Method for network discovery for use in a multi-channel wireless network

Abstract

A method is disclosed for use in a multi-channel wireless network comprising at least three nodes. The method comprises: sending a first request message (for example on a single channel) from a first node containing listening schedule information. The method further comprises: receiving the first request message with a second node; and sending a second request message from the second node on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node. The method further comprises: receiving the second request message with at least a third node; and sending a reply message from each of a set of reply nodes to the first node during a time that is dependent on the listening schedule information, the set of reply nodes comprising at least a third node. The method allows the second node to act as a proxy for the first node in network discovery process for the first node.

Description

[0001] METHOD FOR NETWORK DISCOVERY FOR USE IN A MULTI-CHANNEL WIRELESS NETWORK

[0002] The present invention relates to a method for use in a multi-channel wireless network. For example, it may relate to a method for use in a time slotted channel hopping (TSCH) wireless network or any other operated wireless mesh network.

[0003] It is known to construct smart infrastructure from a plurality of internet of things (loT) enabled devices with wireless capabilities. For example, such an infrastructure may be used to enable smart meters and the like to communicate information regarding utilities usage across a network to a centrally located server for monitoring and analysis. Metering devices may be deployed at businesses, homes, and other premises for measuring consumption of resources, such as electricity, water, and gas. While some metering devices may provide only basic metering functions, other metering devices, known in the art as “smart meters”, may provide more advanced functionality, such as control and communications functionality

[0004] In an example, some metering devices may be configured to communicate information relating to consumption of resources. In another example, some metering devices may be configured to receive information such as billing information and control signals, such as service disconnect control signals or the like. In examples, transmission of information relating to consumption of metered resources may simplify automated billing, reduce operational costs, and may enable advanced analytics of resource consumption.

[0005] While in some examples a metering device may communicate directly with a router or gateway device, in other examples a wireless mesh network may be formed from multiple metering devices, wherein each metering device operates as an interconnected node and effective endpoint within the wireless mesh network.

[0006] When implemented in a wireless mesh network, a metering device operating as a network node may relay messages to or from a gateway device or router, or a head-end system. In an example, messages may be routed along a path by hopping from node to node, e.g. from metering device to metering device until said messages reaches a target destination, e.g. the gateway / router or a target metering device. The proximity of such devices to each other in terms of distance can vary from very close to very distant depending on the application requirements. Such devices can be powered up using an AC power supply or can be powered using a battery end point. These end points can form Wireless Mesh network to communicate with a central coordinator like an access point or a collector device to send sensor data (for example indicative of utilities usage).

[0007] Typically, the communication is via a parent node in the mesh network. A device transmits all its information data to a centrally located server routing through its parent. The parent for each device is chosen based on a list of neighbours with whom it can transmit and receive data packets. There can be multiple parameters based on which a node can select a parent.

[0008] It may be desirable to provide an alternative methods for operating devices on a multichannel wireless network and / or apparatus or devices for use with such a multi-channel wireless network which at least partially addresses one or more of the problems of the prior art, whether such problems are identified herein or elsewhere.

[0009] According to a first aspect of the present disclosure invention there is provided a method for use in a multi-channel wireless network, the method comprising: sending a first request message from a first node containing listening schedule information; receiving the first request message with a second node; sending a second request message from the second node on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node; receiving the second request message with at least a third node; and sending a reply message from each of a set of reply nodes to the first node during a time that is dependent on the listening schedule information, the set of reply nodes comprising at least a third node.

[0010] The method according to the first aspect of the present disclosure effectively allows the second node to act as a proxy for the first node in sending a request message on multiple channels. This is advantageous as it significantly reduces the power consumption of the first node. For example, the first node may be battery powered whereas the second node may be connected to mains electricity. The method according to the first aspect of the present disclosure may be a network discovery method for the first node but may allow the bulk of the transmissions (and therefore the power consumption) to be carried out by the second node acting as a proxy for the first node.

[0011] The network may comprise at least one node operating under a time slotted channel hopping (TSCH) protocol. However, the method according to the first aspect of the present disclosure is not limited to use in time slotted channel hopping (TSCH) wireless networks. The first node may comprise a low-functionality node (LFN), for example a battery operated end point (BEP) node. In contrast, the second node may comprise a fully-functionality node (FFN). A FFN may be a node having capability to route packets and is typically mains or AC powered.

[0012] A device connected to such a wireless network may have to perform a network discovery process at certain times such as, for example: when it boots up; on a periodic basis; or when it loses connectivity with a parent node. So, in the overall lifetime of such a device this activity can happen multiple times and it consumes a significant amount of energy. Furthermore, such a network discovery is rather power intensive as it typically involves transmitting packets on multiple different channels, and this may be repeated multiple times, in order to find a suitable stable network and a stable parent in its vicinity so that it can join the mesh and become part of mesh network topology.

[0013] Using the method according to the present disclosure, a device (the first node) can handover this process of discovery to the second node (for example a FFN).

[0014] Upon receipt of the first request message, the second node (for example a FFN) relays the listening schedule information on multiple channels operating in the mesh network. If the listening schedule information comprises a time delay (from the first request message) at which a listening window will open (as opposed to an absolute time) then the second node will send this listening schedule information as an adjusted time delay, which is less than the first time delay by an amount of time between the first and second request messages.

[0015] The identifier of the first node may, for example, comprise a medium access control (MAC) address of the first node (for example a LFN). Once other nodes (for example FFN nodes) belonging to the network receive the second request message (proxy discovery packet), if they can become a parent node to the first node then they will send a reply message to the first node. That is, the set of reply nodes comprises all such nodes which received the second request message and which are eligible to become a parent node to the first node.

[0016] The first request message may be sent on a single channel.

[0017] The first node may comprise a low-functionality node (LFN) or a battery operated end point (BEP).

[0018] The listening schedule information contained in the second request message may be an adjusted version of the listening schedule information contained in the first request message. For example, the listening schedule information contained in the first request message may indicate that the first node will start listening in 100 seconds time. The second node may send the second request message 10 seconds after it receives the first request message and the listening schedule information contained in the second request message may indicate that the first node will start listening in 90 seconds time.

[0019] Note that the second request message is sent on a plurality of channels and may comprise a plurality of packets, each packet being sequentially sent on a different channel. Therefore, the listening schedule information may be represented by a different time delay for each channel.

[0020] The listening schedule information may comprise any combination of the following: a time delay after the first request message when the first node will start listening for reply messages; and a time duration of a period during which the first node will listen for reply messages.

[0021] The listening schedule information may comprise any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node will listen for reply messages on each channel in the hopping sequence. The second request message and / or the reply message may comprise a discovery packet suitable for the wireless network.

[0022] For example, the second request message may comprise an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

[0023] The reply message may comprise an enhance beacon (EB) as defined in the IEEE 802.15.4 specification.

[0024] The first request message may comprise a unicast message sent to the second node.

[0025] That is, the first node may send the first request message directly to the second node (requesting that it send the second request message so as to perform a proxy discovery process). For such embodiments, there are various ways in which the second node may be selected.

[0026] The first node needs to be able to communicate with the second node. This can be achieved if the network is centrally synchronized such as in TSCH network or if the first node is already maintaining basic synchronization to communicate with the second node by following a channel hopping pattern.

[0027] The second node may comprise a parent node of the first node.

