PACE: Simple Multi-hop Scheduling for Single-radio 802.11-based Stub Wireless Mesh Networks

IEEE 802.11-based Stub Wireless Mesh Networks (WMNs) are a cost-effective and flexible solution to extend wired network infrastructures. Yet, they suffer from two major problems: inefficiency and unfairness. A number of approaches have been proposed to tackle these problems, but they are too restrictive, highly complex, or require time synchronization and modifications to the IEEE 802.11 MAC. PACE is a simple multi-hop scheduling mechanism for Stub WMNs overlaid on the IEEE 802.11 MAC that jointly addresses the inefficiency and unfairness problems. It limits transmissions to a single mesh node at each time and ensures that each node has the opportunity to transmit a packet in each network-wide transmission round. Simulation results demonstrate that PACE can achieve optimal network capacity utilization and greatly outperforms state of the art CSMA/CA-based solutions as far as goodput, delay, and fairness are concerned

Contributions to the routing of traffic flows in multi-hop IEEE 802.11 wireless networks

The IEEE 802.11 standard was not initially designed to provide multi-hop capabilities. Therefore, providing a proper traffic performance in Multi-Hop IEEE 802.11 Wireless Networks (MIWNs) becomes a significant challenge. The approach followed in this thesis has been focused on the routing layer in order to obtain applicable solutions not dependent on a specific hardware or driver. Nevertheless, as is the case of most of the research on this field, a cross-layer design has been adopted. Therefore, one of the first tasks of this work was devoted to the study of the phenomena which affect the performance of the flows in MIWNs. Different estimation methodologies and models are presented and analyzed. The first main contribution of this thesis is related to route creation procedures. First, FB-AODV is introduced, which creates routes and forwards packets according to the flows on the contrary to basic AODV which is destination-based. This enhancement permits to balance the load through the network and gives a finer granularity in the control and monitoring of the flows. Results showed that it clearly benefits the performance of the flows. Secondly, a novel routing metric called Weighted Contention and Interference routing Metric (WCIM) is presented. In all analyzed scenarios, WCIM outperformed the other analyzed state-of-the-art routing metrics due to a proper leveraging of the number of hops, the link quality and the suffered contention and interference. The second main contribution of this thesis is focused on route maintenance. Generally, route recovery procedures are devoted to the detection of link breaks due to mobility or fading. However, other phenomena like the arrival of new flows can degrade the performance of active flows. DEMON, which is designed as an enhancement of FB-AODV, allows the preemptive recovery of degraded routes by passively monitoring the performance of active flows. Results showed that DEMON obtains similar or better results than other published solutions in mobile scenarios, while it clearly outperforms the performance of default AODV under congestion Finally, the last chapter of this thesis deals with channel assignment in multi-radio solutions. The main challenge of this research area relies on the circular relationship between channel assignment and routing; channel assignment determines the routes that can be created, while the created routes decide the real channel diversity of the network and the level of interference between the links. Therefore, proposals which join routing and channel assignment are generally complex, centralized and based on traffic patterns, limiting their practical implementation. On the contrary, the mechanisms presented in this thesis are distributed and readily applicable. First, the Interference-based Dynamic Channel Assignment (IDCA) algorithm is introduced. IDCA is a distributed and dynamic channel assignment based on the interference caused by active flows which uses a common channel in order to assure connectivity. In general, IDCA leads to an interesting trade-off between connectivity preservation and channel diversity. Secondly, MR-DEMON is introduced as way of joining channel assignment and route maintenance. As DEMON, MR-DEMON monitors the performance of the active flows traversing the links, but, instead