Basic Service Set Research Articles

Acontecimientos adversos causados por medicamentos en pacientes ingresados en medicina interna

Objective Adverse drug events (ADE) are a public health problem, the dimension of which is difficult to quantify because it is under-reported. We have aimed to identify and describe the ADEs recorded in the minimum basic data set (MBDS) of the Internal Medicine Services during the years 2005–7. Patients and methods A cross-sectional study. Those episodes coded as such, according to the ICD-9-CM, in the discharge reports of all the patients hospitalized during 2005–07 in the entire Spanish territory, were selected. The sociodemographic variables, diagnostic categories and types of drugs, among others, were described and analyzed. Results Of the 1,567,659 discharges coded in the Minimum Basic Data Set" (MBDS), 96,607 ADEs were recorded in 86,880 episodes (5.55%). Of these 82.86% were not preventable and 17.14% were preventable. A total of 4.5% of the episodes recorded an adverse drug reaction (ADR). The ADE's were more frequent in women and the appearance of an ADR during admission was accompanied by an increase in the hospital stay. Conclusions The MBDS is a useful tool for the identification, quantification and analysis of the ADRs, however, it is limited by the low recording of the discharge reports.

A pure P2P synchronous collaborative system

This paper presents design and implementation of a collaborative system, called Decentralised Synchronous Collaboration (DSC), based on a pure P2P architecture without using any server at all. It relies on group agents located on peers' computers to coordinate group as well as peer management, and provides a message handler to deal with the correct message passing directly among group peers. DSC is implemented using JXTA technology that includes virtual JXTA networks, a set of standard protocols and basic services to let peers finding each other, forming groups, and exchanging messages across firewalls and Network Address Translators (NATs).

AMCLM: ADAPTIVE MULTI-SERVICES CROSS-LAYER MAC PROTOCOL FOR IEEE 802.11 NETWORKS

In wireless networks, the radio link vulnerability attributed to effects such as noise, interference, free-space loss, shadowing and multipath fading, must be considered. MAC protocols developed for these networks do not take into account these perturbations. It was shown, in the literature, that 802.11 suffers from what is called 'the 802.11 anomaly'. This anomaly concerns two aspects: all nodes throughput, in a 802.11 network, falls to the worst one of all nodes and the bandwidth will be divided by the number of the mobile nodes of the network. In order to improve the quality of service of a BSS (Basic Service Set) and to solve 802.11 anomaly, Cross-layer approaches are developed. These approaches are especially based on information given by the Physical layer. In this study we propose a new cross-layer scheme: AMCLM (Adaptive Multi-services Cross-Layer MAC). The goal of this protocol is to improve the Quality-of-Service (QoS) of Mobile Nodes (MNs) connected in a BSS by a temporary disassociation of the ones for which the SNR (Signal to Noise Ratio) is under a defined threshold. In this way, the network's throughput is improved. Our approach aims to improve global networks QoS by unselfishness decisions of nodes. In order to show the benefit of our method, a performance evaluation of this protocol has been made. We have built the discrete Markov Chain associated to the behavior of AMCLM protocol to analyze the throughput of mobile nodes connected to the BSS.

A capacity analysis framework for the IEEE 802.11e contention-based infrastructure basic service set

We propose a multimedia capacity analysis framework for the Enhanced Distributed Channel Access (EDCA) function of the IEEE 802.11e standard. Our analysis shows that the multimedia capacity of the EDCA function for each Access Category (AC) can accurately be estimated by appropriately weighing the service time predictions of a saturation model over different number of active stations. We propose a simple and generic cycle time model to derive the service time in saturation which we employ in the calculation of an accurate station- and AC-specific queue utilization ratio. Based on the estimated queue utilization ratio, we design a simple model-based admission control scheme. We show that the proposed call admission control algorithm maintains satisfactory user-perceived quality for coexisting voice and video connections in an infrastructure Basic Service Set (BSS) and does not present over-or under-admission problems of previously proposed models in the literature.

