With its abundant bandwidth and worldwide availability, the 60 GHz band has been considered as a promising solution to provide multi-Gbps wireless transmission. Different standard bodies and industrial interest groups start various projects to develop technologies in the 60 GHz band for applications such as high-definition (HD) and fast file transfer. However, until now very little efforts are made to ensure interference-free coexistence between these technologies. In this paper, we investigate the interference problem in the 60 GHz band. The ECMA-387 standard is used as a study case to illustrate how some simple techniques can mitigate the interference among heterogenous devices in the 60 GHz band. We conduct both mathematical analysis and simulations to demonstrate the performance of these simple techniques and identify some problems for future improvements.
In data-centric sensor networks each device is like a minimal computer with cpu and memory able to sense, manage and transmit data performing in-network processing by means of insertions, querying and multi-hop routings. Saving energy is one of the most important goals, therefore radio transmissions, which are the most expensive operations, should be limited by optimizing the number of routings. Moreover the network traffic should be balanced among nodes in order to avoid premature discharge of some devices and then network partitions. In this paper we present a fully decentralized infrastructure able to self-organize fully functional data centric sensor networks from local interactions and learning among devices. Differently from existing solutions, our proposal does not require complex devices that need global information or external help from systems, such as the Global Positioning System (GPS), which works only outdoor with a precision and an efficacy both limited by weather conditions and obstacles. Our solution can be applied to a wider number of scenarios, including mesh networks and wireless community networks. The local learning occurs by exploiting implicit cost-free overhearing at sensors. The work reports an extensive number of comparative experiments, using several distributions of sensors and data, with a well-know competitor solution in literature, showing that an approach fully based on self-organization is more efficient than traditional solutions depending on GPS.
A novel approach for achieving high Quality of Service (QoS) in sensor networks via topology control is introduced and experimentally assessed in this paper. Our approach falls in the broader discipline of graph structural mining, and exploits a leading concept initially studied in the context of Social Network Analysis (SNA), namely betweenness. Particularly, in our research betweenness is applied in terms of a graph structural mining measure embedded in the core layer of our proposed topology control algorithm, called Edge Betweenness Centrality (EBC). EBC allows us to evaluate relationships between entities of the network (e.g., nodes, edges), and hence identify different roles among them (e.g., brokers, outliers). In turn, deriving knowledge is further exploited to define raking operators that look at structural properties of the graph modeling the target sensor network. Based on these amenities, our topology control algorithm is able of providing an “insight” of the graph structure of the network on top which control over information flow, message delivery, latency and energy dissipation among nodes can be easily deployed.
Localization of mobile users in wireless mesh networks (WMN) generally relies on some sort of flooding-based technique. Broadcasting the network is good for reliability but leads to increased latency and broadcast storm problems. This results in low efficiency of the location management mechanism in terms of packets loss and disconnection time. In this paper, we investigate a new DHT-based location management scheme through experimental evaluation on our WMN testbed. The main features of our proposed scheme are that broadcast packets are totally avoided and node localization becomes transparent to the users. We compare it to our previous flooding-based location scheme, namely EMM (Enhanced Mobility Management). Our results show improved performance both in terms of dropped packets and handover latency introduced to re-establish open sessions after a user moves.
The deployment of sensor networks is both widespread and varied with more niche applications based on these networks. In the case study provided in this work, the network is provided by two football teams with sensors generating continuous heart rate values for the duration of the activity. In wireless networks such as these, the requirement is for complex methods of data management in order to deliver more and more powerful query results. In effect, what is required is a traditional database-style query interface where domain experts can continue to probe for the answers required in more specialised environments. This paper describes a system and series of experiments that requires powerful data management capabilities to meet the requirements of sports scientists.
Wireless roaming means that a mobile device is able to switch from one network cell to another while keeping the link to active services. Recent researches [13] showed that it increases the security to establish an authenticated and confidential tunnel directly to a home network which then acts as service provider respectively proxy server for further external services. In this paper we extend the trust assumptions and formal security goals for wireless roaming via tunnels (WRT) that were given by Manulis et al.[7].Additonally, we propose an efficient protocol that realizes the authentication and key agreement for establishing the secure tunnel, whereby considering the delay restrictions that are given by current multimedia services like VoIP or video streaming.Furthermore we discuss the accounting problem and present a solution that ensures a fair accounting for the foreign network.
In this paper we consider a provider that offers a SOA application implemented as a composite service to several users with different Qos requirements. For such a system, we present a scalable framework to the QoS-aware self-adaptation based on a two layer reference architecture. The first layer addresses the adaptation at the provisioning level: operating at a slower time scale, its role is to identify the set of candidate services to implement the system functionality at the required user QoS. The second layer addresses the adaptation at the service selection level: operating on a faster time scale, its role is to determine at running time the actual services which are bound to each user request while meeting both provider and user QoS. We formulate the adaptation strategy of both layers as suitable optimization problems which can be efficiently solved using standard techniques. Numerical experiments show the effectiveness of the proposed approach.
