16 research outputs found

    LOGICAL TOPOLOGY DESIGN FOR SURVIVABILITY IN IP-OVER-WDM NETWORKS

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    IP-over-WDM networks integrate Wavelength Division Multiplexing (WDM) technology with Internet Protocol (IP) and are widely regarded as the architecture for the next generation high-speed Internet. The problem of designing an IP-over-WDM network can be modeled as an embedding problem in which an IP network is embedded in a WDM network by establishing all optical paths between IP routers in the WDM network. Survivability is considered a vital requirement in such networks, which can be achieved by embedding the IP network in the WDM network in such a way that the IP network stays connected in the presence of failure or failures in the WDM network. Otherwise, some of the IP routers may not be reachable.The problem can be formulated as an Integer Linear Program (ILP), which can be solved optimally but is NP-complete. In this thesis, we have studied and proposed various efficient algorithms that can be used to make IP-over-WDM networks survivable in the presence of a single WDM link (optical fiber cable or cables) failure.First we evaluate an existing approach, named Survivable Mapping Algorithm by Ring Trimming (SMART), which provides survivability for an entire network by successively considering pieces of the network. The evaluation provides much insight into the approach, which allowed us to propose several enhancements. The modified approach with enhancements leads to better performance than the original SMART.We have also proposed a hybrid algorithm that guarantees survivability, if the IP and the WDM networks are at least 2-edge connected. The algorithm uses a combination of proactive (protection) and reactive (restoration) mechanisms to obtain a survivable embedding for any given IP network in any given WDM network.Circuits and cutsets are dual concepts. SMART approach is based on circuits. The question then arises whether there exists a dual methodology based on cutsets. We investigate this question and provide much needed insight. We provide a unified algorithmic framework based on circuits and cutsets. We also provide new methodologies based on cutsets and give a new proof of correctnessof SMART. We also develop a method based on incidence sets that are a special case of cutsets. Noting that for some IP networks a survivable embedding may not exist, the option of adding new IP links is pursued. Comparative evaluations of all the algorithms through extensive simulations are also given in this dissertation

    Robustness to failures in two-layer communication networks

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    A close look at many existing systems reveals their two- or multi-layer nature, where a number of coexisting networks interact and depend on each other. For instance, in the Internet, any application-level graph (such as a peer-to-peer network) is mapped on the underlying IP network that, in turn, is mapped on a mesh of optical fibers. This layered view sheds new light on the tolerance to errors and attacks of many complex systems. What is observed at a single layer does not necessarily reflect well the state of the entire system. On the contrary, a tiny, seemingly harmless disruption of one layer, may destroy a substantial or essential part of another layer, thus making the whole system useless in practice. In this thesis we consider such two-layer systems. We model them by two graphs at two different layers, where the upper-layer (or logical) graph is mapped onto the lower-layer (physical) graph. Our main goals are the following. First, we study the robustness to failures of existing large-scale two-layer systems. This brings us some valuable insights into the problem, e.g., by identifying common weak points in such systems. Fortunately, these two-layer problems can often be effectively alleviated by a careful system design. Therefore, our second major goal is to propose new designs that increase the robustness of two-layer systems. This thesis is organized in three main parts, where we focus on different examples and aspects of the two-layer system. In the first part, we turn our attention to the existing large-scale two-layer systems, such as peer-to-peer networks, railway networks and the human brain. Our main goal is to study the vulnerability of these systems to random errors and targeted attacks. Our simulations show that (i) two-layer systems are much more vulnerable to errors and attacks than they appear from a single layer perspective, and (ii) attacks are much more harmful than errors, especially when the logical topology is heterogeneous. These results hold across all studied systems. A natural next step consists in improving the failure robustness of two-layer systems. In particular, in the second part of this thesis, we consider the IP/WDM optical networks, where an IP backbone network is mapped on a mesh of optical fibers. The problem lies in designing a survivable mapping, such that no single physical failure disconnects the logical topology. This is an NP-complete problem. We introduce a new concept of piecewise survivability, which makes the problem much easier in practice. This leads us to an efficient and scalable algorithm called SMART, which finds a survivable mapping much faster (often by orders of magnitude) than the other approaches proposed to date. Moreover, the formal analysis of SMART allows us to prove that a given survivable mapping does or does not exist. Finally, this approach helps us to find vulnerable areas in the system, and to effectively reinforce them, e.g., by adding new links. In the third part of this thesis, we shift our attention one layer higher, to the application-over-IP setting. In particular, we consider the design of Application-Level Multicast (ALM) for interactive applications, where a single source sends a delay-constrained data stream to a number of destinations. Interactive ALM should (i) respect stringent delay requirements, and (ii) proactively protect the system against overlay node failures and against (iii) the packet losses at the IP layer. We propose a two-layer-aware approach to this problem. First, we prove that the average packet loss rate observed at the destinations can be effectively approximated by a purely topological metric that, in turn, drops with the amount of IP-level and overlay-level path diversity available in the system. Therefore, we propose a framework that accommodates and generalizes various techniques to increase the path diversity in the system. Within this framework we optimize the structure of ALM. As a result, we reduce the effective loss rate of real Internet topologies by typically 30%-70%, compared to the state of the art. Finally, in addition to the three main parts of the thesis, we also present a set of results inspired by the study of ALM systems, but not directly related to the 'two-layer' paradigm (and thus moved to the Appendix). In particular, we consider a transmission of a delay-sensitive data stream from a single source to a single destination, where the data packets are protected by a Forward Error Correction (FEC) code and sent over multiple paths. We show that the performance of such a scheme can often be further improved. Our key observation is that the propagation times on the available paths often significantly differ, typically by 10-100ms. We propose to exploit these differences by appropriate packet scheduling, which results in a two- to five-fold improvement (reduction) in the effective loss rate

