We are using simulation to validate and evaluate the performance of the proposed IEEE 802.4 Token-Passing Bus Medium Access Control (MAC) Protocol for local area networks. We will use our discussion of this modeling study to present our technique for protocol validation. We will also present some of our validation and performance results. Our modeling technique is unusual in two important respects. First, it transforms the formal specification of the protocol by a direct and simple technique into a simulation program. Second, testable assertions about the protocors expected behavior, under both normal and abnormal conditions, are easily transformed into simulation test cases. Our protocol validation technique runs test cases on the simulation model. These test cases are based upon "behavioral assertions" which were derived from the design objectives and expected use of the protocol. Our validation results are discussed in terms of the behavioral assertions tested and the success or failure of meeting these assertions. We also report on simulation performance predictions for some special test cases.