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Survivability of internet services is a significant and crucial challenge in designing optical networks. A robust infrastructure and transmission protocols are needed to maintain communication, despite the existence of one or more failed components on the system. Here, we present a generalized approach to tolerate any set of failure scenarios to the extent network users can still communicate with the remaining components, where a scenario is an arbitrary set of links in a non-operational state. We propose a joint solution to assess the survivability problem. The issues to be solve simultaneously are as follows: the set of primary routes, a collection of alternate routes associated with each failure scenario, and the capacity required on the network to allow communication between all users, in spite of any considered failure scenario, while satisfying for each user a specific predefined quality of service threshold, defined in the Service Level Agreement (SLA). Numerical results show that the proposed approach not only enjoys the advantages of low complexity and ease of implementation, but it is also able to achieve significant resource savings compared to existing methods. The savings are higher than 30% on single link failures and more than 100% on two simultaneous link failures cases or in more complex failure scenarios.

Flexgrid optical networking technology allows for a more flexible consumption of bandwidth. The spectrum allocation problem consists of the conflict-free assignment of consecutive spectrum space of different sizes to lightpaths. In this article, we study the computational complexity of spectrum allocation with and without demand uncertainty. First, it is shown that the problem becomes already NP-hard for cases where wavelength assignment is still polynomial time solvable. Next, five different ways to define the robust counterpart are compared. It is shown (amongst others) that on a single network edge, the two least efficient models are less computationally demanding than the other variants. A computational study using comparable integer linear programming formulations reveals that the additional slots required by these models directly depend on the restrictions of the employed technology. (c) 2017 Wiley Periodicals, Inc. NETWORKS, Vol. 70(4), 342-359 2017

The circuit switched optical network on chip (ONoC) is popularly employed since the optical buffer is not available. However, this technique suffers from limited transmission bandwidth, high setup-time overhead, and high network resource contention, which consequentially induces long latency and degraded throughput. In this paper, we propose a new ONoC architecture aiming at ultralow setup cost, improved scalability, and contention-free communication. We first utilize wavelength division multiplexing (WDM) to introduce the basic version of this ONoC with efficient wavelength assignment. A series of potential versions are developed by using multiple waveguides to relieve the pressure on the number of wavelengths. These potential versions can make a tradeoff between required wavelengths and waveguides and improve the scalability. The new architectures employ two layers relying on the interlayer coupler, which contributes to the decrease of crossing losses. The simulation results show that the architecture can achieve 133% saturated bandwidth improvement compared with the traditional mesh ONoC employing WDM technology under the uniform traffic pattern.

Survivability of internet services is a significant and crucial challenge in designing future optical networks. A robust infrastructure and transmission protocols are needed to handle such a situation so that the network users can maintain communication despite the existence of one or more failed components on the network. For this reason, in this work, we present a generalized approach to tolerate any set of failure scenarios, to the extent the user can still communicate with the remaining components, where a scenario corresponds to an arbitrary set of links in a non-operational state. To assess the survivability problem, we propose a joint solution to the problems listed next. We show how to find: a set of primary routes, a set of alternate routes associated to each failure scenario, and the capacity required on the network to allow communication between all users, in spite of any failure scenario, while satisfying for each user a specific predefined quality of service threshold, defined in the Service Level Agreement (SLA). Numerical results show that the proposed approach not only enjoys the advantages of low complexity and ease of implementation but is also able to achieve significant resource savings compared to existing methods. The savings are higher than 30% on single link failures and more than a 100% on two simultaneous link failures scenarios and in more complex failure scenarios.

The problem of grooming is central in studies of optical networks. In graph-theoretic terms, this can be viewed as assigning colors to the lightpaths so that at most g of them (g being the grooming factor) can share one edge. The cost of a coloring is the number of optical switches (ADMs); each lightpath uses two ADMs, one at each endpoint, and in case g lightpaths of the same wavelength enter through the same edge to one node, they can all use the same ADM (thus saving g−1 ADMs). The goal is to minimize the total number of ADMs. This problem was shown to be NP-complete for g=1 and for a general g. Exact solutions are known for some specific cases, and approximation algorithms for certain topologies exist for g=1. We present an approximation algorithm for this problem. For every value of g the running time of the algorithm is polynomial in the input size, and its approximation ratio for a wide variety of network topologies—including the ring topology—is shown to be 2lng+o(lng). This is the first approximation algorithm for the grooming problem with a general grooming factor g.

