Fault-tolerant routing for wavelength routed all-optical networks using the WDM scheme has not been studied in detail in the literature. Most of the studies use a predetermined protection mechanism and hence assume that the protection path is not faulty. This paper presents a distributed algorithm to construct fault-avoiding lightpaths between source-destination end-node pairs using knowledge of fault occurrences gathered in prior routings. This paper extends the idea of the dynamic fault management scheme (presented earlier by one of these authors for fault avoidance) on the basis of knowledge of fault occurrence. The performance degradations of the network because of fault occurrence are then studied in terms of blocking probability and setup time through simulations.

A technique is presented for analyzing the relationships among the predicates in a predicate-based security model for database management systems. The principal tool of the technique is the Boolean difference, which is used to examine the relationships among the predicates when users are allowed to be members of more than one user group. The effects of deleting or adding predicates on the user group definition are identified by the technique. The technique is most valuable to information security authorizers who define and maintain access-control rules.

This correspondence deals with the fault-tolerant realization of a sequential machine using error-correcting (n,k) linear codes. Earlier works in the same area confine their attention to modified Reed-Muller Code and perfect Hamming Code and achieve the realization using a number of majority logic gates, which makes the entire realization quite complex. The realization discussed in this paper needs a smaller number of circuit components with less complexity.

Given a synchronous sequential machine M, this correspondence deals with the fault-tolerant realization M of M and also its fail-safe realization M on the assumption that the faults that can occur to the circuitry of M or M are of permanent stuck-at type and the total number of faults can be at most some preset positive integer r. First, the realization of M or M is derived for r = 1 and then the same idea is extended to have the realization for any arbitrary r. It has been shown that the realization of M is such that it is also able to tolerate faults of nonpermanent nature.