FR2848756A1 - Ethernet network for frame transmission, has fault state in which part of primary ring is short circuited by part of secondary ring in case of fault and frame is transmitted to commutators when frame circulates in primary ring - Google Patents

Abstract

The network (100) has a normal functioning state in which useful data frame circulating in a primary ring (F1) is received and emitted by a primary receiver and emitter (Rpi, Epi). A portion short-circuits a part of the ring F1 by a part of a secondary ring (F2) when fault occurs in the ring F1, and the useful data frame is transmitted to Ethernet commutators (Ci) when they circulate in the ring F1, in a fault functioning state. The primary emitter and receiver are provided in each of multiple repeaters.

Description

ETHERNET NETWORK

  The present invention relates to an Ethernet network for the transmission of data frames.

  In known manner, an Ethernet network is a local area network 5 comprising a plurality of Ethernet switches connected by the same communication line such as an optical fiber; each of the switches receives useful data frames from equipment such as personal computers and transmits these data frames to the other switches which will transmit said data to other equipment. Each of the Ethernet switches has a plurality of ports connected to the equipment and to the other switches. Each of the switches inspects the source and destination addresses of the frames, draws up a table which allows it to know which equipment is connected to which port of the switch; this process is done by self-learning, that is to say automatically as the frames are exchanged. Thus, knowing the recipient's port, the switch will only transmit the message on the appropriate port, the other ports therefore remaining free for other transmissions that can occur simultaneously.

  One of the problems of this type of network relates to the operation of said network when a fault such as a break in the optical fiber or a fault on an optical port occurs.

  A known solution to this problem consists in using a redundant optical network of the type shown in FIG. 1. The optical network 100 comprises three Ethernet switches 111, 112 and 113. The switches 111, 112 and 113 are connected together by a primary ring 123 and by a secondary ring 124. The two rings 123 and 124 are for example optical fiber rings. The rings 123 and 124 are counter-rotating rings, that is to say that the frames have opposite directions of transmission from one another as indicated by the arrows.

  In normal operation, the frames are transmitted on the two rings except on sections 123A and 124A.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPO1 \ TEXTE DÉPOSE.doc In the event of a fault, for example a break in the section of optical fiber 123B connecting switch 113 to switch 112, a frame can no longer be sent from switch 113 to the switch 112. The section 124A then becomes active to allow the transmission of a frame 5 from switch 113 to switch 112. This frame is transmitted by switch 113 to switch 111 which itself transmits the frame to switch 112, transmission being done entirely on fiber 124.

  This process thus makes it possible to switch from normal operation to fault operation.

  However, the implementation of such a solution poses certain difficulties. Indeed, the opening of the section 124A initially inaccessible to the traffic of useful data entirely modifies the path traveled by the frames. Such a modification of the path requires a reset of all of the routing tables of the Ethernet switches. This reset results in a significant recovery time for self-learning of new routing tables.

  The present invention aims to provide an Ethernet network for the transmission of frames comprising a plurality of repeaters and making it possible both to ensure efficient passage during fault operation and not to reset the routing tables of the switches. Ethernet in the event of a switch to fault operation.

  The present invention proposes for this purpose an Ethernet network comprising a plurality of Ethernet switches and a plurality of repeaters exchanging frames of useful data coming from external equipment, each of said repeaters being associated with one of said Ethernet switches and comprising: - a transmitter primary and a secondary transmitter, a primary receiver and a secondary receiver, said plurality of repeaters being connected together by a primary ring of transmission via said primary transmitters and receivers and by a secondary ring of transmission via said transmitters and F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DÉPOSE.doc secondary receivers, the direction of transmission of the frames circulating in said primary ring being opposite to the direction of transmission of the frames circulating in said secondary ring, said network being characterized in that it comprises two states: - a first state known as normal operation lo the useful data frames circulate only on said primary ring being received and transmitted respectively by said primary receiver and said primary transmitter of each of said repeaters, a second state known as operating on fault, said network 10 comprising means for short- circuit a part of said primary ring with a part of said secondary ring in the event of a fault on said primary ring, the useful data frames being transmitted to said Ethernet switches only when they circulate on said primary ring.

