GB2132446A - Telecommunication exchange system - Google Patents

Abstract

British Patent Specification No. 1122924 (ISEC; H. Mantel 1) described a system with two telecommunication networks in the same exchange, one for telephone traffic and one for teleprinter traffic. Each network has its own control means, and there is further control means for both networks. The further control means is used in call handling, especially when a subscriber with access to both networks wishes to use both of them during a call. The present arrangement extends the above general idea to a multi-node system of the digital type, in which some at least of the nodes can handle two or more types of traffic. Thus such a node has one layer (3,6,2,8,9,10) which handles normal telephone traffic (known as Plain Ordinary Telephone Service) or circuit switched data, another layer (11, 13) for, in this case, packet switching, and a control layer (4, 7, 5, 11, 12) with equipment at all of the nodes which serves both layers - or all of the layers if there are more than two "traffic" layers. <IMAGE>

Description

SPECIFICATION Telecommunication exchange system This invention relates to an automatic telecommunication system in which intelligence of two or more different types can be conveyed via respective switching networks.

An arrangement of the above type is described in British Patent Specification No. 1 122924 (ISEC; H. Mantel 1) which describes a system with two switching networks within the same exchange, one of which serves telephone subscribers and one of which serves teleprinter subscribers. Each network has its own control equipment, and there is also further control equipment associated with both networks. This further control equipment is involved in call handling, especially when a subscriber with access to both networks, wishes to use both of those networks during the same call.

An object of the present invention is to produce a system which would in general be a multinode (i.e. multi-exchange or switching centre) system and which extends the principles inherent in the exchange described in the above-mentioned Patent Specification.

According to the invention there is provided an automatic telecommunication system, which includes a number of networks arranged functionaily in accordance with a multi-layer architecture, wherein the networks include a first digital switching network via which calls are set up between subscribers for telephone or circuit switched data service, a control network having access to the first switching network for the control of the establishment of calls via that switching network, and at least one further digital switching network via which calls may be set up for a different form of traffic such as wideband switched data, wherein the control network also has access to the or each said further switching network for controlling the establishment of calls through such network or networks, so that the same control network is effective for call setting in all of said switching networks, and wherein for some at least of the subscribers served the same call can use one of more of said switching networks as and when required by the subscribers involved in the call.

According to the invention there is also provided an automatic telecommunication system, which includes a number of networks arranged functionally in accordance with a multi-layer architecture, wherein the networks include a first digital network which interconnects a number of switching nodes of the system and via which calls are set up between subscribers for telephone or circuit switched data service, a control network having access to the first swtiching network for the control of the establishment of calls via that switching network, which control network includes processing means at some at least of said nodes, and at least one further switching network via which calls may be set up for a different form of digital traffic such as wideband switched data, said further switching network interconnecting some at least of the nodes of the system, wherein the control network has access, at each said node which is connected to the or each said further switching network, to the or each said switching network for controlling the establishment of calls through such network or networks, so that the same control network is effective for the control of call setting in all of said switching networks, and wherein for some at least of the subscribers served the same call can use one or more of said switching networks as and when required during a call by the subscribers involved in that call.

The arrangements described herein relate to the use of the invention in a fully electronic network, which consists of a number of fully digital switching centres, often referred to as nodes, interconnected by digital links which in many cases are TDM-PCM links. Subscriber's lines may also be fully digital, but in some cases would be analogue between the subscriber's premises and the associated line circuit at the exchange. As will have been seen from the statement of invention, a system embodying the invention is a plural-layer system, of which one layer is a control network layer while each other layer is a switching network layer.In this respect the resemblance to the exchange'described in the above-quoted Specification No. 1122924 will be noted, but the present system considerably extends the principles on which the arrangement described in that Specification is based.

Thus in a digital network of the type referred to above in which only speech is handled we have a network layer for control and signalling which controls a layer of circuit switching equipment, which functions in one case at 64 Kbiljsec. In the present system one or more further switching layers is or are provided to give the additional facilities needed by an evolving system of the Integrated Service Digital Network (ISDN) type.