Given a network G and a demand D of communication requests on G, a routing for (G,D) is a set of directed paths of G, each from the source to the destination of one request of D. The Routing and Wavelength Assignment Problem seeks a routing R for (G,D) and an assignment of wavelengths to the directed paths in R such that the number of wavelengths used is minimized, subject to that any two directed paths with at least one common arc receive distinct wavelengths. In the case where G is a ring, this problem is known as the Ring Routing and Wavelength Assignment Problem (RRWA). If in addition D is symmetric (that is, (s,t)∈D implies (t,s)∈D) and the directed paths for requests (s,t) and (t,s) are required to be reverse of each other, then the problem is called the Symmetric Ring Routing and Wavelength Assignment Problem (SRRWA). A demand is called a permutation demand if, for each vertex v of G, the number of requests with source v and the number of requests with destination v are the same and are equal to 0 or 1. A symmetric permutation demand is called an involution demand. In this paper we prove that both RRWA and SRRWA are NP-complete even when restricted to involution demands. As a consequence RRWA is NP-complete when restricted to permutation demands. For general demands we prove that RRWA and SRRWA can be solved in polynomial time when the number of wavelengths is fixed. Finally, we answer in the negative an open problem posed by Gargano and Vaccaro and construct infinitely many counterexamples using involution demands.

Motivated by the increasing importance of multifiber WDM networks we study a routing and wavelength assignment problem in such networks. In this problem the number of wavelengths per fiber is given and the goal is to minimize the cost of fiber links that need to be reserved in order to satisfy a set of communication requests; we introduce a generalized setting where network pricing is non-uniform, that is the cost of hiring a fiber may differ from link to link. We consider two variations: undirected, which corresponds to full-duplex communication, and directed, which corresponds to one-way communication. Moreover, for rings we also study the problem in the case of pre-determined routing. We present exact or constant-ratio approximation algorithms for all the above variations in chain, ring and spider networks. (c) 2005 Elsevier B.V. All rights reserved. Computer Networks

This paper concerns connection provisioning for optical networks employing wavelength division multiplexing. A heuristic algorithm is developed and numerically studied for routing and wavelength assignment of a set of static connection requests. The algorithm runs much faster than the optimum solution of this problem. An adaptation of the algorithm is proposed to design restorable networks which can handle a specified set of failures. The proposed algorithm is based on taking all failures into consideration simultaneously, and performs better than developing independent designs for each failure. Association for Computing Machinery IEEE Computer Society IEEE Communications Society

We consider large optical networks in which nodes employ wavelength-routing switches which enable the establishment of wavelength-division-multiplexed (WDM) channels, called lightpaths, between node pairs. We propose a practical approach to solve routing and wavelength assignment (RWA) of lightpaths in such networks. A large RWA problem is partitioned into several smaller subproblems, each of which may be solved independently and efficiently using well-known approximation techniques. A multicommodity flow formulation combined with randomized rounding is employed to calculate the routes for lightpaths. Wavelength assignments for lightpaths are performed based on graph-coloring techniques. Representative numerical examples indicate the accuracy of our algorithms.

In this letter we evaluate the performance of optical cross connect (OXC) architectures with wavelength conversion capability and in which the number of wavelength converters (WCs) is optimized by means of WC sharing. Dimensioning models of WCs are proposed and the number of WCs is evaluated according to an efficient wavelength assignment that allows to obtain a high saving of WCs.

Introducing a WDM dimension on the top of a TDM PON system is a natural evolution to increase the capacity of an optical access network, and this can also offer additional flexibility options. Several hybrid WDM/TDM PON architectures can be designed, each with a different degree of flexibility, going from fully static, over partially flexible to fully flexible architectures. The more flexible architectures, however, are either more expensive, experience a higher power loss or are less secure. A question that arises is if a fully flexible architecture is really needed, or if a partially flexible architecture already can serve several flexibility advantages, like energy efficiency, network migration and network extensibility. An important assessment parameter is the number of needed wavelengths at a certain network load. For a fully flexible architecture, it is clear that the number of needed wavelengths can be optimally minimized, but how big is the gain of a fully flexible architecture compared to a partially flexible one, and what is the minimum degree of flexibility required to have a significant advantage of the offered flexibility. In this paper we evaluate through simulation different architectural options for a hybrid WDM/TDM PON, in terms of flexibility. For this purpose, we use an underlined well-suited medium access control (MAC) protocol that exploits the offered flexibility in terms of dynamic wavelength allocation.

