An optimized QoS scheme for IMS-NEMO in heterogeneous networks

The network mobility (NEMO) is proposed to support the mobility management when users move as a whole. In IP Multimedia Subsystem (IMS), the individual Quality of Service (QoS) control for NEMO results in excessive signaling cost. On the other hand, current QoS schemes have two drawbacks: unawareness of the heterogeneous wireless environment and inefficient utilization of the reserved bandwidth. To solve these problems, we present a novel heterogeneous bandwidth sharing (HBS) scheme for QoS provision under IMS-based NEMO (IMS-NEMO). The HBS scheme selects the most suitable access network for each session and enables the new coming non-real-time sessions to share bandwidth with the Variable Bit Rate (VBR) coded media flows. The modeling and simulation results demonstrate that the HBS can satisfy users' QoS requirement and obtain a more efficient use of the scarce wireless bandwidth

Measurement and Optimization of LTE Performance

4G Long Term Evolution (LTE) mobile system is the fourth generation communication system adopted worldwide to provide high-speed data connections and high-quality voice calls. Given the recent deployment by mobile service providers, unlike GSM and UMTS, LTE can be still considered to be in its early stages and therefore many topics still raise great interest among the international scientific research community: network performance assessment, network optimization, selective scheduling, interference management and coexistence with other communication systems in the unlicensed band, methods to evaluate human exposure to electromagnetic radiation are, as a matter of fact, still open issues. In this work techniques adopted to increase LTE radio performances are investigated. One of the most wide-spread solutions proposed by the standard is to implement MIMO techniques and within a few years, to overcome the scarcity of spectrum, LTE network operators will offload data traffic by accessing the unlicensed 5 GHz frequency. Our Research deals with an evaluation of 3GPP standard in a real test best scenario to evaluate network behavior and performance

Connection Robustness for Wireless Moving Networks Using Transport Layer Multi-homing

Given any form of mobility management through wireless communication, one useful enhancement is improving the reliability and robustness of transport-layer connections in a heterogeneous mobile environment. This is particularly true in the case of mobile networks with multiple vertical handovers. In this thesis, issues and challenges in mobility management for mobile terminals in such a scenario are addressed, and a number of techniques to facilitate and improve efficiency and the QoS for such a handover are proposed and investigated. These are initially considered in an end-to-end context and all protocols and changes happened in the middleware of the connection where the network is involved with handover issues and end user transparency is satisfied. This thesis begins by investigating mobility management solutions particularly the transport layer models, also making significant observation pertinent to multi-homing for moving networks in general. A new scheme for transport layer tunnelling based on SCTP is proposed. Consequently a novel protocol to handle seamless network mobility in heterogeneous mobile networks, named nSCTP, is proposed. Efficiency of this protocol in relation to QoS for handover parameters in an end-to-end connection while wired and wireless networks are available is considered. Analytically and experimentally it has been proved that this new scheme can significantly increase the throughput, particularly when the mobile networks roam frequently. The detailed plan for the future improvements and expansion is also provided

A usage oriented analysis of vehicular networks: from technologies to applications

The research world is paying a lot of attention on vehicular networks nowadays. Novel vehicular services need a suitable communication channel in order to extend in-car capabilities and, generally, be aware about surrounding events. Such networks, however, present some special features, such as high mobility or specific topologies. These properties affect the performance of applications, and more effort should be directed to identify the necessities of the network. Few works deal with application requirements which should be considered when the vehicular network is designed. In this paper, we fill the gap, and propose an analysis of application requirements considering available technologies for the lower and network layer. This study contains key factors which must be taken into account not only at the designing stage of the vehicular services, but also when applications are evaluated.The authors would like to thank the Spanish Ministerio the Educación y Ciencia for sponsoring the research activities under the grant AP2005-1437, in frames of the FPU program

