In this paper, elements of an object-oriented implementation of the upper layer OSI protocols are presented. Our goal in the paper is two-fold. First, to communicate to software engineers, particularly those developing systems software, that object-oriented programming techniques facilitate and enhance the implementation of layered architectures. Second, to convey to language designers our experience using object-oriented language features in building communications protocols. We focus on the requirements for the upper layer OSI protocols and illustrate how inheritance, subtyping, and polymorphic function effect their implementation.