In those networking scenarios (e.g., the stationary/mobile wireless paradigm) where limited energy storagecapabilities is a limiting factor, power efficiency has been studied extensively for a long time. In the last fewyears, the steadily growing power consumption figures of ICT [1][2] along with a recent public awareness of thepossible environmental effects, broadened the focus of the research efforts towards more power conscioussolutions also for wired networks. One promising solution going in this direction is represented by transparentwavelength division multiplexing (WDM) networks, where all-optical circuits (or lightpaths) carry the networktraffic from the source to the destination node in the optical domain, i.e. without any optical-to-electrical(O-E-O) conversion. To further improve network power efficiency, several approaches have been proposed inthe literature attempting to reduce the power consumption in transparent WDM networks [3][4]. Among them,power aware (PA) routing and wavelength assignment (RWA) algorithms are receiving a lot of attention. Onepossible solution for the PA-RWA problem is to limit the number of devices in the network that need to bepowered-on to support the lightpath requests [5]. These methods, however, have an adverse impact on the lengthof the provisioned lightpaths. In order to efficiently use as much powered-on network resources as possible, thepath length is, on average, longer than the one found with traditional (and less power efficient) shortest pathsolutions. This is in contradiction with the goal of classical RWA algorithms that tend to minimize the resourceusage (i.e., wavelengths and fibers) within the network, in order to minimize the blocking probability. Whenavailability of network resources becomes something that cannot be overlooked, a trade off needs to be assessedbetween power savings and blocking probability.In this talk, a non-conventional solution to the PA-RWA problem is presented. It is based on the intuitionthat, in some cases, relaxing the power minimization constraint can have beneficial effects on the overallnetwork performance, i.e., it can contribute to the reduction of resource fragmentation in the network and, in thisway, lower the blocking probability. The proposed algorithm leverages on a cost function that considers both thepower status of network elements (in this particular case the in-line optical amplifiers on fiber links only) and theinformation about wavelength usage. The algorithm has been tested using a Pan-European core network (i.e.,COST 239). Performance results confirm the presence of a trade-off between energy saving and blockingprobability. They also suggest that a “binary” approach using only the powered-on/powered-off informationmight not always be the best choice. © 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. QC 20120202

The high data rates employed by wavelength division multiplexing transparent optical networks make them most suitable for today's growing network traffic demands. However, their transparency imposes several vulnerabilities in network security, enabling malicious signals to propagate from the source to other parts of the network without losing their attacking capabilities. Furthermore, detecting, locating the source, and localizing the spreading of such physical-layer attacks is more difficult since monitoring must be performed in the optical domain. While most failure and attack management approaches focus on network recovery after a fault or an attack has already occurred, we suggest a novel safety strategy, proposing a prevention-oriented method to aid attack localization and source identification in the planning phase. In this paper, we propose attack-aware wavelength assignment that minimizes the worst-case potential propagation of in-band crosstalk jamming attacks. We define a new objective criterion for the wavelength assignment (WA) problem, called the propagating crosstalk attack radius (P-CAR), and develop heuristic algorithms aimed at minimizing both the P-CAR and the number of wavelengths used. Our aim is to achieve better protection, but without the need for extra resources. We compare our algorithms with existing WA approaches, illustrating their benefits with respect to transparent optical networks' security, as well as the associated wavelength utilization.

Several computer tools addressing the routing and wavelength assignment (RWA) problem are available today within the research community. However, these tools have low flexibility and are difficult to use for remote or casual users. This paper shows how to allow a remote access to various existing RWA tools using Web Services. In this way, software components implementing routing and/or wavelength assignment are turned into Web Services made available over the internet and accessible through a simplified interface. This dispenses the user to perform a local implementation, allows better code reuse, and offers an easy way to confront results from distinct models. Moreover, making tools available on the web increases their credibility and visibility. In our approach, a multilayer network description (MND) format is used to describe both input data and computed results. It offers common basic structure while guaranteeing a large extensibility, and thus makes possible the interaction between various tools. The viability of this approach is illustrated through an example of implementation.

