GB2125252A

GB2125252A - Telecommunication exchange network

Info

Publication number: GB2125252A
Application number: GB08221645A
Authority: GB
Inventors: Frederick Henry Rees
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-07-27
Filing date: 1982-07-27
Publication date: 1984-02-29
Also published as: GB2125252B

Abstract

In many telecommunication exchange networks which consist of mostly of analogue exchanges (2), e.g. of the TXE4 or TXE4A type, the subscribers served include PABX's (1) which are also analogue exchanges. If any digital exchanges (4) such as System X exchanges penetrate the network, assumed to be by an overlay network connected to the existing analogue network, the subscribers served by the digital exchanges have access to more facilities than do the subscribers served by analogue exchanges. To extend these facilities to PABX subscribers, an analogue PABX (1) is provided with a digital extension unit (3) coupled to its PABX (1) via an interworking unit (5) and also coupled to a digital exchange (4) in the public network. Any call using digital facilities is set up wholly in the digital network (3, 4) while a call not using digital facilities may use either the analogue network (2, 4) or in certain circumstances the digital network. This arrangement, like that described in our Application No. 8217334, enables the PABX and its subscribers to retain their directory number unchanged. <IMAGE>

Description

SPECIFICATION Telecommunication exchange network This invention relates to automatic telecommunication exchange systems which include public exchanges and PABX's.

In many such systems the public exchanges are non-digital but relatively modern, for instance exchanges of the TXE4 or TXE4A type, while the PABX's, although also relatively modern are also non-digital. As digital techniques penetrate the system, e.g. due to the spread of System X exchanges, the facilities provided by the digital exchanges are greater in number and complexity than those provided by the non-analogue exchanges. Hence the subscribers connected to the non-digital parts of the network wish to have access to the full range of facilities provided by the digital parts of the system.

An object of the invention is to facilitate this extension of such facilities.

According to the invention there is provided an automatic telecommunication exchange network, which includes a non-digital PABX connected to a non-digital public telephone exchange, a digital extension unit for the PABX which is connected to a digital public exchange, and an interworking unit interconnecting the non-digital PABX and its digital extension, in which the combination of the non-digital PABX, the digital extension unit and the interworking unit together from a hybrid exchange identified by the directory number of the non-digital PABX, and, in which all calls, whether originating or terminating, which use facilities provided by the digital extension unit but not by the non-digital PABX are established from or to terminals connected to the digital extension unit and are routed via the digital public exchange.

The arrangement to be described herein resembles to some extent that of our Application No. 8217334 (F. H. Rees 26), which also relates to the penetration of digital exchanges into a nondigital network. In the specification of that application a system is described in which digital exchanges, e.g. System X, are being added to a mainly analogue, e.g. TXE4 or TXE4A network, and it is needed to provide analogue exchange subscribers with digital facilities not normally available to subscribers on the analogue exchanges. To do this, a line on an analogue exchange for which digital facilities are to be made available is connected to a digital line circuit parented on a digital exchange. Outgoing calls and incoming calls for such a line are set up via the digital exchange as for a call through such a digital exchange.An incoming analogue call for such a line is set up to the analogue exchange and therefrom to the digital exchange and the subscriber's line circuit. This enables that subscriber to retain his original directory number.

It will be appreciated that the present invention is related to that of the above-mentioned application, and that both the present invention and the invention of the above-mentioned application can be used in the same network.

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

With the network to be described herein an existing non-digital PABX can be provided with additional facilities normally available only to digital exchanges. Such facilities need "crossnetwork" digital paths, but it is considered undesirable for any subscribers, whether on a public exchange or on the PABX, to have their directory numbers changed. To do this, the existing PABX is overlayed by an extension unit, which is in effect a digital PABX, capable of affording the required "digital-type" facilities and which need digital paths. This digital extension unit is connected, not to the existing non-digital public exchange, but to a new and fully digital public exchange which is in effect an overlay on the existing public network. The non-digital PABX remains connected to the old non-digital public network.Thus the same directory number is used for the non-digital PABX and the new PABX extension unit. The network routes calls routed via the digital overlay to or from the new unit and calls not needing digital paths may be routed to the existing, i.e. the non-digital PABX.

The existing PABX 1 is non-digital, but it may be processor-controlled, and it is connected to an existing analogue exchange 2 in the public exchange network. To provide the digital facilities, the PABX has a digital extension unit 3 which is connected to a digital exchange 4 in the public network. This extension unit 3 is coupled via an interworking unit 5 to the non-digital PABX 1.

Extensions for which digital facilities are to be provided are connected to the digital extension unit 3. The interworking unit 5 controls connections between lines on the non-digital PABX 1 and lines on the digital extension unit 3.

In one implementation this interworking unit includes a duplex message channel for addressed messages between the non-digital PABX and the digital extension unit and interconnecting circuits involving digital to analogue and analogue to digital conversion.

In some embodiments of the invention, the terminals on the digital extension unit do not provide telephony facilities and therefore an interworking unit 5 is not required if the public network directs all calls which are telephony to the non-digital PABX. Similarly interworking unit 5 is not required if all telephony calls to the digital extension unit are of the voice/data type and if the public network directs all calls, which are telephony to the non-digital PABX.

