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Date 19-25 April 2009

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Displaying Results 1 - 25 of 113
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  • A Control Theoretic Framework for Performance Optimization of IEEE 802.11 Networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    In this paper we propose to model the behavior of a WLAN from a control theoretic perspective to achieve optimal performance in terms of e.g. throughput or delay. Control theory has been commonly used in industrial applications to provide the analytical tools for the design of closed-loop systems, in order to guarantee stable operation without lessening the ability to react to changes. We therefore propose to model a WLAN as a closed loop, where the controlled system is the wireless network and the controller is a module which adjusts the parameters of the WLAN based on the observed state of the network. View full abstract»

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  • A Framework for Rank Computation and Aggregation in Fuzzy Environments

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (450 KB) |  | HTML iconHTML  

    In many network and IT systems, users submit loosely-defined (or fuzzy) requests to obtain answers, solutions or resources. In this paper, we focus on trouble-shooting problem tickets in an IT service management system. In such a system, problems are typically reported using vague user-generated descriptions of the symptoms (e.g., 'my email is not working!') in a ticket. IT Specialists are then responsible for identifying the troubled component from the reported symptoms. Usually, the ticket is sent to one Specialist at a time until it is resolved hence, an efficient mechanism to select the (next) potential Specialist becomes critical towards a timely resolution of the ticket. In this paper, we introduce a framework to deal with fuzzy requests in a distributed environment. We first show the importance of considering both the traditional graph-based network routing efficiency as well as social network theory to generate important ranking metrics. For each newly arrived ticket, we propose several selection and ranking policies to choose and rank IT Specialists who can potentially resolve the ticket. We evaluate the ranking system with synthetic tickets, generated by an in-depth simulated IT management model that closely mimics an operational system. Our preliminary results suggest the importance of considering both routing efficiency and social connectivity to minimize the resolution time of a ticket. View full abstract»

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  • A Generalized Group Communication Network Stack and its Application to Hybrid Multicast

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (382 KB) |  | HTML iconHTML  

    Group communication services are most efficiently implemented on the lowest layer available. Network layer multicast transparently delegates group distribution to the link layer wherever possible. Native multicast deployment, though, has been mainly limited to 'walled gardens' within provider domains. Overlay multicast overcomes these deployment restrictions on the price of a performance penalty. Current activities focus on hybrid approaches which dynamically combine multicast in overlay and underlay, and adaptively optimize group communication. The basic requirement for such a flexibly deployable architecture is a layer-transparent group communication stack that integrates variable multicast protocols by a common API. In this paper, we present a common group communication stack which serves the requirements of data distribution and maintenance for multicast and broadcast on a middleware abstraction layer, suitable for underlay and overlay communication. We discuss its application in the context of hybrid multicast schemes. View full abstract»

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  • A Joint Approach to Routing Metrics and Rate Adaptation in Wireless Mesh Networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (86 KB) |  | HTML iconHTML  

    This work proposes MARA, a joint method for automatic rate selection and route quality evaluation in wireless mesh networks. This method targets at avoiding the problem of inaccurate link quality estimates, common to main existing proposals of multi-hop wireless routing metrics. In this proposal, the statistics collected by the routing protocol are used by the rate adaptation algorithm to compute the best rate for each wireless link. This coordinated decision aims at providing better routing and rate choices. Simulation results indicate that MARA leads to an overall improvement in network performance. View full abstract»

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  • A Learning-Based Channel Allocation Protocol for Multi-Radio Wireless Mesh Networks

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (75 KB) |  | HTML iconHTML  

    We propose a novel approach to distributed multi-radio channel allocation that is based on learning and a protocol following this approach (termed LCAP). Each node in LCAP independently and iteratively learns the channel allocation using a probabilistic adaptation algorithm that ensures network connectivity while reducing interference. Key enabler of the proposed approach is a novel neighbor discovery mechanism that exploits the mesh network deployment model in practice while being compliant to the 802.11 standard. LCAP addresses the limitations of prior work by not placing any restriction on network structure or traffic patterns, while being localized and negotiation-free for scalable operation. View full abstract»

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  • A More Accurate Scheme to Detect SYN Flood Attacks

