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

ILP formulations for p-cycle design without candidate cycle enumeration

The concept of p-cycle (preconfigured protection cycle) allows fast and efficient span protection in wavelength division multiplexing (WDM) mesh networks. To design p-cycles for a given network, conventional algorithms need to enumerate cycles in the network to form a candidate set, and then use an integer linear program (ILP) to find a set of p-cycles from the candidate set. Because the size of the candidate set increases exponentially with the network size, candidate cycle enumeration introduces a huge number of ILP variables and slows down the optimization process. In this paper, we focus on p-cycle design without candidate cycle enumeration. Three ILPs for solving the problem of spare capacity placement (SCP) are first formulated. They are based on recursion, flow conservation, and cycle exclusion, respectively. We show that the number of ILP variables/constraints in our cycle exclusion approach only increases linearly with the network size. Then, based on cycle exclusion, we formulate an ILP for solving the joint capacity placement (JCP) problem. Numerical results show that our ILPs are very efficient in generating p-cycle solutions. © 2009 IEEE.published_or_final_versio

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 analysis of resilient geometric routing on Internet topology

Scalable routing schemes for large-scale networks, especially future Internet, are required. Geometric routing scheme is a promising candidate to solve the scalability issue of routing tables in conventional IP routing based on longest prefix matching. In this scheme, network nodes are assigned virtual coordinates and packets are forwarded towards their intended destination following a distance-decreasing policy. Dynamics in the network such as node/link failures might affect this forwarding and lead packets to a dead end. We proposed recovery techniques in geometric routing to deliver packets to the destination in case of failures. In this paper, we perform an analysis on the availability of the proposed protection techniques on the Internet graph. The routing scheme over optical transport network is considered and the reliability data of physical components and a known network availability model are used. This evaluation is compared with the shortest cycle scheme which finds two node disjoint paths between every source and destination in the topology and also with geometric routing with no protection. The results show that the proposed scheme performs reasonably well compared to the shortest cycle scheme and significantly enhances the availability compared to geometric routing without any protection

A matrix-based analytical approach to connection unavailability estimation in shared backup path protection

This letter introduces a matrix-based approach to connection unavailability estimation in shared backup path protection (SBPP). The proposed approach yields accurate results for networks of national size using simple matrix operations, being therefore suitable for online routing algorithms. The accuracy of the unavailability estimates is verified through simulations.9984484

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