Method of operating linear network

Abstract

A method of operating an arrangement of a plurality of network nodes arranged in a linear configuration includes determining and assigning an explicit and separate rank to each of the plurality of network nodes, each of the network nodes being capable of direct communication with n neighboring network nodes located in any direction of the linear network node arrangement. The ranks are sequentially incremented from one end to the other end of the linear network node arrangement, each of the ranks indicating a location of the respective network node within the linear network. The network nodes are configured to coordinate switching between a first mode of operation and a second mode of operation. The power consumption of the network nodes in the first mode of operation is lower than in the second mode. Messages are transmitted along the linear network node arrangement via the network node in the second mode of operation using an asynchronous, zero signaling, stateless multipath, and multi-hop message routing protocol.

Description

Technical Field

[0001] The present invention relates to operating linear networks and communicating in linear networks, which are networks in which the network nodes connected therein are arranged in series in a row (i.e., extending in one spatial dimension). Aspects of the present invention relate to network discovery, management of active and standby modes, data transfer or messaging, fault detection, and reconfiguration in the event of a fault or change in the network topology. Background Art

[0002] The increasing use of sensors and corresponding data analysis in all technical and business fields has led to a need to access sensor data. Local data storage in sensor nodes requires physically "visiting" the sensor nodes to access and extract data, which can be cumbersome, costly, or generally impractical.

[0003] Accordingly, an increasing number of sensor nodes are equipped with a communication interface that provides access to a communication network. Such "connected sensors" can transmit sensor data at regular intervals or in response to corresponding requests. The sensors can be connected via wired and / or wireless communication technologies. In many applications, wireless communication may be preferred.

[0004] Depending on the respective deployment of the sensor nodes, the communication network may not be a more common type such as GSM, UMTS, LTE, WiFi, etc., in which any node can access a base station and the base station relays data to a data receiver via a backbone network under the control of a network management service or vice versa. Instead, a common type of communication network may not be available at all, and data may need to be transmitted from one node to the next, with each node relaying the data until the data finally reaches the data receiver.

[0005] A particular type of network is a linear network, in which all nodes are arranged in a row in a linear arrangement and each node has a direct communication link only with a limited number of adjacent nodes, for example due to the limited range of wireless communication or due to the way the wired connections are arranged.

[0006] Examples of such linear networks can be found, for example, in the oil and gas industry, where the transportation of fluids is typically carried out using multiple hose segments that are connected to form longer hoses, especially in underwater environments. For example, the transfer of crude oil from an offshore oil tanker to an onshore refinery is carried out using hoses deployed underwater. In these environments, the hoses are subject to adverse conditions that may trigger phenomena such as fluid leakage. This requires periodic hose monitoring, which is preferably performed by sensors arranged on the hoses. Sensors attached to hose segments can be used to monitor the integrity of the hose segments and the connections. Since wireless communication in seawater is limited in range, sensor nodes need to communicate via a wired network (which hinders the flexible arrangement of hose segments as needed) or via a short-range multi-hop wireless network.

[0007] In multi-hop communication, in order to transfer a message from one end of a linear arrangement to the other end, or from any node within a series arrangement to one or more other nodes, a message transmitted from one node is received by adjacent nodes within the wireless range and will have to be forwarded along the linear arrangement towards the intended recipient. Thus, in multi-hop communication, the message "hops" through multiple intermediate network nodes before it reaches the intended message recipient.

[0008] Ideally, in multi-hop communication, each node knows the arrangement of all nodes within the linear network node arrangement, in which case only those nodes located between the transmitter and the receiver need to forward the message, thus saving energy in the other nodes. However, typically, nodes may not initially know at which position within the linear network node arrangement they are located, and further, the nodes may not be statically arranged in the linear arrangement. Instead, the arrangement of the nodes may change more or less dynamically without notice. Regarding the example of a hose formed by connected hose segments, one or more network nodes can be attached to or arranged on the hose segments, and the arrangement and / or orientation of these hose segments may change depending on the use. Further, the movement of the hose segments caused by waves, etc. may temporarily bring different network nodes within the wireless range, thus actually changing the arrangement of the network nodes within the linear network node arrangement. Summary of the Invention

[0009] Accordingly, there is a need for a discovery protocol that not only discovers the presence of nodes but also discovers their positions within a linear arrangement, and thereby provides greater flexibility when nodes are arranged in a linear network node arrangement or when the arrangement of network nodes changes over time. Additionally, there is a need for a protocol that manages the messaging of nodes along a linear network node arrangement. Further, it is generally desirable to control the power or operating state of nodes to achieve enhanced energy efficiency. Yet further, there is a need to detect network nodes that fail to participate in messaging.

[0010] The methods and apparatuses detailed in the independent claims address the above needs. Advantageous embodiments and developments of the methods and apparatuses are provided in the corresponding dependent claims.

[0011] In the context of this specification, a communication connection can be wired or wireless, unless explicitly stated or obvious from the corresponding context. Wireless communication can include acoustic and electromagnetic waves, where electromagnetic waves can be subdivided into optical communication, radio frequency electromagnetic communication, and magnetic induction communication. A linear network or topology is defined herein as a network in which each device or node is arranged one after another in a sequential chain. It is assumed that communication can flow in both directions along a linear network node arrangement and that each node can communicate directly with the n nearest neighbors in each direction (where n > 1), but no node can communicate directly with all other nodes (this is due, for example, to the limited range of a wireless transmitter or to the arrangement of wired connections). The limited range of wireless communication can be caused by power limitations for legal or regulatory reasons or for energy conservation, or due to environmental effects (e.g., underwater or in other environments that have high attenuation for wireless signals or exhibit noise that limits the range of wireless communication). Communication between nodes in a linear network node arrangement thus uses multi-hop to permit communication between all nodes. In multi-hop communication, a transmitter emits a message to one or more other nodes, and each node forwards the message until the message finally reaches the intended target or recipient. Communication can thus include transmission and reception, although not necessarily simultaneously.

[0012] According to a first aspect of the present invention, there is presented a method of operating an arrangement of a plurality of network nodes initially randomly arranged in a linear configuration. Each of the nodes is configured to or capable of directly communicating with n adjacent network nodes in either direction along the linear network node arrangement / alignment, for example via a wireless connection with a limited range or via any other type of connection (e.g., cable). However, no network node can directly communicate with every other network node in the linear network node arrangement. There will always be network nodes that are outside the direct communication range of the transmitting node, i.e., those network nodes that typically will be located further away from the transmitting node than the nth network node. In this context, randomly arranged means that at least initially, the network nodes do not know in advance their respective positions in the linear network node arrangement, nor do they know their neighbors within the direct communication range. The method includes determining and assigning to each network node in the plurality of network nodes a distinct and individual rank. The rank of each network node includes a primary rank, and at least one network node has a secondary rank. The ranks increasing sequentially from one end of the linear network node arrangement to the other indicate the position of the corresponding network node within the linear network node arrangement and relative to its adjacent nodes within the direct communication range. The method further includes configuring the plurality of network nodes to coordinate switching between a first operating mode and a second operating mode. The power consumption of the network nodes is lower in the first operating mode than in the second operating mode, for example, by turning off components such as transceivers when in the first operating mode. The method further includes: transmitting messages between the network nodes in the linear network node arrangement via network nodes in the second operating mode using an asynchronous or non - synchronous, zero - signaling, stateless multi - path and multi - hop message routing protocol. Coordinating the switching between the first operating mode and the second operating mode may include: switching all network nodes to the first or second operating mode such that at least for a specific period of time, all network nodes are in the second operating mode simultaneously; or switching selected network nodes among the network nodes to the first or second operating mode in such a way that network nodes within the direct communication range of the transmitting network node and in the propagation direction of a message forwarded through a chain of adjacent network nodes are in the second operating mode. The propagation direction may also be considered as the direction of information flow.

