Method for monitoring a Half Duplex Ethernet network and associated Half Duplex Ethernet network

Abstract

Method for monitoring a Half Duplex Ethernet network and associated Half Duplex Ethernet network The present invention relates to a method for monitoring a Half Duplex Ethernet network comprising a plurality of nodes and having a PLCA operating mode and a CSMA / CD operating mode, each node being defined by an identifier. The method comprises the following steps implemented by each node: - retrieving (110) an internal state of the node describing the operating mode of the network; - transmitting (120) the internal state to all the other nodes; - analyzing (130) the external states received corresponding to the internal states transmitted by other nodes; - based on this analysis, reconfiguring (140) the node or maintaining its current configuration. Figure for abstract: Figure 2

Description

Title of the invention: Method for monitoring a Half Duplex Ethernet network and associated Half Duplex Ethernet network

[0001] The present invention relates to a method for monitoring a Half Duplex Ethernet network. The present invention also relates to such a Half Duplex Ethernet network.

[0002] In particular, the Half Duplex Ethernet type network according to the invention complies with one of the following standards: 10BASE-T1S, 100BASE-T1S, 10BASE-T1L, 100BASE-T1L. These standards comply with the IEEE STD 802.3cg type standard.

[0003] In a manner known per se, networks of this type make it possible to transmit data originating, for example, from a plurality of sensors to a central switch. This type of network is a Half Duplex network, insofar as it makes it possible to transmit frames in both directions of circulation between the nodes constituting this network on the same pair of conductors.

[0004] Furthermore, in a particular operating mode, this type of network implements a collision management technique optimized to use the maximum of the bandwidth available for exchanges between different nodes of the network.

[0005] This mode of operation is known as PLCA (Physical Layer Collision Avoidance) and is mainly based on the presence of a master node on the network which periodically sends a synchronization signal called BEACON.

[0006] This synchronization signal allows other nodes to synchronize and determine their own opportunities for transmitting frames in the network.

[0007] The absence of the synchronization signal on the network, due for example to a failure of the master node called Master, forces the different nodes of the network to reconfigure the collision management mode by switching from the PLCA operating mode to a degraded operating mode called CSMA / CD (from the English “Carrier Sense Multiple Access / Collision Detection”).

[0008] Switching to such a mode involves a significant reduction in network performance. Indeed, when the network is in this degraded operating mode, each node wishing to transmit a frame on the network first checks whether there is another node that is already transmitting frames on the network. In such a case, this first node will wait a random time before performing this test again.

[0009] In certain fields and in particular in the avionics field, the network of the aforementioned type presents an interesting alternative to the networks currently used.

[0010] For example, in the avionics field, the use of ARINC 429 type networks is known for connecting sensors to a centralized switch. However, the type of network conforming to this standard has a very low throughput, typically around 100 Kbit / s and is only unidirectional.

[0011] On the contrary, for example the 10BASE-T1S type network has a flow rate of 10 Mbit / s and the 100BASE-T1S type network has a flow rate of 100 Mbit / s.

[0012] In addition, a Half Duplex type network that allows frames to be transmitted in both directions over the same pair of conductors would reduce the necessary use of cables. Indeed, for existing networks, a pair of conductors is required to ensure the circulation of frames in each direction.

[0013] However, replacing existing networks with this type of network presents a number of difficulties.

[0014] In particular, when the network, for example of the 10BASE-T1S type, enters its degraded operating mode, the transmission time of the frames can no longer be limited.

[0015] This then makes the network of this type non-deterministic. The use of non-deterministic networks is problematic in certain areas, particularly in the avionics field.

[0016] The present invention aims to solve this problem and to make the Half Duplex Ethernet type network (such as 10BASE-T1S, 100BASE-T1S, 10BASE-T1L, 100BASET-1L) deterministic.

[0017] This will then allow its use in many fields and in particular in the avionics field.

[0018] To this end, the invention relates to a method for monitoring a Half Duplex Ethernet type network comprising a plurality of nodes and having a PLCA operating mode and a CSMA / CD operating mode, each node being defined by an identifier.

[0019] In the PLCA operating mode, a master node sends a synchronization signal to all other nodes for transmission of their frames.

[0020] In the CSMA / CD operating mode, all nodes transmit their frames according to random time intervals.