  The process according to the invention making it possible to pass from normal operation to fault operation will be called in the following self-healing process.

  Thanks to the invention, on detection of a fault, the traffic is diverted to the secondary ring and this to the repeater following the fault, thereby allowing effective self-healing. In addition, the frames of useful data, that is to say the frames transmitted by a device to another device, are processed by the Ethernet switches only when they circulate on the primary ring and in no case on the ring. secondary. Thus, the routing tables of the Ethernet switches remain unchanged in self-healing mode; the self-healing process does not interfere with the self-learning of Ethernet switches.

  Advantageously, each of said repeaters comprises switching means so that said useful data frames can circulate according to three states: - a first state, known as normal operation, where the useful data frames circulate from said primary receiver to said primary transmitter, F : \ Salle \ FP000431 \ PREMDEP \ DEPOTETEXTE DEPOSE.doc - a second state where the useful data frames flow from said primary receiver to said secondary transmitter, - a third state where the useful data frames flow from said secondary receiver to said primary transmitter.

  Advantageously, said primary and secondary rings are optical rings.

  Advantageously, operation control frames, called stuffing frames, circulate permanently on said secondary ring when said network is in said normal operating state, each of said stuffing frames being transmitted by a repeater then deleted on reception. by the next repeater, said adjacent receiver.

  Advantageously, said useful data and stuffing frames transmitted on said network each comprise a so-called fault bit, each of said repeaters comprising means for passing said fault bit into an active state in order to signal to the adjacent repeater, a fault of operation and to impose the passage of said network in operating state on fault.

  According to a particular embodiment, each of said repeaters comprises a buffer memory, said useful and stuffing data frames comprising a so-called saturation bit, each of said repeaters comprising means for passing said saturation bit into an active state in order to report a buffer overflow to the adjacent repeater. Advantageously, stuffing frames also circulate on said primary ring in the absence of useful data frames.

  According to a particularly advantageous embodiment, each of said repeaters includes means for interrupting the circulation of a frame of useful data that said repeater has itself transmitted.

  Thus, it is unnecessary to have a dedicated switch for opening the ring to evacuate the frames. According to the invention, the frames sent by a repeater go around the ring. The circuit is opened by the repeater F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc transmitter to interrupt the flow of the frame when the repeater receives a frame it has sent.

  Advantageously, each of said payload frames comprises an address byte, said address corresponding to the address of the repeater having transmitted said payload frame, the circulation of said payload frame being interrupted when a repeater recognizes its own address in said useful data frame.

  Advantageously, each of said stuffing frames comprises an address byte, said address being identical for each of the stuffing frames 10.

  Advantageously, according to this latter embodiment, each of the useful data frames comprises a counter byte, said counter being incremented each time said frame passes through a repeater while circulating on said primary ring.

  Advantageously, each of said repeaters includes means for deleting a useful data frame when its counter byte exceeds the total number of repeaters on said network.

  Advantageously, according to a first variant, each of said repeaters comprises said Ethernet switch which is associated with it.

  Advantageously, according to a second variant, each of said Ethernet switches is outside the repeater associated with it.

  Advantageously, the structure of each of said data frames is modified with respect to the structure of a standard Ethernet frame so that the start of each of said frames comprises said fault bit and / or said saturation bit and / or said byte address and / or said counter byte.

  Advantageously, said start of each of said frames includes a CRC cyclic redundancy check byte.

  Advantageously, said start is the preamble to said standard Ethernet frame.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc Other characteristics and advantages of the present invention will appear in the following description of an embodiment, given by way of illustration and in no way limiting.

  In the following figures - Figure 1 shows schematically an Ethernet network according to the prior art, - Figure 2 shows schematically a network according to the invention in normal operation, - Figure 3 shows schematically a network according to the invention 10 in operation on default, - Figures 4 to 6 schematically represent three states of a repeater used in a network according to the invention.

  Figure 1 has already been described in relation to the state of the art.

  FIG. 2 schematically represents an Ethernet network 10 15 according to the invention in normal operation. This network uses optical technology of the 10OBaseFX type. A 4B / 5B and NRZ1 type coding from Ethernet to 1 OOMbs ensures permanent activity on the optical links.

