Patent Description:
A PAN architecture may have a hysteresis in network topology to prevent thrashing when there is a temporary disruption in the network, such as a temporary loss of backhaul connection. However, some systems and devices cannot tolerate a temporary loss of backhaul connection and need to switch PANs once the backhaul connection becomes unavailable.

Generally, a root node does not routinely communicate the status of the backhaul connection to the other nodes in the PAN. Instead, each node has to determine the state of the backhaul connection by sending upper layer messages and receiving a response from the backhaul. Since a node cannot send an upper layer message until it joins a PAN, a node cannot determine the status of the backhaul connection prior to joining. A node that requires a backhaul connection may join a PAN and then determine that a backhaul connection is unavailable.

<CIT> relates to a method and system for conveying backhaul link information for intelligent selection of a mesh access point (MAP) in a mesh network. The mesh network includes a plurality of MAPs. The MAPs send backhaul link information regarding backhaul connections between each MAP and any interconnections in the mesh network to a WTRU (wireless transmit/receive unit). The WTRU then determines a performance value with respect to the MAPs based on the backhaul link information and selects one of the MAPs to associate with based on the performance value. The WTRU may send information about interconnection needs of the WTRU to the MAPs, and the MAPs may generate the backhaul link information based on the interconnection needs of the WTRU. The WTRU may estimate the expected throughput for the end-to-end connection, which allows the WTRU to associate to a MAP that provides the best performance from the point of view of both the WTRU and the overall system.

A node that determines that the backhaul connection for its current PAN is unavailable, may determine that it needs to switch PANs. However, the node may not have direct visibility to another PAN, which may delay the switch to a different PAN.

When a node switches PANs, any child nodes remain with the current PAN by finding a new parent node or switch to the new PAN by unjoining the current PAN and joining the new PAN. This process is time consuming and causes the child node to be unavailable until it locates a new parent or completes the unjoining/joining process.

Aspects of the invention provide improvements to the way that a node determines the status of a backhaul connection and joins or switches to a PAN with an available backhaul connection. Additional aspects of the invention provide a more efficient way to switch PANs when a node has a child node. The node may bring its child node with it when it switches regardless of the reason for the switch.

A node may consider the status of a backhaul connection prior to joining a PAN. The node may be a critical node that requires an available backhaul connection. The status of the backhaul connection may be included in a layer <NUM> message, such as a beacon. In one example, backhaul status information is included in an information element in the beacon.

Once a critical node joins a PAN, a critical path may be established from the critical node to the root of the PAN. In one example, layer <NUM> messages, such as DAO messages are used to establish the critical path. Nodes along the critical path may seek to join a new PAN when the backhaul connection for the current PAN becomes unavailable.

When a node switches to a new PAN, it may coordinate the switch with its child nodes. The switching node identifies a new PAN and obtains timing synchronization information for the new PAN. The switching node sends timing synchronization information for the new PAN and a time for switching to the new PAN to its child nodes. The switching node and the child nodes maintain timing synchronization information for both the current PAN and the new PAN. At the time for switching, the switching node and its child nodes switch to the new PAN. A node may coordinate the switch to the new PAN with its child node whenever a switch occurs. The coordination is not limited to a switch based on a loss of a backhaul connection.

These illustrative aspects and features are mentioned not to limit or define the invention, but to provide examples to aid understanding of the inventive concepts disclosed in this application. Other aspects, advantages, and feature of the present invention will become apparent after review of the entire application.

These and other features, aspects, and advantages of the present disclosure are better understood when the following Detailed Description is read with reference to the accompanying drawings, where:.

The present invention is directed to systems and methods for managing nodes in mesh networks, including joining a critical node to a PAN, creating and maintaining a critical path, PAN switching by critical path nodes, and maintaining parent/child relationships when switching PANs. A critical node may consider the status of the backhaul connection for a PAN prior to joining the PAN. Once joined, a critical path from the critical node to the root is identified and nodes along the critical path, including the critical node, may attempt to join a new PAN if the backhaul connection for the current PAN becomes unavailable. The status of the backhaul connection for a PAN may be communicated in an information element (IE) in a beacon. If a critical path node is a parent node with one or more child nodes and it switches PANs, then the critical path node and the child nodes may switch PANs while maintaining their parent-child relationship. A parent node may maintain its parent-child relationship with its child node when it switches PANs for reasons other than a loss of a backhaul connection.