[0021] The method comprises the following steps implemented by each node:

[0022] - recovery of an internal state of the node describing the operating mode of the network ;

[0023] - transmission of the internal state to all other nodes;

[0024] - analysis of the external states received corresponding to the internal states transmitted by other nodes;

[0025] - depending on this analysis, reconfiguration of the node or maintenance of its confi- current configuration.

[0026] According to other advantageous aspects of the invention, the method comprises one or more of the following characteristics taken in isolation or in all technically possible combinations:

[0027] - each internal state indicates the operating mode of the network seen by the node correspondent;

[0028] - each internal state further indicates whether the corresponding node receives or transmits a synchronization signal;

[0029] - the step of transmitting the internal state comprises the integration of this internal state in each frame emitted by the corresponding node;

[0030] - the step of reconfiguring each node comprises a deactivation of this node or a shift in its identifier;

[0031] - the identifier offset includes:

[0032] - the allocation of a new identifier chosen according to the maximum number of nodes in the network when the corresponding node is the master node;

[0033] - reducing the identifier to “1” for all other cases;

[0034] - the step of analyzing the received external states includes a validation sub-step including selecting a valid state from the set of received states;

[0035] - the analysis step comprises an analysis of at least three external states from different nodes;

[0036] - the validation sub-step includes the comparison of the received external states and the selection of the valid state corresponding to a common state of a majority of the external states received;

[0037] - valid state indicates:

[0038] - the PLCA operating mode, the current configuration of the corresponding node is maintained;

[0039] - CSMA / CD operating mode, the corresponding node is reconfigured by a shift in its identifier;

[0040] - none of these operating modes, the corresponding node is reconfigured by a deactivation of this node;

[0041] - the analysis step comprises a sub-step of activating the operating mode CSMA / CD operation when the corresponding node does not receive any frame in a first time interval;

[0042] - following activation of the CSMA / CD operating mode, the reconfi step guration includes an offset of the identifier of the corresponding node when this node receives at least one frame in a second time interval and a deactivation of the node otherwise.

[0043] The invention also relates to a Half Duplex Ethernet type network comprising a plurality of nodes and having a PLCA operating mode and a CSMA / CD operating mode, each node being defined by an identifier;

[0044] - in the PLCA operating mode, a master node being able to send to all other nodes a synchronization signal for transmitting their frames;

[0045] - in the CSMA / CD operating mode, all the nodes being able to emit their frames at random time intervals;

[0046] each node being configured to implement the method as defined previously.

[0047] The invention will appear more clearly on reading the description which follows, given solely by way of non-limiting example and made with reference to the drawings in which: - [Fig.l] [Fig.l] is a schematic view of a Half Duplex Ethernet type network according to the invention, the network comprising in particular a plurality of nodes; - [Fig.2] [Fig.2] is a flowchart of a network monitoring process of [Fig.l]; - [Fig.3][Fig.4][Fig.5][Fig.6][Fig.7] figures 3 to 7 are different illus steps of the implementation of the process of [Fig.2].

[0048] [Fig.l] in fact illustrates a network 10 according to the invention.

[0049] This network 10 is a Half Duplex Ethernet type network which complies with one of the 10BASE-T1S, 100BASE-T1S, 10BASE-TIL or 100BASE-T1L standards. Generally, such a standard is standardized in the IEEE STD 802.3cg type standard. By "type X standard" is meant the X standard of the current version or any later or earlier version when this version makes it possible to implement the characteristics described in relation to this standard below.

[0050] As illustrated in [Fig.l], the network 10 comprises a plurality of nodes 12-0, ... 12-N which are connected by a cable 13. The cable 13 advantageously has a cable with a differential pair, for example a twisted pair cable.

[0051] Each of the nodes 12-0, ... 12-N is integrated into a device which is capable of generating digital data to send to other devices via the network 10 and / or of receiving digital data from these devices. The digital data is transferred via the network 10 in the form of frames.

[0052] In particular, according to one embodiment of the invention, the network 10 can be used in the avionics field, for example the network 10 is on board an aircraft.

[0053] By an aircraft is meant any flying machine which is controllable in a manner at least partially manually and / or at least partially automatically.

[0054] According to an exemplary embodiment, at least some of the devices integrating the nodes 12-0, ... 12-N have avionics sensors 14 and a device integrating at least one of these nodes has a switch 15. Such a switch 15 is configured to transmit data generated by the sensors to a centralized computer.

