• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 22
  • 2
  • 2
  • 2
  • 2
  • 1
  • Tagged with
  • 36
  • 36
  • 18
  • 15
  • 10
  • 9
  • 9
  • 8
  • 8
  • 8
  • 7
  • 7
  • 7
  • 7
  • 6
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Studying the Performance of Wireless Mesh Networks Using the HxH Transport Control Protocol

Larsen, Timothy Scott 09 February 2010 (has links) (PDF)
As the need to remain connected increases, more and more people are turning to wireless mesh networks because they reduce the need for network infrastructure. Unfortunately, TCP does not perform well in such networks. HxH, an alternate protocol, has shown great promise in simulations, but since it relies on exploiting passive feedback, real measurements are needed to determine how effective the protocol really is. This thesis uses a measurement study on a wireless mesh network to characterize the performance of the HxH protocol in real-world networks. Several aspects of the HxH protocol do in fact perform well on real networks, but the high rate of packet loss renders other aspects of the protocol ineffective.
22

SIPman : A penetration testing methodology for SIP and RTP

Wallgren, Elin, Willander, Christoffer January 2022 (has links)
Background. SIP and RTP are two protocols that are widely used, and they play an important role in VoIP services. VoIP is an integral part of many communication services, e.g., Microsoft Teams, Skype, Discord, and communications over cellular networks (VoLTE and VoWiFi). Since these technologies are so widely used, a high level of security is paramount. Objectives. The aim of this study is threefold: (1) To investigate if it is possible to create a penetration testing methodology for SIP and RTP, where the target group is penetration testers with no previous knowledge of these protocols. (2) To identify previously discovered vulnerabilities and attacks. (3) Due to the lack of domain experts, a methodology of this kind will hopefully help penetration testers without prior knowledge, easing them into a new work area. Further, the aim is to increase awareness of potential vulnerabilities in such systems. Methods. Through a literature review, threat modeling, and exploratory penetration testing on three different testbeds, several vulnerabilities and attacks were identified and validated. From the results, a methodology was compiled. For evaluation purposes, it was evaluated by a third party, who tested it on a testbed and gave feedback. Results. The results from our research show that SIP and RTP are susceptible to a wide array of different attacks even to this day. From our literature study, it was determined that most of these attacks have been known for a long time. Using exploratory penetration testing, we managed to verify most of these attacks on three different systems. Additionally, we discovered a few novel attacks that we did not find in previous research. Conclusions. Our literature study suggests that SIP and RTP based systems are relatively susceptible to multiple attacks. Something we also validated during the exploratory testing phase. We successfully executed multiple existing attacks and some new attacks on three different testbeds. The methodology received mostly positive feedback. The results show that many of the participants appreciated the simplicity and concrete model of the methodology. Due to the low number of participants in the evaluation, an improvement to the study and results would be to increase the population and also have multiple novice penetration testers test several different systems. An increase in the number of testbeds would also further support the results and help generalize the methodology. / Bakgrund. SIP och RTP  är två protokoll som är vitt använda och spelar en väldigt viktig roll i VoIP-tjänster. VoIP utgör en viktig del i många kommunikationstjänster, t.ex. Microsoft Teams, Skype och Discord, men även i kommunikation över mobilnätet (VoLTE och VoWiFi). Eftersom dessa teknologier används i så stor utsträckning, är säkerhet av största vikt. Syfte. Syftet med denna studie är trefaldig: (1) Undersöka om det är möjligt att utforma en penetration testningsmetod för SIP och RTP, för en målgrupp av penetrationstestare utan förkunskaper kring dessa protokoll. (2) Att identifiera sårbarheter och attacker från tidigare studier. (3) På grund av brist på kompentens inom området penetrationstestning och telekommunikation kan en sådan här metod förhoppningsvis hjälpa till att introducera penetrationstestare utan tidigare erfarenhet till det här specifika området. Ytterligare är också målet att att öka medvetheten när det kommer till sårbarheter i sådana system. Metod. Genom en literaturstudie, hotmodellering och utforskande penetrationstestning på tre olika testmiljöer har ett flertal sårbarheter och attacker identifieras och utförts. Från resultatet utformades en metod för penetrationstesning, som sedan evaluerades genom att en tredje part testade metoden och gav återkoppling som rör metodens format och struktur. Resultat. Resultaten från vår studie visar att SIP och RTP är sårbara för en rad olika attacker än idag. Resultaten från vår litteraturstudie visar att många av dessa attacker har varit kända under en lång tid. Vi lyckades verifiera de flesta av dessa attacker genom utforskande penetationstestning på tre olika system. Dessutom lyckades vi identifiera ett antal nya attacker som inte tidigare nämnts i forskning inom området. Slutsatser. Resultaten från vår litteraturstudie visar att system som använder sig av SIP och RTP är relativt sårbara för en mängd olika attacker. Detta bekräftades i den utforskande testningen, där ett flertal kända samt nya attacker utfördes framgångsrikt. Den interna evalueringen i studien visar på att metoden kan appliceras framgångsrikt på ett flertal olika system, med begränsningen att endast tre system testats. Resultaten från den externa evalueringen, där penetrationstestare blev tillfrågade att utvärdera och testa metoden visar att de hade en relativt positiv inställning till metoden. För att ytterligare underbygga detta påstående krävs en större population, både för testningen och utvärderingen. Det krävs också att en större mängd testmiljöer används för att kunna generalisera metoden.
23

