4.1 Evaluated Result:
Simulator Validation: In order to validate the performance of this study author has adjusted the parameters of table 4 with the real world deployed blockchain. For determining the stale block rate author has crawled 24000 Bitcoin,1000,000 Litecoin and 240,000 Dogecoin blocks. The performance achieved from this model is quite like the real world blockchain. Stale block rates of Dogecoin and Litecoin are particularly close and Bitcoin’s stale block rate falls in some cases like where relay network and unsolicited block push is not used by miner.
Figure 17: Geographical Location of Bitcoin miner’s in study simulator.
Block Interval: Author has tested block interval with a range of .5 sec to 25 minutes in the simulator. It is tested for four different block request management system namely 1. Standard block request management 2. Standard block request management enhanced by unsolicited block push from miners 3. Standard propagation mechanism with relay network 4. Send header mechanism with unsolicited block push and relay network.
For standard block request management system with 10 minutes block interval study simulator produces stale block rate 1.85 % in compare to 1.69 % reported by Wattenhoffer.
Stale block rate reduces significantly after introduction of unsolicited block push for miner because of two main reason—a. miners profit most out of unsolicited block push because they are interconnected b. propagation method is crucial to reach the majority of the network rapidly. To measure the impact of the block interval author has feed the resulting stale block into MDP models. It is found for an adversary with 30% of total mining power relative revenue is inversely proportional to consensus time.
Impact of Block Size: From the study it is found block propagation time has linear relationship with block size. But this linear relationship is valid up to 4 MB block size. From 4 MB to 8 MB stale block rate increases exponentially with propagation times. If block size increases relative revenue of selfish miner also increase but double spending value decreases. Author has also found efficient block propagation mechanism to increase the security of the block chain. The results of this study for four previously discussed block request management system is shown in the table 5.
Table 5: Impact of the block size on the median block propagation time (tMBP) in seconds
The stale block rate is rs, vd and rrel, given the current Bitcoin block generation interval and an adversary with ? = 0.3 and k = 6.
Throughput: Author has varied block size (.1 MB-8 MB) and block interval (.5 second-25 Minutes) to capture different blockchain throughput. Throughput is calculated in transaction per second (tps). Stale block rate and infer are represented with vd and rrel. The result author has got is shown in the below table -6.
Table 6: Impact of throughput for K=6 and 16 mining pool with 30% adversarial mining power.
From this table it can be seen 60tps throughput can be achieved with existing security in the bitcoin by changing the input parameters like block size and block interval.
5. Conclusion: In this study author has proposed a quotative framework to measure the security and performance of different POW based blockchains. The impact of network level parameters on the security of blockchain is evaluated in this study. From the study it is found 37 Ethereum block confirmation equals 6 Bitcoin block confirmation. It means Bitcoin blocks are more secured than Ethereum’s. It is also proved that 60 tps of Bitcoin throughput can be achieved without sacrificing the existing security by varying input the parameters.
1. On the Security and Performance of Proof of Work Blockchains by Arthur Gervais, Ghassan O. Karame, Karl Wüst, Vasileios Glykantzis, Hubert Ritzdorf, Srdjan ?Capkun.
2. Shai Rubin What is blockchain –youtube