Efficient collision detection for auto rate fallback algorithm

The physical rate adaptation in 802.11 is a deeply investigated, though still open issue. Since 802.11 uses the random access Distributed Coordination Function (DCF) mechanism to access the medium, collisions can occur when two or more stations want to transmit data simultaneously. The challenge of rate adaptation schemes is to adapt the physical transmission rate based on channel-related losses, i.e. collisions should not influence the choice of the rate. In this paper we propose a new rate adaptation algorithm that behaves like Auto Rate Fallback (ARF), but makes use of the RTS/CTS handshake, when necessary, to decide whether the physical transmission rate should be changed. Main advantages of this algorithm are its simple implementation and the good performance it attains in presence of collisions. We evaluate the performance of this new rate adaptation algorithm, comparing it with other well known algorithms, by using the new NS–3 simulator.

Autoria e simulação de cenários de redes em NS-3

Este trabalho aborda a crescente necessidade de verificação e testes das redes antes da sua implementação no mundo real. Variáveis como o investimento, estudo qualidade-custo, questões de gestão, fiabilidade e tempo de vida útil são parte das principais preocupações associadas a existentes e futuras redes. É sobretudo neste âmbito que este projecto opera, fornecendo uma solução para uma optimização da autoria de cenários de redes visando a sua execução na ferramenta de simulação de redes NS-3. As tecnologias emergentes são os alvos mais comuns de ferramentas de simulação de redes e este facto é determinante ao decidir que simulador de redes usar para simular os seus cenários. Com este trabalho, o principal objectivo é fornecer aos utilizadores uma ferramenta colaborativa que permite descrever os seus próprios cenários de redes, baseando-se numa linguagem XML denominada por NSDL e traduzir esta estrutura XML para um script C++ que possa ser executado num ambiente evolucionário, como é o caso do NS-3. A solução proposta permite a rápida criação de cenários de redes através de estruturas de dados XML para posterior tradução para C++ e então, execução no NS-3. A maior problemática associada a esta solução é a necessidade de actualização constante em estruturas de validação e de tradução de documentos XML, aquando da actualização da ferramenta NS-3, o que tem vindo a acontecer muito frequentemente devido à sua própria evolução.Universidade da Madeir

Balance de tráfico y provisión de QoS en redes IEEE 802.11

El trabajo fin de grado ha consistido en la implementación en el software de código libre Network Simulator 3 y su posterior evaluación de diferentes soluciones y estrategias de balanceo de tráfico entre distintos puntos de acceso en despliegues multicelulares de redes de área local IEEE 802.11g. Para evaluar y comparar las distintas estrategias de una forma realista se han considerado distribuciones de usuarios y de tráficos variables a la vez que se han empleado los parámetros establecidos en las normas IEEE 802.11 y se ha modelado las condiciones del canal radio de una forma lo más realista posible. Como conclusión se han elaborado unos algoritmos que, a partir de los múltiples resultados que se han obtenido de las diferentes simulaciones realizadas, intentan maximizar la calidad de servicio que una red de área local puede ofrecer al usuario, marcando como objetivo maximizar el throughput y reducir el retardo que deben soportar en sus transmisiones

Design of rate-adaptive MAC and medium aware routing protocols for multi-rate, multi-hop wireless networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiver’s feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics based rate adaptation solution uses an on-demand incremental strategy for selecting a rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the route discovery process. The 802.11 mandates the use of different transmission rates for broadcast and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as ‘reachable neighbours’ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority queue 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 severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end delay and throughput

Comunicação entre elementos da rede numa gestão autonómica

Mestrado em Engenharia Electrónica e TelecomunicaçõesCom o aumento da dimensão, complexidade e dinamismo das redes de próxima geração, os protocolos de gestão tradicionais tornar-se-ão ineficientes devido às suas características centralizadas e limitações em termos de escalabilidade. É neste ponto que surge a necessidade de criar diferentes soluções de gestão de rede que respondam a requisitos como a automatização da resposta às alterações nas condições do meio, a optimização de recursos, a adaptabilidade às mudanças de topologia, a escalabilidade e a eficiência de processos. Como resposta às necessidades apresentadas surge o paradigma de In- Network Management (INM) cuja ideia principal é inserir nas várias entidades que compõem a rede, capacidades e funcionalidades de forma a que estas se tornem autónomas e a gestão da rede deixe de depender de entidades agregadoras externas/servidores. Isto implica um nível elevado de automatização, sincronismo e actualização da informação entre os vários elementos, podendo facilmente conduzir a um forte aumento do overhead. É no contexto do paradigma de INM que a presente dissertação se insere, na qual são propostos vários mecanismos de interacção entre entidades, de modo a incluir processos de comunicação cooperativa. De modo sucinto, ao nível das redes com fios, é testado um protocolo de descoberta, baseado na estratégia Hide & Seek. Ao nível das redes sem fios, usando como base o protocolo 802.11 MAC, são propostos mecanismos de comunicação entre entidades e um critério de classificação baseado em relações sociais entre nós (métrica social). As soluções apresentadas são avaliadas segundo diferentes parâmetros, em cenários com e sem fios. Os cenários de redes com fios foram avaliados numa testbed virtual, ao nível do overhead de mensagens e do tempo de convergência da informação do protocolo de descoberta desenvolvido, tendo sido ainda elaborada uma análise comparativa com outros protocolos. Nos cenários de redes sem fios implementados no simulador NS-3, analisou-se o impacto ao nível de alguns parâmetros de nível MAC. É objectivo futuro a avaliação do impacto ao nível da camada IP.With the increasing size, complexity and dynamism of next generation networks, the traditional management protocols will become highly inefficient due to their centralizing characteristics and limitations in terms of scalability. This is the point where the need to create different network management solutions that answer to requirements such as automation of the response to changes in environmental conditions, resource optimization, adaptability to topology changes, scalability and efficiency. In response to the needs presented, the In-Network Management (INM) paradigm arises, whose main idea is to place capabilities and features into the various entities that comprise the network, so that they become autonomous and network management no longer rely on external servers. This implies a high level of automation, synchronization and update of the information among all elements, which can easily lead to a high increase in overhead. This Master's Thesis works in part of the architecture proposed by the INM paradigm, in the proposed mechanisms of interaction between entities in order to enable the overall process of cooperative communication. Briefly, in the wired networks, we propose a discovery protocol, based on the Hide & Seek strategy. In terms of wireless networks, using the 802.11 MAC protocol as base, we propose mechanisms for communication between entities and a social based classification criterion (social metric). The presented solutions are evaluated according to different parameters, in wired and wireless scenarios. In wired scenarios, the discovery protocol developed was evaluated in terms of messages overhead and convergence time on a virtual testbed, and it was also performed a comparative analysis with other protocols. The wireless scenario was implemented in the NS-3 simulator with an analysis of the impact on some MAC level parameters. It is also a future goal the evaluation of the impact on IP layer parameters

Design of rate-adaptive MAC and medium aware routing protocols for multi-rate, multi-hop wireless networks

The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiver’s feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics based rate adaptation solution uses an on-demand incremental strategy for selecting a rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the route discovery process. The 802.11 mandates the use of different transmission rates for broadcast and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as ‘reachable neighbours’ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority queue 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 severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end delay and throughput.EThOS - Electronic Theses Online ServiceGBUnited Kingdo