<FIG> illustrates two PANs, PAN A and PAN B. Node <NUM> is the root for PAN A and node <NUM> is the root for PAN B. PAN A includes nodes A-<NUM> through A-<NUM> and PAN B includes nodes B-<NUM> and B-<NUM>. Backhaul connection <NUM> connects PAN A with a central system <NUM> and backhaul connection <NUM> connects PAN B with the central system. Although not shown in <FIG>, there may be any number of intervening devices between a PAN and the central system <NUM>.

Node <NUM> and node <NUM> monitor the status of their respective backhaul connections and include information about the status of their backhaul connections in their beacons. In one example, they determine whether they are connected to an NTP server and if so, determine that their backhaul connection is available. Other implementations may consider other factors to determine whether their backhaul connection is available or unavailable including, but not limited to, connection to a specific system or server or connection to a time source. Each node includes its current backhaul status information in an IE in its respective beacon. The IE may be a new IE or may be an existing IE. If an existing IE is used, then the backhaul status information may be appended to the IE. Any type of IE that includes backhaul status information is referred to herein as a backhaul status IE. The backhaul status information may be conveyed in one bit where a first value indicates that the backhaul connection is available and a second value indicates that the backhaul connection is unavailable or unknown. In some implementations, the backhaul status information includes additional information, such as how long the backhaul connection has been in its current state. For example, a timestamp indicating the time of the last status change may be used. In the example illustrated in <FIG>, the backhaul connection <NUM> is available and the backhaul connection <NUM> is unavailable.

In <FIG>, node N is a critical node that is not joined to either PAN. A critical node is a node that requires a backhaul connection. It may not be able to wait for the backhaul connection to reconnect if it becomes available. One example of a critical node is a node associated with DA (Distribution Automation) equipment, such as line sensors, switches, and re-closers. A node may be designated as a critical node upon installation or may be designated as a critical node after installation.

Node N receives Beacon A from PAN A and Beacon B from PAN B. In this example, Beacon A includes a backhaul status IE that indicates that backhaul connection <NUM> is available and Beacon B includes a backhaul status IE that indicates that backhaul connection <NUM> is unavailable. Since node N is a critical node, it joins PAN A. Critical nodes may be configured to avoid joining a PAN with an unavailable backhaul connection, even though other factors, e.g., rank, load, etc. may be favorable to joining the PAN.

<FIG> illustrates PAN A after node N joins. After node N joins, it sends a DAO message that identifies node N as a critical node. In one example, node N sets a bit in the DAO flag field to indicate that it is a critical node. Based on the DAO message, node <NUM>, which is the root for PAN A, determines a critical path for node N and stores information describing the critical path for node N, i.e., the path including node N, node A-<NUM>, node A-<NUM>, and node A-<NUM>. The root may send a DAO-ACK message to Node N with a bit set to indicate that a critical path is in place.

In some implementations, as each node between the root and Node N receives the DAO-ACK message, the node checks the bit and determines that it is a critical path node. If a node does not support critical path nodes, then after it receives the message, it does not forward the message. Instead, it may discard the message or send an error message.

Node N may use other types of messages or other fields to indicate that it is a critical node including, but not limited to an indication in a hop-by-hop extension header of an IPv6 message. In one example, Node N sets a bit in a hop-by-hop extension header to indicate that it is a critical node and is requesting a critical path. When node A-<NUM> supports critical path nodes, it receives the message, checks the bit, enters a pre-critical path state, and forwards the message to the next node. This process repeats until the message reaches the root of PAN A. When the root sends a message back to Node N indicating that a critical path is in place, the nodes between the root and Node N may examine the message and transition from a pre-critical path state to a critical path state.

Since PAN A may be a wireless mesh network, the critical path for node N may change. If the critical path changes, then the critical path for node N may include additional or different nodes. The critical path information maintained by the root and the critical path status of each node affected by the change are updated to reflect the change in the critical path.

After node N joins PAN A, it generates and sends beacons that include a backhaul status IE. Node N obtains the information for the backhaul status IE from the beacons that it receives from its parent node A-<NUM> or other nodes in PAN A.

