Lightpath Reconfiguration Research Articles

Survivability with Adaptive Routing and Reactive Defragmentation in IP-over-EON after A Router Outage

The occurrence of a router outage in the IP layer can lead to network survivability issues in IP-over-elastic-optical networks with consequent effects on the existing connections used in transiting the router. This usually leads to the application of a path to recover any affected traffic by utilizing the spare capacity of the unaffected lightpath on each link. However, the spare capacity in some links is sometimes insufficient and thus needs to be spectrally expanded. A new lightpath is also sometimes required when it is impossible to implement the first process. It is important to note that both processes normally lead to a large number of lightpath reconfigurations when applied to different unaffected lightpaths. Therefore, this study proposes an adaptive routing strategy to generate the best path with the ability to optimize the use of unaffected lightpaths to perform reconfiguration and minimize the addition of free spectrum during the expansion process. The reactive defragmentation strategy is also applied when it is impossible to apply spectrum expansion because of the obstruction of the neighboring spectrum. This proposed strategy is called lightpath reconfiguration and spectrum expansion with reactive defragmentation (LRSE+RD), and its performance was compared to the first Shortest Path (1SP) as the benchmark without a reactive defragmentation strategy. The simulation conducted for the two topologies with two traffic conditions showed that LRSE+RD succeeded in reducing the lightpath reconfigurations, new lightpath number, and additional power consumption, including the additional operational expense compared to 1SP.

Energy- and fatigue-aware RWA in optical backbone networks

Connection provisioning in Wavelength Division Multiplexing (WDM) networks needs to account for a number of crucial parameters. On the one hand, operators need to ensure the connection availability requirements defined in Service Level Agreements (SLAs). This is addressed by selecting an appropriate amount of backup resources and recovery strategies for the connections over which services are provisioned. Services requiring less strict availability requirements can be routed over unprotected lightpaths. Services with more strict availability requirements are provisioned over protected lightpaths in order to cope with possible failures in the network. Another important aspect to consider during the provisioning process is energy efficiency. Green strategies leverage on setting network devices in Sleep Mode (SM) or Active Mode (AM) depending on whether or not they are needed to accommodate traffic. However, frequent power state changes introduce thermal fatigue which in turn has a negative effect on the device lifetime. Finally, in multi-period traffic scenarios, it is also important to minimize the number of reconfigurations of lightpaths already established in the network in order to avoid possible traffic disruptions at higher layers. The work presented in this paper tackles the connection provisioning paradigm in an optical backbone network with a multi-period traffic scenario. More specifically the paper looks into the interplay among (i) energy efficiency, (ii) thermal fatigue, and (iii) lightpath reconfiguration aspects. To this end, the Energy and Fatigue Aware Heuristic with Unnecessary Reconfiguration Avoidance (EFAH-URA) is introduced, showing that it is possible to balance the three aspects mentioned above in an efficient way. When compared to the pure energy-aware strategies, EFAH-URA significantly improves the average connection availability for both unprotected and protected connections. On the other hand, it is done at the expense of reduced energy saving.

Energy-Efficient Dynamic Lightpath Adjustment in a Decomposed AWGR-Based Passive WDM Fronthaul

To cope with the explosion of mobile traffic demand, cloud radio access networks (C-RAN) have been recently proposed. In C-RANs, the two main elements of traditional base stations (BSs), i.e., the baseband unit (BBU) and the remote radio head (RRH), are separated, and the BBU can be virtualized and located in a remote location together with BBUs of other BSs. High-bandwidth digitized baseband signals must be exchanged between BBUs and RRHs through a large-capacity fronthaul network. Wavelength division multiplexing (WDM) technology is an efficient solution to provide sufficient fronthaul bandwidth with a large number of optical transceivers. With the fixed connections between BBUs and RRHs in the traditional C-RAN, the utilization of optical transceivers as well as BBUs is inefficient. In this paper, we propose a decomposed arrayed waveguide grating router (AWGR)-enabled passive WDM fronthaul, and we formulate the minimal energy consumption problem as integer linear programming, with the objective of minimizing the energy consumption caused by optical transceivers and BBUs, etc. We also design two dynamic lightpath adjustment heuristics by light-path reconfiguration to improve energy efficiency. In addition, we take AWGR decomposition into consideration to reduce the tuning range of tunable transceivers and free spectrum range of AWGR, hence lowering the deployment cost of transport network components. Numerical evaluation shows that our proposed schemes achieve significant energy savings compared to fixed lightpath allocation.