of alerting the source when noticing degradation, it permits reallocating the flows to less interfered channels. Joining route recovery instead of route creation simplifies its application, since traffic patterns are not needed and channel reassignments can be locally decided. The evaluation of MR-DEMON proved that it clearly benefits the performance of IDCA. Also, it improves DEMON functionality by decreasing the number of route recoveries from the source, leading to a lower overhead.El estándar IEEE 802.11 no fue diseñado inicialmente para soportar capacidades multi-salto. Debido a ello, proveer unas prestaciones adecuadas a los flujos de tráfico que atraviesan redes inalámbricas multi-salto IEEE 802.11 supone un reto significativo. La investigación desarrollada en esta tesis se ha centrado en la capa de encaminamiento con el objetivo de obtener soluciones aplicables y no dependientes de un hardware específico. Sin embargo, debido al gran impacto de fenómenos y parámetros relacionados con las capas físicas y de acceso al medio sobre las prestaciones de los tráficos de datos, se han adoptado soluciones de tipo cross-layer. Es por ello que las primeras tareas de la investigación, presentadas en los capítulos iniciales, se dedicaron al estudio y caracterización de estos fenómenos. La primera contribución principal de esta tesis se centra en mecanismos relacionados con la creación de las rutas. Primero, se introduce una mejora del protocolo AODV, que permite crear rutas y encaminar paquetes en base a los flujos de datos, en lugar de en base a los destinos como se da en el caso básico. Esto permite balacear la carga de la red y otorga un mayor control sobre los flujos activos y sus prestaciones, mejorando el rendimiento general de la red. Seguidamente, se presenta una métrica de encaminamiento sensible a la interferencia de la red y la calidad de los enlaces. Los resultados analizados, basados en la simulación de diferentes escenarios, demuestran que mejora significativamente las prestaciones de otras métricas del estado del arte. La segunda contribución está relacionada con el mantenimiento de las rutas activas. Generalmente, los mecanismos de mantenimiento se centran principalmente en la detección de enlaces rotos debido a la movilidad de los nodos o a la propagación inalámbrica. Sin embargo, otros fenómenos como la interferencia y congestión provocada por la llegada de nuevos flujos pueden degradar de forma significativa las prestaciones de los tráficos activos. En base a ello, se diseña un mecanismo de mantenimiento preventivo de rutas, que monitoriza las prestaciones de los flujos activos y permite su reencaminamiento en caso de detectar rutas degradadas. La evaluación de esta solución muestra una mejora significativa sobre el mantenimiento de rutas básico en escenarios congestionados, mientras que en escenarios con nodos móviles obtiene resultados similares o puntualmente mejores que otros mecanismos preventivos diseñados específicamente para casos con movilidad. Finalmente, el último capítulo de la tesis se centra en la asignación de canales en entornos multi-canal y multi-radio con el objetivo de minimizar la interferencia entre flujos activos. El reto principal en este campo es la dependencia circular que se da entre la asignación de canales y la creación de rutas: la asignación de canales determina los enlaces existentes la red y por ello las rutas que se podrán crear, pero son finalmente las rutas y los tráficos activos quienes determinan el nivel real de interferencia que se dará en la red. Es por ello que las soluciones que proponen unificar la asignación de canales y el encaminamiento de tráficos son generalmente complejas, centralizadas y basadas en patrones de tráfico, lo que limita su implementación en entornos reales. En cambio, en nuestro caso adoptamos una solución distribuida y con mayor aplicabilidad. Primero, se define un algoritmo de selección de canales dinámico basado en la interferencia de los flujos activos, que utiliza un canal común en todos los nodos para asegurar la conectividad de la red. A continuación, se introduce un mecanismo que unifica la asignación de canales con el mantenimiento preventivo de las rutas, permitiendo reasignar flujos degradados a otros canales disponibles en lugar de reencaminarlos completamente. Ambas soluciones demuestran ser beneficiosas en este tipo de entornos.Postprint (published version

