## 3 State-of-the-Art for WirelessHART Routing Schemes
### Non-WirelessHART Routing Algorithms
#### 3.4.1 Comparative Analysis  
In order to obtain relevant information about the described routing algorithm proposals, we will discuss the items described in the list below. Furthermore, Table 4 presents an overview of the analyzed proposals. * Objective: Different routing algorithms are developed to solve different kinds problems or to improve specific characteristics in a network. This item shows the goal that the authors intend to achieve with the developed algorithm proposal. * Metric: The metric consists of which characteristics were chosen to guide the routing decisions of the algorithm. This is an important matter, since the metrics chosen will have a direct impact on the performance of the network and on whether the objective of that algorithm will be achieved. * Implement uplink, downlink and broadcast graphs: The three graphs presented in the WirelessHART specification have distinct features; thus, it is to be expected that some algorithms deal differently with the construction of each graph. This item identifies with which types of graph the proposal deals. * Uses node history: This item identifies whether the algorithm uses the past states (e.g., the energy levels or the success rate) of the node in order to make the routing decisions. * Implementation and validation: Different proposals vary in how they are conveyed to the reader, ranging from a description of the policies to be used, up to describing the steps in an actual algorithm. This item describes how the authors present their proposal and also describes the means of validation (e.g., simulation, testbeds). Objective: In terms of the objective, all of the proposals have the same concern for maximizing the network lifetime, which is relevant in a battery-powered IWSN environment. However, the most recent re-add [64] proposal includes in its objectives the robustness of the network, reaffirming the WirelessHART robustness feature. Metric: The comparison presented in Table 4 shows the concern for mixing different metrics in order to balance obtained results. Furthermore, the JRMLR and re-add proposals present the uses of weights to tune the function and prioritize a specific characteristic. Implement uplink, downlink and broadcast graphs: Of the proposals, only the Han routing algorithm presents a specific treatment for each one of them, meaning that it is nearer to an actual network manager implementation that can fulfill the WirelessHART specification. Uses node history: As a dynamic environment, a WSN is subject to variations in its communications, due to issues like interference, for example. These variations could imply anything from a small bit loss up to the incapacitation of whole channels, lasting from milliseconds to days of interference. Such a \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Items/Algorithms** & **Han Routing Alg.[52]** & **JRMLR**[62] & **Re-Add**[64] \\ \hline Objective & Maximize network lifetime & Maximize network lifetime & Robustness and maximize network lifetime \\ \hline Metric & Average number of hops (degree) & Node data load, transmission energy, residual energy & Quality of the link, residual and transmission energy, degree \\ \hline Implement uplink, downlink and broadcast graphs & Yes & Builds uplink and states that the downlink would come from setting the algorithm objective to the destination device & Uplink only \\ \hline Uses node history & No & No & Yes \\ \hline Implementation and validation &
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \end{tabular} & No & No & No pseudocode is presented; presents simulation results, but no further details on the platform used were given \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of the routing algorithms for WirelessHART. situation should be relevant to the routing algorithms in order to provide an adequate response to an interference situation.