# A Robust Sharding-Enabled Blockchain with Efficient Hashgraph Mechanism for MANETs
## 7 Performance Evaluation
### Experimental Evaluation
#### 7.2.2 Experimental Results  
* Intra-sharding consensus  
Table 2 presents the comparison of the PBFT, traditional hashgraph consensus, the consensus in [PERSON] et al. [23], the consensus in [PERSON] et al. [24], and our proposed scheme. Consensus in [23] is based on PoW. The consensus process in [24] contains two rounds, the first round of which is realized by a primary and primary candidates based on hashgraph, and the second round of which is a primary synchronizing macro-block to accounting nodes. To make the explanation clear, blocks in the PBFT, refs. [23; 24], are regarded as events. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Consensus Scheme** & **Consistency** & **Leader-Based** & **Fault Tolerance** &
\begin{tabular}{c} **Neighbors Selection for** \\ **Events Propagationn** \\ \end{tabular} \\ \hline PBFT & Strong & Leader & less than 1/3 of all nodes & Random \\ traditional hashgraph & Eventual & Leaderless & less than 1/3 of all nodes & Random \\ [PERSON] et al. [23] & Eventual & Leader & less than 1/2 of all nodes & Random \\ [PERSON] et al. [24] & Eventual & Leader & less than min (\(r1 FT,r2 FT\)) & Random \\ our scheme & Eventual & Leaderless & less than 1/3 of all nodes & Selective \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison among popular consensus and our scheme in MANETs. \(r1 FT\) is 1/3 of a primary and primary candidates, and \(r2 FT\) is 1/2 of a primary and accounting nodes. Figure 8 presents the changes of event throughput and traffic throughput with the increase of consensus nodes. In Figure 8a, our proposed scheme is better than other schemes, because five nodes generate events in parallel in our scheme, while only one miner/leader/primary generates events in the PBFT, as shown in [PERSON] et al. [23] and [PERSON] et al. [24]. With the increase of consensus nodes, the throughput drops and the gap between our scheme and another scheme becomes smaller. The reason is that the increasing events generated by more nodes result in network congestion, especially events in our scheme growing faster. However, since our scheme adopts sharding technology, the number of nodes can be controlled effectively. In Figure 8b, traffic information includes events traffic, control traffic and routing traffic. The performance of our scheme is also better than that in other schemes. Although the traffic throughput of our scheme is very close to [24] when the number of nodes is 66, more events in our scheme are generated according to Figure 8a. In other words, less control traffic and routing traffic are consumed to be associated with event updates in our scheme, so our communication overhead is efficient. In addition, the traffic throughput of the PBFT is more than that of [23], while the event throughput of [23] is better. It is because more synchronous messages are generated in the PBFT, and these messages lead to a high delay of consensus in opportunistic communications. The PBFT is not very suitable for mobile consensus in terms of throughput. Figure 9 presents the changes in event throughput and traffic throughput with the increase of event generation interval. In Figure 9a, the event throughput of our scheme is better than other schemes, because more than one node generates events in our scheme. After an interval of 1 s, the event throughput of [PERSON] et al. [23], [PERSON] et al. [24] and the PBFT are very similar, because there are more available network resources and the same number of events can be updated in a similar amount of time. Furthermore, the gap of event throughput between our scheme and another scheme becomes smaller in Figure 9a, while the gap of traffic throughput between our scheme and another scheme remains stable after an interval of 2 s in Figure 9b. It is because our scheme uses gossip about gossip as a propagation method. When the interval of event generation increases, fewer gossip messages lead to more control traffic being generated. In other words, lower data rates can reduce the performance of our scheme.