A Clean-Slate Architecture for Reliable Data Delivery in Wireless Mesh Networks

In this paper, we introduce a clean-slate architecture for improving the delivery of data packets in IEEE 802.11 wireless mesh networks. Opposed to the rigid TCP/IP layer architecture which exhibits serious deficiencies in such networks, we propose a unitary layer approach that combines both routing and transport functionalities in a single layer. The new Mesh Transmission Layer (MTL) incorporates cross-interacting routing and transport modules for a reliable data delivery based on the loss probabilities of wireless links. Due to the significant drawbacks of standard TCP over IEEE 802.11, we particularly focus on the transport module, proposing a pure rate-based approach for transmitting data packets according to the current contention in the network. By considering the IEEE 802.11 spatial reuse constraint and employing a novel acknowledgment scheme, the new transport module improves both goodput and fairness in wireless mesh networks. In a comparative performance study, we show that MTL achieves up to 48% more goodput and up to 100% less packet drops than TCP/IP, while maintaining excellent fairness results

Effects of physical channel separation on application flows in a multi-radio multi-hop wireless mesh network: An experimental study on BilMesh testbed

Cataloged from PDF version of article.In this paper, we introduce BilMesh, an indoor 802.11 b/g mesh networking testbed we established, and we report about our performance experiments conducted on multi-hop topologies with single-radio and multi-radio relay nodes. We investigate and report the effects of using multi-radio, multi-channel relay nodes in the mesh networking infrastructure in terms of network and application layer performance metrics. We also study the effects of physical channel separation on achievable end-to-end goodput perceived by the applications in the multi-radio case by varying the channel separation between the radio interfaces of a multi-radio relay node. We have observed that the difference between TCP and UDP goodput performances together with the delay and jitter performance depends on the hop count. We also observed that assigning overlapping channels with a central frequency separation of 5-15 MHz may render the CSMA mechanism used in 802.11 MAC ineffective and hence reduce the overall network performance. Finally, we provide some suggestions that can be considered while designing related protocols and algorithms to deal with the observed facts. (C) 2013 Elsevier Ltd. All rights reserved

ActMesh- A Cognitive Resource Management paradigm for dynamic mobile Internet Access with Reliability Guarantees

Wireless Mesh Networks (WMNs) are going increasing attention as a flexible low-cost networking architecture to provide media Internet access over metropolitan areas to mobile clients requiring multimedia services. In WMNs, Mesh Routers (MRs) from the mesh backbone and accomplish the twofold task of traffic forwarding, as well as providing multimedia access to mobile Mesh Clients (MCs). Due to the intensive bandwidth-resource requested for supporting QoS-demanding multimedia services, performance of the current WMNs is mainly limited by spectrum-crowding and traffic-congestion, as only scarce spectrum-resources is currently licensed for the MCs' access. In principle, this problem could be mitigated by exploiting in a media-friendly (e.g., content-aware) way the context-aware capabilities offered by the Cognitive Radio (CR) paradigm. As integrated exploitation of both content and context-aware system's capabilities is at the basis of our proposed Active Mesh (ActMesh) networking paradigm. This last aims at defining a network-wide architecture for realizing media-friendly Cognitive Mesh nets (e.g., context aware Cognitive Mesh nets). Hence, main contribution of this work is four fold: 1. After introducing main functional blocks of our ActMesh architecture, suitable self-adaptive Belief Propagation and Soft Data Fusion algorithms are designed to provide context-awareness. This is done under both cooperative and noncooperative sensing frameworks. 2. The resulting network-wide resource management problem is modelled as a constrained stochastic Network Utility Maximization (NUM) problem, with the dual (contrasting) objective to maximize spectrum efficiency at the network level, while accounting for the perceived quality of the delivered media flows at the client level. 3. A fully distributed, scalable and self-adaptive implementation of the resulting Active Resource Manager (ARM) is deployed, that explicitly accounts for the energy limits of the battery powered MCs and the effects induced by both fading and client mobility. Due to informationally decentralized architecture of the ActMesh net, the complexity of (possibly, optimal) centralized solutions for resource management becomes prohibitive when number of MCs accessing ActMesh net grow. Furthermore, centralized resource management solutions could required large amounts of time to collect and process the required network information, which, in turn, induce delay that can be unacceptable for delay sensitive media applications, e.g., multimedia streaming. Hence, it is important to develop network-wide ARM policies that are both distributed and scalable by exploiting the radio MCs capabilities to sense, adapt and coordinate themselves. We validate our analytical models via simulation based numerical tests, that support actual effectiveness of the overall ActMesh paradigm, both in terms of objective and subjective performance metrics. In particular, the basic tradeoff among backbone traffic-vs-access traffic arising in the ActMesh net from the bandwidth-efficient opportunistic resource allocation policy pursued by the deployed ARM is numerically characterized. The standardization framework we inspire to is the emerging IEEE 802.16h one

ActMesh- A Cognitive Resource Management paradigm for dynamic mobile Internet Access with Reliability Guarantees

