Showing papers on "Heterogeneous network published in 2006"

Resource Allocation and Cross Layer Control in Wireless Networks

Abstract: Information flow in a telecommunication network is accomplished through the interaction of mechanisms at various design layers with the end goal of supporting the information exchange needs of the applications. In wireless networks in particular, the different layers interact in a nontrivial manner in order to support information transfer. In this text we will present abstract models that capture the cross-layer interaction from the physical to transport layer in wireless network architectures including cellular, ad-hoc and sensor networks as well as hybrid wireless-wireline. The model allows for arbitrary network topologies as well as traffic forwarding modes, including datagrams and virtual circuits. Furthermore the time varying nature of a wireless network, due either to fading channels or to changing connectivity due to mobility, is adequately captured in our model to allow for state dependent network control policies. Quantitative performance measures that capture the quality of service requirements in these systems depending on the supported applications are discussed, including throughput maximization, energy consumption minimization, rate utility function maximization as well as general performance functionals. Cross-layer control algorithms with optimal or suboptimal performance with respect to the above measures are presented and analyzed. A detailed exposition of the related analysis and design techniques is provided.

XORs in the air: practical wireless network coding

Abstract: This paper proposes COPE, a new architecture for wireless mesh networks. In addition to forwarding packets, routers mix (i.e., code) packets from different sources to increase the information content of each transmission. We show that intelligently mixing packets increases network throughput. Our design is rooted in the theory of network coding. Prior work on network coding is mainly theoretical and focuses on multicast traffic. This paper aims to bridge theory with practice; it addresses the common case of unicast traffic, dynamic and potentially bursty flows, and practical issues facing the integration of network coding in the current network stack. We evaluate our design on a 20-node wireless network, and discuss the results of the first testbed deployment of wireless network coding. The results show that COPE largely increases network throughput. The gains vary from a few percent to several folds depending on the traffic pattern, congestion level, and transport protocol.

Node clustering in wireless sensor networks: recent developments and deployment challenges

Abstract: The large-scale deployment of wireless sensor networks (WSNs) and the need for data aggregation necessitate efficient organization of the network topology for the purpose of balancing the load and prolonging the network lifetime. Clustering has proven to be an effective approach for organizing the network into a connected hierarchy. In this article, we highlight the challenges in clustering a WSN, discuss the design rationale of the different clustering approaches, and classify the proposed approaches based on their objectives and design principles. We further discuss several key issues that affect the practical deployment of clustering techniques in sensor network applications.

Handoffs in fourth generation heterogeneous networks

Abstract: As mobile wireless networks increase in popularity and pervasiveness, we are faced with the challenge of combining a diverse number of wireless networks. The fourth generation of wireless communications is expected to integrate a potentially large number of heterogeneous wireless technologies in what could be considered a huge step forward toward universal seamless access. One of the main challenges for seamless mobility is the availability of reliable horizontal (intrasystem) and vertical (intersystem) handoff schemes. Efficient handoff schemes enhance quality of service and provide flawless mobility. This article presents different and novel aspects of handoff and discusses handoff related issues of fourth generation systems. Desirable handoff features are presented. Handoff decisions, radio link transfer, and channel assignment are described as stages of the complete handoff process. A vertical handoff decision function, which enables devices to assign weights to different network parameters, is also presented

CRAWDAD: a community resource for archiving wireless data at Dartmouth

Abstract: Wireless network researchers are seriously starved for data about how real users, applications, and devices use real networks under real network conditions. CRAWDAD, a Community Resource for Archiving Wireless Data at Dartmouth, is a new NSF-funded project to build a wireless network data archive for the research community. We host wireless data, and provide tools and documents to make it easy to collect and use wireless network data. We hope that this resource will help researchers identify and evaluate real and interesting problems in mobile and pervasive computing. This report outlines the CRAWDAD project, the kick-off work-shop that was held at MobiCom 2005, and the latest news. how real users, applications, and devices use real networks under real conditions, and how mobile users actually move about. This data helps us to identify and understand the real problems, to evaluate possible solutions, and to evaluate new applications and services.

