FR2768579A1 - Telecommunication connection system for local area network - Google Patents

Abstract

The use of multiple interconnections between sub-networks reduces dependency on individual components of system.- DETAILED DESCRIPTION - The network (RLb) comprises several sub-network in a ring (ST1 - ST3). Each ring sub-network (ST1) comprises connection modules (M1b, M3b, M6b) connected together in a manner to form at least one ring (Al1 - AlN1). The rings of each sub-network (ST1) traverse directly at least one connection module of other sub-networks (ST2, ST3). Each connection module of the network is connected to two other connection modules, not necessarily of the same sub-network, by bundles of optical fibers (NP1 - NP8). Furthermore each connection module is divided into several sub-modules connected together by internal module connectors, such that each sub-module may be replaced independently of the other sub-modules

Description

 The present invention relates generally to telecommunications networks, and more particularly to local telecommunications networks.

 Local telecommunication networks are known in the prior art.

 Local networks called "star hierarchical" include concentrator boxes (called "hubs" in English) to which stations or servers are connected, and buses formed by metallic cables or optical fibers to connect the concentrator boxes together. Buses typically have a bit rate of 10 to 100 Mbit / s (or even 155 Mbit / s with ATM technology). In these local networks, which are for example of the Ethemet (registered trademark) type, the useful bandwidth is shared between the different users.

 In order to remedy this drawback and avoid that the stations all use the same bit rate resource, other local networks, also hierarchical in star form, use switches. However, to significantly increase throughput, it is necessary to increase the complexity of the network structure in terms of routing information.

 In addition, any failure occurring in one of the above networks, such as the breaking of a physical link or the failure of one of the elements of the network, results in the loss of part of the network. One solution to reduce the sensitivity of the network to failures is to use redundant equipment to increase the number of possible paths for the routing of information. This solution also increases the complexity of the network structure.

 In addition, when operations must be carried out on the network to, for example, connect new stations for which no connection socket was initially planned, or to replace hubs with switches in order to increase the speed, the operation of the network is generally very disturbed.

 In other local networks of the prior art, called "double ring networks", stations are linked together in series by unidirectional links so as to form primary and secondary rings. In normal operation, all communications exchanged between stations are routed through the primary ring. The secondary ring is only used when a fault has been detected in the network. The primary and secondary rings are then brought into contact at points in the network located on either side of the fault in order to restore the continuity of the network. This type of double ring network is limited in speed in that a single ring transmits communications in normal operation.

 In the prior art, some local networks include interconnected subnets. Terminals connected to a first subnet can then exchange data with terminals connected to a second subnet. These subnetworks are arranged according to structures which are generally physically separated.

 Also, in the case of a building shared by several companies, each company occupying its own room in the building, it is necessary to wait for the final internal configuration of the building, that is to say the allocation of different rooms companies, before being able to install independent local networks for them. Each of these networks then comprises its own switches and its own cables which are physically completely independent of the switches and cables used by other local networks in the building, except at possible interconnection points between these networks.

 The present invention aims to provide a simple general structure of a network divided into functionally independent or interconnected subnets, in which the configuration of the subnets can be easily modified or supplemented once the basic elements of the network, such as cables and the overall structure of the connection boxes installed.

 To this end, a telecommunications network comprising several ring subnets, each ring subnetwork comprising connection modules linked together so as to form at least one ring, is characterized in that it has a general ring configuration and in that said at least one ring of each sub-network passes directly through at least one connection module of another sub-network.

 Typically, each network connection module is connected to two other connection modules, not necessarily from the same sub-network, by layers of optical fibers.

 Also, each connection module is divided into several submodules connected to each other by connectors internal to the module so that each submodule can be replaced independently of the other submodules, whether energized or not.

 Thus, it is possible according to the invention to install beforehand the overall structure of the network in a building, by making each room of the building pass through a layer of optical fibers and by equipping each room with one or more connection modules, then adapt the network to a desired configuration by opening the connection modules and inserting appropriate sub-modules.

 Means can then be provided, in one of the connection modules, for interconnecting at least two subnetworks.

