Modelling Full Interoperability of International Payment Systems: Towards a Unified Framework for Global Financial Infrastructure

Interoperability has long been a central issue for payment systems, which are sometimes siloed and operate in parallel. International payment systems form the backbone of the global economy, but their technical, regulatory, and protocol fragmentation creates costly frictions, latencies, and systemic vulnerabilities. Through the auspices of the BIS, several initiatives have been launched to ensure smooth and inexpensive processing of cross-border payments, with outcomes that are more or less successful. The same is true at the level of economically and monetarily integrated regions, such as the SEPA, or sometimes for regions which are intentionally open to free trade, such as ASEAN and AfCFTA, more recently. Whereas existing studies often focus on only one aspect, this paper proposes a formal modeling framework for full interoperability—the ability for any payment system to interact natively with any other system, regardless of jurisdiction, underlying technology, or governance model. We introduce a reference architecture based on three layers—protocol, semantics and governance—and demonstrate how communicating automata modeling and shared ontology allow to describe, verify and implement real interoperability. Our simulations show that full interoperability would reduce cross-border transaction costs by 40-60% and settlement times from days to minutes, while enhancing the resilience of the overall financial system.