Design of interface selection protocols for multi-homed wireless networks

This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University on 10 December 2010.The IEEE 802.11/802.16 standards conformant wireless communication stations have multi-homing transmission capability. To achieve greater communication efficiency, multi-homing capable stations use handover mechanism to select appropriate transmission channel according to variations in the channel quality. This thesis presents three internal-linked handover schemes, (1) Interface Selection Protocol (ISP), belonging to Wireless Local Area Network (WLAN)- Worldwide Interoperability for Microwave Access (WiMAX) environment (2) Fast Channel Scanning (FCS) and (3) Traffic Manager (TM), (2) and (3) belonging to WiMAX Environment. The proposed schemes in this thesis use a novel mechanism of providing a reliable communication route. This solution is based on a cross-layer communication framework, where the interface selection module uses various network related parameters from Medium Access Control (MAC) sub-layer/Physical Layer (PHY) across the protocol suite for decision making at the Network layer. The proposed solutions are highly responsive when compared with existing multi-homed schemes; responsiveness is one of the key factors in the design of such protocols. Selected route under these schemes is based on the most up to date link-layer information. Therefore, such a route is not only reliable in terms of route optimization but it also fulfils the application demands in terms of throughput and delay. Design of ISP protocol use probing frames during the route discovery process. The 802.11 mandates the use of different rates for data transmission frames. The ISP-metric can be incorporated into various routing aspects and its applicability is determined by the possibility of provision of MAC dependent parameters that are used to determine the best path metric values. In many cases, higher device density, interference and mobility cause variable medium access delays. It causes creation of ‘unreachable zones’, where destination is marked as unreachable. However, by use of the best path metric, the destination has been made reachable, anytime and anywhere, because of the intelligent use of the probing frames and interface selection algorithm implemented. The IEEE 802.16e introduces several MAC level queues for different access categories, maintaining service requirement within these queues; which imply that frames from a higher priority queue, i.e. video frames, are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result, these factors are not considered which result in channel performance degradation. To meet such challenges, the thesis presents FCS and TM schemes for WiMAX. For FCS, Its solution is to improve the mobile WiMAX handover and address the scanning latency. Since minimum scanning time is the most important issue in the handover process. This handover scheme aims to utilize the channel efficiently and apply such a procedure to reduce the time it takes to scan the neighboring access stations. TM uses MAC and physical layer (PHY) specific information in the interface metric and maintains a separate path to destination by applying an alternative interface operation. Simulation tests and comparisons with existing multi-homed protocols and handover schemes demonstrate the effectiveness of incorporating the medium dependent parameters. Moreover, show that suggested schemes, have shown better performance in terms of end-to-end delay and throughput, with efficiency up to 40% in specific test scenarios

Descubrimiento dinámico de servidores basado en información de localización usando una tabla de Hash distribuida balanceada

