Selecting a parent node in a time-slotted channel hopping network

1. A method comprising:

synchronizing, by a low-energy node, communications with a channel hopping pattern of a primary time-slotted channel hopping (“TSCH”) network to synchronize a clock of the low-energy node with the primary TSCH network;

after synchronizing the communications, transmitting, by the low-energy node, a selection-phase enhanced beacon request that requests an enhanced beacon from TSCH nodes with availability to accept child nodes and with at least a specified link quality;

receiving, by the low-energy node, a selection-phase enhanced beacon from a first TSCH node;

transmitting, by the low-energy node, an adoption request to the first TSCH node requesting the first TSCH to adopt the low-energy node as a child node; and

receiving, by the low-energy node, an adoption response from the first TSCH node indicating the first TSCH node agrees to adopt the low-energy node as a child node and is managing the primary TSCH network join on behalf of the low-energy node.

2. The method of claim 1 , wherein the selection-phase enhanced beacon is a first selection-phase enhanced beacon, the method further comprising:

receiving, by the low-energy node, a second selection-phase enhanced beacon from a second TSCH node;

comparing link quality information from the first selection-phase enhanced beacon with link quality information from the second selection-phase enhanced beacon; and

when the comparison indicates that the first TSCH node provides better link quality than the second TSCH node, then selecting the first TSCH node as a parent node.

3. The method of claim 1 , wherein synchronizing communications with the channel hopping pattern of the primary TSCH network comprises:

transmitting, by the low-energy node, a synchronization-phase enhanced beacon request on a low-energy network channel; and

receiving, by the low-energy node, a synchronization-phase enhanced beacon including information for synchronizing communications with the channel hopping pattern of the primary TSCH network.

4. The method of claim 3 , wherein synchronizing communications with the channel hopping pattern of the primary TSCH network further comprises:

listening, by the low-energy node, a predetermined amount of time for the synchronization-phase enhanced beacon; and

in response to not receiving the synchronization-phase enhanced beacon during the predetermined amount of time, transmitting, by the low-energy node, another synchronization-phase enhanced beacon request.

5. The method of claim 1 , further comprising:

waking, by the low-energy node, from a sleep state; and

resynchronizing, by the low-energy node, communications with the channel hopping pattern of the primary TSCH network.

6. The method of claim 5 , wherein the selection-phase enhanced beacon request is a first selection-phase enhanced beacon request, the selection-phase enhanced beacon is a first selection-phase enhanced beacon, the adoption request is a first adoption request, and the adoption response is a first adoption response, the method further comprising:

transmitting, by the low-energy node, a second selection-phase enhanced beacon request that requests another enhanced beacon from the TSCH nodes with availability to accept children and with at least the specified link quality using the resynchronized communications;

receiving, by the low-energy node, a second selection-phase enhanced beacon from a second TSCH node;

transmitting, by the low-energy node, a second adoption request to the second TSCH node; and

receiving, by the low-energy node, a second adoption response from the second TSCH node indicating the second TSCH node is managing the low-energy node rejoining the primary TSCH network on behalf of the low-energy node.

7. The method of claim 6 , further comprising:

transmitting, by the low-energy node, an emancipation request to the first TSCH node requesting that the first TSCH node release the low-energy node; and

receiving, by the low-energy node, an emancipation response from the first TSCH node.

8. A system comprising:

a plurality of time-slotted channel hopping (“TSCH”) nodes communicatively coupled to each other in a primary TSCH network; and

a low-energy node comprising:

a processor; and

a non-transitory computer readable medium on which instructions are stored for causing the processor to:

synchronize communications of the low-energy node with a channel hopping pattern of the primary TSCH network to synchronize a clock of the low-energy node with the primary TSCH network;

after synchronizing the communications, transmit a selection-phase enhanced beacon request that requests an enhanced beacon from TSCH nodes of the plurality of TSCH nodes with availability to accept child nodes and with at least a specified link quality;

receive, a selection-phase enhanced beacon from a first TSCH node of the plurality of TSCH nodes;

transmit an adoption request to the first TSCH node requesting the first TSCH node to adopt the low-energy node as a child node; and

receive an adoption response from the first TSCH node indicating the first TSCH node agrees to adopt the low-energy node as a child node and is managing the primary TSCH network join on behalf of the low-energy node.

9. The system of claim 8 , wherein the selection-phase enhanced beacon is a first selection-phase enhanced beacon, wherein the instructions further cause the processor to:

receive a second selection-phase enhanced beacon from a second TSCH node of the plurality of TSCH nodes;

compare link quality information from the first selection-phase enhanced beacon with link quality information from the second selection-phase enhanced beacon; and

when the comparison indicates that the first TSCH node provides better link quality than the second TSCH node, then select the first TSCH node as a parent node.