An energy-efficient ant-based routing algorithm for wireless sensor networks

Abstract: Wireless Sensor Networks are characterized by having specific requirements such as limited energy availability, low memory and reduced processing power. On the other hand, these networks have enormous potential applicability, e.g., habitat monitoring, medical care, military surveillance or traffic control. Many protocols have been developed for Wireless Sensor Networks that try to overcome the constraints that characterize this type of networks. Ant-based routing protocols can add a significant contribution to assist in the maximisation of the network lifetime, but this is only possible by means of an adaptable and balanced algorithm that takes into account the Wireless Sensor Networks main restrictions. This paper presents a new Wireless Sensor Network routing protocol, which is based on the Ant Colony Optimization metaheuristic. The protocol was studied by simulation for several Wireless Sensor Network scenarios and the results clearly show that it minimises communication load and maximises energy savings.

Run-time dynamic linking for reprogramming wireless sensor networks

Abstract: From experience with wireless sensor networks it has become apparent that dynamic reprogramming of the sensor nodes is a useful feature. The resource constraints in terms of energy, memory, and processing power make sensor network reprogramming a challenging task. Many different mechanisms for reprogramming sensor nodes have been developed ranging from full image replacement to virtual machines.We have implemented an in-situ run-time dynamic linker and loader that use the standard ELF object file format. We show that run-time dynamic linking is an effective method for reprogramming even resource constrained wireless sensor nodes. To evaluate our dynamic linking mechanism we have implemented an application-specific virtual machine and a Java virtual machine and compare the energy cost of the different linking and execution models. We measure the energy consumption and execution time overhead on real hardware to quantify the energy costs for dynamic linkin.Our results suggest that while in general the overhead of a virtual machine is high, a combination of native code and virtual machine code provide good energy efficiency. Dynamic run-time linking can be used to update the native code, even in heterogeneous networks.

A Client-Driven Approach for Channel Management in Wireless LANs

Abstract: We propose an efficient client-based approach for channel management (channel assignment and load balancing) in 802.11-based WLANs that lead to better usage of the wireless spectrum. This approach is based on a “conflict set coloring” formulation that jointly performs load balancing along with channel assignment. Such a formulation has a number of advantages. First, it explicitly captures interference effects at clients. Next, it intrinsically exposes opportunities for better channel re-use. Finally, algorithms based on this formulation do not depend on specific physical RF models and hence can be applied efficiently to a wide-range of in-building as well as outdoor scenarios. We have performed extensive packet-level simulations and measurements on a deployed wireless testbed of 70 APs to validate the performance of our proposed algorithms. We show that in addition to single network scenarios, the conflict set coloring formulation is well suited for channel assignment where multiple wireless networks share and contend for spectrum in the same physical space. Our results over a wide range of both simulated topologies and in-building testbed experiments indicate that our approach improves application level performance at the clients by upto three times (and atleast 50%) in comparison to current best-known techniques.

Signal threshold adaptation for vertical handoff in heterogeneous wireless networks

Abstract: The convergence of heterogeneous wireless access technologies has been envisioned to characterize the next generation wireless networks. In such converged systems, the seamless and efficient handoff between different access technologies (vertical handoff) is essential and remains a challenging problem. The heterogeneous co-existence of access technologies with largely different characteristics results in handoff asymmetry that differs from the traditional intra-network handoff (horizontal handoff) problem. In the case where one network is preferred, the vertical handoff decision should be carefully executed, based on the wireless channel state, network layer characteristics, as well as application requirements. In this paper, we study the performance of vertical handoff using the integration of 3G cellular and wireless local area networks as an example. In particular, we investigate the effect of an application-based signal strength threshold on an adaptive preferred-network lifetime-based handoff strategy, in terms of the signalling load, available bandwidth, and packet delay for an inter-network roaming mobile. We present an analytical framework to evaluate the converged system performance, which is validated by computer simulation. We show how the proposed analytical model can be used to provide design guidelines for the optimization of vertical handoff in the next generation integrated wireless networks.