[0013] In one or more embodiments of the method, determining and assigning a distinct individual rank to each of a plurality of network nodes includes a first network node located at a first end of a linear network node arrangement assuming a first master rank, e.g., 0. The network nodes may operate in this manner in response to a command or initiation message received from a convergence node communicatively connected to the end at which the first node of the linear network node arrangement is located in such a way that the command is received only by the first node, e.g., via an electrical or optical wired connection or via a narrow beam wireless connection. The first network node broadcasts a pilot message into the linear network node arrangement to announce the master rank it has assumed to those network nodes within direct communication range. After a first power-up and when distinct ranks / tiers have not yet been determined and assigned, all nodes of the linear network node arrangement are in a second operating mode, i.e., ready to receive and transmit messages, and will remain in the second operating mode until a command is received in response to which the nodes switch to the first operating mode. For up to n adjacent network nodes that receive the pilot message transmitted by the first network node within the direct communication range of the first network node, the pilot message is a respective first pilot message. Other network nodes outside the wireless range will continue to wait to receive their respective first pilot messages. In response to receiving the respective first pilot message, each network node assumes a master rank that is incremented by 1 above the master rank received in the first pilot message, and the network node itself broadcasts a pilot message to announce the master rank it has respectively assumed. The pilot message broadcast by a network node in response to receiving the respective first pilot message is again received by up to n adjacent network nodes within the direct communication range of the respective network node that transmitted the pilot message, and may represent a first pilot message to one or more of those adjacent network nodes. The process is repeated along the linear network node arrangement until the pilot message reaches the last node at the opposite end of the linear network node arrangement, which last node is also referred to as a leaf node. Eventually, each of the network nodes in the linear network node arrangement will receive a first pilot message announcing the master rank at some point in time. When each network node re-broadcasts its own pilot message, each of the network nodes in the linear network node arrangement will also receive additional pilot messages, i.e., pilot messages received after the first pilot message has been received. Up to 2*n network nodes may receive a pilot message from a transmitting network node. However, it is readily apparent that if a network node does not have n adjacent network nodes on either side, the number of network nodes receiving the broadcast is less than 2*n. Each network node may receive up to 2*n - 1 additional pilot messages, i.e., pilot messages after the first pilot message has been received, and each network node will store the master ranks received in these additional pilot messages.After having received the pilot messages from at least n adjacent network nodes and / or when a predetermined timeout period started in response to the reception of the first pilot message expires, each network node calculates its secondary rank from the received and stored primary ranks.

[0014] During the determination and assignment phase, multiple network nodes may assume the same primary rank because multiple network nodes may receive the same pilot message from the same upstream node in a linear arrangement, and any intermediate node will only announce its rank after it has incremented the primary rank. The time taken to increment the primary rank and broadcast it in an intermediate node is longer than the time required for the signal from the upstream node to reach the second next node. Thus, the second next node will increment its rank based on the first pilot message received from the upstream node in the linear arrangement rather than based on the subsequently received pilot message from the intermediate node. Then, both the intermediate node and the second next node will broadcast pilot messages announcing the same rank they have assumed. However, to allow for proper communication, it is necessary to distinguish all nodes and know exactly their relative positions within the linear arrangement. Although the fact that signals are transmitted via direct communication connections reaching more than one network node has led to double assignments, this nature of the communication connections can also be used to resolve double assignments. The transmitted signal can be received by two network nodes in either direction (i.e., upstream or downstream) of the linear arrangement, for example due to attenuation of the wireless signal, due to a particular arrangement or connection of the transmitter and receiver, or for other reasons, and given that no two nodes will be in exactly the same location or position within the linear arrangement, each node will receive at least one pilot message from nodes that announce different primary ranks (higher or lower primary ranks) within the linear arrangement. Considering the primary ranks broadcast by their respective adjacent network nodes, the nodes can now ascertain whether they are closer or farther from the first node than another node that has broadcast the same primary rank. Throughout this specification, upstream may refer to the direction from which a message is received in a linear network node arrangement, the message being intended to propagate down the linear network node arrangement. Accordingly, downstream may refer to the direction in the linear network node arrangement in which the network node has not yet received a message.

[0015] To resolve incorrect double assignments, the primary rank can be supplemented by a secondary rank. If a node has received pilot messages from two neighbors that announce a primary rank lower than its own rank, then the node is closer to the first node than another node that has assumed the same rank and thus assumes a secondary rank of 1. Otherwise, if a node has received pilot messages from two neighbors that announce a higher primary rank, then the node is farther from the first node and assumes a secondary rank of 2. In the case where a node does not have two neighbors that announce the same rank (which may occur, for example, at the ends of the linear arrangement), the node will default to assuming a secondary rank of 2, unless the node is a neighbor of a node with a primary rank of 0, in which case the node will instead assume a secondary rank of 1.

[0016] The network node can transmit a unique static identifier (e.g., MAC address, etc.) along with the bootstrap message, thereby allowing, for example, the identification of bootstrap messages that may be repeatedly transmitted by the same network node, and these bootstrap messages can be ignored.

[0017] In one or more embodiments of the method, each network node waits for a backoff time randomly selected from the backoff time interval before broadcasting its own bootstrap message. This can help avoid conflicts between the relayed bootstrap messages from two network nodes that have already received their first bootstrap message.

[0018] In one or more embodiments of the method, as the master rank increases, the lower limit of the backoff time interval starts to increase from the initial lower limit, while keeping the length of the backoff time interval constant or also increasing the backoff time interval. This can help ensure that the bootstrap messages from all network nodes are correctly received before calculating the secondary rank, and thus avoid incorrect calculation of the secondary rank in network nodes that are farther away from the first node in a linear network node arrangement. The time that expires before a network node can send its own bootstrap message can be equal to the corresponding backoff time selected from the backoff time interval plus the processing time required to assume the master rank in the corresponding node.

[0019] The predetermined timeout period that needs to expire before a network node calculates its secondary rank can be calculated as twice the number n of adjacent nodes within the direct communication range multiplied by the maximum value of the corresponding backoff time interval. However, the predetermined timeout period can also be configured by a corresponding value broadcast in the bootstrap message.

[0020] In one or more embodiments of the method, each network node repeatedly broadcasts its own bootstrap message y times, where y≥0 is preset at deployment in all network nodes, and any repetition occurs only after the expiration of the bootstrap time period T b The repeated broadcast of the bootstrap message can enhance the resilience of the process, thereby compensating for lost messages. The number of repetitions can be set, for example, according to the expected perturbation of the communication or the error rate of the communication channel. The bootstrap time period T b is preferably selected to be long enough to ensure that the repeated bootstrap messages do not interfere with the previously sent bootstrap messages at any point within the corresponding direct communication range. For example, the bootstrap time period T bIt can be not less than 2*n + 1 times the initial upper limit of the initial backoff time plus a non-zero safety margin in the case where the lower limit of the backoff time interval increases with the increase of the master rank. Waiting for the expiration of the boot time period before repeating the broadcast of the boot message ensures that the network node at the farthest end of the direct communication range of the transmitting network node does not receive a duplicate boot message before all downstream network nodes in the linear network node arrangement have broadcast their boot messages. The number of repetitions y can be preset before arranging the network nodes in the linear network node arrangement, or can be transmitted to the network nodes in the boot message or a later message.

[0021] In one or more embodiments of the method, a network node that only receives a boot message (including the first boot message) announcing a master rank lower than its own adopted master rank will broadcast a boot completion message after the expiration of the boot time period T in the last repetition of the y repetitions. b The network node located at the end of the linear network node arrangement opposite to the aggregation node can be referred to as a leaf node. Similar to the boot message, the boot completion message will be received by at most n network nodes in the propagation direction of the message, and each network node will broadcast the boot message after the expiration of the backoff time determined as further described above. The boot completion message will propagate along the linear network node arrangement in the opposite direction to the boot message until it finally reaches the first network node and is ultimately transmitted to the aggregation node and / or the central or control node.

[0022] If the leaf node does not receive any additional message within a predetermined time period after initially broadcasting the boot completion message, the leaf node can repeat the broadcast of the boot completion message. The additional message can be, for example, a command to place the network node in the first operating mode.

[0023] At this time, the linear network node arrangement is fully configured and sorted, that is, each of the nodes has determined its rank, and each node knows at least the ranks of the adjacent nodes that can communicate directly with it (that is, the nodes within the direct communication range, preferably all the nodes in the linear network node arrangement). The rank of the node allows for the explicit positioning of each network node within or along the linear network node arrangement or at least relative to its adjacent nodes within the direct communication range. Any defective intermediate network node can be identified by analyzing the ordered sequence of the master rank and the secondary rank of the nodes, which will appear different from the normal ordered sequence in the case where an intermediate node does not broadcast a boot message.

