A Survey of Limitations and Enhancements of the IPv6 Routing Protocol for Low-power and Lossy Networks: A Focus on Core Operations <s> 3) Routing Discovery and Maintenance Key Challenges <s> Wireless sensor networks consist of small nodes with sensing, computation, and wireless communications capabilities. Many routing, power management, and data dissemination protocols have been specifically designed for WSNs where energy awareness is an essential design issue. Routing protocols in WSNs might differ depending on the application and network architecture. In this article we present a survey of state-of-the-art routing techniques in WSNs. We first outline the design challenges for routing protocols in WSNs followed by a comprehensive survey of routing techniques. Overall, the routing techniques are classified into three categories based on the underlying network structure: flit, hierarchical, and location-based routing. Furthermore, these protocols can be classified into multipath-based, query-based, negotiation-based, QoS-based, and coherent-based depending on the protocol operation. We study the design trade-offs between energy and communication overhead savings in every routing paradigm. We also highlight the advantages and performance issues of each routing technique. The article concludes with possible future research areas. <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> 3) Routing Discovery and Maintenance Key Challenges <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> 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> 3) Routing Discovery and Maintenance Key Challenges <s> This document presents home control and automation application ::: specific requirements for Routing Over Low power and Lossy networks ::: (ROLL). In the near future many homes will contain high numbers of ::: wireless devices for a wide set of purposes. Examples include ::: actuators (relay, light dimmer, heating valve), sensors (wall switch, ::: water leak, blood pressure) and advanced controllers (RF-based AV ::: remote control, Central server for light and heat control). Because ::: such devices only cover a limited radio range, routing is often ::: required. The aim of this document is to specify the routing ::: requirements for networks comprising such constrained devices in a ::: home control and automation environment. <s> BIB003
In general, there are two routing discovery maintenance schemes in the context of LLNs; proactive and reactive  BIB001 . In proactive routing, the process of establishing routes is carried out in advance and maintained periodically, which induces a large amount of overhead, although with minimal forwarding delay  . On the other hand, in reactive routing, the routes are only discovered when needed, thus suffering from higher delay compared to proactive schemes  . Reactive routing schemes have been the preferred option when the network features a high number of mobile nodes whereas proactive schemes are preferred in stationary networks (e.g. LLNs). However, the resource-constrained nature of these networks imposes several challenges on proactive route maintenance. Despite the stationary nature of the majority of scenarios, LLNs do exhibit some dynamicity that may render the network unstable, dictating the need for a rapid and reactive response BIB003 [55]   . Choosing small update intervals has the advantage of faster propagation, but with a high communication overhead; long update intervals, on the other hand, have lower communication overhead, but disseminate routing information slowly BIB002 . To address these problems, Trickle BIB002 has introduced the notion of adaptive and dynamic interval size. The idea is to start propagating routing information at a high transmission rate then gradually reduce when the network reaches its steady phase, ensuring rapid propagation and low overhead. Trickle uses the term inconsistency to describe the point of time at which the network must start transmitting at its fastest rate. Although Trickle and its extensions have defined how information exchange should proceed in the consistent and inconsistent sates of the network, they fail to define clearly what constitutes inconsistent or consistent transmission in the context of routing. We argue that an efficient routing maintenance should clearly define what constitutes consistent and inconsistent state and define corresponding detection mechanisms.