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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2010.03.003 Byline: Oleg Berzin Keywords: Host mobility; Network mobility; MPLS; MPLS/VPN; MP-BGP Abstract: Hierarchical Mobility Label Based Network (H-MLBN) is a new approach to the network layer mobility management problem that relies on MPLS-aware control plane and MPLS-based forwarding plane to provide IP mobility support for IPv4 and IPv6 mobile hosts and routers while being able to ensure optimal traffic delivery between the communicating devices. The hierarchical system is capable of both macro- and micro-mobility support without the use of Mobile IP and its derivatives thus eliminating the user and network facing performance penalties associated with triangular routing and bi-directional tunneling. This paper presents a system model and provides performance analysis for H-MLBN and compares its performance with the Mobile IP based schemes. The results indicate significant performance improvements in the forwarding plane traffic delivery as well as the control plane network update costs. Author Affiliation: Verizon Communications, Philadelphia, PA, United States Article History: Received 29 June 2009; Revised 15 January 2010; Accepted 10 March 2010 Article Note: (miscellaneous) Responsible Editor: L. Jiang Xie

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

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2010.02.005 Byline: Fragkiskos Papadopoulos Keywords: IEEE 802.11; Wireless local area networks (WLANs); Scaling properties; Sustaining user performance Abstract: The IEEE 802.11 MAC protocol has gained widespread popularity and has been adopted as the de-facto layer 2 protocol for wireless local area networks (WLANs). However, it is well known that as the number of competing stations increases, the performance of the protocol degrades dramatically. Given the explosive growth in WLANs' usage, the question of how to sustain each user's perceived performance when a large number of competing stations are present, is an important and challenging open research problem. Motivated by this, in this paper we analyze the behavior of 802.11-based WLANs as the number of competing stations increases, and attempt to provide concrete answers to the following fundamental questions: (i) is there a set of system and protocol parameters that we can scale in order to sustain each individual user's perceived performance, and (ii) what is the minimum scaling factor? Using theoretical analysis coupled with extensive simulations we show that such a set of parameters exists, and that the minimum scaling factor is equal to the factor by which the number of users increases. Our results reveal several important scaling properties that exist in today's 802.11-based wireless networks, and set guidelines for designing future versions of such networks that can efficiently support a very large number of users. Author Affiliation: Department of Electrical and Computer Engineering, University of Cyprus, Kallipoleos 75, Nicosia 1678, Cyprus Article History: Received 11 February 2009; Revised 13 January 2010; Accepted 8 February 2010 Article Note: (miscellaneous) Responsible Editor: A. Abouzeid

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.comnet.2009.07.013 Byline: Kuo-Feng Ssu, Wei-Tong Wang, Wen-Chung Chang Keywords: Wireless Sensor Networks; Security; Sybil attacks Abstract: As the prevalence of Wireless Sensor Networks (WSNs) grows in the military and civil domains, the need for network security has become a critical concern. In a Sybil attack, the WSN is subverted by a malicious node which forges a large number of fake identities in order to disrupt the network's protocols. In attempting to protect WSNs against such an attack, this paper develops a scheme in which the node identities are verified simply by analyzing the neighboring node information of each node. The analytical results confirm the efficacy of the approach given a sufficient node density within the network. The simulation results demonstrate that for a network in which each node has an average of 9 neighbors, the scheme detects 99% of the Sybil nodes with no more than a 4% false detection rate. The experiment result shows that the Sybil nodes can still be identified when the links are not symmetric. Author Affiliation: Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan, ROC Article History: Received 3 November 2008; Revised 22 April 2009; Accepted 28 July 2009 Article Note: (miscellaneous) Responsible Editor: J. Misic

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2009.05.007 Byline: Carlos T. Calafate, P. Manzoni, Juan-Carlos Cano, M.P. Malumbres Keywords: Hidden Markov models; Mobile ad hoc networks; Video codec tuning Abstract: Mobile ad hoc networks (MANETs) show very significant difference with respect to other computer networks due to the presence of extremely large packet loss bursts. The development of protocols for mobile ad hoc networks, especially multimedia protocols, require extensive evaluation either through simulation or real-life tests. Such testing consumes a great amount of resources both in terms of time and trace file sizes. Therefore, finding efficient means of reducing the amount of data that is stored and processed is quite important to accelerate the evaluation of different audio/video streaming applications. If, moreover, we are able to model the loss pattern experienced, we can further accelerate the evaluation process. In this work we propose two models based on hidden Markov chains that are able to grasp both packet arrivals and packet loss patterns in MANETs. A simpler two-state model is proposed to model losses when proactive routing protocols are used, while a more complex three-state model is proposed for reactive routing protocols. We also introduce a new set for packet loss pattern measurements that can be of interest for the evaluation of audio/video streaming applications. Experimental results show that the proposed models can adequately reproduce extremely long packet loss patterns, typical of MANET environments, with a high degree of accuracy. Overall, we find that the proposed models are able to significantly reduce both the simulation time and the trace file sizes required. Author Affiliation: Universidad Politecnica de Valencia, Camino de Vera, S/N, 46022 Valencia, Spain Article History: Received 30 May 2008; Revised 11 February 2009; Accepted 13 May 2009 Article Note: (footnote) [star] A preliminary version of this article entitled "Speeding up the evaluation of multimedia streaming applications in MANETs using HMMs" was presented at the 7th ACM International Symposium on Modeling, Analysis and Simulation of Wireless and Mobile Systems (MSWiM'04).