Simulating a Blockchain Network with SimBlock
Ryohei Banno

Kazuyuki Shudo

Tokyo Institute of Technology
banno@computer.org

Tokyo Institute of Technology
shudo@is.titech.ac.jp

Node A

Abstract—Blockchain techniques are attracting growing interest due to their capability of immutable and anonymousrecording without any centralized authority. One of the difficulties blockchain researchers are facing is a lack of ways
to verify behaviors of large scale blockchain networks. In thisdemonstration, we present SimBlock, a blockchain network
simulator. It simulates the peer-to-peer network of a publicblockchain, e.g., Bitcoin, which consists of thousands of nodes, aswell as parameters related to a blockchain and its network are
flexibly configurable. SimBlock can also visualize nodes’ behavior
and block propagation. By giving some example studies, such as
exploring better neighbor selection strategies and assessing theinfluence of relay networks, we show that SimBlock can facilitate
blockchain network research.
Index Terms—Blockchain, Simulator, Peer-to-peer network

Node B

Block generation

Fig. 1. Block propagation protocol between two nodes.

I. I NTRODUCTION
Blockchain elicits increasing attention in recent years as oneof the key technologies of cryptocurrencies. It has been giving
rise to lots of research topics not only for security researchers
but for network researchers.
However, blockchain “network” researchers have difficulty
in research means; because of its P2P-based scalable architecture, researchers are faced with the following issues:• In a large scale public blockchain network, it is hard toobtain information about the whole network, unless they
provide most of the nodes by themselves. Even if they canobtain, ambitious experiments do not receive a welcome.
• In a small scale private blockchain network, they cannot
observe actual behaviors in practical scale networks.
For that reason, it is hard to conduct experiments in practical large scale blockchain networks. This has also caused
insufficient quantitative evaluation of emerging blockchain
techniques, despite their giving rise to launch of various
venture businesses.
To solve such problems, we developed a blockchain network
simulator SimBlock [1]. In this demonstration, we present
actual usage of SimBlock with some examples, such as
exploring better neighbor selection strategy and assessing theinfluence of relay networks. By these, we show that SimBlockcan facilitate blockchain network research.
II. S IM B LOCK
SimBlock was developed by Distributed Systems group,Tokyo Institute of Technology to facilitate blockchain network978-1-7281-1328-9/19/$31.00 c 2019 IEEE

research. It simulates the peer-to-peer network of a publicblockchain such as Bitcoin [2] and Litecoin [3] that consistsof thousands of nodes, on a single computer.
It was designed as an event-driven simulator wherein eachparticipating node behaves according to generated events,e.g., block generation and exchanging messages as shown inFigure 1.
Typical configurable parameters are as follows:
Block size.
Difficulty of block generation, expressed as an average
generation interval.
• Number of nodes.
• Number of neighbor nodes on every node.
• Geographical regions each node is located in.
• Block generation capacity of every node.
• Network bandwidth (up/down) between each pair ofregions.
• Average network delay between each pair of regions.
••

In the default setting, blocks are generated by a probability
assuming Proof of Work and propagated along the simulated
blockchain network. Other schemes such as Proof of Stake canbe simulated by changing block generation-related parameters.
Furthermore, SimBlock has a visualizer for drawing nodes’
behavior and block propagation.
To evaluate whether SimBlock appropriately simulates
blockchain networks, we compared the simulated environments by SimBlock and the actual environments in regard
to three public blockchain networks: Bitcoin, Litecoin, andDogecoin [1]. Specifically, we compared the median numberof block propagation time and the ratio of the fork occurrence.

Proc. 2019 IEEE Int'l Conf. on Blockchain and Cryptocurrency(IEEE ICBC 2019), pp.3-4, May 2019

Normal Bitcoin nodes

9200

Proposed Algorithm

Median block propagation time (msec)

Median block propagation time (msec)

9400
9000
8800
8600
8400
8200
8000
7800

10000
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All nodes

8000

Not involved nodes

7000

Involved nodes

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4000

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Fig. 3. Median of block propagation time with a relay network.