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    We propose to use the SYN/ACK-CliACK pair's behavior to detect the various SYN flood attacks more accurately. The SYN/ACK packets carry the full information of the TCP connections and it is impossible for the attacker to evade the detection by spoofing the control packets. Moreover, we use a space efficient data structure, counting Bloom filter, to recognize the CliACK packet and the memory cost is 2 MB even for 10 Gbps link speeds. We need to fully compare our scheme with the existing detection mechanisms in future. View full abstract»

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  • A Novel Algorithm for Maximizing the Lifetime of Sensor Networks and the Use of an m²-Mote to Refresh Battery Power On-the-Fly

    Page(s): 1 - 3
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    In this paper we present a novel algorithm that significantly improves the efficiency of wireless sensor networks, while providing a low and stable energy consumption profile irrespective of the number of nodes. We also present a modified- mica Mote (m2-Mote) that uses a rectenna to produce DC-power from scavenged RF-energy for charging the node batteries. From our analysis and simulation of a 500 node network with one sink node, we found that our approach results in 99% reduction in the amount of energy consumed with the addition of each new node to the sensor network when compared with LEACH. Similarly, it doubles the average lifespan of LEACH based networks and gives more than five times the average lifetime of networks based on direct communication. View full abstract»

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  • A P2P File Sharing Network Topology Formation Algorithm Based on Social Network Information

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB) |  | HTML iconHTML  

    This paper applies the theory of social networks to P2P systems, creating a social-network-based P2P network topology formation algorithm for file sharing. The algorithm extends the Gnutella P2P file sharing technology, which uses super nodes for searching and for relaying shared files between network leafs that are located behind Firewalls/NATs. The topology of the P2P network is based on the actual social relationship between peers (users). The idea is that users are willing to contribute their resources to a P2P network if they know that their resources directly benefit their friends and family. Following this approach, free-riding in P2P networks will be avoided by not providing better-than-basic service if peers do not reveal their social relationships. Within the paper, we simulate the proposed topology formation algorithm, considering the real characteristics of the Gnutella P2P network and realistic network topologies. The simulation shows the effectiveness of the topology formation algorithm and the high utility of nodes under this new file sharing scheme. View full abstract»

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  • A Real-Time Peer-to-Peer Streaming System for Mobile Networking Environment

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (310 KB) |  | HTML iconHTML  

    Peer-to-peer is emerging as a potentially disruptive technology for content distribution in the mobile Internet. In addition to the already well-known peer-to-peer file sharing, realtime peer-to-peer streaming is gaining popularity. This paper presents an effective real-time peer-to-peer streaming system for the mobile environment. The basis for the system is a scalable overlay network which groups peers into clusters according to their proximity using RTT values between peers as a criteria for the cluster selection. The actual media delivery in the system is implemented using the partial RTP stream concept: the original RTP sessions related to a media delivery are split into a number of so-called partial streams according to a pre-defined set of parameters in such a way that it allows low-complexity reassembly of the original media session in real-time at the receiving end. Partial streams also help in utilizing the upload capacity with finer granularity than just per one original stream. This is beneficial in mobile environments where bandwidth can be scarce. View full abstract»

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  • A Scalable Bloom Filter Based Prefilter and Hardware-Oriented Predispatcher

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (338 KB) |  | HTML iconHTML  

    Presented in this paper a scalable bloom filter based prefilter and a hardware-oriented predispatcher pattern matching mechanism for content filtering applications, which are scalable in terms of speed, the number of patterns and the pattern length. Prefilter algorithm is based on a memory efficient multi-hashing data structure called bloom filter. According to the statistics of simulations, the filter ratio can reach up to 60% if the whole engine has been trained well. It has been showed that this engine could enhance the capabilities of general-purpose IDS solutions. View full abstract»

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  • A Study of the Performance of SSL on PDAs

