## 5 Results and Evaluation
### Results of Comparative Evaluation  
We performed extensive simulations based on the previously described settings (see Table 1). We investigated the scalability of the protocols by varying network density from 80 sensor nodes to 240 sensor nodes within the network area.  
In Figure 4(a), we investigated lifetime of the sensor nodes. As defined earlier, we were interested in the dissipation of the first node, not the overall network. In this evaluation, we also show the performance of TEAR protocol with \(\xi_{E_{MIN}}=0.25\). TEAR protocol has more than 4 times higher lifetime of the sensor node than Epidemic or AODVjr protocols in all cases, and when \(\xi_{E_{MIN}}=0.25\), it has more than 5 times higher lifetime. Moreover, the lifetime of the TEAR protocol increased by more than 45% in average, when poison process is used.  
Figure 4(b) shows control overhead on logarithmic scale. Epidemic protocol completely fails, causing significant control overhead in dense network (when 240 sensor nodes, control overhead is 65 times higher than TEAR protocol). Epidemic routing protocol exchanges message vectors when new sensor node is connected. Denser network increases probability of new connection, thus the sensor node performs exchange of message vectors more often. Moreover, all nodes are generating messages, thus every sensor node has many messages buffered. Therefore, the vector containing all buffered message identifiers is of very large size, causing overhead. Control overhead of AODVjr protocol also grows with the growing density, reaching 4 times higher values than TEAR protocol. This reflects to the issue of flooding. AODVjr protocol uses network flooding technique when requesting the route towards the data sink. TEAR protocol does not cause extra overhead in dense network.  
In Figure 4(c), we compared packet delivery ratio of TEAR protocol, AODVjr and Epidemic protocol. In low density scenario, the Epidemic protocol overcomes other protocols as it stores the messages and transmits when connection becomes available. As the density of the network increases, the performance of the Epidemic protocol degrades significantly. This is caused by the buffer size. As the network density increases and all the sensor nodes are generating data, the buffer of the sensor node overflows, thus many data packets are dropped. TEAR and AODVjr protocols are fairly robust in the terms of the network density.  
increase with the network density. This result is influenced by higher energy dissipation of the sensor nodes due to the previously described flooding issue resulting in high control overhead. For network with 240 sensor nodes, the AODV protocol has more than 4 times higher energetic cost than TEAR protocol.  
Finally, end-to-end delay is compared in Figure 4(e). Epidemic protocol reaches very high delay by its nature. This delay is decreasing due to more frequent message exchange in dense network. AODVjr protocol has almost the same average delay as TEAR protocol when 80 sensor nodes in the network, however, it has 8 times higher end-to-end delay in very dense network (240 sensor nodes).  
Figure 4: Protocol performance comparison _vs._ different density of nodes.