## 6 Experimentation
### Real Deployment Experiments  
In a real evaluation we aimed to investigated whether ZERO compromises the reliability of the network. The experiments were conducted using the G3 node from WorldSensing (Figure 6). The G3 nodes are equiped with an Atmel Atmega microcontroller and a CC2420 radio at 866 Mhz. They make use of TinyOS as operating system. Both triangular and proportional metrics of ZERO have been implemented. As CTP regards, the TinyOS implementation have been used. Finally the evaluation of both routing techniques has been carried out using our receiver oriented MAC layer. A network of 10, 21 and 54 motes have been deployed at our lab. Motes were randomly placed indoor and outdoor with the restriction of ensuring full network connectivity. Experiments for 10 nodes were repeated 102 times, for 21 nodes 30 times and for 54 nodes 10 times for both CTP and ZERO routing protocols. In total data from 2197 nodes were collected. Delivery ratio as a proportion of packets issued  
Figure 5: Average number of messages per relay (in average for the 50 repetitions of the experiment). Figure 6: WorldSensing G3 more used in the experimentation. w.r.t acknowledgements received was computed for each node. For ZERO this time the proportional distance metric has been used. Figure 7 shows the distribution of the delivery ratio for all the studied nodes. For CTP implementation nodes exhibit a mean delivery ratio of 84.32% while for ZERO a 99.35%. That 15% of increment is attributed to the path diversity introduced by ZERO that reduces the probability of collision at a node. The effects of selecting other than the optimal path calculated by CTP are inappreciable in our experiments due to that they are compensated by the reduction of collisions at relaying nodes. Regarding energy consumption a cost-benefit metric \(\eta\) has been used as in [13]. In our scenario nodes transmitted at the same rate in a many to one fashion so the only factor that introduced variations in the energy consumption of individual nodes depends on the delivery ratio of routing nodes to the sink (_i.e._, the number of retransmission due to failure in the delivery or due to multiple hops). Likewise [13] the cost benefit function has been calculated as a ratio of the total number of packets received by the sink with respect to the total relayed packets by routing nodes. Let N be the total number of nodes in the network, let R be the subset of nodes routing information. The benefit function then is the total number of issued packets in the network w.r.t the cost function. The cost function calculates the total number of retransmissions of packets until they reach the sink. \[\eta=\frac{\sum_{i\in N}P_{i}}{\sum_{j\in R}ETX_{j}^{-1}}\]  
Figure 7: Distribution of delivery ratio per node. (a) CTP, (b) ZERO. Figure 8 shows the cost-benefit ratio of CTP and ZERO as regards to the load of the network. Due to path diversity ZERO mitigates the effects of congestion, represented as rapid increase of the ETX in CTP due to unsuccessful packet transmissions. The experiment was carried out using 21 motes generating traffic to the sink. Experiment was repeated for different packet rates (1 to 6 packets per second). Although ZERO not always favours the most reliable link it outperforms CTP as congestion increases. The Figure 9 presents the number of packets relayed by different nodes in the network. The data presented in Figure 9 has been obtained for the deployments of 21 and 54 motes. ZERO again makes use of more relay nodes but the load of all of them (excepting sink node) is lower than most overloaded nodes in CTP. Finally Figure 10 shows the results of an experiment of 11 nodes for both CTP and ZERO. The diagrams present the topology of the network created by the routing protocol. Figures for experiments of 21 and 54 nodes have not been included due to their size and the confusing amount of information. Circles represent nodes identified by their ID and below the mean delivery ratio achieved during the experiment.