20 research outputs found
Scanless Fast Handoff Technique Based on Global Path Cache for WLANs
Wireless LANs (WLANs) have been widely adopted and are more convenient as they are inter-connected as wireless campus networks and wireless mesh networks. However, timesensitive multimedia applications, which have become more popular, could suffer from long end-to-end latency in WLANs.This is due mainly to handoff delay, which in turn is caused by channel scanning. This paper proposes a technique called Global Path-Cache (GPC) that provides fast handoffs in WLANs.GPC properly captures the dynamic behavior of the network andMSs, and provides accurate next AP predictions to minimize the handoff latency. Moreover, the handoff frequencies are treated as time-series data, thus GPC calibrates the prediction models based on short term and periodic behaviors of mobile users. Our simulation study shows that GPC virtually eliminates the need to scan for APs during handoffs and results in much better overall handoff delay compared to existing methods
Controlo de mobilidade com segurança em redes estruturadas 802.11
Mestrado em Engenharia ElectrĂłnica e TelecomunicaçÔesEsta dissertação aborda o problema da gestĂŁo da mobilidade com segurança em redes 802.11. Assim, começa por apresentar um estudo detalhado do protocolo 802.11, do handoff de dispositivos mĂłveis entre pontos de acesso e de soluçÔes apresentadas por diversos autores com o objectivo de reduzir o tempo dispendido neste processo, com e sem segurança associada. Seguidamente, sĂŁo apresentadas mĂ©tricas e atributos de rede que podem ser considerados no estabelecimento de polĂticas de mobilidade que gerem as transiçÔes de AP que cada dispositivo mĂłvel efectua. Uma vez feito este estudo inicial, Ă© apresentada uma solução que potencĂa handoffs rĂĄpidos e seguros em redes estruturadas 802.11 e que minimiza o tempo da sua preparação. Este novo protocolo representa uma evolução do trabalho desenvolvido por Rodolphe Marques no trabalho intitulado âSegurança e Mobilidade em Redes Estruturadas 802.11â referenciado em [1]; a sua novidade consiste em usar tramas 802.11 de reconhecimento da rede (Probe Request/Response) para difundir associaçÔes de segurança com os pontos de acesso ao alcance de cada dispositivo mĂłvel. A nova abordagem implica mudanças reduzidas na arquitectura de rede considerada em [1] e permite que, no Ăąmbito das operaçÔes de reconhecimento de pontos de acesso, que sĂŁo comuns e necessĂĄrias, um equipamento mĂłvel instale paralelamente associaçÔes de segurança nos APs que poderĂĄ vir a usar num futuro prĂłximo, ou seja, todos os que estĂŁo ao seu alcance.
ABSTRACT: This thesis handles the problem of mobility management with security in 802.11 networks. Therefore it begins by presenting a detailed study of the 802.11 protocol, the handoff process of roaming mobile nodes between access points and solutions presented by many authors with the common goal of reducing the time spent in this process, with and without associated security. After this we present metrics and attributes of the network that may be considered on the establishment of mobility policies that handle the AP transitions made by every mobile node. Once finished this initial study we present a solution that enhances fast and secure handoffs in structured 802.11 networks and minimizes the time spent in its setting. This new protocol represents an evolution on the work developed by the author Rodolphe Marques in his work named âSecurity and Mobility in 802.11 Structured Networksâ referred in [1]; its new feature consists in using 802.11 network scanning frames (Probe Request/Response) to distribute security associations to all access points in range of each mobile node. This new approach implies some changes on the architecture proposed in [1] and allows a mobile node to install security associations simultaneously while browsing the neighborhood for access points that may be used in a near future
SIGMA: A mobility architecture for terrestrial and space networks.
