To provide the energy balance among the sensor nodes, it selects a WCN based on three metrics: current energy level, how many times the sensor node works as a Coordinator Node ([N.sub.WCN]), and sensor node priority ([S.sub.NP]).
Nevertheless WCN rotation algorithm is adapted to the isMAC protocol in order to distribute the energy usage among the member nodes of the WBAN.
In addition, isMAC has three main features: multi-channel architecture, WCN rotating, and collision preventing mechanisms.
Our presented protocol has two primary goals: (i) to prolong the network lifetime by rotating the WCN role among WBAN member nodes and by using different transmission powers for the WCN and WBAN member nodes, (ii) to prevent packet collisions during intra-WBAN and inter-WBAN communication.
The central node (CN) in a cluster assigns a time slot for each WCN. To ensure the quality of service (QoS), the CN can allocate non-sequential multiple time slots for a WBAN according to its nodes' requirements.
In the setup phase, a WCN is determined as follows:
If a node has the lowest priority level for its WBAN ID, it becomes the WCN and starts playing the "WCN role".
Then, the WCN begins listening to the CN during the contention period.
If a member node has data to send, and does not know its current WBAN communication channel, it begins listening to the 15th channel and keeps waiting for the information packet to be sent by its WCN. After receiving WCN information via this channel, it immediately joins the inter-BAN contention period.
However, free channel management is not necessary for isMAC protocol because, when a collision is detected by a WCN, it changes the inter-BAN communication channel to avoid repetition of the collision [28].
In the second method, if there is a collision, the WCN assigns a different communication channel for the related WBAN.
In isMAC protocol, if the WCN detects a collision during data gathering process or gets a packet which contains different WBAN ID, it distinguishes that there is another WBAN in the communication area.