On the Cross-Layer Orchestration to Address IP Router Outages With Cost-Efficient Multilayer Restoration in IP-Over-EONs

Due to the flexibility and adaptivity of elastic optical networks (EONs), IP-over-EON would be a promising infrastructure for next-generation backbone networks. As a backbone network usually carries massive traffic, one always needs to properly address its network survivability issue. The network survivability of an IP-over-EON can be affected not only by the fiber cuts in the EON layer but also by the router outages in the IP layer. In this work, we study how to realize the cross-layer orchestration to address IP router outages with cost-efficient multilayer restoration (MLR) in IP-over-EONs. Specifically, we consider the situation in which a single router outage happens in an IP-over-EON and propose MLR algorithms to minimize the additional operational expense (OPEX) due to MLR. We first design three MLR strategies to fully explore the flexibility and adaptivity of IP-over-EONs. Then, with the strategies, we formulate an integer linear programming (ILP) model to find the MLR scheme in which the additional OPEX due to incremental usages of sliceable bandwidth-variable transponders (SBV-Ts) and frequency slots (FSs) and lightpath reconfigurations is minimized. We also propose an auxiliary graph (AG) based heuristic algorithm to reduce the time complexity. The proposed algorithms are evaluated with extensive simulations, and the results indicate that, compared with an existing benchmark, they can effectively reduce the additional OPEX of MLR.

Experimental demonstration of fronthaul flexibility for enhanced CoMP service in 5G radio and optical access networks.

The RAN architecture towards mobile 5G and beyond is undergoing a fundamental evolution, which brings optics into the radio world. Fronthaul is a new segment that leverages on the advantages of optical communication for RAN transport. However, the current fronthaul architecture shows a fixed connection between an RRH and a BBU, which leads to inefficient resource utilization. In this paper, we focus on the fronthaul flexibility that allows "any-RRH to any-BBU" connection. In particular, we consider a CoMP service and discuss how flexible optical fronthaul helps to improve its performance. To achieve this goal, we propose an SDN-enabled orchestration for coordinating radio and optical access networks. Under this unified control manner, the agile RRH-BBU mapping can be reached through lightpath reconfiguration. To further verify the benefits of flexibility, we experiment the CoMP service in the cloud radio over flexible optical fronthaul (CRoFlex) testbed. Experimental results demonstrate the proposed SDN-enabled flexible optical fronthaul can improve the CoMP performance by optimizing the RRH-BBU mapping.

Reconfigurable Optical Mobile Fronthaul Networks for Coordinated Multipoint Transmission and Reception in 5G

The fifth generation of mobile communication is characterized by ultra-dense cellular networks, where massive small cells are deployed in hot spots to increase the network capacity. As a promising technology in the small-cell scenario, coordinated multipoint (CoMP) is proposed to improve cell-edge user throughput by converting inter-cell interference into useful signals. In this paper, we study how reconfigurable fronthaul enabled by optical networks can help improve the CoMP service. According to the baseband unit (BBU) that serves the purposes of coordination, we classify the CoMP service into intra-BBU CoMP and inter-BBU CoMP. Inter-BBU CoMP will cause data exchange between the BBUs, which requires backhaul to support a large bandwidth and low latency. Our proposal is to associate coordinated RRHs with a single BBU to reduce the data exchange. To achieve this goal, we propose two heuristic algorithms: a minimum-cut graph-based lightpath reconfiguration (MCG-LR) and a BBU weightbased lightpath reconfiguration (BW-LR). The two algorithms are emulated on a time and wavelength division multiplexing passive optical network-based fronthaul under different cell conditions. The simulation results show that the reconfigurability of fronthaul can improve the CoMP service through elastic radio resource allocation. In addition, we can observe that MCG-LR achieves a lower inter-BBU CoMP ratio and lower BBU migration than BW-LR after lightpath (wavelength) reconfiguration.

