Optical Backbone Networks Research Articles

The Dispersion Research Based on its OTN Network Backbone Optical Transmission Network

In this paper, based on the practice optical transport network (OTN) electric power communication network business, through the modeling analysis shows the specific influence dispersion optical pulses, then discussed the dispersion compensation technology, through modeling and simulation analysis of the dispersion compensation fiber (DCF) and dispersion compensation module (DCM), at the same time with reference to its OTN equipment dispersion tolerance, form a light layer of dispersion compensation quantity calculation method of the experience and grid OTN networking dispersion compensation scheme, reduce the effects of dispersion as far as possible.

Minimizing the Risk From Disaster Failures in Optical Backbone Networks

Failures caused by disasters (e.g., weapons of mass destruction (WMD) attacks, earthquakes, hurricanes, etc.) can create huge amount of loss and disruptions in optical backbone networks. Due to major network disruptions in recent disasters, network operators need solutions to prevent connections from disasters, and recover them after disasters. 1) Prevention requires proactive approaches where the damage from a possible disaster should be estimated. Specifically, we propose disaster-risk-aware provisioning, which minimizes loss to a network operator in case of a disaster. 2) Recovery methods should consider that, after the initial failure, more connections might be disconnected by correlated cascading failures. Thus, we investigate a reprovisioning scheme to recover disrupted connections. Numerical examples conducted for different disaster types (WMD attack, earthquake, and tornado) show that our schemes significantly reduce the risk and loss in case of a disaster.

Degraded Service Provisioning in Mixed-Line-Rate WDM Backbone Networks Using Multipath Routing

Traffic in optical backbone networks is increasing and becoming more heterogeneous with respect to bandwidth and QoS requirements due to the popularity of high-bandwidth services (such as cloud computing, e-science, telemedicine, etc.), which need to coexist with traditional services (HTTP, etc.). Mixed-line-rate (MLR) networks that support lightpaths of different rates such as 10, 40, 100 Gb/s, etc., are being studied to better support the heterogeneous traffic demands. Here, we study the important topic of degraded services in MLR networks, where a service can accept some degradation (i.e., reduction) in bandwidth in case of a failure in exchange for a lower cost, a concept called partial protection. Network operators may wish to support degraded services to optimize network resources and reduce cost. We propose using multipath routing to support degraded services in MLR networks, a problem that has not been studied before and is significantly more challenging than in single-line-rate (SLR) networks. We consider minimum-cost MLR network design (i.e., choosing which transponder rates to use at each node), considering the opportunity to exploit multipath routes to support degraded services. We propose a mixed-integer-linear-program (MILP) solution and a computationally efficient heuristic, and consider two partial-protection models. Our illustrative numerical results show that significant cost savings can be achieved due to partial protection versus full protection and is highly beneficial for network operators. We also note that multipath routing in MLR networks exploits volume discount of higher-line-rate transponders by cost-effectively grooming requests over appropriate line rates to maximize transponder reuse versus SLR.

Virtual Network Reconfiguration With Adaptability to Traffic Changes

One approach to accommodating time-varying traffic is to construct a virtual network over an optical backbone network by connecting nodes with optical paths. The virtual network is dynamically reconfigured by adding or deleting optical paths so as to suit the current traffic. However, a large number of optical paths have to be added when there are large traffic changes, and this may entail a large overhead. To avoid adding a large number of optical paths, we should construct a virtual network that is adaptive to traffic changes, wherein congestion caused by traffic changes can be mitigated by adding only a small number of optical paths. In this paper, we propose a method to control a virtual network that adapts to traffic changes. We propose a new index, called flow inclusive relation modularity (FIRM), inspired by a model of lifeforms that survive and evolve under significant environmental changes. Through simulation, we clarify that the virtual network with high FIRM can handle traffic changes by adding a small number of optical paths. Moreover, we find that a virtual network embodying FIRM reduces the number of optical paths that have to be added when there are significant traffic changes compared with a virtual network configured only on the basis of the utilization of optical paths.