[0055] According to this example, the data generated by the sensors 14 present, for example, measurement data which are then transmitted to the central computer via the network 10 and in particular the switch 15.

[0056] Thus, in the example of the main figure, the node 12-0 is integrated into such a switch 15 and the other nodes 12-1 to 12-N are integrated into the sensors 14.

[0057] Furthermore, the node 12-0 is also capable of transmitting data to the other nodes. This data presents, for example, configuration data of the corresponding sensors 14.

[0058] In a manner known per se, each node 12-0, ... 12-N has a physical interface often implemented by a component called PHY. This physical interface PHY notably includes an internal register storing different operating parameters of the node.

[0059] Furthermore, each node 12-0, ... 12-N is associated with a unique identifier in the network 10. For example, the identifiers of the nodes 12-0, ... 12-N correspond to the number of the node assigned within the network and ranging from 0 to N.

[0060] The node identifiers may be changed, as will be described in more detail later.

[0061] In a manner known per se, the network 10 has two operating modes.

[0062] In a first operating mode, also called PLCA operating mode, all exchanges of frames in the network 10 are controlled by a synchronization signal transmitted to all the nodes by the master node.

[0063] This master node generally has the identifier "0" which then distinguishes it from the other nodes of the network. This master node is then configured to periodically send a synchronization signal, also called BEACON. All the other nodes are able to receive this synchronization signal and to transmit their frames in a time slot predetermined for the corresponding node. This time slot is determined locally by the corresponding node using the synchronization signal. The master node is also configured to act like the other nodes, that is to say, it is also configured to transmit frames in a determined time slot.

[0064] When the corresponding node has no frame to send in its slot, this slot remains empty and no frame is sent into the network during this slot.

[0065] Advantageously, each slot may have a variable duration. For example, each slot may correspond to a duration during which the node can begin to transmit. Each slot therefore has a minimum duration corresponding to an absence of a frame, but this duration can extend to the duration of the frame to be transmitted in the presence of such a frame. In such a case, the next transmitting node will only start transmitting at the end of the frame transmission by the first node, that is, the next transmitting node will only start transmitting after the detection of a "silence" in the network.

[0066] The second operating mode of the network 10, also known by the abbreviation of the CSMA / CD operating mode, is triggered in the network when no synchronization signal is received by the nodes at the end of a cycle, i.e. after the speaking time of all the nodes. In such a case, each node is able to send its frames according to random time intervals to avoid collisions. In particular, when a node tries to send a frame while another node is sending another frame at that same time, the first node will wait a random time before trying to send its frame again.

[0067] According to the invention, each node is further configured to implement a monitoring method according to the invention which makes it possible to reconfigure the network when it switches to the CSMA / CD operating mode, in order to return to the PLCA operating mode. This method is for example implemented periodically in the network 10. In other words, the steps 110 to 140 described below can be re-looped according to a predetermined periodicity.

[0068] This process will now be explained with reference to [Fig.2] showing a flowchart of its steps.

[0069] Initially, it is considered that the network 10 operates according to the PLCA operating mode and the set of nodes 12-0, ..., 12-N are able to send and receive frames.

[0070] It is further considered that the steps described below are carried out by each of the nodes 12-0, ..., 12-N. Thus, these steps will be described with reference to a single node (for example node 12-1) knowing that all the other nodes are able to implement the same steps.

[0071] During an initial step 110, the node 12-1 recovers an internal state making it possible to describe the current operating mode of the network 10 from the point of view of this node.

[0072] In particular, this internal state indicates the operating mode of the network, either the PLCA operating mode or the CSMA / CD operating mode. This internal state also indicates whether this node receives or transmits a synchronization signal.

[0073] More particularly, the internal state may indicate the PLCA operating mode and the fact that this node is transmitting a synchronization signal. In other words, this internal state indicates that the corresponding node is the master node in the network 10.

[0074] According to another example, this internal state may indicate that the network is in the PLCA operating mode and the corresponding node receives a sync signal. nization. In such a case, the corresponding node is a slave node which then receives a synchronization signal from a master node.

[0075] The internal state may also indicate that the operating mode of the network 10 is the CSMA / CD mode and that the corresponding node is not receiving any signaling signal. This case then corresponds to normal operation of the node in this CSMA / CD operating mode of the network 10. According to yet another example, the internal state of the node may indicate that the network 10 is in the CSMA / CD operating mode while the corresponding node is receiving or transmitting a synchronization signal. This latter state indicates a malfunction of the network which will then be treated as will be explained with reference to the following steps of the method.

