Power-aware virtual optical network provisioning in flexible bandwidth optical networks [Invited]

Considering the virtual network infrastructure as a service, optical network virtualization can facilitate the physical infrastructure sharing among different clients and applications that require optical network resources. Obviously, mapping multiple virtual network infrastructures onto the same physical network infrastructure is one of the greatest challenges related to optical network virtualization in flexible bandwidth optical networks. In order to efficiently address the virtual optical network (VON) provisioning problem, we can first obtain the virtual links’ order and the virtual nodes’ order based on their characteristics, such as the bandwidth requirement on virtual links and computing resources on virtual nodes. We then preconfigure the primary and backup paths for all node-pairs in the physical optical network, and the auxiliary graph is constructed by preconfiguring primary and backup paths. Two VON mapping approaches that include the power-aware virtual-links mapping (PVLM) approach and the power-aware virtual-nodes mapping (PVNM) approach are developed to reduce power consumption for a given set of VONs in flexible bandwidth optical networks with the distributed data centers. Simulation results show that our proposed PVLM approach can greatly reduce power consumption and save spectrum resources compared to the PVNM approach for the single-line rate and the mixed-line rate in flexible bandwidth optical networks with the distributed data centers.     

Optimizing amplifier placements in a multiwavelength opticalLAN/MAN: the equally powered-wavelengths case

Wavelength division multiplexing (WDM) provides the ability to utilize the enormous bandwidth offered by optical networks, using today's electronics. WDM-based optical networks employing passive-star couplers have been proposed for deployment in local and metropolitan areas. Optical amplification is often required in such networks to compensate for the signal attenuation along the fiber links and the splitting and coupling losses in the network. However, an optical amplifier has constraints on the maximum gain and the maximum output power it can supply; thus optical amplifier placement becomes a challenging problem. A simplifying assumption for analytical tractability requires that all wavelengths, present at a particular point in a fiber, be at the same power level, viz, the equally powered-wavelengths case. However, previous studies did not minimize the total number of amplifiers while achieving power equalization. In this paper, we formulate the minimization of amplifiers with power equalization as a mixed integer linear program (MILP) that can be solved by a linear program solver. Illustrative examples on sample networks are presented, which demonstrate the characteristics and the advantages of our optimal amplifier placement algorithm     

Traffic grooming in an optical WDM mesh network

In wavelength-division multiplexing (WDM) optical networks, the bandwidth request of a traffic stream can be much lower than the capacity of a lightpath. Efficiently grooming low-speed connections onto high-capacity lightpaths will improve the network throughput and reduce the network cost. In WDM/SONET ring networks, it has been shown in the optical network literature that by carefully grooming the low-speed connection and using wavelength-division multiplexer (OADM) to perform the optical bypass at intermediate nodes, electronic ADMs can be saved and network cost will be reduced. In this study, we investigate the traffic-grooming problem in a WDM-based optical mesh topology network. Our objective is to improve the network throughput. We study the node architecture for a WDM mesh network with traffic-grooming capability. A mathematical formulation of the traffic-grooming problem is presented in this study and several fast heuristics are also proposed and evaluated     

Multicast backup reprovisioning problem for Hamiltonian cycle-based protection on WDM networks

As networks grow in size and complexity, the chance and the impact of failures increase dramatically. The pre-allocated backup resources cannot provide 100% protection guarantee when continuous failures occur in a network. In this paper, the multicast backup re-provisioning problem (MBRP) for Hamiltonian cycle (HC)-based protection on WDM networks for the link-failure case is studied. We focus on how to recover the protecting capabilities of Hamiltonian cycle against the subsequent link-failures on WDM networks for multicast transmissions, after recovering the multicast trees affected by the previous link-failure. Since this problem is a hard problem, an algorithm, which consists of several heuristics and a genetic algorithm (GA), is proposed to solve it. The simulation results of the proposed method are also given. Experimental results indicate that the proposed algorithm can solve this problem efficiently.     

