40200748
Optimal Vertex Ordering of Graphs
In this paper we consider an optimal vertex ordering problem of graphs. The vertex ordering and an optimality measure are defined. It is proved that the optimal ordering problem under consideration can be transformed into the well-known minimum-weight spanning tree problem and is therefore solvable in low-polynomial time. We also investigate some properties of optimal vertex orderings.
12399461
On the Minimum Common Supergraph of Two Graphs
Abstract The minimum common supergraph of two graphs, g1 and g2, is defined as the smallest graph that includes, as subgraphs, both g1 and g2. It is shown that minimum common supergraph computation can be solved by means of maximum common subgraph computation. For the latter problem, algorithms are known from the literature. It will also be shown that for a certain class of cost functions, the concept of graph edit distance is closely related with the minimum common supergraph.
12069557
Blocking behaviors of crosstalk-free optical Banyan networks on vertical stacking
Banyan networks are attractive for constructing directional coupler (DC)-based optical switching networks for their small depth and self-routing capability. Crosstalk between optical signals passing through the same DC is an intrinsic drawback in DC-based optical networks. Vertical stacking of multiple copies of an optical banyan network is a novel scheme for building nonblocking (crosstalk-free) optical switching networks. The resulting network, namely vertically stacked optical banyan (VSOB) network, preserves all the properties of the banyan network, but increases the hardware cost significantly. Though much work has been done for determining the minimum number of stacked copies (planes) required for a nonblocking VSOB network, little is known on analyzing the blocking probabilities of VSOB networks that do not meet the nonblocking condition (i.e., with fewer stacked copies than required by the nonblocking condition). In this paper, we analyze the blocking probabilities of VSOB networks and develop their upper and lower bounds with respect to the number of planes in the networks. These bounds depict accurately the overall blocking behaviors of VSOB networks and agree with the conditions of strictly nonblocking and rearrangeably nonblocking VSOB networks respectively. Extensive simulation on a network simulator with both random routing and packing strategy has shown that the blocking probabilities of both strategies fall nicely within our bounds, and the blocking probability of packing strategy actually matches the lower bound. The proposed bounds are significant because they reveal the inherent relationships between blocking probability and network hardware cost in terms of the number of planes, and provide network developers a quantitative guidance to trade blocking probability for hardware cost. In particular, our bounds provide network designers an effective tool to estimate the minimum and maximum blocking probabilities of VSOB networks in which different routing strategies may be applied. An interesting conclusion drawn from our work that has practical applications is that the hardware cost of a VSOB network can be reduced dramatically if a predictable and almost negligible nonzero blocking probability is allowed.
30106346
A Genetic Algorithm for Dynamic Routing and Wavelength Assignment in WDM Networks
In this paper, we study the challenging problem of Dynamic Routing and Wavelength Assignment (DRWA) in WDM (Wavelength-Division-Multiplexing) networks with wavelength continuity constraint, and propose an improved genetic algorithm (GA) for it. By adopting a new fitness function to consider simultaneously the path length and number of free wavelengths in cost estimation of a route, the new genetic RWA algorithm can achieve a good load balance among route candidates and result in a lower blocking probability than both the fixed alternative routing algorithm and the previous GA-based algorithm for DRWA, as verified by an extensive simulation study upon the ns-2 network simulator and some typical network topologies.
7279689
An Architectural Approach to Preventing Code Injection Attacks
Code injection attacks, despite being well researched, continue to be a problem today. Modern architectural solutions such as the execute-disable bit and PaX have been useful in limiting the attacks; however, they enforce program layout restrictions and can oftentimes still be circumvented by a determined attacker. We propose a change to the memory architecture of modern processors that addresses the code injection problem at its very root by virtually splitting memory into code memory and data memory such that a processor will never be able to fetch injected code for execution. This virtual split memory system can be implemented as a software-only patch to an operating system and can be used to supplement existing schemes for improved protection. Furthermore, our system is able to accommodate a number of response modes when a code injection attack occurs. Our experiments with both benchmarks and real-world attacks show the system is effective in preventing a wide range of code injection attacks while incurring reasonable overhead.
858944
Ubiquitous computing for firefighters: field studies and prototypes of large displays for incident command
In this paper, we demonstrate how field studies, interviews, and low-fidelity prototypes can be used to inform the design of ubiquitous computing systems for firefighters. We describe the artifacts and processes used by firefighters to assess, plan, and communicate during emergency situations, showing how accountability affects these decisions, how their current Incident Command System supports these tasks, and some drawbacks of existing solutions. These factors informed the design of a large electronic display for supporting the incident commander, the person who coordinates the overall response strategy in an emergency. Although our focus was on firefighters, our results are applicable for other aspects of emergency response as well, due to common procedures and training.
18153606
Virtual distributed environments in a shared infrastructure
We have developed a middleware system that integrates and extends virtual machine and virtual network technologies to support mutually isolated virtual distributed environments in shared infrastructures like the grid and the PlanetLab overlay infrastructure. Integrating virtual network and on-demand virtual machine creation and customization technologies makes virtual distributed environments a reality. The Violin-based middleware system integrates and enhances such technologies to create virtual distributed environments.