Design and provisioning of WDM networks for traffic grooming

Wavelength Division Multiplexing (WDM) is the most viable technique for utilizing the enormous amounts of bandwidth inherently available in optical fibers. However, the bandwidth offered by a single wavelength in WDM networks is on the order of tens of Gigabits per second, while most of the applications\u27 bandwidth requirements are still subwavelength. Therefore, cost-effective design and provisioning of WDM networks require that traffic from different sessions share bandwidth of a single wavelength by employing electronic multiplexing at higher layers. This is known as traffic grooming. Optical networks supporting traffic grooming are usually designed in a way such that the cost of the higher layer equipment used to support a given traffic matrix is reduced. In this thesis, we propose a number of optimal and heuristic solutions for the design and provisioning of optical networks for traffic grooming with an objective of network cost reduction. In doing so, we address several practical issues. Specifically, we address the design and provisioning of WDM networks on unidirectional and bidirectional rings for arbitrary unicast traffic grooming, and on mesh topologies for arbitrary multipoint traffic grooming. In multipoint traffic grooming, we address both multicast and many-to-one traffic grooming problems. We provide a unified frame work for optimal and approximate network dimensioning and channel provisioning for the generic multicast traffic grooming problem, as well as some variants of the problem. For many-to-one traffic grooming we propose optimal as well as heuristic solutions. Optimal formulations which are inherently non-linear are mapped to an optimal linear formulation. In the heuristic solutions, we employ different problem specific search strategies to explore the solution space. We provide a number of experimental results to show the efficacy of our proposed techniques for the traffic grooming problem in WDM networks

Wavelengths switching and allocation algorithms in multicast technology using m-arity tree networks topology

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.In this thesis, the m-arity tree networks have been investigated to derive equations for their nodes, links and required wavelengths. The relationship among all parameters such as leaves nodes, destinations, paths and wavelengths has been found. Three situations have been explored, firstly when just one server and the leaves nodes are destinations, secondly when just one server and all other nodes are destinations, thirdly when all nodes are sources and destinations in the same time. The investigation has included binary, ternary, quaternary and finalized by general equations for all m-arity tree networks. Moreover, a multicast technology is analysed in this thesis to transmit data carried by specific wavelengths to several clients. Wavelengths multicast switching is well examined to propose split-convert-split-convert (S-C-S-C) multicast switch which consists of light splitters and wavelengths converters. It has reduced group delay by 13% and 29% compared with split-convert (S-C) and split-convert-split (S-C-S) multicast switches respectively. The proposed switch has also increased the received signal power by a significant value which reaches 28% and 26.92% compared with S-C-S and S-C respectively. In addition, wavelengths allocation algorithms in multicast technology are proposed in this thesis using tree networks topology. Distributed scheme is adopted by placing wavelength assignment controller in all parents’ nodes. Two distributed algorithms proposed shortest wavelength assignment (SWA) and highest number of destinations with shortest wavelength assignment (HND-SWA) algorithms to increase the received signal power, decrease group delay and reduce dispersion. The performance of the SWA algorithm was almost better or same as HND-SWA related to the power, dispersion and group delay but they are always better than other two algorithms. The required numbers of wavelengths and their utilised converters have been examined and calculated for the researched algorithms. The HND-SWA has recorded the superior performance compared with other algorithms. It has reduced number of utilised wavelengths up to about 19% and minimized number of the used wavelengths converters up to about 29%. Finally, the centralised scheme is discussed and researched and proposed a centralised highest number of destinations (CHND) algorithm with static and dynamic scenarios to reduce network capacity decreasing (Cd) after each wavelengths allocation. The CDHND has reduced (Cd) by about 16.7% compared with the other algorithms