  The network 10 comprises: - a primary ring of optical fiber F1, - a secondary ring of optical fiber F2, - a plurality of repeaters 1 to 5, - a plurality of Ethernet switches C1 to C5, - a plurality of equipment (ej ) i <j <1.

  Each of the repeaters i (1 <i <5) comprises 25 - a primary receiver Rpi, - a secondary receiver Rsi, - a primary transmitter Epi, - a secondary transmitter Esi.

  Each of the repeaters i is associated with an Ethernet switch Ci.

  The primary ring F1 transmits frames entering by the receivers Rpi and leaving by the transmitters Epi.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DÉPOSE.doc The secondary ring F2 transmits frames entering by the receivers Rsi and leaving by the transmitters Esi.

  All the frames which circulate on the primary ring F1 and arrive on a repeater i, are transmitted to the Ethernet switch Ci and are transmitted at the same time to the next repeater.

  The two rings FI and F2 run in opposite directions with respect to each other.

  In normal operation, the useful data frames, that is to say the frames sent by the equipment (ej) ij 51, circulate only on the primary ring F1 but we will see with reference to FIG. 3 that the data frames useful can also circulate on the secondary ring F2.

  In normal operation, operating control frames, called stuffing frames, circulate permanently on the secondary ring F2. Jam frames are never retransmitted by a repeater i. They are checked and then deleted upon receipt.

  In the absence of useful data frames on the primary ring F1, stuffing frames circulate on the ring F1.

  All the frames which circulate on the two optical rings F1 and 20 F2 are modified compared to the standard Ethernet frames in 10OBase FX technology. Thus, four specific bytes are used in the preamble and take the place of four bytes in the preamble of the standard Ethernet frame. These four bytes are added by the repeater i when a useful data frame sent by an equipment ej is received and deleted when a useful data frame is output to an equipment. The stuffing frames also have these four specific bytes.

  All the useful data frames include an address byte coded from 1 to 127: the value of this byte depends on the address of the repeater; this byte is not modified by crossing repeaters 1 to 5. The stuffing frames are coded with an address equal to 0.

  Thus, when a data frame is transmitted by a repeater i, it goes around the ring Fl. The repeater i then receives the frame which it has read itself F: \ Salle \ FP000431 \ PREMDEP \ DEPOI \ TEXTE DROPPED .doc sent and opens the circuit to interrupt the circulation of the frame. This prevents a data frame from constantly circulating on the ring. All the frames circulating on the rings F1 and F2 include a 5 counter byte. This counter byte is incremented by each of the repeaters 1 to 5 when a frame circulates on the primary ring F1. When the frame is sent by a repeater i, the first to send the frame, the counter is at zero. The counter is then incremented by each repeater when the frame passes through the primary Epi / Rpi link. No processing is carried out when the frames pass through a repeater through the secondary ring F2.

  When a repeater i is out of operation, it can no longer delete the frames which it has itself sent. The counter byte makes it possible to avoid having a frame circulating permanently on the network. Frame 15 is eliminated by another repeater when the counter byte exceeds the total number of repeaters initially present on the network.

  All the frames circulating on the rings F1 and F2 have a status byte. This status byte includes at least - one fault bit, - one saturation bit.

  A repeater i uses the saturation bit when it detects a saturation of its buffer memory, not shown. To do this, it sets the saturation bit of a stuffing frame to 1 and sends this stuffing frame on the secondary ring to the adjacent repeater. For example, if the repeater 2 is saturated, it sends a stuffing frame with a saturation bit set to 1 to the repeater 1 on the secondary ring F2.

  The use of the fault bit will be more precisely described with reference to FIG. 3.

  All the frames circulating on the rings F1 and F2 comprise a 30 byte of cyclic redundancy check CRC; this CRC byte is different from the CRC byte of the standard Ethernet frame.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEX-rE DEPOSE.doc Note that this principle of management of rings F1 and F2 thanks to the modification by the repeaters i of the frames compared to the standard Ethernet frames is independent of the type of network used and can therefore be used for networks other than an Ethernet network; this principle is also applicable to Ethernet networks not comprising switches but comprising only hubs or repeaters connected directly to equipment.

