Maximizing Reliability in WDM Networks through Lightpath Routing

We study the reliability maximization problem in WDM networks with random link failures. Reliability in these networks is defined as the probability that the logical network is connected, and it is determined by the underlying lightpath routing and the link failure probability. We show that in general the optimal lightpath routing depends on the link failure probability, and characterize the properties of lightpath routings that maximize the reliability in different failure probability regimes. In particular, we show that in the low failure probability regime, maximizing the “cross-layer” min cut of the (layered) network maximizes reliability, whereas in the high failure probability regime, minimizing the spanning tree of the network maximizes reliability. Motivated by these results, we develop lightpath routing algorithms for reliability maximization.National Science Foundation (U.S.) (Grant CNS-0830961)National Science Foundation (U.S.) (Grant CNS-1017800)United States. Defense Threat Reduction Agency (Grant HDTRA1-07-1-0004)United States. Defense Threat Reduction Agency (Grant HDTRA-09-1-0050

A robust optimization approach to backup network design with random failures

This paper presents a scheme in which a dedicated backup network is designed to provide protection from random link failures. Upon a link failure in the primary network, traffic is rerouted through a preplanned path in the backup network. We introduce a novel approach for dealing with random link failures, in which probabilistic survivability guarantees are provided to limit capacity over-provisioning. We show that the optimal backup routing strategy in this respect depends on the reliability of the primary network. Specifically, as primary links become less likely to fail, the optimal backup networks employ more resource sharing amongst backup paths. We apply results from the field of robust optimization to formulate an ILP for the design and capacity provisioning of these backup networks. We then propose a simulated annealing heuristic to solve this problem for largescale networks, and present simulation results that verify our analysis and approach.National Science Foundation (U.S.) (grant CNS-0626781)National Science Foundation (U.S.) (grant CNS-0830961)United States. Defense Threat Reduction Agency (grant HDTRA1-07-1-0004)United States. Defense Threat Reduction Agency (grant HDTRA-09-1-005

Maximizing Reliability in WDM Networks Through Lightpath Routing

We study the reliability maximization problem in wavelength division multiplexing (WDM) networks with random link failures. Reliability in these networks is defined as the probability that the logical network is connected, and it is determined by the underlying lightpath routing, network topologies, and the link failure probability. By introducing the notion of lexicographical ordering for lightpath routings, we characterize precise optimization criteria for maximum reliability in the low failure probability regime. Based on the optimization criteria, we develop lightpath routing algorithms that maximize the reliability, and logical topology augmentation algorithms for further improving reliability. We also study the reliability maximization problem in the high failure probability regime.National Science Foundation (U.S.) (Grant CNS-0830961)National Science Foundation (U.S.) (Grant CNS-1017800)United States. Defense Threat Reduction Agency (Grant HDTRA1-07-1-0004)United States. Defense Threat Reduction Agency (Grant HDTRA-09-1-0050

Availability constrained routing and wavelength assignment techniques for optical WDM networks

