Availability-aware service provisioning tries to satisfy the availability requirements of clients on demand and can improve the resource efficiency in optical networks. This paper studies the problem of flexible availability-aware differentiated protection (ADP) in elastic optical networks (EONs). We first consider the unique features in EONs, e.g., flexible spectrum allocation and bandwidth-squeezed protection, describe the problem of ADP, and present a theoretical analysis on service availability. Then, we develop an ADP algorithm that can change the path protection scheme to adapt to different service availability requirements. An availability-aware backup reprovisioning strategy is also proposed as a supplement of the ADP algorithm to further improve the protection efficiency. We also discuss the system design for OpenFlow-based software-defined EON (SD-EON) framework to facilitate the ADP scheme. Finally, to demonstrate the overall design, we construct an SD-EON control plane testbed that consists of 14 standalone nodes, implement the proposed algorithms in the OpenFlow controller, and perform experiments to evaluate their performance. The results indicate that the system performs well, and the proposed algorithms can reduce blocking probability effectively without sacrificing the service availability of requests.

Flexible Availability-Aware Differentiated Protection in Software-Defined Elastic Optical Networks

This paper highlights the complexity and challenges of providing reliable services in the evolving communications infrastructure. The hurdles in providing end-to-end availability guarantees are discussed and research problems identified. Avenues for overcoming some of the challenges examined are presented. This includes the use of a highly available network spine embedded in a physical network together with efficient crosslayer mapping to offer survivability and differentiation of traffic into classes of resilience.

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Resilient network design: challenges and future directions

In wavelength division multiplexed networks (WDM) with 1:1 path protection, a link-disjoint protection (backup) path is also set up at the time of setting up a working (primary) path. Hence, the failure of a single fiber-link does not cause huge data losses. This paper considers on-line routing and wavelength assignment (RWA) of protection paths in such networks. In particular, we study two strategies based on the 1:1 path protection scheme. The Static strategy establishes protection paths such that once a route and wavelength have been chosen they are not allowed to change. On the other hand, the Dynamic strategy allows for re-arrangement of protection paths, that is, both the route and wavelength chosen for a protection path can change so as to accommodate a new request. With either strategy, we assume that the working paths cannot be re-arranged. This is to prevent the disruption of on-going traffic. The two strategies are compared on the basis of the number of connections requests that can be satisfied for a given number of wavelengths, assuming that the requests come one at a time, and wavelengths are assigned according to the First-Fit policy. One of the results of our study is that, contrary to intuition, the Static strategy performs better than the Dynamic strategy.

Static versus dynamic establishment of protection paths in WDM networks

The three-stage Clos networks remain the most popular solution to many practical switching systems to date. The aim of this paper is to show that the modular structure of Clos networks is invariant with respect to the technological changes. Due to the wavelength routing property of arrayed-waveguide gratings (AWGs), non-blocking and contention-free wavelength-division-multiplexing (WDM) switches require that two calls carried by the same wavelength must be connected by separated links; otherwise, they must be carried by different wavelengths. Thus, in addition to the non-blocking condition, the challenge of the design of AWG-based multistage switching networks is to scale down the wavelength granularity and to reduce the conversion range of tunable wavelength converters (TWCs). We devise a logic scheme to partition the WDM switch network into wavelength autonomous cells and show that the wavelength scalability problem can be solved by recursively reusing similar, but smaller, set of wavelengths in different cells. Furthermore, we prove that the rearrangeably non-blocking (RNB) condition and route assignments in these AWG-based three-stage networks are consistent with that of classical Clos networks. Thus, the optimal AWG-based non-blocking Clos networks also can achieve 100% utilization when all input and output wavelength channels are busy.

AWG-based non-blocking Clos networks

In an optical network a signal can only travel a maximum distance dmax before its quality deteriorates to the point that it must be regenerated by installing regenerators at nodes of the network. As the cost of a regenerator is high, we wish to deploy as few regenerators as possible in the network, while ensuring all nodes can communicate with each other. In this paper we introduce the generalized regenerator location problem (GRLP) in which we are given a set S of nodes that corresponds to candidate locations for regenerators, and a set T of nodes that must communicate with each other. If S = T = N, we obtain the regenerator location problem (RLP), which we have studied previously and shown to be NP-complete. Our solution procedure to the RLP is based on its equivalence to the maximum leaf spanning tree problem (MLSTP). Unfortunately, this equivalence does not apply to the GRLP, nor do the procedures developed previously for the RLP. To solve the GRLP, we propose reduction procedures, two construction he...