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (293 KB) |  | HTML iconHTML  

    PDAs and smart phones are increasingly being used as handheld computers. Today, their network connectivity and their usages for various tasks over the Internet require privacy and authenticity. In this paper, we conduct a comprehensive and comparative study of the performance of the SSL protocol for PDA and laptop clients, both in WEP secured and open Wi-Fi environments. Unlike previous studies [1], [2], the measurements are at sub-protocol granularity allowing for researchers to consider appropriate optimizations for these resource-constrained devices. Unsurprisingly, we find that SSL handshake costs 3 times more at a PDA client than it does for a laptop client, but surprisingly most of the delay comes from network latency and other PDA architecture issues, not cryptographic computation. This suggests that more effort should be spent in minimizing communication rounds in future cryptographic protocols that will be used by PDAs, even at the cost of more cryptographic operations. View full abstract»

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  • A Unified Security Backplane for Trust and Reputation Systems in Decentralized Networks

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (83 KB) |  | HTML iconHTML  

    Presented in this paper a preliminary proposal of a security framework for delivering security properties to Trust and Reputation management systems in decentralized networks. When TR metrics are used in this framework, nodes can be held responsible for their actions and identity spoofing is prevented. By protecting trust reply messages and/or the interaction with trust holding agents, false reporting or message alteration is not possible anymore. Therefore, the security backplane delivers a unified framework for TR metrics allowing easy secure deployment. We plan to evaluate our framework with different TR metrics using simulations with colluding malicious nodes. Furthermore, we will analyze in details how different views can impact the overall behavior of the network and the overhead imposed by our solution. View full abstract»

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  • A Walkable Kademlia Network for Virtual Worlds

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (98 KB) |  | HTML iconHTML  

    In this work, we design and evaluate Walkad, a P2P architecture for the management of range queries in virtual worlds. We design Walkad as an extension of Kademlia, a very popular DHT successfully adopted in eMule. Walkad organizes the Kademlia keyspace in a reverse binary trie, i.e., a tree-based data structure where nodes of each level of the tree are labeled using the Gray Code. View full abstract»

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  • Adaptive System for 802.11 Scanning

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (239 KB) |  | HTML iconHTML  

    In this context, a mobile user may deal with a high variety of scenarios. These scenarios consist on heterogeneous access point (AP) deployments characterized by overlapping frequencies, traffic load and high interference. Moreover, these conditions cannot be anticipated by the mobile user while moving between APs and thus an appropriate scanning algorithm is needed. The change of AP, also known as handover, involves scanning for APs, authentication and association. During the handover process, a mobile station (MS) cannot send or receive data, so the handover latency must be as low as possible. Related work particularly focuses on the reduction of the scanning latency, representing 90% of the whole handover process. View full abstract»

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  • Advanced Multimedia Search in P2P Overlays

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (113 KB) |  | HTML iconHTML  

    This paper presents the ongoing PhD work in the cross-domain area of P2P networking and advanced multimedia search methods. The author identifies and solves the problems encountered during the application of Query by Example search technique in structured and unstructured P2P overlays. A set of benchmarking methods as well as the results of large scale user tests are presented. View full abstract»

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  • Alternate Multihop Routing in Limited Reconfigurable Optical Networks

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    In this paper, we investigate the performance of limited reconfigurable optical networks when multihopping is used. Multihopping is achieved by dropping a wavelength at an intermediate node and transmitting on another wavelength at that node (O-E-O). A route can consist of several such hops each obeying the wavelength continuity constraint individually. Considering that a receiver and a transmitter are used for add/drop at a node, multihopping is restricted by the number of transponders and their tunabilities. We develop a dynamic routing strategy based on the availability and tunability of transponders as well as the wavelength availability. We adopt a share-per-link model for the usage of transponders within a reconfigurable node, and each node is assumed to be equipped with a ROADM which can add/drop any wavelength to any of the ports. We show that the proposed routing strategy improves the blocking performance significantly compared to fixed routing with or without multihopping or alternate routing methods without multihopping. View full abstract»

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  • An Encoding Method to Signal 3 States with a Single PCN Bit

    Page(s): 1 - 2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (79 KB) |  | HTML iconHTML  