Implementation of an Available Bit Rate Service for Satellite IP Networks using a Performance Enhancing Proxy

Reddy, Pavan K 29 April 2004 (has links)
The transport control protocol (TCP) is one of the most heavily used protocols on the Internet, offering a reliable, connection oriented transport service. However, the quality of service (QoS) provided by the TCP protocol deteriorates when it is used over satellite IP networks. With the increased usage of Internet applications by the military in remote geographical regions, there is an increased need to address some of the shortcomings of TCP performance in satellite IP networks. In this research we describe our efforts at designing and testing a performance enhancing proxy (PEP) that can be used improve the QoS provided by the TCP service in large latency networks. We also show how one can use such a proxy to create a new transport service similar to the Available Bit Rate (ABR) service provided by ATM networks without needing ATM infrastructure, this new service offers a connection oriented, reliable, best effort transport service with minimal queuing delay, jitter and throughput variation.
24

Analyse des performances et routage dans les constellations de nano-satellites : modèles et applications pour les régions éloignées / Performance analysis and routing in nanosatellite constellations : models and applications for remote regions

Burlacu, Maria-Mihaela 03 December 2010 (has links)
La réduction des budgets du domaine spatial et les missions scientifiques traditionnelles ayant des coûts et une complexité croissants a amené la communauté scientifique à se concentrer sur les petits satellites qui fournissent non seulement des résultats scientifiques de valeur, mais permettent aussi de nouvelles applications dans le domaine de la télédétection, de la surveillance environnementale et des télécommunications. De plus, le concept de vol en formation de petits satellites est une technologie-clé pour beaucoup de missions spatiales futures, en améliorant la capacité de survie et réduisant le coût des missions. Ce travail de recherche a un double but : la proposition de modèles innovants de constellations de nano-satellites et de nouvelles approches de routage pour les réseaux de nano-satellites. Cette thèse propose et analyse trois modèles de constellations de nano-satellites dénommés NanoDREAM, NanoiCE et NanoSPHERE, qui fournissent des services de télécommunications aux régions éloignées. Le modèle NanoDREAM est conçu pour le Désert Salar de Uyuni en Bolivie, une région qui détient 70% de la réserve mondiale de lithium. Le modèle NanoiCE est destiné aux Régions Polaires, pour satisfaire les besoins de télécommunications de la communauté scientifique. Le modèle NanoSPHERE est conçu pour fournir une couverture globale de la Terre pour un marché de télécommunications concurrentiel. De plus, nous avons proposé une architecture pour le segment terrestre basée sur la technologie sans fil. Cette architecture a été déployée sur la zone d'exploitation du Désert Salar de Uyuni. Ces modèles ont été développés analytiquement et mis ensuite en œuvre dans le simulateur SaVi afin d'identifier la meilleure constellation satisfaisant les requis de la mission en terme de couverture et en réduisant au minimum le nombre de nano-satellites de la constellation. […] / The growth in cost and complexity of traditional scientific missions along with the reduction in space budgets have determined space community to focus on small satellites that not only provide valuable scientific returns, but also allow completely new applications in remote sensing, environmental monitoring and communications. Furthermore, small satellite flying in formation is a key technology for many future space science missions, by improving mission survivability and reducing mission costs, and offering multi-mission capabilities, achieved through reconfiguration of formations.The main goal of this thesis is two-fold: proposing innovative nanosatellite