[0028] The method may further comprise: selecting the second node from a plurality of nodes, the selection being based on proximity to the first node.

[0029] In some embodiments, the first node can determine that there is a second node which is most suitable to perform the proxy discovery process, based on geographical location. This second node may be the parent node or some other node. The second node will be a node that the first node is in communication with. The second node may be on a neighbour list of the first node.

[0030] The selection of the second node may be made by the first node. Alternatively, the selection of the second node may be made centrally and the method may comprise sending a message to the first node containing an identifier of the second node. The first node may send the first request message to the second node upon receipt of such a message.

[0031] That is, the second node (proxy node) can be selected centrally, for example by an administrator or software running on a server machine which has overall view of network topology and can select the best second node to act as the second node (proxy) for the first node. Note that it may be the case that the best second node for the proxy discovery process does not ultimately become the parent node for various reasons.

[0032] The method may further comprise sending a message to the first node from its parent node informing the first node that the parent node is about to migrate to another personal area network (PAN) and the first node may send the first request message to the second node upon receipt of such a message.

[0033] That is, the parent node can inform the first node when it is about to do PAN migration. On receiving this information the first node can request one or more nodes in the current PAN to perform proxy discovery in order to determine a new parent. Advantageously, this allows the first node to remain joined to same PAN.

[0034] The second node may comprise a field diagnostic tool node.

[0035] The field diagnostic tool node may be a portable node. For example, the field diagnostic tool node may be disposed on a drone or the like.

[0036] The location of the second node (relative to the first node) plays an important role in determining the best parent for the first node. In particular, the method according to the first aspect may encounter some hidden node problems if the second node (which acts as proxy) is located at a distance from the first node. This can be solved if a portable node is deployed or if multiple reply nodes are selected to perform discovery.

[0037] The second node may comprise a portable node. Before the first request message is sent, the method may comprise: physically moving the portable node so that it is proximate to the first node; joining the network with the portable node; and establishing communication with the first node.

[0038] For example, at a scheduled time a field diagnostic tool node can be placed in close proximity to the first node, preferably as close to the first node as possible. Once the field diagnostic tool node is near the first node it becomes part of the mesh network. Once it is part of the mesh network, the field diagnostic tool node establishes a communication with the first node. Once the field diagnostic tool node and the first node can communicate, the field diagnostic tool node may send a message to the first node to initiate proxy discovery process.

[0039] The second node may be mounted on a drone. The method may comprise: using the drone to physically move the second node so that it is proximate to the first node.

[0040] An example, of such a drone-mounted field diagnostic tool node is disclosed in US9907046, which is incorporated herein by reference in its entirety.

[0041] The or each reply message may be sent at a random or pseudo-random time during a listening time period specified in the listening schedule information.

[0042] The first request message may comprise a broadcast message that is received by the second node.

[0043] In some embodiments, the first node can send a broadcast on single channel so that any nodes receiving this broadcast can perform the proxy discovery process. Advantageously, this may allow for a wider range of potential parents to be considered.

[0044] The method may further comprise: listening for any reply messages in accordance with the listening schedule information using the first node.

[0045] The method may further comprise: receiving at least one reply message from one of the set of reply nodes with the first node. The method may further comprise: upon receipt of a reply message from one of the set of reply nodes, determining with the first node if the node which sent that reply message is suitable to become a parent node for the first node.

[0046] Such an assessment of suitability to act as parent node for the first node may be based on the various criteria, as is known in the art.

[0047] The first node may receive a reply message from each of a plurality of reply nodes and the method may further comprise: selecting one of the plurality of reply nodes to send a unicast message to in order to establish two-way communication with that reply node.

[0048] Such selection may be based on assessment of the suitability of each reply node to act as parent node for the first node. Again, this may be based on the various criteria, as is known in the art.

[0049] The first node can also do a unicast transmission to a suitable reply node to ensure two- way communication.

[0050] The method may further comprise: using the first node to initiate a joining process with a reply node that: (a) has been determined to be suitable to become a parent node for the first node; and / or (b) has been selected.

[0051] The method may further comprise: sending a first unicast message to a reply node from the set of reply nodes in order to establish two-way communication with that reply node.

[0052] The first unicast message may comprise a discovery packet.

[0053] The method may further comprise: upon receipt of the first unicast message, sending a second unicast message from the reply node back to the first node.

[0054] This may be dependent on the first unicast message meeting received signal strength indication (RSSI) requirements.

[0055] According to a second aspect of the present disclosure there is provided a method to be carried out by a node in a multi-channel wireless network, the method comprising: sending a first request message on a single channel from the node, the first request message containing listening schedule information and requesting another node to transmit a second request message on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node; and listening for any reply messages in accordance with the listening schedule information using the first node.

[0056] The method according to the second aspect of the present disclosure is the method that is implemented by the first node during the method according to the first aspect of the present disclosure.

[0057] The identifier of the first node may, for example, comprise a medium access control (MAC) address of the first node (for example a LFN).

[0058] The node may comprise a low-functionality node (LFN) or a battery operated end point (BEP).

[0059] The listening schedule information may comprise any combination of the following: a time delay after the first request message when the first node will start listening for reply messages; and a time duration of a period during which the first node will listen for reply messages.

[0060] The listening schedule information may comprise any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node will listen for reply messages on each channel in the hopping sequence.

[0061] The second request message may comprise an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

[0062] The first request message may comprise a unicast message sent to the second node.

[0063] The second node may comprise a parent node of the first node. The method may further comprise: selecting the second node from a plurality of nodes, the selection being based on proximity to the first node.

[0064] For example, the node can determine that there is a second node which is most suitable to perform the proxy discovery process, based on geographical location. This second node may be the parent node or some other node. The second node will be a node that the first node is in communication with. The second node may be on a neighbour list of the node.

[0065] The method may comprise receiving a message containing an identifier of the second node. The node may send the first request message to the second node upon receipt of such a message.

[0066] That is, the second node (proxy node) can be selected centrally, for example by an administrator or software running on a server machine which has overall view of network topology and can select the best second node to act as the second node (proxy) for the first node. Note that it may be the case that the best second node for the proxy discovery process does not ultimately become the parent node for various reasons.

[0067] The method may further comprise receiving a message from a parent node of the node informing the node that the parent node is about migrate to another personal area network (PAN). The node may send the first request message to the second node upon receipt of such a message.

[0068] That is, the parent node can inform the first node when it is about to do PAN migration. On receiving this information the first node can request one or more nodes in the current PAN to perform proxy discovery in order to determine a new parent. Advantageously, this allows the first node to remain joined to same PAN.

[0069] The first request message may comprise a broadcast message that is received by the second node.

[0070] In some embodiments, the first node can send a broadcast on single channel so that any nodes receiving this broadcast can perform the proxy discovery process. Advantageously, this may allow for a wider range of potential parents to be considered. The method may further comprise: receiving at least one reply message.

[0071] The method may further comprise: upon receipt of a reply message from a reply node, determining if the reply node is suitable to become a parent node for the node.

[0072] Such an assessment of suitability to act as parent node for the node may be based on the various criteria, as is known in the art.

[0073] The node may receive a reply message from each of a plurality of reply nodes and the method may further comprise: selecting one of the plurality of reply nodes to send a unicast message to in order to establish two-way communication with that reply node.