The multi-layer network design problem and the mobile backhaul problem are both interesting from the perspective of choosing the correct technology and protocol as well as choosing the appropriate node architecture to meet a wide variety of overlay traffic demands. Network operators encounter two variants of the multi-layer/ backhaul problem: 1) For a given set of uncertain traffic demands, which set of technologies would minimize the network cost? 2) Would these technology choices be invariant to the changing traffic demands? This problem of technology choice can essentially be abstracted to a switching and grooming problem with the added complexity of unknown traffic demands, which at best may be approximated to some known statistical parameters. To solve this complex switching and grooming problem, our goal is to make use of the theory of robust optimization with the assumption of known boundary conditions on traffic. We present a comprehensive optimization model that considers technology choices in terms of protocols, physical layer parameters, link boundary conditions, and transmission layer constraints. Validated by simulations, our model shows the stand-off conditions between various technologies and how a network operator must take proactive steps to be able to meet requirements of the next-generation networks and services. Our main result showcases network design using two technology alternatives [1) Multi-Protocol Label Switching (MPLS) + Optical Transport Network (OTN) + Reconfigurable Optical Add-Drop Multiplexer (ROADM) and 2) Carrier Ethernet (CE) + OTN + ROADM] and the effect of robustness on these choices. A heuristic is used for comparative purposes as well as to exhaustively model the dynamic case of brown-field networks.

Minimizing the number of electronic switches in optical networks is a main research topic in recent studies. In such networks we assign colors to a given set of lightpaths. Thus the lightpaths are partitioned into cycles and paths. The switching cost is minimized when the number of paths is minimized. The problem of minimizing the switching cost is NP-hard, and approximation algorithms have been suggested for it. Many of these algoritms have a preprocessing stage, in which they first find cycles. The basic algorithm eliminates cycles of size at most l, and is known to have a performance guarantee of $OPT+\frac{1}{2}(1+\epsilon)N$, where OPT is the cost of an optimal solution, N is the number of lightpaths, and $0 \leq \epsilon \leq \frac{1}{l+2}$, for any given odd l. Without preprocessing phase (i.e. l=1), this reduces to $OPT + \frac{2}{3} N$. We develop a new technique for the analysis of the upper bound and prove a tight bound of $OPT+ \frac{3}{5}N$ for the performance of this algorithm.

Optical fiber has been used as the physical medium for high rate data transmission since late 1960s. Early applications of optical fiber communications modulated data onto a single optical carrier frequency that is commonly referred to as a wavelength. The carried data rate is therefore limited by the speed of electronics that generate the signal, thereby grossly underutilizing the tens of THz of useful bandwidth available on the fiber[1]. The Wavelength Division Multiplexing (WDM) technology now allows multiplexing everal optical carriers on the same fiber, opening up the available potential. Current deployments of WDM are based on point-to-point links. This entails demodulating the optical signal at each switching node and carrying out switching electronically. Remarkable increase in the carried data rates due to the WDM technology make these switches inherent bottlenecks in the network. One promising approach to solve this problem is optical switching which entails switching entire wavelengths without any electronic processing.

In the context of the future Internet, all-optical wavelength switched optical networks will play an important role in either evolutionary or revolutionary design paradigms. In any paradigm, dense wavelength domain multiplexing (DWDM) is the most cost-effective technology to increase bandwidth capacity. DWDM provides the basis for a core optical transport infrastructure supporting a wide range of heterogeneous services. However, such all-optical networks raise well-known challenges such as the wavelength continuity constraint (WCC). The WCC is hard to address in a multiarea scenario when provisioning an end-to-end lightpath owing to network topology hiding requirements and the limited exchange of information between areas. The Internet Engineering Task Force (IETF) is currently standardizing the path computation element (PCE) architecture, a good candidate to perform multidomain path computation. In such an architecture, the approach named backwards recursive path computation (BRPC), also under standardization at the IETF, aims at overcoming the limitations of the per-domain mechanism. However, although BRPC does provide end-to-end shortest paths, it fails to take into account the WCC, which is the main motivation for this work. We extend the BRPC algorithm and the companion PCE protocol in order to address the end-to-end WCC efficiently. We perform a quantitative comparative analysis of the different approaches, experimentally showing the improvements of the conceived solution, which has been evaluated in a GMPLS-controlled network of the ADRENALINE testbed.