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The Generalized Regenerator Location Problem

Protection techniques for optical networks mainly rely on pre-allocated backup bandwidth, which may not be able to provide full protection guarantee when multiple failures occur in a network. To protect against multiple concurrent potential failures and to utilize the available resources more efficiently, strategies such as backup reprovisioning rearrange backups of protected connections after one failure occurs or, more generally, whenever the network state changes, e.g., when a new request arrives or terminates. Recently, new solutions for automatized management in Optical networks promise to allow customers to specify on-demand the terms of the service level agreement (SLA) to be guaranteed by the service provider. In this paper we show that is possible to further reduce the capacity requirements of backup reprovisioning techniques exploiting the knowledge, among the other service level specifications (SLS), of the connection holding-time. Our main contributions are as follows. First, we prove that the problem of backup reprovisioning for all the lightpaths requiring shared-path protection under a current network state is NP-complete. Second, we provide a mathematical ILP model of the reprovisioning problem considering the additional holding-time information. Third, since the problem is NP-complete and we can not efficiently rely on exact approaches, a new global reprovisioning algorithm called Ph-GBR is proposed which can significantly reduce the resource overbuild exploiting the information about connection durations. By means of simulative experiments, we compare capacity requirement and computational complexity of Ph-GBR to those of another holding-time unaware, yet efficient algorithm, called GBR, considering a dynamic traffic in a wavelength-convertible WDM mesh network scenario.

Improving Efficiency of Backup Reprovisioning in WDM Networks

Survivability is a key concern in modern network design. This paper investigates the problem of survivable dynamic connection provisioning in general telecom backbone networks, that are mesh structured. We assume differentiated services where connections may have different availability requirements, so they may be provisioned differently with protection (if needed) based on their availability requirements and current network state. The problem of effectively provisioning differentiated-service requests, that has been widely investigated for connections routed at the physical layer, assumes peculiar features if we consider sub-wavelength requests at the logical layer that have to be protected (or more generically, whose availability target has to be guaranteed), but also have to be groomed for an efficient use of network resources. An integrated multilayer approach is necessary that considers requirements and grooming of connections at the logical layer as well as their routing and availability at the physical layer. Joint availability-guaranteed routing and traffic grooming may lead to a negative interaction, since the objective of the first problem (guaranteeing a given level of availability to the connections) clashes with the objective of the other problem (minimizing resource consumption). For a multilayer WDM mesh network, we propose new multilayer routing strategies that perform effective availability-guaranteed grooming of sub-wavelength connections. These strategies jointly considers connection availability satisfaction and resource optimization and are developed under two different practical hypotheses: guaranteed target, i.e., a connection is routed only if its availability target is satisfied, and best-effort target, a connection is always routed and, when the availability target cannot be guaranteed, the path with the best possible availability is provisioned. Numerical results are reported and discussed for the two approaches mentioned above. In both cases, the results show high effectiveness of our provisioning strategy.

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Multilayer Protection with Availability Guarantees in Optical WDM Networks

In this paper we provide a mathematical ILP model for the Regeneration Placement Problem (RPP) which minimizes the total number of regeneration nodes allocated in a translucent optical network ensuring that all the node pairs can always reach one another via two link-disjoint lightpaths under physical-impairment constraints. Since RPP is NP-complete, large-site design problem can not be solved relying upon exact approaches. We then propose a game-theoretic approach to model RPP as a non-cooperative game and solve it applying the best response dynamic concept. Finally, we evaluate the performance of the proposed approach in terms of closeness of the obtained results to these provided by ILP: a MILP formulation is given in order to study the quality of the Nash equilibria by comparison to Price-of-Anarchy and Price-of-Stability bounds.

On the Efficiency of a Game Theoretic Approach to Sparse Regenerator Placement in WDM Networks

For a WDM mesh network with shared-path protection, we propose to exploit the holding time of a connection to re(de)fine the customer's availability targets and achieve significant reduction in blocking probability.

Dynamic SLA Redefinition for Shared-Path-Protected Connections with Known Duration

Recently, new solutions for automatized management in optical networks promise to allow customers to specify on-demand the terms of the Service Level Agreement (SLA) to be guaranteed by the service provider. In this paper we show that is possible to design a highly efficient load balancing algorithm, called RABBIT, for the dynamic provisioning of connections exploiting the knowledge, among the other Service Level Specifications (SLS), of the connections duration. The core idea of RABBIT consists in routing connections based on the transient probability of future-link congestion, that can be estimated with higher precision when the knowledge of connections durations is given. So, we introduce a time-dependent link-weight assignment that evaluates future link congestions probability based on the transient analysis of the Markovian model of the link, making it computationally feasible by means of an effective approximation technique. By means of an extensive set of simulative experiments, we compare our approach to other traditional holding-time agnostic, yet efficient, dynamic routing algorithms. We consider different performance metrics, among which the Blocking Probability (BP), in a wavelength-convertible WDM mesh network scenario. For a typical US nationwide network, RABBIT obtains savings on BP of up to 20% for practical scenarios.

Diego Lucerna

Papers

Improving Efficiency of Backup Reprovisioning in WDM Networks

Multilayer Protection with Availability Guarantees in Optical WDM Networks

On the Efficiency of a Game Theoretic Approach to Sparse Regenerator Placement in WDM Networks

Dynamic SLA Redefinition for Shared-Path-Protected Connections with Known Duration

Dynamic Routing of Connections with Known Duration in WDM Networks