Dalgaboyu bölmeli çoğullama (WDM) tekniği ile optik ağlar tarafından sunulan yüksek bandgenişliği, optik hatlarda veya ağ bileşenlerinde oluşabilecek hatalar karşısında da yoğun miktarda veri kaybı riskini beraberinde getirmektedir. Bu durumun önüne geçmek için, bağlantılar belirli bir sürdürülebilirlik politikası ile korunarak kurulmaktadır. Ağda oluşabilecek hata durumlarınnda da bağlantının kullanılabilir ve sunulan hizmetin kesintisiz olması kullanıcılar tarafından beklenmektedir. Bu nedenle, bağlantı istekleri kurulurken, yol ve dalgaboyu atamasında, ilgili sürdürülebilirlik politikası altında kullanılabilirlik kısıtının göz önünde bulundurulması gerekmektedir. Bu çalışmada, paylaşımlı yol koruma politikası altında kurulan bağlantıların kullanılabilirlik isteklerini göz önünde bulundurarak yol ve dalgaboylarını atayan iki farklı teknik önerilmektedir. Bu tekniklerden ilki, G-DAP (Global Differentiated Availability-Aware Provisioning) sezgisel olarak yedek dalgaboyu kanalları üzerinde, her bir kullanılabilirlik sınıfı için global bir paylaşım derecesi kestirir. Diğer teknik LBL-DAP (Link-By-Link Differentiated Availability-Aware Provisioning) ise bir optimizasyon modeli kullanarak, her bir kullanılabilirlik sınıfı için yedek kanallar üzerindeki paylaşım derecesini, her bir optik hat için ayrıca hesaplar. Bağlantı isteklerinin %98, %99, %99.9, %99.99% ve %99.999 kullanılabilik düzeyinin birinden geldiği ortamda yapılan testlerde, önerilen teknikler yaygın olan CAFES (Compute-A-Feasible Solution) algoritmasıyla NSFNET ve EON topolojilerinde karşılaştırılmıştır. Bağlantıların sınıflar arasında düzgün ve heterojen dağıldığı ortamlarda toplanan sonuçlar, önerilen tekniklerin daha yüksek bağlantı kabul oranı ve kullanılabilirlik sağladığını göstermektedir. Ayrıca, yedek kaynak kullanım oranını düşürmesi nedeniyle LBL-DAP’ın en iyi başarımı sağladığı görülmüştür. Anahtar Kelimeler: Optik ağlar, dalgaboyu bölmeli çoğullama, kullanılabilirlik, yol atama.As a result of the increase in the bandwidth demand of the next generation Internet applications, Optical Wavelength division Multiplexing (WDM) networks seem to be the most appropriate technology that can be deployed in the backbone. Optical WDM networks introduce the advantage of offering bandwidth partitioned into a number of gigabits per second wavelength channels. However, the advantage introduced by the huge bandwidth offer also introduces a disadvantage when the network experiences a failure. Service interrupts on any component along the lightpath may lead to significant amount of data loss since the fiber capacity is huge. Factors like multiple errors, long fault recovery duration, and component failure characteristics introduce availability constraint for the network elements, and also for the connections. Therefore, connections are required to be provisioned by taking availability constraint into consideration. In short, availability stands for the probability of a network component, a channel or a link being in the operational state at any time t. Significant amount of the previous work is concerned with availability aware routing and wavelength assignment (RWA) under shared backup protection. The first and the most common availability aware routing scheme is compute-a-feasible-solution (CAFES). In this scheme, a number of candidate working paths are selected. For each working path, a corresponding backup path is selected by forcing the backup channels to be shared. The working and backup path pair that leads to the highest availability or another lowest cost metric is selected, and assigned to the incoming connection request. In this work, we present two dynamic connection provisioning schemes for differentiated availability-constrained RWA. Both of the schemes are derived from the conventional reliable provisioning scheme CAFES. In the dynamic environment, connections arrive with the availability requirements of 98% (class-1), 99% (class-2), 99.9% (class-3), 99.99% (class-4), and 99.999% (class-5). First scheme is called Global Differentiated Availability-aware Provisioning (G-DAP). This scheme monitors the average availability per connection for each class and resource-overbuild throughout the network. In order to enhance the performance of the connection provisioning, G-DAP also takes the advantage of the trade-off between resource overbuild and connection unavailability where resource overbuild is the ratio of the number of backup channels to the number of working channels in the network, and unavailability is one's complement of the availability. Based on the change in these two parameters it attempts to specify a feasible global sharing degree for all wavelength channels per availability class. The trade-off function is defined as the product of these two parameters. Hence, if the tradeoff is monitored to be decreasing for the related availability class, the last action (increment or decrement) taken on the sharing degree of that class is repeated; otherwise, it is reversed. The second scheme is called Link-by-Link Differentiated Availability-aware Provisioning (LBL-DAP). LBL-DAP estimates a separate feasible sharing degree per class for the channels of each link. It periodically runs an integer linear programming (ILP) function to obtain the feasible sharing degrees on each link. When searching for a backup RWA configuration, both schemes modify the link costs based on the feasible sharing degree obtained for the availability class of the incoming connection and current load for the connection?s class on the link respectively. Since we aim to improve the performance in terms of resource overbuild, connection availability, and blocking probability, we use the conventional reliable provisioning scheme, CAFES as a base in our simulations. Moreover, since connections arrive with differentiated availability requirements, we also modify CAFES to enable a connection to be provisioned unprotected if a selected working path can meet its availability requirement. Thus, resource consumption overhead of this scheme is modified for its favor. Performance of G-DAP and LBL-DAP are compared to that of CAFES by simulation under NSFNET and EON topologies. Simulation results are collected under two different conditions where the connection requests are distributed uniformly and heterogeneously among the availability classes. It is shown that the proposed schemes lead to enhanced blocking ratio and connection availability. Moreover, by taking the advantage of optimization and considering the feasible sharing degrees for the links separately, LBL-DAP also introduces significant decrease in resource overbuild. Keywords: Optical networks, wavelength division multiplexing, availability, routing

