Showing papers in "Photonic Network Communications in 2012"

Power consumption modeling in optical multilayer networks

Abstract: The evaluation of and reduction in energy consumption of backbone telecommunication networks has been a popular subject of academic research for the last decade. A critical parameter in these studies is the power consumption of the individual network devices. It appears that across different studies, a wide range of power values for similar equipment is used. This is a result of the scattered and limited availability of power values for optical multilayer network equipment. We propose reference power consumption values for Internet protocol/multiprotocol label switching, Ethernet, optical transport networking and wavelength division multiplexing equipment. In addition we present a simplified analytical power consumption model that can be used for large networks where simulation is computationally expensive or unfeasible. For illustration and evaluation purpose, we apply both calculation approaches to a case study, which includes an optical bypass scenario. Our results show that the analytical model approximates the simulation result to over 90% or higher and that optical bypass potentially can save up to 50% of power over a non-bypass scenario.

Modeling the routing and spectrum allocation problem for flexgrid optical networks

Abstract: Flexgrid optical networks are attracting huge interest due to their higher spectrum efficiency and flexibility in comparison with traditional wavelength switched optical networks based on the wavelength division multiplexing technology. To properly analyze, design, plan, and operate flexible and elastic networks, efficient methods are required for the routing and spectrum allocation (RSA) problem. Specifically, the allocated spectral resources must be, in absence of spectrum converters, the same along the links in the route (the continuity constraint) and contiguous in the spectrum (the contiguity constraint). In light of the fact that the contiguity constraint adds huge complexity to the RSA problem, we introduce the concept of channels for the representation of contiguous spectral resources. In this paper, we show that the use of a pre-computed set of channels allows considerably reducing the problem complexity. In our study, we address an off-line RSA problem in which enough spectrum needs to be allocated for each demand of a given traffic matrix. To this end, we present novel integer lineal programming (ILP) formulations of RSA that are based on the assignment of channels. The evaluation results reveal that the proposed approach allows solving the RSA problem much more efficiently than previously proposed ILP-based methods and it can be applied even for realistic problem instances, contrary to previous ILP formulations.

Exploring online virtual networks mapping with stochastic bandwidth demand in multi-datacenter

Abstract: Network virtualization serves as a promising technique for providing a flexible and highly adaptable shared substrate network to satisfy the diversity of demands and overcoming the ossification of Internet infrastructure. As a key issue of constructing a virtual network (VN), various state-of-the-art algorithms have been proposed in many research works for addressing the VN mapping problem. However, these traditional works are efficient for mapping VN which with deterministic amount of network resources required, they even deal with the dynamic resource demand by using over-provisioning. These approaches are obviously not advisable, since the network resources are becoming more and more scarce. In this paper, we investigate the online stochastic VN mapping (StoVNM) problem, in which the VNs are generated as a Poisson process and each bandwidth demand x i follows a normal distribution, i.e., x i ~ N(μ i , ? i 2 ). Firstly, we formulate the model for StoVNM problem by mixed integer linear programming, which with objective including minimum-mapping-cost and load balance. Then, we devise a sliding window approach-based heuristic algorithm w-StoVNM for tackling this NP-hard StoVNM problem efficiently. The experimental results achieved from extensive simulation experiments demonstrate the effectiveness of the proposed approach and superiority than traditional solutions for VN mapping in terms of VN mapping cost, blocking ratio, and total net revenue in the long term.

Optimal provisioning for virtual network request in cloud-based data centers

Abstract: Today applications and services are migrating to a cloud-computing-based paradigm in which the users access the applications and services hosted in data centers, by using thin-clients on the user terminal device. These applications/services are typically hosted and run on virtual machines in interconnected data centers. Different applications from the same user may need to access and change shared data or information. Thus, we may abstract the applications from same user as a virtual network (VN). For better performance and efficiency, it is critical that the VN request be accommodated with optimal provisioning under the current resource state of data centers. In this paper, for addressing the issue of how to design an optimal provisioning scheme for the VN request such that the total revenue of is maximized, we first develop a framework for the optimal provisioning of VN request by using mixed integer programming. Since the optimal provisioning problem is NP-hard, we also propose a genetic algorithm---based heuristic algorithm for addressing the problem of optimal provisioning for VN with unsplittable flow and optimal provisioning for VN with splittable flow problems. We demonstrate the effectiveness of our approach in improving the total revenue by conducting extensive simulations on different networks.

