## 9 Discussion of Results  
Energy consumption has been known to be one of the greatest challenges of WSNs and will continue to be an immense challenge for the deployment of WSNs because the advancement in battery technology has been slower than the growth of processing power and data communication rates. This challenge has attracted researchers to introduce several new energy-efficient protocols to address this problem [48]. To address this challenge, several MAC protocols have been introduced at the MAC level. Hybrid MAC protocols are of paramount importance because they have lower energy consumption and better scalability than other categories of MAC protocols. In this section, we discuss and compare the strengths and weaknesses of BN-MAC versus other hybrid MAC protocols. The Z-MAC protocol belongs to the hybrid family that supports multi-hop topology, and the nodes are fixed at their positions. The global time synchronization is used to synchronize the nodes, and slots are assigned to nodes but not fixed for each node. Z-MAC competes for the channel within any slot for data transmission. The assigned node is given high priority, which reduces collisions. The latency is increased, and the throughput is moderated. Z-MAC faces some problems because of the use of long preamble messages with a destination address, which increases the duty cycle and energy consumption. The fixed topology limits the node scalability of WSNs. The setup of the network phase becomes more difficult when a new node joins or leaves the network. Mobile nodes are unable to receive and send data packets. As a result, the network paths are broken. Speck-MAC is a variant of the B-MAC protocol but exhibits redundant short-packet transmission and integrated destination addresses. Speck-MAC is efficient in transmitting the unicast messages, but the sender wastes excess energy by sending additional frames even though the receiver has already received the frames. The additional frames consume channel bandwidth and thus reduce the packet delivery rate. Speck-MAC supports mobility when the network path is broken, which increases latency. LPRT-MAC is based on an efficient bandwidth allocation mechanism and uses super frames fixed into mini-slots to communicate with the base station. LPRT-MAC reduces the power consumption and coordinates with the channel. LPRT-MAC exhibits significant packet loss, which is affected by bit errors. LPRT-MAC also suffers from the star topology. Once the central node fails, the entire network suffers because the node maintenance requires a longer period of time in the WSN. This situation reduces the throughput and increases latency. Additionally, there is no dynamic node selection in LPRT-MAC, which could help to replace the node prior to its failure. The star topological network also exhibits low mobility because the nodes are tightly linked and cannot leave or join the network. LPRT-MAC also cannot be used for other communication topologies because it is not suitable for multi-hop WSNs due to topological constraints. A-MAC is based on a collision-free and non-overhearing mechanism and is particularly suitable for surveillance and monitoring applications. The nodes are attentive and inactive for longer periods of time until an event is detected. The major advantage of A-MAC is that it allows nodes to be notified in advance. However, A-MAC exhibits rather high idle listening and packet overhead. A-MAC consumes high amount of energy due to advertisements. Additionally, the high level of latency reduces the throughput. Sensor nodes are deployed tightly in A-MAC, causing mobility issues. ADC-SMAC improves upon two features of S-MAC: node utilization and sleep delay. The advantage of ADC-SMAC is that it introduces flexible duty cycles and forwards new scheduling information to the neighbor sensor nodes. ADC-SMAC also supports real-time data communication. However, local synchronization in ADC-SMAC consumes a significant amount of energy and increases the latency.