Holding time and delay tolerance aware, availability-guaranteed connection provisioning in WDM networks

Optik dalga boyu bölmeli çoğullama (Wavelength Division Multiplexing- WDM) ağlarında, yeni teknolojilerdeki ilerleme, yüksek bant genişliği isteyen uygulamalara yüksek kapasite sağlamak üzere kiralanabilir devrelerin dinamik ve kısa vadeli olarak kurulup serbest bırakılmasına olanak sağlamaktadır. Yüksek hızlı optik bağlantının kesilmesi, büyük veri kaybına neden olduğundan, bu bağlantıların arızalara karşı korunması gerekmektedir. Diğer yandan, veri, ses ve video gibi verilerin farklı trafik tiplerinin hızla artması, kullanılabilirliği garantili bant genişliğinin yanı sıra farklılaştırılmış hizmetler gerektirmektedir. Bu nedenle, ilerideki ağ taşıyıcılarının, HDA (Hizmet Düzeyi Anlaşması) (Service Level Agreement- SLA) ilkelerini karşılaması ve böylece belli bir hizmet düzeyi garantilemesi ve verimli kaynak kullanımı sağlaması gerekmektedir. Bu amaçla bu çalışmada farklı sürdürülebilir yol kurulum teknikleri bağlantı isteklerinin düzeyine göre tercih edilmektedir. Hizmet kalitesine bağlı olarak korunmasız, yol paylaşımlı korumalı ve yol atamalı korumalı bağlantı kurulumunun tercihli kullanımı sonucunda, isteklerin farklılaşmış kullanılabilirlik gereklilikleri karşılanmaktadır. Bu çalışmada yedek kapasite kullanım oranının ve bloke olma olasılığının düşürülmesi amacıyla farklı iki teknik tanıtılmıştır. Birinci teknik, yeni gelen isteğin bağlantısını kurmadan önce sistemde önceden kurulmuş bağlantıların hizmet sürelerinden yararlanarak paylaşımı artırma esasına dayanmaktadır. İkinci yöntem ise bloke olma olasılığını düşürmek amacıyla kullanıcı tarafından belirlenen zaman toleransı parametresinden yararlanmaktadır. Bu iki yöntem önceki benzer amaca yönelik algoritmalarla karşılaştırılmaktadır. Sonuç olarak önerilen algoritmaların kaynak kullanımını azalttığı, bloke olma oranını ise yeni kaynak eklenmesine gerek duyulmaksızın düşürdüğü gözlemlenmiştir.  Anahtar Kelimeler: Optik ağlar, dalga boyu bölmeli çoğullama, kullanılabilirlik, yol atama.With the development of agile optical switches, dynamic optical circuit switching has become possible and connections are set up and torn down on- demand basis. The explosive growth of different traffic types such as data, voice and video requires the support of differentiated services in terms of survivability measures and timing requirements. In order to guarantee a specific level of survivability, availability-guaranteed bandwidth provisioning is considered. On the other hand, connections are set up and released for specific time durations, with sliding or fixed set-up times. Connection requests arrive to the network provider with specified holding times, delay tolerances and availability requirements which need to be satisfied. Delay tolerance is defined as the maximum time which a request can tolerate before the connection is set up. Future network carriers need to meet strict SLA (Service Level Agreement) guidelines, thus guaranteeing a level of service, as well as achieving efficient resource utilization. Connection availability is an important metric to measure the quality of service (QoS) in a survivable network. It is defined as the probability that a connection will be found in the operating state at a random time in the future (Clouqueur et al., 2002). It is affected by many factors such as network component failure probabilities, failure repair times, etc. Usually, the availability target for a connection is specified in a Service Level Agreement (SLA), which is a contract between a service provider (e.g., a network operator) and one of its customers (e.g., a large institutional user of bandwidth). An SLA violation may result in a penalty to be paid by the network operator to the customer according to the contract (Grover, 1999). In order to provide the appropriate level of availability stated in the SLAs, different recovery mechanisms can be used to provision different connection requests. In this study, we consider unprotected, shared-path protected and dedicated-path protected provisioning mechanisms at the same time to satisfy different QoS requirements in a dynamic manner. Previous studies, while maximizing sharability by routing backup paths in a dynamic traffic environment, do not make any estimation on future sharability of resources. They take the current link states into consideration to choose sharable links. Reference (Tornatore et al., 2005a,b) shows that resource overbuild (RO) in shared-path protection can be decreased by exploiting the holding-time information of connections which have already been provisioned in the network. Since holding times of incoming traffic demands may be known in advance for a variety of applications, this information about the future states of the links makes the route decision more intelligent by allowing the choice of more sharable paths. In this paper, unprotected, shared-path, and dedicated-path protection techniques are used to meet the differentiated availability requirements. Recently, among the other Service Level Specifications (SLSs), many new applications are identified by known-in-advance holding-time and delay tolerance. So, in this paper, for dynamic provisioning of availability-guaranteed connections in an optical mesh network, we propose two new algorithms which exploit 1-the knowledge of connection holding times to accomplish minimum backup capacity allocation as compared to the previous holding-time-unaware approach and 2- the knowledge of delay tolerances to degrease the blocking probability in the conditions that the system resources are not available to satisfy the SLS demands of connection requests. Here we also propose a new routing mechanism for backup paths optimizing backup resources considering the future departure time of existing connections. In order to show the performance gain; the first proposal, AGSDP_HT (Holding-time aware Availability-Guaranteed Service-Differentiated Provisioning) is compared by a base line algorithm AGSDP. The second proposal ADT (Availability-guaranteed, service differentiated provisioning with Delay Tolerance) is compared by a base line approach which does not consider delay tolerance. For the second proposal, both algorithms dedicated protection is not used as a choice, since blocking is decreased by delay tolerance. Keywords: WDM Networks, availability aware provisioning, survivability

