Wireless medium access control (MAC) and routing protocols are fundamental building blocks of the Internet of Things (IoT). As new IoT networking standards are being proposed and different existing solutions patched, evaluating the end-to-end performance of the network becomes challenging. Specific solutions designed to be beneficial, when stacked may have detrimental effects on the overall network performance. In this paper, an analysis of MAC and routing protocols for IoT is provided with focus on the IEEE 802.15.4 MAC and the IETF RPL standards. It is shown that existing routing metrics do not account for the complex interactions between MAC and routing, and thus novel metrics are proposed. This enables a protocol selection mechanism for selecting the routing option and adapting the MAC parameters, given specific performance constraints. Extensive analytical and experimental results show that the behavior of the MAC protocol can hurt the performance of the routing protocol and vice versa, unless these two are carefully optimized together by the proposed method.
Within the literature related to the study of the routing protocols for IoT applications, @cite_18 presents an experimental performance evaluation of RPL using the basic hop count routing metric and the expected transmissions count (ETX) @cite_3 metric. The ETX is a reliability metric that indicates the number of retransmissions a node expects to execute to successfully deliver a packet to the destination node. However, the study in @cite_18 does not consider the performance of RPL when a contention-based MAC protocol is active and there is no proposal about new routing metrics. In the back-pressure collection protocol (BCP) @cite_20 , an extension of the ETX metric lead to the introduction of a dynamic back-pressure routing metric. In BCP, the routing and forwarding decisions are made on a per-packet basis by computing a back-pressure weight of each outgoing link that is a function of the queues of the nodes and the link state information. BCP is tested over a low power contention-based MAC. However, the effects of the limited number of backoffs and retransmissions, present in the IEEE 802.15.4 standard, are not taken into account.
@cite_18 @cite_20 @cite_3
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In this paper, a performance evaluation of the Routing Protocol for Low power and Lossy Networks (RPL) is presented. Detailed simulations are carried out to produce several routing performance metrics using a set of real-life scenarios. A real outdoor network was reproduced in simulation with the help of topology and link quality data. Behaviors of such a network in presence of RPL, their reason and potential areas of further study improvement are pointed out. This paper presents the expected transmission count metric (ETX), which finds high-throughput paths on multi-hop wireless networks. ETX minimizes the expected total number of packet transmissions (including retransmissions) required to successfully deliver a packet to the ultimate destination. The ETX metric incorporates the effects of link loss ratios, asymmetry in the loss ratios between the two directions of each link, and interference among the successive links of a path. In contrast, the minimum hop-count metric chooses arbitrarily among the different paths of the same minimum length, regardless of the often large differences in throughput among those paths, and ignoring the possibility that a longer path might offer higher throughput.This paper describes the design and implementation of ETX as a metric for the DSDV and DSR routing protocols, as well as modifications to DSDV and DSR which allow them to use ETX. Measurements taken from a 29-node 802.11b test-bed demonstrate the poor performance of minimum hop-count, illustrate the causes of that poor performance, and confirm that ETX improves performance. For long paths the throughput improvement is often a factor of two or more, suggesting that ETX will become more useful as networks grow larger and paths become longer.