A significant obstacle to achieving heterogeneous system interconnection is the need to maintain compatible network protocols on all communicating systems. Protocol standardization and profiling has long been viewed as a way to overcome this obstacle. The exclusive nature of this approach, however, presents limitations such as the exclusion of sometimes superior technology and the necessity for strict agreement among systems. In this paper we consider an inclusive approach to achieving inter-operability based on the use of multi-protocol architectures. We begin with a detailed description of a framework and model for describing and constructing multi-protocol architectures. We then describe a case study based on architectures that mix protocols from the OSI and Internet suites. We identify and propose solutions to the problem of determining which set of protocols to use for a particular communication task.