Finding the worst-case message response time is important for guaranteeing message deadlines in any hard real-time communication environment. This paper proposes an $O(n)$-time algorithm for exactly capturing the worst-case synchronous message response time in an FDDI network for any given set of synchronous message streams whose message deadlines are no longer than periods. The proposed algorithm can be used to form an optimal test on whether or not a given setting of network parameters can meet the message deadline constraints for a considered synchronous message set with deadlines no longer than periods.

Exactly capturing the minimum available time for a network node to transmit its synchronous messages during any given length of time is important for guaranteeing the transmission of synchronous messages before their deadlines in a timed token ring network (such as FDDI) where the timed token medium access control protocol is used. Previous results which only give a lower bound on the minimum transmission time could be too pessimistic for supporting the timely delivery of synchronous traffic in a hard real-time communication environment. This paper presents an O(n)-time algorithm for exactly determining the minimum available transmission time. The algorithm can be used to test whether or not a given allocation of synchronous bandwidths can guarantee a synchronous message set with message deadlines no more than periods; the test so formed is better than any previous testing method whose test is sufficient only, in the sense that it is both sufficient and necessary and therefore optimal.

We study the problem of guaranteeing deadlines of synchronous messages with their deadlines no more than periods in an FDDI network. In order to guarantee the transmission of a synchronous message before its deadline, a precise knowledge of the worst-case situation for such transmission is required. This paper studies the worst-case scenario for transmission of a synchronous message in an FDDI network, in which the time elapsed between arrival of the message and completion of its transmission will reach its maximum (i.e., the longest possible interval). A few conditions under which the worst-case situation can happen are formally derived.

A property is said to emerge if not all of its constituent components satisfy the property. The paper proves the existence of emergent properties and investigates how a property might emerge. The authors introduce a condition called stability on properties that allows one to predict under what circumstances a property might emerge.

We present a general theory of possibilistic security properties. We show that we can express a security property as a predicate that is true of every set containing all the traces with the same low level event sequence. Given this security predicate, we show how to construct a partial ordering of security properties. We also discuss information flow and present the weakest property such that no information can flow from high level users to low level users. Finally, we present a comparison of our framework and McLean's (1994) Selective Interleaving Functions framework.

This paper examines the effects of the structure of the system on the composability of Generalized Non-Interference (GNI). It is proven that in a system constructed from GNI secure components, the only possible interconnection that can cause the system not to satisfy GNI occurs when two components are composed with feedback. We also present necessary and sufficient conditions for the composition of GNI secure components to yield a system that is GNI secure. The theorems are then used to provide a procedure to the system designer to construct a GNI secure system from GNI secure components. We also investigate reasons behind the composability of restrictiveness and n-forward correctability. It is shown that these properties compose because they eliminate one of the conditions that causes the composition of GNI secure components to fail.

The failure of non-interference to be preserved under composition is discussed. Two theorems are presented to this effect. The first proves McCullough's conjecture that non-interference is composable without feedback. The second provides a method of composition that preserves the non-interference property in the presence of feedback.

The failure of non-interference to be preserved under composition is discussed. Two theorems are presented to this effect. The first proves McCullough's conjecture that non-interference is composable without feedback. The second provides a method of

The goal of this paper is to present a study of the compatibility of policies, security or other. Two policies are said to be compatible at a given system if the system behaviours satisfy the requirements of both policies. Incompatibility can be a result of the environment in which the system is intended to operate, or, of the actual behavioural requirements on the system and its components. We introduce a means of assessing the compatibility of policies, and the requirements for compatible policies, in a closed system model.

Media-access delays in HUBNET, a high-performance local area network, are examined. An experimental technique for loading such a network with data up to 97.5% of its nominal bit rate is described. The results of a series of measurements of the packet-access delay in a network operating at loads up to 87.5% of capacity are presented. A modeling technique for this process is developed, and the results of calculations based on that model are compared to the experimental results. Extremely good agreement is obtained. The model is then used to examine the network behavior comprehensively over an extensive range of parameters.>

The principles, some of the implementation details, and some performance results for Hubnet are given, Hubnet is a 50 Mbit/s local area network using glass fiber as a transmission medium. The performance of the network for different topologies and loads is analyzed. This analysis is supported by experience with prototype hardware. The network is shown to have excellent performance up to loads which are a large fraction of capacity. Hubnet uses a dual rooted tree structure with twin-fiber communications paths. This structure has not been reported previously in just this form. The network uses all seven layers of an early version of the proposed ISO Reference Model for Open Circuit Interconnection to implement its protocols. The protocols execute in 16 bit microprocessors embedded in the network access controllers within the network.

The environment desirable for the teaching of systems software programming is described, and after examining some current systems a need for a high level language available on a minicomputer with minimal hardware is exhibited. The OLGA language, designed to fill that need, is described. Included in the language are a form of data abstraction, type declarations, modules, and procedures, functions and operators. Access to objects, local or non-local, is controlled by explicit declaration. The compiler for OLGA is one-pass, and fits in 3K words of memory. A cluster of LSI-11s which makes use of the minimal hardware property of OLGA is described. The cluster is a very economical way of increasing access to a software development system.

Many-valued switching systems have been of considerable academic interest, despite the apparent inability to use them in practical applications. The main drawbacks, as pointed out by a number of authors, are the difficulties associated with the implementation of the functional basic set and the lack of adequate simplification techniques.