The current Internet includes a large number of distributed services. In order to guarantee the QoS of the communications in these services, a client has to select a close-by server with enough available resources. To achieve this objective, in this Thesis, we propose a simple and practical solution for Dynamic and Location Aware Server Discovery based on a Distributed Hash Table (DHT). Specifically, we decide to use a Chord DHT system (although any other DHT scheme can be used). In more detail, the solution works as follows. The servers offering a given service S form a Chord-like DHT. In addition, they register their location (topological and/or geographical) information in the DHT. Each client using the service S is connected to at least one server from the DHT. Eventually, a given client C realizes that it is connected to a server providing a bad QoS, then, it queries the DHT in order to find an appropriate server (i.e. a close-by server with enough available resources). We define 11 design criteria, and compare our solution to the Related Work based on them. We show that our solution is the most complete one. Furthermore, we validate the performance of our solution in two different scenarios: (i) NAT Traversal Server Discovery and (ii) Home Agent Discovery in Mobile IP scenarios. The former serves to validate our solution in a highly dynamic environment whereas the latter demonstrates the appropriateness of our solution in more classical environments where the servers are typically always-on hosts. The extra overhead suffered from the servers involved in our system comes from their participation in the Chord DHT. Therefore, it is critical to fairly balance the load among all the servers. In our system as well as in other P2P systems (e.g. P2PSIP) the stored objects are small, then routing dominates the cost of publishing and retrieving objects. Therefore, in the second part of this Thesis, we address the issue of fairly balancing the routing load in Chord DHTs. We present an analytical model to evaluate the routing fairness of Chord based on the well accepted Jain’s Fairness Index (FI). Our model shows that Chord performs poorly. Following this observation, we propose a simple enhancement to the Chord finger selection algorithm with the goal of mitigating this effect. The key advantage of our proposal as compared to previous approaches is that it adds a neglible overhead to the basic Chord algorithm. We validate the goodness of the proposed solution analytically and by large scale simulations.-------------------------------------------------------------------------------------------------------------------------------------------------------------En los últimos años un gran número de servicios distribuídos han aparecido en Internet. Para garantizar la Calidad de Servicio de las comunicaciones en estos servicios sus clientes deben conectarse a un servidor cercano con suficientes recursos disponibles. Para alcanzar este objetivo, en esta Tesis, se propone una solución simple y práctica para el Descubrimiento Dinámico de Servidores basado en Información de Localizació usando una Tabla de Hash Distribuída (DHT). En concreto, hemos decidido usar una DHT de tipo Chord (aunque cualquier otro tipo de DHT puede usarse). A continuación describimos brevemente nuestra solución. Los servidores que ofrecen un servicio específico S forman una DHT tipo Chord donde registran su información de localización (topológica y/o geográfica). Cada cliente que usa el servicio S está conectado al menos a un servidor de la DHT. En caso de que un cliente C perciba que el servidor al que está conectado está ofreciendo una mala Calidad de Servicio, C consulta la DHT para encontrar un servidor más apropiado (p.ej. un servidor cercano con suficientes recursos disponibles). En la Tesis se definen 11 criterios de diseño y se compara nuestra solución con las soluciones existentes en base a ellos, demostrando que la nuestra es la solución más completa. Además, validamos el rendimiento de nuestra solución en dos escenarios diferentes: (i) Descubrimiento de Servidores para atravesar Traductores de Direcciones de Red (NATs) y (ii) Descubrimiento de Agentes Hogar (HAs) en escenarios de Movilidad IP. El primero sirve para validar el rendimiento de nuestra solución en escenarios altamente dinámicos mientras que el segundo demuestra la validez de la solución en un escenario más clásico donde los servidores son máquinas que están ininterrumpidamente funcionando. Los servidores involucrados en nuestro sistema sufren una sobrecarga debido a su participación en la DHT tipo Chord. Desafortunadamente, esta sobrecarga es inherente al sistema anteriormente descrito y no se puede eliminar. En cambio lo que sí podemos hacer es balancear la carga de la manera más justa posible entre todos los servidores. En nuestro sistema, al igual que en otros sistemas P2P (p.ej. P2PSIP) los objetos almacenados tienen un tamaño pequeño, produciendo que sea la tarea de enrutamiento la que domina el coste de publicar y obtener objetos. Por lo tanto, en la segunda parte de esta Tesis abordamos el reparto equilibrado de la carga de enrutamiento en DHTs tipo Chord. En primer lugar, definimos un modelo analítico para evaluar el reparto de la carga de enrutamiento entre los nodos que forman una DHT tipo Chord. Para ello nos basamos en una métrica aceptada por la comunidad investigadora como es el Jain’s Fairness Index (FI). El modelo resultante demuestra que Chord tiene un rendimiento pobre en el reparto justo de la carga de enrutamiento. Basándonos en esta observación proponemos una modificación simple al algoritmo de selección de punteros de Chord para mejorar el reparto de la carga de enrutamiento. La ventaja fundamental de nuestra solución en comparación con otras propuestas anteriores es que nuestra solución añade un coste despreciable al algoritmo básico de Chord. Finalmente, validamos el rendimiento de nuestra solución analíticamente y por medio de simulaciones a gran escala