Virtual Topology Design Research Articles

Squeezed Protection in Elastic Optical Networks Subject to Multiple Link Failures

Elastic optical network (EON) is fast becoming a key solution for designing optical network with better usage of spectrum resources or other objectives of interest to tenant and/or operators. A primary concern of EONs is to protect the network against failures of its elements, because this kind of event can provoke the loss of substantial amount of traffic. In this paper, we propose a new mixed integer linear programming (MILP) formulation for protecting the network traffic against multiple link failures. The key idea is to use bandwidth squeezing together with grooming capability to provide few extra traffic for protection and guarantee a minimum bandwidth for each source-destination node pair under multiple failure events. The proposed formulation solves the virtual topology design problem jointly with the grooming, routing, modulation and spectrum allocation (RMSA) tasks. Due to the non-deterministic polynomial time (NP-hard) nature of the proposed MILP formulation, a heuristic strategy (referred to as two-step MILP) for large networks is also proposed. The solutions and performance of the proposed MILP formulation and two-step MILP analyzed through case studies in a small network. In addition, the performance of three large networks is assessed for cases scenarios where connections are under different service-level agreement (SLA). In view of proposed formulation and two-step MILP, it is possible to identify the configurations that ensure better usage of spectrum resources with different kinds of protection against single or multiple link failures.

On the Cross-Layer Network Planning for Flexible Ethernet Over Elastic Optical Networks

This article studies the cross-layer network planning that tries to combine flexible Ethernet (FlexE) and elastic optical networks (EONs), for FlexE-over-EONs. We focus our investigation on the most challenging setting, i.e., the FlexE-over-EONs based on the FlexE-aware architecture, and consider both single-hop and multi-hop scenarios for the cross-layer planning. For the single-hop scenario, we assume that all the client flows are routed over end-to-end lightpaths in the EON. We formulate a mixed integer linear programming (MILP) model for this problem, transform it into the class constrained bin packing problem (CCBP), and leverage the primal-dual interior-point (PDIP) method to propose a polynomial-time approximation algorithm for it. Then, for the multi-hop scenario, we use a more realistic assumption that each client flow can be routed over multiple lightpaths in the EON. We show that after solving the virtual topology design, the cross-layer planning in this scenario can be transformed into that in the single-hop scenario. Therefore, an integer linear programming (ILP) model is formulated to tackle the virtual topology design, and we design a polynomial-time approximation algorithm for it by modifying the well-known branch-and-bond method. To evaluate the performance of our two-step method for the multi-hop scenario, we also propose a heuristic algorithm. Extensive simulations verify that regarding large-scale cross-layer planning for FlexE-over-EONs, our approximation algorithms are significantly more time-efficient than the ILP/MILP models, and their solutions have bounded gaps to the optimal ones and are much better than those of the heuristic.

Virtualization of elastic optical networks and regenerators with traffic grooming

An elastic optical network (EON) plays an important role in transport technology for virtualization of networks. A key aspect of EONs is to establish lightpaths (virtual links) with exactly the amount of spectrum that is needed and with the possibility of grooming, the process of grouping many small traffic flows into larger units, creating a super-lightpath. Grooming eliminates the need for many guard bands between lightpaths and also saves transceivers; however, it often leads to the need to perform optical–electrical–optical conversions to multiple-data-rate optical signals at intermediate nodes. The aim of this paper is to provide a mixed-integer linear programming (MILP) formulation, as well as heuristic and meta-heuristic approaches, for the design of multiple virtual optical networks (VONs) in an elastic optical substrate network with bandwidth-variable lightpaths, modulation format constraints, and virtual elastic regenerator placement. Traffic grooming is allowed inside each VON, and a distance-adaptive modulation format technique is employed to guarantee efficiency in terms of bandwidth for a physical substrate, subject to several virtual topologies. A reduced MILP formulation without grooming capability is also proposed for comparison. The complete MILP formulation jointly solves the virtual topology design, regenerator placement, and grooming problems, as well as the routing, modulation, and spectrum assignment (RMSA) problem. The reduced MILP formulation, heuristics, and meta-heuristic, on the other hand, separate the virtual topology design problem from the RMSA problem. It is shown that the grooming approach can provide good results, since it solves the problem for a complete design when compared to the approach without grooming. Furthermore, heuristic solutions for large networks are proposed, which present good performance (in terms of saving spectrum) for the design with large instances.