Thus one such layer may provide wider band switching than is needed for speech, and another may be provided for packet switching. Such an extra layer or layers is or are controlled from the original control layer with relatively minor alteration to that control layer.

The full integration of the control provided by the present arrangement, wherein the same controi/signalling layer serves all switching layers, affords great economies in the provision and operation of the system, and can provide services involving a mix of facilities provided by different network layers as and when required. Thus as an example during a normal telephone call, the subscriber may wish to enhance a switched 64 Kbit/sec connection by the addition of a switched wide band connection for short periods during a call. Such a connection could be unidirectional or bidirectional. As these are more expensive than the normal telephone service, such switching for short periods, as and when needed, is useful.

In some cases the routing through the system may differ in that the paths provided across the different intelligence "transport" layers may vary, especially where one layer is relatively underprovided as compared with the or each other layer. Thus the wide band routes, which may not be as busy as the other routes, may be extended via two or more switching centres whereas the more busy routes may have direct routing. Thus the controlled network layers may well differ considerably one from the other. Recent developments in.technology, e.g. the advent of optical fibre communication with the much higher bit rates possible, renders the provision of wide band networks more attractive than was hitherto the case.It is possible for a wide band layer to have two or more "sub-layers", e.g. one for GO and one for RETURN, and circuits between two layers extend via multiplexers to and wide band switches within the sub-layers. Such switches are in general multiple assemblies of high speed gates.

With packet switching it is possible for access to be to a D channel (8 Kbits/sec) or to a b channel (64 Kbits/sec). Thus a subscriber may be able to change, as desired, between the two types of channel, dependent on the nature of the call. This change would involve a supplementary service request, i.e. by "dialling" a special code. The D channel also carries signalling information between the line controller and subscriber used for control purposes.

In order to implement the packet layer, see the attached drawing, a digital concentrator module has an additionai device 1, a packet module controller in the packet layer. The concentrator includes a PCM switch 2, known as a DSSS circuit switch: this is the main switching element of the concentrator. It is fed by digital line terminations (DLT) such as 3, each of which acts as the interface to the concentrator fort PCM-TDM link from a digital PBS or a remote multiplexer serving subscriber line units (SLU). This link conveys intelligence at 2.048 Mb/sec, and has associated with it a line controller 4, which is under the control of a module controller 5.

The switch 2 is controlled by the module controller S, and is also fed from subscriber line units (SLU) such as 6 each of which terminates up to 1 5 lines from digital subscribers. On these lines intelligence is conveyed at 80 Kbits/sec. Each SLU such as 6 has associated with a line controller 7 via which the intelligence passes to the switch 2.

The units such as 7 are also under the control of the module controller 5. This latter also sends message information to and receives message information from DLT's such as 8, 9 via which intelligence is conveyed at 2.048 Mbits/sec to the central part of a local exchange whose main switching network DSSS is shown at 10.

The switch 10 is controlled by a processing unit (PU) 11, which communicates with the DSSS via a message transmission portion (MTSG) 12. The processing unit 11 also controls a packet routing sub-system 13, which is coupled as shown to the packet module controller 1. This includes firmware-controlled hardware.

Thus the elements 3, 6, 2, 8, 9, 10 form the normal "telephone" switching network layer, the elements 4, 7, 5, 11, 12 form a control network layer, and the elements 1, 13 form a packet switching layer. This, it will be noted, uses 2.048 Mbits/sec transmission but is not TDM as each packet carries information related to the routing of that packet. Note that the control network layer exercises its influence on the other two layers, elements such as the line controller 4 acting in effect as interfaces. The rectangular regions at the left of the elements 1 and 5 are the central access to and from those elements. Note that the module controller 5 has access as shown to a wider band switch layer (not shown), and that the block 1 3 has access to interfaces (not shown) to a packet switched network (PSN).