Resource Savings in Submarine Networks Using Agility of Filterless Architectures

Filterless submarine networks based on broadcast-and-select nodes equipped with coherent transceivers are promising solutions for flexible capacity allocation. This letter shows how the agility allowed by filterless architectures can save resources through lightpath reconfiguration in subsea networks.

Dynamic embedding of workflow requests for bandwidth efficiency in data centers

In this paper, we address the problem of embedding dynamically-arriving workflow requests in data centers. Workflows pose challenges due to data precedence and time disjointness among tasks, thus driving the need for intelligent methods to embed workflows in data centers while improving the bandwidth efficiency as well as guaranteeing the application performance. We first formulate an integer programming optimization model for the embedding problem that minimizes the amount of bandwidth required for workflow execution. We then develop two algorithms namely Critical Path Workflow Embedding (CPWE) and Edge Priority Workflow Embedding (EPWE) to solve this problem. We consider two data center network architectures: packet switching electrical networks and circuit switching optical wavelength division multiplexed (WDM) networks. While WDM-based optical networks have much larger bandwidth capacity to meet the ever-growing traffic demand in data centers, they pose challenges due to wavelength continuity constraint and the nature of circuit switching. We thus additionally propose methods for selecting appropriate Top-of-the-Rack (ToR) switches and wavelengths during the embedding process so as to increase the chance of accommodating many requests that span over multiple ToRs. We evaluate CPWE and EPWE through comprehensive simulations. The results show that CPWE and EPWE significantly reduce the bandwidth required for a workflow request by up to 66% for random workflows and 80% for realistic-application workflows compared to baseline algorithms. The results also show that the proposed methods for ToR selection and wavelength selection in optical data centers outperform other methods by reducing the rejection ratio by up to 47% with dynamic reconfiguration of lightpaths and 40% with incremental configuration of lightpaths.

Demonstrations of Efficient Online Spectrum Defragmentation in Software-Defined Elastic Optical Networks

Elastic optical networks (EONs) facilitate agile spectrum management in the optical layer. When coupling with software-defined networking, they function as software-defined EONs (SD-EONs) and provide service providers more freedom to customize their infrastructure dynamically. In this paper, we investigate how to overcome spectrum fragmentation in SD-EONs with OpenFlow-controlled online spectrum defragmentation (DF), and conduct system implementations to facilitate highly-efficient online DF. We first consider sequential DF, i.e., the scenario that involves a sequence of lightpath reconfigurations to progressively consolidate the spectrum utilization. We modify our previous DF algorithm to make sure that the reconfigurations can be performed in batches and the “make-before-break” scheme can be applied to all of them. The modified algorithm is implemented in an OpenFlow (OF) controller, and we design OF extensions to facilitate synchronous batch reconfiguration. Then, we further simplify the DF operations by designing and implementing parallel DF that can accomplish all the DF-related lightpath reconfigurations simultaneously. All these DF implementations are experimentally demonstrated in an SD-EON control plane testbed that consists of $14$ stand-alone OF agents and one OF controller, which are all implemented based on high-performance Linux servers. The experimental results indicate that our OF-controlled online DF implementations perform well and can improve network performance in an efficient way.

