# Reduced Overhead Routing in Short-Range Low-Power and Lossy Wireless Networks +
## 3 Related Work  
In [3], the authors argue that interoperability between RPL's storing and non-string MoPs can result in a network that is more effective and fault-resilient. First, the authors demonstrate that coexistence of RPL's storing and non-storing MoPs in the same network can lead to different problems, such as network partitioning and routing loops. Then different enhancements to the RPL protocol are proposed. The modified protocol resolves the identified problems and facilitates interoperability between RPL's MoPs in the same network. Another approach to the coexistence of RPL's storing and non-storing MoPs is presented in [4]. The drawback of the stated approaches is that the MoP is configured statically, hence nodes cannot switch between MoPs dynamically. To overcome memory limitations of RPL's storing mode, a modification to the RPL protocol called D-RPL is proposed in [5]. D-RPL overcomes the limitation by replacing storing mode forwarding with multicast dissemination. If a node's memory limits are reached, D-RPL activates to overcome the limitation. In [6], an analysis of the RPL protocol from an Internet of Things (IoT) perspective is presented. The analysis considers the following benchmarks: reliability and robustness, mobility, resource heterogeneity, and scalability. The article concludes that to remain a viable option in the IoT domain, RPL needs improvement, especially in P2P communications, to support emerging IoT use cases. Experimental performance evaluation of RPL using hop-count and/or ETX routing metrics is presented in [7; 8; 9], and RPL performance evaluation for multi-gateway networks using different objective functions is presented in [10]. To reactively discover P2P communication paths, enhancements for RPL are proposed in [11; 12]. However, the enhancements require additional control messages and substantial changes to the RPL routing protocol. In [13], a mechanism is presented to create a software-defined WSN. In a software-defined WSN, a gateway/controller needs to have complete information about a network's topology. To enable the controller to discover the network topology, each node in the network transmits addresses of its direct neighbors to the controller. A node in a typical WSN can have tens of neighbors, therefore each node transmitting IPv6 or IEEE 802.15.4 MAC address of each of its direct neighbors results in considerable overhead in such a network. To eliminate the stated problem, each node in a network uses a Bloom Filter (BF) based approach to transmit information about its direct neighbors to the controller. The protocol presented in the paper is only limited to topology discovery at the controller. In [14], an opportunistic routing protocol based on RPL is presented. Instead of using unicast, the protocol proposes the use of anycast for MP2P forwarding. In this case, whenever a node receives an anycast message, and if the rank of the node is less than the rank of the transmitting node, the node forwards the packet and sends an ACK to the transmitting node. Instead of using RPL's unicast DAO message for P2P route discovery, the protocol proposes the use of a routing set. A node periodically broadcasts its routing set using RPL's trickle timer, and the routing set contains information about the nodes in the node's sub-DODAG. If the network topology is known at the time of the network deployment, the routing sets are constructed using a bitmap. However, if the network topology is not known at the time of network deployment, and if the topology can change dynamically, the protocol compresses the routing set information in a BF. Therefore, nodes in a network do not need to store a traditional routing table, instead they store routing sets. This results in lower memory requirements to forward P2P data packets. However, this technique can only work in RPL's storing MoP. In the non-storing MoP, for P2 MP and P2P data forwarding the protocol still uses source routing. In [15], a behavioral study of RPL under network partitioning is presented.