Blockchain Transmission Protocol (BTP) is a standard set of rules that allow users and smart contracts on a blockchain to communicate with other blockchains. Additionnlly, we designed BTP version 0.5 by utilizing record event message on the source blockchain and relaying it to the destination blockchain. For example, assume that Sender on “Blockchain A” wants to transfer a token to Receiver on “Blockchain B”. In that case, a pair of token scores should be deployed, one for each blockchain. The Sender sends a transaction to the token score on “blockchain A”, including an identifier for the destination blockchain, address of the Receiver and amount to be sent. Then, the token score on “blockchain A” records the transaction data as a BTP message on “Blockchain A”. Servers called Relayers always looks for BTP messages. When the Relayer finds a BTP message, it forwards the message to blockchain that corresponds to BTP message information. Finally, the token score on “blockchain B” will receive the contents of the BTP message then mint proper amount of tokens to be sent to user B. This PoC is intended to explain how to transfer a token between blockchains and provides python projects to run as an example.

SrcChain and DstChain consist of a single node blockchain respectively.

Three scores, Token, BTP Menagement Center(BMC) and BTP Message Verifier(BMV) scores, must be deployed in advance on each blockchain.

The Forward Relayer relays BTP message to DstChain if it encounters a BTP message while monitoring the SrcChain. In contrast, the Backward Relayer finds the BTP msg in DstChain and passes it to SrcChain. Therefore, two unidirectional Relayers work for BTP.

This PoC project shows that user A on SrcChain sends token to user B on DstChain.

icon-btp-0.5-PoC (project root) has three sub-projects:

This guide will get you two local loopchain with 3 scores(smart contract) and 2 Relayer servers. With this tutorial you will able to send tokens to user B of DstChain from user A of SrcChain. Note that in order to demonstrate the scenario, you have to run at least 5 programs. It is recommended to run each program through the teminal.

This PoC requires the following environments.

• Python
  • Version: Python 3.7+ (recommended 3.7.x)
  • IDE: Pycharm is recommended.

Install and run two blockchains distinguishable by nids. Each blockchain consists of a single loopchain node running locally. Please refer to the following link: Guide for install Loopchain

For BTP 0.5, three scores, Token, BMC, BMV, should be deployed on each blockchain. Both loopchains should be running before deploying the scores. Fortunately, we provide everything you need for deployment. Sub-project contract-poc includes the score source code and the deployer program. Please run the deployer program specified in the following link: Run Deployer

Relayers regularly monitor for new BTP messages from the read-chain. If a BTP message detected, the Relayer generates a proof of existance(PoE) value. The PoE value is used to verify the existence of the BTP message, and is then forwarded to the write-chain along with the contents of the BTP message itself.
There are 2 types of Relayers, Forward Relayer and Backward Relayer. The only difference between the two is configuration. Forward Relayer sets SrcChain to read-chain and Dstchain to write-chain, while Backward Relayer sets the reverse. It means that both of Relayers standing different direction are requeired. You can run the Relayers by following the link: Run Relayer

In this PoC, user A sends 3 transactions to SrcChain. First one requests tokens to faucet of token score for transfer testing. And second deposits an appropriate amount of tokens to BMC. After 2 transactions complete, user A sends sendToken transaction to BMC. it decreses deposit in BMC, record BTP message on SrcChain as a transaction receipt.
When the sendtoken transaction completed, the Forward Relayer detects BTP message and send it to BMC on DstChain with PoE. the transaction makes token score mint tokens owned user B and BMC generate BTP message that contains specific work is complete. Then, Backward Relayer finds BTP message in DstChain and sends it to SrcChain in the same way of Forward Relayer. If the last transaction sent by the Backward Relayer succeeds, the BTP transfer is completed.
user-poc represents the scenario described above and is available at link: User Behavior