Spectrum defragmentation in flexgrid optical networks using a genetic algorithm

SUMMARYFlexgrid optical networking is an attractive solution for efficiently matching allocated bandwidth with link demand but suffers from inevitable spectrum fragmentation. Spectrum fragmentation impairs network performance and results in high blocking rate and low spectrum utilization efficiency. Therefore, an optimization mechanism handling spectrum fragmentation is of vital importance in flexgrid optical networks. In this paper, we propose a genetic algorithm for solving the spectrum fragmentation problem with the objective of compacting occupation of the spectrum in flexgrid optical networks. A string of lightpaths are coded as the chromosome. The spectrum fusion degree and fragment fusion degree are introduced as the fitness functions to conduct the evolution in genetic algorithm, which can also be used to assess the degree of spectrum fragmentation in the network. As a result, the genetic algorithm provides a lightpath reconfiguration map, which identifies the candidate lightpaths to be reallocated, their reconfiguration sequence, and new locations. The proposed algorithm is compared with commonly used approaches under different network conditions. Simulation results demonstrate the ability of the proposed algorithm to efficiently solve the problem of spectrum defragmentation in flexgrid optical networks. Copyright © 2013 John Wiley & Sons, Ltd.

Optical IP network system using 16 wavelengths of Coarse WDM technologies and Layer-3 switch

We have proposed and experimentally demonstrated an optical network system using 16 wavelengths of Coarse Wavelength-Division-Multiplexing (CWDM) technology and Layer-3 Switch. For keeping the speed of 1000Mbps at the bus IFs, CWDM technology is employed, and 16 wavelengths are allocated to 16 bus IF, respectively. The system consists of a gateway which contains a controller and a server to connect terminals and public providers. The optical IP networks can be scalable by adjusting the number of wavelengths and optical transceiver. We believe this novel scheme is a practical scheme to be applied for future broadband networks. Full Text: PDF References Adel A. M. Saleh and Jane M. Simmons, "Architectural principles of optical regional and metropolitan access networks", J. Lightwave Tech., vol.17, pp.2431-2448, 1999. CrossRef Jeremy De Clercq and Olivier Paridaens, "Scalability implications of virtual private networks", IEEE Comm. Magazines, vol.40, pp.151-157, 2002. CrossRef A. Jourdan, D. Chiaroni, and E. Dotaro, "The perspective of optical packet switching in IP dominant backbone and metropolitan networks ", IEEE Comm. Magazines, vol.39, pp.136-141, 2001. CrossRef B.St Arnaud, Jing Wu and B.Kalali, "Customer-controlled and -managed optical networks", J. Lightwave Tech., vol. 21, pp. 2804-2810, Nov 2003. CrossRef M Hashimoto, A Ueno, M Taniue, S Kawase, O Koyama and Y Katsuyama, "Design and Control System for Regional CWDM Optical IP Networks with Reconfigurable Optical Add/Drop Multiplexers ", The 9th International Conference on Telecommunications, Zagreb, Croatia, 23-30, June 2007. CrossRef M. Hashimoto, A. Ueno, M. Taniue, S. Kawase, O. Koyama, and Y. Katsuyama, International Journal of Innovative Computing, Information and Control, 4, No.6, pp. 1299-1313, 2008. DirectLink M. Hashimoto, O. Koyama, M.D. Nooruzzaman, and Y. Katsuyama, "Bi-directional lightpath reconfiguration in regional IP-over-WDM networks by a centralized control system", IEEJ Trans. Electrical and Electronic Engineering, vol.4, no.3 pp.425-434, 2009 CrossRef M.D. Nooruzzaman, Y. Harada, O. Koyama, and Y. Katsuyama, "Proposal of Stackable ROADM for Wavelength Transparent IP-over-CWDM Networks", IEICE Trans. Commun., vol.E91-B, no.10, pp.3330-3333, Oct. 2008. CrossRef S. Fujimoto, K. Tsujimura, S. Hayashi, J. Wang and Y. Katsuyama, in Proc. of 7th APCC, pp.9-12, Tokyo, Sept., 2001.