FWM aware evolutionary programming algorithm for transparent optical networks

Abstract: This paper proposes and evaluates a four-wave mixing (FWM) aware evolutionary programming algorithm for dynamically setting up lightpaths in an optical wavelength division multiplexed network (WDM network). The proposed algorithm also considers the effect of amplified spontaneous emission noise (ASE noise) on a lightpath during propagation of the optical signal from any source to the intended destination. As crosstalk due to FWM and ASE noise are two transmission impairments that degrade the quality of optical signal even at low to medium data rates, it is mandatory for an algorithm for dynamic routing and wavelength assignment in a WDM network to consider the effect of these two impairments on the lightpath to be established. The distinguishing feature of the proposed algorithm is that it is based on an initial population of a single individual and uses a fitness function that is expressed in terms of the number of hops, path cost, variance contributions due to FWM crosstalk, amplifier noise, and different beat noises at the receiver. The performance of a newly introduced FWM aware priority-based wavelength assignment technique is compared with few of the existing wavelength assignment techniques in the present work.

Novel strategies for sparse regenerator placement in translucent optical networks

Abstract: In this paper, we propose two strategies for sparse regenerator placement (RP) in translucent optical networks, named most used regenerator placement (MU-RP), and most simultaneous used regenerator placement (MSU-RP). Our proposals are compared to well known RP algorithms presented in literature for two different network topologies for different network loads, distribution of load along the networks and number of translucent nodes. MSU-RP presented remarkable results and outperformed all previous approaches in all cases, while MSU-RP obtained a slightly superior or similar performance when compared to previous approaches presented in the literature.

Multicast multi-granular grooming based on integrated auxiliary grooming graph in optical networks

Abstract: In order to improve the bandwidth utilization efficiency and reduce the blocking probability for multicast requests in optical networks, the multicast traffic grooming approach was proposed to groom a lot of low-speed traffic to a few of high-speed light-trees. At the same time, in order to save the ports and the cost of optical cross-connect, the multicast waveband grooming approach was proposed to groom multiple light-trees to a few of waveband tunnels. However, the existing approaches all did not consider the joint performances of improving bandwidth utilization efficiency, reducing blocking probability and saving ports for multicast requests. Therefore, in this article, we propose a new multicast multi-granular grooming approach to perform the hierarchical sequential grooming to improve the joint performances based on a newly developed integrated auxiliary grooming graph (IAGG) that includes multiple wavelength integrated grooming graphs (WIGGs) and one waveband virtual topology layered graph (BVLG) to support both the multicast traffic grooming and multicast waveband grooming. In order to achieve the map of light-tree to the virtual topology layer in WIGG or BVLG, we present a light-segment map method, where a light-tree will be divided to several light-segments each of which will be independently mapped to the virtual topology layer. Since different definitions of blocking probability may lead to different objectives, we define two kinds of blocking probability, mean blocking probability of requests (MBPR) and mean blocking probability of users (MBPU). According to the two definitions of blocking probability, we propose two multicast multi-granular grooming heuristic algorithms, Heuristic Algorithm with minimizing MBPR and Heuristic Algorithm with minimizing MBPU based on IAGG. Simulation results show that the two proposed algorithms are both efficient and have better performances than traditional multicast grooming algorithm.

Study on dynamic routing and spectrum assignment in bitrate flexible optical networks

Abstract: The exponential growth of Internet traffic necessitates high-capacity optical networks and has also highlighted the importance of bandwidth-flexible and multi-granularity transport platforms. Improving both transport capacity and bandwidth flexibility is a significant challenge in optical networks. A bitrate flexible network architecture that is based on orthogonal frequency division multiplexing has been proposed as a promising solution for meeting this challenge. In the current study, we focus on the online routing and spectrum assignment problems in the aforementioned network architecture and introduce a general solution for dynamic bitrate flexible traffic in distributed environments. A novel spectrum representation method based on continuous spectrum segments is introduced into the networks. Segment-based routing and signaling mechanisms provide general solutions that support both the conventional slot-based networks and the ideal fully gridless networks. The routing algorithms and spectrum selection approaches are demonstrated and compared in a simulation. Performance estimation indicates that random spectrum segment assignment achieves the lowest capacity blocking rate in light traffic, whereas the adaptive routing plus minimum residual spectrum scheme obtains the lowest capacity blocking rate under heavy traffic.

