An alternative to FDDI: DPMA and the Pretzel ring

| This paper proposes an eecient, fair, and simple capacity{1 protocol replacing fddi. In the recent years, two network protocols gained predominance in very fast Local and in Metropolitan Area Networks: fddi and dqdb. The fddi ring{protocol combination is well-suited for large local (\campus") area networks. However , for larger networks, fddi users suuer excessive access delays, even under very light traac. Moreover, fddi achieves full capacity only in special circumstances, and heavy load is not a suucient condition for achieving it. We propose a network topology that is very similar to the dual ring and a token-passing protocol that yield a true capacity{1 network even for modest values of the ttrt. Its additional properties include total fairness and very small access delays under light load. This makes the proposed protocol a reasonable option to use in combination with the dual counter-rotating ring. The proposed network should not be diicult to implement using standard fddi components.