ON THE EFFECTIVENESS OF THE FDDI-M MEDIUM ACCESS PROTOCOL FOR REAL-TIME TRAFFIC

FDDI networks have been widely deployed to support real-time traffic s uch as voice and video communications. However FDDI's medium access co ntrol (MAC) protocol can transmit synchronous messages up to at most o ne half of the total bandwidth of the FDDI network. In a recent paper by K. Shin and Q. Zheng [Shin95], a modification to the FDDI MAC proto col, called FDDI-M, has been proposed to double a ring's ability to su pport synchronous traffic. In this paper we present an analytical stud y of the timing properties of the FDDI-M protocol. Using the Worst Cas e Achievable Utilization (WCAU) as the performance metric, we first ev aluate the performance of various synchronous bandwidth allocation (SE A) schemes in guaranteeing synchronous message deadlines. It is found that, in comparison with FDDI, the FDDI-M protocol results in a higher WCAU for the normalized proportional SEA scheme. However, for the loc al SEA schemes, the WCAU values remain zero. Next, other performance m etrics such as throughput and percentage of frames missing deadlines a re examined using simulation. A series of simulations using actual MEP G video traffic confirms that FDDI-M does provide superior synchronous transmission characteristics.