There are several contact tracing solutions, some are for closed user groups, some are for the residents of a country, and some are open solutions with no clear boundary defined. These independent solutions are not adequate to support pre-pandemic global mobility. Ideally, what is needed is a global solution that can support decentralized control over data and at the same time support proximity data exchange among Apps developed by different vendors and for different countries. This paper proposes a family of contact tracing designs with low-risk anonymity that includes a centralized design, a distributed design, and a federated design for global solution.
