A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> 1) Listen-only Period <s> We present Trickle, an algorithm for propagating and maintaining code updates in wireless sensor networks. Borrowing techniques from the epidemic/gossip, scalable multicast, and wireless broadcast literature, Trickle uses a "polite gossip" policy, where motes periodically broadcast a code summary to local neighbors but stay quiet if they have recently heard a summary identical to theirs. When a mote hears an older summary than its own, it broadcasts an update. Instead of flooding a network with packets, the algorithm controls the send rate so each mote hears a small trickle of packets, just enough to stay up to date. We show that with this simple mechanism, Trickle can scale to thousand-fold changes in network density, propagate new code in the order of seconds, and impose a maintenance cost on the order of a few sends an hour. <s> BIB001 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> 1) Listen-only Period <s> RPL (IPv6 Routing Protocol for Low Power and Lossy networks) is a routing protocol recently standardized by the IETF. RPL has been designed to operate in energy-constrained networks with thousands of nodes, and therefore it is one of the most promising candidate routing protocols for Advanced Metering Infrastructure (AMI) networks. In this paper a performance evaluation of RPL is presented. An extensive study of the protocol is carried out with particular focus on Trickle, the algorithm adopted to control routing update distribution across the network. The performance of the protocol is analyzed considering different Trickle parameters in order to capture their impact on route formation and node power consumption. Results highlight that the nondeterministic nature of Trickle can lead to sub-optimal route formation especially when high message suppression is per-formed. In order to mitigate this issue, an enhanced version of the protocol, namely Trickle-F, is proposed in order to guarantee fair broadcast suppression. Trickle-F is demonstrated to be effective in obtaining more efficient routes with the same power consumption of the original version. <s> BIB002 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> 1) Listen-only Period <s> The Trickle Algorithm has enjoyed much popularity and widespread use as a basic network primitive ensuring low-cost data consistency in lossy networks. Trickle is shaped by the so-called short-listen problem, hence the imposition of a listen-only period. Such a period allows Trickle to robustly address the short-listen problem at the expense of increased latency. In this letter, we introduce a simple yet powerful optimization to Trickle that can dramatically decrease Trickle's latency with virtually no additional overhead to its scalability and robustness. Extensive simulation and testbed experiments are reported here, yielding greater than a factor of 10 decrease in propagation time. <s> BIB003 </s> A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> 1) Listen-only Period <s> Routing Protocol for Low Power and Lossy networks (RPL) is the de-facto standard for routing in resource-constrained low-power and lossy networks (LLNs) which represent the building block for the ever-growing Internet of Things (IoT). RPL along with other routing protocols make the deployment of Trickle algorithm as a mechanism for controlling and maintaining the routing traffic frequency. Trickle employs two different techniques to manage the routing traffic efficiently. Firstly, the suppression phase where a node suppresses its control data transmission if it is redundant. Secondly, the traffic frequency adaptation, where the nodes increase their sending rate when discovering inconsistency while slow down their rate as the network becomes stable. The efficiency of Trickle has been approved in terms of power consumption and scalability, however, imposing the so-called listen-only period as a solution for the short-listen problem comes at the expense of increased convergence time. Thus, in this paper, an enhanced version of Trickle is proposed, namely, E-Trickle which solves the short-listen problem without imposing the listen-only period. Simulation results show that E-Trickle have decreased the convergence time by up to 43% while preserving the same efficiency of Trickle in terms of power consumption, scalability and reliability. <s> BIB004
A key issue in Trickle is the introduction of listen-only period in the first half of each Trickle's interval (I) BIB003 BIB004 . The goal behind the listen period is to solve the so-called short-listen problem in asynchronous networks BIB001 . In a network with no listen-only period, a node may start sending its current DIO very soon after starting a new interval, a behavior that may result in turning down the suppression mechanism in the current and subsequent intervals, leading to significant redundant transmissions and limiting the algorithm scalability BIB001 . However, the listen-only period comes with its own shortcomings. Firstly, the period imposes a delay of at least I/2 before trying to propagate the new information. In an m-hop network, an inherited delay will progressively accumulate at each hop resulting in an overall delay proportional to the number of hops BIB003 BIB004 . Secondly, the listen-only period may result in uneven load distribution among network nodes with some nodes transmitting less than others do during the operational time BIB002 . In the worstcase scenario, the transmitting period of a node may substantially overlap with the listen-only period of a neighboring node, preventing the former from sending for a long time. A key issue here is that the blocked node may be one whose transmission is vital for resolving network inconsistences BIB003 . Furthermore, the absence of load balancing among Trickle nodes may render some routes undiscoverable even though they might be more efficient than those already active in the network BIB002 .