Survivability issues in WDM optical networks

WDM optical networks make it possible for the bandwidth of transport networks to reach a level on which any failures would cause tremendous data loss and affect a lot of users. Thus, survivability issues of WDM optical networks have attracted a lot of research work. Within the scope of this dissertation, two categories of problems are studied, one is survivable mapping from IP topology to WDM topology, the other is p-cycle protection schemes in WDM networks.;Survivable mapping problem can be described as routing IP links on the WDM topology such that the IP topology stays connected under any single link failure in the WDM topology. This problem has been proved to be NP-complete [1]. At first, this dissertation provides a heuristic algorithm to compute approximated solutions for input IP/WDM topologies as an approach to ease the hardness of it. Then, it examines the problem with a different view, to augment the IP topology so that a survivable mapping can be easily computed. This new perspective leads to an extended survivable mapping problem that is originally proposed and analyzed in this dissertation. In addition, this dissertation also presents some interesting open problems for the survivable mapping problem as future work.;Various protection schemes in WDM networks have been explored. This dissertation focuses on methods based on the p-cycle technology. p-Cycle protection inherits the merit of fast restoration from the link-based protection technology while yielding higher efficiency on spare capacity usage [2]. In this dissertation, we first propose an efficient heuristic algorithm that generates a small subset of candidate cycles that guarantee 100% restorability and help to achieve an efficient design. Then, we adapt p-cycle design to accommodate the protection of the failure of a shared risk link group (SRLG). At last, we discuss the problem of establishing survivable connections for dynamic traffic demands using flow p-cycle

Survivable mesh-network design & optimization to support multiple QoP service classes

Every second, vast amounts of data are transferred over communication systems around the world, and as a result, the demands on optical infrastructures are extending beyond the traditional, ring-based architecture. The range of content and services available from the Internet is increasing, and network operations are constantly under pressure to expand their optical networks in order to keep pace with the ever increasing demand for higher speed and more reliable links

Design and operation of mesh-restorable WDM networks

The explosive growth of Web-related services over the Internet is bringing millions of new users online, thus creating a growing demand for bandwidth. Wavelength Division Multiplexed (WDM) networks, employing wavelength routing has emerged as the dominant technology to satisfy this growing demand for bandwidth. As the amount of traffic carried is larger, any single failure can be catastrophic. Survivability becomes indispensable in such networks. Therefore, it is imperative to design networks that can quickly and efficiently recover from failures.;In this dissertation, we explore the design and operation of survivable optical networks. We study several survivability paradigms for surviving single link failures. A restoration model is developed based on a combination of these paradigms. We propose an optimal design and upgrade scheme for WDM backbone networks. We formulate an integer programming-based design problem to minimize the total facility cost. This framework provides a cost effective way of upgrading the network by identifying how much resources to budget at each stage of network evolution. This results in significant cost reductions for the network service provider.;As part of network operation, we capture multiple operational phases in survivable network operation as a single integer programming formulation. This common framework incorporates service disruption and includes a service differentiation model based on lightpath protection. However, the complexity of the optimization problem makes the formulation applicable only for network provisioning and o2ine reconfiguration. The direct use of such methods for online reconfiguration remains limited to small networks with few tens of wavelengths. We develop a heuristic algorithm based on LP relaxation technique for fast, near optimal, online reconfiguration. Since the ILP variables are relaxed, we provide a way to derive a feasible solution from the relaxed problem. Most of the current approaches assume centralized information. They do not scale well as they rely on per-flow information. This motivates the need for developing dynamic algorithms based on partial information. The partial information we use can be easily obtained from traffic engineering extensions to routing protocols. Finally, the performance of partial information routing algorithms is compared through simulation studies

Protection and restoration algorithms for WDM optical networks

Currently, Wavelength Division Multiplexing (WDM) optical networks play a major role in supporting the outbreak in demand for high bandwidth networks driven by the Internet. It can be a catastrophe to millions of users if a single optical fiber is somehow cut off from the network, and there is no protection in the design of the logical topology for a restorative mechanism. Many protection and restoration algorithms are needed to prevent, reroute, and/or reconfigure the network from damages in such a situation. In the past few years, many works dealing with these issues have been reported. Those algorithms can be implemented in many ways with several different objective functions such as a minimization of protection path lengths, a minimization of restoration times, a maximization of restored bandwidths, etc. This thesis investigates, analyzes and compares the algorithms that are mainly aimed to guarantee or maximize the amount of remaining bandwidth still working over a damaged network. The parameters considered in this thesis are the routing computation and implementation mechanism, routing characteristics, recovering computation timing, network capacity assignment, and implementing layer. Performance analysis in terms of the restoration efficiency, the hop length, the percentage of bandwidth guaranteed, the network capacity utilization, and the blocking probability is conducted and evaluated