 Also, a means can be provided, in one of the connection modules, for interconnecting a subnetwork with another telecommunications network.

 Preferably, at least one of the subnetworks comprises at least two rings transmitting signals in opposite directions, so that in the event of a failure in the subnetwork, the continuity of the subnetwork can be restored.

 Also, at least one of the subnetworks may comprise means for switching data to at least one additional backup ring of the subnetwork in the event of rupture of the ring or rings of the subnetwork.

 The present invention further aims to provide a local network at high speed, and in particular at a much higher bit rate than the ring networks of the prior art.

 To this end, at least one of the subnets comprises several rings, and each connection module of this subnetwork comprises means for selecting one of said several rings in response to reception by said data connection module. delivered by a first terminal connected to said connection module and intended for a second terminal connected to another connection module of the subnetwork, and means for transmitting said data on the selected ring to the second terminal.

 According to one aspect of the invention, said selected ring is the ring of the sub-network which is the least congested.

 According to another aspect of the invention, said selected ring is the one for which the path to be traveled by said data from the first terminal to the second terminal is the shortest.

 Typically, each network connection module comprises a transmission-reception sub-module including transmission means and reception means for respectively transmitting and receiving signals on rings of the corresponding sub-network, a sub-module of switching to switch data received from at least one terminal connected to the connection module to the transmission means and to switch data received from the rings of the corresponding sub-network by the transmission-reception sub-module to said at least one terminal or to said rings as a function of addresses contained in this data, and an interface submodule providing the interface between said at least one terminal and the switching submodule.

 Preferably, the transmission means and the reception means respectively comprise lasers and photodetectors operating at a wavelength between 750nm and 1300nm. Lasers and photodetectors can be of the type conventionally used in optical disc drives and operating at a wavelength of around 850nm.

In addition, in order to minimize the number of connection modules per room in the building, at least one of said connection modules can comprise several connectors to which several respective terminals can be connected to connect these to the network. The respective terminals may be a computer terminal, a telephone terminal, or a building management terminal managing for example a sensor alarm system in the building, or a multimedia terminal conforming to the P 1394 standard established by the IEEE ( Institute of Electrical and Electronic Engineers). In the case where a telephone terminal is connected to the connection module, the network according to the invention comprises a private automatic branch exchange of the PABX type (Private
Automatic Branch Exchange) connected to the public switched telephone network.

 The data transmitted through the network according to the invention can be multimedia type data, combining images, texts and the volx.

Other characteristics and advantages of the invention will emerge from the following description of particular embodiments, given by way of examples with reference to the appended drawings, in which
- Figure 1 is a block diagram of a local telecommunications network in double ring according to the prior art;
- Figure 2 is a block diagram of a local ring telecommunications network used by the present invention;
- Figure 3 is a block diagram of a local telecommunications network according to the invention, according to a first embodiment;
- Figure 4 is a diagram of a sheet of optical fibers used in the network of Figure 3
- Figure 5 is a block diagram of a local telecommunications network according to the invention, according to a second embodiment
- Figure 6 is a block diagram of a connection module used in particular in the network of Figure 3, according to a first embodiment;
- Figure 7 is a block diagram of a connection module used in particular in the network of Figure 3, according to a second embodiment; and
- Figure 8 is a schematic block diagram of a connection module used in particular in the network of Figure 3, according to a third embodiment.

 FIG. 1 shows a local telecommunication network in RL rings according to the prior art. The local area network RL comprises connection modules Ml to M6 interconnected in series according to a double ring structure by two sets of physical links, or transmission lines, unidirectional LP and LS. A ring is defined as a closed path through connection modules, on which signals can flow. The links LP constitute with the connection modules M1 to M6 a ring called "primary" AP, the links LS constitute with the connection modules M1 and M6 a ring called "secondary" AS.

 Telecommunication terminals T1 to T6 are respectively connected to the connection modules M1 to M6 and can thus exchange data through the RL network. The terminals T1 to T6 are for example stations or computers of the PC (Personal Computer) type.

 The connection modules M1 to M6 are designed so that the direction of propagation of the signals circulating on the primary ring AP is opposite to the direction of propagation of the signals circulating on the secondary ring AS.

