## 3 Basic System Operation
### SBD Routing
As shown in Figure 10b, the total number of hops for SBD, LEACH and Car Pooling is almost the same due to their similar clustering nature. However, despite having similar hop counts SBD outperforms all other approaches in energy consumption because SBD employs GCA to allocate conflict free scheduling. This helps to avoid packet retransmission as the chances of packet loss due to interference or collision is very low (see Section 5.1.2, Figure 11b). #### 5.1.2 Latency

The setting for this experiment was the same as for the reliability experiment except for the total number of remote storage updates and queries, which were set to 100 each (generating 300 application packets including 100 storage updates, 100 query requests and 100 query responses). Figure 12a shows the latency of each method. Here, latency is defined as the time from the source sending a remote packet (storage update/query/response) to the destination receiving it. As expected, the latency of each method increases gradually with the increase in network size except for one case. It is observed that DD leads to the highest latency with a higher value than the other methods especially when there are 80 nodes. This happened because DD broadcasts 100 queries among the small number of nodes, which makes it more likely to generate congestion. LEACH, SBD and Car Pooling show similar low latency. Figure 12b depicts an interesting explanation for the result provided in Figure 12a. In Figure 12b, it is noted that the number of total Request to Send (RTS) sent by SBD is almost equal to the number of remote packets (remote update, query and response) while for DD it is almost a factor of two and for the other algorithms it is one and a half. However, despite having lower packet loss and lower retransmission compared to LEACH and Car Pooling, SBD shows similar latency due to its store and forward technique. Figure 11: **(a)** Percentage of packets successfully delivered and **(b)** number of packets that failed due to interference. Figure 10: **(a)** Average energy consumption per node (joule) and **(b)** total number of hops (number of hops in storage and query routing). ### Querying Performance

In this section, the performance of DCSMSS with SBD and LEACH routing algorithm is evaluated in comparison with SDS, DD and GHT. As mentioned earlier, DD broadcasts a query to search for all of the desired data. GHT applies a hash function on the attribute name to find the location of the data and merges the located data to the query result. SDS uses the Locality Sensitive Hash (LSH) function and the number of hash values for a data item after the LSH operation was set to 5. #### 5.2.1 Point Query

This experiment was conducted to evaluate the performance of each approach for point queries, which returns a single data item if it finds an exact match. The experiment was conducted using a 90 m \(\times\) 90 m rectangular field, in which 180 nodes were randomly and independently disseminated. 300 queries, in total, were generated uniformly from different parts of the network. Queries were generated as a group referred to as a _batch_, which is sent out at the same time. The next group was released once all the queries of the previous batch were resolved or the maximum response waiting time was exceeded. Figure 12(a) shows the success rate of different methods. Success rate is defined as the ratio between the number of successfully resolved queries and the total number of queries generated. This metric is used to reflect the effectiveness of a data storage method. From Figure 12(a), it is observed that DD exhibits the worst performance and its success rate falls sharply as the number of queries per batch increases. With increased number of queries per batch DD's broadcasting causes excessive messages, which leads to congestion and high packet loss. DCSMS\(+\)SBD maintain a low packet loss due to its collision avoidance technique. The other three approaches--GHT, DCSMSS \(+\) LEACH and SDS fall in the middle. However, amongst these three, GHT's performance is slightly lower.