<FIG> illustrates the scenario where PAN A's backhaul connection becomes unavailable and PAN B's backhaul connection is available. When node <NUM> detects that its backhaul connection is unavailable, then it may generate a beacon, Beacon A, that includes backhaul status information in the backhaul status IE. The information regarding the status of the backhaul connection is propagated through the network until node N receives a beacon with a backhaul status IE indicating that the backhaul connection for PAN A is unavailable. Since node N is a critical node, it may begin searching for a new PAN to join once it determines that the backhaul connection for its current PAN is unavailable. If node N receives a beacon from a different PAN, such as Beacon B from PAN B, it may consider whether the backhaul connection for PAN B is available when determining whether to switch PANs. If it decides to switch PANs, then it may follow a similar process to that described above in connection with <FIG> for joining PAN B. In this instance, the other nodes joined to PAN A may remain joined to PAN A, as shown in <FIG>.

When node N joins PAN B, its parent node, node A-<NUM> determines that node N is no longer a child node. In one example, node N sends a disassociation message to node A-<NUM> prior to joining PAN B to inform node A-<NUM> of the switch. Node N determines whether it has any other child nodes that are critical nodes or critical path nodes. If it does not have any other child nodes that are critical nodes or critical path nodes, then it determines that it is no longer on a critical path and sends a DAO message indicating that it is no longer a critical path node. Similarly, if node A-<NUM> has no child nodes that are critical nodes or critical path nodes, then it sends a DAO message indicating that is it no longer a critical path node. If node A-<NUM> has no child nodes that are critical nodes or critical path nodes, then it sends a DAO message to its parent node, node <NUM>, and node <NUM> removes the critical path for node N. Node A-<NUM> may remain a critical path node if it has another child node, e.g. Node A-<NUM>, that is a critical node or critical path node. In this situation, node <NUM> stores critical path information for Node A-<NUM>. Once a node, e.g. node A-<NUM>, is no longer a critical path node, then it may remain joined to its current PAN or switch to a target PAN based on factors other than the status of the backhaul connection for its current PAN and a target PAN.

In some instances, a critical node may only rarely receive a beacon from another PAN. Once a node on the critical path receives a beacon from another PAN with an available backhaul connection while the backhaul connection for the current PAN is unavailable, it may switch PANs. For example, if node A-<NUM> receives a beacon from node A-<NUM> or another node in PAN A with a backhaul status IE indicating that the backhaul connection for PAN A is unavailable, then node A-<NUM> may search for a different PAN to join. Since node A-<NUM> is on a critical path, it may be more aggressive in seeking a different PAN than if it weren't on a critical path. In some implementations, the node considers its RPL layer in determining how aggressively to seek a different PAN. For example, a layer <NUM> node may be less aggressive than a lower layer node.

If node A-<NUM> receives a beacon from a different PAN, such as Beacon B from PAN B, it may determine whether to switch PANs based on whether the backhaul connection for PAN B is available. When the backhaul connection for PAN B is available, node A-<NUM> joins PAN B, as shown in <FIG> illustrates that after node A-<NUM> joins PAN B, its child nodes, node A-<NUM> and node N may not be joined to either PAN A or PAN B. Since node A-<NUM> is not a critical node and does not have a child node that is a critical node in <FIG>, it does not identify itself as a critical node or a critical path node after joining PAN B. In some implementations, node A-<NUM> and node N each execute a separate joining process. Each node may rejoin PAN A by finding a new parent node, join PAN B through node A-<NUM> (its PAN A parent node), or join PAN B by finding a different parent node. Since node N is a critical node and the backhaul connection for PAN A is unavailable, node N joins PAN B. In the scenario where node N joins PAN B as a child node of node A-<NUM>, node N sends a DAO message that identifies node N as a critical node. A critical path is established in a manner similar to that discussed above in connection with <FIG>.

In some implementations, a secondary backhaul connection, such as Ethernet or cellular, may be available. If so, when a critical path node receives a beacon with a backhaul status IE indicating that the backhaul connection is unavailable, then the node may choose to remain on the current PAN and use the secondary backhaul connection.