The LP and LS links are typically formed by pairs of metal wires, coaxial cables or optical fibers. In the latter case, the local area network RL is for example a network conforming to the FDDI standard (Fiber
Distributed Data Interface).

According to the RL network of the prior art, in normal operation, that is to say in the absence of failure, all communications between the terminals T1 to T6 are transmitted on the primary ring AP only. The secondary ring
AS is a backup ring which is used only when a fault, such as a line break or a failure of one of the connection modules, occurs in the network and causes the primary ring AP to open.

 Thus, when for example the double ring AP, AS is broken between the modules M1 and M6 as shown by the reference CP in FIG. 1, which causes the network to stop working, the terminals A and B of the connection module Ml located on the side of the M6 connection module are brought into contact, as are the terminals C and D of the M6 connection module located on the side of the M 1 module. This loopback upstream and downstream of the CP fault enables continuity to be restored of the network and to transmit communications again between the terminals T1 to T6.

 An interconnection of the RL network with another local network of the same type (not shown) can also be carried out in a known manner.

 FIG. 2 shows a local telecommunications network RLa, the type of operation of which is used by the present invention. The local network RLa comprises connection modules M la to M6a for connecting terminals T la to T6a to the network. The connection modules Mla to M6a are connected together in series according to a ring structure by an integer N of sets of physical links Li to LN. The links L1 to LN are identical unidirectional transmission lines, for example with optical fiber, and constitute with the modules Mla to M6a N concentric rings, designated by A1 to AN. The integer N is greater than or equal to 2.

 In the embodiment shown in Figure 2, a single terminal is connected to each connection module. However, several terminals can be associated with a given connection module, as will be explained later with reference to FIG. 6.

 Unlike the network RL in FIG. 1, the local network RLa uses, in normal operation, several rings to ensure the exchange of data between the terminals T 1a to T 6a. The signals circulate in opposite directions on at least two of the N rings, for example the rings A1 and A2, in order to authorize a loopback comparable to that described with reference to FIG. 1 in the event of a failure in the network.

To transmit data from a first terminal, such as the terminal Tla, to a second terminal, such as the terminal T59, one of the N rings A1 to
AN is previously selected according to a predetermined criterion. For example, the selected ring is the one on which the congestion is the least at the time of the reception by the connection module Mla of the data delivered by the terminal Tla. Said data are then routed on the selected ring from the connection module Mla to the connection module M5a, which transmits them to the terminal T5a.

 As a variant, in particular in the case where the integer N is equal to 2, the two rings Al and A2 transmitting signals in opposite directions indicated respectively by the arrows Fl and F2, The selected ring is the one on which the path to browse through the data from the first terminal to the second terminal is the shortest. In the example of the network RLa in FIG. 2 and of the terminals Tla and T5a, the selected ring is the ring A2 since the data delivered by the terminal T la have to pass through only three connection modules, namely the modules Mla, M6a and M5a, to reach the destination terminal T5a.

 The data exchanged in the RLa network is multimedia type data, and is thus representative of texts, voice signals and / or images. The data exchange protocol used in the RLa network is for example a protocol of the asynchronous transfer mode ATM (Asynchronous Transfer Mode) type. The data is then presented in the form of cells.

The total bit rate of transmission through the network RLa, that is to say the total bit rate available for communications between the terminals T 1a to T 6a, is equal to N times the bit rate on each of the rings A1 to AN, and therefore at N times the bit rate through the network RL of figure 1. Thus, within the framework of a network
ATM, the bit rate through the RLa network can reach approximately N x 155 Mbit / s.