Performance Modeling and Analysis of WDM Optical Networks under Wavelength Continuity Constraint using MILP

Objective: Optical networks exploit the Wavelength Division Multiplexing (WDM) to meet the ever-growing bandwidth demands of upcoming communication applications. This is achieved by dividing the enormous transmission bandwidth of fiber into smaller communication channels. The major problem with WDM network design is to find an optimal path between two end users and allocate an available wavelength to the chosen path for the successful data transmission. Methods: This communication over a WDM network is carried out through lightpaths. The merging of all these lightpaths in an optical network generates a virtual topology which is suitable for the optimal network design to meet the increasing traffic demands. But, this virtual topology design is an NP-hard problem. This paper aims to explore Mixed Integer Linear Programming (MILP) framework to solve this design issue. Results: The comparative results of the proposed and existing mathematical models show that the proposed algorithm outperforms with the various performance parameters. Conclusion: Finally, it is concluded that network congestion is reduced marginally in the overall performance of the network.

Genetic Algorithm for Holistic VNF-Mapping and Virtual Topology Design

Next generation of Internet of Things (IoT) services imposes stringent requirements to the future networks that current ones cannot fulfill. 5G is a technology born to give response to those requirements. However, the deployment of 5G is also accompanied by profound architectural changes in the network, including the introduction of technologies like multi-access edge computing (MEC), software defined networking (SDN), and network function virtualization (NFV). In particular, NFV poses diverse challenges like virtual network function (VNF) placement and chaining, also called VNF-mapping. In this paper, we present an algorithm that solves VNF-placement and chaining in a metro WDM optical network equipped with MEC resources. Therefore, it solves the VNF-mapping in conjunction with the virtual topology design of the underlying optical backhaul network. Moreover, a version of the method providing protection against node failures is also presented. A simulation study is presented to show the importance of designing the three problems jointly, in contrast to other proposals of the literature that do not take the design of the underlying network into consideration when solving that problem. Furthermore, this paper also shows the advantages of using collaboration between MEC nodes to solve the VNF-mapping problem and the advantage of using shared protection schemes. The new algorithm outperforms other proposals in terms of both service blocking ratio, and number of active CPUs (thus reducing energy consumption). Finally, the impact of deploying different physical topologies for the optical backhaul network is also presented.

Virtual 3D environments as composition and performance spaces

In the present text, I will reflect upon the composition of works that use virtual 3D environments in which the performers are represented as interacting avatars. In particular, I will explain the musical possibilities offered by this work with virtual environments, detailing the effects that the design of virtual topologies has on the interactive sound sources and sound events contained in these topologies. I will focus particularly upon how performers can musically influence said effects by navigating with the avatars acting within the topology.

SLA Formulation for Squeezed Protection in Elastic Optical Networks Considering the Modulation Format

In spectrum-sliced elastic optical path networks (SLICE), the lightpath bandwidth is variable, and the virtual topology overlay on a physical topology shall be designed to optimize the spectrum utilization. Under static traffic, SLICE networks are typically designed through a mixed integer linear programming (MILP) with the aim of minimizing the spectrum utilization. In this paper, a new MILP formulation for protection in SLICE networks is proposed, which uses the concept of bandwidth squeezing and grooming to guarantee a minimum agreed bandwidth for each source-destination pair in the surviving bandwidth. The route for each demand on the physical topology is determined by balance equations together with physical layer constraints in the formulation, so that no pre-calculated routes are required and the modulation format of each established lightpath may be chosen with enough quality of transmission and to save network spectrum. Therefore, the proposed formulation jointly solves the virtual topology design and physical topology design problems. The first results evaluate the effectiveness of the MILP formulation for two small networks when connections are under different service-level agreement (SLA) requirements and are provisioned by an appropriate protection scheme and different modulation formats. Due to the NP-hard nature of the proposed MILP formulation, a heuristic algorithm for moderately large networks is also proposed. Case studies are carried out to analyze the basic properties of the formulation and the performance of the proposed heuristic. With the proposed formulation, it is possible to identify the configurations that ensure minimum spectrum occupation with different kinds of protection for each lightpath. Different kinds of modulation formats are considered and contrasted to the benchmark case of a single modulation format and using the same kind of protection for all lightpaths.

