  The adoption of permissioned blockchain networks in enterprise settings has
seen an increase in growth over the past few years. While encouraging, this is
leading to the emergence of new data, asset and process silos limiting the
potential value these networks bring to the broader ecosystem. Mechanisms for
enabling network interoperability help preserve the benefits of independent
sovereign networks, while allowing for the transfer or sharing of data, assets
and processes across network boundaries. However, a naive approach to
interoperability based on traditional point-to-point integration is
insufficient for preserving the underlying trust decentralized networks
provide. In this paper, we lay the foundation for an approach to
interoperability based on a communication protocol that derives trust from the
underlying network consensus protocol. We present an architecture and a set of
building blocks that can be adapted for use in a range of network
implementations and demonstrate a proof-of-concept for trusted data-sharing
between two independent trade finance and supply-chain networks, each running
on Hyperledger Fabric. We show how existing blockchain deployments can be
adapted for interoperation and discuss the security and extensibility of our
architecture and mechanisms.