    Survivable Logical Topology Mapping under Multiple Constraints in IP-over-WDM Networks

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    The survivable logical topology mapping problem in an IP-over-WDM network deals with the cascading effect of link failures from the bottom (physical) layer to the upper (logical) layer. Multiple logical links may get disconnected due to a single physical link failure, which may cause the disconnection of the logical network. Here we study survivability issues in IP-over-WDM networks with respect to various criteria.We first give an overview of the two major lines of pioneering works for the survivable design problem. Though theoretically elegant, the first approach which uses Integer Linear Programming (ILP) formulations suffers from the drawback of scalability. The second approach, the structural approach, utilizes the concept of duality between circuits and cutsets in a graph and is based on an algorithmic framework called Survivable Mapping Algorithm by Ring Trimming (SMART). Several SMART-based algorithms have been proposed in the literature.In order to generate the survivable routing, the SMART-based algorithms require the existence of disjoint lightpaths for certain groups of logical links in the physical topology, which might not always exist. Therefore, we propose in Chapter 4 an approach to augment the logical topology with new logical links to guarantee survivability. We first identify a logical topology that admits a survivable mapping against one physical link failure. We then generalize these results to achieve augmentation of a given logical topology to survive multiple physical link failures.We propose in Chapter 5 a generalized version of SMART-based algorithms and introduce the concept of robustness of an algorithm which captures the ability of the algorithm to provide survivability against multiple physical link failures. We demonstrate that even when a SMART-based algorithm cannot be guaranteed to provide survivability against multiple physical link failures, its robustness could be very high.Most previous works on the survivable logical topology design problem in IP-over-WDM networks did not consider physical capacities and logical demands. In Chapter 6, we study this problem taking into account logical link demands and physical link capacities. We define weak survivability and strong survivability in capacitated IP-over-WDM networks. Two-stage Mixed-Integer Linear Programming (MILP) formulations and heuristics to solve the survivable design problems are proposed. Based on the 2-stage MILP framework, we also propose several extensions to the weakly survivable design problem, considering several performance criteria. Noting that for some logical networks a survivable mapping may not exist, which prohibits us from applying the 2-stage MILP approach, our first extension is to augment the logical network using an MILP formulation to guarantee the existence of a survivable routing. We then propose approaches to balance the logical demands satisfying absolute or ratio-weighted fairness. Finally we show how to formulate the survivable logical topology design problem as an MILP for the multiple failure case.We conclude with an outline of two promising new directions of research

