the lines of the PABX to assess their current conditions, which scanner communicates the results of its scans to a line status memory in the emulator, a feature status record memory also in the emulator which records the status of the additional features provided via said emulator, and control means in the emulator responsive to requests for the additional features to provide said features if the status of the lines and features permit it.

An embodiment of the invention will now be described with reference to the accompanying highly schematic block diagram.

The particular form of signalling system for which the present arrangement was developed is used when there is more than one of the modern digital exchanges in the network with that capability. The present equipment, which is known as an emulator, can be added to any PABX of the older type.

The emulator unit provides an interface between a digital link to a distant exchange and some at least of the line circuits on the local exchange. The equipment includes an extension line scanner which monitors the status of the lines served by the emulator unit such that the emulator can initiate the correct response to an incoming calling condition. The unit includes a programmable area of memory to which access is possible via a terminal. This area is given the details of the features in the local exchange which can be invoked from the distant end, which features are made available to the lines served by the emulator.

The scanner, in addition to monitoring the busy/free status of all lines it serves, records the invoke/revoke codes dialled by the extensions such that they can be sent forward when appropriate. In the preferred arrangement this scanner is part of the emulator although it could be separate from the emulator.

The emulator, plus the scanner if a separate item, is modular, such that it can be used on small key systems as well as on large PABXs.

The DPNSS emulator also has the ability to accept data transmission from data transmission equipments, and to send such signals to, for instance, a British Telecom Megastream Unit.

In the setting up of connections for which the DPNSS emulator, see the accompanying block diagram, is used, a sender/receiver 1 in the emulator receives digital signals incoming from a distant PABX using the DPNSS feature mentioned above. These signals it passes to a DPNSS decoder 2 since they use the protocol appropriate to DPNSS. Certain DPNSS signals are returned to the originating exchange, since the signalling operates in a compelled mode.

If the initial data thus received is for an extension on the PABX 3 that information is tested against the data . stored in an extension line status record memory 4. As can be seen, the lines of the PABX for which the additional features are available are scanned by a scanner 5 which assesses their condition cum status. The results of the assessment by the scanner 5 not only include the free/busy condition of the lines but their status, i.e. it determines what features those lines can have. The scanning results are communicated to the status record memory 4 already mentioned, and also to a feature code record memory unit 6, which can also communicate with the memory 4.

If the result of the test of the received data against the information in the memory 4 indicates that the wanted line is free, and can have the required feature, an instruction is sent to the SSMF4 sender/receiver to signal to the PABX 3 to cause establishment of the connection. This sender transmits the call set up indications using four-frequency voice frequency. The block 7 can also receive since such call set-up involves in well-known manner signalling back to the "calling" exchange. Such signalling to the calling exchange is digital, via the DPNSS sender/receiver 1.

However, if the extension is found to be busy in the memory 4, a signal to that effect is reverted to the caller via the blocks 7 and 1. This instructs the originating exchange to send busy tone to the caller.

The distant caller can then clear down, or initiate intrusion or camp-on busy. In the case of intrusion, and if the feature status record in the block 6 indicates that this is permitted, an SSMF4 instruction is passed to the wanted line via the blocks 4 and 7. If the feature is not available, then busy tone would continue to be sent to the caller.

Note that the scanner 5, in addition to monitoring the status of the lines as to busy, free etc., also passes to the feature code record 6 any features codes dialled by the extensions on the PABX 3. Hence it is involved in the provision of features for the PABX 3, at least to the extent of maintaining a record of the extent of use of those featues. Thus this record might indicate that although a wanted extension is allowed access to certain features, the required feature may itself be busy, or even out of order.

The emulator also includes a programming interface 9, which enables the feature status record unit 10 to be programmed. This unit contains a record of which features are available to which of the lines served by the PABX 3. The interface 9 also enables the unit 6 which retains current records of the level of use of the features to be programmed. Thus the features status record unit 10 is programmed to indicate which featues can be invoked across the network, and its content varies from one PABX to another. The feature code record unit 6 stores the features invoke/revoke digits from the extension on the PABX 3. These digits vary not only between different PABXs, but may also vary between PABXs of the same type.

The emulator can also be used on tandem connections, i.e. on incoming-to-outgoing connections to allow the DPNSS signals to be passed across a network.

This would also use the SSMF4 sender/receiver 7.

Claims (5)

1. An add-on equipment assembly, for use in association with an automatic telephone exchange to provide additional subscriber features for the lines served by that exchange, which assembly includes first memory means in which details of the features to be provided for said lines are stored, a line scanner to scan the lines of an associated exchange to be afforded said facilities for the assessment of the current condition of those lines, further memory means wherein the results of said scanning are recorded, and control means responsive, when the assembly is in use, to request in respect of an incoming call for a said feature to implement the feature for that call if the condition of the line involved in that call permits the implementation of the feature.

2. An assembly as claimed in claim 1, and which includes a sender/receiver unit connected, when the assembly is in use, to a link to a remote exchange, which unit responds to the signalling protocol of the remote exchange, and a further sender/receiver unit connected to the associated exchange and which puts the signals into the format acceptable to the associated exchange.

3. An add-on assembly for use in association with a PABX, substantially as described with reference to the accompanying drawing.

4. A PABX, which includes as an add-on unit, a features emulator for providing the PABX with additional features for the use of calls incoming to the PABX, in which the PABX includes a line scanner which scans the lines of the PABX to assess their current conditions, which scanner communicates the results of its scans to a line status memory in the emulator, a feature status record memory also in the emulator which records the status of the additional features provided via said emulator, and control means in the emulator responsive to requests for the additional features to provide said features if the status of the lines and features permit it.

5. A PABX, substantially as described with reference to the accompanying drawing.