A heuristic algorithm for lightpath scheduling in next-generation WDM optical networks

Abstract: We study the routing and wavelength assignment (RWA) problem of scheduled lightpath demands (SLDs) in all-optical wavelength division multiplexing networks with no wavelength conversion capability We consider the deterministic lightpath scheduling problem in which the whole set of lightpath demands is completely known in advance The objective is to maximize the number of established lightpaths for a given number of wavelengths Since this problem has been shown to be NP complete, various heuristic algorithms have been developed to solve it suboptimally In this paper, we propose a novel heuristic RWA algorithm for SLDs based on the bee colony optimization (BCO) metaheuristic BCO is a newborn swarm intelligence metaheuristic approach recently proposed to solve complex combinatorial optimization problems We compare the efficiency of the proposed algorithm with three simple greedy algorithms for the same problem Numerical results obtained by numerous simulations performed on the widely used realistic European Optical Network topology indicate that the proposed algorithm produces better-quality solutions compared to those obtained by greedy algorithms In addition, we compare the results of the BCO---RWA---SLD algorithm with four other heuristic/metaheuristic algorithms proposed in literature to solve the RWA problem in the case of permanent (static) traffic demands

A novel method to evaluate clustering algorithms for hierarchical optical networks

Abstract: The routing issues in multi-layer and multi-domain optical networks have drawn much attention in current research. With the introduction of the path computation element, routes can be calculated more efficiently in multi-domain optical networks. However, the optimal degree of routing approach in multi-layer and multi-domain optical networks is also determined by the clustering algorithms deployed for construction of hierarchical networks. Therefore, it is important to investigate the way to evaluate the impact of the clustering algorithm on the routing approach (e.g., blocking probability) in optical networks with dynamic traffic, which has not been studied sufficiently. In this paper, a novel method to describe and evaluate the clustered structures generated by different clustering algorithms for hierarchical optical networks is proposed. This method deploys a novel evaluation metric that represents blocking probability of clustered optical networks, so it can be used as guidelines for designing clustered structures. Besides theoretical analysis, simulations are carried out on different network topologies and clustered types to validate the effectiveness of the method presented.

Analysis and simulation of a delay-based service differentiation algorithm for IPACT-based PONs

Abstract: In passive optical networks employing the interleaved polling with adaptive cycle time (IPACT), the literature has focused on providing bandwidth-based service differentiation strategies This work shows how to provide different levels of delay-based differentiation and provides a model to characterise the proportional differentiation achieved, which is further validated with extensive simulations Furthermore, we show that the delay variance of our algorithm is smaller with respect to conventional IPACT, with the subsequent jitter reduction for high-priority traffic, and we further present a mechanism to limit the maximum delay experienced by high-priority traffic

Blocking probability evaluation of end-to-end dynamic WDM networks

Abstract: Two mathematical methods for blocking probability evaluation of end-to-end dynamic WDM networks are proposed. The first method can be applied to networks operating with static (fixed) routes. By diminishing the impact of the link independence assumption, the method proposed improves a recently proposed mathematical procedure that assumes link blocking independency and non-Poisson traffic. To do so, the so-called streamline effect is taken into account in the equations. As a result, values closer to that of simulation are obtained. The second method applies to networks operating with alternate routing. In this case, the method simultaneously relaxes three non-realistic assumptions of previous works: the link blocking independence, the Poisson traffic arrival and the homogeneity of the traffic load offered to the network links. Both methods were applied to different network topologies, and their results were compared to those of simulation. Results show that the match between simulation and the proposed methods is excellent, and better than assuming link blocking independence, in all the topologies studied.