  FIG. 3 schematically represents the network 10 as shown in FIG. 2 for which the link of the primary ring F1 between the emitter Ep2 and the receiver Rp3 is broken.

  In such a case, the repeater 3 no longer receives frames on the receiver Rp3 and thus detects a break in the optical fiber of the primary ring FI.

  The repeater 3 then uses a stuffing frame represented by the dotted arrow in which the fault bit is set to 1; this stuffing frame is sent to the adjacent repeater 2.

  The useful data traffic is then diverted to the secondary ring F2. In other words, the useful data frames pass through the secondary transmitter Es2 then circulate on the secondary ring F2 to the secondary receiver Rs3. The network is thus self-healing.

  The useful data frames are only transmitted to the switches Ci when they circulate on the primary ring FI.

  Thus, the routing tables of the switches Ci remain unchanged even in the event of a fault and these routing tables are therefore not reset to zero.

  Another reason that can lead to self-healing is the specific CRC byte. Thus, when the CRC indicates a transmission fault, for example between a transmitter and a receiver, the network is also self-healing.

  A repeater i as shown in FIGS. 2 and 3 can take at least three possible states depending on the operating state of the network 10.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc Figure 4 schematically represents a first state, called state A, of a repeater i.

  The repeater i comprises - three ports P1, P2 and P3, - switching means 13, 14 and 15, - means 11 for deleting specific bytes, - means 12 for inserting specific bytes, - first means 17 for modifying specific bytes and sending stuffing frames, - second means 18 for modifying specific bytes and sending stuffing frames, - first means 16 for processing frames, - second means 19 frame processing, - the primary receiver Rpi, - the secondary receiver Rsi, - the primary transmitter Epi, - the secondary transmitter Esi.

  The three ports Pi, P2 and P3 are ports of the Mll (Media Independent Interface) type.

  The PI port is the port to the Ethernet switch Ci not shown. The ports P2 and P3 are the sending and receiving ports of the frames on the primary and secondary rings.

  The means 12 make it possible to insert the specific bytes into the preamble of the standard Ethernet frames of useful data received from the equipment via the port PI of the Ethernet switch.

  The means 11 make it possible to delete the specific bytes of the useful data frames before they are sent to the port Pi of the Ethernet switch and then to the equipment.

  Each of the switching means 13, 14 and 15 can switch between two configurations.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc The switching means 13, 14 and 15 are such that a frame TAi arriving on the primary receiver Rpi is: - either re-emitted by the primary transmitter Epi, - is deleted by the processing means 16 when it is a frame sent by the transmitter itself or a stuffing frame or when the counter byte is exceeded.

  This TAI frame is also transmitted to the port Pl towards the Ethernet switch when it is a useful data frame; the means 11 delete the specific bytes of the TAI frame which again becomes a standard Ethernet frame.

  Similarly, the switching means 13, 14 and 15 are such that a frame TA2 arriving on the secondary receiver Rsi is - either re-sent by the primary transmitter Esi, - or deleted by the processing means 19 when it it is a frame sent by the transmitter itself or a stuffing frame or when the counter byte is exceeded.

  Unlike the TAI frame, this TA2 frame is not transmitted to port Pl to the Ethernet switch; in this way, in the case of self-healing, the useful data frames of the TA2 type are very transparent with respect to the Ethernet switches when they circulate on the secondary ring.

  A new useful data frame TA3 received via the port PI is first modified by the means 12 which insert the specific bytes in the preamble of said frame; it is then transmitted to the primary transmitter Epi which sends it to the primary ring.

  In normal operation, the TAI frames are useful data frames and the TA2 frames are stuffing frames. This is the configuration of repeaters 1 to 5 shown in FIG. 2. In this case, it is also possible that the frames TAi are stuffing frames in the absence of useful data frames.

  In the event of a fault, means 17 and 18 allow the fault bit of a frame sent to pass to an adjacent repeater in an active state F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc (from 0 to 1) in order to signal to the adjacent repeater, a malfunction. The means 17 and 18 also make it possible to pass the saturation bit of a transmitted frame to an adjacent repeater in an active state (from 50 to 1) in order to signal to the adjacent repeater a saturation of the buffer memory of the repeater i.