[0076] Advantageously, the internal state of the node is kept in its internal register.

[0077] The recovery of such a state therefore comprises the recovery of this state from this internal register of node 12-1.

[0078] In the following step 120, the node 12-1 transmits its internal state to all the other nodes 12-0, 12-2 to 12-N.

[0079] To do this, the node 12-1 integrates its identifier as well as the internal state in each frame transmitted by this node in the network 10.

[0080] To do this, different techniques are possible.

[0081] According to a first technique illustrated in [Fig.3], the node 12-1 integrates additional data D into a header of each frame. This header corresponds for example to the MAC HEADER type header. This additional data D can be integrated more particularly into the field indicating the origin of the frame, called the MAC Source field.

[0082] According to a second technique illustrated in [Fig.4], the additional data D are integrated into the payload of the corresponding frame.

[0083] This payload is known by the English abbreviation of Payload.

[0084] According to yet another technique (not illustrated), the additional data D can be integrated into a field independent of the Payload useful application data field. This then involves reducing the maximum size of the Payload field.

[0085] During the following step 130, the node 12-1 analyzes external states received from the other nodes of the network 10 or possibly, the case when these external states have not been received. In particular, by external states, we mean the internal states determined by the other nodes of the network and then transmitted to the corresponding node using the frames sent by these nodes.

[0086] The analysis step 130 makes it possible to determine whether it is necessary in particular to reconfigure the node 12-1 or to maintain its current configuration during the step 140, in order to reestablish, if necessary, the PLCA operating mode of the network 10.

[0087] Different examples of implementation of these steps 130 and 140 are possible. In addition, as will be explained later, it is necessary in certain cases to implement these steps 130 and 140 several times in order to achieve the PLCA operating mode of the network 10.

[0088] An example of a possible implementation of these steps is illustrated in [Fig.5].

[0089] With reference to this [Fig.5], the analysis step 130 comprises a first sub-step 131 during which the node 12-1 waits for the reception of the external states from the other nodes. When no external state, i.e. no frame, is received from the other nodes after a first time interval, the node 12-1 implements the sub-step 132 during which it forces the transition to the CSMA / CD operating mode. Then, the node 12-1 again waits for the reception of the external states, i.e. the frames from the other nodes, during the sub-step 133.

[0090] When, at the end of a second time interval which is for example equal to the first time interval, the node 12-1 still does not receive a frame from the other nodes, it is considered that the node is faulty and should then be deactivated during step 140. In [Fig.5], the deactivation of the node then corresponds to the action designated by the reference 141. When, in the opposite case, the node 12-1 receives frames from the other nodes, the node implements a validation sub-step 134 of the external statuses received. This validation sub-step 134 will be explained in more detail later.

[0091] When, at the end of step 134, the status of the network indicating the CSMA / CD operating mode is considered invalid, it is again considered that the node is faulty and it is then deactivated during step 140 by action 141.

[0092] When, on the contrary, the status indicating the operating mode of the CSMA / CD network is considered to be valid during step 134, it is considered that the network 10, and in particular the corresponding nodes 12-0 to 12-N, must be reconfigured during step 140 to reestablish the PLCA operating mode.

[0093] With reference to [Fig.5], this action is then noted by the reference 142 and will be explained in more detail later.

[0094] When, during sub-step 131, the node 12-1 receives frames from the other nodes, i.e. external states, it implements sub-step 134 of validation of the PLCA status of the network 10.

[0095] When this status is considered valid at the end of sub-step 134, it is considered that the network 10, and in particular the node 12-1, is operating normally in the PLCA operating mode and during step 140, the current configuration of the network is maintained.

[0096] With reference to [Fig.5], this action of maintaining the current network configuration corresponds to reference 143.

[0097] When, on the contrary, after the first implementation of the validation step 134, the state indicating the PLCA operating mode of the network 10 is considered invalid, the node 12-1 again implements the validation step 134 during which it this time verifies the validity of the state indicating the CSMA / CD operating mode.

[0098] When, at the end of this second implementation of sub-step 134, the state indicating the CSMA / CD operating mode is considered to be valid, it is considered that the network 10 and in particular the node 12-1 must be reconfigured during step 140 to re-establish the PLCA operating mode of the network 10.