constellation models andnew routing approaches for nanosatellite network telecommunications. Therefore, this research work proposes and analyzes three models of nanosatellite constellations, named NanoDREAM, NanoiCE, NanoSPHERE, that provide telecommunication services to remote regions of the Earth. NanoDREAM mode! is designed for Bolivia's Salar de Uyuni Desert, a region which detains 70% of the global lithium reserve. NanoiCE model is intended for Polar Regions, in order to meet the voice and data transfer needs of the entire Antarctic and Arctic scientific community. NanoSPHERE is aimed to provide global coverage in the context of a robust telecommunications market. Additionally, a ground segment architecture based on wireless technology and deployed over the exploitation area of Salar de Uyuni Desert was proposed. Moreover, two new methodologies were proposed: the first one is a method for estimating the number of nano-satellites needed to cover a specific region was, and the second one is a Markov modeling­ based method for evaluating the performance of nanosatellite constellations. [...]
25

Transport Services for Soft Real-Time Applications in IP Networks

Grinnemo, Karl-Johan January 2006 (has links)
In recent years, Internet and IP technologies have made inroads into almost every communication market ranging from best-effort services such as email and Web, to soft real-time applications such as VoIP, IPTV, and video. However, providing a transport service over IP that meets the timeliness and availability requirements of soft real-time applications has turned out to be a complex task. Although network solutions such as IntServ, DiffServ, MPLS, and VRRP have been suggested, these solutions many times fail to provide a transport service for soft real-time applications end to end. Additionally, they have so far only been modestly deployed. In light of this, this thesis considers transport protocols for soft real-time applications. Part I of the thesis focuses on the design and analysis of transport protocols for soft real-time multimedia applications with lax deadlines such as image-intensive Web applications. Many of these applications do not need a completely reliable transport service, and to this end Part I studies so-called partially reliable transport protocols, i.e., transport protocols that enable applications to explicitly trade reliability for improved timeliness. Specifically, Part I investigates the feasibility of designing retransmission-based, partially reliable transport protocols that are congestion aware and fair to competing traffic. Two transport protocols are presented in Part I, PRTP and PRTP-ECN, which are both extensions to TCP for partial reliability. Simulations and theoretical analysis suggest that these transport protocols could give a substantial improvement in throughput and jitter as compared to TCP. Additionally, the simulations indicate that PRTP-ECN is TCP friendly and fair against competing congestion-aware traffic such as TCP flows. Part I also presents a taxonomy for retransmission-based, partially reliable transport protocols. Part II of the thesis considers the Stream Control Transmission Protocol (SCTP), which was developed by the IETF to transfer telephony signaling traffic over IP. The main focus of Part II is on evaluating the SCTP failover mechanism. Through extensive experiments, it is suggested that in order to meet the availability requirements of telephony signaling, SCTP has to be configured much more aggressively than is currently recommended by IETF. Furthermore, ways to improve the transport service provided by SCTP, especially with regards to the failover mechanism, are suggested. Part II also studies the effects of Head-of-Line Blocking (HoLB) on SCTP transmission delays. HoLB occurs when packets in one flow block packets in another, independent, flow. The study suggests that the short-term effects of HoLB could be substantial, but that the long-term effects are marginal.
26

