The paper presented a functional view of end-system protocol implementations whereby the protocol is decomposed into various functions, each causing a change in the protocol state. This view makes the interactions and the relationships among the various functional modules explicit. In terms of this view, currently prevalent architectural optimizations for performance improvement (such as `parallel executions' and `integrated layer processing') can be easily described as a set of control flow relationships among modules. If a protocol implementation is analyzed using our functional model, the possible architectural optimizations in the protocol can be easily identified and implemented without violating correctness. Thus, our approach can be used to optimize existing implementations by casting the underlying protocols in our framework, and it is particularly useful in developing implementatio