[0074] Such selection may be based on assessment of the suitability of each reply node to act as parent node for the first node. Again, this may be based on the various criteria, as is known in the art.

[0075] The first node can also do a unicast transmission to a suitable reply node to ensure two- way communication.

[0076] The method may further comprise: initiating a joining process with a reply node that: (a) has been determined to be suitable to become a parent node for the node; and / or (b) has been selected.

[0077] The method may further comprise: sending a first unicast message to a reply node from the set of reply nodes in order to establish two-way communication with that reply node.

[0078] The first unicast message may comprise a discovery packet.

[0079] The or each reply message may comprise an enhance beacon (EB) as defined in the IEEE 802.15.4 specification.

[0080] According to a third aspect of the present disclosure there is provided a method to be carried out by a node in a multi-channel wireless network, the method comprising: receiving a first request message with the node, the first request message containing listening schedule information; and sending a second request message from the node on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node.

[0081] The method according to the third aspect of the present disclosure is the method that is implemented by the second node during the method according to the first aspect of the present disclosure.

[0082] The identifier of the first node may, for example, comprise a medium access control (MAC) address of the first node (for example a LFN).

[0083] Once other nodes (for example FFN nodes) belonging to the network receive the second request message (proxy discovery packet), if they can become a parent node to the first node then they will send a reply message to the first node.

[0084] The listening schedule information contained in the second request message may be an adjusted version of the listening schedule information contained in the first request message. For example, the listening schedule information contained in the first request message may indicate that the first node will start listening in 100 seconds time. The second node may send the second request message 10 seconds after it receives the first request message and the listening schedule information contained in the second request message may indicate that the first node will start listening in 90 seconds time.

[0085] Note that the second request message is sent on a plurality of channels and may comprise a plurality of packets, each packet being sequentially sent on a different channel. Therefore, the listening schedule information may be represented by a different time delay for each channel.

[0086] The listening schedule information may comprise any combination of the following: a time delay after the first request message when the first node will start listening for reply messages; and a time duration of a period during which the first node will listen for reply messages.

[0087] The listening schedule information may comprise any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node will listen for reply messages on each channel in the hopping sequence.

[0088] The second request message may comprise a discovery packet suitable for the wireless network send on behalf of another node that sent the first request message.

[0089] The second request message may comprise an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

[0090] The node may comprise a field diagnostic tool node.

[0091] The field diagnostic tool node may be a portable node. For example, the field diagnostic tool node may be disposed on a drone or the like.

[0092] The location of the node (relative to a node that sent the first request message) plays an important role in determining the best parent for the first node. In particular, the method according to the first aspect may encounter some hidden node problems if the second node (which acts as proxy) is located at a distance from the first node. This can be solved if a portable node is deployed or if multiple reply nodes are selected to perform discovery.

[0093] The node may comprise a portable node. Before the first request message is received, the method may comprise: physically moving the portable node so that it is proximate to another node; joining the network with the portable node; and establishing communication with the other node.

[0094] For example, at a scheduled time a field diagnostic tool node can be placed in close proximity to the other node, preferably as close to the other node as possible. Once the field diagnostic tool node is near the other node it becomes part of the mesh network. Once it is part of the mesh network, the field diagnostic tool node establishes a communication with the other node. Once the field diagnostic tool node and the other node can communicate, the field diagnostic tool node may send a message to the other node to initiate proxy discovery process. The node may be mounted on a drone. The method may comprise: using the drone to physically move the node so that it is proximate to another node from which the first request message will originate.

[0095] An example, of such a drone-mounted field diagnostic tool node is disclosed in US9907046, which is incorporated herein by reference in its entirety.

[0096] According to a fourth aspect of the present disclosure there is provided a computer- readable medium having instructions for carrying out the method according to the first aspect of the present disclosure. The computer-readable medium may be a non- transitory computer-readable medium.

[0097] According to a fifth aspect of the present disclosure there is provided a computer- readable medium having instructions for carrying out the method according to the second aspect of the present disclosure. The computer-readable medium may be a non- transitory computer-readable medium.

[0098] According to a sixth aspect of the present disclosure there is provided a computer- readable medium having instructions for carrying out the method according to the third aspect of the present disclosure. The computer-readable medium may be a non- transitory computer-readable medium.

[0099] According to a seventh aspect of the present disclosure there is provided a network of nodes for use in a wireless network, the network comprising: a first node operable to send a first request message containing listening schedule information; a second node operable to: receive the first request message; and send a second request message on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node; and a set of reply nodes, each operable to send a reply message to the first node during a time that is dependent on the listening schedule information, and wherein the set of reply nodes comprises at least a third node.

[0100] Each node may comprise: a transceiver; at least one processor; and storage media, the storage media having instructions to cause the at least one processor to carry out one or more steps of the method according to the first aspect of the present disclosure. According to an eighth aspect of the present disclosure there is provided a node for carrying out the method according to the second aspect of the present disclosure, the node comprising: a transceiver; at least one processor; and storage media, the storage media having instructions to cause the at least one processor to carry out one or more steps of the method according to the second aspect of the present disclosure.

[0101] According to a ninth aspect of the present disclosure there is provided a node for carrying out the method according to the third aspect of the present disclosure, the node comprising: a transceiver; at least one processor; and storage media, the storage media having instructions to cause the at least one processor to carry out one or more steps of the method according to the third aspect of the present disclosure.

[0102] Various aspects and features of the disclosure set out above or below may be combined with various other aspects and features of the disclosure as will be readily apparent to the skilled person.

[0103] Embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0104] Figure 1 depicts a block diagram of an example of a mesh network;

[0105] Figure 2 is a schematic illustration of a new method according to an embodiment of the present disclosure use in a multi-channel wireless network, the method allowing a second node to act as a proxy for a first node as part of a network discovery process;

[0106] Figure 3 Figure 3 schematically shows, for an example system of nodes (for example a mesh network of the type shown in Figure 1 ), how messages are exchanged between the nodes when implementing the method shown in Figure 2;

[0107] Figure 4 shows a modified method comprising the method shown in Figure 2 plus some additional, optional steps;

[0108] Figure 5 is a schematic illustration of an node for a network according to an embodiment of the present disclosure, which may represent a node of the mesh network shown in Figure 1 and which may implement the methods illustrated in Figure 6 or Figure 7 and which may partially implement the methods shown in Figures 2 to 4; Figure 6 schematically shows a first method according to the present disclosure to be carried out by a single node in a multi-channel wireless network; note that the steps of the first method to be carried out by a single node correspond to some (but not all) of the steps of the method shown in Figure 2 and / or the method shown in Figure 4; and

[0109] Figure 7 schematically shows a second method according to the present disclosure to be carried out by a single node in a multi-channel wireless network; note that the steps of the second method to be carried out by a single node correspond to some (but not all) of the steps of the method shown in Figure 2 and / or the method shown in Figure 4.

[0110] Figure 1 depicts an example of mesh network 100. The example network 100 may be a time-synchronized channel hopping (TSCH) network, as defined by IEEE 802.15.4. The mesh network 100 may be a network of (radio-frequency) operated wireless mesh network nodes. The mesh network 100 is an example of a mesh network upon which the present invention may be implemented. In examples, the mesh network 100 may comprise a full mesh topology, e.g. where any node can communicate with any node within range, or a partial mesh topology with more limited or selected connectivity between nodes.