  In the event of self-healing of the network, the frames TAI and TA2 are useful data frames. This is the configuration of the repeaters 1, 4 and 5 shown in FIG. 3. In this case, it is also possible that the frames 10 TAi and TA2 are stuffing frames in the absence of useful data frames.

  FIG. 5 schematically represents a second state, called state B, of a repeater i.

  The switching means 13, 14 and 15 are such that a frame TB1 15 arriving on the primary receiver Rpi is: - either retransmitted by the secondary transmitter Esi, - or deleted by the processing means 16 when it is a question a frame sent by the transmitter itself or a stuffing frame or when the counter byte is exceeded.

  This TBI frame is also transmitted to the PI port to the Ethernet switch when it is a payload frame; the means 11 delete the specific bytes of the frame TB1 which again becomes a standard Ethernet frame.

  A new useful data frame TB2 received via the port PI is first modified by the means 12 which insert the specific bytes in the preamble of said frame; it is then transmitted to the secondary transmitter Esi which sends it to the secondary ring.

  This configuration is that of the repeater 2 shown in FIG. 3.

  FIG. 6 schematically represents a third state, called state C, of a repeater i.

  The switching means 13, 14 and 15 are such that a frame TC1 arriving on the secondary receiver Rsi is: F: \ Room \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc - either re-emitted by the secondary transmitter Epi, - is deleted by the processing means 19 when it is a frame sent by the transmitter itself or a stuffing frame or when the counter byte is exceeded.

  This frame TC1 is also transmitted to the port Pl towards the Ethernet switch when it is a useful data frame; the means 11 delete the specific bytes of the frame TB1 which again becomes a standard Ethernet frame.

  A new useful data frame TC2 received via the port P1 is first modified by the means 12 which insert the specific bytes in the preamble of said frame; it is then transmitted to the primary Epi transmitter which sends it to the primary ring.

  This configuration is that of the repeater 3 shown in FIG. 3.

  Of course, the invention is not limited to the embodiment which has just been described.

  In particular, the invention has been described in relation to an optical network but it can be transposed to an electrical network.

  In addition, only two types of frames have been described, but it is also possible to envisage a third type of frame such as an identification frame. This frame makes it possible to manage the phases of initialization of the network and appearance / disappearance of repeater on the ring. This frame emitted by a repeater goes around the ring. It is propagated by the repeaters on the ring as a payload frame but it is not sent to the Pi port. The counter byte is incremented with each passage of the frame in a repeater by the primary ring . On its return, the repeater knows the number of repeaters present on the ring. This value is stored in the repeater.

  F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXrE DEPOSE.doc

Claims (20)

