GB2138651A

GB2138651A - Local Area Networks Comprised of Interconnected Sub Networks

Info

Publication number: GB2138651A
Application number: GB08310895A
Authority: GB
Inventors: Robert Ian Swindle; Ronald Frank Rous
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1983-04-21
Filing date: 1983-04-21
Publication date: 1984-10-24
Also published as: GB8310895D0; GB2138651B

Abstract

A telecommunications system of the LAN type uses closed loops (e.g. Subset 1) each of which has a number of nodes for subscribers and facilities circuits, communication being by digital messages. Each such loop can be a system such as that of our Application No. 8235157 (R. F. Rous 2). The loops are interconnected by interconnection units (I1-2, I1-3, I2-3) each of which provides both way communication between its two loops. Each interconnection unit includes two stores, one per direction of transmission, and a controller which monitors each message which its unit receives. If the message is for a difficult loop it goes into one of the stores from which it is released to the other loop when traffic permits. Thus the loops are treated traffic-wise as if they are one big loop instead of several interconnected loops. Note that a message can pass via two or more loops to each its destination. <IMAGE>

Description

SPECIFICATION Local Area Networks Comprised of Interconnected Sub Networks This invention relates to a local area network (LAN), which is a telecommunications system serving a relatively small area. Such a system often uses a closed-loop arrangement for the interconnection of the nodes, each of which acts as an interface with the system. One example of such a system is described in our Application No.

8235157 (R. F. Rous 2).

The number of attachments or nodes (user terminal, resource units (facilities, outlets to other networks, etc.) on a LAN ring, or bus, is often limited by the constraints imposed on performance because of increased delay or attenuation due to equipment at the point of connection for the attachment. Equally, the equipment can contribute to the failure rate of the network so that the permitted mean time between failures falls to an unacceptable level.

A solution to the problem is to arrange the LAN as a number of interconnected sub-networks each a ring or bus, and each with its own group of attachments. Communications between attachments on different rings or buses then uses means which recognise whether a message from one sub-network is destined for that sub-network or for another of the sub-networks. In the latter case the message is routed after reference to a list giving the identity of the sub-network corresponding to the address of the wanted attachment.

The disadvantage of such an arrangement is that additional control and translation equipment is introduced in each sub-network, and that each time an attachment is moved from a node on one sub-network to a node on another sub-network, the new location must be registered at each subnetwork. Thus the freedom of movement which a single network conferred on the user terminal is now lost.

An object of this invention is to provide an arrangement which minimises or overcomes this disadvantage, and allows a freedom of movement within a LAN comprising a number of subnetworks.

According to the invention, there is provided an automatic telecommunication switching system of the local area network type, which includes a plurality of sub-networks each of which serves a number of system nodes, the nodes including nodes for subscriber's served by the system, and a plurality of interconnection units each of which interconnects two of the sub-networks, in which each said interconnection unit includes storage means for each direction of transmissions between the two sub-networks, and a controller, in which the controller at a said interconnection unit monitors each message reaching that unit and determines from its destination information where that message should go, and in which if as a result of said monitoring the controller decides that the message should pass from one subnetwork to the other it is placed in said storage means from which it is sent to the other of the sub-networks interconnected by that unit, so that the sub-networks are used in a manner similar to a single network serving ali of said nodes.

An embodiment of the invention will now be described with reference to the accompanying drawing, in which Fig. 1 is a highly schematic representation of a system embodying the invention, while Fig. 2 shows schematically one of the interconnection units of Fig. 1.

In Figure 1, three sub-networks are shown, although the principle covers arrangements of two or more sub-networks serves a number of nodes (not shown), and each such sub-network is a system of the type described in the abovementioned application. Each pair of sub-networks is associated with an interconnection unit 1 which is responsible for the flow of messages in both directions. Thus unit 1,-2 handles the flow of messages from sub-network 1 to sub-network 2 and vice versa.

Figure 2 shows an interconnection unit attached to two sub-networks A and B by transmitter-receiver elements TXA/RXA and TXB/RXB. The receivers are responsible for reception of all messages from the associated rings. The transmitters are responsible for the transmission of messages from one sub-network to another, and may also be responsible for onward transmission of messages within a subnetwork. In the latter case, however, the possibility of simple "transparency" within the TX/RX element for onward transmission is not precluded. Each transmitter/receiver is connected to an inlet and an outlet of a pair of storage elements SAB and SBA via an interface unit 1 under the control of a controller C.Received messages for interconnection are normally permitted by the controller to cross the unit's interface 1 and to enter a score such as SAB and remain there until the controller has ascertained that transmission is permissable to the other subnetwork.