On the optimization of CAPEX and OPEX for the design of island-based translucent optical backbone networks

The transmission reach of signals in optical transmission systems is limited. To go beyond these transparent reach limits, signal regeneration is necessary to re-amplify, re-shape, and re-time the optical signals. Translucent optical networks use a set of sparsely but strategically placed regenerators for the purpose of signal regeneration. These networks are emerged as a promising solution achieving both opaque-networks Quality-of-Transmission (QoT) requirements and transparent-networks cost-effectiveness. Despite massive progress, there are many outstanding issues regarding the design of translucent networks. Mainly, two approaches have been proposed in the literature to deal with the design of such networks, namely, island-of-transparency and sparse-regeneration. In our present work, we adopted the island-based approach which suits much better the operator׳s expectations especially in terms of network scalability and operational expenses, to address the problem of designing translucent WDM backbone networks. Based on such an approach, we present an original two-phase heuristic which locates the regeneration-sites and determines the number of electronic regenerators to be installed in, according to an efficient strategy that aims at minimizing both Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) inherent to regeneration while ensuring QoT requirements. Compared to previously presented island-based approaches, our algorithm is, to the best of our knowledge, the first island-based algorithm that aims at minimizing simultaneously CAPEX and OPEX while using an accurate QoT estimator incorporating all major linear and nonlinear physical-layer impairment effects during the design and dimensioning process. The performances of the proposed heuristic are evaluated through multiple simulations and compared to those of previously presented approaches in order to highlight the main improvements.

Exploiting Excess Capacity for Survivable Traffic Grooming in Optical Backbone Networks

Backbone networks usually have some excess capacity (EC) to accommodate traffic fluctuations and to avoid early capacity exhaustion. Network operators can exploit EC in optical wavelength division multiplexed (WDM) backbone networks to support survivable traffic grooming, where connection requests are of subwavelength granularity and each provisioned request has to be protected from single-link failures. We investigate novel EC management techniques that can improve network performance, in terms of Service-Level Agreement (SLA) violations and bandwidth blockings, with no requirement of deploying additional capacity. We investigate exploiting and managing EC by the following techniques. i) Preprovisioning: When traffic is light, network resources are reserved by a preprovisioning scheme, i.e., a connection can be provisioned on reserved protected links to increase availability. We show that preprovisioning also decreases connection setup time, an important metric for delay-sensitive services. ii) Backup reprovisioning: Since high-availability protection schemes usually consume more resources, connections in our solution can be switched to a protection scheme that provides lower availability (but higher resource efficiency) by reprovisioning backup resources when traffic increases. iii) Hold-lightpath: We propose a new “hold-lightpath” scheme to exploit EC. This scheme prevents the termination of pre-established (but unused) resources to increase availability and decrease connection setup time. We compare our techniques with traditional protection schemes for typical daily fluctuating traffic on typical backbone network topologies and find that significant improvements can be achieved in terms of decreasing SLA violations, bandwidth blocking, and connection setup time.

Robust Network Design for Stochastic Traffic Demands

This paper addresses the problem of logical topology design for optical backbone networks subject to stochastic traffic demands. The network design problem is broken into three tasks: traffic routing, capacity allocation, and link placement. While the routing and capacity allocation subproblem can be formulated using convex optimization, it is prohibitive to add the link placement component to the nonlinear formulation since the link placement problem involves integer variables. To address this issue, we develop a linear formulation for the routing and capacity allocation subproblem by applying tools from robust optimization. We show that this linear formulation performs comparably to the optimal nonlinear formulation. Our formulation can then be used to solve the link-placement subproblem for stochastic traffic. We show that optimal logical topologies for deterministic traffic demands are not necessarily optimal for stochastic traffic demands. We develop algorithms for finding logical topologies optimized for stochastic traffic.