Scalable Single-Fiber CWDM Ring Networks With Stackable ROADMs

Stackable reconfigurable optical add–drop multiplexers (S-ROADMs) have been proposed for single-fiber coarse wavelength division multiplexing (CWDM) ring networks so as to perform lightpath reconfiguration remotely. The S-ROADM consists of some modules with different wavelengths required in the node, and with this facility manual ROADM reconfiguration can be performed for low-cost transmission systems. The experimental results clarified that the S-ROADM could multiplex and demultiplex the wavelengths successfully without limiting the wavelengths passing through, making the network’s wavelength transparent. The self-healing performance was investigated during a fiber cut in the single-fiber ring networks. Insertion of a new module inside the in-service S-ROADM was also accomplished to increase bandwidth for new users. The experimental results clarify that S-ROADMs provide more flexible CWDM networks in terms of reconfigurability and scalability.

Congestion removing performance of stackable ROADM in WDM networks under dynamic traffic

Congestion removing performance has been investigated in IP-over-CWDM networks with reconfigurable optical add/drop multiplexers (ROADMs) for the best-effort transmissions specified by the service level agreement (SLA). Mathematical models and experimental results for two approaches: automated addition of new lightpath and creation of a static bypass route in other existing lightpaths, were presented in this paper. The experimental results clarified that the congestions were removed successfully in both the approaches. Addition of new lightpath approach can provide effective adjustment of larger traffic whereas the creation of a static bypass route approach can provide fine granularity adjustment of small traffic to be switched without lightpath reconfiguration. The degraded throughput was recovered within the recovery time specified by the SLA.

Extending software defined network principles to include optical transport

Software defined networks are based on the principle of a centralized control plane separated from the network forwarding or switching plane that it controls. The switching plane can be heterogeneous, composed of network elements from multiple vendors, and it can provide distinct services with different characteristics, configurations, and control at the packet and/or optical layers. Abstracting the control plane from the network elements allows network-platform- specific characteristics and differences that do not affect services to be hidden. In addition, software defined networking (SDN) is based on the principle that applications can request needed resources from the network via interfaces to the control plane. Through these interfaces, applications can dynamically request network resources or network information that may span disparate technologies. For instance, the application layer can dynamically request and obtain network resources at the packet flow, circuit, or even optical level based on application layer requirements. Current SDN implementations focus on Ethernet switching primarily for data center resource optimization. This article reviews the benefits and challenges of extending SDN concepts to various transport network architectures that include optical wavelength and fiber switches, circuit switches, and sub-wavelength optical burst switches. Control plane implementations for optical networks are more complex since they must account for physical constraints including optical signal reachability, bandwidth availability and granularity, light path routing, and light path reconfiguration speed. The longterm goal is to apply SDN concepts across multi-layer multivendor networks in order to support a unified control structure.

Stackable ROADM with optical amplifier for use in IP‐Over‐CWDM ring networks

AbstractA stackable module with a bidirectional coarse wavelength division multiplexing (CWDM) amplifier is proposed to introduce the optical amplifier into an stackable‐reconfigurable optical add/drop multiplexers (S‐ROADM) for use in an IP‐over‐CWDM ring network, and the performance is evaluated experimentally. Packet transfer changes are monitored during the lightpath reconfiguration, which needs optical amplification. The result clarify that the lightpaths are reconfigured successfully, including the remote activation of the amplifiers. As a result, the stackable feature of the amplifier module enables us to provide a cost‐effective introduction into the network on an implement‐it‐when‐necessary base in a fully compatible way with the existing S‐ROADM modules when constructing the S‐ROADM with an amplifier. Therefore, the amplifier module can be used in the same way as the ROADM modules to construct the S‐ROADM, providing manually adding capability of the amplifier to in‐service networks. Thus, the amplifier module has a big advantage to use it flexibly and economically in the IP‐over‐CWDM ring networks. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Principle and verification of novel optical virtual private networks over multiprotocol label switching/optical packet switching networks

A novel realization method of the optical virtual private networks (OVPN) over multiprotocol label switching/optical packet switching (MPLS/OPS) networks is proposed. In this scheme, the introduction of MPLS control plane makes OVPN over OPS networks more reliable and easier; OVPN makes use of the concept of high reconfiguration of light-paths offered by MPLS, to set up secure tunnels of high bandwidth across intelligent OPS networks. Through resource management, the signal mechanism, connection control, and the architecture of the creation and maintenance of OVPN are efficiently realized. We also present an OVPN architecture with two traffic priorities, which is used to analyze the capacity, throughput, delay time of the proposed networks, and the packet loss rate performance of the OVPN over MPLS/OPS networks based on full mesh topology. The results validate the applicability of such reliable connectivity to high quality services in the OVPN over MPLS/OPS networks. Along with the results, the feasibility of the approach as the basis for the next generation networks is demonstrated and discussed.

