ATMR (Asynchronous Transfer Mode Ring) and CRMA-II (Cyclic Reservation Multiple Access II) are two media access control (MAC) protocols for local and metropolitan area networks (LANs and MANs) working in the Gbit/s range. In this paper the basic access mechanisms of both protocols are described and compared. Our simulation results demonstrate the major performance characteristics of the MAC protocols which are highly suitable for Gbit/s-LANs but differ in some characteristics like access delay, transmission delay and throughput. Both protocols offer high utilization of network bandwidth by destination release and global fairness by special bandwidth sharing mechanisms.

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