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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.compeleceng.2008.04.009 Byline: Hamid Reza Shahriari (a), Mohammad Sadegh Makarem (a), Marjan Sirjani (b)(c), Rasool Jalili (a), Ali Movaghar (a) Keywords: Security analysis; Vulnerability analysis; Actor; Model checking; Rebeca language Abstract: Increasing use of networks and their complexity make the task of security analysis more and more complicated. Accordingly, automatic verification approaches have received more attention recently. In this paper, we investigate applying of an actor-based language based on reactive objects for analyzing a network environment communicating via Transport Protocol Layer (TCP). The formal foundation of the language and available tools for model checking provide us with formal verification support. Having the model of a typical network including client and server, we show how an attacker may combine simple attacks to construct a complex multiphase attack. We use Rebeca language to model the network of hosts and its model checker to find counter-examples as violations of security of the system. Some simple attacks have been modeled in previous works in this area, here we detect these simple attacks in our model and then verify the model to find more complex attacks which may include simpler attacks as their steps. We choose Rebeca because of its powerful yet simple actor-based paradigm in modeling concurrent and distributed systems. As the real network environment is asynchronous and event-based, Rebeca can be utilized to specify and verify the asynchronous systems, including network protocols. Author Affiliation: (a) Department of Computer Engineering, Sharif University of Technology, Azadi Avenue, Tehran, Iran (b) Department of Electrical and Computer Engineering, University of Tehran, Kargar Street, Tehran, Iran (c) School of Computer Science, Institute for Studies in Theoretical Physics and Mathematics, Niavaran Square, Tehran, Iran

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.sysarc.2010.05.006 Byline: Antonio Flores, Manuel E. Acacio, Juan L. Aragon Keywords: Tiled chip multiprocessor; Energy-efficient architecture; Cache-coherence protocol; Heterogeneous on-chip interconnection network Abstract: High performance processor designs have evolved toward architectures that integrate multiple processing cores on the same chip. As the number of cores inside a Chip MultiProcessor (CMP) increases, the interconnection network will have significant impact on both overall performance and energy consumption as previous studies have shown. Moreover, wires used in such interconnect can be designed with varying latency, bandwidth and power characteristics. In this work, we show how messages can be efficiently managed in tiled CMP, from the point of view of both performance and energy, by combining both address compression with a heterogeneous interconnect. In particular, our proposal is based on applying an address compression scheme that dynamically compresses the addresses within coherence messages allowing for a significant area slack. The arising area is exploited for wire latency improvement by using a heterogeneous interconnection network comprised of a small set of very-low-latency wires for critical short-messages in addition to baseline wires. Detailed simulations of a 16-core CMP show that our proposal obtains average improvements of 10% in execution time and 38% in the energy-delay.sup.2 product of the interconnect. Additionally, the sensitivity analysis shows that our proposal performs well when either OoO cores or caches with higher latencies are considered. Author Affiliation: Departamento de Ingenieria y Tecnologia de Computadores, University of Murcia, 30100 Murcia, Spain Article History: Received 2 December 2008; Revised 27 April 2010; Accepted 7 May 2010

Directed networks are ubiquitous and are necessary to represent complex systems with asymmetric interactions--from food webs to the World Wide Web. Despite the importance of edge direction for detecting local and community structure, it has been disregarded in studying a basic type of global diversity in networks: the tendency of nodes with similar numbers of edges to connect. This tendency, called assortativity, affects crucial structural and dynamic properties of real-world networks, such as error tolerance or epidemic spreading. Here we demonstrate that edge direction has profound effects on assortativity. We define a set of four directed assortativity measures and assign statistical significance by comparison to randomized networks. We apply these measures to three network classes--online/social networks, food webs, and word-adjacency networks. Our measures (i) reveal patterns common to each class, (ii) separate networks that have been previously classified together, and (iii) expose limitations of several existing theoretical models. We reject the standard classification of directed networks as purely assortative or disassortative. Many display a class-specific mixture, likely reflecting functional or historical constraints, contingencies, and forces guiding the system's evolution. doi/ 10.1073/pnas.0912671107

