## 2 State of the Art
### A Range of Communications Solutions  
It is widely published that there are a large range and increasing number of communications solutions available for the IoT networks [7; 8; 9]. Much of the previous recent work in the research community has been conducted in Wireless Sensor Networks (WSN) delivering alternative performance characteristics from the network for the needs of applications or tackling specific network conditions. Early work in this regard included Collection Tree Protocol (CTP) [10], LEACH [11] and SPIN [12]. Evaluation for the CTP protocol is predominantly based on packet reliability and was conducted over twelve open testbeds. While this is certainly considered rigorous testing it can be argued that the range of testing scenario does not exhaust the range of potential deployment scenario for the protocol. To give application developers an idea of overall performance other metrics must be included for evaluation. The LEACH protocol is designed for efficient use of energy using hierarchical routing techniques. LEACH is used as a comparison protocol for many other solutions throughout the literature. While this information is useful it is fragmented and difficult for use for direct comparison with new or other competing protocol. The evaluation of LEACH [11] is conducted on a single simulated environment. Energy efficiency is the single metric evaluated for nodes with network diameter, in terms of meters from a basestation, used as an independent variable. The evaluation of SPIN is similar with testing performed on a single testbed. Energy efficiency and useful reception rate are evaluated over nodes with varying network density. In both cases it is difficult to either directly compare or evaluate if the solutions are fit for purpose for a deployment with a specific set of requirements. A number of recently introduced solutions such as TREnD [13] as well as a number of modified Routing for low Power and Lossy networks (RPL) protocols have added value to the IoT protocol discussion. There is a constant theme throughout the evaluation process in each of the papers, however, which echoes the issues discussed above. TREnD is examined using energy efficiency, latency and reliability as evaluation metrics. The testing is conducted in a single testbed making it difficult to predict how the protocol may perform in another deployment. Each protocol discussed is tested using a standalone environment or process ultimately making it difficult to compare solutions and select a solution for an application or deployment. Recent efforts have seen a greater push towards protocol standardisation from both industry and academia. Amongst others IPv6 datagrams in Low Power and Lossy Networks (6 LoWPAN) [14], RPL [15] and Constrained Application Protocol (CoAP) [16] are current protocol involved in standardisation. The three protocols constitute part of a possible communications stack proposed for smart city applications. These applications are envisaged to contain hundreds to thousands of sensors which are regarded as resources which can be accessed by the application. Handling Internet Protocol (IP) packets is regarded as essential for successful integration of IoT resources into current web systems. 6 LoWPAN was developed as an encapsulation technique to allow IP packets to be passed through an IoT network without some of the unnecessary overhead of IP. RPL is a routing standard that is growing in support and adoption within IoT communities and projects. RPL uses a tree-like Destination Oriented Directed Acyclic Graph (DODAG) structure to connect all nodes to a single ingress/egress point for the DODAG. CoAP is a lightweight protocol which allows applications to request resources from the IoT using a HTTP-like RESTful interface. The standardisation of protocol is essential for the adoption of IoT technology but also for interoperability within and between IoT networks and we believe that this type of communications stack will form the basis of future deployments.