## 5 BN-MAC Protocol Design
### Intra-Semi-Synchronized Transmission Schedule  
This mode is based on a semi-synchronized low duty cycle (the ratio between active time and the complete active/sleeping time; a low duty-cycle MAC protocols obviously has a much extended lifetime for operation, but pauses for the all-node-active assumption). The intra-semi-synchronized process starts with channel sampling. The node wakes up for a short period of time to sample the medium. Channel sampling is performed once during the channel allocation time. After channel sampling, each node initially sends a short preamble message asynchronously using the Anycast approach within the one-hop neighbor node to obtain the list of one-hop neighbor nodes. When the sender receives a reply from the one-hop neighbor nodes, the sender attempts to fix the schedule with the intended one-hop neighbor nodes (nodes that are chosen for future communication) before sending the data. Each node knows the wake-up and sleep schedule of its intended neighbors. These dual features of sending a short preamble asynchronously to obtain the list of neighbor nodes and fixing the schedule synchronously reduce the network overhead. When the sender completes the scheduling process with the intended nodes, the sender chooses the shortest efficient path for sending the data using the LDSNS model, as explained in [33]. This model helps to reduce energy consumption and the links with the network layer. The use of a short preamble message allows for reductions in overhead and latency at each hop. The short-preamble-enabled MAC protocols have an advantage over the long-preamble-enabled MAC protocols due to their low-power duty cycle mechanism. The existing lower power listening (LPL) technique uses a long preamble and suffers from the overhearing problem, which increases energy consumption in non-targeted receivers, such as Z-MAC. LPL also increases latency at each hop [34]. In the long-preamble techniques, the node must wait until the long preamble is received before it starts receiving data and acknowledgments. This approach increases energy consumption on both the sender and receiver sides. Targeted receivers are also affected because the targeted receivers have to wait until the long preamble is received, causing increased energy consumption. X-MAC uses a short preamble message to reduce the energy consumption and latency, but one disadvantage of X-MAC is that the destination address of the node is inserted into each short preamble message. X-MAC forces all nodes to check the preamble to determine whether they are targeted nodes, which increases energy consumption and the duty cycle (wake-up process). X-MAC is based on an asynchronous mechanism, and no schedule of neighbor nodes is maintained, making it more difficult for each node to send data without prior scheduling information. Unlike X-MAC, BN-MAC deploysboth asynchronous features for sending short preamble messages to obtain the list of one-hop neighbor nodes and synchronous features for fixing the schedule with the intended neighbors. The MAC protocol should be capable of handling spatial correlation while also adjusting to changes in the number of competing nodes [35]. When multiple nodes want to communicate with the same neighbor node within the region, BN-MAC uses a slotted contention window. Then, the nodes randomly select a slot in the contention window. The winner of the slot obtains access to the medium for communication. Thus, there is small probability of collision at the medium. BN-MAC has more contention slots to compete, which reduces congestion in the WSNs. BN-MAC has another feature the helps to reduce packet loss. If multiple nodes attempt to select the same slot, BN-MAC uses sampling and randomization such that each node has an equal probability of accessing the channel. Furthermore, BN-MAC uses 256 congestion window slots, whereas the other MAC protocols use 1-32 contention windows for randomized listening before sending the preamble messages.