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jss.2009.07.036 Byline: Leijun Huang, Sanjeev Setia, Robert Simon Keywords: Wireless sensor networks; Multi-channel sensor networking Abstract: This paper presents McTorrent, a reliable bulk data dissemination protocol for sensor networks. The protocol is designed to take advantage of multiple radio channels to reduce packet collisions and improve the latency of large object dissemination. We evaluated the performance of McTorrent via detailed simulations and experiments based upon an implementation on the TinyOS platform. Our results show that in comparison to Deluge, the de facto network reprogramming protocol for TinyOS, McTorrent significantly reduces the number of packet transmissions and the amount of time required to propagate a large data object through a sensor network. Author Affiliation: Department of Computer Science, George Mason University, Fairfax, VA 22030, United States Article History: Received 2 January 2008; Revised 9 July 2009; Accepted 10 July 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jss.2008.05.011 Byline: Daniel Lacks (a), Taskin Kocak (b) Keywords: Computer networks; Distributed computing; Grid computing; Software simulation; C++/CLR Abstract: In this work, first, we present a grid resource discovery protocol that discovers computing resources without the need for resource brokers to track existing resource providers. The protocol uses a scoring mechanism to aggregate and rank resource provider assets and Internet router data tables (called grid routing tables) for storage and retrieval of the assets. Then, we discuss the simulation framework used to model the protocol and the results of the experimentation. The simulator utilizes a simulation engine core that can be reused for other network protocol simulators considering time management, event distribution, and a simulated network infrastructure. The techniques for constructing the simulation core code using C++/CLR are also presented in this paper. Author Affiliation: (a) School of Electrical Engineering and Computer Science, University of Central Florida, Orlando, FL 32816, USA (b) Department of Electrical and Electronic Engineering, University of Bristol, Bristol BS8 1UB, UK Article History: Received 6 February 2008; Revised 8 May 2008; Accepted 10 May 2008

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.sysarc.2008.07.005 Byline: Andres Ortiz (a), Julio Ortega (b), Antonio F. Diaz (b), Pablo Cascon (b), Alberto Prieto (b) Keywords: Full-system simulation; HDL simulation; LAWS model; Protocol offloading; Network interfaces; Simics Abstract: In the last years, diverse network interface designs have been proposed to cope with the link bandwidth increase that is shifting the communication bottleneck towards the nodes in the network. The main point behind some of these network interfaces is to reach an efficient distribution of the communication overheads among the different processing units of the node, thus leaving more host CPU cycles for the applications and other operating systems tasks. Among these proposals, protocol offloading searches for an efficient use of the processing elements in the network interface card (NIC) to free the host CPU from network processing. The lack of both, conclusive experimental results about the possible benefits and a deep understanding of the behavior of these alternatives in their different parameter spaces, have caused some controversy about the usefulness of this technique. The contributions of this paper deal with the implementation and evaluation of offloading strategies and with the need of accurate tools for researching the computer system issues that, as networking, require the analysis of interactions among applications, operating system, and hardware. Thus, in this paper, a way to include timing models in a full-system simulator (Simics) to provide a suitable tool for network subsystem simulation is proposed. Moreover, we compare two kinds of simulators, a hardware description language level simulator and a full-system simulator (including our proposed timing models), in the analysis of protocol offloading at different levels. We also explain the results obtained from the perspective of the previously described LAWS model and propose some changes in this model to get a more accurate approach to the experimental results. From these results, it is possible to conclude that offloading allows a relevant throughput improvement in some circumstances that can be qualitatively predicted by the LAWS model. Author Affiliation: (a) Department of Communications Engineering, University of Malaga, Spain (b) Department of Computer Architecture and Technology, University of Granada, Spain Article History: Received 27 May 2007; Revised 24 March 2008; Accepted 17 July 2008

In wireless packet-forwarding networks with selfish nodes, application of a repeated game can induce the nodes to forward each others' packets, so that the network performance can be improved. However, the nodes on the boundary of such networks cannot benefit from this strategy, as the other nodes do not depend on them. This problem is sometimes known as the curse of the boundary nodes. To overcome this problem, an approach based on coalition games is proposed, in which the boundary nodes can use cooperative transmission to help the backbone nodes in the middle of the network. In return, the backbone nodes are willing to forward the boundary nodes' packets. Here, the concept of core is used to study the stability of the coalitions in such games. Then three types of fairness are investigated, namely, min-max fairness using nucleolus, average fairness using the Shapley function, and a newly proposed market fairness. Based on the specific problem addressed in this paper, market fairness is a new fairness concept involving fairness between multiple backbone nodes and multiple boundary nodes. Finally, a protocol is designed using both repeated games and coalition games. Simulation results show how boundary nodes and backbone nodes form coalitions according to different fairness criteria. The proposed protocol can improve the network connectivity by about 50%, compared with pure repeated game schemes. Index Terms--Game theory, coalition game, cooperative transmission, and packet forwarding network.