This work presents a Call Admission Control (CAC) system for a SIP-based IP Telephony platform. Configured for a multi-branch enterprise environment, the system enables international calls to be established in two steps: one step using Voice over IP (VoIP) through the Internet between the local office and a VoIP-PSTN gateway placed at destination country, and a second step by means of PSTN, from the gateway to the end-user, accounted with local tariffs. CAC decisions are based on Quality of Service (QoS) measurements, call tariffs and also on the number of available lines in the gateway. The CAC has been implemented within a test platform based on virtualization. Measurements to evaluate and validate CAC's impairment on call establishment delays have been obtained.
Buffered crossbar switches are special crossbar switches with each crosspoint equipped with a small exclusive buffer. The crosspoint buffers decouple input ports and output ports, and simplify switch scheduling. In this paper, we propose a scheduling algorithm called Fair and Localized Asynchronous Packet Scheduling (FLAPS) for buffered crossbar switches, to provide tight performance guarantees. FLAPS needs no speedup for the crossbar and handles variable length packets without segmentation and reassembly (SAR). With FLAPS, each input port and output port independently make scheduling decisions and rely on only local queue statuses. We theoretically show that a crosspoint buffer size of 4L is sufficient for FLAPS to avoid buffer overflow, where L is the maximum packet length. In addition, we prove that FLAPS achieves strong stability, and provides bounded delay guarantees. Finally, we present simulation data to verify the analytical results.
Transmit power control has been largely proposed as a solution to improve the performance of packet radio systems in terms of increased throughput, spatial reuse and battery lifetime for mobile terminals. However, the benefits of transmit power control schemes on these different performance figures may strongly depend on the employed PHY technology and channel access mechanism. In this paper, we focus on the effects of power control on the energy consumption of WiFi network cards. By means of several experimental tests carried out under different operation conditions and modulation schemes, we try to justify why the reduction of the transmission power has a marginal effect on the overall energy consumption.
This paper evaluates the performance of QoS-aware Mobile IP Fast Authentication Protocol (QoMIFA) compared to the well-known Simple QoS signaling protocol (Simple QoS) via simulation studies modeled in the ns2. The evaluation comprises the investigation of network load impact on both protocols with respect to the time required to reserve resources, number of dropped packets per handoff and number of packets sent as best-effort after the handoff is completed and until resources are reserved. Our simulation results show that QoMIFA is capable of achieving fast and smooth handoffs in addition to its capability of reserving resources very quickly. QoMIFA is approximately 97.75 % and 73.92 % faster than Simple QoS with respect to the average time required to reserve resources on downlink and uplink, respectively. It drops 79.63 % less on downlink and 46.6 % less on uplink and results in 98.40 % less packets sent on downlink as best-effort.
This paper focuses on an environment of more than one proxy server that serve homogeneous or even heterogeneous client preferences for streaming of video files. Under a hierarchical tree topology system of proxies, the prefixes of the videos are stored in small size proxy caches each located very close to the corresponding client community, while larger caches located further away from the client communities are used to cache the latter segments of the videos requested by more than one client community. Frequency-Based Cache Management Policies are used in order to efficiently and dynamically cache the content of the most popular videos among the various proxies. Our event-driven simulations have shown that the hierarchical tree topology of proxies achieves a much higher byte-hit ratio with less cache management overhead, when using the same overall cache capacity with a simple topology of independent proxies and in general provides better performance characteristics.
The growing popularity of mobile and location aware devices allows the deployment of infomobility systems that provide access to information and services for the support of user mobility. Current systems for infomobility services assume that most information is already available on the mobile device and the device connectivity is used for receiving critical messages from a central server. However, we argue that the next generation of infomobility services will be characterized by collaboration and interaction among the users, provided through real-time bidirectional communication between the client devices and the infomobility system.In this paper we propose an innovative architecture to support next generation infomobility services providing interaction and collaboration among the mobile users that can travel by several different transportation means, ranging from cars to trains to foot. We discuss the design issues of the architecture, with particular emphasis on scalability, availability and user data privacy, which are critical in a collaborative infomobility scenario.
This paper presents our work regarding the testing and evaluation of DiffServ QoS mechanisms over IPv6 and IPv4 in dual stack software based platforms. IPv6 introduces some additional features (like flow label) and the current support for QoS mechanisms in IPv6 implementations approaches the corresponding QoS support in IPv4. Therefore, a number of tests with DiffServ QoS mechanisms applied on IPv6 traffic have been carried out on a testbed created specifically for this purpose, in order to validate the mechanisms and evaluate the router's overall performance. Our evaluations cover the load incurred to the routing devices from the implementation of the mechanisms, the level of support for QoS IPv6 features and the comparison of performance over IPv4 and IPv6.
