GB2132449A - Decentralised PABX - Google Patents

Abstract

A telecommunication system, such as a PABX or a Local Area Network (LAN) has a closed loop communications cable to interconnect a number of system nodes. These nodes include subscriber nodes, operator nodes, facilities (e.g. conference) nodes, and junction nodes (which give access to a PAX, or PABX, and LAN, or a public telephone network). Each such node includes control and processing equipment including a half-call controller so that from the control aspect the system is fully decentralised. Note that the system can also be of the open bus type, and can also be of the "Stand-alone" type. <IMAGE>

Description

SPECIFICATION Decentralised PABX The present invention relates to an automatic telecommunication switching system.

According to the invention there is provided an automatic telecommunication switching system, which includes a number of system nodes interconnected by a communications cable, in which the nodes include nodes for subscribers served by the system, which subscribers include voice subscribers, and nodes for facilities circuits and in which the system control is fully decentralised in that for each call set up between two of the system nodes the control functions are performed by equipment at these nodes.

According to the invention there is also provided an automatic telecommunication switching system, which includes a number of system nodes interconnected by a communications cable, in which the nodes include nodes for subscribers served by the system, which subscribers include voice subscribers, and nodes for facilities circuits, in which the nodes also include at least one node via which the system has access to a PABX, to a PAX, or to a public telecommunications network, and in which the system control is fully decentralised in that for each call set up between two of the system nodes the control functions are performed by equipment at these nodes.

Thus it will be seen that the invention provides a telecommunication, e.g. telephone, switching system (which may itself be a PABX or a PAX) in which the control of call switching is decentralised so that responsibility for call control is divided among a number of separate nodes.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure 1 is a highly schematic representation of a system embodying the invention, while Figure 2 of the nodes of the system of Figure 1 in more detail.

Figure 1 shows an arrangement in which the various nodes for the users, e.g. subscribers, maintenance man, operator and junction (Public Exchange and Tie Lines), and facilities (e.g.

conference, call booking) nodes are connected to a common transmission medium which can, for example, be a ring or bus. Each node is equipped with a controller, which includes processor and memory, which is responsible for a portion of call control, and also contains a data base. In the example shown, the common transmission medium is of the closed loop type, and is electrical in nature.

An advantage of such an arrangement is that it is suitable for attachment to a Local Area Network (LAN) initially designed for data facilities. Thus voice and data services are integrated in a common arrangement. In addition, the individual user nodes for voice and data connections can in another version of the integrated system be replaced by multi-service nodes.

The manner in which calls are distributed to public exchange lines, or tie lines to a PABX must avoid total failure of a route due to one faulty device. Therefore, the subscriber nodes are arranged to hunt for a free junction in a different manner on successive calls. Cyclic or homing arrangements may be used when hunting for a free outlet, but in either case there are variations in the starting point of the sequence, or subdivision,into two sequences for each route.

In the organisation of queues for the PABX operator, if there is only a single operator, the queueing arrangement is integrated in the single node, so that there is one queue dealt with by that node, when two or more operator positions are equipped, calls are offered from subscribers and junctions so that they are uniformly distributed amongst the operator positions, which thus have individual queues. To avoid the traffic inefficiency inherent in the divided queues, it may be necessary to pass supplementary messages between operator nodes and between operator and subscriber nodes. It is also possible to allow all calls to queue at such operator nodes and for those nodes to interchange information when a call is served. Hence if one operator has an overload is can be passed off to one or more other operators.

Call diversions due to temporary change of location by the user are in general unnecessary.

The order in which the user nodes appear on the ring or bus is unimportant, and hence if desired a user's equipment to be plugged in at any vacant socket. That is, the cable of the ring is provided with plug-in points each with a socket which can receive a plug on a nodal equipment. Alternatively, the portability may be confined to a card or similar arrangement for defining the user identity which can be associated with any user node. Where, however, calls are transferred from one user to another to cover for the temporary absence of one party, the transfer is agreed between the two nodes. Thus calls may either arrive at one node and be connected onwards to another, or one node may temporarily recognise two or more user addresses.

Where conferenece facilities are needed, a conference link is selected by the calling node in a similar manner to the selection of a public exchange line - with similar safeguards on the hunting arrangement. Then the conference link's node is connected to all nodes involved in the call - up to the maximum capacity of a conference link.

Maintenance and routine checks of the system are performed by probe checks and simple calls between a maintenance node and all other nodes.

If non-volatile memory is provided in a secure manner in some nodes, it is also possible for maintenance staff to update local data bases via the maintenance node. Changes in user class of service arrangements, and in barring code tables could then, be possible.

Where connections are wanted for calls to the Public Service Telephone Network (PSTN) or to an Integrated Services Digital Network (ISDN), this can be provided using digital links, such as 2 Mb/s PCM links. In such a case failure of one node involves failure of up to 30 communication channels as the provision of redundant equipment within the node is then highly desirable.