If the backhaul status IE indicates that the backhaul connection is unavailable and includes information about how long the backhaul connection has been unavailable, then a critical path node may consider how long the backhaul connection has been unavailable when determining when to switch to a new PAN.

Although the foregoing examples discuss the use of the backhaul status IE in connection with critical nodes, the backhaul status IE may be used whenever backhaul status information is useful. It is not limited to use by critical path nodes.

A node may maintain existing parent-child relationships when it switches to a new PAN. The switch may occur because a backhaul connection is lost or for any other reason.

Continuing with the example of <FIG>, node A-<NUM> may bring its child nodes with it when it joins PAN B. Once node A-<NUM> determines that it is going to switch to a target PAN, then the node maintains timing synchronization information for both its current PAN, e.g. PAN A, and its target PAN, e.g., PAN B. Node A-<NUM> obtains the timing synchronization information for the target PAN from a beacon in the target PAN. Node A-<NUM> communicates the timing synchronization information for the target PAN to its child nodes node A-<NUM> and node N, as well as a time when it plans to switch to the target PAN. The timing synchronization information and the switch time may be communicated in a beacon from node A-<NUM>. For example, IEs in the beacon currently provide information about the network and include absolute slot number, channel hopping sequence, and timeslot offset information. An IE in the beacon may be modified to include a PAN switching timestamp. Only nodes that recognize node A-<NUM> as their parent node may act upon the timing synchronization information and the switch time. Once nodes A-<NUM> and node N receive the beacon with the timing synchronization information and the switch time, the nodes maintain timing synchronization information for both PAN A and PAN B. At the switch time, node A-<NUM> and its child nodes, node A-<NUM> and node N, switch from PAN A, as shown in <FIG>, to PAN B, as shown in <FIG>. After the switch, node A-<NUM> may send a DIS message to node B-<NUM> to trigger a DIO message from node B-<NUM>. In response to the DIO message, node A-<NUM> may send a DAO message that indicates that its child node, node N, is a critical node and that node A-<NUM> is on a critical path. Once node A-<NUM> receives a DAO-ACK message, it may send a DIO message to its child nodes that it brought from PAN A, e.g., node A-<NUM> and node N, via a unicast, multicast, or broadcast method so that the child nodes may obtain a new network prefix.

After the nodes switch to PAN B, the critical path includes node A-<NUM>, node B-<NUM>, node B-<NUM>, and node <NUM>. By switching node A-<NUM>, node A-<NUM>, and node N to the target PAN together, the timing and network connectivity are maintained and the availability of the child nodes, e.g., node A-<NUM> and node N, is improved.

The parent-child relationship between nodes may be maintained when the parent node determines that it is switching to a target PAN for any reason. It is not limited to the situation where the parent node is a critical path node or when the switch is based on a backhaul connection status.

<FIG> illustrates a critical node <NUM> seeking to join a PAN. The node <NUM> initially determines whether to join a PAN corresponding to mesh network <NUM>. At <NUM>, the backhaul connection for network <NUM> becomes unavailable. Subsequently at <NUM>, the border router or root node for network <NUM> communicates the loss of backhaul connection to the network. In one example, the border router sends a beacon with a backhaul status IE indicating that the backhaul connection is unavailable. Critical node <NUM> begins listening for beacons at <NUM> to find a network to join. At <NUM>, node <NUM> receives a beacon from network <NUM>. The beacon includes a backhaul status IE indicating that network <NUM> has lost its backhaul connection. Since node <NUM> is a critical node, it continues to listen for additional beacons to find a network with an available backhaul connection.

At <NUM>, the backhaul connection for a PAN corresponding to mesh network <NUM> is available. At <NUM>, the border router for network <NUM> communicates the availability of the backhaul connection to the network. In one example, the border router sends a beacon with a backhaul status IE indicating that the backhaul connection is available. At <NUM>, node <NUM> receives a beacon from network <NUM>. Since the beacon from network <NUM> indicates that the backhaul connection is available, node <NUM> determines that it will try to join network <NUM>. Node <NUM> and network <NUM> conduct a message exchange <NUM>, <NUM> at layer <NUM>. The message exchange may include an association request and an association response message. Other types of message exchanges are also possible. Once joined at layer <NUM>, node <NUM> and network <NUM> conduct another message exchange at layer <NUM>. For example, node <NUM> may send a DAO message indicating that it is a critical node and a node within network <NUM> may respond with a DAO-ACK message.

