16749457
Approximate Performance Analysis of Web Services Flow Using Stochastic Petri Net
Web services provide a language-neutral, loosely-coupled, and platform-independent way for linking applications within organizations or enterprises across the Internet. In such a scenario, quantitative characteristics such as service execution throughput should be evaluated to measure the system performance. Usually, the first step is to define an abstract workflow model, for example Stochastic Petri Net Models. However, large system always raises the problem of state explosion. In this paper, we discuss a set of simplification rules for five basic structures of web service flow: sequential, parallel, conditional, loop and mutex. Our approach can effectively reduce the state space and is applied to the performance analysis of a web service flow management system.
15949067
Security authentication of 3G-WLAN interworking
With the development of wireless Internet, the interworking of the third generation (3G) wide area wireless networks and wireless local area networks (WLAN) has become a focus of research. 3G systems have their advantages in charging management, roaming, and security facilities, and WLAN systems have the advantages of high bandwidth and low investment cost. Interworking of 3G-WLAN offers characteristics that complement each other perfectly. Several authentication protocols have been proposed to improve security. In this paper, we firstly introduce the architectures of 3G-WLAN interworking and discuss existing problems related to authentication and key agreement procedures. Then, we present two schemes by applying authentication based on EAP-TLS (extensible authentication protocol-transport layer security) and EAP-TTLS (tunneled TLS) into integrated 3G and WLAN to achieve high end-to-end security and authentication for the users. Finally, we conduct a series of performance evaluation on the energy consumption and latency of standard authentication protocols.
12254119
Wireless network security
18052662
Probabilistic analysis on mesh network fault tolerance
Mesh networks are among the most important interconnection network topologies for large multicomputer systems. Mesh networks perform poorly in tolerating faults in the view of worst-case analysis. On the other hand, such worst cases occur very rarely in realistic situations. In this paper, we study the fault tolerance of 2-D and 3-D mesh networks under a more realistic model in which each network node has an independent failure probability. We first observe that if the node failure probability is fixed, then the connectivity probability of these mesh networks can be arbitrarily small when the network size is sufficiently large. Thus, it is practically important for multicomputer system manufacture to determine the upper bound for node failure probability when the probability of network connectivity and the network size are given. We develop a novel technique to formally derive lower bounds on the connectivity probability for 2-D and 3-D mesh networks. Our study shows that these mesh networks of practical size can tolerate a large number of faulty nodes thus are reliable enough for multicomputer systems. For example, it is formally proved that as long as the node failure probability is bounded by 0.5%, a 3-D mesh network of up to a million nodes remains connected with a probability larger than 99%.
16150333
Self-healing group key distribution with time-limited node revocation for wireless sensor networks
Abstract A novel key distribution scheme with time-limited node revocation is proposed for secure group communications in wireless sensor networks. The proposed scheme offers two important security properties: the seal-healing re-keying message distribution which features periodic one-way re-keying with implicitly authentication, efficient tolerance for the lost re-keying messages, and seamless Traffic Encryption Key (TEK) switch without disrupting ongoing data transmissions; and the time-limited dynamic node attachment and detachment, so that both forward and backward secrecy is assured by dual directional hash chains. It is shown that the communication and computation overhead of the proposed protocol is light, and the protocol is robust under poor communication channel quality and frequent group node topology change.
28815316
Stability analysis of buffer priority scheduling policies using Petri nets
A Petri net approach to determining the conditions for stability of a re-entrant system with buffer priority scheduling policy is described in this paper. The concept of buffer boundedness based on the dynamic behavior of the marking in the system model is emphasized. The method is used to demonstrate the stability of the first buffer first served (FBFS) and the last buffer first served (LBFS) scheduling policies. finally a sufficient condition for instability of systems with a positive feedback loop (PFL) is established, and an example is given.
7556493
Using mixins to build flexible widgets
When it comes to software that runs on devices as varied as cell phones, PDAs and desktops, one size does not fit all. This paper describes how mixin layers, a kind of nested generic type, can be used to implement a graphical user interface library that can be configured to run on platforms with widely dissimilar capabilities. We describe the language support needed to incrementally build software in layers, and we describe how crosscutting concerns can be encapsulated within a layer. We then show how layers can be reconfigured to meet changing requirements. We also show how a new design pattern, the Sibling pattern, can be used with mixin layers to coordinate changes to multiple classes in the same inheritance hierarchy. When used appropriately, the Sibling pattern increases our ability to separate design concerns and to reuse code.
195347973
On Balloon Drawings of Rooted Trees
Among various styles of tree drawing, balloon drawing, where each subtree is enclosed in a circle, enjoys a desirable feature of displaying tree structures in a rather balanced fashion. We first design an efficient algorithm to optimize angular resolution and aspect ratio for the balloon drawing of rooted unordered trees. For the case of ordered trees for which the center of the enclosing circle of a subtree need not coincide with the root of the subtree, flipping the drawing of a subtree (along the axis from the parent to the root of the subtree) might change both the aspect ratio and the angular resolution of the drawing. We show that optimizing the angular resolution as well as the aspect ratio with respect to this type of rooted ordered trees is reducible to the perfect matching problem for bipartite graphs, which is solvable in polynomial time. Aside from studying balloon drawing from an algorithmic viewpoint, we also propose a local magnetic spring model for producing dynamic balloon drawings with applications to the drawings of galaxy systems, H-trees, and sparse graphs, which are of practical interest.
17509188
Client-Driven Pointer Analysis
This paper presents a new client-driven pointer analysis algorithm that automatically adjusts its precision in response to the needs of client analyses. We evaluate our algorithm on 18 real C programs, using five significant error detection problems as clients. We compare the accuracy and performance of our algorithm against several commonly-used fixed-precision algorithms. We find that the client-driven approach effectively balances cost and precision, often producing results as accurate as fixed-precision algorithms that are many times more costly. Our algorithm works because many client problems only need a small amount of extra precision applied to the right places in each input program.
5783340
Zero-error information hiding capacity of digital images
We derive a theoretical capacity for digital image watermarking with zero transmission errors. We present three different discrete memoryless channel model to represent the watermarking process. Given the magnitude bound of noise set by applications and the acceptable watermark magnitude determined by the just-noticeable distortion, we estimate the zero-error capacity by applying Shannon's (1948) adjacency-reducing mapping technique. The capacity we estimate here corresponds to a deterministic guarantee of zero error, different from the traditional theorem approaching zero error asymptotically.
7754068
Optimal state feedback based resource allocation for resource-constrained control tasks
In many application areas, including control systems, careful management of system resources is key to providing the best application performance. Most traditional resource management techniques for real-time systems with multiple control loops are based on open-loop strategies that statically allocate a constant CPU share to each controller, independent of their current resource needs. This provides average control performance with minimal overhead but in general fails to provide the best performance possible within the available resources. We show that by using feedback to dynamically allocate resources to controllers as a function of the current state of their controlled systems, control performance can be significantly improved. We present an optimal resource allocation policy that maximizes control performance within the available resources and provide experimental results showing that the optimal policy 1) significantly increases control performance compared to traditional control system implementations (by more than 20% in our experiments), 2) maximizes control performance over other feedback-based policies, 3) saves resources when perturbations occur infrequently, and 4) incurs negligible overhead.