Multi-granularity Optical Networks Research Articles

Energy-efficient design for multi-granular optical transport networks with optical reach consideration

Energy consumption of the optical backbone is expected to contribute to a significant portion of the energy consumed by the telecommunication networks. As an enhanced bandwidth utilization and management extent of the optical Wavelength Division Multiplexing (WDM) technology, multi-granular switching concept has been shown to guarantee energy savings when compared to the traditional traffic grooming. However, Multi-Granular Optical Transport Network (MG-OTN) design and planning still calls for legitimate and self-contained design specifications. In this paper, we revisit the Routing and Multi-Granular Path Assignment (RMGPA) problem by having the objective of minimized power consumption and integrating the optical reach limitation of optical signals in the design and planning problem. The new problem is formulated as a Mixed Integer Linear Programming (MILP) model. For large scale design scenarios, we propose an efficient heuristic approach that is capable of solving the power minimization problem in feasible runtime. The heuristics is verified within 2% average approximation to the MILP solutions under small scale scenarios, and the numerical results of the design and planning problem heuristic show that significant power savings up to 55% in MG-OTNs can be achieved with the proper selection of the wavelength capacity, waveband size, number of wavebands per fiber, and the value of the optical reach. Furthermore, the proposed heuristic has been shown to guarantee high fairness among the nodes with respect to the power fairness index, which is at the order of 92–99% under various traffic scenarios.

Field Trial of an OpenFlow-Based Unified Control Plane for Multilayer Multigranularity Optical Switching Networks

Software defined networking and OpenFlow, which allow operators to control the network using software running on a network operating system within an external controller, provide the maximum flexibility for the operator to control a network, and match the carrier's preferences given its centralized architecture, simplicity, and manageability. In this paper, we report a field trial of an OpenFlow-based unified control plane (UCP) for multilayer multigranularity optical switching networks, verifying its overall feasibility and efficiency, and quantitatively evaluating the latencies for end-to-end path creation and restoration. To the best of our knowledge, the field trial of an OpenFlow-based UCP for optical networks is a world first.

Survivable integrated grooming in multi-granularity optical networks

Survivability is an important issue to ensure the service continuity in optical network. At the same time, with the granularity of traffic demands ranging from sub-wavelength-level to wavelength-level, traffic demands need to be aggregated and carried over the network in order to utilize resources effectively. Therefore, multi-granularity grooming is proposed to save the cost and reduce the number of switching ports in Optical-Cross Connects (OXCs). However, current works mostly addressed the survivable wavelength or waveband grooming. Therefore, in this paper, we propose three heuristic algorithms called Multi-granularity Dedicated Protection Grooming (MDPG), Multi-granularity Shared Protection Grooming (MSPG) and Multi-granularity Mixed Protection Grooming (MMPG), respectively. All of them are performed based on the Survivable Multi-granularity Integrated Auxiliary Graph (SMIAG) that includes one Wavelength Integrated Auxiliary Graph (WIAG) for wavelength protection and one waveBand Integrated Auxiliary Graph (BIAG) for waveband protection. Numerical results show that MMPG has the lowest average port-cost, the best resource utilization ratio and the lowest blocking probability among these three algorithms. Compared with MDPG, MSPG has lower average port-cost, better resource utilization ratio and lower blocking probability.

Identified Traffic Partition Grooming in Multi-Granularity Optical Network

Currently, the required bandwidth of users tends to be diversity, i.e., coarse-granularity demands (e.g., terabit/circuit routing) and small-granularity demands (e.g., sub-rate traffic streams). Only employing traffic grooming or waveband switching may result in several traffic-diversity problems. Therefore, the traffic partition grooming technique with considering traffic transferring is proposed in this paper to solve the traffic-diversity problems, especially for achieving blocking probability reduction and port savings. Correspondingly, we devise the heuristic and Identified MG-IGAG (IMG-IGAG) algorithm based on Granularity-Layered Graph (GLG) since the problem of grooming is the NP-hard. The simulation results show that our IMG-IGAG is more effective and practical than other state-of-the-art methods.

A Study of Dynamic Waveband Switching in Multi-granular Optical Networks

The basic principle of waveband switching (WBS) is to group multiple wavelengths together as a band or fiber and switch the group using a single port whenever possible. To support waveband grouping in WBS networks, multi-granular optical cross-connects (MG-OXCs) are introduced to switch the traffic at the fiber, band, and wavelength layers. One important goal in WBS networks is to minimize the number of ports at the MG-OXCs. For WBS networks with dynamic or on-line traffic, both the port consumption and call blocking probability should be considered during the process of accommodating unpredictable traffic demands with limited resources. Call blocking can be caused by port insufficiency as well as wavelength shortage in WBS networks with dynamic traffic. Our study in this work starts with an analysis of a reconfigurable MG-OXC architecture and various cases of port consumption on this architecture. We then analyze the lower/upper bounds for the design parameter of the reconfigurable MG-OXC architecture. Based on the insights obtained from the analysis, we propose a new algorithm, namely, weighted graph-based waveband assignment (WGB), which employs an auxiliary weighted graph technique to make efficient dynamic routing and waveband assignment. The proposed algorithm is simulated in WBS networks with fully dynamic or incremental traffic patterns. Our results show that the proposed scheme can satisfy up to 40% more lightpath requests than the existing scheme, maximum overlap ratio (MOR), before a certain blocking ratio is observed in the network. Our study also shows that with limited resources, WBS can obtain port savings by limiting the design parameter while achieving an allowable blocking probability.