[0024] Messages can now be exchanged between individual nodes or broadcast along the entire linear network node arrangement. To allow for proper transmission of messages over multiple hops and to prevent access conflicts on the shared communication medium, and further to ensure that each node can transmit a message during the communication period, the nodes use an ordered access in which the nodes are permitted to transmit according to their relative positions along the linear node arrangement. According to the invention, all messages are transmitted respectively by broadcast and retransmission through the nodes along the linear network node arrangement, and even though the direct communication range may cover multiple nodes in either direction, it may be preferred to retransmit the message without skipping intermediate nodes, especially for redundancy reasons.

[0025] Accordingly, a method for transmitting messages between nodes arranged in a hierarchical network node arrangement, such as nodes sorted according to an embodiment of the method described above (the nodes being configured to communicate directly with two or more adjacent nodes in either direction of the hierarchical network node arrangement), includes: broadcasting a first message by a source node having a first rank, wherein the first message includes the rank of the source node and the rank of a first destination node. If the rank of the first destination node is two or more higher than the rank of the source node, all intermediate nodes whose respective ranks are higher than the rank of the source node and lower than the rank of the first destination node retransmit the message in ascending order of their ranks and starting from the intermediate node whose rank is one higher than the rank of the source node. If the rank of the destination node is two or more lower than the rank of the source node, all intermediate nodes whose ranks are lower than the rank of the source node and higher than the rank of the first destination node retransmit the message in descending order of their ranks and starting from the intermediate node whose rank is one lower than the rank of the source node. It is obvious that if the destination node is the next adjacent network node, retransmission by other network nodes is unnecessary. The first message will be received by the first destination node at least when a first intermediate node within the direct communication range of the first destination node has retransmitted the message. However, all remaining intermediate nodes will repeat the retransmission.

[0026] According to one or more embodiments of the method for transmitting messages, although an intermediate node has received the first message from a node whose rank is respectively at least two higher or lower than its own rank, the intermediate node retransmits the first message only after having received a retransmission of the first message from a node having a rank respectively one higher or lower, or after not having received a retransmission from a node having a rank respectively one higher or lower within a predetermined period of time. To this end, each intermediate node adds an explicit identifier (such as its own rank) to the first message before retransmission, which explicit identifier identifies the corresponding node and thus the position of the corresponding node within the linear network node arrangement or relative to its adjacent network nodes, and allows other nodes to determine whether and when it is their turn to retransmit.

[0027] According to one or more embodiments of the method for transmitting messages, each intermediate node may append its own data or messages to be propagated in the same propagation direction as the first message before relaying, and if the destination node of the appended message or data is different from that of the first message, the message or data may optionally include the rank or identifier of the corresponding destination node. In this context, the same propagation direction should be understood as being related to the propagation of the first message in the ascending or descending direction along the linear arrangement of network nodes.

[0028] In a special case, the first message is always transmitted by the node at the very end of the linear network node arrangement, and the destination node is always the node at the corresponding opposite end of the linear network node arrangement. In this special case, it is not necessary to provide the source node and the destination node in the message. However, according to the method of the present invention, regardless of whether any node relaying the message adds a message or data, it must still add its own explicit rank or identifier for correct relaying.

[0029] Since each intermediate node always appends or adds its rank or explicit identifier to the message before relaying the message, all nodes receiving the message can ascertain whether and when (if applicable) to relay the message. This can particularly involve analyzing the received message for the rank of the source node, the rank of the destination node, or multiple ranks for multiple destination nodes in the case where additional messages for other destination nodes are propagated together in one message and / or the explicit identifier of the node that has transmitted or relayed the message. Any message or data added by the relaying node can be ignored by nodes other than the corresponding destination node. Network nodes not in the direction of the first destination node can avoid relaying any message. This can occur, for example, when the source node is not at the very end of the linear network node arrangement.

[0030] According to one or more embodiments of the method for transmitting messages, any destination node deletes the message originally destined for it and broadcasts any additional messages destined for (other) destination nodes in the propagation direction of the first message. Even if there are no additional messages to relay and the last destination node is not the network node at the very end of the linear network node arrangement, the last destination node can still forward a general message in the propagation direction of the first message, so that all nodes between the last destination node and the corresponding network node at the end of the linear network node arrangement have the opportunity to transmit their own messages. The general message may carry the rank of the network node at the corresponding end of the linear network node arrangement to correctly maintain the propagation direction of the first message.

[0031] The message may have, for example, a frame structure based on the IEEE 802.15.4 standard format, which was developed with an emphasis on efficient communication in small networks.

[0032] The methods or protocols for transmitting messages presented above do not use acknowledgment messages because acknowledgment messages would have a negative impact on the energy consumption and time required for messages to propagate across a linear network node arrangement. Moreover, any access control signaling is always implicit, which takes advantage of the shared transmission medium and the linear node arrangement. When a message is forwarded through a hierarchical network by broadcasting (i.e., in both directions along the linear arrangement of the nodes that have already broadcast), the protocol and the knowledge of the positions of adjacent network nodes within the direct communication range will ensure that only the nodes located in the communication direction will rebroadcast the message. This implicit access control keeps the communication overhead low and also reduces energy consumption because the transmission for signaling is avoided. A direct communication range n of two or greater (i.e., the transmission can reach two or more network nodes in either direction along the linear network node arrangement) together with the fallback option provided in the method for transmitting messages provides multiple possible paths and thus adds resilience to the system using this method.

[0033] Since the broadcast message is received in either direction along the linear network node arrangement, a node that has transmitted or relayed the message can use the relayed message of a respectively upstream or downstream node in the linear network node arrangement as an implicit acknowledgment of receipt. For example, when a message is transmitted from a node with a higher rank to a node with a lower rank, the node with the higher rank listens for the broadcast of the node with the lower rank and can verify the message content without using any explicit acknowledgment or other signaling. If a node fails to relay, the failure can be identified and an error map can be generated. If a node repeatedly fails to relay, the error map can be used for repair, rerouting, etc. Accordingly, a method for locating a fault in a hierarchical network node arrangement (wherein the network nodes of the hierarchical network node arrangement are configured to communicate directly with two or more adjacent nodes in either direction of the linear network node arrangement, but no network node in the hierarchical network node arrangement can communicate directly with all network nodes) includes: sending a topology check message through a network node at one end of the linear network node arrangement. Each node that receives the topology check message relays the topology check message after appending its own topology check message. The relaying by each respective network node is coordinated in the manner further described above, i.e., each network node relays its own composite topology check message only after it has received a topology check message or a composite topology check message from a direct neighbor upstream in the propagation direction in the linear network node arrangement, or after a backoff time interval has expired and it has not received a relay of the topology check message from a direct neighbor upstream in the propagation direction of the topology check message in the linear network node arrangement. All intermediate network nodes in the linear network node arrangement relay the composite topology check message. The network nodes at opposite ends of the linear network node arrangement can analyze the composite topology check message for identifying a broken wireless connection. Any network node whose rank is not shown in the composite topology check message can be considered defective.

[0034] In an exemplary linear network node arrangement of six network nodes ranked from 1 to 6 (where network node 4 is defective), this can be shown as follows. Network node 1 broadcasts a topology check message received by network node 2. Network node 2 relays the topology check message from network node 1 after appending its own topology check message. Network node 3 receives the topology check messages of network nodes 2 and 3, appends its own topology check message, and broadcasts a composite topology check message. Since network node 4 is defective, network node 5 receives the composite topology check messages from network nodes 1, 2, and 3, waits for the backoff time interval to expire, and transmits the topology check messages of the first three network nodes after appending its own topology check message. Network node 6 receives the topology check messages from network nodes 1 to 3 and 5 and can immediately identify network node 4 as defective.

[0035] Since each network node knows its rank and the ranks of the n network nodes within its direct communication range, receives topology check messages from all network nodes within its direct communication range, and relays the topology check messages when its turn comes, it will be possible to identify at most n - 1 broken communication links between network nodes within the direct communication range while still being able to send the topology check messages along the entire linear network node arrangement. If one or more adjacent network nodes upstream in the propagation direction of the topology check message fail to relay the topology check message, the downstream network node in the propagation direction will wait for a predetermined period of time before relaying the topology check message. The topology check message can be sent from one end of the linear network node arrangement to the corresponding opposite end in either direction. It may be advantageous to send the topology check message regularly in both directions (i.e., forward and backward) to check the integrity of the linear network node arrangement. The analysis result of the composite topology check message received by the network node at the opposite end of the linear network node arrangement can be returned to the initiator via a regular message. Alternatively, the last network node that receives the topology check message can simply add another topology check message to the composite topology check message it receives and broadcast the composite topology check message into the linear network node arrangement, where the composite topology check message will only be relayed in the opposite propagation direction, i.e., back to the first network node. Finally, the first network node (i.e., the initiator of the first topology check message) will receive the composite topology check message. In the case where no network node is defective, all intermediate network nodes should appear twice in the composite topology check message. Otherwise, the defective network node will be missing at least once. The returned topology check message can be identified by the intermediate network nodes by analyzing the ranks of the network nodes to which they have attached their own topology check messages.