Wireless Mesh Networks (WMNs) are going increasing attention as a flexible low-cost networking architecture to provide media Internet access over metropolitan areas to mobile clients requiring multimedia services. In WMNs, Mesh Routers (MRs) from the mesh backbone and accomplish the twofold task of traffic forwarding, as well as providing multimedia access to mobile Mesh Clients (MCs). Due to the intensive bandwidth-resource requested for supporting QoS-demanding multimedia services, performance of the current WMNs is mainly limited by spectrum-crowding and traffic-congestion, as only scarce spectrum-resources is currently licensed for the MCs' access. In principle, this problem could be mitigated by exploiting in a media-friendly (e.g., content-aware) way the context-aware capabilities offered by the Cognitive Radio (CR) paradigm. As integrated exploitation of both content and context-aware system's capabilities is at the basis of our proposed Active Mesh (ActMesh) networking paradigm. This last aims at defining a network-wide architecture for realizing media-friendly Cognitive Mesh nets (e.g., context aware Cognitive Mesh nets). Hence, main contribution of this work is four fold: 1. After introducing main functional blocks of our ActMesh architecture, suitable self-adaptive Belief Propagation and Soft Data Fusion algorithms are designed to provide context-awareness. This is done under both cooperative and noncooperative sensing frameworks. 2. The resulting network-wide resource management problem is modelled as a constrained stochastic Network Utility Maximization (NUM) problem, with the dual (contrasting) objective to maximize spectrum efficiency at the network level, while accounting for the perceived quality of the delivered media flows at the client level. 3. A fully distributed, scalable and self-adaptive implementation of the resulting Active Resource Manager (ARM) is deployed, that explicitly accounts for the energy limits of the battery powered MCs and the effects induced by both fading and client mobility. Due to informationally decentralized architecture of the ActMesh net, the complexity of (possibly, optimal) centralized solutions for resource management becomes prohibitive when number of MCs accessing ActMesh net grow. Furthermore, centralized resource management solutions could required large amounts of time to collect and process the required network information, which, in turn, induce delay that can be unacceptable for delay sensitive media applications, e.g., multimedia streaming. Hence, it is important to develop network-wide ARM policies that are both distributed and scalable by exploiting the radio MCs capabilities to sense, adapt and coordinate themselves. We validate our analytical models via simulation based numerical tests, that support actual effectiveness of the overall ActMesh paradigm, both in terms of objective and subjective performance metrics. In particular, the basic tradeoff among backbone traffic-vs-access traffic arising in the ActMesh net from the bandwidth-efficient opportunistic resource allocation policy pursued by the deployed ARM is numerically characterized. The standardization framework we inspire to is the emerging IEEE 802.16h one

An analytical model of IEEE 80211 DCF for multi-hop wireless networks and its application to goodput and energy analysis

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 168-181.In this thesis, we present an analytical model for the IEEE 802.11 DCF in multihop networks that considers hidden terminals and works for a large range of traffic loads. A goodput model which considers rate reduction due to collisions, retransmissions and hidden terminals, and an energy model, which considers energy consumption due to collisions, retransmissions, exponential backoff and freezing mechanisms, and overhearing of nodes, are proposed and used to analyze the goodput and energy performance of various routing strategies in IEEE 802.11 DCF based multi-hop wireless networks. Moreover, an adaptive routing algorithm which determines the optimum routing strategy adaptively according to the network and traffic conditions is suggested. Viewed from goodput aspect the results are as follows: Under light traf- fic, arrival rate of packets is dominant, making any routing strategy equivalently optimum. Under moderate traffic, concurrent transmissions dominate and multihop transmissions become more advantageous. At heavy traffic, multi-hoppingbecomes unstable due to increased packet collisions and excessive traffic congestion, and direct transmission increases goodput. From a throughput aspect, it is shown that throughput is topology dependent rather than traffic load dependent, and multi-hopping is optimum for large networks whereas direct transmissions may increase the throughput for small networks. Viewed from energy aspect similar results are obtained: Under light traf- fic, energy spent during idle mode dominates in the energy model, making any routing strategy nearly optimum. Under moderate traffic, energy spent during idle and receive modes dominates and multi-hop transmissions become more advantageous as the optimum hop number varies with processing power consumed at intermediate nodes. At the very heavy traffic conditions, multi-hopping becomes unstable due to increased collisions and direct transmission becomes more energy-efficient.The choice of hop-count in routing strategy is observed to affect energyefficiency and goodput more for large and homogeneous networks where it is possible to use shorter hops each covering similar distances. The results indicate that a cross-layer routing approach, which takes energy expenditure due to MAC contentions into account and dynamically changes the routing strategy according to the network traffic load, can increase goodput by at least 18% and save energy by at least 21% in a realistic wireless network where the network traffic load changes in time. The goodput gain increases up to 222% and energy saving up to 68% for denser networks where multi-hopping with much shorter hops becomes possible.Aydoğdu, CananPh.D

