The first is interoperability between the primary protocol suite and other protocol suites. The second is resource sharing between the primary protocol suite and other protocol suites. Both interoperability and sharing may happen at multiple levels in the protocol suites. Achieving interoperability and resource sharing is difficult, and often unanticipated interactions occur. Interoperability can be difficult for reasons such as lack of common semantics.
Resource sharing can run into problems due to lack of common operational paradigms.
For example, sharing bandwidth on a link may not work effectively if one protocol suite backs off in its demands and the other does not. The challenge in this area, then, is to develop mechanisms for interoperability and resource sharing that have minimal negative affect on the primary protocol suite. The very attempts to achieve interoperability and resource sharing therefore lead to an attempt to bring the multiple protocol suites into some level of harmonization, even if it is just to simplify the problems of interoperability and sharing. Furthermore, the communications between the communities also leads to a level of harmonization. These processes, together with the normal process of evolution, lead to changes in the primary protocol suite, as well as the other suites.