[0036] When all network nodes receive at most n topology check messages relayed by the downstream network nodes in the propagation direction and know their respective positions in the linear network node arrangement, it will also be possible to detect whether n consecutive network nodes are defective based on the missing relayed topology check messages. In this case, the network node that does not receive the relayed message from one of the at most n downstream network nodes known to be in the propagation direction of the topology check message broadcasts a topology check message error message, which is relayed by all intermediate network nodes between the network node that broadcasts the topology check message error message and the first network node in the propagation direction opposite to the propagation direction of the topology check message. Since the topology check message error message contains the rank of the network node that sends it, the first network node will be able to identify the first defective network node and all defective network nodes within the direct communication range. Obviously, no information can be obtained from the network nodes behind the defective network node.

[0037] After a topology check message has indicated an error, the process of determining and assigning ranks can be repeated. If all intermediate nodes append at least their ranks to the received message before relaying it, other messages transmitted across the linear network node arrangement can also be used for the purpose of topology check messages. This allows the network nodes that ultimately receive the composite message to verify whether the operating mode of each network node has been correctly switched and whether the transceivers of each network node are functioning. When the method of locating faults is repeated at appropriate intervals, the dynamically changing arrangement of the network nodes in the linear network node arrangement can be taken into account. Such a dynamically changing arrangement can occur, for example, in the following items: trains, where the passenger or freight carriages are randomly arranged for each journey; trucks or other land vehicles that temporarily travel along the same route, where the leading vehicle controls the trailing vehicle or at least provides information about the road ahead of the trailing vehicle, which is commonly referred to as platooning; unmanned aerial vehicles or drones that temporarily fly in groups; industrial environments where mobile robots operate in groups; and last but not least, marine applications where coupled hose segments equipped with sensors and communication nodes are in constant motion, which may bring network nodes into direct contact with changing network nodes.

[0038] In a linear network node arrangement where the nodes are battery-powered and not easily accessible to recharge or replace the batteries, and in other applications, energy savings can be an important issue. In particular, the energy used by the transceiver even when it is not actively transmitting but is in a receive-only mode can be significant compared to the energy consumed by other components of the network node. Therefore, at least the transceiver of the network node can be deactivated or powered down when not needed and can be activated or powered up only when needed. It goes without saying that other components of the network node can be deactivated or powered down and activated or powered up separately along with the transceiver.

[0039] When a message propagates along the nodes of a linear network node arrangement by coordinated relaying by the nodes in the propagation direction of the message, the nodes in the power-saving mode must switch to a second operating mode in which messages can be received and transmitted in a coordinated manner before returning to the power-saving mode.

[0040] Accordingly, a method for coordinating the switching of a network node arranged in a fully configured and discovered linear network node arrangement that communicates directly with up to n adjacent network nodes between a first operating mode (wherein at least the transceiver is inactive or powered off, i.e., does not consume or only consumes very little energy while being unable to receive or transmit) and a second operating mode (wherein at least the transceiver is active or powered on, i.e., is able to receive or transmit, but correspondingly consumes more energy than in the first operating mode) includes: broadcasting a duty cycle message (work cycle message) by a first network node of the linear network node arrangement into the linear network node arrangement, wherein the duty cycle message includes at least a wake-up time defining when to switch the network node to the second operating mode; and coordinating the rebroadcasting of the duty cycle message by all network nodes of the linear network node arrangement, for example, according to the method of transmitting messages presented above.

[0041] The first network node itself can receive a command or instruction to broadcast the duty cycle message from a sink node or a central control node, and the duty cycle message can define the wake-up time. The wake-up time can be defined as an absolute time, or as a time period that expires after a triggering event (e.g., after having rebroadcast the duty cycle message and having received a rebroadcast from an adjacent network node further downstream / more downstream in the linear network node arrangement). Here, as throughout the entire specification, in the context of messages transmitted along the linear network node arrangement, the expressions "more downstream" or "more upstream" refer to the direction of message propagation, i.e., "more downstream" can refer to the network node at the position where the message is propagating in the linear network node arrangement, while "more upstream" can refer to the network node at the position from which the message has been received in the linear network node arrangement.

[0042] After having rebroadcast the duty cycle message, the network node can switch to the first operating mode, and the network node will switch to the second operating mode according to the wake-up time received in the duty cycle message.

[0043] If either the first network node or the intermediate network node does not receive a relay of the duty cycle message from one or all of the network nodes that are further downstream in the linear network node arrangement and within the direct communication range after the expiration of a predetermined time period (e.g., at the end of the respective backoff time periods of all network nodes within the direct communication range), either the first network node or the intermediate network node may repeat broadcasting or relaying the duty cycle message. Generally, the time period that expires before repeating the broadcasting or relaying of the duty cycle message should be selected such that it provides sufficient time to receive the relay from the downstream network nodes along the linear network node arrangement while ensuring that the downstream network nodes have not entered the first operating mode. The number of repetitions of the duty cycle message can be selectable according to the communication channel quality, i.e., it can be set higher in the case of a less reliable communication channel exhibiting a higher error rate. A network node may switch to the first operating mode only when the network node has received a relay of the duty cycle message from one or all of the network nodes that are further downstream in the linear network node arrangement and within the direct communication range.

[0044] Alternatively, or in addition to the wake-up time, the duty cycle message may also include a sleep time that defines when the network node is to switch to the first operating mode after having relayed the duty cycle message at least once. Similar to the wake-up time, the sleep time can be an absolute time or a (relative) time based on a triggering event.

[0045] Since the network node at the very end of the linear network node arrangement has known since the boot phase that there are no additional network nodes further downstream in the linear network node arrangement, in order to inform adjacent network nodes that it has received the duty cycle message and, if applicable, according to the sleep time provided in the duty cycle message, this network node may switch to the first operating mode after having relayed the duty cycle message. Alternatively, like any other network node, the network node at the very end of the linear network node arrangement simply needs to switch to the first operating mode after having repeated the relay of its duty cycle message a predetermined number of times and without having received a relay from a network node further downstream in the linear network node arrangement (which, quite obviously, does not exist for the network node at the very end of the linear network node arrangement).

[0046] In one or more embodiments, if the network node itself has received a relay of the duty cycle message from one or all of the network nodes that are further downstream in the linear network node arrangement and within the direct communication range at the end of the respective backoff time period, the network node may switch to the first operating mode only after having broadcast or relayed the duty cycle message.

[0047] The duty cycle message may also include the duration of the active period after waking up, as specified in the wake-up time, before returning to the first operating mode, during which the network nodes are in the second operating mode. Alternatively, the network nodes may remain in the second operating mode after waking up until they receive another duty cycle message indicating a new wake-up time.

[0048] The duration of the wake-up time, sleep time, and / or active period may be the same for all network nodes, i.e., all network nodes are in the same operating mode simultaneously. Alternatively, the duration of the wake-up time, sleep time, and / or active period may be adjusted according to the corresponding positions of the network nodes in the linear network node arrangement and the propagation direction of the message, in order to ensure that the corresponding network nodes are in the second operating mode long enough to receive the message and transmit a response (if applicable). The adjustment may take into account the time required for the transmission itself (which may be significant in direct communication with a low data rate), and may also take into account the processing time in the corresponding network nodes. Further, the adjustment may take into account that intermediate network nodes may add their own messages to the corresponding received messages, which will result in an increase in the amount of data that must be transmitted as the message is passed through the network nodes of the linear network node arrangement. Different wake-up times across the linear network node arrangement may be considered as a "sliding window" during which the network nodes within the sliding window are in the second operating mode, and the window slides along the linear network node arrangement together with the transmitted message.