Multiservice unicast/multicast communications over IEEE 802.11e networks

Wireless communications are nowadays one of the most active research and development areas in telecommunications. The widespread use of wireless networks and the development of high-rate infrastructure are in turn enabling the introduction and deployment of many new end-user applications. During the past few years, the IEEE 802.11e (EDCA) standard has been working on defining the required QoS mechanisms to be incorporated into the IEEE 802.11 protocol architecture. However, recent studies have shown that EDCA performs poorly when the medium is highly loaded due to the high collision rate. Numerous proposals have been reported in the literature aiming to overcome this main drawback. However, EDCA and the proposed mechanisms continue to have a serious problem with a specific type of application: the multicast traffic. In EDCA (as in DCF) the multicast service is defined as an unreliable service, i.e., it does not include the use of ACK frames. Furthermore, different to the unicast service, the multicast service makes use of a single rate out of the various rates included in the Basic Service Set (BSS) defined by the IEEE 802.11 standard. This situation has led many researchers to design techniques aiming to improve the multicast transmission. In this paper, we analyze the inter-operability of two prominent multicast mechanisms recently reported by the authors and the channel access method defined by the IEEE 802.11e EDCA standard. We further consider the use of B-EDCA: an enhanced version of EDCA recently introduced by the authors. We carried a comparative performance evaluation of the aforementioned mechanisms when supporting unicast and multicast traffic. Our simulation results show the effectiveness of the enhanced protocol architectures when jointly supporting unicast and multicast traffic.

Kittyhawk: Enabling cooperation and competition in a global, shared computational system

Kittyhawk represents our vision for a Web-scale computational resource that can accommodate a significant fraction of the world's computation needs and enable various parties to compete and cooperate in the provisioning of services on a consolidated platform. In this paper, we explain both the vision and the system architecture that supports it. We demonstrate these ideas by way of a prototype implementation that uses the IBM Blue Gene®/P platform. In the Kittyhawk prototype, we define a set of basic services that enable the allocation and interconnection of computing resources. By using examples, we show how higher layers of services can be built by using our basic services and standard open-source software.

DOA and TOA Based Localization Services Protocol in IEEE 802.11 Networks

In this paper we introduce an innovative technique for localization services in IEEE 802.11 networks. We introduce a localization protocol that can make use of either Time Of Arrival or Direction Of Arrival measurements. The proposed architecture integrates the classical Basic Service Set topology with a set of Location Service Support nodes, that measure those parameters related to a pre-selected localization algorithm. A fast and accurate Time Of Arrival estimator, operating directly on the output of the OFDM demodulator, is also presented. The whole procedure has been designed with the intent of weaken the requirements on temporal synchronization among nodes, at the expenses of a small increase in the protocol overhead and a small accuracy loss.

Traffic scheduling mechanism based on graph theory for Power Saving mode of IEEE 802.11 distributed coordinator function

In IEEE 802.11 Power Saving (PS) mode specified for Independent Basic Service Set (IBSS), mobile stations announce their pending data packets within Announcement Traffic Indication Message (ATIM) window immediately after the reception of Time Synchronisation Function (TSF) beacon. This paper proposed modifications to the PS mode by transmitting the TSF beacon at the end of each ATIM window. Upon actively overhearing the traffic announcements, a mobile station can function as the centralised coordinator by piggyback transmission scheduling information within the beacon. Different traffic scheduling mechanisms are proposed that will ensure the data packets transmission to be contention-free and minimise the total time that mobile stations have to stay in the active state. The complexity and performance of the proposed algorithms are analysed using simulation and analytical method. The results show that the proposed algorithms improve the power efficiency and performance compared with original IEEE 802.11 protocol.

A cluster‐chain‐based context transfer mechanism for fast basic service set transition in the centralized wireless LAN architecture

AbstractThe emergence of centralized WLAN architectures is proposed to solve the problems of large scale deployment of WLANs. In the centralized WLAN, access point (AP) is split into two pieces: wireless termination point (WTP), and access controller (AC). An AC is the centralized controller for a large number of WTPs. A station (STA) has the demand to move from one WTP to another within the same extended service set (ESS). Such behavior is called a basic service set (BSS) transition. In this paper, we propose the cluster‐chain‐based context (C3T) mechanism with a cluster member selection (CMS) algorithm to reduce the BSS transition delay in the centralized WLAN architecture. The proposed mechanism can have lower signaling cost for context transfer and does not have the ping‐pong problem comparing with the existing context transfer schemes in terms of BSS transition, such as the proactive neighbor caching (PNC) scheme, the configuration and provisioning for wireless APs handoff protocol (CAPWAPHP), and so on. Furthermore, since the original 802.11r fast BSS transition does not specify how to work in the centralized WLAN architecture, we incorporate the C3T mechanism into IEEE 802.11r that works in the centralized WLAN architecture. Copyright © 2008 John Wiley & Sons, Ltd.

