Currently the SDN research community considers in-line dynamic network functions too complex for SDN, leading to calls to purge them from the forwarding plane. This paper introduces a comprehensive framework that tames this complexity and allows network administrators to deploy complex network functions into the SDN forwarding plane to provide enhanced and provable network properties. We first illustrate mapping complex network functions to a network to determine location and their sphere of influence. Through analysis we identify properties common to all network functions and we provide formalisms to specify the behaviour of a generic network function using typed functions, the basis of many modern programming languages. We extend this generic network function to demonstrate two types of firewall providing security properties and also demonstrate chaining which is the basis of Unified Threat Management firewalls and Deep Packet Inspection. This paper is a foundation for ongoing research into proving properties of black box implementations of network functions.

Abstract In this paper, we give simple example abstract data types, with atomic operations, that are related by data refinement under a definition used widely in the literature, but these same abstract data types are not related by singleton failure refinement. This contradicts results found in the literature.

This paper presents supervisory control theory in a process-algebraic setting, and proposes a way of synthesising modular supervisors that guarantee nonblocking. The framework used includes the possibility of hiding actions which results in nondeterminism. As modularity crucially depends on the process equivalence used, the paper studies possible equivalences and points out that, in order to be consistent with respect to the nonblocking property and to supervisor synthesis, a conflict-preserving equivalence must be used. It applies the results to synthesise nonblocking modular supervisors for a manufacturing system.

Development by formal stepwise refinement offers a guarantee that an implementation satisfies a specification. But refinement is frequently defined in such a restrictive way as to disallow some useful development steps. Here we define feature refinement to overcome some limitations of refinement and show its usefulness by applying it to examples taken from the literature. Using partial relations as a canonical state-based semantics and labelled transition systems as a canonical event-based semantics, we define functions formally linking the state- and event-based operational semantics. We can then use this link to move notions of refinement between the event- and state-based worlds. An advantage of this abstract approach is that it is not restricted to a specific syntax or even a specific interpretation of the operational semantics.