[0049] The first duty cycle message is preferably transmitted immediately after the linear network node arrangement is fully configured and discovered and all nodes know their corresponding ranks. In the case where no duty cycle message or different types of messages are received at the leaf node within a predetermined period after the leaf node has transmitted the boot completion message, the leaf node will retransmit the boot completion message.

[0050] The method of transmitting messages presented above achieves an elastic and fast transmission of information along the linear network node arrangement, while reducing the possibility of collision transmissions that may occur in the shared communication medium. Compared with the protocol using time slots, where all network nodes need to maintain a very accurate clock, the coordinated switching between the first operating mode and the second operating mode and asynchronous communication can be more energy-efficient, especially in a linear network node arrangement where messages are transmitted sparsely and / or at irregular time intervals. Moreover, the arbitrarily set duration and frequency of switching to the second operating mode (during which messages can be transmitted and received) bring great flexibility for multiple use cases. The automatic discovery of the arrangement of network nodes within the linear network node arrangement eliminates the need to always arrange the network nodes in a predetermined order or manually program a specific arrangement order into each network node.

[0051] In the case where a network node fails to retransmit due to a fault, messages will still be passed across the linear network node arrangement regardless of whether an adjacent transmitting node is not working or the message is not received at the node and thus cannot be retransmitted. In such a case, the linear network node arrangement will continue to operate as defined by the duty cycle message. If a node is not working, its message will simply not be part of the aggregated message transmitted across the linear network node arrangement. On the other hand, if the message fails to reach an intermediate network node, the message should be received by another neighbor within the communication range. Description of the Drawings

[0052] In the following sections, the present invention will be described with reference to the drawings, in which:

[0053] Figure 1 A simplified flowchart showing an exemplary method of operating an arrangement of a plurality of network nodes randomly arranged in a linear network node arrangement is shown.

[0054] Figure 2 An exemplary schematic linear network node arrangement during various stages of determining and assigning ranks in accordance with the present invention is shown.

[0055] Figure 3 A first message flow diagram between network nodes during various stages of determining and assigning ranks is shown.

[0056] Figure 4 A graphical flowchart showing an exemplary method of determining and assigning a distinct individual rank to each of a plurality of network nodes in a linear network node arrangement is shown.

[0057] Figure 5 A second message flow diagram between network nodes during various stages of determining and assigning ranks is shown.

[0058] Figure 6 An example of a message propagating from one end of a linear network node arrangement to the opposite end is shown.

[0059] Figure 7 A part of a first exemplary message flow for switching a network node to a first operating mode according to a duty cycle message is shown.

[0060] Figure 8 A part of a second exemplary message flow for switching a network node to a first operating mode according to a duty cycle message is shown.

[0061] Figure 9 A schematic and exemplary arrangement of network nodes along a hose pipeline composed of coupled hose segments is shown.

[0062] Figure 10Shows a schematic and exemplary flowchart of a method for locating a fault in a linear network node arrangement operating according to the present invention, and

[0063] Figure 11 shows a simplified block diagram of a network node according to the present invention.

[0064] In the drawings, the same or similar elements may be referred to by the same reference numerals. Detailed Description

[0065] Figure 1 Shows a simplified flowchart of an exemplary method 100 for operating an arrangement of a plurality of network nodes A to F randomly arranged in a linear network node arrangement, where the network nodes are configured to communicate directly with n adjacent network nodes but not with all network nodes of the linear network node arrangement. In step 101, the network nodes of the linear network node arrangement are powered on and default to a second operating mode in which the transceivers of the network nodes are powered and operational. In step 110, a distinct and individual rank is determined and assigned to each of the plurality of network nodes. In step 120, the plurality of network nodes are configured to coordinate switching between the second operating mode and a first operating mode in which the power consumption of the network nodes is lower than in the first operating mode, for example, by turning off components such as transceivers that may consume a large amount of power. In step 130, it is determined whether the network node is in the second operating mode. If not, the "no" branch of step 130, the method may return to step 120 or simply wait until the network node is in the second operating mode. If the network node is in the second operating mode, the "yes" branch of step 130, the method continues with step 140 in which messages are transmitted between the network nodes of the linear network node arrangement.

[0066] Figure 2 Shows an exemplary schematic linear arrangement of network nodes A to E during the respective stages of determining and assigning a primary rank R and a secondary rank r according to the present invention. Each of the nodes may have a unique identifier, for example, a MAC address, etc., but no node knows any of its neighbors, nor its position within the linear network node arrangement, or the primary rank R and the secondary rank r. Once all nodes are powered on, they will default to the listening mode. When the first node located at the end of the linear network node arrangement receives a corresponding signal from the aggregation node, for example, via a wired communication connection or a communication connection that generally only reaches the first node, the determination and assignment of ranks may begin. This first node takes the primary rank R as 0.

[0067] In Figure 2In a), node A has taken the main rank R as 0 and broadcasts a bootstrap message announcing its rank. In this figure, the announced rank is indicated by an exclamation mark. According to the method of the present invention, unlike all other nodes, the first node does not have or require a secondary rank r. The sectors extending from node A to both sides in the long dashes indicate the range of direct communication connections. The signal range can cover the full radius around the node, but obviously this is irrelevant in a linear node arrangement. In this example, the range of the direct communication connection reaches up to two adjacent nodes at most, namely, nodes B and C.

[0068] In response to receiving the bootstrap message from node A, network nodes B and C take a main rank R that is 1 higher than the main rank of node A. In this example, both nodes B and C take the main rank R as 1. Nodes D and E have not received the bootstrap message from any node and remain in the listening mode.

[0069] Both node B and node C broadcast their respective bootstrap messages to announce their own rank R in response to having taken their main rank R as 1, as Figure 2 shown in b). To prevent two nodes from broadcasting their bootstrap messages simultaneously, each node waits for a backoff time randomly selected from a backoff time interval before broadcasting its bootstrap message. Whenever the shared communication channel is occupied, for example, according to the CSMA / CA mechanism, other nodes within the direct communication range will not transmit. The respective ranges of the direct communication starting from node B and node C are indicated by the dashed sectors and the double-dashed sectors respectively. The bootstrap message from node B will be received by nodes A, C, and D. The bootstrap message from node C will be received by nodes A, B, D, and E.

[0070] Nodes D and E that receive their respective first bootstrap messages will take a main rank R that is 1 higher than the main rank R announced in the received first bootstrap message. In this example, both nodes D and E take the main rank R as 2.

[0071] Similar to the previous nodes B and C, nodes D and E announce the main rank they have taken by transmitting their own bootstrap messages in response to having taken their main rank R as 2, as Figure 2 shown in c). The respective ranges of the direct communication starting from node D and node E are indicated by the dashed sectors and the solid sectors respectively. The bootstrap message from node D will be received by nodes B, C, and E and one node further downstream in the row (if any). The bootstrap message from node E will be received by nodes C and D and one or two nodes further downstream in the row (if any).

[0072] Figure 2 a) to Figure 2 The process shown in c) will continue until the last node in the row has transmitted its own bootstrap message.

[0073] Figure 3 shows a first message flow diagram among network nodes during various stages of determining and assigning rank R_r. In this diagram, six nodes A to F are arranged in a linear network node arrangement. The behavior of the nodes is the same as that of Figure 2 the nodes. The process of determining and assigning rank R_r starts after the first node (here node A) has received the corresponding signal. The corresponding time points at which the nodes transmit pilot messages are indicated by dashed double circles.

[0074] At T1, node A transmits in the corresponding pilot message that its taken primary rank R is 0, which is received by nodes B and C. Nodes B and C accordingly take primary rank R as 1.

[0075] At T2, node B transmits that its taken primary rank R is 1, which is received by nodes A, C, and D. Although node C has taken rank R as 1 in response to the pilot message from node A and only records the rank received in this second pilot message, this pilot message is the first pilot message for node D (which has not been ranked yet). Therefore, node D increments the primary rank R received in the "first" pilot message to 2 and takes this primary rank.

[0076] At T3, node C also transmits in the corresponding pilot message that its taken primary rank R is 1. This pilot message will be received by nodes A, B, D, and E. Similarly, only one node (node E) has not been ranked and receives its "first" pilot message, and the first primary rank R it receives is 1. Therefore, like the previous node D, node E also increments the primary rank R received in the "first" pilot message to 2 and takes this primary rank.