Survivability algorithms in MPLS and WDM optical networks

In modern ultra-wide bandwidth, high speed and high reliable communication networks, the failure of network components including equipment (such as routers) and transmission media (such as fibers) may cause a huge volume of data loss. Therefore network survivability mechanisms, by which the disrupted traffic upon failures can be restored, are crucial in network design and deserve thorough investigation. In this thesis, we propose some survivability approaches to survive failures in MPLS and WDM optical networks. MPLS is a promising technology that enables much faster failure recovery than conventional IP rerouting in IP networks. While the traditional MPLS path-based protection scheme is capacity efficient, it is relatively slow in restoration; on the other hand, while traditional MPLS link-based scheme has fast restoration speed, its capacity efficiency is low. In this thesis, we propose a new restoration scheme called UNIFR, which can provide fast restoration as link-based scheme while achieving better capacity efficiency than link-based scheme. We present a MPLS resilience framework that supports UNIFR and give two ILP formulations to solve the spare capacity optimization problem for UNIFR-based restoration model. Simulation study shows that the capacity efficiency of UNIFR-based model is much better than that of link-based model and close to that of path-based model. In WDM optical networks, although lots of pervious works have been done in both protection and restoration survivability techniques, to our best knowledge, little study focuses on improving the dynamic restoration success ratio. To address this problem, we first identify two restoration blocking types called primary holding and mutual competition. To address primary holding, we propose a dynamic routing and wavelength assignment algorithm for connection establishment that takes the future possible failures into consideration and choose route and wavelength for the working lightpath that could lead to higher chance of successful restoration for the potential failures. To address mutual competition, we present some heuristics ideas to increase restoration success ratio. Simulation shows that our algorithms can clearly reduce the restoration blocking probability while not affecting primary blocking probability and restoration speed much

Link failure protection and restoration in WDM optical networks

In a wavelength-division-multiplexing (WDM) optical network, the failure of fiber links may cause the failure of multiple optical channels, thereby leading to large data loss. Therefore the survivable WDM optical networks where the affected traffic under link failure can be restored, have been a matter of much concern. On the other hand, network operators want options that are more than just survivable, but more flexible and more efficient in the use of capacity. In this thesis, we propose our cost-effective approaches to survive link failures in WDM optical networks. Dynamic establishment of restorable connections in WDM networks is an important problem that has received much study. Existing algorithms use either path-based method or link-based method to protect a dynamic connection; the former suffers slow restoration speed while the latter requires complicated online backup path computation. We propose a new dynamic restorable connection establishment algorithm using p-cycle protection. For a given connection request, our algorithm first computes a working path and then computes a set of p-cycles to protect the links on the working path so that the connection can survive any single link failure. The key advantage of the proposed algorithm over the link-based method is that it enables faster failure restoration while requires much simpler online computation for connection establishment. Tree-based schemes offer several advantages such as scalability, failure impact restriction and distributed processing. We present a new tree-based link protection scheme to improve the hierarchical protection tree (p-tree) scheme [31] for single link failure in mesh networks, which achieves 100% restorability in an arbitrary 2-connected network. To minimize the total spare capacity for single link failure protection, an integer linear programming (ILP) formulation is provided. We also develop a fast double-link failure restoration scheme by message signaling to take advantage of the scalable and distributed processing capability of tree structure

Survivable network design of all-optical network.