    Pre-congestion notification (PCN) is currently being developed by the IETF to provide admission control in DiffServ networks for non-elastic flows. Various marking schemes are being proposed as part of this effort. We evaluate a new marking behaviour that could be used to signal three different states by means of a single bit. This scheme is of interest to networks operating with MPLS as the label QoS coding space is limited to three EXP bits. Similar to the ECN standard for MPLS, this research assumes that just two codepoints will be available to indicate different congestion states. Of these two codepoints, one would be used to differentiate between PCN and non-PCN traffic and the other would be used for PCN marking. This paper outlines the approach and presents the advantages and limitations of the proposal using the evaluations performed. A comparison of the method with a two bit PCN marking approach is also studied. View full abstract»

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  • An Experimental Study on Wi-Fi Ad-Hoc Mode for Mobile Device-to-Device Video Delivery

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (234 KB) |  | HTML iconHTML  

    The demand for video content is continuously increasing as video sharing on the Internet is becoming enormously popular recently. This demand, with its high bandwidth requirements, has a considerable impact on the load of the network infrastructure. As more users access videos from their mobile devices, the load on the current wireless infrastructure (which has limited capacity) will be even more significant. Based on observations from many local video sharing scenarios, in this paper, we study the tradeoffs of using Wi-Fi ad-hoc mode versus infrastructure mode for video streaming between adjacent devices. We thus show the potential of direct device-to-device communication as a way to reduce the load on the wireless infrastructure and to improve user experiences. Setting up experiments for Wi- Fi devices connected in ad-hoc mode, we collect measurements for various video streaming scenarios and compare them to the case where the devices are connected through access points. The results show the improvements in latency, jitter and loss rate. More importantly, the results show that the performance in direct device-to-device streaming is much more stable in contrast to the access point case, where different factors affect the performance causing widely unpredictable qualities. View full abstract»

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  • Application Driven Comparison of T-MPLS/MPLS-TP and PBB-TE - Driver Choices for Carrier Ethernet

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    This paper describes qualitatively and through applications the comparison of PBB-TE and T-MPLS/MPLS-TP approaches to Carrier Ethernet. Carrier Ethernet has currently been proposed as a method to transport Ethernet in metro networks with carrier class service attributes. Two approaches have been considered - one based on backbone bridging called PBB-TE and the other based on T- MPLS/MPLS-TP that has evolved from MPLS minus some redundant features. We qualitatively understand the two technologies, delve into their working and compare these from multiple standpoints. We then develop scenarios where these are used including data-center, mobile back-haul and IPTV (video on demand). Both PBB-TE and T-MPLS are applied to each of these three leading metro application (that are expected to dominate much of future metro services). Cost and performance comparisons are shown. View full abstract»

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  • Applying Network Coding to Cyclic Networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (173 KB) |  | HTML iconHTML  

    This work addresses the application of network coding on cyclic networks. Cycles and delay are indispensable factors when designing and implementing data networks. However, most attention in the literature of network coding has been on acyclic networks. Hence, in order to bridge the gap of network coding and the practical networks, Convolutional Network Coding (CNC) with delay as an essential part was proposed for network coding on cyclic networks. View full abstract»

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  • Architecture and Incentive Design of Integrated Cellular and Disruption Tolerant Networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (77 KB) |  | HTML iconHTML  

    The most common and seamless way of getting Internet access today for vehicles is through the use of cellular network, for example, GPRS, 3G or HSDPA. Even though performance of cellular network has improved significantly over the years, in particular with deployment of HSDPA, the data rate is still limited, due to the requirement of providing ubiquitous coverage to a large number of users. Meanwhile, many cities around the world have witnessed large scale deployment of open IEEE 802.11 or WiFi hot spots. While the WiFi link provides higher bandwidth at cheaper price, it is only usable when the vehicle is in range, and the contact is both fleeting and intermittent. In comparison, while the speed of cellular link is lower than WiFi, it has higher availability. In this paper, the architecture and incentive design of integrated cellular and disruption tolerant networks are discussed. View full abstract»

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  • Assortative Mixing in BitTorrent-Like Networks

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    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (87 KB) |  | HTML iconHTML  

    In this work, we propose a simple model to understand the mechanisms within the BitTorrent protocol that are responsible for driving the system into high levels of AM. Using the model, we investigate the influence that system parameters have on the emergence AM. In particular, we show that the "optimistic unchoke" mechanism of BitTorrent plays a major role in this process. View full abstract»

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