    Crosslayer Survivability in Overlay-IP-WDM Networks

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    As the Internet moves towards a three-layer architecture consisting of overlay networks on top of the IP network layer on top of WDM-based physical networks, incorporating the interaction between and among network layers is crucial for efficient and effective implementation of survivability.This dissertation has four major foci as follows: First, a first-of-its-kind analysis of the impact of overlay network dependency on the lower layer network unveils that backhaul, a link loop that occurs at any two or more lower layers below the layer where traffic is present, could happen. This prompts our proposal of a crosslayer survivable mapping to highlight such challenges and to offer survivability in an efficient backhaul-free way. The results demonstrate that the impact of layer dependency is more severe than initially anticipated making it clear that independent single layer network design is inadequate to assure service guarantees and efficient capacity allocation. Second, a forbidden link matrix is proposed masking part of the network for use in situations where some physical links are reserved exclusively for a designated service, mainly for the context of providing multiple levels of differentiation on the network use and service guarantee. The masking effect is evaluated on metrics using practical approaches in a sample real-world network, showing that both efficiency and practicality can be achieved. Third, matrix-based optimization problem formulations of several crosslayer survivable mappings are presented; examples on the link availability mapping are particularly illustrated. Fourth, survivability strategies for two-layer backbone networks where traffic originates at each layer are investigated. Optimization-based formulations of performing recovery mechanisms at each layer for both layers of traffic are also presented. Numerical results indicate that, in such a wavelength-based optical network, implementing survivability of all traffic at the bottom layer can be a viable solution with significant advantages.This dissertation concludes by identifying a roadmap of potential future work for crosslayer survivability in layered network settings

    Survivable Virtual Network Embedding in Transport Networks

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    Network Virtualization (NV) is perceived as an enabling technology for the future Internet and the 5th Generation (5G) of mobile networks. It is becoming increasingly difficult to keep up with emerging applications’ Quality of Service (QoS) requirements in an ossified Internet. NV addresses the current Internet’s ossification problem by allowing the co-existence of multiple Virtual Networks (VNs), each customized to a specific purpose on the shared Internet. NV also facilitates a new business model, namely, Network-as-a-Service (NaaS), which provides a separation between applications and services, and the networks supporting them. 5G mobile network operators have adopted the NaaS model to partition their physical network resources into multiple VNs (also called network slices) and lease them to service providers. Service providers use the leased VNs to offer customized services satisfying specific QoS requirements without any investment in deploying and managing a physical network infrastructure. The benefits of NV come at additional resource management challenges. A fundamental problem in NV is to efficiently map the virtual nodes and virtual links of a VN to physical nodes and paths, respectively, known as the Virtual Network Embedding (VNE) problem. A VNE that can survive physical resource failures is known as the survivable VNE (SVNE) problem, and has received significant attention recently. In this thesis, we address variants of the SVNE problem with different bandwidth and reliability requirements for transport networks. Specifically, the thesis includes four main contributions. First, a connectivity-aware VNE approach that ensures VN connectivity without bandwidth guarantee in the face of multiple link failures. Second, a joint spare capacity allocation and VNE scheme that provides bandwidth guarantee against link failures by augmenting VNs with necessary spare capacity. Third, a generalized recovery mechanism to re-embed the VNs that are impacted by a physical node failure. Fourth, a reliable VNE scheme with dedicated protection that allows tuning of available bandwidth of a VN during a physical link failure. We show the effectiveness of the proposed SVNE schemes through extensive simulations. We believe that the thesis can set the stage for further research specially in the area of automated failure management for next generation networks

    Scalable Column Generation Models and Algorithms for Optical Network Planning Problems