As already specified, the local network RLa used in the invention is able to restore its continuity when one of the modules Mla to M6a fails or the transmission lines connecting two adjacent connection modules are broken (cf. mark CPa), by bringing the two rings Al and A2 into contact at respective points Aa, Ba and at respective points Ca, Da located on either side of the fault. During the failure, communications between the terminals T la to T6a are routed only on the new ring formed by the parts of the rings
Al and A2 located respectively between points Aa and Ca and between points Ba and
Da and opposed to the CPa failure. The bit rate through the RLa network during the failure is reduced compared to normal operation, and is equal to the bit rate of the ring A1 or A2. Once the network is repaired, i.e. normal operation restored, the total bit rate again becomes N times that of the ring A1 or A2. This ease of cutting off the network can also be implemented to insert a new module without disturbing the operation of the other modules and therefore of the various connected terminals. Indeed, the opening of the network will be identified by the adjacent modules as a failure and consequently lead to an automatic loopback.

Figure 3 shows a local telecommunication network RLb according to the invention. The RLb network has a general ring configuration, and more specifically concentric rings, and includes connection modules
Mlb to M8b to which respective terminals Tlb to T8b are connected. In the embodiment illustrated in Figure 3, a single terminal is connected to each connection module. However, several terminals can be associated with a given connection module, as will be explained later with reference to FIG. 6.

 The modules Mlb to M8b are interconnected according to several independent ring structures, also called subnets. Only three of these subnetworks, designated by ST1, ST2 and ST3, are shown in FIG. 3, for reasons of clarity.

The first STl sub-network includes the Mlb connection modules,
M3b and M6b, and an integer N1 of unidirectional link sets
Ll1 to L1N1 connecting these modules together in series so as to constitute Nl rings All to AINE. The second sub-network ST2 comprises the M2b modules,
M5b and M7b, and an integer N2 of unidirectional link sets
L21 to L2N2 connecting these modules together in series so as to constitute N2 rings A21 to A2N2. The third sub-network ST3 comprises the connection modules M4b and M8b, and an integer number N3 of sets of unidirectional links L31 to L3N3 connecting these modules together so as to constitute N3 rings A31 to A3N3. The integers N1, N2 and N3 are greater than or equal to 1. According to a typical embodiment of the present invention, these integers are equal to 2.

As shown in dotted lines in FIG. 3, the rings of a given sub-network pass directly through the connection modules of the other sub-networks. Thus, the data circulating on the links Ll I to LINI are analyzed and switched by the connection modules Mlb, M3b and M6b of the first sub-network STI, but directly pass through the connection modules M2b, M5b and M7b of the second sub-network ST2 and the connection modules M4b and M8b of the third subnet ST3. Similarly, the data circulating on the links L21 to L2N2 of the second subnet ST2 are analyzed and switched by the connection modules M2b, M5b and M7b of the second subnet ST2, but pass directly through the connection modules Mlb, M3b and M6b of the first subnet ST2 and the connection modules M4a and M8a of the third subnet
ST3. Also, the data circulating on the links L31 to L3N2 of the third subnet ST3 are analyzed and switched by the connection modules
M4b and M8b of the third subnet ST3, but pass directly through the connection modules Mlb, M3b and M6b of the first subnet ST1 and the connection modules M2b, M5b and M7b of the second subnet ST2.

 In practice, the STI to ST3 subnetworks are independent. For example, the RLb network according to the invention is installed in a building which is shared by different companies, each company occupying part of the building. The subnetworks of the RLb network are then allocated respectively to said companies (three in number in the example corresponding to the embodiment in FIG. 3).

 The physical links, or transmission lines, Ll1 to L1NI, L21 to L2N2, and L31 to L3N3 are typically optical fibers. The physical links connecting two adjacent connection modules given Mib and Mi + lb of the RLb network, where i is an integer between 1 and 7, are in the form of a sheet of optical fibers NPi. The NPi sheet is illustrated in more detail in Figure 4.

 Thus, the STI to ST3 subnetworks of the RLa network are "functionally" independent, but arranged according to a common structure composed of connection modules Mlb to M8b and layers of optical fibers NP1 to NP8.

 According to a variant of the RLb network according to the invention, one of the connection modules Mlb to M8b, for example the module M3b, comprises a switching means, shown diagrammatically in dotted lines in FIG. 3, for interconnecting the sub -networks ST1 to ST3, that is to say to switch data between these subnets, or to interconnect only two of these subnets. The switching means is described in more detail in the following description.