Heuristic Approaches for Periodic Reconfiguration of Lightpath-based Networks under Multi-hour Traffic

Periodic lightpath reconfiguration of virtual topologies in transparent optical networks has been recently investigated as a mechanism to more efficiently adapt the network to predictable periodic traffic variations along a day or week. Scheduling periodic reconfigurations involves tuning a trade-off between a lower network cost obtained through better resource allocation, and undesired traffic disruptions that these reconfigurations may cause. This paper presents and compares two algorithms for planning a reconfigurable virtual topology suitable for exploring this trade-off. The first is based on a Lagrangean Relaxation of the planning problem, and the second is based on a Tabu Search meta-heuristic. The merits of both algorithms are assessed for moderate network sizes through comparison with analytical lower bounds and exact solutions obtained by a MILP formulation.

Wavelength‐transparent IP‐over‐CWDM network with stackable ROADMs for best effort performance

AbstractStackable reconfigurable optical add/drop multiplexers (S‐ROADMs) have been proposed for use in IP over coarse wavelength‐division multiplexing (CWDM) networks so as to provide capabilities of remote lightpath reconfiguration and manual ROADM reconfiguration under the best effort transmission specified by the service level agreement. The S‐ROADM can be constructed by connecting modules with different wavelengths required in the node. The experimental results clarify that the S‐ROADM can add/drop or pass through the wavelengths successfully, providing no limit to the passing‐through (PT) wavelengths, that is, ensuring the wavelength transparency in the network. The S‐ROADMs could remove congestions by adding a lightpath remotely within a recovery time with degraded SLA. The transmission break time was also within the recovery time when adding a module manually to the in‐service S‐ROADM to increase bandwidth to be provided to new users. As a result, the S‐ROADMs provide more flexible CWDM networks in terms of scalability and reconfigurability. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Lightpath Reconfiguration in WDM Networks

Lightpath reconfiguration is a networking task that can be performed in order to improve resource utilization. The lightpath reconfiguration problem becomes nontrivial when a new set of lightpaths requires the release of resources previously seized by the (working) lightpaths currently in place, but, in order to ensure continuity of the traffic flow, the working lightpaths cannot be torn down before the new ones are set up. Under this condition the reconfiguration can fall into a deadlock state, and deadlocks can only be solved by temporary disruption of some connections. At this point, traffic disruptions are necessary, and network operators must compensate customers with penalty fees for the service disruption. In this paper we focus on minimizing the number of simultaneously disrupted connections at any time during the reconfiguration process. In this paper, we propose a mixed-integer program (MIP) model, an exact algorithm, and a heuristic for solving the problem considering our objective.

Bi‐directional lightpath reconfiguration in regional IP‐over‐WDM networks by a centralized control system

AbstractBi‐directional lightpath reconfiguration performance has been evaluated experimentally for regional IP‐over‐wavelength‐division multiplexing network applications, making the network scalable and stable when traffic changes occur. The reconfiguration performance was examined in an experimental network with reconfigurable optical add/drop multiplexers (ROADMs) to connect four nodes with bi‐directional dual‐fibers. The experiment was conducted by controlling the ROADMs. The control signals were sent by a developed system. The lightpaths were added or deleted by the control system in the experimental network, and IP packets were monitored. The results clarified that lightpaths could be reconfigured by controlling the ROADMs, and IP packets could be routed dynamically by Open Shortest Path First so as to adapt the lightpath changes. The reconfiguration functions of the system together with the ROADMs provide network administrators with easy management of the network in a skill‐less, centralized and remotely controlled way. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.