Multilayer Protection with Availability Guarantees in Optical WDM Networks

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Network protection with multiple availability guarantees

We develop a novel network protection scheme that provides guarantees on both the fraction of time a flow has full connectivity, as well as a quantifiable minimum grade of service during downtimes. In particular, a flow can be below the full demand for at most a maximum fraction of time; then, it must still support at least a fraction q of the full demand. This is in contrast to current protection schemes that offer either availability-guarantees with no bandwidth guarantees during the downtime, or full protection schemes that offer 100% availability after a single link failure. We develop algorithms that provide multiple availability guarantees and show that significant capacity savings can be achieved as compared to full protection. If a connection is allowed to drop to 50% of its bandwidth for 1 out of every 20 failures, then a 24% reduction in spare capacity can be achieved over traditional full protection schemes. In addition, for the case of q = 0, corresponding to the standard availability constraint, an optimal pseudo-polynomial time algorithm is presented.National Science Foundation (U.S.) (NSF grants CNS-1116209)National Science Foundation (U.S.) (NSF grants CNS-0830961)United States. Defense Threat Reduction Agency (grant HDTRA-09-1-005)United States. Defense Threat Reduction Agency (grant HDTRA1-07-1-0004)United States. Air Force (Air Force contract # FA8721-05-C-0002

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

Exploiting Excess Capacity for Survivable Traffic Grooming in Optical Backbone Networks

Backbone networks usually have some excess capacity (EC) to accommodate traffic fluctuations and to avoid early capacity exhaustion. Network operators can exploit EC in optical wavelength division multiplexed (WDM) backbone networks to support survivable traffic grooming, where connection requests are of subwavelength granularity and each provisioned request has to be protected from single-link failures. We investigate novel EC management techniques that can improve network performance, in terms of Service-Level Agreement (SLA) violations and bandwidth blockings, with no requirement of deploying additional capacity. We investigate exploiting and managing EC by the following techniques. i) Preprovisioning: When traffic is light, network resources are reserved by a preprovisioning scheme, i. e., a connection can be provisioned on reserved protected links to increase availability. We show that preprovisioning also decreases connection setup time, an important metric for delay-sensitive services. ii) Backup reprovisioning: Since high-availability protection schemes usually consume more resources, connections in our solution can be switched to a protection scheme that provides lower availability (but higher resource efficiency) by reprovisioning backup resources when traffic increases. iii) Hold-lightpath: We propose a new "hold-lightpath" scheme to exploit EC. This scheme prevents the termination of pre-established (but unused) resources to increase availability and decrease connection setup time. We compare our techniques with traditional protection schemes for typical daily fluctuating traffic on typical backbone network topologies and find that significant improvements can be achieved in terms of decreasing SLA violations, bandwidth blocking, and connection setup time

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

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

Availability Formulations for Segment Protection

Abstract-Segment Protection (SP) is an efficient scheme for protection in WDM optical networks. This letter provides algebraic formulations to evaluate SP availability both in the dedicated and shared backup case. The availability models are applied to numerical examples and significant relations between SP availability and relevant connection parameters are identified

Crosslayer Survivability in Overlay-IP-WDM Networks

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

Supporting differentiated classes of resilience in multilayer networks

Services provided over telecommunications networks typically have different resilience requirements and networks need to be able to support different levels of resilience in an efficient manner. This dissertation investigates the problem of supporting differentiated classes of resilience in multilayer networks, including the most stringent resilience class required by critical services. We incorporate an innovative technique of embedding a subnetwork, termed the spine, with comparatively higher availability values at the physical layer. The spine lays a foundation for differentiation between multiple classes of flows that can be leveraged to achieve both high resilience and differentiation. The aim of this research is mainly to explore, design, and evaluate the proposed spine concept model in multilayer networks. The dissertation has four major parts. First, we explore the spine concept through numerical analysis of simple topologies illustrating the potential benefits and the cost considerations of the spine. We develop heuristics algorithms to find suitable spines for a network based on the structural properties of the network topology. Second, an optimization problem is formulated to determine the spine. The problem encompasses estimates of link availability improvements, associated costs, and a total budget. Third, we propose a crosslayer mapping and spine-aware routing design problem with protection given mainly at the lower layer. The problem is designed to transfer lower layer differentiation capability to the upper layer network and flows. We provide two joint routing-mapping optimization formulations and evaluate their performance in a multilayer scenario. Fourth, the joint routing-mapping problem is redesigned with protection given in the upper network layer instead. This will create two isolated logical networks; one mapped to the spine and the other is mapped freely on the network. Flows are assigned a path or path-pair based on their class of resilience. This approach can provide more routing options yielding different availability levels. The joint routing-mapping design problems are formulated as Integer Linear Programming (ILP) models. The goal is to achieve a wider range of availability values across layers and high availability levels for mission-critical services without the need to use higher order protection configurations. The proposed models are evaluated with extensive numerical results using real network topologies