A novel multi-link fault-tolerant algorithm for survivability in multi-domain optical networks

Abstract: With the large-scale deployment of optical network equipments, the problems of separated domains management and the multi-domain-based survivability have become the primary challenge in new generation intelligent optical networks. Aimed at resisting multi-link failures in multi-domain optical networks (MDON), a heuristic multi-link fault-tolerant (MLFT) algorithm for survivability in MDON is proposed in this article, which applied Hamiltonian cycle protection and segment-shared protection to establish a novel survivability strategy for either intra-domain's or inter-domain's multiple links, respectively. Furthermore, a new virtual-link mapping scheme and link-cost formulas are presented to encourage the appropriate routing selection and load balancing, which can also contributed to better resource utilization ratio and blocking ratio. Simulation results show that MLFT realizes the multi-link fault-tolerant survivability at a lower cost with better performances in redundancy ratio, blocking ratio, and computation complexity.

A reliable WDM optical access network enabling dynamic wavelength allocation and triple-play service

Abstract: A reliable dual-fiber ring-tree wavelength-division multiplexing optical access network architecture is proposed in this paper. On the one hand, due to the use of differential phase shift keying modulation, triple-play service including point-to-point service and broadcast service is realized. On the other hand, the wavelengths can be allocated dynamically by means of the special design of the remote node. What is more important is this network architecture can provide flexible protection modes for either single or multiple failures as well. The network survivability could be improved largely.

Hybrid fiber-to-the-x and free space optics for high bandwidth access networks

Abstract: The authors demonstrate an implementation of hybrid fiber-to-the-x (FTTx) and free space optical (FSO) technologies as another alternative solution to bring light-speed performance to the residential users. A simulation experiment was performed with a 20 km single-mode fiber spanning from the Central Office to 1:32 splitter, before the signal propagated through the air to FSO receivers which were individually equipped with an Optical Network Unit (ONU). A downstream performance of the video signal transmitted at 1550 nm wavelength with a bit rate of 1 Gbps was studied under different weather conditions. The results show that for an acceptable bit error rate of 10?9, 32 ONUs are supportable at a combined FSO: FTTx distance ratio of 20:4.8, 20:2, and 20:1.4 km during clear weather, average and heavy rain, respectively.

Traffic scheduling in hybrid WDM---TDM PON with wavelength-reuse ONUs

Abstract: Hybrid WDM---TDM PON (wavelength division multiplexing---time division multiplexing passive optical network) that applies wavelength-independent or colorless ONU (optical network unit) technologies will further reduce implementation and maintenance expenses. The "wavelength-reuse" colorless ONU technology imposes a physical constraint in the hybrid WDM---TDM PON that the same wavelength is used for both upstream and downstream traffic transmission of an ONU. This physical constraint brings a new challenge to developing traffic scheduling algorithms in the network, as upstream traffic scheduling is no longer independent of downstream traffic scheduling and the existing traffic scheduling algorithms that treated the upstream and downstream traffic independently cannot be applied in this case. We propose a new traffic scheduling algorithm that takes both directions' traffic scheduling into account at the same time. A logical PON concept is defined, and wavelength resource sharing is performed based on reconfiguring logical PONs. Simulation study on this algorithm is conducted, and results show that it achieves efficient wavelength and bandwidth resource sharing in the network.

Hierarchical routing and traffic grooming in IP/MPLS-based ASON/GMPLS multi-domain networks

Abstract: Routing, connection setup, and path computation are well-known problems in multi-domain networks, which have been largely analyzed in pure IP (packet) networks. In circuit-switched optical multi-domain networks, there remain, however, a number of routing and path computation challenges. Traffic grooming means combining a number of low-speed traffic streams so that the high capacity of each lightpath may be used as efficiently as possible, as path computation implements the core of the grooming function, it is obvious that solutions for the traffic grooming problem in optical multi-domain networks are still not sufficiently investigated. In this study we propose a methodology to address the problems of routing, connection setup, and traffic grooming in optical multi-domain networks, which adapts a two-level hierarchical routing scheme and full-mesh topology abstraction algorithm to improve routing scalability and lower inter-domain blocking probabilities; additionally our proposed methodology adapts a scheme for traffic grooming in DWDM multi-domain networks to improve the resources usage. To test our proposed methodology we propose a detailed IP/MPLS-based ASON/GMPLS multi-domain multilayer test framework.

