64 research outputs found
High speed all optical networks
An inherent problem of conventional point-to-point wide area network (WAN) architectures is that they cannot translate optical transmission bandwidth into comparable user available throughput due to the limiting electronic processing speed of the switching nodes. The first solution to wavelength division multiplexing (WDM) based WAN networks that overcomes this limitation is presented. The proposed Lightnet architecture takes into account the idiosyncrasies of WDM switching/transmission leading to an efficient and pragmatic solution. The Lightnet architecture trades the ample WDM bandwidth for a reduction in the number of processing stages and a simplification of each switching stage, leading to drastically increased effective network throughputs. The principle of the Lightnet architecture is the construction and use of virtual topology networks, embedded in the original network in the wavelength domain. For this construction Lightnets utilize the new concept of lightpaths which constitute the links of the virtual topology. Lightpaths are all-optical, multihop, paths in the network that allow data to be switched through intermediate nodes using high throughput passive optical switches. The use of the virtual topologies and the associated switching design introduce a number of new ideas, which are discussed in detail
Traffic engineering in dynamic optical networks
Traffic Engineering (TE) refers to all the techniques a Service Provider employs to improve the efficiency and reliability of network operations. In IP over Optical (IPO) networks, traffic coming from upper layers is carried over the logical topology defined by the set of established lightpaths. Within this framework then, TE techniques allow to optimize the configuration of optical resources with respect to an highly dynamic traffic demand. TE can be performed with two main methods: if the demand is known only in terms of an aggregated traffic matrix, the problem of automatically updating the configuration of an optical network to accommodate traffic changes is called Virtual Topology Reconfiguration (VTR). If instead the traffic demand is known in terms of data-level connection requests with sub-wavelength granularity, arriving dynamically from some source node to any destination node, the problem is called Dynamic Traffic Grooming (DTG). In this dissertation new VTR algorithms for load balancing in optical networks based on Local Search (LS) techniques are presented. The main advantage of using LS is the minimization of network disruption, since the reconfiguration involves only a small part of the network. A comparison between the proposed schemes and the optimal solutions found via an ILP solver shows calculation time savings for comparable results of network congestion. A similar load balancing technique has been applied to alleviate congestion in an MPLS network, based on the efficient rerouting of Label-Switched Paths (LSP) from the most congested links to allow a better usage of network resources. Many algorithms have been developed to deal with DTG in IPO networks, where most of the attention is focused on optimizing the physical resources utilization by considering specific constraints on the optical node architecture, while very few attention has been put so far on the Quality of Service (QoS) guarantees for the carried traffic. In this thesis a novel Traffic Engineering scheme is proposed to guarantee QoS from both the viewpoint of service differentiation and transmission quality. Another contribution in this thesis is a formal framework for the definition of dynamic grooming policies in IPO networks. The framework is then specialized for an overlay architecture, where the control plane of the IP and optical level are separated, and no information is shared between the two. A family of grooming policies based on constraints on the number of hops and on the bandwidth sharing degree at the IP level is defined, and its performance analyzed in both regular and irregular topologies. While most of the literature on DTG problem implicitly considers the grooming of low-speed connections onto optical channels using a TDM approach, the proposed grooming policies are evaluated here by considering a realistic traffic model which consider a Dynamic Statistical Multiplexing (DSM) approach, i.e. a single wavelength channel is shared between multiple IP elastic traffic flows
Investigation of the tolerance of wavelength-routed optical networks to traffic load variations.
This thesis focuses on the performance of circuit-switched wavelength-routed optical network with unpredictable traffic pattern variations. This characteristic of optical networks is termed traffic forecast tolerance. First, the increasing volume and heterogeneous nature of data and voice traffic is discussed. The challenges in designing robust optical networks to handle unpredictable traffic statistics are described. Other work relating to the same research issues are discussed. A general methodology to quantify the traffic forecast tolerance of optical networks is presented. A traffic model is proposed to simulate dynamic, non-uniform loads, and used to test wavelength-routed optical networks considering numerous network topologies. The number of wavelengths required and the effect of the routing and wavelength allocation algorithm are investigated. A new method of quantifying the network tolerance is proposed, based on the calculation of the increase in the standard deviation of the blocking probabilities with increasing traffic load non-uniformity. The performance of different networks are calculated and compared. The relationship between physical features of the network topology and traffic forecast tolerance is investigated. A large number of randomly connected networks with different sizes were assessed. It is shown that the average lightpath length and the number of wavelengths required for full interconnection of the nodes in static operation both exhibit a strong correlation with the network tolerance, regardless of the degree of load non-uniformity. Finally, the impact of wavelength conversion on network tolerance is investigated. Wavelength conversion significantly increases the robustness of optical networks to unpredictable traffic variations. In particular, two sparse wavelength conversion schemes are compared and discussed: distributed wavelength conversion and localized wavelength conversion. It is found that the distributed wavelength conversion scheme outperforms localized wavelength conversion scheme, both with uniform loading and in terms of the network tolerance. The results described in this thesis can be used for the analysis and design of reliable WDM optical networks that are robust to future traffic demand variations
Attack-Aware Routing and Wavelength Assignment of Scheduled Lightpath Demands
In Transparent Optical Networks, tra c is carried over lightpaths, creating a vir- tual topology over the physical connections of optical bers. Due to the increasingly high data rates and the vulnerabilities related to the transparency of optical network, security issues in transparent wavelength division multiplexing (WDM) optical net- works have become of great signi cance to network managers. In this thesis, we intro- duce some basic concepts of transparent optical network, the types and circumstances of physical-layer attacks and analysis of related work at rst. In addition, based on the previous researches, we present a novel approach and several new objective cri- terions for the problem of attack-aware routing and wavelength assignment. Integer Linear Programming (ILP) formulation is used to solve the routing sub-problem with the objective to minimize the disruption of physical-layer attack as well as to opti- mize Routing and Wavelength Assignment (RWA) of scheduled transparent optical network
Optical network planning for static applications
Traffic demands on optical transport networks continue to grow, both in numbers
and in size, at an incredible rate. Consequently, the efficient use of network resources has
never been as important as today. A possible solution to this problem is to plan, develop
and implement efficient algorithms for static and/or dynamic applications in order to
minimize the probability of blocking and/or minimizing the number of wavelengths.