Virtual infrastructure mapping in software-defined elastic optical networks

Software-defined networking (SDN) enables efficient and scalable network virtualization, which allows infrastructure resources such as computing and networking resources to be abstracted and outsourced as a service. The SDN technologies can be extended to the optical transport networks to achieve an intelligent and flexible resource management, thus achieving high-capacity, low-cost, and long-reach optical transport networks. In this paper, we introduce an architecture for software-defined elastic optical networks and study the virtual infrastructure (VI) mapping problem with the objective of minimizing the blocking probability. We propose a set of efficient heuristic algorithms, among which the Network followed by Compute Load Balancing (NCLB) algorithm is a novel attempt to solve the VI mapping problem by provisioning the networking resource first followed by allocating the computing resource. Furthermore, we propose a modified version of NCLB, called Network Depth-based NCLB (ND-NCLB), which confines the VI mapping assignment in a small-range sub-network to further optimize the physical network resource consumption. Through comprehensive simulations in various scenarios, we demonstrate that the proposed ND-NCLB algorithm achieves the best performance in terms of blocking probability compared to the other algorithms in this work.     

The backup reprovisioning problem of NEPCs on survivable WDM networks

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. After recovering from the previous failure, if failure occurs again, unprotected or vulnerable lightpaths cannot be recovered. In this paper, the minimal backup reprovisioning (MBR) problem is studied, in which, the node-encircling protecting cycles (NEPCs) scheme is considered for single node-failure on WDM networks. The NEPC Recovery Algorithm is proposed to recover the protecting capabilities of the NEPC. Simulation results show that the performance of the proposed method is better than that of the traditional one.     

Design of grooming architectures for optical WDM mesh networks: limited grooming with electronic wavelength conversion

In this article, we consider the problem of traffic grooming in optical wavelength division multiplexed (WDM) mesh networks under static traffic conditions. The objective of this work is to minimize the network cost and in particular, the electronic port costs incurred for meeting a given performance objective. In earlier work, we have shown the benefits of limited grooming switch architectures, where only a subset of wavelengths in a network are equipped with expensive SONET Add Drop Multiplexers (SADM) that provide the grooming functionality. In this work, we also consider the wavelength conversion capability of such groomers. This can be achieved using a digital cross-connect (DCS) in the grooming switch to switch low-speed connections between the SADMs (and hence, between wavelengths). The grooming switch thus avoids the need for expensive optical wavelength converters. Based on these observations, we propose a limited conversion-based grooming architecture for optical WDM mesh networks. The local ports at every node in this architecture can be one of three types: an add-drop port, a grooming port that allows wavelength conversion or a grooming port that does not allow wavelength conversion. The problem studied is: given a static traffic model, where should the different ports be placed in a network? We formulate this as an optimization problem using an Integer Linear Programing (ILP) and present numerical results for the same. We also present a heuristic-based approach to solve the problem for larger networks.     

Virtual topology reconfiguration on optical WDM networks considering traffic grooming

This paper investigates the virtual topology reconfiguration (VTR) problem of optical WDM networks by taking the traffic grooming factor into consideration. Firstly, by applying a common “divide and conquer” approach, the problem is categorized and handled as two independent sub-problems, triggering policy and the proper algorithm. Secondly, the VTR problem considering traffic grooming is formulated with new variables and constraints by a mixed-integer linear program (MILP). In order to handle the tradeoff between the advantages and disadvantages of VTR, both network resource utilization and network disruption are examined and quantified in terms of measurable parameters. A new multi-objective VTR algorithm called integrated reconfiguration (IR) algorithm is proposed to provide better overall VTR performance. Different from previous studies this newly proposed VTR algorithm combines three main factors (traffic load, traffic grooming ratio and route length of lightpaths) into one single objective and considers them all when reconfiguring. The results of simulations indicate that proposed VTR policy, periodic VTR triggering policy with IR algorithm, achieves performance improvements for overall VTR performance.     

Priority-based Dynamic Lightpath Allocation for Survivable WDM Networks

In recent years, there has been considerable research interest in the design of survivable wavelength division multiplexing (WDM) networks. Many papers have proposed mixed-integer linear program (MILP) formulations as well as heuristics to optimally allocate lightpaths, using protection based schemes. Such schemes provide quick and guaranteed recovery, but do not use resources efficiently. About 50% of allocated resources remain idle, under fault-free conditions. If these “idle” resources were used for low-priority connections (which could be pre-empted if necessary), the resource utilization would improve significantly. This paper introduces two MILP formulations for priority-based dynamic lightpath allocation in survivable WDM networks. We define three different levels of service and allocate resources based on the requested service level. An important advantage of our approach is that while we can handle multiple levels of service, the traditional (single level) shared and dedicated path protection schemes can be treated simply as a special case of the proposed formulations. The first formulation solves the problem optimally, but is quite time consuming. The second formulation makes some simplifications, and is more efficient. The results demonstrate that our approach can significantly improve resource utilization and is feasible for practical sized networks, particularly under low- to medium-traffic load. For large networks and high traffic conditions, simpler heurtistic algorithms are more appropriate. In such cases, the proposed MILP formulation can be a useful tool to validate the performance of the heuristics.     