Towards energy efficiency in virtual topology design of elastic optical networks

SummaryElastic optical networks offer a reliable platform for achieving energy efficiency by supporting extensive optical grooming of variable‐rate data traffic along with the traditional electrical data aggregation methods. The procedure of routing and spectrum allocation in a topology of nodes has explicit effect to the amount of consumed power. A new energy‐efficient method for designing the virtual topology in IP‐over‐elastic networks is introduced and evaluated. It is concluded that it consumes less power under different elastic transponder types, it designs the virtual topology using fewer transponders, and finally, there is a slight increase in the number of end‐to‐end lightpath hops. The proposed method is characterized by high performance and low lightpath establishment complexity. Therefore, it is suitable for a broad range of network configurations and transponder types.

Heuristic and genetic algorithms for solving the virtual topology design problem on elastic optical networks

Heuristic and genetic algorithms for solving the virtual topology design problem on elastic optical networks

Energy-efficient virtual topology design in IP over WDM mesh networks

Energy efficiency has been well recognized as an important objective in design of IP over WDM mesh networks. While previous works always focus on energy minimization through green routing and resource provisioning, the comprehensive performances of the two-layer network cannot be guaranteed. This would be not good for realization of energy-efficient networking methods.In this paper, we first study the problem of getting a good tradeoff between the three-part network comprehensive performances: energy efficiency, resource efficiency and cross-layer survivability efficiency for IP over WDM mesh networks under the static traffic demand. We present the virtual-link energy model for two-layer networks. The energy model is computed from the power consumption value of commercial network devices. Based on the energy-aware two-layer auxiliary graph, we propose a new Energy-Efficient Virtual Topology Design (E2VTD) scheme. The novelty of our proposed E2VTD scheme is mainly twofold as following: the first is the energy-efficient virtual link direct mapping and rerouting and the second is the cross-layer survivability improvement for energy-efficient virtual topology. We use extensive simulations to demonstrate the efficiency of our proposed E2VTD scheme. It is shown that the network comprehensive performances are significantly improved for two-layer networks. Compared with the previous algorithms, network energy consumption is reduced by about 39.8%, network resource is reduced by about 28.2%, and cross-layer topology survivability can be enhanced by about 35.7% in average.

Smart-Grid Backbone Network Real-Time Delay Reduction via Integer Programming.

This research investigates an optimal delay-based virtual topology design using integer linear programming (ILP), which is applied to the current backbone networks such as smart-grid real-time communication systems. A network traffic matrix is applied and the corresponding virtual topology problem is solved using the ILP formulations that include a network delay-dependent objective function and lightpath routing, wavelength assignment, wavelength continuity, flow routing, and traffic loss constraints. The proposed optimization approach provides an efficient deterministic integration of intelligent sensing and decision making, and network learning features for superior smart grid operations by adaptively responding the time-varying network traffic data as well as operational constraints to maintain optimal virtual topologies. A representative optical backbone network has been utilized to demonstrate the proposed optimization framework whose simulation results indicate that superior smart-grid network performance can be achieved using commercial networks and integer programming.

Genetic algorithm for virtual topology design on MLR WDM networks

For the mixed-line-rate (MLR) wavelength-division multiplexing (WDM) networks, each wavelength of fiber can provide different transmitting rates (in 10/40/100Gbps) by using different modulation types. Since the MLR-WDM is becoming the key and a cost-efficient technique for the network upgrading, the problem for constructing an efficient virtual topology becomes an important issue. In this paper, the Virtual Topology Design (VTD) problem on MLR-WDM network is considered. Given the physical backbone network and traffic demand matrix between nodes of the network, the goal of the VTD problem is to determine which node-pairs to be connected by establishing lightpaths, the actual routes of the lightpaths, the transmitting rates of lightpaths, and the assigned wavelengths of lightpaths such that the total cost of deployed transceivers can be minimized. Since the VTD problem on MLR-WDM network is a hard problem, in the paper, a heuristic algorithm (HA) and a genetic algorithm (GA) are proposed to solve it. Experimental results indicate that the proposed GA is robust for this problem.