Toward a theory of in-network computation in wireless sensor networks

Abstract: Sensor networks are not just data networks with sensors being the sources of data. Rather, they are often developed and deployed for a specific application, and the entire network operation is accordingly geared toward satisfying this application. For overall system efficiency, it may be necessary for nodes to perform computations on data, as opposed to simply originating or forwarding data. Thus, the entire network can be viewed as performing an application-specific distributed computation. The topic of this article is to survey some lines of research that may be useful in developing a theory of in-network computation, which aims to elucidate how a wireless sensor network should efficiently perform such distributed computation. We review several existing approaches to computation problems in network settings, with a particular emphasis on the communication aspect of computation. We begin by studying the basic two-party communication complexity model and how to optimally compute functions of distributed inputs in this setting. We proceed to larger multihop networks, and study how block computation and function structure can be exploited to provide greater computational throughput. We then consider distributed computation problems in networks subject to noise. Finally, we review some randomized gossip-based approaches to computing aggregate functions in networks. These are diverse approaches spanning many different research communities, but together may find a role in the development of a more substantial theoretical foundation for sensor networks.

Visual Analysis of Large Heterogeneous Social Networks by Semantic and Structural Abstraction

Abstract: Social network analysis is an active area of study beyond sociology. It uncovers the invisible relationships between actors in a network and provides understanding of social processes and behaviors. It has become an important technique in a variety of application areas such as the Web, organizational studies, and homeland security. This paper presents a visual analytics tool, OntoVis, for understanding large, heterogeneous social networks, in which nodes and links could represent different concepts and relations, respectively. These concepts and relations are related through an ontology (also known as a schema). OntoVis is named such because it uses information in the ontology associated with a social network to semantically prune a large, heterogeneous network. In addition to semantic abstraction, OntoVis also allows users to do structural abstraction and importance filtering to make large networks manageable and to facilitate analytic reasoning. All these unique capabilities of OntoVis are illustrated with several case studies

DRAGON: a framework for service provisioning in heterogeneous grid networks

Abstract: Dynamic resource allocation in GMPLS optical networks (DRAGON) defines a research and experimental framework for high-performance networks required by grid computing and e-science applications. The DRAGON project is developing technology and deploying network infrastructure which allows dynamic provisioning of network resources in order to establish deterministic paths in direct response to end-user requests. This includes multidomain provisioning of traffic-engineering paths using a distributed control plane across heterogeneous network technologies while including mechanisms for authentication, authorization, accounting (AAA), and scheduling. A reference implementation of this framework has been instantiated in the Washington, DC area and is being utilized to conduct research and development into the deployment of optical networks technologies toward the satisfaction of very-high-performance science application requirements.

Mobile router device

Abstract: A wireless mobile router ( 140 ) includes wireless network interfaces ( 202 ) and ( 218 ) attached to a network controller ( 142 ). The wireless network interface ( 202 ) communicates with a cellular network ( 110 ) to access cellular network services. The wireless network interface ( 218 ) and the network controller ( 142 ) comprise a WLAN ( 170 ) or PAN ( 180 ) network router hosting a plurality of client devices. Each client device may access a wide area network, WAN over the cellular network. The wireless mobile router ( 140 ) is configured to exchange various cellular network signals with various WLAN and PAN networks. The wireless mobile router ( 140 ) is particularly suitable for use in a vehicle or at locations where WAN access is not readily available.