 Preferably, each sub-network STI at ST3 operates in the same way as the network RLa described previously with reference to FIG. 2, and routes multimedia type data according to the ATM protocol for example.

Thus, to transmit data through the subnet ST1 from the terminal Tlb connected to the connection module Mlb to the terminal T6b connected to the connection module M6b, one of the rings Ai1 to AINI is selected according to the predetermined criterion d 'congestion of the rings or shortest path as defined above. On the selected ring, the data signal produced by the terminal Tlb passes through connection modules of the subnet ST1, for example the modules Mlb, M3b and M6b, where it is regenerated and analyzed, and passes directly through connection modules other subnets, namely in this case the M2b, M4b and M5b modules.

 Also, each sub-network ST1 to ST3 comprises at least two rings transmitting signals in opposite directions. Thus, in the event of a failure on one of the subnetworks, the same operations as in the RLa network are implemented to restore the continuity of the subnetwork.

However, according to other variants, at least one of the subnetworks ST1 to
ST3 comprises a single ring, or functions in the same way as the double-ring network RL in FIG. 1.

FIG. 5 shows a local telecommunication network RLc according to another exemplary embodiment of the invention. The RLc network comprises connection modules Mlc to M6c linked together so as to form two double-ring subnetworks of the type of the subnetworks ST1 to ST3 in FIG. 3. The network
RLc further comprises a switching means, shown diagrammatically in dotted lines in the module M5c, for interconnecting the network RLc with another network in rings RLT including connection modules M7c and M8c.

 FIG. 6 shows in detail a connection module 10 of the type of the modules Mla to M6a of the network RLa of FIG. 2, of the modules Mlb to M8b of the network RLb of FIG. 3, or of the modules Mlc to M6c of the network RLc of the figure 5.

The connection module 10 is coupled via connectors 101, 102 respectively to two links LI1, LI2 of a first ring
AN1 and respectively to two links LI3, LI4 of a second ring AN2. The links LI1 to LI4 are unidirectional fiber optic transmission lines. The connection module 10 further comprises other connectors 103 to 107 to which respective terminals TR1 to TR5 are connected, a transmit-receive submodule 108, a switching submodule 109 and a user interface submodule 110. The three sub-modules 108, 109 and 110 are supplied by a power supply unit 111 and are connected to each other by internal connectors 112, 113 and! 14 of the flat connector type. The use of internal connectors 112, 113 and 114 allows the possible replacement of a submodule 108, 109 or 110 in the connection module 10.

The role of the transceiver sub-module 108 is to transmit to the connection modules adjacent to the module 10 in the network digital data signals supplied by the switching sub-module 109, and to receive and regenerate signals digital data transmitted by LI2 and LI3 links. For this purpose, the transmission-reception sub-module 108 includes transmission means 115, 116, reception means 117, 118, and modems 119, 120. The transmission 115 and reception 117 means are respectively connected to the links LI1 and LI3 through the connector 101. The transmission 116 and reception 118 means are connected respectively to the links LI4 and
LI2 through the connector 102. The modem 119 is connected to the transmission 115 and reception 117 means, and to the switching submodule 109 through the internal connector 112. The modem 120 is connected to the transmission means 116 and 118, and to the switching submodule 109 through the internal connector 113.

 The transmission means 115, 116 and reception 117, 118 are laser diodes and photodetectors respectively, operating at a wavelength of around 850 nm. Thus, the laser diodes and the photodetectors can be of the type conventionally used in optical disc players.

 The switching sub-module 109 switches to the transmission means 115, 116 of digital data supplied by the user interface sub-module 110 or the transmission-reception sub-module 108. The switching sub-module 109 essentially includes a switching circuit 121 and a control circuit 122. The switching circuit 121 is connected to the modems 119, 120 respectively through the connectors 112, 113, and to the user interface submodule 110 through the connector 114 The control circuit 122 controls the switching circuit 121 and also has a role of administration of the network, in particular to manage failures. The circuit 122 is preferably a microprocessor of the CPU (Central Processing Unit) type.

