Model-based diagnosis of communication protocols

Protocol diagnosis is the act of detecting, localising, and identifying faults in a protocol implementation. When performing model-based diagnosis of protocols, observations of the protocol implementation being diagnosed are compared to expectations based upon a model of the protocol in order to detect errors. The model is derived from the protocol specification and configuration parameters. Fault localisation and identification is performed by finding mutations of the model that improve explanation of the observations. The main advantages of this technique are its generality, reliability, flexibility, and capacity to explain diagnoses. We contribute a detailed and extensive classification of real protocol faults. We extend an automaton formalism, namely finite transducers, in order to facilitate protocol diagnosis and to represent the rich information available in protocol specifications, such as temporal information, guard conditions, actions, and variables. The extended formalism is used as a basis for a novel formulation of protocol diagnosis as a constraint satisfaction problem. This opens the problem domain to a large body of solution results. We establish general classification criteria for defining diagnosis problems and solution approaches. We present a novel approach to protocol diagnosis called the Heuristic Model-based Diagnosis of communication Protocols (HMDP) algorithm. Results are based on experience with the Alternating Bit Protocol and the OSI Transport Class 4 Protocol. The HMDP algorithm and four related existing approaches are described and compared using the defined classification criteria. Important computational issues include observation incompleteness and uncertainty, temporal constraints, and overall tractability. Important aspects of modelling include establishing the best formalism, model incompleteness, multiple correct behaviours, and difficulties in representing diagnosis candidates using the conventional model-based diagnosis framework. We present, justify, and evaluate practical network management architectures integrating a tool based on the HMDP algorithm. These include a generic architecture and an architecture based on the OSI Network Management standards and the CNMA LAN Agent. The proposed architectures contribute to demonstrating the practical feasibility of integrating and using network management tools that perform protocol diagnosis by analysis of observed traffic.