Energy-Aware Scheduling and Resource Allocation for Periodic Traffic Demands

The tremendous growth in high-bandwidth applications and consequent increase in power consumption has underscored the importance of energy efficient design strategies for backbone optical networks. In this paper, we exploit the knowledge of the demand holding times to obtain more power efficient grooming. We consider time-varying, periodic traffic, where the setup and teardown times of the demands may be fixed or vary within a larger time window. The problem of joint scheduling (in time) and traffic grooming, with the goal of minimizing energy consumption for sliding demands, has not been considered previously. We first present an efficient integer linear program formulation for scheduling and allocating resources to a single subwavelength traffic demand, such that incremental energy consumption due to the new demand is minimized. Next, we extend the proposed approach and present a new heuristic that jointly performs scheduling and resource allocation for a large set of periodic demands with the goal of reducing the overall energy consumption of the network for the entire demand set. Through simulations, we demonstrate that significant energy savings can be achieved by considering the demand holding time and show that joint allocation of demands yields additional improvements.

Study on Influence Factors of Nonlinear Finite Element Analysis for High Arch Dams

In communication network, WDM optical backbone network has become the primary long-distance options. In this paper, the structure of WDM optical networks are analyzed, the add-drop system in the architecture of WDM optical networks is discussed. In order to improve network efficiency, we analyzed the characteristics of network routing, and proposed a new routing design method. In communication network, a good routing is very important for network operation. Routing technologies manage the flow of data between network segments in optical communication network. In addition, we also discussed the WDM optical network switching technology.

Disaster survivability in optical communication networks

With the frequent occurrences of natural disasters damaging large portions of communication networks and the rising risk of intentional attacks, network vulnerability to multiple cascading, correlated, and collocated failures has become a major concern. Optical backbone networks provide highly-scalable connectivity across large distances. These networks exploit optical technology to carry huge aggregated data and can support “higher-layer” networks, such as SONET, Ethernet, IP, MPLS, ATM, etc. Given the high complexity and scale of backbone networks, multiple correlated failures can have a devastating impact on topological connectivity, which in turn can cause widespread “end-to-end” connection-level disruptions. These outages may affect many applications/services supported by the optical layer, irrespective of the importance of the service and/or sensitivity of the carried data. Hence, it is crucial to understand the vulnerability of optical backbone networks to disasters and design appropriate countermeasures. In this paper, we present a general classification of the existing research works on disaster survivability in optical networks and a survey on relevant works based on that classification. We also classify disasters based on their characteristics and impact on communication networks and discuss different ways to combat them. We conclude the paper with open issues and challenges.

A distributed framework for energy-efficient lightpaths in computational grids

Over the past decade, the ever-increasing energy demands of IT infrastructures have posed significant challenges for the research community in terms of reducing their total power consumption and minimizing their environmental impact. Optical communication networks are envisioned to be promising candidates to help preventing this problem affecting the Internet backbone, as well as for distributed applications such as computational grids. In this paper, we propose an adaptive and distributed scheme for the establishment of energy-efficient lightpaths in computational grids. The grid is deployed over an optical circuit-switched backbone network, defining an optical grid network. Each node of the backbone network maintains two different dynamic thresholds values and estimates the changes in network performance by evaluating the moving average of the total wavelength channel occupancy on all its input/output links. The nodes have the ability of reducing the energy consumption by entering into an Energy Saving Mode ESM on the basis of a comparison between their channel occupancy and the thresholds. Furthermore, we extend our framework by allowing the thresholds to be dynamically adapted depending on the network performance in terms of blocking probability. We show that the proposed method achieves considerable energy savings when compared to a normal energy-unaware operational mode and still allows to maintain an acceptable level of network performance in terms of blocking probability and end-to-end delay. Numerical results are obtained with a Java event-driven simulator of two different optical network topologies.

