The emerging discipline of responsive systems demands fault-tolerant and real-time performance in uniprocessor, parallel, and distributed computing environments. The new proposal for responsiveness measure is presented, followed by an introduction of a model for responsive computing. The model, called CONCORDS (CONsensus/COmputation for Responsive Distributed Systems), is based on the integration of various forms of consensus and computation (progress or recovery). The consensus tasks include clock synchronization, diagnosis, checkpointing scheduling and resource allocation.

In this paper the two different paradigms for the design of responsive, i.e., distributed fault-tolerant real-time systems, the event-triggered (ET) approach and the time-triggered (TT) approach, are analyzed and compared. The comparison focuses on the temporal properties and considers the issues of predictability, testability, resource utilization, extensibility, and assumption coverage.

Typical processes controlled by hard real-time computer systems undergo several, mutually exclusive modes of operation. By deterministically switching among a number of static schedules, a pre run-time scheduled system is able to adapt to changing environmental situations. This paper presents concepts for specification of mode changes, construction of static schedules for modes and transitions, and timely run-time execution of mode changes. We propose concepts for mode changes in the context pre run-time scheduled hard real-time systems. While MARS is used to illustrate the concepts' application, they are applicable to a variety of systems. Our methods adhere closely to the ones established for single modes. By decomposing the system into a set of disjoint modes, the design process and its comprehension are facilitated, testing efforts are reduced significantly, and solutions are enabled which do not exist if all system activities of all modes are combined into a single schedule.

Space-time tradeoff is a very fundamental issue to design a fault-tolerant real-time (called responsive) system. Routing a message in large computer networks is efficient when each node knows the full topology of the whole network. However, in the hierarchical routing schemes, no node knows the full topology. In this paper, a tradeoff between an optimality of path length (message delay: time) and the amount of topology information (routing table size: space) in each node is presented. The schemes to be analyzed include K-scheme (by Kamoun and Kleinrock), G-scheme (by Garcia and Shacham), and I-scheme (by authors). The analysis is performed by simulation experiments. The results show that, with respect to average path length, I-scheme is superior to both K-scheme and G-scheme, and that K-scheme is better than G-scheme. Additionally, an average path length in I-scheme is about 20% longer than the optimal path length. On the other hand, for the routing table size, three schemes are ranked in reverse direction. However, with respect to the order of size of routing table, the schemes have the same complexity O (log n) where n is the number of nodes in a network.

This paper proposes a group-to-group communications algorithm that can extend the range of distributed systems where we can achieve active replication fault-tolerance to partner model distributed systems, in which all processes communicate with each other on an equal footing. Active replication approach, in which all replicated processes are active, can achieve fault-tolerance with low overhead because checkhpoint setting and rollback are not required for recovery from process failure. This algorithm guarantees that each replicated process in a process group has the same execution history and that communications between process groups keeps consistency even in the presence of process failure and message loss. The number of control messages that must be transmitted between processes for a communication between process groups is only a linear order of the number of replicated processes in each process group. Furthemore, this algorithm reduces the overhead for reconfiguration of a process group by keeping process failure and recovery information local to each process group.

This paper proposes a reconfigurable parallel processor based on a two-dimensional linear celular automaton model. The processor based on the model can be reconfigured quickly by utilizing the characteristics of the automaton used for its model. Moreover, the processor has short data path length between processing elements compared with the length of the processor based on one-dimensional linear cellular automaton model which has been already discussed. The processing elements of the processor based on the two-dimensional linear cellular automaton model are regarded as cells and the operational states of the processor are treated as the states of the automaton. When faults are detected, the processor can be reconfigured by changing its state under the state transition function of the processor determined by the weighting function of the automaton model. The processor can be reconfigured within a clock period required for making a state transition. This processor is extremely effective for real-time data processing systems required high reliability.

A responsive network architecture is essential in future open distributed systems. In this paper, a framework that provides the foundations for a responsive network architecture for an internetworking environment is proposed. It is called the Virtually Separated Link (VSL) model. By incorporating this framework, communication of both data and control information can be completed in bounded time. Consequently, a protocol can initiate a recovery mechanism in bounded time, or allow an application to do the same. Its functionalities augment existing resource reservation protocols that support multimedia communication. An overview of a real-time network protocol that is based on this framework is also presented.

Responsive protocols are communication protocols which ensure timely and reliable recovery when error events occur. Protocol synthesis for design of responsive protocols is to derive a protocol specification based on a service specification. In the previous methods, if the service specification includes simultaneous transmission of primitives from a high layer to a low layer through different service access points, then the derived protocol specification includes protocol errors of unspecified reception caused by message collisions. Also, they only includes a recovery function such as retransmission of messages. This is not enough for recovery from abnormal states due to coordination loss. This paper extends a class of derived protocol specifications to include message collisions which usually occur in real communication protocols. Furthermore, this paper proposes a new method for synthesis of a responsive protocal specification derived from a service specification such that the derived protocol specification is free from protocol erros of unspecified receptions caused by message collisions and includes two recovery functions: message retransmission and checkpoint restart functions.