Method and apparatus for maintaining a fingerprint for a wireless network

Abstract: The disclosure is directed to a mobile communication device that measures characteristics or attributes of a first communications network that vary according to physical location within that first communications network to create a fingerprint, or signature, of a location within the first communications network. When the fingerprint of the current location of the mobile device is created it can be compared to a known fingerprint associated with a second communication network to determine the mobile device's proximity to the second communications network. Furthermore, the second and subsequent fingerprint that are generated for a particular communications network can be used to modify the stored fingerprint so as to refine it to improve detecting the proximity to the communications network.

Autonomous and heterogeneous network discovery and reuse

Abstract: In some embodiments, a method is disclosed involving a mobile device discovery and use of target wireless networks which are at least partly within a coverage area of another wireless network which provides location information which includes: acquiring data from a plurality of said target wireless networks; acquiring location information from said another wireless network; mapping said data from said plurality of said target wireless networks with said location information; and selecting one of said plurality of target wireless networks based on said mapped data.

Open MPI: A High-Performance, Heterogeneous MPI

Abstract: The growth in the number of generally available, distributed, heterogeneous computing systems places increasing importance on the development of user-friendly tools that enable application developers to efficiently use these resources. Open MPI provides support for several aspects of heterogeneity within a single, open-source MPI implementation. Through careful abstractions, heterogeneous support maintains efficient use of uniform computational platforms. We describe Open MPI's architecture for heterogeneous network and processor support. A key design features of this implementation is the transparency to the application developer while maintaining very high levels of performance. This is demonstrated with the results of several numerical experiments.

Two-tier wireless broadband access network

Abstract: A wireless access network is based on a two-tier access point (AP) structure to provide effective and efficient wireless communication into an individual home/office building. A first tier of the network utilizes “neighborhood” APs, relatively low power, and utilized to provide wireless communication with a “nanocell” boundary (e.g., 300-1000 feet). A second tier of the network utilizes a set of “network concatenation devices” (window bridge), with a separate network concatenation device at each permanent facility in the nanocell that houses wireless devices. The network concatenation device is attached to a window, for example, of a home in communication with the neighborhood AP. The network concatenation device functions as a bridge to couple to each of the wireless devices within the home. This communication is then relayed in an efficient manner between the network concatenation device and the neighborhood AP. By using a number of neighborhood APs, rather extensive wireless coverage can be obtained.

Vulnerability of weighted networks

Abstract: In real networks complex topological features are often associated with a diversity of interactions as measured by the weights of the links. Moreover, spatial constraints may also play an important role, resulting in a complex interplay between topology, weight, and geography. In order to study the vulnerability of such networks to intentional attacks, these attributes must therefore be considered along with the topological quantities. In order to tackle this issue, we consider the case of the worldwide airport network, which is a weighted heterogeneous network whose evolution and structure are influenced by traffic and geographical constraints. We first characterize relevant topological and weighted centrality measures and then use these quantities as selection criteria for the removal of vertices. We consider different attack strategies and different measures of the damage achieved in the network. The analysis of weighted properties shows that centrality driven attacks are capable of shattering the network's communication or transport properties even at a very low level of damage in the connectivity pattern. The inclusion of weight and traffic therefore provides evidence for the extreme vulnerability of complex networks to any targeted strategy and the need for them to be considered as key features in the finding and development of defensive strategies.

Experimental Characterization of Home Wireless Networks and Design Implications

Abstract: Anecdotal evidence suggests that home wireless networks may be unpredictable despite their limited size. In this work, we deploy six-node wireless testbeds in three houses in the United States and the United Kingdom. We examine the quality of links in home wireless networks and the effect of (i) transmission rate, (ii) transmission power, (iii) node location, (iv) type of house, and (v) 802.11 technology. We provide empirical evidence suggesting that homes are challenging environments for wireless communication. Wireless links in the home are highly asymmetric and heavily influenced by precise node location, transmission power, and encoding rate, rather than physical distance between nodes. In our measurements, many links were unable to utilize the maximum transmission rate of the deployed 802.11 technology, and a few provided no connectivity at all. These results suggest that creating an AP-based topology with maximum coverage and throughput in this environment is challenging. Our findings have implications on the design of future home wireless networks and requirements for future wifi-enabled consumer electronic devices. We show that coverage and performance can be improved using a multi-hop topology, implying that mesh capabilities may actually be needed in consumer electronics for seamless connectivity across the home.