Reliable Real-time Video Communication In Wireless Sensor Networks

Ayran, Orhan 01 February 2007 (has links) (PDF)
Many wireless sensor network (WSN) applications require efficient multimedia communication capabilities. However, the existing communication protocols in the literature mainly aim to achieve energy efficiency and reliability objectives and do not address the multimedia communication challenges in WSN. In this thesis, comprehensive performance evaluation of the existing transport protocols is performed and it has been shown that the existing proposals achieve very poor performance in terms of large set of metrics such as packet delivery rate, end-to-end packet delay, bandwidth and energy efficiency, frame peak signal-to-noise ratio (PSNR), delay-bounded frame PSNR, frame delivery probability, frame end-to-end delay and jitter. Based on these results, an energy-efficient real-time and reliable video sensor communication protocol (VSCP) is introduced for WSN. VSCP estimates video quality perceived by sink using lost segments of video frames and aims to maintain the overall reliability at a given level with minimum energy expenditure. Source data rates are adjusted in a quality adaptable manner according to the network conditions and the overall reliability computed by sink. QSC (quality scalable coding) encoding technique is used to produce a nearly constant quality video at a given maximum data rate during adjustment of source data rates. Performance evaluations show that VSCP protocol significantly outperforms the existing proposals in terms of multimedia communication performance metrics in WSN.
27

Carrier ethernet network solutions: transport protocol and optical backplane design

Estevez, Claudio Ignacio 15 January 2010 (has links)
The Metro Ethernet network (MEN) expands the advantages of Ethernet to cover areas wider than LAN. MENs running Ethernet Services as specified by the Metro Ethernet Forum (MEF) are known as Carrier Ethernet Networks (CENs). CENs can cover not only metro areas, but it can expand to cover global areas by connecting multiple MENs. Next-generation CENs are expected to support 100 GbE. With arising technologies for Ultra Long-haul (ULH) networks the bandwidth bottleneck of CENs is shifting to other areas like the transport layer protocol (such as the Transport Control Protocol or TCP) and the chip-to-chip channel capacity found at the network edge, which in general has an electrical backplane. Traditional TCP is well known to have difficulties reaching the full available bandwidth, due to its inefficient AIMD mechanisms under a high-delay-bandwidth-product environment. At the network edge, network equipment with electrical backplanes poses many problems including inductive-capacitive effects that limit its bandwidth. These are the two main issues addressed in this work. To resolve the transport layer issue, this work proposes a transport protocol that fully utilizes the available bandwidth while preserving TCP-friendliness and providing QoS support that is compatible with Ethernet Services. It can guarantee throughputs above the Committed Information Rate (CIR), which is specified in the Service Level Agreement (SLA). To resolve the physical layer limitations, a novel optical coupling technique is examined to encourage the use of optical backplanes for network-edge and core technology. The proposed technique consists of aligning the normal of the laser emission plane, waveguide plane and the normal of the photodetector active region plane with the purpose of reducing optical power loss caused by common methods of light manipulation. By addressing the shortcomings of both Traditional TCP and electrical backplane technology the overall throughput can be significantly increased.
28

Towards a versatile transport protocol

Jourjon, Guillaume, Electrical Engineering & Telecommunications, Faculty of Engineering, UNSW January 2008 (has links)
This thesis presents three main contributions that aim to improve the transport layer of the current networking architecture. The transport layer is nowadays dominated by the use of TCP and its congestion control. Recently new congestion control mechanisms have been proposed. Among them, TCP Friendly Hate Control (TFRC) appears to be one of the most complete. Nevertheless this congestion control mechanism, as with TCP, does not take into account either the evolution of the network in terms of Quality of Service and mobility or the evolution of the applications. The first contribution of this thesis is a specialisation of TFRC congestion control to provide a QoS-aware Transport Protocol specifically designed to operate over QoS-enabled networks with bandwidth guarantee mechanisms. This protocol combines a QoS-aware congestion control, which takes into account network-level bandwidth reservations, with full ordered reliability mechanism to provide a transport service similar to TCP. As a result, we obtain the guaranteed throughput at the application level where TCP fails. This protocol is t he first transport protocol compliant with bandwidth guaranteed networks. At the same time the set of network services expands, new technologies have been proposed and deployed at the physical layer. These new technologies are mainly characterised by communications done without wire constraint and the mobility of the end-systems. Furthermore, these technologies are usually deployed on entities where the CPU power and memory storage are limited. The second contribution of this thesis is therefore to propose an adaptation of TFHC to these entities. This is accomplished with the proposition of a new sender-based version of TFHC. This version has been implemented, evaluated and its numerous contributions and advantages compare to usual TFHC version have been demonstrated. Finally, we proposed an optimisation of actual implementations of TFHC. This optimisation first consists in the proposition of an algorithm based on a numerical analysis of the equation used in TFHC and the use of the Newton's algorithm. We furthermore give a first step, with the introduction of a new framework for TFRC, in order to better understand TFHC behaviour and to optimise the computation of the packet loss rate according to loss probability distributions.
29