Virtual Topology Reconfiguration in Optical Networks by Means of Cognition: Evaluation and Experimental Validation [Invited

In optical networking, virtual topologies have been introduced mainly to provide service providers with logical connections equipped with a reserved amount of bandwidth, which can be exploited to interconnect their equipment at the edges of the transport infrastructure. Virtual topologies are thus basically an abstraction of the real substrate, created by means of a process called virtual topology design (VTD). VTD is a complex task, affected by many parameters and constraints, and among them current traffic conditions are very relevant. Indeed, it is possible that after a certain time a virtual topology becomes inappropriate to serve current traffic. In such cases, the virtual topology can be reconfigured by creating new lightpaths or modifying or deleting existing ones, thus possibly creating some service interruptions. In this paper a new virtual topology reconfiguration technique is presented. In this technique, a cognitive entity designs and reconfigures virtual topologies by exploiting traffic forecasting solutions and taking advantage of past history. Moreover, a new transition method is also proposed to reduce the impact of instable routing tables during the reconfiguration process. We demonstrate, by means of simulation, the advantages of the proposed methods, as they reduce both the operational costs and the resources in operation while maintaining low packet loss ratio. Furthermore, we validate the operation of the proposed solutions in an emulated testbed.

Virtual topology design scheme with energy efficiency for IP over elastic optical networks

The rapid growth of the Internet raises the importance of resource planning of Internet protocol (IP) over elastic optical networks (EONs), which is a challenging task due to more complex and obscure physical ­constraints of it. Compared with network cost, the power consumption may eventually become the barrier to the expansion of the Internet. We present an energy-efficient virtual topology design (VTD) scheme for IP over EON. We explicitly explain and analyze the mixed integer linear programming model and the heuristic algorithm for this scheme. Numerical results show that the proposed VTD scheme can significantly save power consumption.

Toward energy‐proportional Internet core networks: an energy‐minimized routing and virtual topology design for Internet protocol layer

SummaryWith the exponential growth of Internet traffic, the energy consumption issue of core networks is increasingly becoming critical. Today's core networks are highly underutilized most of the time because of the over‐provisioning and redundancy dimensioning, which results in severe energy inefficiency. In previous work, many non‐deterministic polynomial‐time hard mathematics formulation models have been proposed to minimize the energy consumption of core networks. However, effective heuristics are needed to solve these models in medium/large‐size networks. This work studies the energy‐minimized routing and virtual topology design problem of the power‐hungry Internet protocol (IP) layer in core networks, aiming to achieve an energy‐proportional IP layer by exploiting the variation of traffic with hours to reconfigure virtual topology and reroute traffic. We formulate energy‐minimized routing and virtual topology design as an Integer linear programming problem and propose a LR algorithm, a heuristic based on the Lagrangian relaxation, to solve this problem in a polynomial‐time. The simulation results indicate that the LR algorithm outperforms the best previous algorithm and can achieve a near energy‐proportional IP layer with significant power saving. Furthermore, a detailed analysis of simulation results is conducted, which suggests a design principle of network equipment to facilitate the power saving. Copyright © 2013 John Wiley & Sons, Ltd.

Joint scheduling and virtual topology design for sliding periodic traffic

Two possible approaches can be considered for solving the virtual topology design problem for periodic (multi-hour) traffic demands. The first approach attempts to design a static topology that can accommodate all the traffic variations over time. The second option is to determine an appropriate series of virtual topologies to accommodate the different traffic loads at different times. This can lead to some savings in terms of the number of transceivers needed, but it requires the use of costly reconfigurable switching equipment. So, strategies for stable virtual topology design have received considerable attention in recent years. However, all the works reported in the literature so far, focus on the fixed window scheduled traffic model, where the start and end times of the demands are known in advance. In this paper, we propose a new integrated approach using the more general sliding window model, for jointly scheduling the demands in time and designing a logical topology that can accommodate all the scheduled demands. The goal is to a find a suitable static topology that can handle fluctuations in the offered sub-wavelength traffic load, without requiring the use of reconfigurable optical switching equipment. We first present a comprehensive integer linear program (ILP) formulation for designing a cost-efficient, stable logical topology for time-varying demands, and then propose an integrated heuristic algorithm capable of handling larger networks. Simulation results demonstrate the advantages of the proposed approaches, not only compared to holding time unaware models, but also over the traditional fixed window model.

