QoS Considerations in OBS Switched Backbone Net-Works

Optical Burst Switching (OBS) was proposed as a hybrid switching technology solution to handle the multi-Terabit volumes of traffic anticipated to traverse Future Generation backbone Networks. With OBS, incoming data packets are assembled into super-sized packets called data bursts and then assigned an end to end light path. Key challenging areas with regards to OBS Networks implementation are data bursts assembling and scheduling at the network ingress and core nodes respectively as they are key to minimizing subsequent losses due to contention among themselves in the core nodes. These losses are significant contributories to serious degradation in renderable QoS. The paper overviews existing methods of enhancing it at both burst and transport levels. A distributed resources control architecture is proposed together with a proposed wavelength assignment algorithm

A review burst assembly techniques in optical burst switching (OBS)

Optical Burst Switching (OBS) is perceived as the most favorable switching method for the next generation all optical networks to support the growth of the number of Internet users and to satisfy bandwidth demands for greedy-bandwidth applications which are in continuous growth. OBS consists of an edge node and a core node. The edge node is responsible for burst assembly which is the first process in an OBS network. Currently, there is only one review paper for burst assembly; the paper is limited in number of techniques reviewed. In this paper, we have undertaken a comprehensive review of burst assembly techniques proposed for OBS where techniques are reviewed by category. The aim is to identify strengths and weaknesses of these techniques. The analysis of the paper will assist researchers in finding problems; thus, a significant amount of time will be saved which can be used in developing appropriate solutions for OBS networks

Enhancing the quality of service for real time traffic over optical burst switching (OBS) networks with ensuring the fairness for other traffics

Optical burst switching (OBS) networks have been attracting much consideration as a promising approach to build the next generation optical Internet. A solution for enhancing the Quality of Service (QoS) for high priority real time traffic over OBS with the fairness among the traffic types is absent in current OBS ’ QoS schemes. In this paper we present a novel Real Time Quality of Service with Fairness Ratio (RT-QoSFR) scheme that can adapt the burst assembly parameters according to the traffic QoS needs in order to enhance the real time traffic QoS requirements and to ensure the fairness for other traffic. The results show that RT-QoSFR scheme is able to fulfill the real time traffic requirements (end to end delay, and loss rate) ensuring the fairness for other traffics under various conditions such as the type of real time traffic and traffic load. RT-QoSFR can guarantee that the delay of the real time traffic packets does not exceed the maximum packets transfer delay value. Fur- thermore, it can reduce the real time traffic packets loss, at the same time guarantee the fair- ness for non real time traffic packets by determining the ratio of real time traffic inside the burst to be 50 – 60%, 30 – 40%, and 10 – 20% for high, normal, and low traffic loads respectively

Congestion window-based adaptive burst assembly for TCP traffic in OBS networks

Burst assembly is one of the key factors affecting the TCP performance in optical burst switching (OBS) networks. When the TCP congestion window is small, the fixed-delay burst assembler waits unnecessarily long, which increases the end-to-end delay and thus decreases the TCP goodput. On the other hand, when the TCP congestion window becomes larger, the fixed-delay burst assembler may unnecessarily generate a large number of small-sized bursts, which increases the overhead and decreases the correlation gain, resulting in a reduction in the TCP goodput. In this paper, we propose adaptive burst assembly algorithms that use the congestion window sizes of TCP flows. Using simulations, we show that the usage of the congestion window size in the burst assembly algorithm significantly improves the TCP goodput (by up to 38.4% on the average and by up to 173.89% for individual flows) compared with the timerbased assembly, even when the timer-based assembler uses the optimum assembly period. It is shown through simulations that even when estimated values of the congestion window size, that are obtained via passive measurements, are used, TCP goodput improvements are still close to the results obtained by using exact values of the congestion window. © Springer Science+Business Media, LLC 2010

Resource allocation and scalability in dynamic wavelength-routed optical networks.

This thesis investigates the potential benefits of dynamic operation of wavelength-routed optical networks (WRONs) compared to the static approach. It is widely believed that dynamic operation of WRONs would overcome the inefficiencies of the static allocation in improving resource use. By rapidly allocating resources only when and where required, dynamic networks could potentially provide the same service that static networks but at decreased cost, very attractive to network operators. This hypothesis, however, has not been verified. It is therefore the focus of this thesis to investigate whether dynamic operation of WRONs can save significant number of wavelengths compared to the static approach whilst maintaining acceptable levels of delay and scalability. Firstly, the wavelength-routed optical-burst-switching (WR-OBS) network architecture is selected as the dynamic architecture to be studied, due to its feasibility of implementation and its improved network performance. Then, the wavelength requirements of dynamic WR-OBS are evaluated by means of novel analysis and simulation and compared to that of static networks for uniform and non-uniform traffic demand. It is shown that dynamic WR-OBS saves wavelengths with respect to the static approach only at low loads and especially for sparsely connected networks and that wavelength conversion is a key capability to significantly increase the benefits of dynamic operation. The mean delay introduced by dynamic operation of WR-OBS is then assessed. The results show that the extra delay is not significant as to violate end-to-end limits of time-sensitive applications. Finally, the limiting scalability of WR-OBS as a function of the lightpath allocation algorithm computational complexity is studied. The trade-off between the request processing time and blocking probability is investigated and a new low-blocking and scalable lightpath allocation algorithm which improves the mentioned trade-off is proposed. The presented algorithms and results can be used in the analysis and design of dynamic WRONs