Rádiová přístupová síť mobilní sítě / Radio Access Network of a Cellular Network

Duda, Michal January 2016 (has links)
The aim of the work is the radio access network of mobile networks second, third and fourth generation. The main objective is a description of the radio access network of the second, third and fourth generation, their elements, interfaces and signaling procedures. The next part describes the emergency services and the architecture of the fourth generation mobile networks. The practical part is then devoted to identify actions needed to prepare radio access network to testing emergency services, identify actions needed to conversion of transport protocol fixed part of the radio access network from IPv4 to IPv6 and describe the intervention to radio access network to change the active segment of the core network.
30

Design and implementation of simulation tools, protocols and architectures to support service platforms on vehicular networks

Báguena Albaladejo, Miguel 18 July 2017 (has links)
Tesis por compendio / Products related with Intelligent Transportation Systems (ITS) are becoming a reality on our roads. All car manufacturers are starting to include Internet access in their vehicles and to integrate smartphones directly from the dashboard, but more and more services will be introduced in the near future. Connectivity through "vehicular networks" will become a cornerstone of every new proposal, and offering an adequate quality of service is obviously desirable. However, a lot of work is needed for vehicular networks to offer performances similar to those of the wired networks. Vehicular networks can be characterized by two main features: high variability due to mobility levels that can reach up to 250 kilometers per hour, and heterogeneity, being that various competing versions from different vendors have and will be released. Therefore, to make the deployment of efficient services possible, an extensive study must be carried out and adequate tools must be proposed and developed. This PhD thesis addresses the service deployment problem in these networks at three different levels: (i) the physical and link layer, showing an exhaustive analysis of the physical channel and models; (ii) the network layer, proposing a forwarding protocol for IP packets; and (iii) the transport layer, where protocols are proposed to improve data delivery. First of all, the two main wireless technologies used in vehicular networks where studied and modeled, namely the 802.11 family of standards, particularly 802.11p, and the cellular networks focusing on LTE. Since 802.11p is a quite mature standard, we defined (i) a propagation and attenuation model capable of replicating the transmission range and the fading behavior of real 802.11p devices, both in line-of-sight conditions and when obstructed by small obstacles, and (ii) a visibility model able to deal with large obstacles, such as buildings and houses, in a realistic manner. Additionally, we proposed a model based on high-level performance indicators (bandwidth and delay) for LTE, which makes application validation and evaluation easier. At the network layer, a hybrid protocol called AVE is proposed for packet forwarding by switching among a set of standard routing strategies. Depending on the specific scenario, AVE selects one out of four different routing solutions: a) two-hop direct delivery, b) Dynamic MANET On-demand (DYMO), c) greedy georouting, and d) store-carry-and-forward technique, to dynamically adapt its behavior to the specific situation. At the transport layer, we proposed a content delivery protocol for reliable and bidirectional unicast communication in lossy links that improves content delivery in situations where the wireless network is the bottleneck. It has been designed, validated, optimized, and its performance has been analyzed in terms of throughput and resource efficiency. Finally, at system level, we propose an edge-assisted computing model that allows reducing the response latency of several queries by placing a computing unit at the network edge. This way, traffic traversal through the Internet is avoided when not needed. This scheme could be used in both 