# On Applicability of Network Coding Technique for 6 LoWPAN-based Sensor Networks
## 2 Related Work
Presented simulation results confirm that an optimal cluster size can be determined considering the PIM overhead and a target decoding performance. This approach is interesting but should also be analyzed in terms of practical implementation in WSNs. The NC has also been proposed recently for routing support in variety of sensor networks. The example solution, named Cooperative and Adaptive Network Coding for Gradient Based Routing (CoAdNC-GBR), is described and discussed in [30]. The CoAdNC-GBR considers the network density as dynamically defined by the average number of neighboring nodes, to perform linear network coding operations on the interest messages. Authors of [30] argue that the cooperation of multiple sinks that were used in the proposed routing mechanism, improves the transmission reliability of links lowers the number of transmissions and the propagation latency and enhances the energy efficiency of the network when comparing to typical gradient-based routing schemes. The NC application for underwater wireless sensor network routing protocol can also be found in [31], where cross-layer interactions are used to mix transport layer packets and the maintenance and correction of paths in the network are operated along with data packets. Simulation results confirm that this solution significantly improves the network performance in terms of energy consumption, end-to-end delay, and packet delivery ratio as compared with other routing protocols. The other proposals for WSNs that support both routing and network lifetime are described in [32; 33; 34]. Most of the solutions that are mentioned above are mainly aimed at an increased packet delivery ratio and an increased reliability of broadcast (multicast) transmission in IEEE 802.11-based networks. The main difference between the network coding schemes, dedicated for sensor network when comparing the solutions for other wireless networks, is maximal simplicity forced by limited resources. Currently, a limited number of network coding-based solutions exist, allowing for us to decrease the unicast traffic in 6 LoWPAN-based networks. Bearing in mind that the 6 LoWPAN standard is proposed for the IoT architecture, we can expect significant growth of traffic in such networks what can lead to overload and decrease in the network lifetime. In order to increase the WSN lifetime, through decreasing the network load, the authors of this paper propose the NC6 LoWPAN inter-session network coding technique for encoding unicast streams of fragments of IPv6 packets. The 6 LoWPAN standard assumes that IPv6 packets can be compressed and fragmented, while these operations can change the format of the datagrams from hop-to-hop. Almost all of the similar solutions on the NC, which are presented in the papers, assume that encoded packets should contain some portion of the original packets that are exactly the same as the buffered packets (to ensure decoding). This paper proposes an appropriate NC header that deals with the changing 6 LoWPAN headers. The packet buffering mechanism, which is tailored to the available sensor motes resources, is used to increase coding opportunity, and in consequence, to decrease the overall traffic in 6 LoWPAN-based WSNs, and in consequence to minimize energy that is consumed by the sensor motes.