At <NUM> , the backhaul connection for network <NUM> becomes unavailable. Subsequently at <NUM>, the border router for network <NUM> communicates the loss of backhaul connection to the network. At <NUM>, a beacon from network <NUM> indicates that the backhaul connection for network <NUM> is unavailable. In response to receiving the beacon, node <NUM> begins searching for a new PAN at <NUM>.

Although <FIG> uses a beacon to communicate backhaul status information, other implementations may use a different type of message including, but not limited to, another type of layer <NUM> message or a propriety frame.

<FIG> illustrates an exemplary node <NUM>. The node may include a processor <NUM>, memory <NUM>, and a transceiver device <NUM> each communicatively coupled via a bus <NUM>. The components of node <NUM> can be powered by an A/C power supply or a low energy source, such as a battery (not shown). The transceiver device <NUM> can include (or be communicatively coupled to) an antenna <NUM> for communicating with other nodes. In some examples, the transceiver device is a radio-frequency ("RF") transceiver for wirelessly transmitting and receiving signals.

The processor may include a microprocessor, an application-specific integrated circuit ("ASIC"), a state machine, a field programmable gate array ("FPGA") or other suitable computing device. The processor can include any number of computing devices and can be communicatively coupled to a computer-readable media, such as memory <NUM>. The processor can execute computer-executable program instructions or access information stored in memory to perform operations, such as those described herein. The instructions may comprise processor-specific instructions generated by a compiler and/or an interpreter from code written in any suitable computer-programming language. When instructions, such as those provided in a critical path module <NUM>, are executed, they may configure the node to perform any of the operations described herein. Although the processor, memory, bus, and transceiver device are depicted in <FIG> as separate components in communication with one another, other implementations are possible. The systems and components discussed herein are not limited to any particular hardware architecture or configuration.

Claim 1:
A method for joining a node (N, <NUM>) to a mesh network (<NUM>, <NUM>; <NUM>, <NUM>), the method comprising:
receiving, by the node (N, <NUM>), a first beacon (A) from a first network (<NUM>, <NUM>) that includes an indication of a status of a backhaul connection (<NUM>) between the first network (<NUM>, <NUM>) and a central system (<NUM>);
analyzing, by the node (N, <NUM>), the first beacon (A) to determine whether the backhaul connection (<NUM>) between the first network (<NUM>, <NUM>) associated with the first beacon (A) and the central system (<NUM>) is available;
when the backhaul connection (<NUM>) for the first network (<NUM>, <NUM>) associated with the first beacon (A) is not available, then continuing to listen, by the node (N, <NUM>), for additional beacons;
receiving, by the node (N, <NUM>), a second beacon (B) from a second network (<NUM>, <NUM>) that includes an indication of a status of a backhaul connection (<NUM>) between the second network (<NUM>) and the central system (<NUM>);
analyzing, by the node (N, <NUM>), the second beacon (B) to determine whether the backhaul connection (<NUM>) between the second network (<NUM>) associated with the second beacon (B) and the central system (<NUM>) is available; and
when the backhaul connection (<NUM>) for the second network (<NUM>, <NUM>) associated with the second beacon (B) is available, then joining the node (N, <NUM>) to the second network (<NUM>, <NUM>) associated with the second beacon (B) by:
sending, by the node (N, <NUM>), a first message to join the second network (<NUM>) associated with the second beacon (B); and
after joining the second network (<NUM>), sending, by the node (N, <NUM>), a second message indicating that the node (N, <NUM>) is a critical node that requires the backhaul connection (<NUM>) between the second network (<NUM>, <NUM>) and the central system (<NUM>);
receiving, by a root node (<NUM>, <NUM>), a third message corresponding to the second message, wherein the third message includes identifying information for each node between the critical node (N, <NUM>) and the root node (<NUM>, <NUM>) that forwarded a message corresponding to the second message; and
identifying, by the root node (<NUM>, <NUM>), a critical path between the root node (<NUM>, <NUM>) and the critical node (N, <NUM>), the critical path including each node between the critical node (N, <NUM>) and the root node (<NUM>, <NUM>) that forwarded a message corresponding to the second message.