802.11p and cellular networks, and in this thesis we decided to focus on its evaluation using LTE networks. The platform presented in this thesis combines all the individual efforts to create a single efficient platform. This new environment could be used by any provider to improve the quality of the user experience obtainable through the proposed vehicular network-based services. / Los productos relacionados con los Sistemas Inteligentes de Transporte (ITS) se están transformando en una realidad en nuestras carreteras. Todos los fabricantes de coches comienzan a incluir acceso a internet en sus vehículos y a facilitar su integración con los teléfonos móviles, pero más y más servicios se introducirán en el futuro. La conectividad usando las "redes vehiculares" se convertirá en la piedra angular de cada nueva propuesta, y ofrecer una calidad de servicio adecuada será, obviamente, deseable. Sin embargo, se necesita una gran cantidad de trabajo para que las redes vehiculares ofrezcan un rendimiento similar al de las redes cableadas. Las redes vehiculares quedan definidas por sus dos características básicas: alto dinamismo, pues los nodos pueden alcanzar una velocidad relativa de más de 250 km/h; y heterogeneidad, por la gran cantidad de propuestas diferentes que los fabricantes están lanzando al mercado. Por ello, para hacer posible el despliegue de servicios sobre ellas, se impone la necesidad de hacer un estudio en profundidad de este entorno, y deben de proponerse y desarrollarse las herramientas adecuadas. Esta tesis ataca la problemática del despliegue de servicios en estas redes a tres niveles diferentes: (i) el nivel físico y de enlace, mostrando varios análisis en profundidad del medio físico y modelos derivados para su simulación; (ii) el nivel de red, proponiendo un protocolo de difusión de la información para los paquetes IP; y (iii) el nivel de transporte, donde otros protocolos son propuestos para mejorar el rendimiento del transporte de datos. En primer lugar, se han estudiado y modelado las dos principales tecnologías inalámbricas que se utilizan para la comunicación en redes vehiculares, la rama de estándares 802.11, en concreto 802.11p; y la comunicación celular, en particular LTE. Dado que el estándar 802.11p es un estándar bastante maduro, nos centramos en crear (i) un modelo de propagación y atenuación capaz de replicar el rango de transmisión de dispositivos 802.11p reales, en condiciones de visión directa y obstrucción por pequeños obstáculos, y (ii) un modelo de visibilidad capaz de simular el efecto de grandes obstáculos, como son los edifcios, de una manera realista. Además, proponemos un modelo basado en indicadores de rendimiento de alto nivel (ancho de banda y retardo) para LTE, que facilita la validación y evaluación de aplicaciones. En el plano de red, se propone un protocolo híbrido, llamado AVE, para el encaminamiento y reenvío de paquetes usando un conjunto de estrategias estándar de enrutamiento. Dependiendo del escenario, AVE elige entre cuatro estrategias diferentes: a) entrega directa a dos saltos, b) Dynamic MANET On-demand (DYMO) c) georouting voraz, y d) una técnica store-carry-and- forward, para adaptar su comportamiento dinámicamente a cada situación. En el plano de transporte, se propone un protocolo bidireccional de distribución de contenidos en canales con pérdidas que mejora la entrega de contenidos en situaciones en las que la red es un cuello de botella, como las redes inalámbricas. Ha sido diseñado, validado, optimizado, y su rendimiento ha sido analizado en términos de productividad y eficiencia en la utilización de recursos. Finalmente, a nivel de sistema, proponemos un modelo de computación asistida que permite reducir la latencia en la respuesta a muchas consultas colocando una unidad de computación en el borde de la red, i.e., la red de acceso. Este esquema podría ser usado en redes basadas en 802.11p y en redes celulares, si bien en esta tesis decidimos centrarnos en su evaluación usando redes LTE. La plataforma presentada en esta tesis combina todos los esfuerzos individuales para crear una plataforma única y eficiente. Este nuevo entorno puede ser usado por cualquier proveedor para mejorar