  1. Ethernet network (10) comprising a plurality of Ethernet switches (Ci) and a plurality of repeaters (i) exchanging frames of useful data coming from external equipment (ej), each of said 5 repeaters (i) being associated with a said Ethernet switches (Ci) and comprising: a primary transmitter (Epi) and a secondary transmitter (Esi), - a primary receiver (Rpi) and a secondary receiver (Rsi), - said plurality of repeaters (i) being connected together by a primary ring (Fl) of transmission via said transmitters (Epi) and primary receivers (Rpi) and by a secondary ring (F2) of transmission via said transmitters (Esi) and secondary receivers (Rsi), the direction of transmission of frames circulating in said primary ring (FI) being opposite to the direction of transmission of the frames circulating in said secondary ring (F2), said network (10) being characterized in that it comprises two states: - a first state called functional normal operation where the useful data frames circulate only on said primary ring (FI) while being received and transmitted respectively by said primary receiver 20 (Rpi) and said primary transmitter (Epi) of each of said repeaters (i), - a second state said to operate on fault, said network (10) comprising means for short-circuiting a part of said primary ring (Fl) by a part of said secondary ring (F2) in the event of a fault on said primary ring (Fl), the frames of useful data 25 being transmitted to said Ethernet switches (Ci) only when they circulate on said primary ring (F1).   2. Ethernet network (10) according to the preceding claim characterized in that each of said repeaters (i) comprises switching means (13, 14, 15) so that said useful data frames can circulate according to three states: F: \ Saile \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE. doc - a first state (A), called normal operation, where the useful data frames flow from said primary receiver (Rpi) to said primary transmitter (Epi), - a second state (B) where the useful data frames flow from said primary receiver (Rpi) to said secondary transmitter (Esi), - a third state (C) where the useful data frames flow from said secondary receiver (Rsi) to said primary transmitter (Epi).   3. Ethernet network (10) according to one of the preceding claims characterized in that said primary (FI) and secondary (F2) rings 10 are optical rings.   4. Ethernet network (10) according to one of the preceding claims characterized in that operation control frames, called stuffing frames, circulate permanently on said secondary ring (F2) when said network (10) is in said normal operating state, each of said stuffing frames being transmitted by a repeater then suppressed on reception by the next repeater, said adjacent receiver.   5. Ethernet network (10) according to the preceding claim, characterized in that said useful data and padding frames transmitted on said network each comprise a so-called fault bit, each of said repeaters comprising means (17, 18) for passing said fault bit in an active state in order to signal to the adjacent repeater, a malfunction and to force the passage of said network into operating state on fault.   6. Ethernet network (10) according to one of claims 4 or 5 characterized in that each of said repeaters comprises a buffer memory, said useful and stuffing data frames comprising a so-called saturation bit, each of said repeaters (i) comprising means (17, 18) for passing said saturation bit into an active state in order to signal a saturation of its buffer memory to the adjacent repeater.   F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc 7. Ethernet network (10) according to one of claims 4 to 6 characterized in that stuffing frames also circulate on said primary ring (F1) in the absence of useful data frames.   8. Ethernet network (10) according to one of the preceding claims 5 characterized in that each of said repeaters (i) comprises means (16, 19) for interrupting the circulation of a frame of useful data as said repeater (i) has issued itself.   9. Ethernet network (10) according to the preceding claim characterized in that each of said useful data frames comprises an address byte 10, said address corresponding to the address of the repeater (i) having sent said useful data frame, the the circulation of said useful data frame being interrupted when a repeater (i) recognizes its own address in said useful data frame.   10. Ethernet network (10) according to one of claims 4 to 9 characterized in that each of said stuffing frames comprises an address byte, said address being identical for each of the stuffing frames. 11. Ethernet network (10) according to one of the preceding claims, characterized in that each of the useful data frames comprises a counter byte, said counter being incremented each time that said frame passes through a repeater (i) while circulating. on said primary ring (Fl).   12. Ethernet network (10) according to the preceding claim characterized in that each of said repeaters (i) comprises means (16, 19) for deleting a useful data frame when its counter byte exceeds the total number of repeaters (i ) of said network (10).   13. Ethernet network (10) according to one of the preceding claims characterized in that each of said repeaters (i) comprises said Ethernet switch (Ci) which is associated with it.   14. Ethernet network according to one of the preceding claims characterized in that each of said Ethernet switches (Ci) is outside the repeater (i) which is associated with it.   F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc 15. Ethernet network according to one of claims 5 to 14 characterized in that the structure of each of said data and padding frames is modified relative to the structure of a standard Ethernet frame so that the start of each of said frames includes said fault bit.   16. Ethernet network according to one of claims 6 to 15 characterized in that the structure of each of said data and padding frames is modified relative to the structure of a standard Ethernet frame so that the start of each of said frames includes 10 said saturation bit.   17. Ethernet network according to one of claims 9 to 16 characterized in that the structure of each of said data and padding frames is modified relative to the structure of a standard Ethernet frame so that the start of each of said frames includes said address byte.   18. Ethernet network according to one of claims 1 1 to 17 characterized in that the structure of each of said data and padding frames is modified relative to the structure of a standard Ethernet frame so that the start of each of said frames includes said counter byte.   19. Ethernet network according to one of claims 4 to 18 characterized in that the structure of each of said data and padding frames is modified relative to the structure of a standard Ethernet frame so that the start of each of said frames has a CRC cyclic redundancy check byte.   20. Ethernet network according to one of claims 15 to 19 characterized in that said start is the preamble of said standard Ethernet frame.   F: \ Salle \ FP000431 \ PREMDEP \ DEPOT \ TEXTE DEPOSE.doc