Fig. 2. Median of block propagation time with a neighbor selection technique.

We confirmed that most of the measured values in the simulated environments and the actual environments are close.
III. E XAMPLE USAGE
This section shows our studies that SimBlock has enabled.
A. Exploring better neighbor selection strategies
One of the examples of our research topics that requires
SimBlock is neighbor selection techniques.
Achieving high throughput is a challenge contributing towiden applicability of blockchain. The expected throughputof blockchain is the quotient obtained by dividing the numberof transactions included in each block by the average block
generation interval. In the case of Bitcoin, it is approximately
seven transactions per second. This is quite small comparedwith Visa (approximately 1, 700 transactions per second [4])and PayPal (approximately 290 transactions per second [5]).
One technique to safely improve the throughput is reducing
the block generation interval by shortening the block propagation time [6]. Therefore, we are considering a better neighborselection technique in blockchain networks.
Our algorithm makes each node to attempt to connect withnodes which send INV messages to it faster than existingneighbors. Besides, a few neighbors are randomly selectedfrom all known nodes to find better neighbors.
Figure 2 shows the difference of block propagation time
between our algorithm and the normal one used in Bitcoin. Itis shown that blocks are propagated faster with our technique.
B. Assessing the influence of relay networks
The other example is assessment of relay networks.
Relay networks, e.g., bloXroute [7] and Falcon [8], arenetworks dedicated to block propagation. These are aiming
to improve the propagation time, so that they could enlarge
the throughput as like neighbor selection strategies.
However, the actual influence of relay networks is not
sufficiently clarified, due to the difficulties of experiments as

described in Section I. Therefore, we conduct some experiments to observe their influence by using SimBlock.
Figure 3 shows the block propagation times when changing
the participation rate of the node to the relay network. We cansee that high participation ratios involve remarkable improvement of the propagation time. Even if the participation rate in
the relay network is as low as 5%, the propagation time of allnodes is improved to less than 70% of the original propagationtime.
IV. C ONCLUSION
We developed a blockchain network simulator SimBlock.
SimBlock can easily change the behavior of nodes, so thatit enables to investigate the influence of nodes behavior on
blockchains. To show practical usage, we conducted twoexperiments which clarify the influence of neighbor node
selection algorithms and relay networks on the block propagation time. The simulator could depict the effects of thetwo techniques on block propagation time.
SimBlock is publicly available1 , so that it facilitates studies
to clarify the potential of blockchain techniques.
R EFERENCES[1] Y. Aoki, K. Otsuki, T. Kaneko, R. Banno, and K. Shudo, “SimBlock:A blockchain network simulator,” in Proc. CryBlock 2019 (in conj. withIEEE INFOCOM 2019), Apr. 2019.
[2] S. Nakamoto, “Bitcoin: A peer-to-peer electronic cash system,” 2008.
[3] “Litecoin,” https://litecoin.com, (accessed Jan. 10, 2019).
[4] “VisaNet — Electronic Payments Network,” https://usa.visa.com/aboutvisa/visanet.html, (accessed Jan. 10, 2019).
[5] “PayPal, Inc — PayPal Reports Second Quarter 2018 Results,”
https://investor.paypal-corp.com/news-releases/news-releasedetails/paypal-reports-second-quarter-2018-results?ReleaseID=1072972,(accessed Jan. 10, 2019).
[6] C. Decker and R. Wattenhofer, “Information propagation in the bitcoin
network,” in Proc. IEEE P2P’13, Sep. 2013.
[7] U. Klarman, S. Basu, A. Kuzmanovic, and E. G. Sirer, “bloXroute: A
scalable trustless blockchain distribution network whitepaper.”[8] “Falcon - A Fast Bitcoin Backbone,” https://www.falcon-net.org/, (accessed Jan. 10, 2019).

1 We will release SimBlock in April 2019.

Proc. 2019 IEEE Int'l Conf. on Blockchain and Cryptocurrency(IEEE ICBC 2019), pp.3-4, May 2019