A novel design of orthogonal frequency division multiplexing-based passive optical networks

Abstract: Orthogonal frequency division multiplex (OFDM) has been successfully used in wireless communications, and now people begin to see it as an excellent candidate technique in optical access networks. In this article, we first make comparison between OFDM-based passive optical network (PON) and traditional PONs, and then review some previous work of OFDM PON. After that we introduce our physical layer scheme. In addition, network architecture, medium access control (MAC) protocol, and three dynamic bandwidth allocation schedules that optimized for OFDM communication are recommended. At last, computer simulation results are given to demonstrate the performance of the three schedules.

An efficient column generation design method of p-cycle-based protected working capacity envelope

Abstract: The protected working capacity envelope (PWCE) concept was proposed by Grover (2004) in order to simplify network operations and management in survivable wavelength division multiplexing (WDM) networks. In this paper, we focus on the design of PCWE and investigate a new design method based on column generation (CG) for designing survivable WDM networks based on p-cycle PWCE. Proposed design algorithms for PWCE and p-cycle proceed in two steps: A first step where a large (sometimes huge) number of cycles is enumerated followed by a second step where the selection of the most promising p-cycles is made with the help of combinatorial optimization tools. In this paper, we develop a new (single-step) method based on large scale optimization tools, that is, CG techniques, where the generation of cycles is dynamic and embedded within the optimization process. The key advantage of CG techniques is that no a priori cycle enumeration step is required ahead of the optimization process: The generation of the relevant cycles, only one or few at a time, is embedded in the optimization process. We conducted intensive computational experiments to compare the performances of our CG algorithms with four other algorithms in the literature. The different algorithms were compared with regard to several design metrics and running time. Results obtained in the experiments on five different network instances show that the CG-based algorithm outperforms by far all proposed algorithms in the literature, both with respect to the scalability (much smaller computing times for large network instances) and also with respect to the quality of the solutions.

Optimal regenerator assignment and resource allocation strategies for translucent optical networks

Abstract: Physical layer impairments in wavelength-routed networks limit the maximum distance, a signal can travel in the optical domain, without significant distortion. Therefore, signal regeneration is required at some intermediate nodes for long-haul lightpaths. In translucent WDM networks, sparsely located regenerators at certain nodes can be used to offset the impact of physical layer impairments. The routing and wavelength assignment (RWA) techniques in such translucent networks need to take into consideration the availability of regenerators and the maximum optical reach of the transparent lightpaths (without any regeneration). Although there has been significant research interest in RWA algorithms for translucent networks, much of the research has focused on dynamic RWA techniques. Only a handful of recent papers have considered the static (offline) case, and they typically propose heuristic algorithms to solve this complex design problem for practical networks. In this paper, we propose a generalized integer linear program (ILP) based formulation for static regenerator assignment and RWA in translucent WDM optical networks, with sparse regenerator placement. To the best of our knowledge, such a formulation that optimally allocates resources for a set of lightpaths for translucent networks, given the physical network, the locations of the regenerators, and the maximum optical reach has not been considered before. The proposed formulation is important for two reasons. First, it can serve as a benchmark for evaluating different heuristic approaches that may be developedin the future. Second, we show that using a novel node representation technique, it is possible to drastically reduce the number of integer variables. This means that unlike existing ILP formulations, our approach can actually be used to generate optimal solutions for practical networks, with hundreds of lightpath demands.

Dynamic hybrid grooming based on power efficiency in green IP over WDM networks

Abstract: Due to the rapid growth of various applications, the network devices scale and complexity are significantly increased. Meanwhile, to deal with the burst IP traffic, the network devices need to provide continuous services, which will result in the excessive power consumption. Meanwhile, with the development of IP network and intelligent optical switch network, the backbone network tends to be an IP over wavelength-division-multiplexing (WDM) network. Therefore, it has attracted wide interests in both academic and industrial communities to build power-efficient (i.e., green) IP over WDM network, where we can switch several IP-level requests as one unit in the WDM optical layer. This method is called hybrid grooming and it requires less component power than that of electronic IP routers in the IP layer. Under this hybrid approach, the traffic grooming multiplexes many IP-level requests into a high-capacity lightpath; meanwhile the reduction in power consumed by optical-electrical-optical conversions is achieved through optical bypass. However, the power consumed by components used to establish lightpaths should also be considered. One network with the higher power efficiency not only saves more power followed by hybrid grooming but also requires the lower power consumption of establishing lightpaths. In this paper, to improve the power efficiency of dynamic IP over WDM network, we design two kinds of Wavelength Integrated Auxiliary Graphs (WIAGs), each of which contains one Virtual Topology Layer and multiple Wavelength-Plane Layers. Based on WIAGs, we propose two heuristic algorithms named single-hop grooming with considering power efficiency and multi-hop grooming with considering power efficiency (MGPE) since grooming is NP-hard. Simulation results demonstrate that MGPE obtains the higher power efficiency, although it has the slightly higher time complexity; the power efficiency mainly depends on the kind of grooming strategy (single- or multi-hop) we use while the increasing number of available transceivers in each node cannot improve the power efficiency, although it can make blocking probability decrease.