la calidad de la experiencia de usuario en los servicios desplegados sobre redes vehiculares. / Els productes relacionats amb els sistemes intel · ligents de transport (ITS) s'estan transformant en una realitat en les nostres carreteres. Tots els fabri- cants de cotxes comencen a incloure accés a internet en els vehicles i a facilitar- ne la integració amb els telèfons mòbils, però en el futur més i més serveis s'hi introduiran. La connectivitat usant les xarxes vehicular esdevindrà la pedra angular de cada nova proposta, i oferir una qualitat de servei adequada serà, òbviament, desitjable. No obstant això, es necessita una gran quantitat de treball perquè les xarxes vehiculars oferisquen un rendiment similar al de les xarxes cablejades. Les xarxes vehiculars queden definides per dues característiques bàsiques: alt dinamisme, ja que els nodes poden arribar a una velocitat relativa de més de 250 km/h; i heterogeneïtat, per la gran quantitat de propostes diferents que els fabricants estan llançant al mercat. Per això, per a fer possible el desplegament de serveis sobre aquestes xarxes, s'imposa la necessitat de fer un estudi en profunditat d'aquest entorn, i cal proposar i desenvolupar les eines adequades. Aquesta tesi ataca la problemàtica del desplegament de serveis en aquestes xarxes a tres nivells diferents: (i) el nivell físic i d'enllaç , mostrant diverses anàlisis en profunditat del medi físic i models derivats per simular-lo; (ii) el nivell de xarxa, proposant un protocol de difusió de la informació per als paquets IP; i (iii) el nivell de transport, on es proposen altres protocols per a millorar el rendiment del transport de dades. En primer lloc, s'han estudiat i modelat les dues principals tecnologies sense fils que s'utilitzen per a la comunicació en xarxes vehiculars, la branca d'estàndards 802.11, en concret 802.11p; i la comunicació cel · lular, en partic- ular LTE. Atès que l'estàndard 802.11p és un estàndard bastant madur, ens centrem a crear (i) un model de propagació i atenuació capaç de replicar el rang de transmissió de dispositius 802.11p reals, en condicions de visió directa i obstrucció per petits obstacles, i (ii) un model de visibilitat capaç de simular l'efecte de grans obstacles, com són els edificis, d'una manera realista. A més, proposem un model basat en indicadors de rendiment d'alt nivell (ample de banda i retard) per a LTE, que facilita la validació i l'avaluació d'aplicacions. En el pla de xarxa, es proposa un protocol híbrid, anomenat AVE, per a l'encaminament i el reenviament de paquets usant un conjunt d'estratègies estàndard d'encaminament. Depenent de l'escenari , AVE tria entre quatre estratègies diferents: a) lliurament directe a dos salts, b) Dynamic MANET On-demand (DYMO) c) georouting voraç, i d) una tècnica store-carry-and- forward, per a adaptar-ne el comportament dinàmicament a cada situació. En el pla de transport, es proposa un protocol bidireccional de distribució de continguts en canals amb pèrdues que millora el lliurament de continguts en situacions en què la xarxa és un coll de botella, com les xarxes sense fils. Ha sigut dissenyat, validat, optimitzat, i el seu rendiment ha sigut analitzat en termes de productivitat i eficiència en la utilització de recursos. Finalment, a nivell de sistema, proposem un model de computació assistida que permet reduir la latència en la resposta a moltes consultes col · locant una unitat de computació a la vora de la xarxa, és a dir, la xarxa d'accés. Aquest esquema podria ser usat en xarxes basades en 802.11p i en xarxes cel · lulars, si bé en aquesta tesi decidim centrar-nos en la seua avaluació usant xarxes LTE. La plataforma presentada en aquesta tesi combina tots els esforços indi- viduals per a crear una plataforma única i eficient. Aquest nou entorn pot ser usat per qualsevol proveïdor per a millorar la qualitat de l'experiència d'usuari en els serveis desplegats sobre xarxes vehiculars. / Báguena Albaladejo, M. (2017). Design and implementation of simulation tools, protocols and architectures to support service platforms on vehicular networks [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/85333 / Compendio

Page generated in 0.0656 seconds