[0111] The example mesh network comprises a head-end system 110. The head-end system 110 may function as a central processing system that transmits and / or receives data, streams of data, data packets and / or messages from nodes 105a - 105h of the mesh network 100, as described in more detail below. The head-end system 110 may generate and / or process the data. In examples, head-end system 1 10 may be communicably coupled to a further system, such as a cloud based system (not shown), for generating and / or processing the data.

[0112] The example mesh network 100 may comprise a root node 1 15. The root node 115 of the mesh network 100 may be configured for communicating with the nodes 105a - 105h to perform operations such as retrieving data from the nodes 105a - 105h and / or transmitting data to the head-end system 110. In some examples, the root node 115 may also operate as a node similar to other nodes 105a-105h. In examples, the root node 115 may comprise a gateway device. The root node 1 15 may be configured to transmit and receive data to / from the head-end system 110 via backhaul 120, such as the Internet, an intranet, or any other data communication network.

[0113] Although only a single root node 1 15 is depicted for illustrative purposes, it will be understood that the mesh network 100 may comprise more than one root node 1 15.

[0114] Similarly, the depicted mesh network 100 comprises multiple nodes 105a-105h. Each node 105a-105h may be an end-node. For purposes of example, only nodes 105a-105h are depicted, but it will be understood that substantially more than eight nodes may be implemented. For example, in a mesh network of metering device, thousands, hundreds of thousands or even millions of devices may be implemented in the mesh network.

[0115] In examples, each node 105a-105h may comprise a device for metering and / or controlling a resource. For example, the device may comprise circuitry and / or components for metering a consumption of a resource, and / or controlling access to the resource, such as by a service disconnect switch or the like. In an example, the mesh network 100 may be associated with a utility network. In such an example, the nodes 105a-105h may comprise circuitry and / or components for metering the resource, for determining various operating characteristics of the utility network, and / or for transmitting collected data through the mesh network 100 to the head-end system 1 10 via the root node 115.

[0116] Furthermore, the nodes 105a-105h may be further configured to communicate with each other such that data may be exchanged between the nodes 105a-105h. That is, the nodes 105a-105h may comprise local processing capabilities, enabling a degree of autonomy over communication with other nodes in the network 100.

[0117] The nodes 105a-105h forming the mesh network 100 may be effectively provided in layers, as annotated in Figure 1 . In this example, the root node 1 15 forms layer 0. Nodes 105a, 105b that are communicably coupled directly to the root node 115 form a first layer, “Layer 1 ”, of the mesh network 100. Similarly, nodes 105c - 105e that are communicably coupled to the mesh network 100 through a “Layer 1 ” node form a second layer, “Layer 2”, of the mesh network 100. Similarly, nodes 105f - 105h that are communicably coupled to the mesh network 100 through a “Layer 2” node form a third layer, “Layer 3”, of the mesh network 100. For data to propagate from the root node 1 15 to a Layer 3 of the mesh network 100 would require three “hops” of the data.

[0118] As used herein, unless stated to the contrary, “node” 105a-105h and “device” refer to a physical entity that can, or is, participating in a mesh network 100. These terms may be used interchangeably. A node 105a-105h or device may be powered by either mains (AC) electricity or by a battery.

[0119] Each node 105a-105h or device may comprise an associated parent node and one or more associated child nodes. For any given node 105a-105h or device, its associated parent node is a node 105a-105h having capability to route traffic from that given node 105a-105h or device. Any node 105a-105h or device can have a primary parent or multiple back up parents. At any given time, the current parent node of a given node 105a-105h or device is a node via which sensor data (for example indicative of utilities usage) is routed from that given node or device (ultimately to a collector device such as the root node 115 and then to a centrally located server such as the head-end system 1 10) as a unicast signal or data packet. At any given time, a child of any given node 105a-105h may be any node 105a-105h whose information is being routed through that given node 105a-105h.

[0120] As used herein, unless stated to the contrary, for any given node 105a-105h or device, a “neighbour node” is intended to mean any node 105a-105h that the given node 105a- 105h or device can exchange information with (i.e. any node 105a-105h within its communication range).

[0121] As used herein, unless stated to the contrary, for any given node 105a-105h or device, a “critical neighbour” is intended to mean any node 105a-105h that the given node 105a- 105h or device exchanges unicast messages with. Critical neighbours include a parent node, any child nodes and nodes 105a-105h running any critical applications. A critical neighbour can exchange information with a node 105a-105h or device by sending information in either a medium access control (MAC) layer packet or an application layer packet. A system administrator can also declare a node 105a-105h as critical and communicate this information to a node 105a-105h or device (via its parent). In other aspects, a node 105a-105h can determine a neighbour as critical based on a number of high priority quality of service (QoS) packets generated by a child node. Similarly, as used herein, unless stated to the contrary, for any given node 105a-105h or device, a “non-critical neighbour” is intended to mean a node 105a-105h that the given node 105a-105h or device can exchange information with but which is not currently important for that node 105a-105h or device to perform any activity of node 105a-105h such as transmitting its own data or data from its child node data to a central server (for example head-end system 110). The performance of a node 105a-105h or device is not dependent on non-critical neighbours. Note that a non-critical neighbour can become a critical neighbour, for example if it becomes a child or the parent of the node 105a-105h or device.

[0122] Some embodiments of the present disclosure relate to a method for use in a multichannel wireless network. The network may, for example be a mesh network 100 of the type shown in Figure 1 . An example of such a method 200 for use in a multi-channel wireless network according to an embodiment of the present disclosure is shown schematically in Figure 2. Figure 3 schematically shows, for an example system of nodes 300 (for example a mesh network 100 of the type shown in Figure 1 ), how messages are exchanged between the nodes when implementing the method 200 shown in Figure 2. The method 200 is now described with reference to Figures 2 and 3.

[0123] Figure 3 shows a first node 310, which is a low-functioning node (LFN), and a second node 320, which is a first fully-functioning node (FFN1 ). The first and second nodes 310, 320 are both joined to the network and are in communication, as indicated by double arrow 312. A time 314 after communication has been established between the first and second nodes 310, 320, a proxy network discovery process may be initiated, as now described.

[0124] The method 200 comprises a step 210 of sending a first request message 316 from a first node 310 containing listening schedule information. The method 200 further comprises a step 220 of receiving the first request message 316 with a second node 320.

[0125] The method 200 further comprises a step 230 of sending a second request message 322 from the second node 320 on a plurality of channels. The second request message 322 contains the listening schedule information and an identifier of the first node 310. The method 200 further comprises a step 240 of receiving the second request message 322 with at least a third node. In the example shown in Figure 3, the second request message 322 may be receive by three nodes 330, 340, 350, which are second, third and fourth fully-functioning nodes (FFN2, FFN3, FFN4).

[0126] The method 200 further comprises a step 250 of sending a reply message from each of a set of reply nodes to the first node 310 during a time 360 that is dependent on the listening schedule information. The set of reply nodes comprises at least a third node. In the example shown in Figure 3, set of reply nodes comprises two nodes 340, 350, which are third and fourth fully-functioning nodes (FFN3, FFN4). Each of these reply nodes 340, 350 sends a reply message to the first node 310.

