Parent Search

Specifies the backoff interval in seconds for a child to not perform a parent search after triggering one.

This is used when device is an MTD child.

Applicable only if periodic parent search feature is enabled (see OPENTHREAD_CONFIG_PARENT_SEARCH_ENABLE).

Specifies the interval in seconds for a child to check the trigger condition to perform a parent search.

Applicable only if periodic parent search feature is enabled (see OPENTHREAD_CONFIG_PARENT_SEARCH_ENABLE).

Define as 1 to enable the periodic parent search feature.

When this feature is enabled, an end device/child (while staying attached) periodically searches for a potentially better parent and switches parents if a better one is found.

The parent search mechanism depends on whether the device is an FTD child or an MTD child.

FTD Child

• An FTD child receives and processes MLE Advertisements from neighboring routers. It uses this information to track the one-way link quality to each, which is later used to compare and select potential new parents.
• Every OPENTHREAD_CONFIG_PARENT_SEARCH_CHECK_INTERVAL seconds, an FTD child tries to select a better parent. The FTD child checks the list of neighboring routers and the tracked link quality information. A new parent is selected only if its average RSS exceeds the current parent's RSS by a margin specified by the configuration OPENTHREAD_CONFIG_PARENT_SEARCH_RSS_MARGIN configuration.
• If the attach attempt to the selected router fails (e.g., the router already has the maximum number of children it can support), the FTD child ensures that the same router cannot be selected again until a "reselect timeout" expires. This avoids repeated attempts to the same router. This timeout is specified by the configuration OPENTHREAD_CONFIG_PARENT_SEARCH_RESELECT_TIMEOUT.

MTD Child

• Every OPENTHREAD_CONFIG_PARENT_SEARCH_CHECK_INTERVAL seconds, an MTD child checks its average RSS to its current parent. The child starts a parent search process only if the average RSS is below OPENTHREAD_CONFIG_PARENT_SEARCH_RSS_THRESHOLD.
• This ensures that an MTD child already attached to a parent with good link quality does not waste energy searching for better parents.
• The MTD child sends an MLE Parent Request to discover possible new parents. Because this process can be power-consuming (the child needs to stay in RX mode to collect parent responses), and to limit its impact on battery-powered devices, after a parent search is triggered on an MTD, the MTD child does not trigger another one before the specified backoff interval (OPENTHREAD_CONFIG_PARENT_SEARCH_BACKOFF_INTERVAL) expires.

This feature is enabled by default on FTD builds. It is recommended that it also be enabled on MTD builds. This may require the platform integrator (device vendor) to select appropriate configuration values for this feature, particularly OPENTHREAD_CONFIG_PARENT_SEARCH_BACKOFF_INTERVAL, which can impact how often a (battery-powered) sleepy child may search for a parent, taking into account its impact on the device's battery life.

Specifies parent reselect timeout duration in seconds used on FTD child devices.

When an attach attempt to a neighboring router selected as a potential new parent fails, the same router cannot be selected again until this timeout expires.

Applicable only if periodic parent search feature is enabled (see OPENTHREAD_CONFIG_PARENT_SEARCH_ENABLE).

Specifies the RSS margin over the current parent RSS for allowing selection of a neighboring router as a potential new parent to attach to.

Used on FTD child devices.

Specifies the RSS threshold used to trigger a parent search.

Applicable only if periodic parent search feature is enabled (see OPENTHREAD_CONFIG_PARENT_SEARCH_ENABLE).