Fast sync recovery in a wireless time-slotted low power and lossy network based on localized search using successively-shifted guard time

1. A method comprising:

detecting, by a constrained network device in a low power and lossy network, a loss of synchronization with a neighboring network device based on a determined absence of a prescribed transmission activity by the neighboring network device within a prescribed listening interval that is limited to a prescribed guard time according to a wireless time-slotted transmission protocol; and

executing, by the constrained network device, localized sync recovery based on shifting a next listening interval to a shifted listening interval based on selectively shifting, based on a selected shift amount, the prescribed guard time of a corresponding next instance of the prescribed listening interval, enabling the constrained network device to recover synchronization with the neighboring network device based on detecting the prescribed transmission activity that is outside the prescribed listening interval and within the shifted listening interval.

2. The method of claim 1 , wherein the executing includes at least one or more of:

first shifting a corresponding next listening interval based on accelerating a corresponding shifted listening interval to start before the corresponding next instance of the prescribed listening interval by at least the selected shift amount; or

second shifting a corresponding next listening interval based on delaying a corresponding shifted listening interval to start after the corresponding next instance of the prescribed listening interval by at least the selected shift amount.

3. The method of claim 2 , wherein the executing further includes:

successively increasing the selected shift amount based on a corresponding determined absence of the prescribed transmission activity following the first shifting and the second shifting; and

repeating, for each successively increased selected shift amount, the first and shifting and second shifting of accelerating the shifted listening interval and delaying the corresponding shifted listening interval, in response to a corresponding determined absence of the prescribed transmission activity in the corresponding shifted listening interval.

4. The method of claim 1 , wherein the executing includes:

successively shifting the next listening interval away from the corresponding next instance of the prescribed listening interval, until detection of the prescribed transmission activity within one of the shifted listening intervals; and

resynchronizing with the neighboring network device in response to detecting the prescribed transmission activity within the one shifted listening interval.

5. The method of claim 4 , wherein the executing includes:

transmitting a beacon request within a first transmission instance associated with a first instance of one of the shifted listening intervals; and

determining whether a beacon response is detected within a second instance, following the first instance, of the one shifted listening interval.

6. The method of claim 1 , wherein the localized sync recovery is based on passive detection in one or more of the shifted listening intervals without transmission of any beacon request.

7. The method of claim 1 , further comprising causing sync recovery for child network devices, having attached to the constrained network device, based on stepwise transition from the prescribed listening interval to the shifted listening interval for data packets transmitted to the child network devices.

8. An apparatus implemented as a physical machine, the apparatus comprising:

non-transitory machine readable media configured for storing executable machine readable code;

a device interface circuit configured for detecting, within a prescribed listening interval, a prescribed transmission activity from a neighboring network device in a low power and lossy network; and

a processor circuit configured for executing the machine readable code, and when executing the machine readable code operable for:

detecting, by the apparatus implemented as a constrained network device in the low power and lossy network, a loss of synchronization with the neighboring network device based on a determined absence of the prescribed transmission activity by the neighboring network device within the prescribed listening interval that is limited to a prescribed guard time according to a wireless time-slotted transmission protocol, and

executing localized sync recovery based on shifting a next listening interval to a shifted listening interval based on selectively shifting, based on a selected shift amount, the prescribed guard time of a corresponding next instance of the prescribed listening interval, enabling the apparatus to recover synchronization with the neighboring network device based on detecting the prescribed transmission activity that is outside the prescribed listening interval and within the shifted listening interval.

9. The apparatus of claim 8 , wherein the processor circuit is configured for executing the localized sync recovery based on at least one or more of:

first shifting a corresponding next listening interval based on accelerating a corresponding shifted listening interval to start before the corresponding next instance of the prescribed listening interval by at least the selected shift amount; or

second shifting a corresponding next listening interval based on delaying a corresponding shifted listening interval to start after the corresponding next instance of the prescribed listening interval by at least the selected shift amount.

10. The apparatus of claim 9 , wherein the processor circuit further is configured for executing the localized sync recovery based on:

successively increasing the selected shift amount based on a corresponding determined absence of the prescribed transmission activity following the first shifting and the second shifting; and

repeating, for each successively increased selected shift amount, the first and shifting and second shifting of accelerating the shifted listening interval and delaying the corresponding shifted listening interval, in response to a corresponding determined absence of the prescribed transmission activity in the corresponding shifted listening interval.

11. The apparatus of claim 8 , wherein the processor circuit is configured for executing the localized sync recovery based on:

successively shifting the next listening interval away from the corresponding next instance of the prescribed listening interval, until detection of the prescribed transmission activity within one of the shifted listening intervals; and

resynchronizing with the neighboring network device in response to detecting the prescribed transmission activity within the one shifted listening interval.

12. The apparatus of claim 11 , wherein the processor circuit further is configured for executing the localized sync recovery based on:

transmitting a beacon request within a first transmission instance associated with a first instance of one of the shifted listening intervals; and

determining whether a beacon response is detected within a second instance, following the first instance, of the one shifted listening interval.

13. The apparatus of claim 8 , wherein the processor circuit is configured for executing the localized sync recovery based on based on passive detection in one or more of the shifted listening intervals without transmission of any beacon request.

14. The apparatus of claim 8 , wherein the processor circuit is configured for causing sync recovery for child network devices, having attached to the constrained network device, based on stepwise transition from the prescribed listening interval to the shifted listening interval for data packets transmitted to the child network devices.

15. One or more non-transitory tangible media encoded with logic for execution by a machine and when executed by the machine operable for:

detecting, by the machine implemented as a constrained network device in a low power and lossy network, a loss of synchronization with a neighboring network device based on a determined absence of a prescribed transmission activity by the neighboring network device within a prescribed listening interval that is limited to a prescribed guard time according to a wireless time-slotted transmission protocol; and

executing, by the constrained network device, localized sync recovery based on shifting a next listening interval to a shifted listening interval based on selectively shifting, based on a selected shift amount, the prescribed guard time of a corresponding next instance of the prescribed listening interval, enabling the constrained network device to recover synchronization with the neighboring network device based on detecting the prescribed transmission activity that is outside the prescribed listening interval and within the shifted listening interval.

16. The one or more non-transitory tangible media of claim 15 , wherein the executing includes at least one or more of:

first shifting a corresponding next listening interval based on accelerating a corresponding shifted listening interval to start before the corresponding next instance of the prescribed listening interval by at least the selected shift amount; or

second shifting a corresponding next listening interval based on delaying a corresponding shifted listening interval to start after the corresponding next instance of the prescribed listening interval by at least the selected shift amount.

17. The one or more non-transitory tangible media of claim 15 , wherein the executing includes:

successively shifting the next listening interval away from the corresponding next instance of the prescribed listening interval, until detection of the prescribed transmission activity within one of the shifted listening intervals; and

resynchronizing with the neighboring network device in response to detecting the prescribed transmission activity within the one shifted listening interval.

18. The one or more non-transitory tangible media of claim 17 , wherein the executing includes:

transmitting a beacon request within a first transmission instance associated with a first instance of one of the shifted listening intervals; and

determining whether a beacon response is detected within a second instance, following the first instance, of the one shifted listening interval.

19. The one or more non-transitory tangible media of claim 15 , wherein the localized sync recovery is based on passive detection in one or more of the shifted listening intervals without transmission of any beacon request.

20. The one or more non-transitory tangible media of claim 15 , further operable for causing sync recovery for child network devices, having attached to the constrained network device, based on stepwise transition from the prescribed listening interval to the shifted listening interval for data packets transmitted to the child network devices.