Although the arrangement described above uses a metallic cable for the inter-node ring or bus, it will be appreciated that optical fibre cables, with the merit of their higher bandwidth capacity, can also be used. In such a case each point in the ring or bus at which there is a node has equipment for conversion between the light used for communication in the fibres and the electrical currents used in the nodal equipment.

Figure 2 shows in somewhat more detail the arrangement of the subscriber, public exchange line and operator nodes. Note that all nodes are connected to the transmission medium via a transmitter TX and a receiver RX. These "sub nodal" devices are responsible for the access to and from the transmission medium and for the resolution of any contention problems that may arise when other nodes are seeking access. The transmitter and receiver are also responsible for conversion between protocols used for the control processes within the node and that employed for transmission.

In a subscriber node, a half-call controller, C, is reponsible for the call processing tasks associated with the subscriber's half of calls to other subscribers, to public exchange lines or tie lines, and to operators. In addition, the controller C handles the protocols used in communicating via the transmission medium, and those used to communicate with the subscriber's peripheral equipments (e.g. telephone and data terminals). A controller has a data base DB containing all the address and order-of-search information needed for it to make calls to other nodes, for assessing subscriber class of service, for recognising closed user group codes, and to recognise local abbreviated number repertoires.An interface unit I between the node's processing means and its input-output means handles and validates messages to and from peripherals, i.e. other nodes, and adapts outgoing messages to a convenient form for processing by the controller.

These peripherals can be telephone keypads, other control buttons, display devices, telephone handsets, and tone callers. Messages from other nodes which reach such a node's interface unit are, of course, already correctly formatted.

Generally, each external route to a public exchange or a PABX, is served by a number of nodes, hereinafter called PE nodes. Other nodes may address these PE nodes in a preset order particular to the calling node. Thus a uniform distribution of traffic and minimisation of call collisions is achieved. The order of search is varied on alternate calls from a calling node to allow continuity of service in the event of a faulty PE node. A PE node also carries incoming call traffic from the public exchange or PABX. The manner in which such calls are offered depends on the hunting rules used by the external source, i.e. by the public exchange or remote PABX. Such incoming calls are directed to the wanted subscriber's node orto an operator node as appropriate to and under the control of the action of the controller C.This controller is also repsonsible for the control of half calls involving the PE node end of a call made to or from a subscriber or operator.

The controller has access to a data base, DB, containing tables of external addresses barred to subscribers of various class of service categories.

This data base may also contain control data for a distribution sequence(s) for presenting incoming calls to operators when there are two or more operators. The sequence may vary from one PE node to another.

Connections to external lines are made via an interface I, which handles the incoming and outgoing signalling conditions, and may validate the received signalling messages prior to sending these to the controller.

The operator node equipment is connected between each operator's console and the transmission medium. A controller handles the half calls (operator end) arising from connections to PE nodes or subscribers. The controller works in association with a data base DB, and a queueing arrangement Q. The data base also contains tables defining the order of hunting when a PE or tie line node is required, and also define priority status for some subscribers when calling the operator(s).

The queueing arrangement allows incoming calls from PE nodes and subscribers to wait and be served in an ordered manner. Some interchange of information on queue lengths between the controllers of the various operation nodes may assist the balancing of queue lengths in the event of slow service in one or more of the nodes.

An interface arrangement in each node, I handles all messages to the operator console including those for the displays. Signals from the console due to key or button operation are therein validated prior to sending to the controller.

It will be appreciated that where the inter-node cable, whether it is of the optical fibre type or of the metallic type, is a closed loop, transmission round it can be unidirectional. Alternatively, two loops could be provided, one for clockwise and one for anti-clockwise transmission.

Claims (5)

1. An automatic telecommunication switching system, which includes a number of system nodes interconnected by a communication's cable, in which the nodes include nodes for subscribers served by the system, which subscribers include voice subscribers, and nodes for facilities circuits and in which the system control is fully decentralised in that for each call set up between two of the system nodes the control functions are performed by equipment at these nodes.

2. An automatic telecommunication switching system, which includes a number of system nodes interconnected by a communications cable, in which the nodes include nodes for subscribers served by the system, which subscribers include voice subscribers, and nodes for facilities circuits, in which the nodes also include at least one node via which the system has access to a PABX, to a PAX, or to a public telecommunications network, and in which the system control is fully decentralised in that for each call set up between two of the system nodes the control functions are performed by equipment at these nodes.

3. A system as claimed in claim 2, in which the cable is provided with a number of connection elements, and in which each said node's equipment is provided with a co-operating connection element so that a said node's equipment can be connected to the cable at any one of a number of different positions.

4. A system as claimed in claim 1, 2 or 3, in which the internode cable is of the closed loop type.

5. An automatic telecommunication system, substantially as described with reference to the accompanying drawing.