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    Column Generation Method has been proved to be a powerful tool to model and solve large scale optimization problems in various practical domains such as operation management, logistics and computer design. Such a decomposition approach has been also applied in telecommunication for several classes of classical network design and planning problems with a great success. In this thesis, we confirm that Column Generation Methodology is also a powerful tool in solving several contemporary network design problems that come from a rising worldwide demand of heavy traffic (100Gbps, 400Gbps, and 1Tbps) with emphasis on cost-effective and resilient networks. Such problems are very challenging in terms of complexity as well as solution quality. Research in this thesis attacks four challenging design problems in optical networks: design of p-cycles subject to wavelength continuity, design of dependent and independent p-cycles against multiple failures, design of survivable virtual topologies against multiple failures, design of a multirate optical network architecture. For each design problem, we develop a new mathematical models based on Column Generation Decomposition scheme. Numerical results show that Column Generation methodology is the right choice to deal with hard network design problems since it allows us to efficiently solve large scale network instances which have been puzzles for the current state of art. Additionally, the thesis reveals the great flexibility of Column Generation in formulating design problems that have quite different natures as well as requirements. Obtained results in this thesis show that, firstly, the design of p-cycles should be under a wavelength continuity assumption in order to save the converter cost since the difference between the capacity requirement under wavelength conversion vs. under wavelength continuity is insignificant. Secondly, such results which come from our new general design model for failure dependent p-cycles prove the fact that failure dependent p-cycles save significantly spare capacity than failure independent p-cycles. Thirdly, large instances can be quasi-optimally solved in case of survivable topology designs thanks to our new path-formulation model with online generation of augmenting paths. Lastly, the importance of high capacity devices such as 100Gbps transceiver and the impact of the restriction on number of regeneration sites to the provisioning cost of multirate WDM networks are revealed through our new hierarchical Column Generation model

    Resource Allocation, and Survivability in Network Virtualization Environments

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    Network virtualization can offer more flexibility and better manageability for the future Internet by allowing multiple heterogeneous virtual networks (VN) to coexist on a shared infrastructure provider (InP) network. A major challenge in this respect is the VN embedding problem that deals with the efficient mapping of virtual resources on InP network resources. Previous research focused on heuristic algorithms for the VN embedding problem assuming that the InP network remains operational at all times. In this thesis, we remove that assumption by formulating the survivable virtual network embedding (SVNE) problem and developing baseline policy heuristics and an efficient hybrid policy heuristic to solve it. The hybrid policy is based on a fast re-routing strategy and utilizes a pre-reserved quota for backup on each physical link. Our evaluation results show that our proposed heuristic for SVNE outperforms baseline heuristics in terms of long term business profit for the InP, acceptance ratio, bandwidth efficiency, and response time

    Survivable virtual topology design in optical WDM networks using nature-inspired algorithms