Auto configuration of portable computers for use in wireless local area networks

Abstract: A method and apparatus for the configuration of a wireless network adapter is disclosed. A wireless network adapter is provided with software that enables the adapter to recognize and connect with one or more networks. Software profiles are loaded onto or created on the adapter. The software profiles each correspond to a unique network.

Performance of VoIP in a 802.11 Wireless Mesh Network

Abstract: Performance in multihop wireless networks is known to degrade with the number of hops for both TCP and UDP traffic. For VoIP, the wireless network presents additional challenges as the perceived quality is dependent on both loss and delay. We investigate several methods to improve voice quality and present experimental results from an 802.11b testbed optimized for voice delivery. Use of multiple interfaces, path diversity and aggregation are shown to provide a combined improvement of 13 times in number of calls supported in our 15 node 802.11 mesh system. VoIP, multihop, mesh

System and method for communication in a wireless mobile ad-hoc network

Abstract: A system and method for improving digital communication in a wireless mobile ad-hoc network. More specifically, the system includes one or more portable network devices operable to support the seamless operation of a self-initializing, self-healing, adaptive portable network. The portable network devices implement protocols that provide bandwidth management capabilities for use with radios, routers and other wireless network devices. Each portable network device includes at least one wireless transceiver, a processor and control software. The processor and control software are logically coupled to the wireless transceiver to facilitate digital communication via a plurality of communication channels with other network devices.

A Node Identity Internetworking Architecture

Abstract: The Internet consists of independent networks that belong to different administrative domains and vary in scope from personal area networks, private home networks, corporate networks to ISP and global operator networks. These networks may employ different technologies, communications mediums, addressing realms and may have widely different capabilities. The coming years will add a significant level of dynamic behavior, such as mobile nodes and moving networks, which the Internet must support. At the same time, there is a need to address the increasing levels of harmful traffic and denial-of-service attacks. The existing Internet architecture does not support dynamic behavior or secure communication to a sufficient degree. This paper outlines a node-identity-based internetworking architecture that allows heterogeneous networks to work together without loss of functionality. Some of techniques employed in this architecture include reliance on cryptographic node identifiers, identity routers and localized addressing realms.

Distributed cognitive coexistence of 802.15.4 with 802.11

Abstract: Thanks to recent advances in wireless technology, a broad range of standards are currently emerging. Interoperability and coexistence between these heterogeneous networks are becoming key issues, which require new adaptation strategies to avoid harmful interference. In this paper, we focus on the coexistence of 802.11 Wireless LAN and 802.15.4 sensor networks in the ISM band. Those networks have very different transmission characteristics that result in asymmetric interference patterns. We propose distributed adaptation strategies for 802.15.4 nodes, to minimize the impact of the 802.11 interference. This interference varies in time, frequency and space and the sensor nodes adapt by changing their frequency channel selection over time. Different distributed techniques are proposed, based on scanning (with increasing power cost) on the one hand, and based on increased cognition through learning on the other hand. These techniques are evaluated both for performance and energy cost. We show that it is possible to achieve distributed frequency allocation approaches that result only in an increase of 20% of the delay performance compared to ideal frequency allocation. Moreover, it is shown that a factor of two in energy consumption can be saved by adding learning to the system.