Internet Protocol (IP) mobility can be handled at different layers of the protocol stack. Mobile IP has been developed to handle mobility of Internet hosts at the network layer. Mobile IP suffers from a number of drawbacks such as the requirement for infrastructure change, high handover latency, high packet loss rate, and conflict with network security solutions. As an alternative solution, a few transport layer mobility protocols have been proposed in the context of Transmission Control Protocol (TCP), for example, MSOCKS and TCP connection migration. In this dissertation, a S&barbelow; eamless I&barbelow; P-diversity-based G&barbelow; eneralized M&barbelow; obility Architecture (SIGMA) is described. SIGMA works at the transport layer and utilizes IP diversity to achieve seamless handover, and is designed to solve many of the drawbacks of Mobile IP. It can also cooperate with normal IPv4 or IPv6 infrastructure without the support of Mobile IP. The handover performance, signaling cost, and survivability issues of SIGMA are evaluated and compared with those of Mobile IP. A hierarchical location management scheme for SIGMA is developed to reduce the signaling cost of SIGMA, which is also useful to other transport layer mobility solutions. SIGMA is shown to be also applicable to managing satellite handovers in space. Finally, the interoperability between SIGMA and existing Internet security mechanisms is discussed
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Application priority framework for fixed mobile converged communication networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The current prospects in wired and wireless access networks, it is becoming increasingly important to address potential convergence in order to offer integrated broadband services. These systems will need to offer higher data transmission capacities and long battery life, which is the catalyst for an everincreasing variety of air interface technologies targeting local area to wide area connectivity. Current integrated industrial networks do not offer application aware context delivery and enhanced services for optimised networks. Application aware services provide value-added functionality to business applications by capturing, integrating, and consolidating intelligence about users and their endpoint devices from various points in the network. This thesis mainly intends to resolve the issues related to ubiquitous application aware service, fair allocation of radio access, reduced energy consumption and improved capacity. A technique that measures and evaluates the data rate demand to reduce application response time and queuing delay for multi radio interfaces is proposed. The technique overcomes the challenges of network integration, requiring no user intervention, saving battery life and selecting the radio access connection for the application requested by the end user. This study is split in two parts. The first contribution identifies some constraints of the services towards the application layer in terms of e.g. data rate and signal strength. The objectives are achieved by application controlled handover (ACH) mechanism in order to maintain acceptable data rate for real-time application services. It also looks into the impact of the radio link on the application and identifies elements and parameters like wireless link quality and handover that will influence the application type. It also identifies some enhanced traditional mechanisms such as distance controlled multihop and mesh topology required in order to support energy efficient multimedia applications. The second contribution unfolds an intelligent application priority assignment mechanism (IAPAM) for medical applications using wireless sensor networks. IAPAM proposes and evaluates a technique based on prioritising multiple virtual queues for the critical nature of medical data to improve instant transmission. Various mobility patterns (directed, controlled and random waypoint) has been investigated and compared by simulating IAPAM enabled mobile BWSN. The following topics have been studied, modelled, simulated and discussed in this thesis: 1. Application Controlled Handover (ACH) for multi radios over fibre 2. Power Controlled Scheme for mesh multi radios over fibre using ACH 3. IAPAM for Biomedical Wireless Sensor Networks (BWSN) and impact of mobility over IAPAM enabled BWSN. Extensive simulation studies are performed to analyze and to evaluate the proposed techniques. Simulation results demonstrate significant improvements in multi radios over fibre performance in terms of application response delay and power consumption by upto 75% and 15 % respectively, reduction in traffic loss by upto 53% and reduction in delay for real time application by more than 25% in some cases
Improving TCP Performance in the Mobile, High Speed, Heterogeneous and Evolving Internet
Ph.DDOCTOR OF PHILOSOPH
Cross-layer Assisted TCP Algorithms for Vertical Handoff
The ever expanding growth of the wireless access to the Internet in recent years has led to the proliferation of wireless and mobile devices to connect to the Internet. This has created the possibility of mobile devices equipped with multiple radio interfaces to connect to the Internet using any of several wireless access network technologies such as GPRS, WLAN and WiMAX in order to get the connectivity best suited for the application. These access networks are highly heterogeneous and they vary widely in their characteristics such as bandwidth, propagation delay and geographical coverage. The mechanism by which a mobile device switches between these access networks during an ongoing connection is referred to as vertical handoff and it often results in an abrupt and significant change in the access link characteristics. The most common Internet applications such as Web browsing and e-mail make use of the Transmission Control Protocol (TCP) as their transport protocol and the behaviour of TCP depends on the end-to-end path characteristics such as bandwidth and round-trip time (RTT). As the wireless access link is most likely the bottleneck of a TCP end-to-end path, the abrupt changes in the link characteristics due to a vertical handoff may affect TCP behaviour adversely degrading the performance of the application.