Energy efficiency in content delivery networks

The increasing popularity of bandwidth-intensive video Internet services has positioned Content Distribution Networks (CDNs) in the limelight as the emerging provider platforms for video delivery. The goal of CDNs is to maximise the availability of content in the network while maintaining the quality of experience expected by users. This is a challenging task due to the scattered nature of video content sources and destinations. Furthermore, the high energy consumption associated with content distribution calls for developing energy-efficient solutions able to cater for the future Internet. This thesis addresses the problem of content placement and update while considering energy consumption in CDNs. First, this work contributed a new energy-efficient caching scheme that stores the most popular content at the edge of the core network and optimises the size of cached content to minimise energy usage. It takes into account the trend of daily traffic and recommends putting inactive segments of caches in sleep-mode during off-peak hours. Our results showed that power minimisation is achieved by deploying switch-off capable caches, and the trend of active cache segments over the time of day follows the trend of traffic. Second, the study explores different content popularity distributions and determines their influence on power consumption. The distribution of content popularity dictates the resultant cache hit ratio achieved by storing a certain number of videos. Therefore, it directly influences the power consumption of the cache. The evaluation results indicated that under video services where the popularity of content is very diverse, the optimum solution is to store the few most popular videos in caches. In contrast, when video popularities are similar, the most power efficient scheme is either to cache the whole library or to avoid caching completely depending on the size of the video library. Third, this thesis contributed an evaluation of the power consumption of the network under real world TV data and considering standard and high definition TV programmes. We proposed a cache replacement algorithm based on the predictable nature of TV viewings. The time-driven proactive cache replacement algorithm replaces cache contents several times a day to minimise power consumption. The algorithm achieves major power savings on top of the power reductions introduced by caching. CDNs are expected to continue to be the backbone for Internet video applications. This work has shown that storing the right amount of popular videos in core caches reduces from 42% to 72% of network power consumption considering a range of content popularity distributions. Maintaining up-to-date cache contents reduces up to 48% and 86% of power consumption considering fixed and sleep-mode capable caches, respectively. Reducing the energy consumption of CDNs provides a valuable contribution for future green video delivery

Multicasting in All-Optical WDM Networks

n this dissertation, we study the problem of (i) routing and wavelength assignment, and (ii) traffic grooming for multicast traffic in Wavelength Division Multiplexing (WDM) based all-optical networks. We focus on the 'static' case where the set of multicast traffic requests is assumed to be known in advance. For the routing and wavelength assignment problem, we study the objective of minimizing the number of wavelengths required; and for the traffic grooming problem, we study the objectives of minimizing (i) the number of wavelengths required, and (ii) the number of electronic components required. Both the problems are known to be hard for general fiber network topologies. Hence, it makes sense to study the problems under some restrictions on the network topology. We study the routing and wavelength assignment problem for bidirected trees, and the traffic grooming problem for unidirectional rings. The selected topologies are simple in the sense that the routing for any multicast traffic request is trivially determined, yet complex in the sense that the overall problems still remain hard. A motivation for selecting these topologies is that they are of practical interest since most of the deployed optical networks can be decomposed into these elemental topologies. In the first part of the thesis, we study the the problem of multicast routing and wavelength assignment in all-optical bidirected trees with the objective of minimizing the number of wavelengths required in the network. We give a 5/2-approximation algorithm for the case when the degree of the bidirected tree is at most 3. We give another algorithm with approximation ratio 10/3, 3 and 2 for the case when the degree of the bidirected tree is equal to 4, 3 and 2, respectively. The time complexity analysis for both these algorithms is also presented. Next we prove that the problem is hard even for the two restricted cases when the bidirected tree has (i) depth 2, and (ii) degree 2. Finally, we present another hardness result for a related problem of finding the clique number for a class for intersection graphs. In the second part of the thesis, we study the problem of multicast traffic grooming in all-optical unidirectional rings. For the case when the objective is to minimize the number of wavelengths required in the network, given an 'a'-approximation algorithm for the circular arc coloring problem, we give an algorithm having asymptotic approximation ratio 'a' for the multicast traffic grooming problem. We develop an easy to calculate lower bound on the minimum number of electronic components required to support a given set of multicast traffic requests on a given unidirectional ring network. We use this lower bound to analyze the worst case performance of a pair of simple grooming schemes. We also study the case when no grooming is carried out in order to get an estimate on the maximum number of electronic components that can be saved by applying intelligent grooming. Finally, we present a new grooming scheme and compare its average performance against other grooming schemes via simulations. The time complexity analysis for all the grooming schemes is also presented