 The user interface sub-module 110 provides the interface between the circuits using the network protocol and the terminals TR1 to TR5 each using their own protocol. The user interface sub-module 110 includes a multiplexer / demultiplexer 123 and protocol conversion circuits 124-1 to 124-5 associated respectively with the terminals TR1 to TR5. The terminals TR1 to TR5 can be of different types. For example, the terminal TR1 is a computer terminal, the terminal TR2 a telephone terminal, the terminal TR3 a building management terminal managing a sensor system such as an alarm system, etc.

In transmission, when the user
TR3 and converted by the associated conversion circuits 124-2, 124-3. The multiplexed data DN3 at the output of the multiplexer / demultiplexer 123 are transmitted through the connector 114 to an input port el of the switching circuit 121. The circuit 121 selects a ring from the rings AN 1 and
AN2 according to one of the predetermined criteria for congestion of rings or shortest path defined above, for the data DN2 originating from the terminal TR1 and contained in the multiplexed data DN3, as well as for the data DN2 ', DN2 "originating from the other terminals TR2, TR3. The switching circuit 121 directs the received DN2 data contained in the multiplexed data DN3 to the transmission means 115, 116 corresponding to the ring AN l, AN2 selected for the data DN2, through the connector 112, 113 and the modem 119, 120 and from a corresponding output port sl, s2 The laser diode 115, 116 transmits a digital optical signal SE1, SE2 in response to the reception of the data signal DN2 modulated by the modem 119, 120. The same operations as above are implemented for the data DN2 'and DN2 "also contained in the data DN3 and coming from the other terminals TR2,
TR3.

On reception, the photodetectors 117, 118 convert digital optical signals SR2, SR1, received from the links LI3, LI1 from the rings AN2,
ANI respectively, in electrical signals Sel2, Sell. The electrical signals Sel2, Sell are demodulated and reshaped by the modems 119 and 120 and transmitted through the connectors 112, 113 to the input ports e2 and e3 of the switching circuit 121. The switching circuit 121 reads the addresses of recipient terminal in each cell of signals Se12, Sell. The cells from each link L12, LI3 and for which the recipient address designates a terminal other than the terminals TRI to TR5 connected to the module 10 are retransmitted from the output access sl, s2 to the link LI1, LI4 respectively through the connector 112, 113, the modem 119, 120 and the transmission means 115, 116. The other cells, for which the recipient address designates one of the terminals TRI to TR5, are directed from an output access s3 to the multiplexer / demultiplexer 123 through the connector 114. The multiplexer / demultiplexer 123 demultiplexes the cells received and routes them to the terminals TRI to TR5 according to the addresses of the destination terminal included therein. The conversion circuits 124-1 to 124-5 convert the data supplied by the circuit 123 according to the protocol or protocols respectively associated with the destination terminals.

 In the case where the connection module 10 is of the type of one of the connection modules of the networks RLb (FIG. 3) and RLc (FIG. 5), the transmitting-receiving sub-module 108 further comprises an integer M greater or equal to 1 of internal links 125-1 to 125-M directly connecting connectors 101 and 102. The internal links 125-1 to 125-M ensure the continuity of M rings AN-I to AN-M belonging to sub- networks other than that of the connection module 10, so that the signals circulating on the rings AN-I to AN-M pass directly through the module 10.

 According to a variant of the module 10, some of the terminals TRi and TR5 are capable of producing and receiving data according to the network protocol.

Their associated conversion circuits 124-1 to 124-5 are then deleted.

 According to another variant, the links Lîl to LI4 of the rings AN1 and AN2 are formed by pairs of metallic wires or coaxial cables. The transmission means 115, 116 and reception 117, 118 are then amplifiers.

 The structure of the connection module 10, in the example illustrated in FIG. 6, is intended to be integrated into a network or sub-network with two rings AIs AN2. This structure can easily be generalized to a larger number of rings, not necessarily even. Each of the rings of the network or subnetwork is then associated with a transmission means, a reception means and a modem in the transmission-reception sub-module, and input and output ports in the switching circuit. .