Iterative resource pooling for bandwidth allocation in TDM-PON: algorithm, convergence and experimental evaluation

Abstract: In this paper, we propose a new dynamic bandwidth allocation technique, SLIding Cycle Time (SLICT) for TDM-PON, specifically focused on ethernet passive optical network (EPON). Based on the sliding cycle time constraint, the proposed algorithm guarantees the maximum polling interval, an essential property for delay-sensitive applications and interactive services. We then introduce an iterative resource pooling that processes bursty best-effort traffic and achieves high throughput even under non-uniform upstream traffic distribution. We prove that greedy iterative resource pooling converges to equal resource allocation exponentially fast. Extensive numerical simulations show that SLICT outperforms existing techniques in all aspects: throughput, delay, packet loss and average queue size. Finally, SLICT has been implemented on an EPON FPGA board and the performance is confirmed under real traffic.

Flow-based load-balancing architecture for the agile all-photonic network

Abstract: A novel routing architecture that balances incoming Internet flows over the agile all-photonic network (AAPN) is proposed. The architecture is based on the adaptive highest random weight (adaptive HRW) algorithm proposed to design load-balanced Internet routers. Extensive numerical evaluation of static and adaptive variations of the routing architecture is studied, and their effect on the network performance in terms of packet drop and flow remapping is presented. The architecture can be seen as a combination of adaptive core node scheduling and adaptive load balancing at the edge nodes. It is stateless and can compute routes quickly based on the packet flow identifier.

Self-adapted algorithm to provide multi-profile bandwidth guarantees in PONs with symmetric and asymmetric traffic load

Abstract: A novel bandwidth assignment algorithm in Ethernet Passive Optical Networks with different coverage, called DySGAB, is proposed to provide subscriber differentiation. In contrast to algorithms which allocate bandwidth based on fixed weighted factors, DySGAB continuously adapts the bandwidth assignation to fulfill the requirements of all profiles, leading to an outstanding performance. This auto-adjustment, which has not been implemented in any of today's algorithms, allows the network to evolve automatically to the stipulated values even if they change in real time. As a result, not only does DySGAB ensure the guaranteed bandwidth for every subscriber, but also is independent of the initial bandwidth restrictions, which is an advantageous characteristic for service providers.

Threshold-based preemption scheme for improving throughput in OBS networks

Abstract: A threshold-based scheme to improve the throughput of optical burst switching networks based on burst preemption is presented. A larger burst can preempt the channel resource reserved by a smaller burst if the size difference is equal to or larger than a threshold. Extensive simulation tests to analyze the performance of this scheme have been conducted using ring, mesh-torus, and the US LongHaul topologies. The tests used the shortest path routing algorithm with just-in-time signaling and operated at different load conditions and threshold values. The tests revealed that the "unrestricted multiple-preemption per wavelength" variant of the scheme gives nearly the same throughput performance as the "restricted single-preemption per wavelength" variant. The improvement of the network throughput depends on the value of the threshold and the value of the threshold that gives maximum throughput increases with the network load. Selecting the candidate burst with the smallest size for preemption gives better throughput than selecting a random burst. An analytical model is developed to compute the throughput of ring networks for the "restricted single-preemption per wavelength" scheme with random burst selection. The ring analytical model is quite accurate and gives results very close to those obtained by simulation.