Kwok-Shing Ho.Thesis (M.Phil.)--Chinese University of Hong Kong, 2002.Includes bibliographical references (leaves 69-71).Abstracts in English and Chinese.List of Figures --- p.viList of Tables --- p.viiChapter Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Overview --- p.1Chapter 1.2 --- Thesis Objectives --- p.6Chapter 1.3 --- Outline of Thesis --- p.8Chapter Chapter 2 --- The Spare Capacity Planning Problem --- p.9Chapter 2.1 --- Mathematical Model of the Spare Capacity Planning Problem --- p.12Chapter 2.1.1 --- Variable Definitions --- p.12Chapter 2.1.2 --- Objective Function and Constraints --- p.15Chapter 2.1.3 --- Complexity --- p.17Chapter 2.2 --- Greedy Algorithm - Spare Capacity Allocation and Planning Estimator (SCAPE) --- p.19Chapter 2.2.1 --- Working Principle of SCAPE --- p.20Chapter 2.2.2 --- Implementation of SCAPE --- p.22Chapter 2.2.3 --- Improved SCAPE --- p.23Chapter 2.3 --- Experimental Results and Discussion --- p.27Chapter 2.3.1 --- Experimental Platform --- p.27Chapter 2.3.2 --- Experiment about Accuracy of SCAPE --- p.27Chapter 2.3.3 --- Experiment about Minimization of Network Spare Capacity --- p.30Chapter 2.3.4 --- Experiment about Minimization of Network Spare Cost --- p.35Chapter 2.4 --- Conclusions --- p.38Chapter Chapter 3 --- Survivable All-Optical Network Design Problem --- p.39Chapter 3.1 --- Mathematical Model of the Survivable Network Design Problem --- p.42Chapter 3.2 --- Optimization Algorithms for Survivable Network Design Problem --- p.44Chapter 3.2.1 --- Modified Drop Algorithm (MDA) --- p.45Chapter 3.2.1.1 --- Drop Algorithm Introduction --- p.45Chapter 3.2.1.2 --- Network Design with MDA --- p.45Chapter 3.2.2 --- Genetic Algorithm --- p.47Chapter 3.2.2.1 --- Genetic Algorithm Introduction --- p.47Chapter 3.2.2.2 --- Network Design with GA --- p.48Chapter 3.2.3 --- Complexity of MDA and GA --- p.51Chapter 3.3 --- Experimental Results and Discussion --- p.52Chapter 3.3.1 --- Experimental Platform --- p.52Chapter 3.3.2 --- Experiment about Accuracy of MDA and GA --- p.52Chapter 3.3.3 --- Experiment about Principle of Survivable Network Design --- p.55Chapter 3.3.4 --- Experiment about Performance of MDA and GA --- p.58Chapter 3.4 --- Conclusions --- p.62Chapter Chapter 4 --- Conclusions and Future Work --- p.63Appendix A The Interference Heuristic for the path restoration scheme --- p.66Bibliography --- p.69Publications --- p.7

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

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

Availability Constrained Routing And Wavelength Assignment And Survivability In Optical Wdm Networks

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2009Bu çalışmada, optik ağlarda kullanılabilirlik kısıtı altında yol ve dalgaboyu atama konusu farklı sürdürülebilirlik politikaları altında çalışılmış ve elde edilen sonuçlar benzetim aracılığıyla doğrulanarak sunulmuştur. Öncelikle paylaşılan yol koruması altında sınırsız kaynak bulunması durumunda kullanılabilirlik kısıtı altında yol ve dalgaboyu atamaya yönelik planlama amaçlı bağlantı kurma yöntemleri sezgisel ve optimizasyona dayalı olarak önerilmiştir. Sonrasında bu teknikler kısıtlı kaynak altında ve farklılaştırılmış kullanılabilirlik düzeyi gereksinimleri ile gelen bağlantı isteklerinin olması koşulu altında çalışabilecek şekilde adapte edilmiş ve başarımları sınanmıştır. Önerilen tekniklerin literatürde yaygın olarak bilinen bağlantı kurma tekniklerinin başarımını bağlantı düşürme olasılığı ve bağlantı kullanılabilirliği açısından yükselttiği, bunun yanında yedek kaynak tüketim fazlasını da gözeterek kabul edilir bir düzeyde tuttuğu gözlenmiştir. Özellikle optimizasyon tabanlı bağlantı kurma tekniğinin, farklılaştırılmış bağlantı isteklerinin bulunduğu ortamda kaynak tüketimini de düşürdüğü gösterilmiştir. Son olarak da, segmanlı koruma için önceden önerilmiş bir kullanılabilirlik analizine rastlanamadığı için, paylaşılan segmanlı koruma için kullanılabilirlik analizi yöntemi önerilerek benzetim aracılığıyla doğrulanmıştır. Bu analiz kullanılarak da segmanlı koruma altında kullanılabilirliği gözeten yol ve dalgaboyu atama yöntemleri oluşturularak başarımları kaynak kısıtlı ve kaynakça zengin ortamlarda denenerek uygulanabilirlikleri belirlenmiştir.In this study, we have proposed availability aware routing and wavelength assignment schemes for optical networks under different survivability policies. The proposed techniques are evaluated by simulation. First, we have proposed heuristic and optimization driven connection provisioning schemes under shared backup path protection in resource plentiful environment. Then, the proposed schemes are modified to work in resource limited environment where connections arrive with differentiated availability requirements. The proposed techniques are compared to a conventional reliable connection provisioning algorithm. The simulation results show that the proposed techniques lead to lower connection blocking probability and better connection availability. Besides this, it is also shown that the proposed techniques also keep the resource overbuild due to protection in a feasible range. Moreover, the experimental results also show that the optimization driven technique leads to a decreased resource overbuild under resource limited environment for connection arrivals with differentiated availability requirements. The last part of this work deals with shared segment protection. Since there is no specific availability analysis method for shared segment protection, an availability analysis method for this protection scheme is proposed and validated by simulation. Based on this analysis, availability aware connection provisioning schemes are constructed, their performance is evaluated in resource plentiful and resource scarce environments, and the applicability of the schemes are determined in terms of environmental constraints.DoktoraPh