[0077] Then, at T4, node D relays the pilot message to announce that its primary rank R is 2, which will be received by its neighbors B, C, E, and F. Node F has not been ranked yet, and this pilot message is the first pilot message for node F. Therefore, node F increments the primary rank R received in the pilot message, which is 2, to 3 and takes 3 as its own primary rank.

[0078] At T5, node E relays the pilot message, also announcing that its primary rank R is 2, which will be received by its neighbors C, D, and F.

[0079] Finally, at T6, node F relays the pilot message to announce that its primary rank R is 3, which will be received by its neighbors D and E. Generally, this process continues until the last node in the row has received the pilot message, taken a rank, and broadcast its own pilot message.

[0080] It should be noted that the transmission order of the corresponding beacon messages depends on the backoff time randomly selected by each node from the backoff time interval. For better understanding, the nodes in the figure are shown to transmit in alphabetical order.

[0081] As further indicated above, each network node requires a distinct rank for proper addressing and message passing. This can be achieved by determining a secondary rank r from all the beacon messages received during this stage of operating a linear network node arrangement. To this end, all nodes that have previously taken their respective primary ranks in response to the first received beacon message will record the ranks received in subsequently received beacon messages or additional beacon messages for determining the corresponding secondary rank r.

[0082] Each node can calculate its secondary rank r from the received primary rank R after it has received beacon messages from at least n adjacent nodes and / or when a predetermined maximum timeout period starting in response to the reception of the first beacon message expires. The following table shows the neighbor list of each node at each given moment as obtained from the message flow shown in Figure 2 At T10, all nodes have safely and deterministically completed the rebroadcast of the beacon messages and can now calculate their respective secondary ranks r.

[0083]

[0084]

[0085] This table should be interpreted as follows: At T3, node C is the sender and announces a primary rank R of 1, indicated by the exclamation mark. Also, at T3, node A has received two beacon messages, one from node B at T2 and one from node C at T3, both announcing a primary rank of 1, and node B has also received two beacon messages, one from node A announcing a primary rank R of 0 and one from node C announcing a primary rank R of 1. The reception is indicated by the ranks in parentheses. Node D had previously received a beacon message at T2 and had taken a primary rank R of 2 and now records the received primary rank R of 1 transmitted from node C. Node E has received its first beacon message to announce a primary rank R of 1 and thus takes a primary rank R of 2, indicated by the arrow. Node F has not received a beacon message and thus has not yet taken a primary rank R (- / -).

[0086] As described above, at T10, all nodes have safely and deterministically received all beacon messages within the wireless range and have transmitted their own beacon messages. Node A has a primary rank R of 0 by definition and does not have a secondary rank r and thus does not need to calculate.

[0087] Assume that the direct communication range n = 2, i.e., two (2) nodes on either side of the transmitting node can receive the transmission. Now, a secondary rank r of 1 or 2 can be assigned to the nodes according to the following set of rules:

[0088] For all nodes that receive 2n (in this example, four (4)) pilot messages, since the nodes that receive more pilot messages indicate a primary rank R lower than their own rank, the secondary rank r is set to 1. For all nodes that receive 2n pilot messages, since the nodes that receive more pilot messages indicate a primary rank R higher than their own rank, the secondary rank r is set to 2. Pilot messages that announce the same primary rank R can be ignored.

[0089] The nodes located at the respective ends of the linear network node arrangement will receive n to 2n - 1 pilot messages.

[0090] Among these nodes, except for the node with a primary rank R of 0 (for which the secondary rank r does not exist or is irrelevant), a secondary rank r of 1 is assigned to all nodes that receive n pilot messages.

[0091] A secondary rank r of 2 is assigned to all nodes that receive 2n - 1 pilot messages, unless a primary rank R of 0 is received, in which case a secondary rank r of 1 is assigned.

[0092] Although the rules for nodes that receive 2n pilot messages should remain valid for all symmetric direct communication ranges, similar rules for the ends of the linear network node arrangement as presented above can apply to direct communication ranges n greater than 2.

[0093] It should be reminded that each node does not know which other nodes within the direct communication range are on which side of the linear network node arrangement. They only know the primary rank R of the corresponding nodes as received through the respective pilot messages. For this example, this results in the following secondary ranks r being assigned to the nodes:

[0094] Node B has received 3 pilot messages, one of which announces a primary rank R of 0. Accordingly, node B assumes a secondary rank r of 1.

[0095] Node C has received 2n pilot messages and the general rule applies. Since there are more pilot messages that announce a higher primary rank R than those that announce a lower primary rank R, a secondary rank r of 2 is assigned to node C.

[0096] Node D has also received 2n pilot messages and the general rule applies. Since there are more pilot messages that announce a lower primary rank R than those that announce a higher primary rank R, a secondary rank r of 1 is assigned to node D.

[0097] Like node B, node E has received 3 pilot messages, i.e., 2n - 1, and the special rule applies. Since the primary rank R of 0 has not been received in any of the pilot messages, the secondary rank r of 2 is assigned to node E.

[0098] Node F has received 2 pilot messages, i.e., n, and the special rule for this case applies. Since the primary rank R of 0 has not been received in any of the pilot messages, the secondary rank r of 1 is assigned to node F.

[0099] Nodes can be configured to repeat the transmission of their pilot messages y times after waiting for a predetermined pilot interval T bi so as to make the pilot process more tolerant to lost pilot messages. m is configurable and will depend in particular on the bit error rate associated with the communication channel.

[0100] After the last repetition, i.e., after y*T bi seconds, each node should have received all the pilot messages required to calculate its primary rank R and secondary rank r and should know the positions of these nodes relative to their neighbors. The absolute position of a node can be determined by passing the corresponding discovery message through a linear network node arrangement, which can be addressed using the primary rank R and secondary rank r, and where each node appends a unique and unambiguous identifier to the message it receives before forwarding the message. The network node at the very end of the linear network node arrangement can return the discovery message to the opposite end, and all intermediate network nodes can store a copy of the map of the linear network node arrangement thus created. Alternatively, nodes can use the corresponding calculation rules to determine their absolute positions. An exemplary calculation rule for n = 2 can be as follows:

[0101] Rank (absolute) = 2*(R - 1)+r

[0102] A node that has received pilot messages from only n other nodes, none of which announce a primary rank R of 0, is the node at the very far end of the linear network node arrangement. This node, which can be called a leaf node (which will also only receive pilot messages announcing a primary rank lower than the primary rank it has adopted itself), will confirm the end of the pilot process by sending a pilot completion message back to the other end of the linear network node arrangement (in the above example back to node A) and from there to the aggregation node and / or the central control node that controls the communication on the final linear network node arrangement.

[0103] Figure 4A graphical flow chart showing an exemplary method for determining and assigning a distinct individual rank to each of a plurality of network nodes arranged in a linear network node arrangement. The method starts at step 1102 after the network nodes are powered on and in a second operating mode, in which the first network node located at the first end of the linear network node arrangement assumes a first master rank. In step 1104, the first network node broadcasts a bootstrap message into the linear network node arrangement to announce its master rank. In step 1106, the network nodes within the communication range of the broadcasting network node receive the bootstrap message. In step 1107, the network nodes check whether the received bootstrap message is the first bootstrap message, and in the affirmative case (the "yes" branch of step 1107), in step 1108, assume a master rank that is incremented by 1 above the master rank received in the corresponding first bootstrap message. In step 1110, after optionally waiting a randomly selected backoff time in step 1109, the network nodes that have received their first bootstrap message and assumed their corresponding master ranks broadcast their newly assumed master ranks into the linear network node arrangement. If the bootstrap message received in step 1106 is not the first bootstrap message for the corresponding network node, the "no" branch of step 1107, the method continues at step 1112. In step 1112, each network node checks whether it has received bootstrap messages from at least n adjacent network nodes and / or whether a predetermined timeout period that started after receiving the first bootstrap message has expired. If not, the method returns to step 1106, in which the network node waits to receive additional bootstrap messages. If the conditions of step 1112 are met, the "yes" branch of step 1112, the network node calculates its secondary rank r from the received master rank R in step 1114.