International audience; We consider the problem of finding a lightpath assignment for a given set of communication requests on a multifiber WDM optical network with wavelength translators. Given such a network and w, the number of wavelengths available on each fiber, k, the number of fibers per link, and c, the number of partial wavelength translations available on each node, our problem stands for deciding whether it is possible to find a w-lightpath for each request in the set such that there is no link carrying more that k lightpaths using the same wavelength nor node where more than c wavelength translations take place. Our main theoretical result is the writing of this problem as a particular instance of integral multicommodity flow, hence integrating routing and wavelength assignment in the same model. We then provide three heuristics mainly based upon randomized rounding of fractional multicommodity flow and enhancements that are three different answers to the trade-off between efficiency and tightness of approximation, and discuss their practical performances on both theoretical and real-world instances.

Dynamic wavelength assignment (DWA) is investigated for managing ultra-dense wavelength division multiplexing-passive optical networks (UDWDM-PONs). The optical network units (ONUs) own lasers under limited thermal tunability and their wavelengths have random distribution in a band. ONU and optical line terminal (OLT) architectures with coherent transceivers are proposed, providing a spectral efficiency suitable for a high capacity PON with large number of users and long-reach approach. In activation processes, ONU acceptances up to 99.99% are obtained with a DWA technique. Under standard environmental conditions, the DWA method is combined with guard bands and then ONU blocking probabilities below 0.1% and availability ratios up to 99.99% are achieved. Index Terms—Limited thermal tunability, Optical Network Unit, Statistical Ultra-Dense Wavelength Division Multiplexing- Passive Optical Network, wavelength assignment.

Physical layer attacks in transparent optical networks are a serious security threat to network operation. We propose a novel protection approach based on wavelength assignment which limits the maximal propagation of intra-channel crosstalk attacks.

We show how inaccuracies of Quality of Transmission (QoT) estimations, caused by imperfect models and lack of monitors in transparent optical networks, can be mitigated using a novel routing and wavelength assignment algorithm.

Optical wavelength-division multiplexing (WDM) is today the most promising technology, that enables us to deal with the enormous growth of traffic in communication networks. A communication between a pair of nodes is using lightpaths. In graph-theoretic terms, a lightpath is a simple path in the network, with a color assigned to it. Given a WDM network comprising of optical nodes and a set of lightpaths, the wavelength assignment task is to assign a wavelength to each lightpath, such that lightpaths that share an edge will get different colors. The switching cost is defined as follows. Each lightpath uses two ADM's, one at each endpoint. If two adjacent lightpaths are assigned the same wavelength, then they can use the same ADM. An ADM may be shared by at most two lightpaths. The objective is to find an assignment of colors to the lightpaths that minimizes the total number of ADMs. The problem was introduced in [1] for ring topology. Approximation algorithm for ring topology with approximation ratio of 3/2 was presented in [2], and was improved in [3, 4] to 10/7 + epsiv and 10/7 , respectively. All these - as well as other - studies concerning this problem dealt with the off-line case, where all the lightpaths are given in advance. Naturally, a more realistic problem to study is the on-line version of the problem, where the requests (lightpaths) arrive at the network on-line, and we have to assign them wavelengths so as to minimize the switching cost. We present an on-line algorithm whose performance is at most 7/4 of the optimal solution (i.e., its competitive ratio - see [5] - is 7/4) for any network topology. We prove that no algorithm has a competitive ratio better than 7/4 even if the topology is a ring. We show that the same algorithm has a competitive ratio of 3/2 in path topologies, and that also this bound is optimal. The lower bound on ring topology does not hold when the ring is of a bounded size; we study the triangle topology, and show a tight bound of 5/3 for the competitive ratio on this topology, using another algorithm. In the analyses of the upper bounds and the lower bounds we use a variety of proof techniques, which are of interest by their own, and which might prove helpful in future research on the topic.