## 7 Testing
Three distinct solutions were implemented using RPL by using three different metrics to calculate routes: ETX, ETX-NH and ETT. This narrow set of solutions is chosen for a number of reasons. It demonstrates the ability of the response characterisation and modelling technique to distinguish between slightly differing solutions. Implementing a system that switches the communication context between many different whole communications solutions requires large amounts additional overhead as discussed in Section 6.3. A system that can make minimal changes to the network, such as switching between the metrics used, to provide a wider range of responses may prove more effective. RPL espouses the ability for a single routing protocol to elicit multiple responses from the network. It does this primarily by using different metrics and constraints to build the routing DODAG. The advantages, as stated, lie in the fact that changing between metrics is a less intensive process than switching between protocol. ETX [30] is an extensively tested metric which has been advised as the default metric within the currently advised standard. ETX is focused on reducing the number of retransmissions to route a packet to a given destination. ETX if focused on delivering high data reliability on each packet transferred in the network, ETX-NH introduces a modification to the ETX metric, adding a mechanism that increases the ability of a solution to absorb change in the routing structure. ETT is based on the round trip time and is solely focused on building a DODAG that is focussed on delivering the packet sin the quickest time frame. the three metrics provide a wide berth of responses within the protocol. In the TOSSIM simulation neither Received Signal Strength Indication (RSSI) or Link Quality Indicator (LQI) is available. These metrics would usually be used to measure the channel quality between nodes. As TOSSIM uses noise traces applied to the nodes to dictate the quality of the channel it is still possible to examine the network under multiple channel conditions. to replicate a real dynamic channel environment noise traces from real experiments are applied to the nodes. Sincea real estimate of channel quality is not available we make a single distinguishing factor between difficult communications conditions and more manageable communications conditions. These factors are determined by the noise trace applied to the channels in the networks. The traces are taken from a set of publicly available set of real noise traces taken from a network in the Meyer library at Stanford University [41]. The \"Meyer light\" trace represents minimal interference noise while the \"Meyer heavy\" trace represents a more difficult communication scenario. This represents \"light\" and \"heavy\" interference in the channel. Figures 10-14 display the statistics collected from the experiments. Figures 10-12 show the network response for each solution as the density, scale and size of the network vary under the light trace. Figure 13 shows how the network response changes when the heavy trace is used. Data for the standard deviation of scale and density is shown in Figure 12.  
Figure 10 shows all evaluation metrics following a general trend towards poorer results as size increases. Reliability and stability for both ETX and ETX-NH are well defined as size varies with latency and efficiency showing poor correlation. Figure 11: Network response from each solution as density varies. Figure 10: Network response from each solution as size varies. Figure 11 shows a large impact on both reliability and latency effected by the change in density for all communication solutions. Neither efficiency nor stability are affected greatly by a change in density, however, density still proves an important tool for comparing each solution with regard to efficiency and stability. Each solution presents significant performance difference in terms of stability using density to compare solutions with NH presenting marked improvements over the other solutions.