Energy saving and cost reduction in multi-granularity green optical networks

With the energy consumption increase and the greenhouse effect becomes more and more serious, the energy saving has become the focus in the whole world. At the same time, as the network traffic largely growing, the size and the cost of network equipments keep increasing so that the network cost reduction is also very important. In recent years, the concept of green Internet was proposed to construct an energy-efficient and cost-optimal green network. In this paper, we firstly present the current studies working on the energy saving and cost reduction in multi-granularity optical network that is the convergence between IP network and optical network to support both the low-speed IP data and the high-speed optical transmission. After analyzing the current studies, in our opinion, the traffic grooming mechanism with optical bypass technology is the feasible solution by binding a lot of low-rate IP data into a few of high-speed lightpaths to reduce a lot of electrical ports consumption in IP routers for saving the energy, the waveband switching mechanism is the feasible solution by binding multiple lightpaths into a few of waveband tunnels to save the optical transmitting ports consumption in Multi-Granularity Optical Cross-Connects (MG-OXCs) for reducing the network costs, and the multi-granularity grooming mechanism is the feasible solution by integrating the traffic grooming with the waveband switching to achieve both the energy saving and cost reduction. Based on our opinion, this paper proposes the challenging issues including the network node model, virtual topology design, certain traffic matrix and uncertain traffic matrix for energy saving and cost reduction in multi-granularity optical network, with possible solutions and preliminary simulation results to guide the future work.

Service-Oriented Multigranular Optical Network Architecture for Clouds

This paper presents a novel service-oriented network architecture to bridge the informational gap between user applications and optical networks providing technology-agnostic multigranular optical network services for clouds. A mediation layer (service plane) between user applications and network control is proposed to facilitate a mapping process between user application requests and the network services. At the network level, a multigranular optical network (MGON) is proposed and implemented to support dynamic wavelength and subwavelength granularities with different transport formats [optical burst switched (OBS), optical burst transport (OBT)], reservation protocols (one-way, two-way), and different quality-of-service (QoS) levels per service type. The service-oriented multigranular optical network has been designed, implemented, and demonstrated on an experimental testbed. The testbed consists of service and network resource provisioning, service abstraction, and network resource virtualization. The service-to-network interoperation is provided by means of a gateway that maps service requests to technology-specific parameters and a common signaling channel for both service and network resource provisioning.

Cost-effective heuristics for planning GMPLS-based transport networks

With the ever-increasing traffic in WDM transport networks, the development of GMPLS (or multi-granular) transport networks becomes essential to avoid the cost explosion of OXCs. Much work has been devoted to the development of Multi-Granular Optical Crossconnect (MG-OXC) architectures and network design and planning methods. Extending these efforts here, we address a new problem of planning the GMPLS-based transport network by (1) considering the whole traffic hierarchy defined in GMPLS; and (2) allowing the bifurcation of multi-granularity traffic demands among different physical routes. We call such a problem the Routing and Multi-Granular Paths Assignment (RMGPA). The objective of the problem is to minimize the total weighted port count in the transport network. Due to the computational complexity of the problem, only very small-sized planning problems can be solved exactly through Mixed Integer Linear Programming (MILP) optimization. In this paper, we propose efficient heuristics that are capable of solving large-sized planning problems in a reasonable amount of time.

On dynamic wavelength assignment in wavelength-convertible multi-granular optical networks

In this paper, we study the dynamic wavelength assignment problem in waveband-switched (WBS) networks composed of wavelength-convertible multi-granular OXCs (MGOXCs). With the aim to minimize the extra port consumption and utilize wavelength converters in an efficient manner, we propose a heuristic wavelength assignment algorithm named Least Weighted Configuration Cost (LWCC). WAPG, an algorithm proposed in previous literature, is compared with LWCC in both blocking performance and converter utilization. Numerical results show that LWCC offers more benefit in waveband grouping, which results in significant improvement in terms of blocking probability.

Performance analysis and dimensioning of multi-granular optical networks

Recent years have demonstrated the limited scalability of electronic switching to realize transport networks. In response, all-optical switching has been identified as a candidate solution to enable high-capacity networking in the future. One of the fundamental challenges is to efficiently support a wide range of traffic patterns, and thus emerges the need for equipment that is both practical and economical to construct and deploy. We have previously proposed the use of multi-granular optical cross-connects (MG-OXC), which support switching on both the wavelength and sub-wavelength level. To this end, the MG-OXCs are equipped with cheap, highly scalable slow switching fabrics, as well as a small number of expensive fast switching ports. The goal of this work is two-fold: first to demonstrate that a small number of fast switching ports suffices to support a wide range of traffic requirements, and second that multi-granular optical switching can offer cost-benefits on a network-wide scale. The first objective is studied through simulation analysis of a single switching node, and results indicate that a limited number of fast switching ports can significantly improve burst blocking performance over slow only switches. Furthermore, under certain circumstances, the MG-OXC can even approach the performance of a fast only switch design. Secondly, we introduce an Integer Linear Programming model for the total network installation cost, and our evaluation indicates that multi-granular optical switching can be a cost-effective solution on the network level, in comparison to slow only or fast only approaches. Furthermore, we can achieve reduced costs of individual OXC nodes, which allows us to minimize scalability problems corresponding to emerging fast switching fabrics.