Investigating TCP performance in mobile ad hoc networks

Mobile ad hoc networks (MANETs) have become increasingly important in view of their promise of ubiquitous connectivity beyond traditional fixed infrastructure networks. Such networks, consisting of potentially highly mobile nodes, have provided new challenges by introducing special consideration stemming from the unique characteristics of the wireless medium and the dynamic nature of the network topology. The TCP protocol, which has been widely deployed on a multitude of internetworks including the Internet, is naturally viewed as the de facto reliable transport protocol for use in MANETs. However, assumptions made at TCP’s inception reflected characteristics of the prevalent wired infrastructure of networks at the time and could subsequently lead to sub-optimal performance when used in wireless ad hoc environments. The basic presupposition underlying TCP congestion control is that packet losses are predominantly an indication of congestion in the network. The detrimental effect of such an assumption on TCP’s performance in MANET environments has been a long-standing research problem. Hence, previous work has focused on addressing the ambiguity behind the cause of packet loss as perceived by TCP by proposing changes at various levels across the network protocol stack, such as at the MAC mechanism of the transceiver or via coupling with the routing protocol at the network layer. The main challenge addressed by the current work is to propose new methods to ameliorate the illness-effects of TCP’s misinterpretation of the causes of packet loss in MANETs. An assumed restriction on any proposed modifications is that resulting performance increases should be achievable by introducing limited changes confined to the transport layer. Such a restriction aids incremental adoption and ease of deployment by requiring minimal implementation effort. Further, the issue of packet loss ambiguity, from a transport layer perspective, has, by definition, to be dealt with in an end-to-end fashion. As such, a proposed solution may involve implementation at the sender, the receiver or both to address TCP shortcomings. Some attempts at describing TCP behaviour in MANETs have been previously reported in the literature. However, a thorough enquiry into the performance of those TCP agents popular in terms of research and adoption has been lacking. Specifically, very little work has been performed on an exhaustive analysis of TCP variants across different MANET routing protocols and under various mobility conditions. The first part of the dissertation addresses this shortcoming through extensive simulation evaluation in order to ascertain the relative performance merits of each TCP variant in terms of achieved goodput over dynamic topologies. Careful examination reveals sub-par performance of TCP Reno, the largely equivalent performance of NewReno and SACK, whilst the effectiveness of a proactive TCP variant (Vegas) is explicitly stated and justified for the first time in a dynamic MANET environment. Examination of the literature reveals that in addition to losses caused by route breakages, the hidden terminal effect contributes significantly to non-congestion induced packet losses in MANETs, which in turn has noticeably negative impact on TCP goodput. By adapting the conservative slow start mechanism of TCP Vegas into a form suitable for reactive TCP agents, like Reno, NewReno and SACK, the second part of the dissertation proposes a new Reno-based congestion avoidance mechanism which increases TCP goodput considerably across long paths by mitigating the negative effects of hidden terminals and alleviating some of the ambiguity of non-congestion related packet loss in MANETs. The proposed changes maintain intact the end-to-end semantics of TCP and are solely applicable to the sender. The new mechanism is further contrasted with an existing transport layer-focused solution and is shown to perform significantly better in a range of dynamic scenarios. As solution from an end-to-end perspective may be applicable to either or both communicating ends, the idea of implementing receiver-side alterations is also explored. Previous work has been primarily concerned with reducing receiver-generated cumulative ACK responses by “bundling” them into as few packets as possible thereby reducing misinterpretations of packet loss due to hidden terminals. However, a thorough evaluation of such receiver-side solutions reveals limitations in common evaluation practices and the solutions themselves. In an effort to address this shortcoming, the third part of this research work first specifies a tighter problem domain, identifying the circumstances under which the problem may be tackled by an end-to-end solution. Subsequent original analysis reveals that by taking into account optimisations possible in wireless communications, namely the partial or complete omission of the RTS/CTS handshake, noticeable improvements in TCP goodput are achievable especially over long paths. This novel modification is activated in a variety of topologies and is assessed using new metrics to more accurately gauge its effectiveness in a wireless multihop environment

Gateway Adaptive Pacing for TCP across Multihop Wireless Networks and the Internet

In this paper, we introduce an effective congestion control scheme for TCP over hybrid wireless/wired networks comprising a multihop wireless IEEE 802.11 network and the wired Internet. We propose an adaptive pacing scheme at the Internet gateway for wired-to-wireless TCP flows. Furthermore, we analyze the causes for the unfairness of oncoming TCP flows and propose a scheme to throttle aggressive wired-to-wireless TCP flows at the Internet gateway to achieve nearly optimal fairness. Thus, we denote the introduced congestion control scheme TCP with Gateway Adaptive Pacing (TCP-GAP). For wireless-to-wired flows, we propose an adaptive pacing scheme at the TCP sender. In contrast to previous work, TCP-GAP does not impose any control traffic overhead for achieving fairness among active TCP flows. Moreover, TCP-GAP can be incrementally deployed because it does not require any modifications of TCP in the wired part of the network and is fully TCP-compatible. Extensive simulations using ns-2 show that TCPGAP is highly responsive to varying traffic conditions, provides nearly optimal fairness in all scenarios and achieves up to 42% more goodput than TCP NewReno