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Tokyo Institute of Technology Identifying Impacts of Protocol and Internet Development on the Bitcoin Network Ryunosuke Nagayama, Ryohei Banno, Kazuyuki Shudo Tokyo Tech Blockchain A distributed ledger on P2P network A node generates a

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Identifying Impacts of Protocol and Internet Development

  • n the Bitcoin Network

Ryunosuke Nagayama, Ryohei Banno, Kazuyuki Shudo Tokyo Institute of Technology

Tokyo Tech

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SLIDE 2

Blockchain

hash nonce Tx Tx Tx hash nonce Tx Tx Tx hash nonce Tx Tx Tx

Block

  • A distributed ledger on P2P network
  • A node generates a "block" including transactions and

a hash value of its parent block. Blockchain

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Node

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Transaction approval

# 𝑝𝑔 π‘’π‘ π‘π‘œπ‘‘π‘π‘‘π‘’π‘—π‘π‘œπ‘‘ π‘—π‘œ 𝑏 π‘π‘šπ‘π‘‘π‘™ πΆπ‘šπ‘π‘‘π‘™ π‘•π‘“π‘œπ‘“π‘ π‘π‘’π‘—π‘π‘œ π‘—π‘œπ‘’π‘“π‘ π‘€π‘π‘š Shorter interval

To make overwriting difficult, transactions should be buried under a sufficient number of blocks.

Shorter interval Larger block size

Transaction throughput Confirmation time

Bitcoin: 10 min Γ— 6 blocks = 1 hour

Less number of blocks until confirmation

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Bitcoin: 7 tx/s

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SLIDE 4

Fork

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The shorter generation interval and larger block size, the more difficult it becomes to share blocks with other nodes. If not shared enough, the blockchain will fork and be inconsistent in the network.

Reduce block propagation delay.

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SLIDE 5

History of block propagation delay on Bitcoin network

Block propagation delay has been reduced

50th percentile ： 8.0 s β†’ 0.4 s 90th percentile ：16.7 s β†’ 2.3 s

β€œBitcoin Network Monitor - DSN Research Group, KASTEL @ KIT,” https://dsn.tm.kit.edu/bitcoin/

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Why has the propagation delay been reduced?

  • Relay network

Relay servers propagate blocks efficiently to participating nodes. [Otsuki, 2019]

  • Development of the Bitcoin protocol
  • Compact block relay (CBR)
  • Improvements of the Internet
  • network latency between peers
  • bandwidth

Relay server 5/18

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Why was the propagation delay reduced?

  • Relay network

Relay servers propagate blocks efficiently to participating nodes. [Otsuki, 2019]

  • Development of the Bitcoin protocol
  • Compact block relay (CBR)
  • Improvements of the Internet
  • network latency between peers
  • bandwidth

Relay server

We evaluate following two factors quantitatively and individually by simulation.

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Experiment

[Aoki, 2019]

A blockchain network simulator that simulates block propagation between nodes. It implements

  • Compact Block Relay is implemented.
  • Internet parameters as of 2015 and 2019 are

implemented.

  • Node distribution

Number of nodes in each country is obtained from Bitnodes.

  • Network latency

Weighted average of latency between countries by number of nodes

  • Bandwidth

Weighted average of bandwidth in countries by number of nodes

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SLIDE 9

Compact Block Relay (CBR)

Tx1

Legacy

hash nonce

ID1 ID2 ID3 GetBlockTx(ID3) Tx 1

CBR

ID3 Tx 3 Tx 2

CBR reduces propagation data size by containing

  • nly transaction IDs.

If a node does not have transactions approved by a received block (block reconstruct fails), the node request them to its peer.

Tx2

hash nonce Tx1 Tx2 Tx3 8/18

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CBR protocol mode

In high bandwidth relaying, nodes send compact block before block validation, and do not send inv message. It wastes bandwidth. β†’ We assume nodes use low bandwidth relaying.

Low Bandwidth Relaying High Bandwidth Relaying 9/18

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Modeling block reconstruct failure

hash nonce ID1 ID2 ID3 GetBlockTx (ID2,ID3) Tx 1 hash nonce ID1 ID2 ID3 GetBlockTx x MB A node fails reconstruct based on failure rate.

Actual CBR Our approximate model

ID3 Tx 3 Tx 2 ID2 x is obtain from the failure size distribution. 10/18

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CBR Parameters

  • Compact block size 18 KB[Ozisik 2016]
  • CBR usage rate 96.4 %
  • The usage rate is based on the versions of protocol used by each

nodes obtained from Bitnodes.

  • Reconstruction failure rate
  • Imtiaz et. al[Imtiaz 2019] measured
  • Churn node 27 %
  • Control node (Stay connected to the network) 13 %
  • Ratio of churn nodes 97.6%
  • Imtiaz et. al[Imtiaz 2019] measured

[Ozisik 2016] A. P. Ozisik et. al, "A secure efficient and transparent network architecture for Bitcoin", 2016. [Imtiaz 2019]Muhammad Anas Imtiaz et. al, Churn in the Bitcoin Network: Characterization and Impact, IEEE International Conference on Blockchain and Cryptocurrency, 2019

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Data size received from peer when reconstruction fails

The data size is obtained from the cumulative distribution that approximates the data measured by Imtiaz et. al[Imtiaz 2019].

[Imtiaz 2019] Muhammad Anas Imtiaz et. al, Churn in the Bitcoin Network: Characterization and Impact, IEEE International Conference on Blockchain and Cryptocurrency, 2019

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Comparison with measured data

Measured[2] Our simulation 50%ile 2015 7,988 ms 9,673 ms 2019 401 ms 1,304 ms 90%ile 2015 16,835 ms 14,056 ms 2019 2,353 ms 2,364 ms

Simulated values are comparable with measured values except to 50th percentile of 2019. β†’ Relay network

Our simulation assumes a random network without a relay network. Relay network efficiently propagates to participating nodes Participation rate 2.65 %[4]

[2] β€œBitcoin Network Monitor - DSN Research Group, KASTEL @ KIT,” https://dsn.tm.kit.edu/bitcoin/ [4] β€œFalcon - a fast bitcoin backbone,” https://www.falcon-net.org/

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Identifying impacts of CBR and Internet improvement on the Bitcoin Network

Better

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Internet 2015 vs 2019

Better

–63.7% –64.6%

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With CBR vs without CBR

Better

–90.1% –87.6%

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Block propagation delay

Better

CBR was more effective.

CBR→ Block size : 0.018 times smaller Internet improvements → Bandwidth : 2~3 times wider

Latency : 0.889 times shorter

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Conclusion

  • CBR significantly improved the propagation

delay.

  • Since CBR can be applied to other blockchains,

it can be expected that CBR shortens the propagation delay in other blockchains.

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