AbStrPctThe Fiber Distributed Data Interface(FDD1) is MW widely accepted as the follow-on LAN for IEEE 802.3 (the ethernet) and 802.5 (the token ring) LANs. However, the advent qf more high-speed LANs is eagerly expected w support higher performMce requirements. In this paper. we describe a new ring access control scheme adopting multipletokens, referred to as the self-token protocol. In the protocol, each station has private tokens, called self-tokens, and has a fixed length register to prevent packets on a ring front collision. Mer approximate analysis of throughput-tranrfer delay characteristics, we show that this protocol is attractive and suitable for a gigabit LAN. We also show thatfairness sfahlsproJocor is k q t goodfor a low number qfse!t-tokens. 1: IntroductionConventional local area networks (LANs), such as the ethemet and the token ring with a link transmission rate (link capacity) of several to several tens Mbps, have been used for data transfer between relatively low-speed peripheral devices and/or terminals. However, environmental change of LAN usage has demanded appearance of LANs with high throughput and low latency [l]. The reasons are as follows: (1) the advent of large-scale LANs and high-speed peripheral devices requires higher throughput, that is, a faster rate of transmission media, (2) resource sharing in system levels is spread widely. In particular, the amount of data exchanged between terminals and devices by means of large-volume file and printer servers is increasing, (3) distributed processing is becoming popular, and this causes frequent intercommunication between system levels, (4) the final factor is the multi-media communications. This requires not only a large amount of throughput but also synchronous transmission to include voice and image data exchanges, which demand a real time response. Recently, the Fiber Distributed Data Interface (FDD1)-I was standardized for 100 Mbps LAN protocol [2] to resolve such requirements. However, a follow-on LAN to FDDI is already anticipated for faster Mbps or Gbps LANs [3]. New gigabit LAN architectures are classified into two methodologies: improvement of conventional multiple-media access architectures [4] and new development of switch-based architectures [5]. The former is of great advantage in inheriting and reusing the conventional LAN architectures [6]. But the latter takes advantage of new ATM-based switch architectum in expectation of the advent of new services [7].Based on the former point of view, this paper proposes and analyzes a new channel access method for ring topology. This protocol is called "self-token protocol" and is expected to provide higher throughput and lower transfer delay.As the token ring (IEEE 802.5) [8] is a single token method, a station that captures a free token is allowed to send a packet, while the others just wait until the free token arrives. The FDDI improved the token ring protocol and got higher throughput by adopting an early token release method and allowing plural packets to exist simultaneously on ...

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To verify the safety of a system, it is desirable to test all the situation, at least, by simulation. However, it is difficult to test the entire situation because the number of situations is almost uncountable. As a promising method, backward simulation which traces back from the undesirable result to causal input(s) is proposed. For such backward simulation, we have to transform the forward model into a backward model. This paper shows an example of transformation in the case of mathematical model of integer factorization, and shows the effectiveness of the backward simulation. Such backward simulation would require case branch processing. And the practicality of the simulation result will be influenced by the efficiency of the case division. We show an effective case branch processing by using stack and threaded actors which are promising schemes applicable to distributed processing.

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