4.2.3 Sleeping End Device’s Time Spans

For correct communication between routers and sleeping end devices, the user must pay special attention to a set of CS parameters. The CS_END_DEVICE_SLEEP_PERIOD parameter performs exactly as the name suggests. On an end device, it specifies the length of the time span that the end device remains asleep when requested to sleep.

The parent of an end device also uses the CS_END_DEVICE_SLEEP_PERIOD to determine whether to keep or drop a message addressed to the end device and to decide if the end device is lost when it fails to send a poll request for a sufficiently long time. Upon receiving a frame for an end device child, the parent saves the message if the CS_MAC_TRANSACTION_TIME is greater than the estimated time remaining until the next poll request from the child is expected. The parent estimates the time of the next poll request by adding the CS_END_DEVICE_SLEEP_PERIOD to the moment of receiving the last poll request.

An end device sends poll requests at intervals specified by the CS_INDIRECT_POLL_RATE parameter, which also helps to calculate the default value for the CS_MAC_TRANSACTION_TIME.