 Figure 7 shows a connection module 20 according to the invention, according to a second embodiment. The connection module 20 is coupled on two opposite sides to connections of four rings ANNI and ANN4 via connectors 201 and 202, and comprises connectors 203 to 207 to which terminals (not shown) are connected. The module 20 further comprises a transmit-receive submodule 208, a switching submodule 209, and a user interface submodule 210. The three submodules 208, 209 and 210 are all powered by a power supply 211 and are connected to each other by internal connectors 212 to 216.

 The transmission-reception sub-module 208 includes four arrangements of transmission-reception elements identical to the arrangements 115-117-119 and 116118-120 of FIG. 6. Each arrangement consists of a transmission means 217 to 220, reception means 221 to 224, and a modem 225 to 228. The first arrangement 217-221-225 and the second arrangement 218-222-226 are respectively coupled to two pairs of links of the rings ANN 1 to ANN4 by the connector 201. The third arrangement 219-223-227 and the fourth arrangement 220-224-228 are respectively coupled to two other pairs of connections of the rings ANNI to ANN4 by the connector 202.

 The switching sub-module 209 comprises a switching circuit 229 controlled by a control circuit 230. Four input ports el 'to e4' of the switching circuit 229 are respectively connected to the reception means 221 to 224 through the modems 225 to 228 and internal connectors 212 to 215.

Four output ports s1 'to s4' of the switching circuit 229 are respectively connected to the transmission means 217 to 220 through the modems 225 to 228 and the internal connectors 212 to 215. A fifth output port s5 'and a fifth input access e5 'of the switching circuit 229 are connected to the user interface sub-module 210 through the connector 216.

 The user interface submodule 210 is identical to the submodule 110 of FIG. 6, and comprises a multiplexer / demultiplexer 231 and protocol conversion circuits 232-1 to 232-5.

According to a first embodiment of the connection module 20, the latter is used in a network or sub-network with four rings of the type respectively of the network RLa shown in FIG. 2 or of the sub-networks ST1 to ST3 of FIG. 3, and performs operations comparable to those of module 10 (FIG. 6). In particular, in transmission, the switching circuit 229 selects
One of the rings ANN 1 to ANN4 for transmitting data from a first terminal connected to the module to a second terminal connected to another module.

In the case of the use of the module 20 in a sub-network, internal links 232 are provided for directly connecting the connectors 201 and 202 and ensuring the continuity of rings of other sub-networks.

 According to a second embodiment of the connection module 20, the latter is used in a network or sub-networks with four rings, but in which only the first two rings are used to transmit data during normal operation, the other two rings serving emergency rings in the event of a breakdown on the first two rings. Thus, in normal operation, the connection module 20 performs the same operations as the module 10 in FIG. 6 using the first and fourth arrangements 217221-225 and 220-224-228 to transmit and receive data on the ANNI rings and ANN2 of the network. In the event of a failure on the rings ANNI, ANN2, all the signals which must initially be transmitted thereon by the connection module 20 are switched by the switching circuit 229 to the emergency rings ANN3 and ANN4 respectively through the second and third arrangements I 218-222-226 and 219-223-227.

 According to a third embodiment of the connection module 20, the latter is of the type of the module M3b of FIG. 3, that is to say the module 20 is capable of achieving the interconnection between two subnets respectively comprising the pairs of rings ANNî-ANN2 and ANN3-ANN4. Switching of data to be transmitted on one or the other of the two subnets is carried out by the switching circuit 229, as a function of the addresses of the data cells supplied by the user interface sub-module 210 to the input access e5 ′ of circuit 229 and of the addresses of the data cells received from the rings ZANNI to ANN4 by the sub-module 208.

Figure 8 schematically shows a connection module 30 according to the invention, according to a third embodiment. The module 30 notably comprises connectors 301, 302 for coupling the module to ring links ANN1 ', ANN2' of a first sub-network, connectors 303 to 307 for connecting respective terminals (not shown) to the module 30 , a transmit-receive submodule 308, a switching submodule 309, a user interface submodule 310 and a power supply unit 311. The submodules 308 and 310 are respectively of the type of the submodules 108 and 110 of FIG. 6. The connection module 30 further comprises two connectors 312 and 313 connected to the switching submodule 309 for coupling the module 30 to ring links ANN3 ', ANN4' of a second sub -network. The switching sub-module 309 ensures the interconnection between the first and second aforementioned subnets in a manner comparable to that described above with reference to FIG. 7, as well as the transmission-reception of the signals on the rings ANN3 ' and
ANN4 '.

