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• A literature review on blockchain Interoperability was conducted.
• The required tools and components for the project were investigated.
• A working environment for multiple blockchain networks was implemented.
• The first version of the messaging broker blockchain was implemented.

2^nd Quarter Progress Report

In the second quarter, the focus was on the implementation of the proposed platform. The platform has three main components: broker blockchain, subscriber blockchains, and publisher blockchain. The broker blockchain is implemented using Hyperledger Fabric V2 and has two chaincodes called broker and pubsub. The broker chaincode holds the topics that are on the pub/sub network. When a publish request to a topic is received, the topic is updated using the broker chaincode. The pubsub chaincode holds the information about all the publisher and subscriber blockchains and their communication interface. As for the subscriber blockchains, currently, Hyperledger Fabric V1.4 and Hyperledger Besu are supported. Example networks, as well as connector smart contacts, have been implemented for each network. Finally, an example publisher network is implemented using Hyperledger Fabric V2. Currently, all the components work together to form a network with a broker, a publisher, and two subscribers. 

To sum up, the following has been done in the first quarter of the project: 

• The broker blockchain keeps track of the topics and it also holds communication interfaces of the publisher and subscriber blockchains. 
• Two example subscriber networks have been implemented using Hyperledger Fabric V1.4 and Hyperledger Besu. 
• An example publisher network has been implemented using Hyperledger Fabric V2.