Multi-subsystem protocol architectures: motivation and experience with an adapter-based approach

Protocol software is often difficult and expensive to implement and test in today´s computing environments. Several things are done to reduce this difficulty: communications software is subdivided into layers and organized into a protocol graph; communications software is developed within a protocol or networking subsystem; and it is often ported rather than developed from scratch. Today, a multitude of subsystems offer different features, functionality, and drawbacks; the differences among them often reduce portability and efficiency of protocol code. We consider these differences in subsystems and their effect on the portability and performance of protocol implementations. We propose an approach for combining the better features of protocol subsystems by constructing protocol graphs composed of protocols residing in different subsystems. Our approach uses adapter modules spanning the inter-subsystem boundary. We relate our experiences designing, implementing, and measuring the performance of several such adapters using an AppleTalk protocol stack we have developed as a baseline