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The MAC protocol (Adhikari, 2014; Ali, Wang, Lv, & Chen, 2014) is proposed and designed to control and regulate the access to the shared wireless medium therefore a collision among the channel's contending nodes is avoided, this should be done with specific determinants and performance.
The MAC protocols schemes are divided into two classes, contention-based (random assignment protocols) (Doudou, Djenouri, Badache, & Bouabdallah, 2014; Sharma, Ganesh, & Key, 2009) and contention-free (schedule-based) (Lin, Rivano, & Le Mouël, 2014) which indoors may be classified into fixed-assignment protocols and demand-assignment protocols. Far from the bad channel utilization of the fixed-assignment and its other cons and far from the additional overhead of demand-assignment through polling and reservation, the contention-based MAC protocol is more logical for accessing the channel, but it is more prone to fail to allocate the medium successfully and result in collision. This depends on the characteristic of the contention-based MAC protocol itself and another high importance factor which is the logical topology that determines the number of talkers, who can talk to who, when and where they can talk, at what range, etc.
Based on that, it is preferred to use contention-based MAC with a good performance works on a logical topology paved for it, especially with respect to predictability and number of contending nodes, where the condition under which these protocols may fail in preventing collisions is the sources' number increase or the sources' transmission rate increase.
The global target of the design intended by this work is to design a standard MAC layer (but complete stack) meets the mentioned requirements and suites all the monitoring applications of the WSN. This MAC layer based on the physical layer of the IEEE802.15.4 standard, and its design composed of a Timing Structure Mechanism (TSM) (or Channel Time Bounding Mechanism (CTBM)), which includes the setup of the logical topology by dividing the network into sub-networks (sub-NWs) using multi-channels and identifying the time structure of the sub-NW members’ work, and a Channel Access Mechanism (CAM), which will be contention-based, but it is out of the scope of this paper and reserved for the subsequent design step.
Classifying the monitoring applications to some categories according to certain categorization elements, each category members share in the characteristics, allows for designing a protocol or protocol integration meets the needs of the monitoring applications may be using convenient modes of operation, and accordingly aids in achieving the global target of the intended design. The monitoring applications can be divided according to nodes distribution to: Random uniform, Deterministic regular, Random non-uniform, and Deterministic irregular. An illustration of these types is depicted in Figure1.
Figure 1. Examples of the monitoring applications classes categorized according to node distribution
The network setup operations can be divided into some phases performed once, periodically or on-demand to, start signal, neighbour discovery, coverage determination, and network logical topology setup.
The main idea of the proposed TSM is to construct a receive schedule has only one node listening for a small period to the channel in the whole network at a time, and each node takes its turn successively according to the schedule. This lowers the listen duty cycle of nodes to a small value. At any time, a node wants to transmit, it can turn its radio to the Tx state and transmit directly in its maximum range or in a range suitable to the currently listening node using a contention-based CAM. But achieving this requires global synchronization and storing a large schedule, rather than that, with the large deployment areas of the WSN, the node maximum radio range may not be able to reach the currently listening node.
We come up with a solution that, the network should be divided into logical divisions (sub-NWs) may have a specific form, requirements, or characteristics. These sub-NWs are made by differentiating the working frequency channels for each group of nodes. Each sub-NW forms an autonomic network.