[0104] Figure 5 A message flow diagram between network nodes after the bootstrap message has been repeated y times and has been received by all nodes and after all nodes have determined their ranks or their positions within the linear network node arrangement. At T1, node F broadcasts a bootstrap completion message that will be received by nodes E and D. Since each node knows its position within the linear network node arrangement or at least relative to its neighbors within the wireless range so far, even if node D receives the bootstrap completion message almost simultaneously with node E, node D will wait for node E to relay the bootstrap completion message. Only after node D has received the bootstrap completion message from node E or after a timeout has occurred will node D relay the bootstrap completion message. The bootstrap completion message is relayed upwards by the other nodes accordingly until the bootstrap completion message has been received by node A representing the opposite end of the linear network node arrangement and finally by the aggregation node connected to node A. To provide some redundancy in case a message is lost, the transmission of the bootstrap completion message can be repeated multiple times, much like the bootstrap message.

[0105] Figure 6 Shows an example of a message propagating from one end of a linear network node arrangement to the opposite end. In this example, a network node of rank 6, which may be located at the very end of the linear network node arrangement, broadcasts a first message that is destined for a network node at the opposite end of the linear network node arrangement. The exemplary message includes a field TYPE that indicates, for example, whether the message is a request, for transmitting data only, or something else. Next, the exemplary message includes a header that particularly includes the rank of the node that initiated the transmission, in this case the network node has a rank of 6. Finally, the exemplary message includes a message content, which in this case is data. The network node 6 broadcasts the message, and the message is received by a network node of rank 5. This network node appends its own header and its message content, and broadcasts the composite message into the linear network node arrangement. The network node of rank 4 receives the message, appends its own header and message content, and broadcasts the composite message. This process is repeated until the message reaches the destination node.

[0106] Each transmission can be received by two or more network nodes in either direction. However, since each network node waits until a node with a higher rank (in this example) has broadcast a composite message, it is possible for a network node to receive duplicate information from its higher-rank neighbor. However, the duplicate portion of the message will be discarded by the network node and not be broadcast. However, if no message is received from an immediately adjacent network node within a predetermined period, for example, because the network node is offline or permanently or temporarily outside the wireless communication range, then instead a message that would otherwise have been discarded as a duplicate message will be broadcast. In this case, the message or data of an intermediate network node that was not broadcast does not form part of the composite message.

[0107] In this example, all nodes send messages of the same message type. If a different type of message is appended, the type can also be appended, for example, between the data field of the previous network node and the rank of the network node that appends the data. Similarly, if the rank of the destination node of the appended message is different from the rank of the destination node of the first message, the rank of the destination node can be indicated, for example, in the header.

[0108] Figure 7Shows a part of a first exemplary message flow for switching a network node to a first operating mode according to a duty cycle message. Assume that the direct communication range n is 2. At T1, network node A broadcasts a duty cycle message received by network nodes B and C. According to the method of transmitting messages in a network node arrangement with hierarchy further described above, network node B will rebroadcast the duty cycle message at T2, and network node C will then rebroadcast the duty cycle message at T3. Network node A will receive the two rebroadcasts and then will switch to the first operating mode at T4. Although the time points T1 to T4 are shown at equal distances, the rebroadcast of the duty cycle message may occur at any time within the backoff time interval, and thus the moments T1 to T3 may vary. If the condition for switching to the first operating mode is receiving rebroadcasts from all network nodes within the direct communication range, T4 may occur immediately after T3. However, if a sleep time is provided in the duty cycle message, the sleep time may be observed as an alternative or supplement to receiving rebroadcasts.

[0109] Figure 8 Shows a part of a second exemplary message flow for switching a network node to a first operating mode according to a duty cycle message. In this example, at T2 (i.e., within the backoff time interval), network node A does not receive a rebroadcast of the duty cycle message from network node B, and thus, at T3, network node A decides that it needs to repeat the broadcast of the duty cycle message. Accordingly, network node A repeats the broadcast of the duty cycle message at T4. At T5, network node A receives a rebroadcast of the duty cycle message from network node B, and may switch to the first operating mode at T6 after also having received a rebroadcast of the duty cycle message from network node C (not shown in the figure).

[0110] Figure 9Shows a schematic and exemplary arrangement of network nodes A to F along a hose line 100 consisting of coupled hose segments 102 to 106. Each hose segment has a network node at each of its two ends, and the network nodes can communicate directly with each other and also with the proximal network node among the network nodes of the correspondingly coupled hose segment. According to the method presented above, it is easy to see how a message can be transmitted from one end of the hose line to the other by forwarding the message from one node in the line to the next node. Compared to skipping every other network node to obtain a smaller number of hops, the shorter physical connections that can be achieved when using all intermediate network nodes may be preferred, for example, to increase the data rate in each individual connection or to reduce errors. Moreover, using each network node to forward messages allows for some automatic resilience, because the role of a network node that fails to forward a message will be automatically assumed by the next network node within direct communication range, without any additional protocol and signaling effort. For example, if a message is transmitted by network node A, the message is received by network nodes B and C. Suppose network node B fails to retransmit the message, then according to the method of transmitting messages presented above, network node C will retransmit the message after a timeout period. A network node that fails to forward a message can be identified by a network node that is further downstream in the propagation direction of the message, and appropriate action can be taken in response.

[0111] Figure 10 Shows a schematic and exemplary flowchart of a method 200 for locating a fault in a linear network node arrangement operating according to the present invention. Method 200 is executed when the network nodes are in a second operating mode that allows messages to be transmitted along the linear network node arrangement. In step 202, a first network node located at one end of the linear network node arrangement broadcasts a topology check message into the linear network node arrangement. All intermediate network nodes append their own topology check messages to the correspondingly received topology check message in step 204 and wait in step 206 until they can retransmit the composite topology check message in step 208, that is, the network nodes check whether they have received a topology check message or a composite topology check message from their direct neighbor network nodes, or whether the backoff period for that network node has expired. Receiving and retransmitting generally follow the same principle as the message transmission presented further above. If the topology check message has reached the network node at the opposite end of the first network node located in the linear network node arrangement, the "yes" branch of step 210, the final network node in the transmission chain analyzes the received composite topology check message in step 212 to find the missing topology check messages. Otherwise, the "no" branch of step 210, retransmission is repeated by the network nodes in the linear network node arrangement that are upstream of the last network node in the linear network node arrangement.

[0112] Figure 11Shows a simplified block diagram of an exemplary network node 500 according to the present invention. The network node 500 includes a microprocessor 502, a volatile memory 504, a non-volatile memory 506, at least one communication interface 508, and a power management component 510 communicatively connected via at least one data connection or bus 512. The non-volatile memory 506 stores computer program instructions that, when executed by the microprocessor 502, cause the network node 500 to at least perform parts of the methods presented previously for determining and assigning ranks, for switching between a first operating mode and a second operating mode, for transmitting messages, and / or for detecting faults.

[0113] List of reference numerals

[0114] 100 Method 1106 Receive bootstrap message

[0115] 101 Power on 1107 Check: Is it the first bootstrap message?

[0116] 110 Determine and assign 1108 Take the received primary rank + 1

[0117] 120 Switch 1109 Wait for backoff time

[0118] 130 Wait for the second operating mode 1110 Broadcast bootstrap message

[0119] 140 Transmit message 1112 Ready to calculate secondary rank?

[0120] 200 Fault detection method 1114 Calculate secondary rank

[0121] 202 First network node broadcasts to A - F network nodes

[0122] Topology check message R primary rank

[0123] 204 Append its own topology check message r secondary rank

[0124] 206 Check: Is transmission allowed?

[0125] 208 Relay

[0126] 210 Reached the end of the linear network node arrangement?

[0127] 212 Analyze composite topology check message

[0128] 500 Network node

[0129] 502 Microprocessor

[0130] 504 Volatile memory

[0131] 506 Non-volatile memory

[0132] 508 Communication Interface

[0133] 510 Power Management

[0134] 512 Bus

[0135] 1102 The first network node assumes the master rank

[0136] 1104 The first network node broadcasts a bootstrap message

Claims

1. A method (100) of operating an arrangement of a plurality of network nodes (A, …, F) arranged in a linear configuration, each of the network nodes (A, …, F) being configured to communicate directly with n adjacent network nodes (A, …, F) located in either direction of the linear network node arrangement, and no network node in the arrangement being able to communicate directly with each of these network nodes, wherein, The method includes: - determining and assigning (110) a distinct and separate rank (R_r) to each of the plurality of network nodes (A, …, F), the rank (R_r) of each network node including a primary rank (R), and at least one network node having a secondary rank (r), wherein the ranks increase sequentially from one end to the other end of the linear network node arrangement, and wherein each rank (R_r) of a network node indicates the position of the corresponding network node (A, …, F) within the linear network node arrangement, - configuring (120) the plurality of network nodes to coordinately switch between a first operating mode and a second operating mode, the power consumption of these network nodes being lower in the first operating mode than in the second operating mode, and - transmitting (140) messages between the network nodes (A, …, F) of the linear network node arrangement via those network nodes (A, …, F) in the second operating mode using an asynchronous or non - synchronous, zero - signaling, stateless multi - path and multi - hop message routing protocol.