Uniform waveband assignment in optical mesh networks

The cost of an optical network in wavelength division multiplexing (WDM) networks can be reduced using optical reconfigurable optical add/drop multiplexers (ROADMs), which allow traffic to pass through without the need for an expensive optical-electro-optical (O-E-O) conversion. Waveband switching (WBS) is another technique to reduce the network cost by grouping consecutive wavelengths and switching them together using a single port per waveband. WBS has attracted the attention of researchers for its efficiency in reducing switching complexity and therefore cost in WDM optical networks. In this paper, we consider the problem of switching wavelengths as non-overlapping uniform wavebands, per link, for mesh networks using the minimum number of wavebands. Given a fixed band size b _s , we give integer linear programming formulations and present a heuristic solution to minimize the number of ROADMs (number of wavebands) in mesh networks that support a given traffic pattern. We show that the number of ROADMs (or number of ports in band-switching cross-connects) can be reduced significantly in mesh networks with WBS compared to wavelength switching using either the ILP or the heuristic algorithm. We also examine the performance of our band assignment algorithms under dynamic traffic.     

An online cost-efficient protection scheme for quick recovery in all-optical WDM mesh networks

Since a single fiber carries a huge amount of data in optical WDM networks, a fiber cut even for a brief period is a very serious event. Designing schemes to prevent disruption of user traffic and recovery techniques from failures is thus an important area of research. Since a single fiber cut is the most common type of fault, in this paper we address the problem of protecting all-optical WDM mesh networks from single link failure. Our proposed online protection scheme is an improvement over an existing approach and is not only cost-efficient in terms of network resource consumption but can also provide quick recovery from a link failure. We first provide an ILP formulation for the problem and then propose a heuristic solution iStreams that can provide near-optimal solution in polynomial time. Performance comparisons with some well-known schemes of protection show that our heuristic algorithm can be a better choice for conserving resource while providing quick recovery from a link failure.     

Partial SRLG-disjoint shared path protection with differentiated reliability in survivable WDM network

This paper addresses the problem of shared path protection algorithm in survivable wavelength-division-multiplexing (WDM) optical networks, taking into consideration of differentiated reliability (DiR) under Shared-Risk-Link-Group (SRLG) constraint. A subset of network links that share the risk of failure at the same time are said to be in a common SRLG. Rather than the conventional complete SRLG-disjoint shared path protection, we introduce a heuristic Partial SRLG-disjoint Shared Path Protection algorithm (Pd-SPP) based on the concept of SRLG conditional failure probability, to provide differentiated reliability protection. The main target of our work is to improve the network resource utilization ratio under the DiR constraint. We adopt the ideas of partial SRLG-disjoint and the K-shortest paths algorithm such we can efficiently solve the “trap” problem. The experimental results show that our algorithm outperforms the complete SRLG-disjoint shared path protection in both blocking probability ratio and network resource utilization, i.e. the results are found to be promising.     

Simulation-based SONET ADM optimization approach for dynamic traffic grooming in WDM optical networks

The article addresses a simulation-based optimization approach for allocation of ADMs in WDM optical networks with stochastic dynamic traffic. Since ADMs are expensive, it is desirable that if each node in WDM optical networks can use a minimum number of ADMs to achieve a near-ideal performance. In this article, first, the utilization statistics of ADMs are gathered by simulation. Then, ADMs are allocated based on the utilization statistics. In this respect, a simple sorting mechanism is used. The distinguished feature of the proposed approach is that it shows the way to allocate ADMs at the nodes of WDM optical networks with stochastic dynamic traffic. The experimental results ensure that the proposed approach can solve the problem of allocating ADMs in practical WDM optical networks considering stochastic dynamic traffic.

Experimental validation of resource allocation in transport network slicing using the ADRENALINE testbed

Transport network virtualization provides the necessary data and control plane technologies as key enablers of future networks. The interaction between network slicing and optical transport network virtualization architectures is under study to automate effective network resource orchestration. In this paper, we present an harmonized network slicing and transport network virtualization architecture, including a network slice planner tool, which is designed and implemented enabling in-operation execution of network slice resource allocation algorithms. We validate the proposed architecture by providing a novel resource allocation algorithm, evaluating its performance and deploying two different slices on top of the ADRENALINE testbed, while measuring both slices key performance indicators.

