Utilising multiple disjoint paths in multiple channels can improve network performance by enabling a node to reroute data along discovered paths seamlessly when link failure is detected. However, depending on a stale/invalid route to recover from a broken link could increase the delay to recover from the broken link and degrade the network performance. In this paper, we propose a new MAC protocol (RIVC-MB) to enhance communication reliability in the multipath multichannel routing protocol. The reliability of transmitting/re-routing the data packet in multipath multichannel routing protocol is improved by providing early route invalidity detection and early switchover. Waiting time to access the medium is also improved, when a node is attempting to access a busy medium, by re-routing the data packet via the alternative route. The RIVC-MB protocol uses the cross-layer interaction between MAC and routing protocols to achieve these goals. The proposed protocol is implemented and extensively evaluated using the NS-2 simulator. Simulation results show that the new proposed protocol reduces the end-to-end delay, and reduces both the number of route error control packets and the number of dropped data packets in the routing layer. It also reduces the collision rate in the MAC layer in a dense network.

The uptake of parallel DBMSs is being hampered by uncertainty about the impact on performance of porting database applications from sequential to parallel systems. The development of tools which aid the system manager or machine vendor could help to reduce this problem. This paper describes an analytical tool which determines the performance characteristics (in terms of throughput, resource utilisation and response time) of relational database transactions executing on particular machine configurations and provides simple graphical visualisations of these to enable users to obtain rapid insight into particular scenarios. The problems of handling different parallel DBMSs are illustrated with reference to three systems – Ingres, Informix and Oracle. A brief description is also given of two different approaches used to confirm the validity of the analytical approach on which the tool is based. Copyright © 1999 John Wiley & Sons, Ltd.

Cache modelling is an important issue in developing an analytical performance evaluator to estimate the performance of applications running on parallel DBMSs. This paper describes a cache model developed for parallel cache management in the Oracle7 parallel server. Some preliminary results have also been obtained by using the cache model to predict the cache hit ratio for varying database sizes and varying numbers of participating processing elements.

Two of the more important concurrent logic programming languages with nonflat guards are GHC and Parlog. They balance the requirements of having clean semantics and providing good control facilities rather differently, and their respective merits are compared and contrasted. Since concurrent logic programming would benefit from both, but neither language is able to express all the programs expressible in the other language, a lingua franca of these languages is defined and justified. A method is given for translating GHC and Parlog to and from it. The method preserves the arities and execution conditions of each clause. It enables a lingua franca implementation to support both languages transparently, and to provide a simple concurrent logic programming language suitable for programming in its own right.>