A symmetric protocol to establish service level agreements
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We present a symmetrical protocol to repeatedly negotiate a desired service level between two parties, where the service levels are taken from some totally ordered finite domain. The agreed service level is selected from the levels proposed by both parties and parties can only decrease the desired service level during a negotiation. The correctness of the protocol is stated using modal formulas and its behaviour is explained using behavioural reductions of the external behaviour modulo weak trace equivalence and divergence-preserving branching bisimulation. Our protocol originates from an industrial use case and it turned out be remarkably tricky to design correctly.
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