Real-Time Distributed Fault-Tolerant Computing is the area considered.
The project investigates those algorithmic and methodological issues that arise with mission-critical, complex, computerized applications that may require certification.
Requirements of logical safety, liveness, timeliness and dependability, that are inevitably associated with such applications, can only be met with Real-time Distributed Fault-tolerant computing Technology, hence the ``TRDF'' acronym.
Research work is aimed at breaking new ground in the areas described below.
1) Composite TRDF algorithms
The goal pursued is to identify, prove and evaluate algorithms and protocols that are solutions to problems arising with real-time, fault-tolerant, distributed/concurrent computations and communications.
Issues of distribution are those arising in the presence of asynchronous parallel computations, with only partial knowledge of global system states. Real-time issues raise the obligation of proving that those timeliness constraints expressed in the specification of some application are always satisfied, for some feasibility conditions.
Fault-tolerance involves demonstrations that correct system behavior is maintained in the presence of given densities of partial failures, for given failure semantics.
For every algorithm/protocol studied, we establish such functions as upper bounds on response times and lower bounds on redundancy. Such functions are established using various techniques (e.g., graph theory, adversary arguments, calculus in (max, +) algebra) and considering deterministic adversaries. We also seek to express distance to optimality (the concept of optimal distributed on-line decision making still is a fundamental research issue). In some instances, we establish that problems have no deterministic solutions.
Examples of problems we have solved are :
We also have demonstrated that current specifications of the Asynchronous Group Membership problem are not satisfactory. Solutions to the Asynchronous Atomic Broadcast problem that are based on virtual synchrony or timers should be revisited.
2) Wireless LANs
The project contributes to the standardization work of HIPERLAN (High PErformance Radio Local Area Network) conducted by ETSI. HIPERLAN is likely to be the first international standard for wireless LANs which defines a contention medium access protocol that is stable in the presence of traffic overload. Furthermore, it guarantees an upper bound on the collision rate. For the routing protocol, the concept of multipoint relay introduced in the LAURA project has been adopted by the ETSI/RES/10 committee. HIPERLAN is also able to support real-time traffic thanks to medium access priorities and an EDF scheduling policy. Deadlines expressed in the quality of service parameters are transformed into medium access priorities.
3) A Systems Engineering Methodology for Complex/Critical Computing Systems
Scientific state-of-the-art cannot be transferred to users/technology providers unless embedded in a methodology that can be used by engineers. Furthermore, it is being recognized that the lack of a methodology for correctly and provably designing and dimensioning mission-critical, complex, computer-based systems is the main reason why a growing number of major failures are being experienced by the industry.
The project has developped a Systems Engineering methodology based on models and TRDF algorithms. The TRDF methodology involves correctness proof obligations. A design correctness proof obligation consists in verifying whether a given design (algorithms + models) solves a given problem. A dimensioning correctness proof obligation consists in verifying whether a valued correct design meets the physical requirements found in the application specification considered.
The specification of a system design/dimensioning that results from applying the TRDF methodology provably satisfies the specification of the application originally considered.
The TRDF methodology is being tested on a Defense application.