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    Tez (Doktora) -- İstanbul Teknik Üniversitesi, Bilişim Enstitüsü, 2012Thesis (PhD) -- İstanbul Technical University, Institute of Informatics, 2012Günümüzde bilgisayar ağları hayatımızın önemli bir parçası ve ihtiyaç haline gelmiştir. İstediğimiz veriye, istediğimiz anda, daha hızlı, daha güvenli ve kesintisiz olarak erişme isteğimiz aslında ağ altyapısının nasıl tasarlanacağını belirlemektedir. Kullanıcıların istekleri sürekli artarken, teknolojik gelişmelerle birlikte yeni yöntem ve algoritmalarla bu istekleri karşılamanın yolları aranmaktadır. Ağdaki aktarım hızı, aktarım ortamından doğrudan etkilenmektedir; bugün uzak mesafelere en yüksek kapasiteli ve hızlı aktarımın yapılabileceği ortam ise fiberdir. Fiber optik ağlar, fiberin üstün özelliklerini (hız, düşük bit hata oranı, elektromanyetik ortamlardan etkilenmeme, düşük işaret zayıflaması, fiziksel dayanıklılık, ucuzluk, güvenlilik, vs.) en iyi kullanacak şekilde tasarlanan ağlardır. Günümüzde dünyadaki iletişim ağ altyapısı, omurga ağlardan erişim ağlarına kadar, hızla fiber optik ağlara dönüşmektedir. Optik ağların en önemli özelliklerinden biri veri aktarım hızıdır, tek bir fiberden teorik olarak 50 Tb/s veri aktarımı yapılabileceği hesaplanmaktadır. Bugün, lider iletişim firmaları 100 Gb/s ya da 1 Tb/s hızda veri aktarımı yapacak kanalllardan bahsedebiliyorsa, bu, fiziksel altyapı optik bir omurgadan oluştuğu içindir. Dalgaboyu bölmeli çoğullama (WDM) teknolojisi sayesinde bir fiber üzerinde aynı anda kurulabilecek kanal sayısı, günümüz teknolojisiyle yüzler mertebesine çıkabilmektedir. Dalgaboyu bölmeli çoğullama teknolojisi ile, optik aktarım birbiriyle çakışmayan dalgaboyu bantlarına bölünür ve her bir dalgaboyu istenen hızda çalışan, ışıkyolu olarak adlandırılan, bir iletişim kanalını destekler. Böylece, yakın gelecek için öngörülen çok yüksek hızlara çıkmadan bile, bir fiberden herbiri birkaç on Gb/s hızda çalışan yüz dolayında ışıkyolu geçebilmektedir. Bu kadar yüksek hızlarda veri aktarımı, özellikle her bir fiberinde çok sayıda kanalın taşındığı omurga ağlarda bir konuya büyük önem kazandırmaktadır: Hataya bağışıklık. En sık rastlanan hata olan, bir fiberin, herhangi bir nedenle kesilmesi (çoğunlukla inşaat makineleri tarafından, ya da doğal afetlerce), fiber tamir edilene kadar, her saniyede birkaç terabitlik veri kaybı anlamına gelecektir. Örnek olarak 10 km uzunlukta bir fiberin kopma sıklığı 11 yılda birdir. Omurga ağlarda yüzlerce, bazen binlerce, kilometrelik fiberler döşendiği gözönüne alındığında, böyle bir hata durumu için tedbir alınmaması düşünülemez. Optik ağ üzerindeki herhangi bir fibere zarar gelmesi demek bu fiber üzerinden yönlendirilmiş olan tüm ışıkyollarının kopması demektir. Her bir ışıkyolu üzerinden yüksek miktarda (40 Gb/s) veri aktarımı yapıldığından, böyle bir zarar ciddi veri kayıplarına neden olabilir. Temel olarak fiber kopmasına karşı geliştirilen iki yaklaşım vardır. Birinci yaklaşımda fiber üzerinden geçen her bir bağlantının, yani ışıkyolunun, yedek yollarla korunmasıdır. İkinci yaklaşım ise, özellikle birçok internet uygulamasına da uygun ve yeterli olacak şekilde, ışıkyollarının oluşturduğu sanal topolojinin bağlı kalmasının sağlanmasıdır. Bu ikinci yaklaşımda herbir ışıkyoluna ayrı ayrı yedek koruma yollarının atanması yerine, sanal topolojinin korunması dikkate alınarak, üst katmanların (paket katmanları) koruma mekanizmalarının devreye girebilmesi için gereken minimum koşulların sağlanması amaçlanmaktadır. Birinci yaklaşım belirli düzeylerde garantili bir koruma sağlarken yüksek miktarda ağ kaynağının atıl durmasına neden olmakta, dolayısıyla bu kadar üst düzey koruma gerektirmeyen uygulamalar için pahalı bir çözüm sunmaktadır. Son yıllarda özellikle dikkat çeken ikinci yaklaşım ise, daha ekonomik bir yöntemle iletişimin kopmaması garantisini vermekte, ancak daha yavaş bir düzeltme sağlamaktadır. Günümüzde birçok uygulama bağlantı kopmadığı sürece paket katmanının, yeni yol bulma gibi hata düzeltme mekanizmalarının devreye girmesi için gerekli olan, dakikalar mertebesindeki gecikmelere toleranslıdır (web dolaşımı, dosya aktarımı, mesajlaşma, uzaktan erişim gibi). Bu yaklaşım ilkine göre daha az ağ kaynağının atıl kalmasına neden olarak kullanıcıya daha ekonomik hizmet verilmesini sağlayacaktır. Bu çalışmada üzerinde durduğumuz hataya bağışık sanal topoloji tasarımı problemi de bu ikinci yaklaşımı benimsemektedir. Hataya bağışık sanal topoloji tasarımı problemi kendi içinde dört alt probleme ayrılmaktadır: ışıkyollarının belirlenmesi (sanal topolojiyi