The focus of this thesis is to study the effect of a vertical handoff on TCP behaviour and to propose algorithms that improve the handoff behaviour of TCP using cross-layer information about the changes in the access link characteristics. We begin this study by identifying the various problems of TCP due to a vertical handoff based on extensive simulation experiments. We use this study as a basis to develop cross-layer assisted TCP algorithms in handoff scenarios involving GPRS and WLAN access networks. We then extend the scope of the study by developing cross-layer assisted TCP algorithms in a broader context applicable to a wide range of bandwidth and delay changes during a handoff. And finally, the algorithms developed here are shown to be easily extendable to the multiple-TCP flow scenario. We evaluate the proposed algorithms by comparison with standard TCP (TCP SACK) and show that the proposed algorithms are effective in improving TCP behavior in vertical handoff involving a wide range of bandwidth and delay of the access networks. Our algorithms are easy to implement in real systems and they involve modifications to the TCP sender algorithm only. The proposed algorithms are conservative in nature and they do not adversely affect the performance of TCP in the absence of cross-layer information.KÀytÀmme enenevissÀ mÀÀrin kannettavia pÀÀtelaitteita (esim. matkapuhelin, kannettava tietokone) erilaisiin sovelluksiin kuten sÀhköpostin lukemiseen, verkon selaamiseen, musiikin lataamiseen ja kuuntelemiseen, pelien pelaamiseen ja laskujen maksamiseen riippumatta olinpaikastamme tai liikkuvuudestamme. Pystymme yhdistÀmÀÀn laitteemme Internetiin milloin tahansa missÀ tahansa.
Langattomat verkot, jotka mahdollistavat laitteen kytkemisen Internetiin radion kautta kÀyttÀvÀt moninaisia teknologioita ja eroavat laajalti ominaisuuksiltaan. Esimerkiksi langaton lÀhiverkko (WLAN), jota voidaan kÀyttÀÀ rakennuksen sisÀllÀ, on matkapuhelinverkkoa (esim. GPRS) nopeampi verkko, kun taas GPRS-kenttÀ voi ulottua kokonaisen kaupungin tai maan alueelle ja laajemmallekin. Kannettava pÀÀtelaite, jossa on monia radioliittymiÀ, voi siirtyÀ kÀyttÀmÀÀn mitÀ tahansa monista saatavilla olevistaverkoista riippuen olinpaikasta tai kÀytettÀvÀn sovelluksen tarpeista. Verkonvaihto viittaa tÀhÀn verkosta toiseen siirtymiseen, ja se tunnetaan vertikaalisena verkonvaihtona, kun siirtymisen kohteena olevien verkkojen teknologia eroaa toisistaan.
TCP on tietoliikenneohjelmisto, jota sekÀ tiedon lÀhettÀjÀ ettÀ vastaanottaja kÀyttÀvÀt kuljettamaan sovelluksen tiedon luotettavasti. TCP sÀÀtelee tiedon lÀhetysnopeutta riippuen Internetin resurssien saatavuudesta. TCP:n kÀyttÀytyminen riippuu pÀÀstÀ-pÀÀhÀn polun ominaisuuksista ja erityisesti pullonkaulayhteydestÀ, siitÀ yhteydestÀ, jolla on minimikapasiteetti polulla. Langaton yhteys, joka yhdistÀÀ kannettavan laitteen Internetiin on usein pullonkaulayhteys, ja Àkillinen muutos sen ominaisuuksissa vertikaalisen siirtymÀn aikana vaikuttaa merkittÀvÀsti TCP:n suorituskykyyn ja siten koko sovelluksen laatuun.
TÀmÀ työssÀ on keskitytty tutkimaan TCP:n toimintaa vertikaalisessa verkonvaihdon yhteydessÀ ja suunnittelemaan algoritmeja, jotka parantavat sen suorituskykyÀ vertikaalisen verkonvaihdon yhteydessÀ. Suunnitellut algoritmit kÀyttÀvÀt hyvÀksi tietoa vertikaaliseen verkonvaihtoon liittyvien langattomien yhteyksien ominaisuuksista. EnsimmÀinen tapaustutkimuskohde liittyy WLAN-GPRS -ympÀristöön, jossa TCP saa minimimÀÀrÀn tietoa verkonvaihtoon liittyen. Tulokset nÀyttÀvÀt, ettÀ TCP:n suorituskykyÀ voidaan parantaa huomattavasti. Tutkimusta on laajennettu kattamaan verkonvaihto yleisemmÀssÀ tapauksessa kÀyttÀen karkeita arvioita ko. verkkojen ominaisuuksista. Kehitettyjen algoritmien toiminnallisuus on evaluoitu simulaatiokokeilla kattaen laajan joukon ominaisuuksiltaan erilaisia verkkoja. Tulokset osoittavat, ettÀ TCP-suorituskykyÀ voidaan parantaa vertikaalisen verkonvaihdon yhteydessÀ huomattavasti tÀtÀ lÀhestymistapaa kÀyttÀen. Kehitetyt algoritmit voivat olla hyödyksi etsiessÀmme ratkaisuja kannettavien laitteiden todellisen kÀytön tarpeisiin