DelosDLMS

DelosDLMS is a novel digital library management system (DLMS) that has been developed as an integration effort within the DELOS Network of Excellence, a European Commission initiative funded under its fifth and sixth framework programs. In this paper, we describe DelosDLMS that takes into account the recommendations of several activities that were initiated by DELOS including the DELOS vision for digital libraries (DLs). A key aspect of DelosDLMS is its novel generic infrastructure that allows the generation of digital library systems out of a set of basic system services and DL services in a modular and extensible way. DL services like feature extraction, visualization, intelligent browsing, media-type-specific indexing, support for multilinguality, relevance feedback and many others can easily be incorporated or replaced. A further key aspect of DelosDLMS is its robustness against failures and its scalability for large collections and many parallel user requests. We discuss the current status of an effort to build DelosDLMS, a Digital Library Management System that integrates in various ways several components developed by DELOS members and showcases a great variety of functionality that is outlined as part of the DELOS vision.

On the 20/40 MHz Coexistence of Overlapping BSSs in WLANs

We investigate the impact of 20/40 MHz coexistence on the performance of wireless local area networks (WLANs). To that end, we present simulation results of overlapping basic service sets (BSSs), a 802.11n BSS operating in 20/40 MHz mode and a legacy BSS operating in 20 MHz mode, where the overlapping channel is the extension channel of the 20/40 MHz BSS. Our results show that if clear channel assessment (CCA) is not used in the overlapping channel, the throughput in legacy BSS is almost zero, while the throughput of 20/40 MHz BSS decreases drastically. If CCA is used in the overlapping channel, the throughput of legacy and 20/40 MHz BSSs increase dramatically compared to the case when no CCA is used. In addition, when stations (STAs)/AP that operate in 20/40 MHz BSS are able to dynamically switch between 20 MHz and 40 MHz transmit/receive modes and CCA is used in the extension channel, the throughput of both BSSs further increases. We also report the impact of 40 MHz operation on legacy BSS when the 20/40 MHz BSS employs IEEE 802.11e enhancements. In addition, the impact on the network performance of RTS/CTS protection mechanism for 40 MHz transmissions are also shown. Reducing transmission opportunity (TXOP) interval for 40 MHz transmissions also improves fairness and throughput for legacy BSSs.

End-to-end fair rate optimization in wired-cum-wireless networks

In this paper, we address the end-to-end rate optimization problem in a wired-cum-wireless network, where CSMA/CA based wireless LANs extend a wired backbone and provide access to mobile users. The objective is to achieve proportional fairness amongst the end-to-end sessions in the network. Since the network contains wireless links whose attainable throughput is a (non-convex and non-separable) function of MAC protocol parameters, the problem requires joint optimization at both the transport and the link layers. A dual-based algorithm is proposed in this paper to solve this cross-layer rate optimization problem. It is implemented in the distributed manner, and works at the link layer to adjust scheduling rates for the wireless links in the basic service sets, and at the transport layer to adjust end-to-end session rates. We prove rigorously that the proposed algorithm converges to the globally optimal rates. Simulation results are provided to support our conclusions.

A MIMO-Based Collision Mitigation Scheme in Uplink WLANs

Although there exist random backoff schemes in WLANs, a collision problem among stations (STAs) is one of the critical factors that degrade the performance of WLAN systems. To mitigate this collision problem, a MIMO-based uplink collision mitigation scheme is proposed by utilizing additional degrees of freedom through multiple antennas, and, consequently, enhances the system performance. Analysis and simulation results show that there is at least 30% throughput enhancement in a basic service set (BSS) with more than 10 STAs, compared to the performance of conventional WLANs in case of saturation traffic.

SELECT: Self-Learning Collision Avoidance for Wireless Networks

The limited number of orthogonal channels and autonomous installations of hot spots and home wireless networks often leave neighboring 802.11 basic service sets (BSSs) operating on the same or overlapping channels, therefore interfering with each other. However, the 802.11 medium access control (MAC) does not work well in resolving inter-BSS interference due to the well-known hidden/exposed-receiver problem, which has been haunting the research community for more than a decade. In this paper, we propose SELECT, an effective and efficient self-learning collision avoidance strategy to address the hidden/exposed-receiver problem in 802.11 wireless networks. SELECT is based on the observation that carrier sense with received signal strength (RSS) measurements at the sender and the receiver can be strongly correlated. A SELECT-enabled sender exploits such correlation using an automated online learning algorithm and makes an informed judgment of the channel availability at the intended receiver. SELECT achieves collision avoidance at packet-level time granularity, involves zero communication overhead, and easily integrates with the 802.11 distributed coordination function (DCF). Our evaluation in analysis, simulations, and prototype experiments show that SELECT addresses the hidden/exposed-receiver problem well. In typical hidden/exposed-receiver scenarios, SELECT improves the throughput by up to 140 percent and the channel access success ratio by up to 302 percent while almost completely eliminating contention-induced data packet drops.