Static Routing and Wavelength Assignment (RWA) algorithms use a given set of optical
path requests and are intended to provide a long-term plan for future traffic. Static RWA
algorithms are important for current and future WDM (Wavelength-Division
Multiplexing) networks, especially when there is no wavelength conversion, the network
is highly connected or the traffic load is moderate to high.
In this dissertation, we propose to develop an optical network planning tool capable
of choosing the best optical path and assigning as few wavelengths as possible. This tool
is structured in five phases: in the first phase, the network physical topology is defined
by the adjacency matrix or by the cost matrix and the logical topology is defined by the
traffic matrix; in a second phase, the Dijkstra algorithm is used to find the shortest path
for each connection; in the third phase, the traffic routing is accomplished considering
one traffic unit between the source and destination nodes; in the fourth phase, the paths
are ordered using various ordering strategies, such as Shortest Path First, Longest Path
First and Random Path Order; finally, in the fifth phase, the heuristic algorithms for
wavelength assignment, such as Graph Coloring, First-Fit and Most-Used are used. This
tool is first tested on small networks (e.g. ring and mesh topologies), and then applied to
real networks (e.g. COST 239, NSFNET and UBN topologies). We have concluded that
the number of wavelengths calculated for each network is almost independent of the
Wavelength Assignment (WA) heuristics, as well as the ordering strategy, when a full
mesh logical topology is considered.Os pedidos de tráfego nas redes de transporte ópticas continuam a crescer, tanto em
nĂşmero como em tamanho, a um ritmo incrĂvel. Consequentemente, a utilização eficiente
dos recursos das redes nunca foi tĂŁo importante como hoje. Uma solução possĂvel para
este problema passa por planear, desenvolver e implementar algoritmos eficientes para
aplicações estáticas e/ou dinâmicas de modo a minimizar a probabilidade de bloqueio
e/ou minimizar o nĂşmero de comprimentos de onda. Os algoritmos de encaminhamento
e de atribuição de comprimentos de onda (RWA) estáticos utilizam um determinado
conjunto de pedidos de caminhos Ăłpticos e visam fornecer um plano de longo prazo para
tráfego futuro. Os algoritmos RWA estáticos são importantes para as redes em
multiplexagem por divisĂŁo de comprimento de onda (WDM) atuais e futuras,
especialmente quando não há conversão de comprimento de onda, a rede é altamente
ligada ou a carga de tráfego é de moderada a alta.
Nesta dissertação, propomos desenvolver uma ferramenta de planeamento de redes
Ăłpticas capaz de escolher o melhor caminho Ăłptico e atribuir o mĂnimo de comprimentos
ondas possĂveis. Esta ferramenta está estruturada em cinco fases: numa primeira fase Ă©
definida a topologia fĂsica de rede pela matriz das adjacĂŞncias ou pela matriz de custo e a
topologia lógica é definida pela matriz de tráfego; numa segunda fase é utilizado o
algoritmo Dijkstra para encontrar o caminho mais curto para cada ligação; na terceira fase
o encaminhamento de tráfego é realizado considerando uma unidade de tráfego entre os
nĂłs de origem e destino; na quarta fase os caminhos sĂŁo ordenados tendo em conta as
várias estratégias de ordenação, tais como Shortest Path First, Longest Path First e
Random Path Order; finalmente, na quinta fase, os algoritmos heurĂsticos sĂŁo utilizados
para atribuição de comprimentos de onda, como Graph Coloring, First-Fit e Most-Used.
Esta ferramenta Ă© primeiramente testada em redes pequenas (por exemplo, topologias em
anel e em malha), e depois Ă© aplicada a redes reais (por exemplo, redes COST 239,
NSFNET e UBN). ConcluĂmos que o nĂşmero de comprimentos de onda calculados para
cada rede Ă© quase independente da heurĂstica para atribuição dos cumprimentos de onda,
bem como da estratégia de ordenação dos caminhos, quando uma topologia lógica em
malha completa Ă© considerada
Integrated voice/data through a digital PBX
The digital voice/data PBX is finally reaching its anticipated potential and becoming a major factor when considering the total communications picture for many businesses today. The digital PBX has always been the choice for voice communications but has lagged behind the LAN industry when it comes to data transfers. The pendulum has begun to swing with the enhanced data capabilities of third and fourth generation PBXs. The battle for the total communication market is quite fierce between the LAN and PBX vendors now. This research thesis looks at the history, evolution, and architecture of voice/data PBXs. It traces development of PBXs through the present fourth generation architectures. From the first manual switches introduced in the late 1800\u27s through the Strowger switch, step-by-step switching, stored program control, common control, digital switches, dual bus architectures, and finally what is anticipated in the future. A detailed description of the new fourth generation dual bus architectures is presented. Lastly, speculations on the future direction PBX architectures will take is explored. A description of the mechanics of a possible Wave Division PBX is presented based on a fiber optic transport system
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