oluşturma), bu ışıkyollarının herhangi bir fiber kopması durumunda bile sanal topolojinin bağlı kalmasını sağlayacak sekilde fiziksel topoloji üzerinde yönlendirilmesi, dalgaboyu atanması, ve paket trafiğinin yönlendirilmesi. Bu alt problemler ayrı ayrı çözülebilir. Ancak, bunlar bağımsız problemler değildir ve bunları tek tek çözmek elde edilen çözümün kalitesinin çok düşük olmasına neden olabilir. Bununla birlikte, hataya bağışık sanal topoloji tasarımı problemi NP-karmaşıktır. Karmaşıklığı nedeniyle bu problemin, gerçek boyutlu ağlar için, klasik optimizasyon teknikleriyle kabul edilebilir zamanda çözülmesi mümkün değildir. Bu çalışmada, fiziksel topolojinin ve düğümler arası paket trafiği yoğunluğunun bilindiği durumlar için, hataya bağışık sanal topoloji tasarımı problemi bütün halinde ele alınmaktadır. Tezin ilk aşamasında, hataya bağışık sanal topoloji tasarımı probleminin alt problemi olan hataya bağışık sanal topoloji yönlendirmesi problemi ele alınmıştır. Verilen bir sanal topoloji için en az kaynak kullanarak hataya bağışık yönlendirme yapmak için iki farklı doğa-esinli algoritma önerilmektedir: evrimsel algoritmalar ve karınca kolonisi optimizasyonu. Öncelikle önerilen algoritmaların problem için uygun parametre kümesi belirlenmiş, daha sonra, algoritmaların başarımını ölçmek için, deneysel sonuçlar tamsayı doğrusal programlama (ILP) ile elde edilen sonuçlarla karşılaştırılmışır. Sonuçlar göstermektedir ki; önerdiğimiz iki algoritma da, tamsayı doğrusal programlama ile uygun bir çözüm bulunamayan büyük ölçekli ağlar için dahi, problemi çözebilmektedir. Bunun yanında, doğa-esinli algoritmalar çok daha az CPU zamanı ve hafıza kullanmaktadır. Elde edilen çözüm kalitesi ve çözüm için kullanılan CPU zamanının kabul edilebilir düzeyde olması, her iki doğa-esinli algoritmanın da gerçek boyutlu ağlar için kullanılabileceğini doğrulamaktadır. İkinci aşamada, hataya bağışık sanal topoloji tasarımı problemini bir bütün halinde çözmek için dört farklı üst-sezgisel yöntem önerilmektedir. Önerilen üst-sezgisel yöntemler alt seviyedeki sezgiselleri seçme asamasında dört farklı yöntem kullanmaktadır: evrimsel algoritmalar, benzetimli tavlama, karınca kolonisi optimizasyonu ve uyarlamalı yinelenen yapıcı arama. Deneysel sonuçlar tüm üst-sezgisel yöntemlerin hataya bağışık sanal topoloji tasarımı problemini çözmede başarılı olduğunu göstermektedir. Ancak, karınca kolonisi optimizasyonu tabanlı üst-sezgisel diğerlerine göre daha üstün sonuçlar vermektedir. Işıkyolları üzerindeki trafik akışını dengelemek için, karınca kolonisi optimizasyonu tabanlı üst-sezgisele akış deviasyonu yöntemi de eklenmiştir. Literatürde hataya bağışık sanal topoloji tasarımı problemini ele alan tüm çalışmalar çift fiber kopması durumunu gözardı etmektedir. Bu çalışmada, önerdiğimiz üst-sezgisel yöntemin başarımını hem tek hem de çift fiber kopması durumları için değerlendirdik. Önerdiğimiz yöntem çoklu fiber kopması durumları için çok kolay şekilde adapte edilebilmektedir. Tek yapılması gereken hataya bağışıklık kontrolünü yapan yordamın değiştirilmesidir. Deneysel sonuçlar göstermiştir ki, önerdiğimiz karınca kolonisi optimizasyonu tabanlı üst-sezgisel hataya bağışık sanal topoloji tasarımı problemini hem tek hem de çift fiber kopması durumları için kabul edilebilir bir sürede çözebilmektedir. Üst-sezgisel yöntemlerin hataya bağışık sanal topoloji tasarımı çözmedeki başarımını değerlendirebilmek amacıyla, karınca kolonisi optimizasyonu tabanlı üst-sezgiselle elde edilen sonuçlar, literatürde bu problem için önerilmiş başka bir yöntemle karşılaştırılmıştır. Sonuçlar üst-sezgisel yöntemlerin, çok daha az CPU zamanı kullanarak, problem için daha kaliteli çözümler verdiğini göstermektedir.Today, computer networking has become an integral part of our daily life. The steady increase in user demands of high speed and high bandwidth networks causes researchers to seek out new methods and algorithms to meet these demands. The transmission speed in the network is directly affected by the transmission medium. The most effective medium to transmit data is the fiber. Optical networks are designed for the best usage of the superior properties of the fiber, e.g. high speed, high bandwidth, low bit error rate, low attenuation, physical strength, cheapness, etc. The world's communication network infrastructure, from backbone networks to access networks, is consistently turning into optical networks. One of the most important properties of the optical networks is the data transmission rate (up to 50 Tb/s on a single fiber). Today, with the help of the wavelength