A large part of the hidden web resides in weblog servers; traditional search engines perform poorly on blogs. We present a method for ranking weblogs utilizing both link graph and similarity, and based on an enhanced and weighted graph of weblogs capturing crucial weblog features. Rankings are then assigned using our algorithm, BlogRank, which is a modified version of PageRank.To validate our method we ran experiments on a weblog dataset, processed and adapted to our search engine: http://spiderwave.aueb.gr/BlogwaveOur experiments suggest that our algorithm enhances the quality of returned results.
Real-time streaming of multimedia content is increasingly becoming a crucial part of networked applications. A logical consequence of this evolution is a growing demand for services that can be applied on these multimedia streams. In this paper, we present our overlay network which provides such multimedia services. Although these services are application-aware and can thus exploit application-specific knowledge, the overlay network itself is completely generic. Consequently, multiple applications can take advantage of the overlay network, even concurrently. Furthermore, the overlay network is highly extensible, meaning additional services can be added to it easily. Besides describing the architecture of the software component of our overlay network, we also discuss the implementation of two example multimedia services. The first service mixes multiple audio streams into a single stream to enable lightweight voice communication in a Networked Virtual Environment. The second service applies face detection on a video stream to generate meaningful avatars in a meeting system called iConnect. The experimental results produced by these two services clearly demonstrate that our overlay network is capable of providing valuable services for a wide range of networked multimedia applications.
Anycasting was introduced to facilitate efficient communication between distributed Internet services and their clients, as it allows client requests to be automatically routed to nearby service instances. However, even though several any-cast implementations have been proposed, their various limitations prevent them from being widely adopted by large-scale distributed systems.This paper identifies the key limitations of existing anycast implementations, and proposes how to implement anycast such that all these limitations are addressed without harming the performance of anycast communication. Our solution relies on address-translation capabilities present in modern operating systems. These capabilities have originally been designed for communication with mobile nodes. However, we demonstrate that one can exploit them to implement versatile anycasting at low cost.
In this paper we present MeshCast, a peer-to-peer (p2p) multicast protocol for applications requiring high bandwidth (such as live video streaming) from a server to a large number of receivers. Traditional tree-based approaches to overlay multicast inefficiently utilise the outgoing bandwidth of participating nodes and poorly adapt to node membership churn. In contrast, MeshCast is based on Chainsaw mesh-based approach to data delivery that better utilises bandwidth and provides excellent adaptation properties. In this paper we identify properties that enable mesh-based overlay multicast protocols to better utilise the available bandwidth and consequently support higher data stream rates in heterogeneous environments. MeshCast uses a gossip-based algorithm to adapt the overlay to peer heterogeneity, while still preserving the advantages of a mesh-based overlay. Our experiments show that MeshCast can support 68% higher stream rates and provides a 22% improvement in buffering delay over the recently proposed Chainsaw protocol for a heterogeneous node bandwidth distribution.
User experience of Web browsing on a mobile device is affected by low bandwidth, low CPU performance and small screen. This is not an essential technical restriction, as some help can be provided by running the browser engine on the server side instead of the mobile client. The approach of Tut-Mobi system introduced in this paper is such that the server side component residing in the fixed network processes the page to a format that consists of page miniature and page element data. Using this method, it is possible to save up to 90 percent of bandwidth, which makes navigating the web pages a considerably faster. This allows practical browsing of complex web pages even with a mobile device. Moreover, user experience is better, because the original layout of the page is saved which makes it easy to browse familiar sites.
This paper describes an infrastructure for the deployment and use of Web Services that are resilient to the failure of the nodes that host those services. The infrastructure presents a single interface that provides mechanisms for users to publish services and to find hosted services. The infrastructure supports the autonomic deployment of services and the brokerage of hosts on which services may be deployed. Once deployed, services are autonomically managed in a number of aspects including load balancing, availability, failure detection and recovery, and lifetime management. Services are published and deployed with associated metadata describing the service type. This same metadata may be used subsequently by interested parties to discover services. The infrastructure uses peer-to-peer (P2P) overlay technologies to abstract over the underlying network to deploy and locate instances of those services. It takes advantage of the P2P network to replicate directory services used to locate service instances (for using a service), Service Hosts (for deployment of services) and Autonomic Managers which manage the deployed services. The P2P overlay network is itself constructed using novel Web services-based middleware and a variation of the Chord P2P protocol, which is self-managing.