A Delay based MILP for Network Planning in Optical Networks

This research investigates a mixed integer linear programming (MILP) framework that solves the virtual topology problem under the communication delay constraint. An arbitrary optical network has been considered with different distances between the nodes and different link capacities. A traffic matrix is assumed for the optical network at an instance and the corresponding virtual topology design is solved by using the mixed integer linear formulation that includes lightpath routing, wavelength assignment, wavelength continuity, flow routing, and traffic losses.The numerical optimization results illustrate the efficiency of the proposed MILP formulation and superior network performances, validating the proposed framework for optimal virtual topology designs. Moreover, the proposed framework may alleviate computational time issues related to the network learning process of some heuristic approaches.

(Non-)Reconfigurable Virtual Topology Design Under Multihour Traffic in Optical Networks

This paper investigates offline virtual topology design in transparent optical networks under a multihour traffic demand. The main problem variant addressed here designs a reconfigurable virtual topology that evolves over time to more efficiently utilize network resources (the MH-VTD-R problem). The case of designing a static non-reconfigurable virtual topology that can accommodate the time-varying traffic (the MH-VTD-NR problem) is also considered. The objectives are to minimize: 1) the number of transceivers, which make up for the main network cost; and 2) the frequency of reconfiguration (for MH-VTD-R), which incurs additional overhead and potential service disruption. We formulate this multiobjective problem as an exact mixed integer linear program (MILP). Due to its high complexity, we propose a very efficient heuristic algorithm called Greedy Approach with Reconfiguration Flattening (GARF). GARF not only solves both (non-)reconfigurable problem variants, but it allows for tuning of the relative importance of the two objectives. Exhaustive experiments on real and synthetic traffic and comparison to previous proposals and bounds reveal the merits of GARF with respect to both solution quality and execution time. Furthermore, the obtained results indicate that the maximal transceiver cost savings achieved by the fully reconfigurable case may not be enough to justify the associated increase in reconfiguration cost. However, results show that an advantageous tradeoff between transceiver cost savings and reconfiguration cost can be achieved by a allowing a small number of virtual topology reconfigurations over time.

Energy-minimised virtual topology design in IP over WDM backbone networks

As the Internet expands in terms of users and exchanged traffic, the energy consumption of the network is rapidly increasing and is becoming a very important issue. In backbone internet protocol (IP) over wavelength division multiplexing networks, it is possible to reduce the energy consumption by properly designing the IP topology and routing the traffic on it. The present study faces such a problem and proposes a novel heuristic algorithm derived from the ‘multi-hop grooming’ strategy. The proposed algorithm is based on an innovative approach as it starts considering the solution given by the ‘single-hop grooming’ strategy and then tries to eliminate unnecessary links by iteratively rerouting traffic flows. To achieve such an objective, a load-dependent cost function is used in the shortest path routing algorithm to compute link weights. Results obtained through simulations show that the proposed solution outperforms other algorithms proposed in the literature and performs close to the optimal solution. Moreover, besides showing a good performance in terms of energy efficiency, the proposed algorithm is also able to limit the maximum path length, saving a considerable amount of bandwidth and limiting the delay experienced by packets in the network.

Multi-layer Virtual Topology Design in Optical Networks Under Physical Layer Impairments and Multi-hour Traffic Demand

In this paper, we consider the virtual topology design (VTD) problem in multi-protocol label switching (MPLS)/wavelength division multiplexing (WDM) networks with an hourly changing traffic pattern, in the presence of physical layer impairments. We propose a multi-layer VTD scheme that satisfies the constraints in both layers with guaranteed bit error rates assuming no wavelength conversion. The proposed scheme involves interaction of the control planes of MPLS and WDM layers and can be applied without the necessity of a unified control plane. When the virtual topology is designed by considering only MPLS layer constraints, some lightpaths in the designed topology cannot be established, and this may result in a large amount of blocked traffic. We show that, by applying interaction between MPLS and WDM layers during topology design, the blocking ratio is reduced by an amount between 53% and 89% in the investigated cases. We also propose different information sharing strategies between the layers and show that, if physical layer information is available to the MPLS layer, a better blocking performance can be achieved and physical layer resource usage can be reduced by an amount up to 21%.