division multiplexing (WDM) technology, hundreds of channels can be built on a single fiber. WDM is a technology in which the optical transmission is split into a number of non-overlapping wavelength bands, with each wavelength supporting a single communication channel operating at the desired rate. Since multiple WDM channels, also called lightpaths, can coexist on a single fiber, the huge fiber bandwidth can be utilized. Any damage to a physical link (fiber) on the network causes all the lightpaths routed through this link to be broken. Since huge data transmission (40 Gb/s) over each of these lightpaths is possible, such a damage results in a serious amount of data loss. Two different approaches can be used in order to avoid this situation: 1. Survivability on the physical layer, 2. Survivability on the virtual layer. The first approach is the problem of designing a backup link/path for each link/path of the optical layer. The second approach is the problem of designing the optical layer such that the optical layer remains connected in the event of a single or multiple link failure. While the first approach provides faster protection for time-critical applications (such as, IP phone, telemedicine) by reserving more resources, the second approach, i.e. the survivable virtual topology design, which has attracted a lot of attention in recent years, aims to protect connections using less resources. The problem that will be studied in this project is to develop methods for survivable virtual topology design, that enables effective usage of the resources. Survivable virtual topology design consists of four subproblems: determining a set of lightpaths (forming the virtual topology), routing these lightpaths on the physical topology (routing and wavelength assignment (RWA) problem), so that any single fiber cut does not disconnect the virtual topology (survivable virtual topology mapping), assigning wavelengths, and routing the packet traffic. Each of these subproblems can be solved separately. However, they are not independent problems and solving them one by one may degrade the quality of the final result considerably. Furthermore, the survivable virtual topology design is known to be NP-complete. Because of its complexity, it is not possible to solve the problem optimally in an acceptable amount of time using classical optimization techniques, for real-life sized networks. In this thesis, we solve the survivable virtual topology design problem as a whole, where the physical topology and the packet traffic intensities between nodes are given. In the first phase, we propose two different nature inspired heuristics to find a survivable mapping of a given virtual topology with minimum resource usage. Evolutionary algorithms and ant colony optimization algorithms are applied to the problem. To assess the performance of the proposed algorithms, we compare the experimental results with those obtained through integer linear programming. The results show that both of our algorithms can solve the problem even for large-scale network topologies for which a feasible solution cannot be found using integer linear programming. Moreover, the CPU time and the memory used by the nature inspired heuristics is much lower. In the second phase, we propose four different hyper-heuristic approaches to solve the survivable virtual topology design problem as a whole. Each hyper-heuristic approach is based on a different category of nature inspired heuristics: evolutionary algorithms, ant colony optimization, simulated annealing, and adaptive iterated constructive search. Experimental results show that, all proposed hyper-heuristic approaches are successful in designing survivable virtual topologies. Furthermore, the ant colony optimization based hyper-heuristic outperforms the others. To balance the traffic flow over lightpaths, we adapt a flow-deviation method to the ant colony optimization based hyper-heuristic approach. We explore the performance of our hyper-heuristic approach for both single and double-link failures. The proposed approach can be applied to the multiple-link failure problem instances by only changing the survivability control routine. The experimental results show that our approach can solve the problem for both single-link and double-link failures in a reasonable amount of time. To evaluate the quality of the HH approach solutions, we compare these results with the results obtained using tabu search approach. The results show that HH approach outperforms tabu search approach both in solution quality and CPU time.DoktoraPh

