A cell based MAC protocol provides both efficient bandwidth utilisation and easy interfacing with the emerging ATM technology. Therefore the slotted approach is being favoured for data transmission and admission control in distributed LANs operating at data rates of more than one Gbit/s. Spatial slot reuse through destination release has been found to be the most effective way towards improving system throughput. That basic mechanism, however, is unfair by giving preference to stations positioned upstream in the ring circulation direction. The paper discusses approaches for an asynchronous media access control in slotted rings. After a general overview of system throughput obtained by an analytical model, the feasibility of various MAC proposals called ATMR, CRMA-II, Distributor, and MetaRing are compared based on simulation results. Differences in the mechanisms are analysed with a particular respect to the tradeoff between high throughput and the guarantee of bounded packet delays. It is shown, that all approaches are generally suitable to meet the requirements of the new LAN generation.>

The pros and cons are discussed of synchronous and isochronous service in FDDI-II, which is an enhanced version of the Fiber Distributed Data Interface (FDDI) protocol. The results make clear that basic FDDI meets the requirements imposed by traditional LAN applications. To overcome the problem of throughput degradation and increasing delays for asynchronous traffic in applications with large fiber length and hard response time requirements, FDDI-II is defined as a promising upward-compatible extension. It is shown that from a performance point of view FDDI-II is an excellent candidate for complex communications environments. This protocol integrates both circuit switched and packet switched services in an efficient way. The results show that, in environments with upcoming hard real-time requirements, changing to the enhanced protocol, i.e., changing from basic FDDI to FDDI-II, is a much better way to meet the demands than to push the old protocol to its limits.>

Performance issues of the FDDI-II protocol, an upward-compatible enhancement of the basic fiber distributed data interface (FDDI), are discussed. The main characteristics of the FDDI protocol are examined. The performance of FDDI-II is studied for scenarios including asynchronous traffic, synchronous traffic and isochronous traffic. The results make clear that basic FDDI meets the requirements imposed by traditional local area network (LAN) application and that from a performance point of view FDDI-II is an excellent candidate for complex communications environments. When compared to the distributed-queue-dual bus (DQDB) protocol, FDDI-II yields much better efficiency in traditional LAN applications.>