[0127] The method 200 shown in Figure 2 and illustrated in Figure 3 effectively allows the second node 320 to act as a proxy for the first node 310 in sending a request message on multiple channels (for example as part of a network discovery process). This is advantageous as it significantly reduces the power consumption of the first node 310. For example, the first node may be battery powered whereas the second node 320 may be connected to mains electricity. The method 200 shown in Figure 2 may be a network discovery method for the first node 310 but may allow the bulk of the transmissions 322 (and therefore the power consumption) to be carried out by the second node 320 acting as a proxy for the first node 310.

[0128] The network may comprise at least one node operating under any type of channel hopping protocol. For example, the network may comprise at least one node operating under a time slotted channel hopping (TSCH) protocol. As in the example shown in Figure 3, the first node 310 may comprise a low-functionality node (LFN), for example a battery operated end point (BEP) node. In contrast, the second node 320 may comprise a f ully-f unctionality node (FFN). A FFN may be a node having capability to route packets and is typically mains or AC powered.

[0129] A device (for example the first node 310) connected to such a wireless network may have to perform a network discovery process at certain times such as, for example: when it boots up; on a periodic basis; or when it loses connectivity with a parent node. So, in the overall lifetime of such a device 310 this activity can happen multiple times and it consumes a significant amount of energy. Furthermore, such a network discovery is rather power intensive as it typically involves transmitting packets on multiple different channels, and this may be repeated multiple times, in order to find a suitable stable network and a stable parent in its vicinity so that it can join the mesh and become part of mesh network topology.

[0130] Using the method 200 shown in Figure 2, a device (the first node 310) can handover this process of discovery to the second node 320 (for example a FFN).

[0131] Upon receipt of the first request message 316, the second node 320 (for example a FFN) relays the listening schedule information on multiple channels operating in the mesh network. If the listening schedule information comprises a time delay 318 (from the first request message 316) at which a listening window 360 will open (as opposed to an absolute time) then the second node 320 will send this listening schedule information as an adjusted time delay 324, which is less than the first time delay 318 by an amount of time 326 between the first and second request messages 316, 322.

[0132] The identifier of the first node 310 may, for example, comprise a medium access control (MAC) address of the first node 310 (for example a LFN).

[0133] Once other nodes 330, 340, 350 (for example FFN nodes) belonging to the network receive the second request message 322 (proxy discovery packet), if they can become a parent node to the first node 310 then they will send a reply message 342, 352 to the first node 310. That is, the set of reply nodes 340, 350 comprises all such nodes which received the second request message 322 and which are eligible to become a parent node to the first node 310.

[0134] In some embodiments, the first request message 316 is sent on a single channel.

[0135] In some embodiments, the first node 310 comprises a low-functionality node (LFN) or a battery operated end point (BEP).

[0136] As noted above, the listening schedule information contained in the second request message 322 may be an adjusted version of the listening schedule information contained in the first request message 316. For example, the listening schedule information contained in the first request message 316 may indicate that the first node will start listening in 100 seconds time. The second node 320 may send the second request message 322 10 seconds after it receives the first request message 316 and the listening schedule information contained in the second request message 322 may indicate that the first node 310 will start listening in 90 seconds time.

[0137] Note that the second request message 322 is sent on a plurality of channels and may comprise a plurality of packets, each packet being sequentially sent on a different channel. Therefore, the listening schedule information in the second request message 322 may be represented by a different time delay for each channel.

[0138] In some embodiments, the listening schedule information may comprise any combination of the following: a time delay 318 after the first request message 316 when the first node 310 will start listening for reply messages; and a time duration of a period 360 during which the first node 310 will listen for reply messages.

[0139] In some embodiments, the listening schedule information may comprise any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node 310 will listen for reply messages on each channel in the hopping sequence.

[0140] In some embodiments, the second request message 322 and / or the reply message(s) 342, 352 may comprise a discovery packet suitable for the wireless network. For example, in some embodiments, the second request message 322 may comprise an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification. Similarly, in some embodiments, the reply message(s) 342, 352 may comprise an enhance beacon (EB) as defined in the IEEE 802.15.4 specification.

[0141] In some embodiments, the first request message 316 may comprise a unicast message sent to the second node 320. That is, the first node 310 may send the first request message 316 directly to the second node 320 (requesting that it send the second request message 322 so as to perform a proxy discovery process). For such embodiments, there are various ways in which the second node 320 may be selected. The first node 310 needs to be able to communicate with the second node 320. This can be achieved if the network is centrally synchronized such as in TSCH network or if the first node 310 is already maintaining basic synchronization to communicate with the second node 320 by following a channel hopping pattern.

[0142] In some embodiments, the second node 320 may comprise a parent node of the first node 310.

[0143] The or each reply message 342, 352 may be sent at a random or pseudo-random time during a listening time period 360 specified in the listening schedule information. The or each reply message 342, 352 may be sent at a random or pseudo-random time 344, 354 after the second request message 322 and during a listening time period 360 specified in the listening schedule information.

[0144] In some embodiments, the first request message 316 may comprise a broadcast message that is received by the second node 320. In some embodiments, the first node 310 can send a broadcast on single channel so that any nodes receiving this broadcast can perform the proxy discovery process. Advantageously, this may allow for a wider range of potential parents to be considered.

[0145] In some embodiments, the second node 320 may comprise a field diagnostic tool node. The field diagnostic tool node may be a portable node. For example, the field diagnostic tool node may be disposed on a drone or the like.

[0146] The location of the second node 320 (relative to the first node 310) plays an important role in determining the best parent for the first node 310. In particular, the method 200 may encounter some hidden node problems if the second node 320 (which acts as proxy) is located at a large distance from the first node 310. This can be solved if a portable node is deployed or if multiple reply nodes are selected to perform discovery.

[0147] The method 200 shown in Figure 2 may further comprise one or more additional, optional steps. Such additional steps are now described with reference to Figure 4, which shows a modified method 400 comprising the method shown in Figure 2 plus some additional, optional steps. In Figure 4, optional steps are indicated by dotted lines. The modified method 400 is now described with reference to Figures 3 and 4. In some embodiments, the method 400 may further comprise a step 410 of selecting the second node 420 from a plurality of nodes, the selection being based on proximity to the first node 410. In some embodiments, the first node 310 can determine that there is a second node 320 which is most suitable to perform the proxy discovery process, based on geographical location. This second node 320 may be the parent node or some other node. The second node 320 will be a node that the first node 310 is in communication with. The second node 320 may be on a neighbour list of the first node 310.

[0148] In some embodiments, this selection 410 of the second node 320 may be made by the first node 310.

[0149] Alternatively, in some embodiments, the selection 410 of the second node 320 may be made centrally and the method may comprise an additional step 412 of sending a message (not shown) to the first node 310 containing an identifier of the second node 320. For such embodiments, the first node may send the first request message 316 to the second node 320 upon receipt of such a message. That is, the second node 320 (proxy node) can be selected centrally, for example by an administrator or software running on a server machine (for example head-end system 110, see Figure 1 ) which has overall view of network topology and can select the best second node to act as the second node 320 (proxy) for the first node 310. Note that it may be the case that the best second node 320 for the proxy discovery process does not ultimately become the parent node for various reasons.