The only other constraint on the flow of messages is that the controller arranges for messages which cross from one sub-network to another to be labelled, and prevents further crossings. Thus a complete and unnecessary circulation of a message around the ring of subnetworks and back to the source sub-network is avoided.

Hence all message traffic flows in all of the sub-networks so that the total traffic capacity of the local area network is no greater than the capacity of one sub-network. The constraints due to an excessive number of attachments on one ring or bus are, however, removed. Messages can now be sent from any attachment to any other attachment simply by addressing the message to the wanted attachment in a manner independent of the sub-network to which the attachment is connected. The address of the attachment is simply a unique identity which can be recognised by the attachment, and which is not changed if the attachment is moved. In some areas where there are more than three rings, a message may reach its destination after having passed through two or more interconnection units.

The attachments or nodes include, as in the above-mentioned application, subscriber's nodes and nodes for resource or facilities circuits. They may also include nodes for operator or maintenance men, and one or more nodes which act as interfaces to a public switched network, or a telephone exchange which may be a PABX.

Claims

1. An automatic telecommunication switching system of the local area network type, which includes a plurality of sub-networks each of which serves a number of system nodes, the nodes including nodes for subscriber's served by the system, and a plurality of interconnectiqn units each of which interconnects two of the subnetworks, in which each said interconnection unit includes storage means for each direction of transmissions between the two sub-networks, and a controller, in which the controller at a said interconnection unit monitors each message reaching that unit and determines from its destination information where that message should go, and in which if as a result of said monitoring the controller decides that the message should pass from one sub-network to the other it is placed in said storage means from which it is sent to the other of the sub-networks interconnected by that unit, so that the subnetworks are used in a manner similar to a single network serving all of said nodes.

2. An automatic telecommunications switching system of the local area network type, which includes a plurality of sub-networks each consisting of a closed loop serving a number of nodes, the nodes including nodes for subscribers served by the system, transmission over the loops of the system being digital, and a plurality of interconnection units each of which interconnects two of the sub-networks, in which each said interconnection unit includes storage means for each direction of transmission between the two sub-networks, and a controller, in which the controller at a said interconnection unit monitors each message which reaches that unit and determines from the destination information where that message should go, and in which if as a result of said monitoring the controller decides that the message should pass from one subnetwork to the other it is placed in said storage means from which it is sent to the other of the sub-networks interconnected by that unit, so that the sub-networks are used in a manner similar to a single closed-loop sub-network serving all of said nodes.

3. An automatic telecommunications switching system, substantially as described with reference to the accompanying drawing.

New Claims or Amendments to Claims filed on 28 Now 1983.

New or Amended Claims:

4. An automatic telecommunication switching system of the local area network type, which includes a plurality of sub-networks each of which serves a number of system nodes, which nodes include nodes for subscribers served by the system, and interconnection units each of which interconnects two of the sub-networks, each said interconnection unit including a controller and storage means for each direction of message transmission between the two nodes interconnected by that interconnection unit, in which each message to be sent has a message header including the address of the node for which that message is destined but no indication as to the sub-network for which the message is destined, in which the controller at a said interconnection unit monitors each message reaching that unit and determines from its address where that message should go, and in which if as a result of said monitoring the controller for that unit decides that the message should pass from one sub-network to-the other that message is placed in that unit's storage means from which it is sent to the other of the sub-networks interconnected by that unit, so that the sub-networks are used in a manner similar to a single network serving all of said nodes.

. An automatic telecommunication switching system of the local area network type which includes a plurality of sub-networks each consisting of a closed loop which serves a number of system nodes, which nodes include nodes for subscribers served by the system, transmission over the loops of the system being digital and interconnection units each of which interconnects two of the sub-networks, each said interconnection unit including a controller and storage means for each direction of message transmission between the two nodes interconnected by that interconnection unit, in which each message to be sent has a message header including the address of the node for which that message is destined but no indication as to the sub-network for which the message is destined, in which the controller at a said interconnection unit monitors each message reaching that unit and determines from its address where that message should go, and in which if as a result of said monitoring the controller for that unit decides that the message should pass from one sub-network to the other that message is placed in that unit's storage means from which it is sent to the other of the sub-networks interconnected by that unit, so that the sub-networks are used in a manner similar to a single network serving all of said nodes.