A Sensor Network Simulator for the Contiki OS

Abstract: This report introduces a new sensor network simulator for the Contiki OS - the COOJA Simulator. The Contiki OS is a portable operating system designed specifically for resource limited devices such as sensor nodes. It is built around an event-driven kernel but supports pre-emptive multithreading at a per-process basis. It also supports a full TCP/IP stack via uIP and the programming abstraction Protothreads. The main design goal of the COOJA Simulator is extendibility, for which Interfaces and Plugins are used. An Interface represents a sensor node property or device, such as a position, a button or a radio transmitter. A Plugin is used to interact with a simulation, for example to control the simulation speed or to watch all network traffic between the simulated nodes. Both new Plugins and Interfaces can easily be created and added to the simulation environment. A number of other parts of the simulator, for example a radio medium responsible for forwarding radio network data, can also be implemented and added to the simulator. And by supporting several different simulation environments at the same time in one simulation, different underlying hardware platforms can be simulated in heterogeneous networks. Java Native Interface is used to connect the new simulator with Contiki, allowing simulated applications to run in a real Contiki system. By using this approach, any simulated application can then be run on a real sensor node unaltered.

Wireless handoffs between multiple wireless networks

Abstract: A wireless communications device is disclosed. The wireless communications device is configured to support a call over a cellular network or an IP network to a remote communications device. The wireless communications device is further configured to handoff the call between the cellular network and the IP network. An Interworking Function (IWF) is configured to maintain a call between a wireless communications device and a communications device as the wireless communications device is handed off between a cellular network and an IP network.

Method of discovering multi-mode mobile terminals

Abstract: A method of discovering multi-mode mobile terminals (13) in a heterogeneous network environment, each multi-mode mobile terminal (13) having at least one interface for sending packet data to and/or receiving packet data from a home radio communication network (11) and a foreign radio communication network (12), said home radio communication network having a different access technology from said foreign radio communication network, each multi-mode mobile terminal (13) performing the steps of: (a) listening to said foreign radio communication network (12); (b) receiving and storing a foreign network indicator for indicating presence of said foreign radio communication network (12); and (c) transmitting said foreign network indicator to said home radio communication network (11); whereby said home radio communication network (11) may store a database comprising a mapping between a multi-mode mobile terminal identity, a home network indicator and a foreign network indicator, to facilitate interworking of said home and foreign radio communication networks.

Supporting handover of mobile terminal

Abstract: The present invention relates to supporting a handover of a mobile terminal. Preferably, the present invention performs a scan of a neighboring network different from a current network of the mobile terminal to determine the presence of an accessible link of the neighboring network for performing a handover, wherein the mobile terminal comprises a heterogeneous network handover module that is configured to provide convergence of information from at least one network interface module associated with one of a homogeneous and heterogeneous network into a unified presentation. An information message is then received from the neighboring network, wherein the information message comprises an information element associated with whether the neighboring network is capable of communicating with the heterogeneous network handover module of the mobile terminal.

Streaming of Scalable Video from Multiple Servers using Rateless Codes

Abstract: This paper presents a framework for efficiently streaming scalable video from multiple servers over heterogeneous network paths. We propose to use rateless codes, or Fountain codes, such that each server acts as an independent source, without the need to coordinate its sending strategy with other servers. In this case, the problem of maximizing the received video quality and minimizing the bandwidth usage, is simply reduced to a rate allocation problem. We provide an optimal solution for an ideal scenario where the loss probvability on each server-client path is exactly known. We then present a heuristic-based algorithm, which implements an unequal error protection scheme for the more realistic case of imperfect knowledge of the loss probabilities. Simulation results finally demonstrate the efficiency of the proposed algorithm, in distributed streaming scenarios over lossy channels.

Network coding for wireless mesh networks: a case study

Abstract: Network coding is a new transmission paradigm that proved its strength in optimizing the usage of network resources. In this paper, we evaluate the gain from using network coding for file sharing applications running on top of wireless mesh networks. With extensive simulations carried out on a simulator we developed specifically for this study, we confirm that network coding can improve the performance of the file sharing application, but not as in wired networks. The main reason is that nodes over wireless cannot listen to different neighbors simultaneously. Nevertheless, one can get more from network coding if the information transmission is made more diverse inside the network. We support this argument by varying the loss rate over wireless links and adding more sources.