 The present invention has been described by way of example only for a network protocol of the ATM type. However, any other protocol, such as the IP (Intemet Protocol) or IPX (registered trademarks) protocols, can be used in the present invention. The cells of the ATM protocol are then replaced by frames conforming to this other protocol.

Claims (15)

 1. Telecommunication network (RLb) comprising several ring subnets (ST1 to ST3), each ring subnetwork (si1) comprising connection modules (Mlb, M3b, M6b) interconnected so as to form at least one ring (All to A1NX), the network being characterized in that it has a general ring configuration and in that said at least one ring of each sub-network (si1) passes directly through at least one connection module d 'another subnetwork (su2, ST3).  2. Telecommunication network according to claim 1, in which each network connection module is connected to two other connection modules, not necessarily from the same sub-network, by layers of optical fibers (NP1 to NP8).  3. Telecommunication network according to claim 1 or 2, in which each connection module comprises several sub-modules (108-110) interconnected by connectors (112-114) internal to the connection module so that each of these sub-modules can be replaced independently of the other sub-modules.  4. Telecommunication network according to any one of claims 1 to 3, comprising means (229), in one (M3b) of said connection modules, for interconnecting at least two of said subnets.  5. Telecommunication network according to any one of claims 1 to 4, comprising means (229), in one (M5c) of said connection modules, for interconnecting at least one of said subnets with another network telecommunications (RLT).  6. Telecommunication network according to any one of claims 1 to 5, in which at least one of said subnets comprises at least two rings transmitting signals in opposite directions, so that in the event of failure in the sub -network, the continuity of the sub-network can be restored.  7. Telecommunication network according to any one of claims 1 to 6, in which at least one of said subnets comprises means (229) for switching data to at least one additional backup ring (ANN3, ANN4) of the sub-network in the event of said at least one ring of the sub-network breaking.  8. Telecommunication network according to any one of claims 1 to 7, in which at least one of the subnets comprises several rings, and each connection module (10) of this subnetwork comprises means (121) for selecting one of said several rings in response to reception by said connection module (10) of data (DN 1) delivered by a first terminal (TR1) connected to said connection module and intended for a second terminal connected to another sub-network connection module, and means (108) for transmitting said data on the selected ring to the second terminal.  The network of claim 8, wherein said selected ring is the least congested subnetwork ring.  10. The network of claim 8, wherein said selected ring is the ring of the subnet for which the path to be traveled by said data from the first terminal to the second terminal is the shortest.  11. Telecommunication network according to claim 3 or any one of claims 4 to 10 when they depend at least on claim 3, wherein said several sub-modules comprise a transmit-receive sub-module (108) including means for transmission (115, 116) and reception means (117, 118) for respectively transmitting and receiving signals on rings of the corresponding subnet, a switching sub-module (109) for switching data received from at at least one terminal (TR1-TR5) connected to the connection module (10) to the transmission means and for switching data received from the rings of the corresponding sub-network by the transmission-reception sub-module (108) towards said minus one terminal (TRI TR5) or to said rings as a function of addresses contained in this data, and an interface sub-module (110) providing the interface between said at least one terminal and the switching sub-module.  12. The telecommunications network as claimed in claim 11, in which the transmission means and the reception means respectively comprise lasers (115, 116) and photodetectors (117, 118).  13. Telecommunication network according to any one of claims I to 12, transmitting multimedia type data.  14. Telecommunication network according to any one of claims 1 to 13, in which at least one of said connection modules (10) comprises several connectors (103 to 107) to which several respective terminals (TR1 to TR5) can be connected. to connect them to the network.  15. The telecommunications network as claimed in claim 14, in which said respective respective terminals (TRI to TR5) comprise at least one of the following terminals: computer terminal, telephone terminal, building management terminal, and multimedia terminal.