Throughput Fairness in Infrastructure-Based IEEE 802.11 Mesh Networks

This paper studies throughput fairness among different basic service sets (BSSs) in infrastructure-based IEEE 802.11 mesh networks, where inter-BSS interference is unavoidable because of the difficulty in frequency and coverage planning and the limited number of nonoverlapping frequency channels that are available for IEEE networks. Two approaches are proposed to achieve fair throughput among the cochannel BSSs: 1) dynamic network allocation vectors (DNAVs), which dynamically adjust the cochannel interference by temporarily stopping transmissions in some BSSs using network allocation vectors (NAVs), and 2) forced handoffs (FHO), which force mobile stations to hand off between neighboring BSSs. An optimization problem is formulated as well as a distributed scheme is proposed for each of the approaches for achieving the required throughput fairness while keeping high transmission throughput in the BSSs. Our results show that 1) the DNAV scheme can always achieve the required throughput fairness; 2) the FHO scheme can achieve the required throughput fairness, provided that there is a sufficient overlapping coverage area between BSSs; and 3) the throughput performance of the proposed distributed schemes is very close to the corresponding optimized one.

Selecting transition process for WLAN security

AbstractIn wireless local area network (WLAN), a station (STA) accesses the Internet through an access point (AP). When switching from one AP to another, the STA executes the transition process, which may incur long delay and result in force‐termination for real‐time applications. The IEEE 802.11r proposes the fast basic service set (BSS) transition to speed up the transiti on process for a STA moving within the same mobility domain (MD). This scheme requires unique MD assignment so that the STA knows whether it should conduct fast BSS transition process (for intra‐MD scenario) or the expensive initial MD association process (for inter‐MD scenario). However, how to guarantee unique MD identifier (MDID) assignment is not mentioned in the specification. This paper proposes a mechanism for IEEE 802.11r fast transition without using MDID, and therefore eliminates the cost for MDID management. Copyright © 2007 John Wiley & Sons, Ltd.

Service-Oriented Architecture and Web 2.0

Consumers rely on the Internet for commerce, banking, email, instant messaging, and a variety of other daily tasks. This current evolution is often referred to as Web 2.0. In this paper service-oriented architecture (SOA) is presented as the important part of increasing software efficiency in Web 2.0 with a basic concept of providing a basic set of services that each application can access to provide this common functionality

MiPeG: A middleware infrastructure for pervasive grids

Grid computing and pervasive computing have affirmed respectively as the paradigm for high performance computing and the paradigm for user-friendly computing. The conjunction of such paradigms are now generating a new one: the Pervasive Grid Computing. This paper presents a middleware for pervasive grid applications. It consists of a set of basic services that aim to enhance classic grid environments with mechanisms for: (i) integrating mobile devices in a pervasive way; (ii) providing context-awareness; (iii) handling mobile users’ sessions; and, (iv) distributing and executing user tasks on the devices (even mobile) active in the environment.

A Service Oriented Architecture-based Approach for Interdomain Optical Network Services

This work presents a service-oriented architecture for interdomain service provisioning in optical networks. The architecture introduces a service layer that concentrates all the interactions among domains necessary for service provisioning. A service layer is an alternative to the GMPLS (Generalized Multiprotocol Label Switching) architecture, but without a rigid control plane as found in GMPLS. We start by defining a set of basic services to provide single end-to-end (e2e) interdomain connections. Then, more sophisticated services are created through the composition of these basic services. The interdomain Optical VPN (Virtual Private Network) service is considered in order to illustrate the composition of services. A prototype of the architecture was designed and implemented using Web services as the main technology. The architecture was evaluated in terms of speed, scalability, and bandwidth consumption necessary to establish e2e interdomain connections and Optical VPNs.

Improving IEEE 802.11 power saving mechanism

This paper presents an optimization of the power saving mechanism in the Distributed Coordination Function (DCF) in an Independent Basic Service Set (IBSS) of the IEEE 802.11 standard. In the power saving mode specified for DCF, time is divided into so-called beacon intervals. At the start of each beacon interval, each node in the power saving mode periodically wakes up for a duration called the ATIM Window. Nodes are required to be synchronized to ensure that all nodes wake up at the same time. During the ATIM window, the nodes exchange control packets to determine whether they need to stay awake for the rest of the beacon interval. The size of the ATIM window has a significant impact on energy saving and throughput achieved by the nodes. This paper proposes an adaptive mechanism to dynamically choose a suitable ATIM window size. We also allow the nodes to stay awake for only a fraction of the beacon interval following the ATIM window. On the other hand, the IEEE 802.11 DCF mode requires nodes to stay awake either for the entire beacon interval following the ATIM window or not at all. Simulation results showthat the proposed approach outperforms the IEEE 802.11 power saving mechanism in terms of throughput and the amount of energy consumed.