Analytic modelling and resource dimensioning of optical burst switched networks

The realisation of optical network architectures may hold the key to delivering the enormous bandwidth demands of next generation Internet applications and services. Optical Burst Switching (OBS) is a potentially cost-effective switching technique that can satisfy these demands by offering a high bit rate transport service that is bandwidth-efficient under dynamic Internet traffic loads. Although various aspects of OBS performance have been extensively investigated, there remains a need to systematically assess the cost/performance trade-offs involved in dimensioning OBS switch resources in a network. This goal is essential in enabling the future deployment of OBS but poses a significant challenge due to the complexity of obtaining tractable mathematical models applicable to OBS network optimisation. The overall aim of this thesis lies within this challenge. This thesis firstly develops a novel analytic performance model of an OBS node where burst contention is resolved by combined use of Tuneable Wavelength Converters (TWCs) and Fibre Delay Lines (FDLs) connected in an efficient share-per-node configuration. The model uses a two-moment traffic representation that gives a good trade-off between accuracy and complexity, and is suitable for extension to use in network modelling. The OBS node model is then used to derive an approximate analytic model of an OBS network of switches equipped with TWCs and FDLs, again maintaining a two-moment traffic model for each end-to-end traffic path in the network. This allows evaluation of link/route loss rates under different offered traffic characteristics, whereas most OBS network models assume only a single-moment traffic representation. In the last part of this thesis, resource dimensioning of OBS networks is performed by solving single and multi-objective optimisation problems based on the analytic network model. The optimisation objectives relate to equipment cost minimisation and throughput maximisation under end-to-end loss rate constraints. Due to non-convexity of the network performance constraint equations, a search heuristic approach has been taken using a constraint-handling genetic algorithm

Estudio e implementación de mecanismos de asignación de longitudes de onda para redes OBS sin colisiones

En la última década, el tráfico en Internet ha crecido exponencialmente. Con el objetivo de dar respuesta a ésta demanda creciente, se ha favorecido la introducción de sistemas basados en el multiplexado por longitud de onda sobre redes de fibra óptica. En ésta evolución hacia una Internet óptica, la técnica de conmutación tiene especial importancia. La conmutación óptica de ráfagas (Optical Burst Switching, OBS) se definió con el objetivo de aprovechar mejor los recursos de la red que utilizando la conmutación óptica de circuitos pero sin las exigencias tecnológicas que requiere la conmutación óptica de paquetes. En OBS los datos de los usuarios se agregan en la entrada de la red formando unidades de datos de mayor longitud, denominadas ráfagas. Antes de la transmisión de cada ráfaga, se transmite un paquete de control con el objetivo de configurar los dispositivos intermedios de la red para que la transmisión de la ráfaga se pueda realizar íntegramente en el dominio óptico. A menudo, la transmisión de una ráfaga se realiza sin tener confirmación sobre la disponibilidad de los recursos en todos los nodos intermedios de la red, con lo cual se pueden producir contiendas (contention) que, si no son resueltas, pueden suponer la pérdida de datos. Se han propuesto varias técnicas para minimizar las pérdidas en redes OBS. En [19] los autores proponen una estrategia de transmisión libre de pérdidas basada en la combinación de un mecanismo de asignación de caminos y longitudes de onda, con esquemas básicos de resolución de contiendas. En éste esquema, para realizar la asignación de caminos y longitudes de onda, se clasifican las comunicaciones según su nivel de interferencia y se modela la red mediante un grafo cuyos vértices representan las comunicaciones y sus aristas, las interferencias. Sobre el grafo resultante, el problema de asignación de caminos y longitudes de onda es equivalente a un problema de coloreado de grafos. En este trabajo se ha desarrollado una aplicación que permite realizar el coloreado de un grafo según diferentes algoritmos

Estudio e implementación de mecanismos de asignación de longitudes de onda para redes OBS sin colisiones

En la última década, el tráfico en Internet ha crecido exponencialmente. Con el objetivo de dar respuesta a ésta demanda creciente, se ha favorecido la introducción de sistemas basados en el multiplexado por longitud de onda sobre redes de fibra óptica. En ésta evolución hacia una Internet óptica, la técnica de conmutación tiene especial importancia. La conmutación óptica de ráfagas (Optical Burst Switching, OBS) se definió con el objetivo de aprovechar mejor los recursos de la red que utilizando la conmutación óptica de circuitos pero sin las exigencias tecnológicas que requiere la conmutación óptica de paquetes. En OBS los datos de los usuarios se agregan en la entrada de la red formando unidades de datos de mayor longitud, denominadas ráfagas. Antes de la transmisión de cada ráfaga, se transmite un paquete de control con el objetivo de configurar los dispositivos intermedios de la red para que la transmisión de la ráfaga se pueda realizar íntegramente en el dominio óptico. A menudo, la transmisión de una ráfaga se realiza sin tener confirmación sobre la disponibilidad de los recursos en todos los nodos intermedios de la red, con lo cual se pueden producir contiendas (contention) que, si no son resueltas, pueden suponer la pérdida de datos. Se han propuesto varias técnicas para minimizar las pérdidas en redes OBS. En [19] los autores proponen una estrategia de transmisión libre de pérdidas basada en la combinación de un mecanismo de asignación de caminos y longitudes de onda, con esquemas básicos de resolución de contiendas. En éste esquema, para realizar la asignación de caminos y longitudes de onda, se clasifican las comunicaciones según su nivel de interferencia y se modela la red mediante un grafo cuyos vértices representan las comunicaciones y sus aristas, las interferencias. Sobre el grafo resultante, el problema de asignación de caminos y longitudes de onda es equivalente a un problema de coloreado de grafos. En este trabajo se ha desarrollado una aplicación que permite realizar el coloreado de un grafo según diferentes algoritmos