High-performance routing for hose-based VPNs in multi-domain backbone networks

By utilizing Layer-1 Virtual Private Networks (L1VPN), a single physical network, e.g., an optical backbone network, can support multiple virtual networks, which form the basic infrastructure for cloud computing and other enterprise networks. The L1VPN hose model is an elegant and flexible way to specify the customers’ bandwidth requirements, by defining the total incoming and outgoing demand for each endpoint. Furthermore, multi-domain physical infrastructures are common in L1VPNs, since these are usually deployed on a global scale. Thus, high-performance Routing for Multi-domain VPN Provisioning (RMVP) for the hose model is an important problem to efficiently support a global virtual infrastructure. In this paper, we formulate the RMVP problem as a Mixed Integer Linear Program (MILP). Also, we propose a Top-Down Routing (TDR) strategy to compute the optimal routing for the hose model L1VPN in a multi-domain backbone network. Results indicate that TDR approaches the minimum routing cost when compared to the ideal case of single-domain routing.

Metaheuristic hybridizations for the regenerator placement and dimensioning problem in sub-wavelength switching optical networks

Physical layer impairments severely limit the reach and capacity of optical systems, thereby hampering the deployment of transparent optical networks (i.e., no electrical signal regenerators are required). Besides, the high cost and power-consumption of regeneration devices makes it unaffordable for network operators to consider the opaque architecture (i.e., regeneration is available at every network node). In this context, translucent architectures (i.e., regeneration is only available at selected nodes) have emerged as the most promising short term solution to decrease costs and energy consumption in optical backbone networks. Concurrently, the coarse granularity and inflexibility of legacy optical technologies have re-fostered great interest in sub-wavelength switching optical networks, which introduce optical switching in the time domain so as to further improve resources utilization. In these networks, the complex regenerator placement and dimensioning problem emerges. In short, this problem aims at minimizing the number of electrical regenerators deployed in the network. To tackle it, in this paper both a greedy randomized adaptive search procedure and a biased random-key genetic algorithm are developed. Further, we enhance their performance by introducing both path-relinking and variable neighborhood descent as effective intensification procedures. The resulting hybridizations are compared among each other as well as against results from optimal and heuristic mixed integer linear programming formulations. Illustrative results over a broad range of network scenarios show that the biased random-key genetic algorithm working in conjunction with these two intensification mechanisms represents a compelling network planning algorithm for the design of future sub-wavelength optical networks.

Distributed Online Optimization of Wireless Optical Networks With Network Coding

Recently, the hybrid wireless-optical broadband network integrating optical backbone networks, passive optical networks (PON), and wireless access networks have been proposed to provide the high-bandwidth, low-cost, and ubiquitous communication connections. In this paper, we consider the design of network coding-based multicast applications in such networks with the objective of maximizing the total network utility and minimizing the deployment cost, subject to QoS constraints. The problem is formulated as a mixed integer nonlinear programming problem and the exact solution is prohibitively complex. In order to make the problem more tractable, we develop a two-step optimization procedure that iteratively selects the optical network unit and gateways for the multicast sessions. During each iteration, two subproblems are solved, i.e., a network coding design problem for the optical network, and a user assignment and bandwidth allocation problem for the wireless network. The former is solved in a distributed way based on the Lagrangian-dual decomposition; the latter is solved based on the generalized bender decomposition. Simulation results are provided to illustrate the effectiveness of the proposed solutions.

Price-Points for Components of Multi-Core Fiber Communication Systems in Backbone Optical Networks

The communication capacity limit of conventional optical fiber is being approached, and spatial multiplexing on strands of optical fiber is being pursued because of its potential to significantly increase the capacity of optical transmission systems and networks. Here, we estimate price-points under several scenarios for some of the critical enabling components of potential ultra-high-capacity optical fiber transmission systems based on multi-core fibers. For the input parameters and scenarios considered—including the case when the existing conduit is exhausted, we find the modeled price-point of multi-core fiber to be in the range 0–15% higher than the price of fiber ribbon cable. We also illustrate how larger increases in the value (price-point) of future network elements can occur if the efficiencies of installation are substantially improved.