     

Power series-based algorithm for dedicated protection in WDM optical networks

WDM optical networks allow the transmission of multiple services with high rates and low cost. Therefore, the occurrence of a failure in any network element can cause loss of several services. Some survival mechanisms may be used to try to overcome this type of failure event. We present in this paper a new dedicated protection algorithm for link-failure survivability in WDM optical networks, referred to as power series routing-based dedicated protection (PSR-DP) algorithm. PSR-DP is based on the evaluation of the network links’ costs by using a power series expansion. This power series expansion uses input variables based on some relevant information of the network such as link physical length and wavelength availability. Other contribution of this paper is to propose a new input variable based on the wavelength continuity constraint. The performance of the proposed algorithm is compared to other well-known algorithms in the literature. We also propose a modification to Suurballe’s algorithm and compare it with our PSR-DP algorithm. Three different topologies are used in our simulations, and statistical analysis is performed on the results of the investigated algorithms. In all simulated cases, PSR-DP algorithm outperformed the other analyzed algorithms.     

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on‐demand provisioning of wavelength‐routed channels with service‐differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol (IP) network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing (WDM) technologies. Because of the availability of ultra long‐reach transport and all‐optical switching, the deployment of all‐optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video‐on‐demand systems, real‐time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment (RWA). The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call‐blocking probability. The dynamic traffic‐grooming problem in wavelength‐routed networks is generally a two‐layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Routing,modulation level and spectrum allocation with dynamic modulation level conversion in elastic optical networks

Elastic optical network is introduced as a promising technology to provide multi-bitrate-friendly data transmission in the optical layer. Elastic optical networks are based on flexible modulation format conversion, which can make more efficient use of spectrum resources than current fix-grid WDM networks. In this paper, we define the routing, modulation level and spectrum resource allocation (RMLSA) problem and then propose two novel dynamic modulation level conversion (MLC) enabled RMLSA algorithms. Numerical simulations are conducted to compare the performance of the path modulation level conversion (Path-MLC) and link modulation level conversion (Link-MLC) with different MLC thresholds with K-shortest paths RSA in terms of blocking rate, occupied spectrum and the number of MLCs across two topologies. The results verify that the Link-MLC with unlimited MLC achieves the lowest blocking rate and moderate spectrum utilization at the expense of intermediate node modulation conversions in two topologies. Smaller MLC threshold has higher blocking rate and occupied less spectrum resource. The results also suggest that the Path-MLC approach is more resource efficient than the Link-MLC with relatively higher blocking rate, and this method maybe more preferable in the networks with tight budget and/or energy constraints.     

Minimum cost dimensioning of ring optical networks

We consider the problem of traffic grooming of low-rate traffic circuits in WDM rings where circuits are associated with a set of heterogeneous granularities. While networks are no longer limited by transmission bandwidth, the key issue in WDM network design has evolved towards the processing capabilities of electronic switches, routers and multiplexers. Therefore, we focus here on traffic grooming with minimum interconnecting equipment cost. We first formulate the problem as an integer linear programming (ILP) or a mixed integer linear programming (MILP) problem depending on the design specifications: UPSR vs BLSR, fixed vs variable wavelength capacities, non-bifurcated vs bifurcated flows, wavelength continuity vs possible signal regeneration on a different wavelength. Considering the case study of the second SONET ring generation with MSPP like interconnection equipment, we define the cost by a function of the number of transport blades, taking into account that the number of MSPP transport blades makes up a significant portion of the overall network design cost. Using the CPLEX linear programming package, we next compare the optimal solutions of the ILP or MILP programs for different design assumptions, including the classical ring network design scheme with a single hub where the lightpaths directly connect the hub to all other nodes.     

Access and metro networks based on WDM technologies

This paper describes the technical issues of access and metro networks based on wavelength division multiplexing (WDM) technologies, some solutions, and an experimental demonstration. A WDM star access network with colorless optical network units (ONUs) is proposed. For realizing the colorless ONU, two approaches are introduced; optical carrier supply and spectrum slicing. In addition, a WDM metro ring network with scalable optical add/drop multiplexers (OADMs), namely the tapped-type OADM, is proposed to effectively accommodate the large amount of traffic issued from access networks. Prototypes are constructed and used to verify the feasibility of the proposed WDM technologies.