Multi-mode capable wireless networks are a key issue in future wireless communication. This paper introduces therefore the realization and application of a generic protocol stack as common part of a multi-mode capable communication protocol software. This can be regarded as an extension of the field of software defined radios with its origin in the physical layer on the upper layers of the protocol stack. The generic protocol stack compromises common functionality and behavior of the communication protocols that is extended through specific parts of a dedicated radio access network technology. In a bottom-up approach, this paper considers fundamental protocol functions realized as parameterizable modules. These protocol functions originally correspond to the data link layer of the ISO/OSI reference model. The system specific aspects of the protocol software are realized through adequate parameterization of the modules' behavior. Further specific functionality and behavior can be added to the generic protocol stack through inheritance or insertion of system specific modules. Thus, the generic protocol stack enables an efficient as well as flexible realization of the protocol software as part of a future communication network of multiple radio access technologies.