It will be noted that the digital facilities provided by the extension unit may include packet switching facilities.

The resulting system is in effect a hybrid exchange formed by the original non-digital PABX, the interworking unit and the digital extension unit.

Hence we provide digital facilities while retaining the PABX's existing public network directory number. This is often highly desirable for business reasons. The modified arrangement enables the hybrid PABX to accept calls which have been digitally routed through the digital network, and also to accept-or set up calls using digital facilities which may not be available to the analogue PABX or in many cases not be available to the analogue public exchanges. It also serves to extend calls not requiring digital facilities to the digital extension unit from the non-digital PABX to the digital extension unit and may extend similar calls from the digital extension unit to the non-digital PABX.

The extension unit connected to the digital public exchange can originate and terminate calls using the "modern" facilities e.g. the ISDN (Integrated Services Digital Network) facilities in a System X network. It can also originate outgoing telephony calls to telephony subscribers parented on non-digital or digital public exchanges elsewhere in the network, or in the rest of the world, via the digital public exchange, assumed in the present case to be a System X exchange. The digital exchange may or may not (as desired) be in the same building as the existing analogue exchange. In either case, we thus provide digital routing for those advanced calls for exchange termination actually located on the digital extension unit, which thus incorporates the desired features.

In some implementations for internal calls, the caller dials a code specific to internal calls, while for digital calls a special prefix is dialled. This is analogous to the normal use of a special prefix for a call from the PABX to the public network.

Since calls needing all-digital paths and facilities are routed over the new network to the digital exchange, it is not necessary to modify the existing analogue local exchange.

In the public network a public exchange has one or more exchange codes assigned to it which serves to identify it, for routing purposes, in the network. A subscriber's directory number contains the relevant exchange code.

In our above-mentioned application the concept was introduced of two exchanges one a non-digital public exchange and the other a digital public exchange sharing the same exchange code.

Thus in the system described in that application, some of the subscribers associated with a particular exchange code were served by a digital public exchange, whilst other subscribers associated with the same exchange code were served by a non-digital public exchange.

In the arrangement here disclosed a PABX subscriber is served both by the non-digital public exchange and by a digital public exchange and has one or more lines to the non-digital exchange and one or more lines to the digital exchange.

Thus in the above-mentioned application, double switching occured in the public network, due to a call arriving at the analogue exchange, being recognised as call destined for the associated digital exchange, and therefore being routed via the public network to the associated digital exchange. However, in the present system such calls arriving at the non-digital PABX or such calls from subscribers, having digital facilities are routed direct to or from the PABX. If they are telephony type calls destined for a subscriber on the digital extension unit, they may be routed by the operator via the interworking unit 5. Similarly telephony type calls arriving at the digital extension may be extended via the interworking unit to the operator.

In some applications all calls traversing the overlay network associated with the directory number of the PABX would be routed to the digital extension unit (e.g. when the public nondigital exchange is of the Strawger type).

To afford the facilities of the invention no change is required in the non-digital public exchange concerned. This exchange need not, as in the cases considered in the above-mentioned application, tandem incoming telephony calls, for giving access to the "modern" facilities.

Claims

1. An automatic telecommunication exchange network, which includes a non-digital PABX connected to a non-digital public telephone exchange, a digital extension unit for the PABX which is connected to a digital public exchange, and an interworking unit interconnecting the nondigital PABX and its digital extension, in which the combination of the non-digital PABX, the digital extension unit and the interworking unit together from a hybrid exchange identified by the directory number of the non-digital PABX, and in which all calls, whether originating or terminating, which use facilities provided by the digital extension unit but not by the non-digital PABX are established from or to terminals connected to the digital extension unit and are routed via the digital public exchange.

2. An automatic telecommunication exchange network, which includes non-digital and digital public exchanges and at least one non-digital PABX connected to a non-digital public exchange, in which to enable PABX subscribers to be afforded access to facilities not normally available on non-digital equipment and which need digital paths the PABX is provided with a digital extension unit, in which the PABX subscribers to be afforded access to the digital facilities are connected to the extension unit, in which an interworking unit connected between the nondigital PABX and the digital extension unit is provided for controlling the operation of calls routed between the non-digitai PABX and its digital extension unit, in which the digital extension unit is connected to a digital exchange in the public network while the non-digital PABX remains connected to a non-digital exchange in the public network, in which connection via the public network to or from PABX lines which do not need digital paths may be set up via the nondigital PABX and the non-digital public exchange to which the non-digital PABX is connected, and in which connections via the public network to or from PABX lines and which need digital paths are set up via the PABX's digital extension unit and the digital public exchange to which that digital extension unit is connected, the arrangement being such that the PABX and its digital extension unit retains the PABX's original directory number or numbers and that the PABX lines also retain their existing numbers on the PABX.

3. An automatic telecommunication exchange network substantially as described with reference to the accompanying drawing.

4. A PABX for use in a network as claimed in claim 1, 2, 3 or 4.

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