[0099] To do this, node 12-1 implements action 142 during step 140, which will be explained in detail later.

[0100] When, on the contrary, at the end of the second implementation of the validation sub-step 134, the state indicating the CSMA / CD operating mode is considered invalid, it is considered that the node 12-1 is faulty and must be deactivated during step 140. Thus, during step 140, the action 141 comprising the deactivation of the node is then implemented.

[0101] [Fig.6] illustrates an example of the implementation of sub-step 134 of validation of the external states received by the corresponding node 12-1.

[0102] Generally, the validation sub-step 134 comprises the comparison of the external states received from different nodes and the selection of the valid state corresponding to a common state according to a majority of the external states received.

[0103] Thus, according to the example of [Fig.6], sub-step 134 comprises the verification of three conditions.

[0104] The first condition (Condition 1 in [Fig.6]) is met when node 12-1 receives two external statuses from the two different nodes.

[0105] When this is not the case, node 12-1 waits until it receives external statuses from two different nodes.

[0106] When two statuses from two different nodes are received, node 12-1 checks the second condition (Condition 2 in [Fig.6]) which consists of comparing the received statuses.

[0107] When the statuses are identical, the node 12-1 concludes that this status is valid. When, on the contrary, the second condition is not verified, that is to say the statuses received from the two different nodes are not identical, the node 12-1 implements the third condition (Condition 3 in [Fig.6]) during which it checks whether it has received an external status from another node different from the first two nodes. When this is not the case, the node 12-1 waits for such a status from a third node different from the first two nodes.

[0108] When this is the case, node 12-1 selects the valid state corresponding to the state common according to the majority of external statuses received. In other words, in such a case, node 12-1 decides the valid status based on the majority.

[0109] Of course, other modes of validation of the received states are also possible. For example, it is possible to perform a double verification of the states received from the same node.

[0110] [Fig.7] illustrates the implementation of action 142 implemented during step 140.

[0111] In particular, this action 142 comprises a shift of the node identifier in order to reestablish the PLCA operating mode of the network 10.

[0112] This shift includes the assignment of a new identifier determined based on the maximum number of nodes in the network when the corresponding node is the master node. In the case of other nodes, the shift includes reducing the identifier of this node by one.

[0113] In its part A, [Fig.7] illustrates the normal operation of the network 10 according to the PLCA operating mode for the nodes having identifiers ranging from 0 to N. Among these nodes, the node having the identifier 0 corresponds to the master node which is able to send a synchronization signal to the other nodes.

[0114] In its part B, [Fig.7] illustrates the case when the node having the identifier 0 must be reconfigured and a new master node must be selected. For this, and as illustrated in part C of [Fig.7], the previous master node receives the identifier corresponding for example to the maximum identifier of the nodes in the network and thus becomes a slave node. In such a case, the identifiers of all the other nodes are decreased by one so that the previous node having the identifier number 1 becomes the node having the identifier 0. Therefore, this node becomes the new master node.

[0115] The other nodes, that is to say the previous nodes having identifiers ranging from 2 to N, remain the slave nodes but change their identifiers which now range from 1 to N-1.

[0116] When, after a first shift of the identifiers, there is no node having the identifier 0, the shift operation is performed once again until such a node having the identifier 0 is obtained. This new shift operation is performed during a new implementation of step 140 and action 142, which are then performed following a new implementation of the analysis step 130.

[0117] Thus, the network 10 can operate again according to the PLCA operating mode. In such a case, the new master node receives and transmits the corresponding synchronization signal.

[0118] It is then understood that the present invention has a certain number of advantages.

[0119] In particular, the invention makes it possible, in a first step, to be able to detect reliably detect a failure on the network. This detection is said to be reliable because it comes from a redundancy of the different states from different nodes. This then makes the probability that the detection is false substantially negligible. In a second step, the invention makes it possible to reconfigure the network to maintain and find the PLCA mode which is then the desired operating mode.

[0120] The invention also implements a technique for verifying transmitted external states in order to protect the integrity of the network.

[0121] When reconfiguring the network, the invention makes it possible to deactivate a dysfunctional node to prevent any anomaly on the network caused by this node.