    Ant Colony Optimization For Survivable Virtual Topology Mapping In Optical Wdm Networks

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    Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2009İnternet kullanımının her geçen gün biraz daha yaygınlaşması, bant genişliği problemini de beraberinde getirmiştir. Bu ihtiyacı karşılamak amacıyla, optik ağlarda WDM (dalga boyu bölmeli çoğullama – wavelength division multiplexing) teknolojisi kullanılarak fiber kabloların kapasitesi, her biri farklı dalga boyunda çalışan yüzlerce farklı iletim kanalına bölünmüştür. Paket iletimi yapan üst katmanların kullanacağı uçtan uca kurulan optik bağlantılara ışıkyolu denir. Ağda kurulan tüm ışıkyolları ağın sanal topolojisini oluşturur. Bir fiber üzerinde farklı dalga boylarında olmak koşuluyla birden fazla ışıkyolu yönlendirilebilir. Fakat bir fiberin herhangi bir şekilde hasara uğraması, üzerinden geçen bütün ışıkyollarının kopması sonucu ciddi boyutlarda veri kaybına neden olur. Bu durumdan korunma yöntemlerinden biri ışıkyollarının fiberler üzerinde hataya bağışık şekilde yönlendirilmesidir öyle ki fiziksel katmanda bir ya da daha fazla bağlantı koptuğunda sanal topoloji hala bağlı kalmalıdır. Bu çalışmanın amacı altı farklı karınca koloni algoritması kullanılarak fiberlerin kapasite kısıtlarını aşmadan ve ağ kaynaklarının kullanımını minimize edecek şekilde ışıkyollarını hataya bağışık olarak fiziksel topoloji üzerinde yönlendirmek ve algoritmaları başarım, hız ve ağ kaynaklarının etkin kullanımı açısından karşılaştırmaktır.As the internet use increases significantly in everyday life, the need for bandwidth increases accordingly. To meet this need, high capacity of fibers used in optical networks, can be divided into many channels, using the WDM technology. End-to-end optical connections that the packet layer (IP, Ethernet, etc.) uses are called lightpaths. All the lightpaths set up on the network form the virtual topology. A fiber is able to route more than one ligthpaths with different wavelengths. Any damage to a fiber causes all the channels routed through this link to be broken, which may result in a serious amount of data loss. As a solution to this problem, the virtual layer can be mapped onto the physical topology, such that, a failure on any physical link does not disconnect the virtual topology. This is known as the survivable virtual topology mapping problem. In this study, our aim is to compare the performance of six different ant colony algorithms in finding a survivable mapping of a given virtual topology while minimizing the used wavelength links and without violating the wavelength capacity of fibers in terms of success rates, speed and resource usage.Yüksek LisansM.Sc
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