Availability-driven optimal design of shared path protection in WDM networks

The success of the Internet has led many activities to be highly dependent on the good quality of the service that the network can provide. Failures can be very disruptive if systems without enough backup resources are in place. In this paper we propose a new way of determining how many backup resources must be provided to guarantee a given level of availability to critical services in the core of the network. The biggest impact of this work lies in how network providers design and deploy their infrastructure

Data Driven Network Design for Cloud Services Based on Historic Utilization

In recent years we have seen a shift from traditional networking in enterprises with Data Center centric architectures moving to cloud services. Companies are moving away from private networking technologies like MPLS as they migrate their application workloads to the cloud. With these migrations, network architects must struggle with how to design and build new network infrastructure to support the cloud for all their end users including office workers, remote workers, and home office workers. The main goal for network design is to maximize availability and performance and minimize cost. However, network architects and network engineers tend to over provision networks by sizing the bandwidth for worst case scenarios wasting millions of dollars per year. This thesis will analyze traditional network utilization data from twenty-five of the Fortune 500 companies in the United States and determine the most efficient bandwidth to support cloud services from providers like Amazon, Microsoft, Google, and others. The analysis of real-world data and the resulting proposed scaling factor is an original contribution from this study

Risk-based Survivable Network Design

Communication networks are part of the critical infrastructure upon which society and the economy depends; therefore it is crucial for communication networks to survive failures and physical attacks to provide critical services. Survivability techniques are deployed to ensure the functionality of communication networks in the face of failures. The basic approach for designing survivable networks is that given a survivability technique (e.g., link protection, or path protection) the network is designed to survive a set of predefined failures (e.g., all single-link failures) with minimum cost. However, a hidden assumption in this design approach is that the sufficient monetary funds are available to protect all predefined failures, which might not be the case in practice as network operators may have a limited budget for improving network survivability. To overcome this limitation, this dissertation proposed a new approach for designing survivable networks, namely; risk-based survivable network design, which integrates risk analysis techniques into an incremental network design procedure with budget constraints. In the risk-based design approach, the basic design problem considered is that given a working network and a fixed budget, how best to allocate the budget for deploying a survivability technique in different parts of the network based on the risk. The term risk measures two related quantities: the likelihood of failure or attack, and the amount of damage caused by the failure or attack. Various designs with different risk-based design objectives are considered, for example, minimizing the expected damage, minimizing the maximum damage, and minimizing a measure of the variability of damage that could occur in the network. In this dissertation, a design methodology for the proposed risk-based survivable network design approach is presented. The design problems are formulated as Integer Programming (InP) models; and in order to scale the solution of models, some greedy heuristic solution algorithms are developed. Numerical results and analysis illustrating different risk-based designs are presented