[0122] Finally, the invention also makes it possible to perform a shift of the identifiers of the nodes across the entire network to allow recovery of the PLCA operating mode as quickly as possible. This operation makes it possible to repeat the shift several times in the event of multiple failures. This multiplicity of reconfiguration possibilities makes it possible to make the network more reliable in an avionics context since the probability of having a system with multiple similar failures is low and decreases with the number of failures.

[0123] The network according to the invention can thus be effectively used in particular in the avionics field to replace existing networks, for example networks according to the ARINC 429 standard.

Claims

Claims

1. Method for monitoring a Half Duplex Ethernet type network comprising a plurality of nodes (12-0, ..12-N) and having a PLCA operating mode and a CSMA / CD operating mode, each node (12-0, ..., 12-N) being defined by an identifier; in the PLCA operating mode, a master node (12-0) sending to all the other nodes (12-1, ..., 12-N) a synchronization signal for transmission of their frames; in the CSMA / CD operating mode, all the nodes (12-0, ..., 12-N) transmitting their frames according to random time intervals; the method comprising the following steps implemented by each node (12-0, ..., 12-N): - recovery (110) of an internal state of the node (12-0, ..., 12-N) describing the operating mode of the network; - transmission (120) of the internal state to all other nodes (12-0, ..., 12-N); - analysis (130) of the external states received corresponding to the internal states transmitted by other nodes; - depending on this analysis, reconfiguration (140) of the node (12-0, ..., 12-N) or maintenance of its current configuration.

2. The method of claim 1, wherein each internal state indicates the mode of operation of the network seen by the corresponding node (12-0, ..., 12-N).

3. The method of claim 2, wherein each internal state further indicates whether the corresponding node (12-0, ..., 12-N) is receiving or transmitting a synchronization signal.

4. Method according to any one of the preceding claims, in which the step of transmitting (120) the internal state comprises the integration of this internal state in each frame transmitted by the corresponding node (12-0, ..., 12-N).

5. Method according to any one of the preceding claims, in which the step of reconfiguring (140) each node (12-0, ..., 12-N) comprises a deactivation (141) of this node or a shift (142) of its identifier.

6. The method of claim 5, wherein the offset (142) of the identifier comprises: - the allocation of a new identifier chosen according to the maximum number of nodes (12-0, ..12-N) in the network when the corresponding node (12-0, ..., 12-N) is the master node; - the reduction of the identifier by “1” for all other cases.

7. A method according to any one of the preceding claims, wherein the step of analyzing (130) the received external states comprises a validation sub-step (134) comprising selecting a valid state from among the set of received states.

8. Method according to claim 7, in which: - the analysis step (130) comprises an analysis of at least three external states originating from different nodes (12-0, ..., 12-N); - the validation sub-step (134) comprises the comparison of the received external states and the selection of the valid state corresponding to a common state of a majority of the received external states.

9. Method according to claim 7 or 8, wherein when the valid state indicates: - the PLCA operating mode, the current configuration of the corresponding node (12-0, ..., 12-N) is maintained; - the CSMA / CD operating mode, the corresponding node (12-0, ..., 12-N) is reconfigured by a shift of its identifier; - none of these operating modes, the corresponding node (12-0, ..., 12-N) is reconfigured by a deactivation of this node (12-0, ..., 12-N).

10. A method according to any preceding claim, wherein the analyzing step (130) comprises a sub-step (132) of activating the CSMA / CD operating mode when the corresponding node (12-0, ..., 12-N) receives no frames in a first time interval.

11. Method according to claim 10, wherein following the activation of the CSMA / CD operating mode, the reconfiguration step (140) comprises an offset (142) of the identifier of the corresponding node (12-0, ..., 12-N) when this node (12-0, ..., 12-N) receives at least one frame in a second time interval and a deactivation (142) of the node (12-0, ..., 12-N) otherwise.

12. Half Duplex Ethernet type network (10) comprising a plurality of nodes (12-0, ..., 12-N) and having a PLCA operating mode and a CSMA / CD operating mode, each node (12-0, ..., 12-N) being defined by an identifier; in the PLCA operating mode, a master node (12-0) being able to send a signal to all the other nodes (12-1, 12-N) synchronization for the transmission of their frames; in the CSMA / CD operating mode, all the nodes (12-0, ..., 12-N) being able to transmit their frames according to random time intervals; each node (12-0, ..., 12-N) being configured to implement the method according to any one of the preceding claims.

Images