As will be seen from the drawing each line controller such as 4 or 7 can send/receive messages via the centralised access for the packet module controller 1. Hence packets of intelligence arriving at a line controller and whose address field shows that they need the services of the controller 1 are routed thereto. Thus each line controller needs at least two user access ports, one to the controller 5 and one to the controller 1.

The controller 1 also has a user access port on each level for communication with the ISDN control structure, via the controller 5. Thus all packets are switched via the packet layer 1-13, so that the controller 1 merely serves to handle packets routed between line controllers and the packet layer.

Much if not all of the "software" for the control of the set up/release of the packet calls is in the PU 11, and this interworks with peripheral microprocessors of the packet layer via the input/output units of the PU. This processor PU contains the packet layer software or firmware used to control the "transport" of packets, as determined by the packet routing software of the control layer during call set up.

Since normal telephony numbering is used in a fully integrated ISDN, the packet control software in the processing unit 11 has access to translation tables for directory number (DN) to equipment number (EN) translation where a local exchange has a local packet routing facility.

The node shown in the accompanying drawing includes both a speech layer and a packet layer. In many cases the packet switching capacity needed is less than the speech capacity, and in such case some of the nodes, especially the ones which are local exchanges, will not have a packet layer. In addition some of the intermediate nodes may be without the packet facility. Indeed, when there is only a small demand for packet switching, it may be handled over a small number of dedicated routes. Naturally this situation will change as the demand for the non-speech facilities increases.

One use of one of the layers of a multi-layer network is to set up a virtual circuit through one of the layers, e.g. one normality used for packet switching while a circuit-switched call is being set up. Such a virtual circuit is set up in parallel with the circuit-switched path. Such an end-to-end virtual circuit call provides the end users, i.e. the interconnected subscribers, with a means whereby they can signal end-to-end. This protects the control layer against excessive demands which could in some cases arise if all of the end-to-end signalling is done via the control layer.

Claims (7)

1. An automatic telecommunication system, which includes a number of networks arranged functionally in accordance with a multi-layer architecture, wherein the networks include a first digital switching network via which calls are set up between subscribers for telephone or circuit switched data service, a control network having access to the first switching network for the control of the establishment of calls via that switching network, and at least one further digital switching network via which calls may be set up for a different form of traffic such as wideband switched data, wherein the control network also has access to the or each said further switching network for controlling the establishment of calls through such network or networks, so that the same control network is effective for call setting in all of said switching networks, and wherein for some at least of the subscribers served the same call can use one of more of said switching networks as and when required by the subscribers involved in the call.

2. An automatic telecommunication system, which includes a number of networks arranged functionally in accordance with a multi-layer architecture, wherein the networks include a first digital network which interconnects a number of switching nodes of the system and via which calls are set up between subscribers for telephone or circuit switched data service, a control network having access to the first switching network for the control of the establishment of calls via that switching network, which control network includes processing means at some at least of said nodes, and at least one further switching network via which calls may be set up for a different form of digital traffic such as wideband switched data, said further switching network interconnecting some at least of the nodes of the system, wherein the control network has access, at each said node which is connected to the or each said further switching network, to the or each switching network for controlling the establishment of calls through such network or networks, so that the same control network is effective for the control of call setting in all of said switching networks, and wherein for some at least of the subscribers served the same call can use one or more of said switching networks as and when required during a call by the subscribers involved in that call.

3. A system as claimed in claim 1 or 2, wherein the layer which conveys the traffic does so in time division multiplex PCM manner, and wherein the other layers include at least one which handles its traffic digitally'but in non-TDM, e.g. packet switching, manner.

4. A system as claimed in claim 1, 2 or 3, wherein the portions of the control layer at different nodes of the system are interconnected by paths independent from those used for the telecommunications traffic, which independent paths are used for inter-node signalling.

5. A system as claimed in claim 1, 2, 3 or 4, wherein during the establishment of a call via the first switching network a virtual circuit is set up between the subscribers involved in that call via a said further switching layer, which virtual circuit is used for end-to-end signalling.

6. A system as claimed in claim 5, wherein the virtual circuit is only in existence during the call establishment.

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