Mixed-line-rate optical network design with wavebanding

To cope with ever increasing and more heterogeneous traffic demands, today’s optical backbone networks are expected to support mixed line rates (MLR) over different wavelength channels. MLR networks can be designed to provide flexible rate assignments to low-bit-rate services and high-bit-rate services in a cost-effective manner. But with increasing number of wavelengths in the network, aggregating wavelengths into wavebands can further reduce the network cost.In this study, we incorporate the idea of waveband switching in MLR network design. Wavebanding or grouping of optical paths reduces the optical switch size at the optical cross-connects (OXCs). When several lightpaths share several common links, they can be grouped together and routed as a single waveband. For optical bypass at a transit node, only two optical ports are required for each waveband, hence reducing the port cost. It can be a challenge for an MLR network to waveband wavelengths of different line rates that have different transmission reaches. In our design, we present a suitable switching architecture and propose an efficient and cost-effective approach for wavebanding in an MLR network. The design problem is formulated as a mixed integer linear program (MILP) where the objective is to minimize transponder cost and port cost. A heuristic algorithm for wavebanding in MLR networks is provided. To further optimize our solution, we also present a Simulated Annealing algorithm for wavebanding. Our results show a significant improvement in cost savings compared to single-line-rate (SLR) networks with wavebanding and an MLR network employing only wavelength switching.

Service Velocity: Rapid Provisioning Strategies in Optical ROADM Networks

The advent of reconfigurable optical add/drop multiplexers with colorless and non-directional add/drop ports enables transponders and regenerators to be pre-deployed, without a priori knowledge of which wavelength or direction they will eventually serve. We study pre-deployment of optical regenerators as a means to drastically reduce the provisioning time, using Monte Carlo simulation of an optical backbone network. With appropriate placement strategies, regenerators can be efficiently pre-deployed so that new connections can be established rapidly, without the delays caused by service visits to intermediate network nodes.

On the Design of Energy-Efficient Mixed-Line-Rate (MLR) Optical Networks

With increasing energy consumption of the Internet, it is now imperative to design energy-efficient network architectures and protocols. Optical technologies have significant promise in improving the energy efficiency of network infrastructures. Future optical backbone networks will be heterogeneous in nature where a single link may carry various line-rate signals. This mixed-line-rate (MLR) network architecture is shown to be cost effective in satisfying heterogeneous traffic demands. In this study, we present mathematical models that can act as references for designing energy- and cost-efficient MLR optical networks. We also perform a comparative study of the energy efficiency of MLR and special cases of MLR design, named as single-line-rate networks (where all the links have same line rates). We explore the scenarios where the MLR networks minimize energy consumption. Finally, we investigate the relationship between energy-minimized and cost-minimized MLR network design.

Energy Aware Resource Allocation Based on Demand Bandwidth and Duration

The tremendous growth in high-bandwidth applications and consequent increase in power consumption has underscored the importance of energy efficient design strategies for backbone optical networks. In this paper, we first present an ef–ficient integer linear program (ILP) formulation for allocating resources to a sub-wavelength traffic demand, such that the increase in energy consumption due to the new demand is minimized. The ILP allocates resources to the new de–mand, based on the bandwidth usage and durations of existing demands, as well as that of the new demand. We then extend this approach, and propose a heuristic that performs resource allocation for a set of scheduled, periodic demands with the goal of reducing the overall energy consumption of the network for the entire demand set. We show through simulations that the proposed ILP can quickly generate solutions for practical networks, with hundreds of demands and demonstrate that knowledge of the demand holding times can be exploited to significantly reduce the overall network energy consumption.

Approximate Analytical Performance Evaluation of Synchronous Bufferless Optical Packet-Switched Networks

We present a method for analytical performance evaluation of synchronous optical packet-switched backbone networks. The proposed method is applicable to networks of any topology built of nodes of any degree with any number of wavelengths, and capable of allowing for deflections. The method provides not only general results such as fiber utilization, but also detailed results on where and at what mean rates packets travel. We analyze the steady-state performance of a network loaded with independent flows. The admission control admits in a fair way at most as many packets as there are output slots available, while the routing algorithm uses classes, distances, deflections, and wavelength conversion. We compare the results of our method with simulation results for a large set of randomly generated test cases, and conclude that the proposed method yields reasonably accurate results.