## 6 Simulation Setting
At the end of the lifetime of the network, all the nodes in all the schemes fully utilized their energy so the total energy consumed by all the schemes remained the same, which was 3500 J.  
Co-ESRVR utilized more energy than ESRVR due to the use of the cooperation of the relay-destination pair with the source node. Such a pair provided multiple copies of the same data to the destination in unfavorable conditions. This pair used extra energy and was not present in ESRVR. Consequently, the energy cost of Co-ESRVR was higher than ESRVR. Figure 8 depicts that the rate with which nodes became dead in a particular scheme correspondingly followed the pattern with which that scheme consumed energy. In other words, the way energy was consumed by the protocols decided the rate at which nodes died. Therefore, nodes died in all three schemes in correspondence with their energy consumption behavior. Thus, Co-ESRVR, ESRVR, and RIAR had dead nodes patterns owing to their correspondingly higher to lower energy consumption behavior. Initially, for the first 50 rounds, nodes died slowly in all the protocols, as most nodes had enough battery power. After that, advancing of data packets consumed more battery power of the nodes. Consequently, nodes started to die at high rate in subsequent rounds. At the end of the lifetime of the network for a particular scheme, all the nodes died, which characterized the total exhaustion of the available energy with all the nodes. Figure 7: Consumed energy. Figure 9 exhibits the comparative delivery ratio (DR) behavior of the schemes. It equaled the packets that reached the sea surface divided by the total packets generated. The involvement of the backward transmission mechanism and the unique packet holding time in ESRVR and Co-ESRVR added to reducing packets' loss and enhancing the delivery of packets to the water surface. Such mechanisms were not present in RIAR. As a result, these protocols had better DR than RIAR. The use of the relay-destination pair with the source node for cooperative routing in Co-ESRVR helped the source node to transfer data to the water surface reliably, especially in unfavorable conditions. This further added to packets' transfer to the sea surface, which made the DR of Co-ESRVR higher than that of ESRVR. The DR of every node was initially higher as more nodes were present in the network for packets' transfer. As time passed, nodes died in the network, which interrupted packets' transfer. As a result, the DR of every scheme exhibited a correspondingly decreasing behavior. The DR of Co-ESRVR was the highest initially because it involved cooperative routing, and all the nodes were available for data routing. The chances of packets loss were minimized with cooperative routing, as packets were sent to the destination directly and via a relayed path. However, as the rounds proceeded, nodes started dying and less nodes were available for involvement in cooperative routing. As a result, the DR of Co-ESRVR dropped, especially in the first 200 rounds. The behavior of total end-to-end delay is exhibited in Figure 10. The RIAR algorithm bore the longest delay due to a number of reasons. Firstly, the surface sink constantly transmitted messages to the sensor nodes in the network so that they could compute the number of hops and the distance from the sink. This consumed a significant amount of time. Secondly, end-to-end paths had to be computed from a source node to the sea surface, which also took time. These two factors were not present in ESRVR and Co-ESRVR. Consequently, these protocols had shorter delay than the RIAR algorithm. The inclusion of relay nodes to source-destination pairs in ESRVR, to make Co-ESRVR, increased the number of paths over which packets were advanced to the destination. As a result, the delay of Co-ESRVR became longer than that of ESRVR. Initially, up to several rounds, the delay of all the schemes was almost the same.