Modeling and Analysis of Reliable Contract Net Protocol Using Timed Colored Petri Nets

Contract Net Protocol (CNP) is probably the most widely used task allocation protocol in distributed multi-agent systems (MAS). However it is limited in some issues and has serious drawbacks if it is applied in such real world applications where temporal interaction aspects are of great importance and fault-tolerance is a crucial issue. Many researchers have proposed various methods to expand and to improve it but those challenges have not been much addressed. To cope with these limitations, this paper proposes a formal model that extends the conventional contract net with real time constraints, often defined as interaction duration and message deadlines, and fault tolerance to handle the agent death exception. In this study we concentrate on the reliability of the awarded contractor which may die while carrying out the assigned task. In the proposed approach a timeout mechanism is modeled to detect the crash failure of the contractor, hence a proper termination of the negotiation process can be timely performed by the manager ensuring the failure recovery. We model the extended CNP with timed colored Petri nets and show that it terminates correctly either in a safety case or in a failure situation. The model analysis by means of CPN tools proves that the protocol meets the key properties namely model correctness, deadline respect, absence of deadlocks and live locks, absence of dead code, agent terminal states consistency, concurrency and validity.