User priority (UP) Fig. 8 Second-round allocation request frame.
When the hub receives the second-round allocation request frame, the hub replies ACK with the added time field to inform the nodes to receive the second-round allocation assignment frame.
Upon receiving the second-round allocation assignment frame, nodes check whether the hub assigns additional slots for it or not.
User priority (UP) Fig. 8 Second-round allocation request frame IEEE 802.15.6 assigns different UPs for different frame types, which vary from UP0 to UP7.
The format of the second-round allocation assignment frame is the same as the first-round allocation assignment frame, as shown in Fig. 6 b.
Then, the hub assigns additional allocation slots for the burst data and writes the allocation interval in the second-round allocation assignment frame.
Upon receiving the second-round allocation request frame, the hub determines the transmit order and the number of allocation slots for burst data of these two nodes.
If the sensor nodes in health monitoring are sensitive to security, the hub will transmit the second-round allocation assignment frame in unicast manner, if not, in broadcast manner.
The format of the second-round allocation request frame is designed as shown in Fig. 8. Considering that the burst data are mostly from nodes in severe condition, TTR MAC should guarantee a lower delay for the severer node.
In order to obtain additional allocation slots for burst data, nodes with burst data should transmit the second-round allocation request frame to the hub in the allocation interval assigned in the first-round reservation.
Since all nodes and hub have established a time reference base and all slots are numbered in order, the hub can determine the interval start and interval end for a specific node, which makes up the first-round allocation assignment frame, as shown in Fig. 7.