[0150] In some embodiments, the method 400 may further comprise a step 420 of sending a message (not shown) to the first node 310 from its parent node informing the first node 310 that the parent node 310 is about migrate to another personal area network (PAN). For such embodiments, the first node 310 may send the first request message 316 to the second node 320 upon receipt of such a message. That is, the parent node can inform 420 the first node 310 when it is about to do PAN migration. On receiving this information the first node 310 can request one or more nodes in the current PAN to perform proxy discovery in order to determine a new parent. Advantageously, this allows the first node 310 to remain joined to same PAN. In some embodiments, the second node 420 may comprise a portable node. For such embodiments, the method 400 may further comprise the following steps. In particular, the method 400 may comprise: a step 430 of physically moving the portable node so that it is proximate to the first node 310; a step 432 of joining the network with the portable node; and a step 434 establishing communication with the first node.

[0151] For example, at a scheduled time a field diagnostic tool node can be placed in close proximity to the first node 310, preferably as close to the first node 310 as possible. Once the field diagnostic tool node is near the first node 310 it becomes part of the mesh network. Once it is part of the mesh network, the field diagnostic tool node establishes a communication with the first node 310. Once the field diagnostic tool node and the first node 310 can communicate, the field diagnostic tool node may send a message (not shown) to the first node 310 to initiate proxy discovery process.

[0152] In some embodiments, the second node 320 may be mounted on a drone and the method may comprise using the drone to physically move the second node 320 so that it is proximate to the first node 310. This may be done as part of step 430 described above. An example, of such a drone-mounted field diagnostic tool node is disclosed in US9907046, which is incorporated herein by reference in its entirety.

[0153] In some embodiments, the method 400 may further comprise a step 440 of listening for any reply messages in accordance with the listening schedule information using the first node 310.

[0154] In some embodiments, the method 400 may further comprise a step 450 of receiving at least one reply message 342, 352 from one of the set of reply nodes 340, 350 with the first node 310.

[0155] In some embodiments, the method 400 may further comprise a step 460 of, upon receipt of a reply message 342, 352 from one of the set of reply nodes 340, 350, determining with the first node 310 if the node 340, 350 which sent that reply message 342, 352 is suitable to become a parent node for the first node 310. Such an assessment of suitability to act as parent node for the first node may be based on the various criteria, as is known in the art. In some embodiments, the first node 310 may receive a reply message 342, 352 from each of a plurality of reply nodes 340, 350. For such embodiments, the method 400 may further comprise a step 470 of selecting one of the plurality of reply nodes 340, 350 to send a unicast message 370 to in order to establish two-way communication with that reply node. For example, in the example shown in Figure 3, a selection 470 may have been made (for example by the first node 310) to select node 340 (FFN3) to send a unicast message 370 to. Such selection may be based on assessment of the suitability of each reply node 340, 350 to act as parent node for the first node 310. Again, this may be based on the various criteria, as is known in the art.

[0156] Therefore, in some embodiments, the first node 310 can send a unicast transmission 370 to a suitable reply node 340 to ensure two-way communication therewith.

[0157] In some embodiments, the method 400 may further comprise a step 480 of sending a first unicast message 370 to a reply node 340 from the set of reply nodes 340, 350 in order to establish two-way communication with that reply node 340. The first unicast message 370 may comprise a discovery packet.

[0158] In some embodiments, the method 400 may further comprise a step 482 or, upon receipt of the first unicast message 370, sending a second unicast message 372 from the reply node back 340 to the first node 310. This step 482 may be dependent on the first unicast message meeting received signal strength indication (RSSI) requirements.

[0159] In some embodiments, the method 400 may further comprising a step 490 of using the first node 310 to initiate a joining process with a reply node 340 that: (a) has been determined to be suitable to become a parent node for the first node 310 (for example at step 460); and / or (b) has been selected (for example at step 470).

[0160] Some embodiments of the present disclosure relate to a computer-readable medium having instructions for carrying out the method 200 shown in Figure 2 and / or the method shown in Figure 4 and as described above with reference to Figures 2 to 4. The computer-readable medium, for example, may be a non-transitory computer-readable medium. It will be appreciated that the computer-readable medium may comprise a system of distributed computer-readable media. Some embodiments of the present disclosure relate to a network of nodes for use in a wireless network 100. The network may comprise: a first node 310 operable to send a first request message 316 containing listening schedule information; a second node 320 operable to: (a) receive the first request message 316; and (b) send a second request message 122 on a plurality of channels, the second request message 122 containing the listening schedule information and an identifier of the first node 310; and a set of reply nodes 330, 340, 350, each operable to send a reply message 342, 352 to the first node 310 during a time that is dependent on the listening schedule information. The set of reply nodes may comprise at least a third node. Note that the set of reply nodes may comprise the second node.

[0161] Each node 310, 320, 330, 340, 350 of such a network may comprise be generally of the form of a node 500 shown schematically in Figure 5. The example node 500 comprises: a transceiver 510; at least one processor 520; and a storage media 530. The node 500 may, for example, represent any of the nodes 105a-105h of a wireless network 100 as described above.

[0162] The at least one processor 520 may include any suitable processing device(s) such as, for example, a microprocessor, an application-specific integrated circuit (ASIC), or a field programmable gate array (FPGA). The at least one processor 520 is communicatively coupled to the storage media 530.

[0163] The storage media 530 may have instructions to cause the at least one processor 520 to carrying out one or more methods disclosed herein. The at least one processor 520 can read from and write to the storage media 530.

[0164] The transceiver 510 may be communicatively coupled to the processor 520 and / or the storage media 530. The transceiver 510 may be used by the apparatus 500 to communicate with neighbouring nodes 105a-105h within a network 100, for example via an antenna 540.

[0165] Some embodiments of the present disclosure relate to methods to be carried out by a single node in a multi-channel wireless network. In particular, they relate to methods to be carried out by a single node, which comprise steps of the method 200 shown in Figure 2 and / or the method 400 shown in Figure 4 which are carried out by a single node. An example of such a first method 600 to be carried out by a single node 310 in a multichannel wireless network is shown schematically in Figure 6. Note that the steps of the first method 600 to be carried out by a node 310 in a multi-channel wireless network correspond to some (but not all) of the steps of the method 200 shown in Figure 2 and / or the method 400 shown in Figure 4. Steps of the first method 600 shown in Figure 6 share common reference numerals with corresponding steps of the method 200 shown in Figure 2 and / or the method 400 shown in Figure 4.

[0166] It will be appreciated that the first method 600 to be carried out by a single node 310 in a multi-channel wireless network shown in Figure 6 may comprise any features of the first node 310 and / or the methods 200, 400 as described above with reference to Figures 2 to 4 to the extent that such methods relate to the first node 310. In Figure 6, optional steps are indicated by dotted lines.

[0167] The first method 600 to be carried out by a node 310 in a multi-channel wireless network comprises: a step 210 of sending a first request message 316 on a single channel from the node 310 containing listening schedule information and requesting another node to transmit a second request message 322 on a plurality of channels, the second request message 322 containing the listening schedule information and an identifier of the first node 310.

[0168] The first method 600 to be carried out by a node 310 in a multi-channel wireless network further comprises: a step 440 of listening for any reply messages in accordance with the listening schedule information using the first node 310.

[0169] Optionally the method 600 shown in Figure 6 may further comprise: a step 410 of selecting the second node 320 from a plurality of nodes, the selection being based on proximity to the first node 310.