IP multicast over WDM networks

Ph.DDOCTOR OF PHILOSOPH

Advanced techniques for multicast service provision in core transport networks

Although the network-based multicast service is the optimal way to support of a large variety of popular applications such as high-definition television (HDTV), videoon- demand (VoD), virtual private LAN service (VPLS), grid computing, optical storage area networks (O-SAN), video conferencing, e-learning, massive multiplayer online role-playing games (MMORPG), networked virtual reality, etc., there are a number of technological and operational reasons that prevents a wider deployment. This PhD work addresses this problem in the context of core transport network, by proposing and analyzing new cost-effective and scalable techniques to support multicast both at the Optical layer and at the Network layer (MPLS-IP networks). In the Optical layer, in particular in Wavelength Division Multiplexing (WDM) Optical Circuit Switched networks, current multicast-capable OXC node designs are of a great complexity and have high attenuation levels, mainly because of the required signal splitting operation plus the traversal of a complex switching stage. This makes multi-point support rarely included in commercial OXC nodes. Inspired in previous works in the literature, we propose a novel architecture that combines the best of splitting and tap-and-continue (TaC), called 2-STC (2-split-tap-and-continue) in the framework of integrated optics. A 2-STC OXC node is a flexible design capable of tapping and splitting over up to two outgoing links in order to obtain lower end-to-end latency than in TaC and an improved power budget distribution over split-and-delivery (SaD) designs. Another advantage of this architecture is its simplicity and the reduced number of components required, scaling well even for implementations of the node with many input/output ports. Extensive simulations show that the binary split (2-split) is quite enough for most real-life core network topologies scenarios, since the average node degree is usually between 3 and 4. A variant of this design, called 2-STCg, for making the node capable of optical traffic grooming (i.e. accommodation of low-speed demands into wavelength-links) is also presented. At the Network layer, one of the main reasons that hinder multicast deployment is the high amount of forwarding state information required in core routers, especially when a large number of medium/small-sized multicast demands arrive to the core network, because the state data that needs to be kept at intermediate core routers grows proportionally to the number of multicast demands. In this scenario, we study the aggregation of multicast demands into shared distribution trees, providing a set of techniques to observe the trade-off between bandwidth and state information. This study is made in the context of MPLS VPN-based networks, with the aggregation of multicast VPNs in different real network scenarios and using novel heuristics for aggregation. Still, the main problem of aggregation is the high percentage of wasted bandwidth that depends mainly on the amount of shared trees used. On the other hand, recent works have brought back Bloom filters as an alternative for multicast forwarding. In this approach the packet header contains a Bloom filter that is evaluated at each hop for matching with the corresponding outgoing link ID. Although this approach is claimed to be stateless, it presents serious drawbacks due to false positives, namely important forwarding anomalies (duplicated flows, packet storms and loops) and the header overhead. In order to solve these drawbacks we propose D-MPSS (Depth-Wise Multi-Protocol Stateless Switching). This technique makes use of a stack of Bloom filters instead of a single one for all the path/tree, each one including only the links of a given depth of the tree. Analytical studies and simulations show that our approach reduces the forwarding anomalies present in similar state-of-the-art techniques, achieving in most network scenarios a forwarding efficiency (useful traffic) greater than 95%. Finally, we study the possibility of using tree aggregation and Bloom filters together, and propose a set of techniques grouped as H-ABF techniques (hybrid aggregation - Bloom filter-based forwarding), which improve D-MPSS and other previously proposed techniques, practically eliminating the forwarding loops and increasing the forwarding efficiency up to more than 99% in most network scenarios. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Aunque el servicio de multidifusión (multicast) basado en redes es la mejor manera de dar soporte a una gran variedad de aplicaciones populares como la televisión de alta definición (HDTV), el video bajo demanda (VoD), el servicio de LAN privadas virtuales (VPLS), la computación grid, las redes de área de almacenamiento óptico (O-SAN), la videoconferencia, la educación a distancia, los juegos masivos de rol en línea de múltiples jugadores (MMORPG), la realidad virtual en red, etc., hay varias razones tecnológicas y operacionales que le impiden un mayor despliegue. Esta tesis doctoral aborda este problema en el contexto de las redes troncales de transporte, proponiendo y analizando técnicas de bajo coste y escalables para dar soporte al multicast tanto para la capa óptica como para la capa de red (redes MPLS-IP). En la capa óptica, en particular en las redes ópticas conmutadas por circuitos con multiplexación de longitud de onda (WDM), los diseños de nodos OXC con capacidades multicast muestran una gran complejidad y altos niveles de atenuación, principalmente debido a la necesaria operación de división de la señal, además del paso de ella a través de una compleja fase de conmutación. Esto hace que el soporte multi-punto sea raramente incluido en los nodos OXC comerciales. Inspirados en trabajos previos de la literatura, proponemos una novedosa arquitectura que combina lo mejor de dividir (splitting) y tap-y-continuar (TaC), llamado 2-STC (2-split-tapand- continue) en el marco de trabajo de la óptica integrada. Un nodo OXC 2-STC es un diseño flexible capaz de hacer tapping (tomar una pequeña muestra de la señal) y dividir la señal hacia un máximo de dos enlaces de salida, con el fin de obtener una menor latencia terminal-a-terminal que en TaC y una mejorada distribución de la disponibilidad de potencia por encima de los diseños split-and-delivery (SaD). Otra ventaja de esta arquitectura es su simplicidad y el número reducido de componentes requerido, escalando bien para las implementaciones del nodo con muchos puertos de entrada/salida. Extensas simulaciones muestran que la división binaria (2-split) es prácticamente suficiente para la mayoría de las topologías de redes de transporte en la vida real, debido a que el grado promedio de los nodos es usualmente 3 y 4. Una variante de este diseño, llamada 2-STCg, para hacer el nodo capaz de realizar grooming (es decir, la capacidad de acomodar demandas de menor velocidad en longitudes de onda - enlaces) de tráfico óptico, es también presentada. En la capa de red, una de las principales razones que obstaculizan el despliegue del multicast es la gran cantidad de información del estado de reenvío requerida en los enrutadores de la red de transporte, especialmente cuando un gran número de demandas multicast de tamaño mediano/pequeño llegan a la red de transporte, ya que los datos de estado a ser almacenados en los enrutadores crecen proporcionalmente con el número de demandas multicast. En este escenario, estudiamos la agregación de demandas multicast en árboles de distribución, proporcionando un conjunto de técnicas para observar el equilibrio entre el ancho de banda y la información de estado. Este estudio está hecho en el contexto de las redes basadas en redes privadas virtuales (VPN) MPLS, con la agregación de VPNs multicast en distintos escenarios de redes reales y utilizando nuevos heurísticos para la agregación. Aún así, el principal problema de la agregación es el alto porcentaje de ancho de banda desperdiciado que depende principalmente de la cantidad de árboles compartidos usados. Por otro lado, trabajos recientes han vuelto a traer a los filtros de Bloom como una alternativa para realizar el reenvío multicast. En esta aproximación la cabecera del paquete contiene un filtro de Bloom que es evaluado en cada salto para emparejarlo con el identificador del enlace de salida correspondiente. Aunque se afirma que esta solución no utiliza información de estado, presenta serias desventajas debido a los falsos positivos, esto es, anomalías de reenvío importantes (flujos duplicados, tormentas de paquetes y bucles) y gasto de ancho de banda por la cabecera de los paquetes. Para poder resolver estos problemas proponemos D-MPSS (Depth- Wise Multi-Protocol Stateless Switching). Esta técnica hace uso de una pila de filtros de Bloom en lugar de uno sólo para todo el camino/árbol, incluyendo cada uno sólo los enlaces de una determinada profundidad del árbol. Estudios analíticos y simulaciones demuestran que nuestra propuesta reduce los anomalías de reenvío presentes en otras técnicas similares del estado del arte, alcanzando en la mayoría de escenarios reales una eficiencia de reenvío (tráfico útil) mayor que 95%. Finalmente, estudiamos la posibilidad de usar agregación de árboles y filtros de Bloom juntos, y proponemos un conjunto de técnicas agrupadas como técnicas HABF (hybrid aggregation - Bloom filter-based forwarding), que mejoran D-MPSS y las otras técnicas propuestas previamente, eliminando prácticamente los bucles e incrementando la eficiencia de reenvío hasta más de un 99% en la mayoría de los escenarios de redes