2. The method (100) according to claim 1, wherein, Determining and assigning (110) a distinct and separate rank (R_r) to each of the plurality of (P) network nodes includes the following steps: - a first network node (A) located at the first end of the linear network node arrangement assumes (1102) a first primary rank (R = 0), and broadcasts (1104) a pilot message to those network nodes within the direct communication range in the linear network node arrangement to announce the assumed primary rank (R), - each of up to n adjacent nodes (A, B, …, n) on either side of the transmitting network node receives (1106) the first pilot message announcing the primary rank (R) at a certain point in time, assumes (1108) a primary rank (R) that is incremented by 1 above the primary rank (R) received in the first pilot message in response to the received first pilot message, and broadcasts (1110) its own pilot message to announce the correspondingly assumed primary rank (R), wherein each network node is capable of receiving up to 2*n - 1 additional pilot messages, and the network node will store the primary ranks (R) transmitted in these additional pilot messages, - after having received pilot messages from at least n adjacent network nodes, and / or when a predetermined timeout period starting in response to receiving the first pilot message has expired, each network node calculates (1114) its secondary rank (r) from the received and stored primary ranks (R).

3. The method (110) according to claim 2, wherein, Each node waits (1109) for a back - off time randomly selected from a back - off time interval before broadcasting (1110) its own pilot message.

4. The method (110) according to claim 3, further comprising increasing a lower limit of the backoff time interval as the main rank increases, while keeping the backoff time interval length constant or also increasing the backoff time interval.

5. The method (110) according to any one of claims 2 to 4, further comprising each network node repeatedly broadcasting its own pilot message a predetermined number of times (y), wherein, Any repetition occurs only after the expiration of the leading time period (T bi ).

6. The method (110) according to claim 5, further comprising: - A network node that has only received a pilot message with a master rank (R) lower than its own master rank (R) broadcasts a pilot completion message to the linear network node arrangement after the expiration of the pilot time period T bi and - All network nodes re - broadcast the pilot completion message.

7. The method (110) according to claim 6, wherein, If the network node broadcasting the pilot completion message does not receive any additional messages, preferably duty - cycle messages, within a predetermined time period after initially broadcasting the pilot completion message, the network node repeats broadcasting the pilot completion message.

8. A method (130) of transmitting a message between nodes (A to F) arranged in a network node arrangement having a hierarchy, the network nodes being configured to communicate directly with two or more adjacent nodes in either direction of the network node arrangement having a hierarchy, but no network node in the network node arrangement having a hierarchy being able to communicate directly with each of these network nodes, the method (130) comprising: - a first message is broadcast by a source node having a first rank R_r(s1), the first message including the rank (R_r(s1)) of the source node and the rank (R_r(d1)) of a first destination node, wherein the method further includes: If the rank of the first destination node (R_r(d1)) is two or more higher than the rank of the source node (R_r(s1)), then: - All intermediate nodes whose rank (R_r(i)) is higher than the rank of the source node (R_r(s1)) relay the first message in ascending order of their ranks (R_r(i)), starting from the intermediate node whose rank (R_r(i1)) is one higher than the rank of the source node (R_r(s1)), or If the rank of the first destination node (R_r(d1)) is two or more lower than the rank of the source node (R_r(s1)), then: - All intermediate nodes whose rank (R_r(i)) is lower than the rank of the source node (R_r(s1)) relay the first message in descending order of their ranks R_r(i), starting from the intermediate node whose rank R_r(i1) is one lower than the rank of the source node (R_r(s1)).

9. The method according to claim 8, wherein, An intermediate node relays the first message only after it has received a relay of the first message from a node with a rank that is respectively one higher or lower than its own rank, or after a predetermined time period has elapsed without receiving a relay from a node with a rank that is respectively one higher or lower than its own rank, even if it has received the first message from a node with a rank that is respectively at least two higher or lower than its own rank.

10. The method according to claim 8 or 9, wherein, Each intermediate node can append its own data or message to be propagated in the same propagation direction as the first message before relaying. If the destination node of the appended message or data is different from the destination node of the first message, the message or data optionally includes the rank or identifier of the corresponding destination node.

11. The method according to any one or more of claims 8 to 10, wherein, Any destination node deletes the message originally destined for it and broadcasts any appended messages destined for destination nodes in the propagation direction of the first message.

12. A method (200) for locating a fault in a network node arrangement having a hierarchy, the network nodes of the network node arrangement having a hierarchy being configured to communicate directly with two or more adjacent nodes in any direction of the network node arrangement having a hierarchy, but no network node in the network node arrangement having a hierarchy being able to communicate directly with all network nodes, the method (200) comprising: - A first network node (A) located at one end of the linear network node arrangement broadcasts (202) a topology check message into the linear network node arrangement, - All intermediate network nodes (B,..., E) append (204) their own topology check messages to the received topology check message and relay (208) the composite topology check message only after they have received the topology check message from their direct upstream neighbor or after the backoff period for the direct upstream neighbor has expired, and - A network node (F) at the opposite end of the linear network node arrangement analyzes (212) the received composite topology check message to find missing topology check messages.

13. The method according to claim 12, further comprising: - The network node at the opposite end of the linear network node arrangement returns the analysis result to the first network node in the form of a regular message, or - The network node at the opposite end of the linear network node arrangement adds its own topology check message to the composite topology check message it has received, broadcasts the composite topology check message, and - All intermediate network nodes between the network node at the opposite end and the first network node append their own additional topology check messages to the received topology check message and relay the composite topology check message only after having received the topology check message from their direct upstream neighbor or after the expiration of the backoff period for that upstream direct neighbor, and - The first network node analyzes the received composite topology check message to find missing topology check messages.

14. The method according to claim 12 or 13, further comprising: If a network node does not receive a relay from one of the up to n network nodes downstream that are known to be in the propagation direction of the topology check message: - Broadcast a topology check message error message, - All intermediate network nodes between the network node that broadcasts the topology check message error message and the first network node relay the topology check message error message.

15. A method for coordinating the switching of network nodes arranged in a fully configured and discovered linear network node arrangement between a first operating mode in which at least the transceiver is inactive or powered off and a second operating mode in which at least the wireless transceiver is active or powered on, these network nodes communicating directly with at most n adjacent network nodes, but no network node in the linear network node arrangement being able to communicate directly with each of these network nodes, the method comprising: - The first network node located at the first end of the linear network node arrangement broadcasts a duty cycle message, where the duty cycle message includes at least a wake-up time defining when to switch these network nodes to the second operating mode, and all network nodes in the linear network node arrangement coordinate to relay the duty cycle message, - Switch each network node that has relayed the duty cycle message to the first operating mode, and - Switch to the second operating mode according to the wake-up time.

16. The method according to claim 15, further comprising: In either the first network node or an intermediate network node, if the relay of the duty cycle message is not received from one or all network nodes downstream in the linear network node arrangement that are within direct communication range at the end of the corresponding backoff period, the duty cycle message is repeated, where at least the first network node and these intermediate network nodes switch to the first operating mode only after having received the relay of the duty cycle message from one or all network nodes downstream in the linear network node arrangement that are within wireless range.

17. The method according to claim 15 or 16, wherein, A network node switches to the first operating mode only when the network node has received the relay of the duty cycle message from one or all network nodes downstream in the linear network node arrangement that are within wireless range or after a predetermined maximum number of repetitions of broadcasting or relaying the duty cycle message.

18. The method according to claim 15 or 16, wherein, The duty cycle message further includes the duration of an active period that defines the period during which a network node is in the second operating mode before returning to the first operating mode.

19. A network node having a microprocessor, associated volatile and non-volatile memories, and a communication interface, wherein, When the microprocessor executes the corresponding computer program instructions stored in the non-volatile memory, the node is configured to perform the method according to one of claims 1 to 18.

20. A linear network node arrangement comprising at least two network nodes according to claim 19.

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