10. The system of claim 8 , wherein causing the processor to synchronize communications with the channel hopping pattern of the primary TSCH network comprises:

transmitting a synchronization-phase enhanced beacon request on a low-energy network channel; and

receiving a synchronization-phase enhanced beacon including information for synchronizing communications with the channel hopping pattern of the primary TSCH network.

11. The system of claim 10 , wherein causing the processor to synchronize communications with the channel hopping pattern of the primary TSCH network further comprises:

listening a predetermined amount of time for the synchronization-phase enhanced beacon; and

in response to not receiving the synchronization-phase enhanced beacon during the predetermined amount of time, transmitting another synchronization-phase enhanced beacon request.

12. The system of claim 8 , wherein the instructions further cause the processor to:

wake the low-energy node from a sleep state; and

resynchronize communications by the low-energy node with the channel hopping pattern of the primary TSCH network.

13. The system of claim 12 , wherein the selection-phase enhanced beacon request is a first selection-phase enhanced beacon request, the selection-phase enhanced beacon is a first selection-phase enhanced beacon, the adoption request is a first adoption request, and the adoption response is a first adoption response, wherein the instructions further cause the processor to:

transmit a second selection-phase enhanced beacon request that requests another enhanced beacon from the TSCH nodes with availability to accept children and with at least the specified link quality using the resynchronized communications;

receive a second selection-phase enhanced beacon from a second TSCH node;

transmit a second adoption request to the second TSCH node; and

receive a second adoption response from the second TSCH node indicating the second TSCH node is managing the low-energy node rejoining the primary TSCH network on behalf of the low-energy node.

14. The system of claim 13 , wherein the instructions further cause the processor to:

transmit an emancipation request to the first TSCH node requesting that the first TSCH node release the low-energy node; and

receive an emancipation response from the first TSCH node.

15. A method comprising:

receiving, by a time-slotted channel hopping (“TSCH”) node of a primary TSCH network, a selection-phase enhanced beacon request from a low-energy node during a TSCH timeslot in a parent selection phase;

transmitting, by the TSCH node, a selection-phase enhanced beacon based on determining that the TSCH node has availability to accept a child node and that the TSCH node has a link quality with the low-energy node that exceeds a threshold value indicated in the selection-phase enhanced beacon request;

receiving, by the TSCH node, an adoption request from the low-energy node requesting the TSCH node to adopt the low-energy node as a child node; and

transmitting, by the TSCH node, an adoption response to the low-energy node indicating the TSCH node agrees to adopt the low-energy node as a child node and is managing the low-energy node joining the primary TSCH network on behalf of the low-energy node.

16. The method of claim 15 , wherein receiving the selection-phase enhanced beacon request comprises receiving the selection-phase enhanced beacon request during a primary portion of the TSCH timeslot indicating the low-energy node is synchronized with the primary TSCH network.

17. The method of claim 15 , wherein prior to receiving the selection-phase enhanced beacon request during the parent selection phase, the method further comprises:

listening, by the TSCH node, during a primary portion of a TSCH timeslot for a communication from another TSCH node on the primary TSCH network;

when no communication is received during the primary portion of the TSCH timeslot, then listening, by the TSCH node, on a low-energy network channel during a secondary portion of the TSCH timeslot for a synchronization-phase enhanced beacon request from the low-energy node; and

transmitting, by the TSCH node, a synchronization-phase enhanced beacon for synchronizing communications between the low-energy node and the primary TSCH network in response to the synchronization-phase beacon enhanced beacon request.

18. The method of claim 17 , wherein transmitting the synchronization-phase enhanced beacon comprises transmitting the synchronization-phase enhanced beacon during a primary portion of a second TSCH timeslot, the second TSCH timeslot subsequent to the TSCH timeslot.

19. The method of claim 15 , wherein transmitting the selection-phase enhanced beacon comprises waiting for a random amount of time before transmitting the selection-phase enhanced beacon to avoid the selection-phase enhanced beacon colliding with another selection-phase enhanced beacon transmitted by another TSCH node on the primary TSCH network.

20. The method of claim 15 , further comprising:

receiving, by the TSCH node, an emancipation request from the low-energy node requesting that the TSCH node release the low-energy node;

releasing, by the TSCH node, resources used by the TSCH node for managing the low-energy node; and

transmitting, by the TSCH node, an emancipation response to the low-energy node.