Evaluation of packet scheduling in hybrid optical/electrical switch

Abstract: This paper presents a hybrid optical/electrical switch for high-capacity future network development. A switch architecture to provide packet switching by solving contention in wavelength and time domains is considered relying on available optical and electrical technology. Physical and logical aspects regarding switch feasibility and management, in relation to the hybrid nature of the switch, are addressed. Scheduling algorithms to support multi-service packet forwarding are compared with optimally exploit optical and electrical subsystems according to traffic characteristics and needs. The main outcomes of the paper suggest criteria to design high-capacity packet switches, based on present-day technology constraints and quality of service requirements, to achieve a fair balance between optical transparency and loss performance.

An enhanced backward recursive PCE-based computation scheme for end-to-end disjoint paths in multi-domain networks

Abstract: To efficiently provide two disjoint end-to-end paths for working and protecting in multi-domain networks is challenging the network industry. The Backward Recursive PCE-based parallel approach (PA) for disjoint paths can achieve best computation performance at high cost of computation complexity and communication overhead. In this paper, we propose an enhanced PA (EPA), based on a no-differentiated in-BNs pair strategy to decrease the computation complex and communication overhead. The simulation results show that the EPA scheme can effectively reduce the computation and communication overhead.

Contention resolution considering multicast traffic in optically burst-switched WDM networks

Abstract: This paper proposes a contention resolution scheme considering multicast traffic in optical burst switching (OBS) networks. In OBS networks, for unicast bursts, contention can be avoided by deflection routing. However, deflection routing cannot be applied to multicast bursts because multicast bursts are transmitted along light-trees which are fixed, tree-shaped routes. Therefore, the loss probability of multicast bursts is generally high. To resolve this problem, the proposed scheme introduces an ingenious offset time assignment strategy which completely avoids contention of multicast bursts due to transmissions of unicast bursts by strategically assigning additional offset times. Furthermore, in the proposed scheme, unicast bursts avoid contention with deflection routing. Through simulation experiments, we show that the proposed scheme improves the loss probabilities of both of unicast bursts and multicast bursts.

Intercycle switching (ICS)-based dynamic reconfiguration of p-cycle for dual-failure survivability of WDM networks

Abstract: Today, the most promising technique used for the survivability of optical transport networks is p-cycle. However, it provides longer restoration path at failure state of the network. The intercycle switching (ICS) is one of the recent approaches that is based on idle p-cycles and is used for shortening the length of restoration path in single-fault model. Utilization of idle p-cycles degrades the inherent dual-failure restorability of single-failure design model of p-cycle, whereas ICS releases the maximum portion of conventional restoration path by utilizing a small segment of the idle p-cycle. Here, the authors proposed a new approach to reconfiguring the released portion of restoration path and unused segment of corresponding idle p-cycle as new cycle(s). In respect of idle p-cycles, the new reconfigured cycle(s) provides more dual-failure restorability in single-failure design of p-cycle. Therefore, the proposed approach mitigates the above-said drawback of ICS and minimizes additional spare capacity requirement for dual-failure survivability.

Availability analysis under multiple link failures in WDM networks with shared-link connections

Abstract: In optical Wavelength Division Multiplexing (WDM) networks, different protection schemes have been proposed in the literature, namely, dedicated protection and shared protection. Shared protection techniques significantly reduce the required spare capacity by providing the same level of availability as dedicated protection. However, current mission critical applications (which heavily depend on the availability of communication resources) require connection availability in the order of 99.999% or higher, which corresponds to a downtime of almost 5 min a year on the average. Therefore, in order to satisfy a connection serviceavailability requirement defined by the users Service Level Agreement in a cost-effective and resource-efficient way, network operators need a systematic mechanism to evaluate the network availability under multiple failure scenario to ensure that current network configuration can meet the required availability degree; otherwise, a network upgrade is required. Unfortunately, under multiple failure scenario, traditional availability analysis techniques based on reliability block diagrams are not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of network availability. In this paper, we propose an analytical model for evaluating the availability of a WDM network with shared-link connections under multiple link failures. The analytical model is also verified using Monte Carlo simulation. The proposed model significantly contributes to the related areas by providing network operators with a quantitative tool to evaluate the system availability and, thus, the expected survivability degree of WDM optical networks with shared connections under multiple link failures.