[0170] Optionally, the method shown in Figure 6 may comprise a step 610 of receiving a message (not shown) and wherein the node 310 sends the first request message 316 to the second node 320 upon receipt of such a message. The message may contain an identifier of the second node 320. For example, the second node 320 (proxy node) may have been selected centrally, for example by an administrator or software running on a server machine which has overall view of network topology and can select the best second node to act as the second node 320 (proxy) for the first node 310 and a message may be sent to the first node 310 containing an identifier of the selected second node 320.

[0171] Alternatively, the message may be from a parent node of the node 310 and may inform the node 310 that the parent node is about migrate to another personal area network (PAN). The node may send the first request message 316 to the second node 320 upon receipt of such a message.

[0172] Optionally, the method 600 shown in Figure 6 may further comprise a step 450 of receiving at least one reply message 342, 352.

[0173] Optionally, the method 600 shown in Figure 6 may further comprise a step 460 of, upon receipt of a reply message 342, 352 from a reply node 340, 350, determining if the reply node 340, 350 is suitable to become a parent node for the node 310.

[0174] In some embodiments, the node 310 may receive a reply message 342, 352 from each of a plurality of reply nodes 340, 350. For such embodiments, optionally, the method 600 shown in Figure 6 may further comprise a step 470 of selecting one of the plurality of reply nodes 340, 350 to send a unicast message 370 to in order to establish two-way communication with that reply node.

[0175] Optionally, the method 600 shown in Figure 6 may further comprise a step 480 of sending 480 a first unicast message 470 to a reply node 340 from the set of reply nodes in order to establish two-way communication with that reply node.

[0176] Optionally, the method 600 shown in Figure 6 may further comprise a step 490 of initiating a joining process with a reply node 340 that: (a) has been determined to be suitable to become a parent node for the node 310 (for example at step 460); and / or (b) has been selected (for example at 470). Some embodiments of the present disclosure relate to a computer-readable medium having instructions for carrying out the method 600 shown in Figure 6 and as described above. The computer-readable medium may be a non-transitory computer-readable medium.

[0177] Some embodiments of the present disclosure relate to a node 310 for carrying out the method 600 shown in Figure 6 and as described above. The node 310 may be generally of the form of the node 500 shown in Figure 5 and described above. For such embodiments, the storage media 530 may have instructions to cause the at least one processor 520 to carry out the method 600 shown in Figure 6 and as described above.

[0178] An example of a second method 700 to be carried out by a single node 320 in a multichannel wireless network is shown schematically in Figure 7. Note that the steps of the second method 700 to be carried out by a node 320 in a multi-channel wireless network correspond to some (but not all) of the steps of the method 200 shown in Figure 2 and / or the method 400 shown in Figure 4. Steps of the second method 700 shown in Figure 7 share common reference numerals with corresponding steps of the method 200 shown in Figure 2 and / or the method 400 shown in Figure 4.

[0179] It will be appreciated that the second method 700 to be carried out by a single node 320 in a multi-channel wireless network shown in Figure 7 may comprise any features of the second node 320 and / or the methods 200, 400 as described above with reference to Figures 2 to 4 to the extent that such methods relate to the second node 320. In Figure 7, optional steps are indicated by dotted lines.

[0180] The second method 700 to be carried out by a node 320 in a multi-channel wireless network comprises a step 220 of receiving a first request message 316 with the node 320, the first request message 316 containing listening schedule information. The second method 700 to be carried out by a node 320 in a multi-channel wireless network further comprises a step 230 of sending a second request message 322 from the node 320 on a plurality of channels, the second request message 322 containing the listening schedule information and an identifier of the first node 310.

[0181] The second request message 322 may comprise a discovery packet suitable for the wireless network send on behalf of another node 310 that sent the first request message 316. For example, the second request message 322 may comprise an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

[0182] In some embodiments, the node 320 may comprise a field diagnostic tool node. The field diagnostic tool node may be a portable node. For example, the field diagnostic tool node may be disposed on a drone or the like.

[0183] In some embodiments, the node 420 may comprise a portable node. For such embodiments, the method 700 may further comprise the following steps. In particular, the method 700 may comprise: a step 430 of physically moving the portable node so that it is proximate to the first node 310; a step 432 of joining the network with the portable node; and a step 434 establishing communication with the first node.

[0184] In some embodiments, the node 320 may be mounted on a drone and the method 700 may comprise using the drone to physically move the node 320 so that it is proximate to another node (for example, the first node 310). This may be done as part of step 430 described above.

[0185] Some embodiments of the present disclosure relate to a computer-readable medium having instructions for carrying out the method 700 shown in Figure 7 and as described above. The computer-readable medium may be a non-transitory computer-readable medium.

[0186] Some embodiments of the present disclosure relate to a node 320 for carrying out the method 700 shown in Figure 7 and as described above. The node 320 may be generally of the form of the node 500 shown in Figure 5 and described above. For such embodiments, the storage media 530 may have instructions to cause the at least one processor 520 to carry out the method 700 shown in Figure 7 and as described above.

[0187] Although in this description reference may be made to metering devices (smart meters) operating as a network node of a mesh network it should be understood that embodiments of the present disclosure may be used by any device that may form part of a multi-channel wireless network (and embodiments of the present disclosure are not limited to such metering devices). Embodiments of the present disclosure may relate to any smart infrastructure, which may comprise internet of things (loT) enabled devices with wireless capabilities.

[0188] In this description reference may be made to a network that may comprise at least one node operating under a time slotted channel hopping (TSCH) protocol. However, embodiments of the present disclosure are not limited to such networks. In general, the embodiments of the present disclosure may relate to any type of network. Furthermore, such networks may be operating under any type of channel hopping protocol. While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.

Claims

CLAIMS:1 . A method for use in a multi-channel wireless network, the method comprising: sending a first request message from a first node containing listening schedule information; receiving the first request message with a second node; sending a second request message from the second node on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node; receiving the second request message with at least a third node; and sending a reply message from each of a set of reply nodes to the first node during a time that is dependent on the listening schedule information, the set of reply nodes comprising at least a third node.

2. The method of claim 1 wherein the first request message is sent on a single channel.

3. The method of claim 1 or claim 2 wherein the first node comprises a low- functionality node (LFN) or a battery operated end point (BEP).

4. The method of any preceding claim wherein the listening schedule information comprises any combination of the following: a time delay after the first request message when the first node will start listening for reply messages; and a time duration of a period during which the first node will listen for reply messages.

5. The method of any preceding claim wherein the listening schedule information comprises any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node will listen for reply messages on each channel in the hopping sequence.

6. The method of any preceding claim wherein the second request message and / or the reply message comprises a discovery packet suitable for the wireless network.

7. The method of any preceding claim wherein the second request message comprises an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

8. The method of any preceding claim wherein the reply message comprises an enhance beacon (EB) as defined in the IEEE 802.15.4 specification.

9. The method of any preceding claim wherein the first request message comprises a unicast message sent to the second node.

10. The method of claim 9 wherein the second node comprises a parent node of the first node.11 . The method of claim 9 or claim 10 further comprising: selecting the second node from a plurality of nodes, the selection being based on proximity to the first node.

