44811250
Consistency of infinitesimal perturbation analysis estimators with rates
We study a class of infinitesimal perturbation analysis (IPA) algorithms for queueing systems with load-dependent service and/or arrival rates. Such IPA algorithms were originally motivated by applications to large queueing systems in conjunction with aggregation algorithms. We prove strong consistency of these estimators through a type of birth and death queue.
2207402
Bias properties of infinitesimal perturbation analysis for systems with parallel servers
Abstract Infinitesimal pertubation analysis (IPA) is a technique for estimating derivatives of performance measures from a single simulation of a stochastic discrete-event system, which might, for example, be modeling a computer/communication network or a manufacturing system. Such derivative estimates are useful in sensitivity analysis of the system and in optimizing—or at least improving—the performance of the system through gradient algorithms. However, it is well-known that IPA gives biased estimates for systems with multiple servers (channels or machines) in parallel when the server characteristics are not identical. In this paper, we investigate the seriousness of the bias both theoretically and experimentally. From our study, we believe the IPA estimator is relatively insensitive to small differences in the service time distributions of the servers. Specifially, we conjecture that for nearly-identical servers, the bias is proportional to the square of the difference between the means of the service time distributions. To support this conjecture, we present a tractable analytical example and investigate, via simulation experiments, more general systems.
11197335
Traffic grooming, routing, and wavelength assignment in optical WDM mesh networks
In this paper, we consider the traffic grooming, routing, and wavelength assignment (GRWA) problem for optical mesh networks. In most previous studies on optical mesh networks, traffic demands are usually assumed to be wavelength demands, in which case no traffic grooming is needed. In practice, optical networks are typically required to carry a large number of lower rate (sub-wavelength) traffic demands. Hence, the issue of traffic grooming becomes very important since it can significantly impact the overall network cost. In our study, we consider traffic grooming in combination with traffic routing and wavelength assignment. Our objective is to minimize the total number of transponders required in the network. We first formulate the GRWA problem as an integer linear programming (ILP) problem. Unfortunately, for large networks it is computationally infeasible to solve the ILP problem. Therefore, we propose a decomposition method that divides the GRWA problem into two smaller problems: the traffic grooming and routing problem and the wavelength assignment problem, which can then be solved much more efficiently. In general, the decomposition method only produces an approximate solution for the GRWA problem. However, we also provide some sufficient condition under which the decomposition method gives an optimal solution. Finally, some numerical results are provided to demonstrate the efficiency of our method.
206976454
Formulation of the traffic engineering problems in MPLS based IP networks
The growth of the Internet has fuelled the development of new technologies that enable IP backbone networks to be engineered efficiently. One such prominent technology, multiprotocol label switching (MPLS) enables IP networks with quality of service to be traffic engineered well. We mathematically formulate the traffic engineering problem's in MPLS based IP networks including constraint based routing, connection admission control, rerouting and capacity planning problems. Unfortunately, obtaining the optimal solution of the traffic engineering problems has undesirable computational complexity since they can be shown to be NP-complete. It is intended that this work will articulate the details and provide insights into the inherent structure of the problems as well as motivate the development of efficient solution techniques.
793040
Congestion-driven codesign of power and signal networks
We present a global wire design methodology that simultaneously considers the performance needs for both signal lines and power grids under congestion considerations. An iterative procedure is employed in which the global routing is performed according to a congestion map that includes the resource utilization of the power grid, followed by a step in which the power grid is adjusted to relax the congestion in crowded regions. This adjustment is in the form of wire removal in noncritical regions, followed by a wire sizing step that overcomes the effects of wire removal. Experimental results show that the overall routability can be significantly improved while the power grid noise is maintained within the voltage droop constraint.
6134766
Compiler-directed instruction duplication for soft error detection
We experiment with compiler-directed instruction duplication to detect soft errors in VLIW datapaths. In the proposed approach, the compiler determines the instruction schedule by balancing the permissible performance degradation with the required degree of duplication. Our experimental results show that our algorithms allow the designer to perform tradeoff analysis between performance and reliability.
16516558
Design and implementation of a CORBA-based genome mapping system prototype
MOTIVATION
CORBA (Common Object Request Broker Architecture), as an open standard, is considered to be a good solution for the development and deployment of applications in distributed heterogeneous environments. This technology can be applied in the bioinformatics area to enhance utilization, management and interoperation between biological resources.


RESULTS
This paper investigates issues in developing CORBA applications for genome mapping information systems in the Internet environment with emphasis on database connectivity and graphical user interfaces. The design and implementation of a CORBA prototype for an animal genome mapping database are described.


AVAILABILITY
The prototype demonstration is available via: http://www.ri.bbsrc.ac.uk/ark_corba/.


CONTACT
jian.hu@bbsrc.ac.uk
612951
Exploring Multiple Design Topologies Using Genetic Programming And Bond Graphs
To realize design automation of dynamic systems, there are two major issues to be dealt with: open-topology generation of dynamic systems and simulation or analysis of those models. For the first issue, we exploit the strong topology exploration capability of genetic programming to create and evolve structures representing dynamic systems. With the help of ERCs (ephemeral random constants) in genetic programming, we can also evolve the sizing of dynamic system components along with the structures. The second issue, simulation and analysis of those system models, is made more complex when they represent mixed-energy-domain systems. We take advantage of bond graphs as a tool for multi- or mixed-domain modeling and simulation of dynamic systems. Because there are many considerations in dynamic system design that are not completely captured by a bond graph, we would like to generate multiple solutions, allowing the designer more latitude in choosing a model to implement. The approach in this paper is capable of providing a variety of design choices to the designer for further analysis, comparison and trade-off. The approach is shown to be efficient and effective in an example of open-ended real-world dynamic system design application, a printer re-design problem.
96005
Fast algorithms for slew constrained minimum cost buffering
As a prevalent constraint, sharp slew rate is often required in circuit design which causes a huge demand for buffering resources. This problem requires ultra-fast buffering techniques to handle large volume of nets, while also minimizing buffering cost. This problem is intensively studied in this paper. First, a highly efficient algorithm based on dynamic programming is proposed to optimally solve slew buffering with discrete buffer locations. Second, a new algorithm is developed to handle the difficult cases in which no assumption is made on buffer input slew. Third, an adaptive buffer selection approach is proposed to efficiently handle slew buffering with continuous buffer locations. Experiments on industrial netlists demonstrate that our algorithms are very effective and highly efficient: we achieve > 100times speed up and save up to 40% buffer area over the commonly-used van Ginneken style buffering