QoS-aware MAC protocols for wireless sensor networks: A survey <s> I-MAC <s> This paper introduces I-MAC, a new medium access control protocol for wireless sensor networks. I-MAC targets at improving both channel utilisation and energy efficiency while taking into account traffic load for each sensor node according to its role in the network. I-MAC reaches its objectives through prioritized and adaptive access to the channel. I-MAC performances obtained through simulations for different network topologies, scenarios and traffic loads show significant improvements in energy efficiency, channel utilization, loss ratio and delay compared to existing protocols. <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> I-MAC <s> This paper presents the design, implementation and performance evaluation of a hybrid MAC protocol, called Z-MAC, for wireless sensor networks that combines the strengths of TDMA and CSMA while offsetting their weaknesses. Like CSMA, Z-MAC achieves high channel utilization and low latency under low contention and like TDMA, achieves high channel utilization under high contention and reduces collision among two-hop neighbors at a low cost. A distinctive feature of Z-MAC is that its performance is robust to synchronization errors, slot assignment failures, and time-varying channel conditions; in the worst case, its performance always falls back to that of CSMA. Z-MAC is implemented in TinyOS. <s> BIB002 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> I-MAC <s> A slot assignment (or scheduling) in TDMA based wireless sensor networks (WSNs) considering energy efficiency, scalability and complexity is presented. The algorithm named DNIB is a new TDMA free collision distributed slot assignment algorithm for WSNs. DNIB relies on two-hop neighborhood information. Performance analysis and simulations show that DNIB is scalable and outperforms existing mechanisms. <s> BIB003
I-MAC BIB001 uses a hybrid TDMA/CSMA scheme for medium access and basically introduces a prioritization mechanism for Z-MAC BIB002 . There are two phases during execution as in Z-MAC: set-up phase in which neighbor discovery, slot assignment, local framing and global synchronization occurs; and transmission phase where time is divided into slots. There are three predefined priority levels mapped to each sensor node according to its role in the network. I-MAC anticipates dynamic prioritization where sensor nodes set their own priority level according to their local observations like traffic load, remaining energy and distance to sink. Authors propose a scheduling algorithm called DNIB BIB003 and time slots are assigned to each sensor node based on this algorithm. Owner of the time slot has guaranteed access in that particular slot and this guarantee is provided by employing Arbitration Interframe Space (AIFS) for non-owner sensor nodes. If the owner has no data to send or the slot is not owned, non-owners can compete for transmission. Service differentiation among nonowners is provided by adopting different CW sizes for each priority level. Advantages and disadvantages: Although I-MAC combines the strength of both TDMA and CSMA schemes, it still needs tight clock synchronization which is a well-known drawback of TDMA schemes. Authors developed a novel scheduling algorithm and achieved better utilization than of Z-MAC. However, possessing up-to-date neighbor information and slot schedule in highly dynamic sensor networks is a major challenge.