12. The method of claim 1 1 wherein the selection of the second node is made by the first node.

13. The method of claim 11 wherein the selection of the second node is made centrally and the method comprises sending a message to the first node containing an identifier of the second node and the first node sends the first request message to the second node upon receipt of such a message.

14. The method of any preceding claim further comprising sending a message to the first node from its parent node informing the first node that the parent node is about migrate to another personal area network (PAN) and the first node sends the first request message to the second node upon receipt of such a message.

15. The method of any preceding claim wherein the second node comprises a field diagnostic tool node.

16. The method of any preceding claim wherein the second node comprises a portable node and wherein before the first request message is sent, the method comprises: physically moving the portable node so that it is proximate to the first node; joining the network with the portable node; and establishing communication with the first node.

17. The method of any preceding claim wherein the second node is mounted on a drone and the method comprises: using the drone to physically move the second node so that it is proximate to the first node.

18. The method of any preceding claim wherein the or each reply message is sent at a random or pseudo-random time during a listening time period specified in the listening schedule information.

19. The method of any preceding claim wherein the first request message comprises a broadcast message that is received by the second node.

20. The method of any preceding claim further comprising: listening for any reply messages in accordance with the listening schedule information using the first node.21 . The method of any preceding claim further comprising: receiving at least one reply message from one of the set of reply nodes with the first node.

22. The method of claim 21 , the method further comprising: upon receipt of a reply message from one of the set of reply nodes, determining with the first node if the node which sent that reply message is suitable to become a parent node for the first node.

23. The method of any claim 21 or claim 22 wherein the first node receives a reply message from each of a plurality of reply nodes and wherein the method further comprises:selecting one of the plurality of reply nodes to send a unicast message to in order to establish two-way communication with that reply node.

24. The method of claim 22 or claim 23 further comprising: using the first node to initiate a joining process with a reply node that: (a) has been determined to be suitable to become a parent node for the first node; and / or (b) has been selected.

25. The method of any one of claims 21 to 24, the method further comprising: sending a first unicast message to a reply node from the set of reply nodes in order to establish two-way communication with that reply node.

26. The method of claim 25 further comprising: upon receipt of the first unicast message, sending a second unicast message from the reply node back to the first node.

27. A method to be carried out by a node in a multi-channel wireless network, the method comprising: sending a first request message on a single channel from the node, the first request message containing listening schedule information and requesting another node to transmit a second request message on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node; and listening for any reply messages in accordance with the listening schedule information using the first node.

28. The method of claim 27 wherein the node comprises a low-functionality node (LFN) or a battery operated end point (BEP).

29. The method of claim 27 or claim 28 wherein the listening schedule information comprises any combination of the following: a time delay after the first request message when the first node will start listening for reply messages; and a time duration of a period during which the first node will listen for reply messages.

30. The method of any one of claims 27 to 29 wherein the listening schedule information comprises any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node will listen for reply messages on each channel in the hopping sequence.31 . The method of any one of claims 27 to 30 wherein the second request message comprises an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

32. The method of any one of claims 27 to 31 wherein the first request message comprises a unicast message sent to the second node.

33. The method of claim 32 wherein the second node comprises a parent node of the first node.

34. The method of claim 32 or claim 33 further comprising: selecting the second node from a plurality of nodes, the selection being based on proximity to the first node.

35. The method of claim 32 or claim 34 wherein the method comprises receiving a message containing an identifier of the second node and wherein the node sends the first request message to the second node upon receipt of such a message.

36. The method of any one of claims 27 to 35 further comprising receiving a message from a parent node of the node informing the node that the parent node is about migrate to another personal area network (PAN) and wherein the node sends the first request message to the second node upon receipt of such a message.

37. The method of any one of claims 27 to 36 wherein the first request message comprises a broadcast message that is received by the second node.

38. The method of any one of claims 27 to 37 further comprising: receiving at least one reply message.

39. The method of claim 38, the method further comprising: upon receipt of a reply message from a reply node, determining if the reply node is suitable to become a parent node for the node.

40. The method of any claim 38 or claim 39 wherein the node receives a reply message from each of a plurality of reply nodes and wherein the method further comprises: selecting one of the plurality of reply nodes to send a unicast message to in order to establish two-way communication with that reply node.41 . The method of claim 39 or claim 40 further comprising: initiating a joining process with a reply node that: (a) has been determined to be suitable to become a parent node for the node; and / or (b) has been selected.

42. The method of any one of claims 39 to 41 , the method further comprising: sending a first unicast message to a reply node from the set of reply nodes in order to establish two-way communication with that reply node.

43. The method of any preceding one of claims 38 to 42 wherein the or each reply message comprises an enhance beacon (EB) as defined in the IEEE 802.15.4 specification.

44. A method to be carried out by a node in a multi-channel wireless network, the method comprising: receiving a first request message with the node, the first request message containing listening schedule information; and sending a second request message from the node on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node.

45. The method of claim 44 wherein the listening schedule information comprises any combination of the following: a time delay after the first request message when the first node will start listening for reply messages; anda time duration of a period during which the first node will listen for reply messages.

46. The method of claim 44 or claim 45 wherein the listening schedule information comprises any combination of the following: a response channel; and / or a hopping sequence of channels and a time duration of a period during which the first node will listen for reply messages on each channel in the hopping sequence.

47. The method of any one of claims 44 to 46 wherein the second request message comprises a discovery packet suitable for the wireless network send on behalf of another node that sent the first request message.

48. The method of any one of claims 44 to 47 wherein the second request message comprises an enhanced beacon request (EBR) as defined in the IEEE 802.15.4 specification.

49. The method of any one of claims 44 to 48 wherein the node comprises a field diagnostic tool node.

50. The method of any one of claims 44 to 49 wherein the node comprises a portable node and wherein before the first request message is received, the method comprises: physically moving the portable node so that it is proximate to another node; joining the network with the portable node; and establishing communication with the other node.51 . The method of any one of claims 44 to 50 wherein the node is mounted on a drone and the method comprises: using the drone to physically move the node so that it is proximate to another node from which the first request message will originate.

52. A computer-readable medium having instructions for carrying out the method of any one of claims 1 to 26.

53. A computer-readable medium having instructions for carrying out the method of any one of claims 27 to 43.

54. A computer-readable medium having instructions for carrying out the method of any one of claims 44 to 51 .

55. A network of nodes for use in a wireless network, the network comprising: a first node operable to send a first request message containing listening schedule information; a second node operable to: receive the first request message; and send a second request message on a plurality of channels, the second request message containing the listening schedule information and an identifier of the first node; and a set of reply nodes, each operable to send a reply message to the first node during a time that is dependent on the listening schedule information, and wherein the set of reply nodes comprises at least a third node.

56. The network of nodes of claim 55 wherein each node comprises: a transceiver; at least one processor; and storage media, the storage media having instructions to cause the at least one processor to carry out one or more steps of the method of any one of claims 1 to 26.

57. A node for carrying out the method of any one of claims 27 to 43, the node comprising: a transceiver; at least one processor; and storage media, the storage media having instructions to cause the at least one processor to carry out one or more steps of the method of any one of claims 27 to 43.

58. A node for carrying out the method of any one of claims 44 to 51 , the node comprising: a transceiver; at least one processor; andstorage media, the storage media having instructions to cause the at least one processor to carry out one or more steps of the method of any one of claims 44 to 51 .

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