Congestion notification and probing mechanisms for endpoint admission control

There has been much interest in admission control schemes that place the burden of admission control decisions on the end users. In these schemes, referred to as Endpoint Admission Control, the decision to join the network is taken by the user, based on the probing of the network using probe packets. Depending on the level of congestion, routers mark the probe packets and thus inform the user of the state of the network. In this paper, we analyze three mechanisms for providing Endpoint Admission Control: virtual-queue marking, random-early marking and tail drop. For each scheme, we analyze the probing duration necessary to guarantee the required QoS and achieve high link utilization. Our main conclusion is that very few probe packets have to be sent when early marking is used, whereas tail drop requires a large number of probe packets.     

Use of Petri nets for resource allocation in projects

Traditional models for project management have not adequately incorporated a number of factors that are important for resource allocation. This paper describes the use of Petri nets to facilitate resource allocation in projects under some conditions commonly encountered in practice. Petri nets provide a powerful formalism for representing and analyzing concurrent systems. To date, however, very little has been done to integrate this graphical and mathematical tool with the area of project management. Petri net models can be used to analyze interdependencies, criticality, substitution, conflicting resource priorities and variations in the availability of resources. This paper proposes a new model and demonstrates the usefulness of the model for real-time activity scheduling in a resource-constrained project environment. The model has been computerized using the C language, and a simple project is chosen as an example to provide step-by-step explanations of the simulation carried out. This paper also discusses the implications of the model and the analysis it supports     

Problems and experiences in nuclear data processing in developing countries

This article offers a summary of many interesting experiences and problems the authors have come across while making attempts to develop RAMBHA, the Kalpakkam processing code system for multigrouping neutron interaction cross section data for fast reactor applications. Many of the problems are due to limitations arising from the nature of computer facility including memory restraints. Also offered here is an interesting comparison of non-adjusted ENDF/B-IV based RRC multigroup cross-section set with 1969 adjusted French set. An attempt is made to highlight the impact of processing uncertainties on reactor parameters by two examples.     

A reinforced movable boundary multiplexing scheme with adaptive interpolation: Modelling and performance evaluation

A novel multiplexing scheme for integrated networks characterized by the coexistence of circuitswitched and packet-switched traffic is described in this paper. The new scheme is realized by a reinforcement of the basic movable boundary hybrid-switching technique, by incorporating an adaptive interpolation within the circuit-switched subsystem. The adaptation mechanism is controlled by the level of congestion in the packet queue. A precise queueing model for the multiplexer is developed and an analytical evaluation of the key performance parameters of interest, namely the loss probability and expected delay of the packet-switched subsystem, and the freeze-out fraction of the circuit-switched subsystem, is conducted. The results of several numerical studies are presented to describe the performance of the multiplexer under different conditions. Of particular significance resulting from these studies is the trade-off between the freeze-out fraction of the circuit-switched subsystem and the loss probability of the packet-switched subsystem; this trade-off may be exploited in a systematic design of the interrated multiplexer tailored to specific applications.     

Correctness within a constant of an optimal buffer allocation ruleof thumb

The problem is to allocate a fixed number of buffers among the nodes of an open network of exponential servers with Bernoulli routing and Poisson arrivals so as to optimize some performance criterion associated with the time to buffer overflow, such as maximizing its mean or maximizing the probability that it exceeds some value. In earlier work, the authors used pathwise probabilistic arguments to derive a simple rule of thumb for this problem: allocate the buffers in inverse proportion to the logarithms of the effective service rates at the nodes. Effective service rate denotes the ratio of the service rate to the stationary arrival rate in the network with infinite buffers. They showed that this rule of thumb is accurate to within a known constant times the logarithm of the number of buffers as the number of buffers to be allocated becomes large. In the present paper, the authors use time reversal and Poisson clumping arguments to show that their rule of thumb is, in fact, much better than previously demonstrated. They show that the optimal buffer allocation is within a constant of the rule of thumb as the number of buffers to be allocated becomes large, although now they cannot estimate the constant. In numerical terms, the earlier result reduced the search space for the optimal buffer allocation from O(N^J-1) to O((log N)^J-1), where J denotes the number of nodes and N the number of buffers to be allocated. The improvement reduces the search space to O(1)     

Surface properties of magnesium oxide obtained from basic magnesium carbonate: Influence of preparation conditions of magnesium carbonate

Surface area, total basicity and base strength distribution (weak, strong and intermediate strength basic sites) of magnesium oxide obtained from basic magnesium carbonate (by its decomposition at 873 K) prepared by precipitation using different magnesium slats, precipitating agents and precipitating conditions (viz. concentration of magnesium salt. pH, temperature, mode of mixing and ageing period) have been thoroughly investigated. The total basicity and base strength distribution of the different magnesium oxide samples have been determined by step-wise thermal desorption of carbon dioxide from 323 to 1253 K. The chemical composition of basic magnesium carbonate and the surface properties and carbon dioxide content of magnesium oxide are found to be strongly influenced by the aforementioned preparation conditions of basic magnesium carbonate.     

Experimental investigation of microwave-optoelectronic interactionsin a microstrip ring resonator

Microwave optoelectronic mixing on a semi-insulating gallium arsenide substrate performed by monolithically integrating Schottky diode photodetectors into a microstrip ring resonator is discussed. When operated in the resistive mixing mode, a low frequency difference signal is extracted from the bias pad of the circuit. In the parametric mode, both degenerate and non-degenerate parametric amplification of an optical carrier signal takes place. The circuit shows good potential for application in wide-band fiberoptic systems     

Self-created Rules and Conflict Management Processes: The Case of Water Users' Associations on Waghad Canal in Maharashtra,India

In India, community participation is receiving much importance in water planning and management. However, in the absence of effective institutional arrangements to govern the allocation and maintenance activities, it is more likely that such participation will fail to achieve the desired results. Therefore, the present study is an attempt to assess the self-created rules adopted by two Water Users' Associations (WUAs) in Maharashtra State, India, to govern the use and distribution of water resources. The paper describes the perception of the members with regard to some of these self-created rules. It was observed that both the WUAs studied had effectively enforced these rules, leading to improved water management and efficient conflict management process. Although preliminary, the findings indicate scope for designing strategies to achieve the objective of forming a federation — better planning and distribution of water among WUAs.