Evaluating Off-chain Transaction Queueing Delay to Ensure Data Integrity by Blockchain

In recent years, society has been promoting the use of big data to improve our daily lives. At the same time, there is a demand to verify the legitimacy of data. For this reason, there have been many proposals to ensure data integrity by a blockchain consensus. However, the blockchain-based system cannot process a lot of transactions in a short period. Therefore, the blockchain technology cannot be simply applied into systems where large amounts of data are added and updated.Off-chain protocols have been proposed to scale blockchains. They guarantee the integrity of data outside the blockchain and reduce the on-chain replication cost by not directly storing data in the blockchain storage. Meanwhile, an off-chain queueing delay is newly introduced since off-chain transactions (OTXs) are processed in a batch manner by periodically posting the OTX summary data on the underlying blockchain. This delay cannot be ignored, especially in the case of frequently updated data, such as IoT data.In this paper, we propose and analyze a queueing model that considers OTX processing time in order to estimate the mean OTX queueing delay. This analytical values help us to previously determine whether the adopted off-chain approach is effective to ensure the integrity of the given data. In numerical examples, we show how the parameters, such as the OTX batch size and the OTX rate, affect the OTX queueing delay.