The simulator is called SimBlock. It allows a user to simulate a blockchain network consisting of a large number of nodes (servers), and modify behavior of the nodes to test effects on performance and security. Users can simulate the impact of changes to an existing blockchain, such as Bitcoin, or to a blockchain of their own design.
Dr Shudo and colleagues at Tokyo Tech developed SimBlock, which can simulate behavior of about 10,000 nodes on the Internet using a single typical PC. The software, which was made open source in July 2018, allows engineers to test improvements on an existing or original blockchain, or even simulate malicious nodes and measure success rates of attack, then apply countermeasures to test its effects.
SimBlock can currently simulate the parameters of Bitcoin, Litecoin, and Dogecoin, mirroring blockchain network size, block generation interval, and communication speed over the Internet. Users can see what changes to node behavior do to a blockchain network by modifying Java code in SimBlock. It is also possible to modify parameters of the blockchain and communication speed.
SimBlock also has a visualizer that shows communication between nodes and block height animated on a world map. A demonstration of the visualizer is available at this web page.