A novel analytical model for dynamic waveband switching

We present a novel framework to analytically model dynamic waveband switching in a multi-granular optical network. The scalable solution consists in modeling each potential carrier of waveband tunnels independently by a Markov chain while modulating the rate of critical transitions, i.e. reserving a new waveband tunnel, by the waveband setup availability computed from the solution of other potential carriers. An iterative procedure is repeated to obtain a consistent numerical solution all over the network. To get an accurate solution we present a novel method to solve the problem of link load correlation in the analysis of circuit-switched networks. Analytical and simulation results are presented to show the effectiveness of the proposed model. The model is also applied to evaluate the performance of waveband cross-connects when introducing waveband conversion.

A novel online wavelength assignment algorithm in wavelength-convertible multi-granular optical networks

As industrial technology gets more mature, a single fiber can offer more and more wavelengths. However, it also results in a large amount of switching ports at optical cross-connects (OXCs). Certainly, it is expected that higher and higher complexity is inevitable to control and manage such large OXCs. In this paper, we study the dynamic wavelength assignment problem in waveband switching (WBS) networks composed of multi-granular OXCs (MG-OXCs). Moreover, in order to relax the wavelength continuity constraint on lightpath establishments, each MG-OXC node is equipped with a certain number of converters. To efficiently minimize the extra port consumption and utilize wavelength converters, we proposed an online wavelength assignment algorithm named Least Weighted Configuration Cost (LWCC). For a new request, LWCC first adopts fixed routing and then exploits the layered-graph approach and a new cost function for edge weight assignment to determine adequate wavelength(s). The performance metrics of interest include both blocking performance and converter utilization. Numerical results show that LWCC is superior in waveband grouping and therefore results in significant performance gain in terms of blocking probability.

A tabu search heuristic for the routing and wavelength assignment problem in multigranular optical networks

This paper proposes a tabu search heuristic for solving the routing and wavelength assignment problem in multigranular optical networks, considering the wavelength-continuity constraint and a set of connections to satisfy. For a number of fibers per link, a number of wavebands per fiber, and a number of wavelengths per waveband, this algorithm attempts to minimize the total number of ports used in the network by efficiently grouping lightpaths into bands and fibers, and switching the whole bands and fibers. The algorithm has been implemented and tested on the NSFNET network, and comparisons have been made with the Balanced Path Routing and Heavy Traffic First (BPHT) algorithm in terms of number of ports. Generally, the results obtained with our tabu search heuristic are better than those provided by this algorithm.

Framework for waveband switching in multigranular optical networks: part II--wavelength/waveband conversion and survivability [Invited

<p><a href="http://www.osa-jon.org/virtual_issue.cfm?vid=22">Feature Issue on Waveband Switching, Routing, and Grooming</a></p>We consider multigranular optical networks using waveband switching (WBS) technology. The use of advanced WDM has significantly increased the available bandwidth in backbone networks by increasing the number of wavelengths. As the number of wavelengths in a fiber is increased, the number of ports or the size of the optical cross connects increases rapidly. Using WBS, wavelengths are grouped into bands and switched as a single entity thus reducing the cost and control complexity of switching nodes by minimizing the port count. Part I of our study [J. Opt. Netw.5, 1043-1055 (2006)] compared the various cross-connect architectures for WBS including the three-layer and single-layer multigranular cross connects. It also discussed various issues relating to waveband switching networks that are different from traditional wavelength routing networks (WRNs), for example, traffic grooming, and it showed why techniques developed for WRNs cannot be simply applied to WBS networks. We study the effect of wavelength and waveband conversion on the performance of WBS networks with reconfigurable multigranular optical cross connects. We present an algorithm for waveband grouping in wavelength convertible networks and evaluate its performance with full, limited, and intraband wavelength conversion. We then focus on survivability in WBS networks and show how waveband and wavelength conversion can be used effectively to recover from failures in WBS networks.

Architecture design and performance evaluation of multigranularity optical networks based on optical code division multiplexing

Feature Issue on Waveband Switching, Routing, and GroomingIn traditional lambda-based multigranularity optical networks, a lambda is always treated as the basic routing unit, resulting in low wavelength utilization. On the basis of optical code division multiplexing (OCDM) technology, a novel OCDM-based multigranularity optical cross-connect (MG-OXC) is proposed. Compared with the traditional lambda-based MG-OXC, its switching capability has been extended to support fiber switching, waveband switching, lambda switching, and OCDM switching. In a network composed of OCDM-based MG-OXCs, a single wavelength can be shared by distinct label switched paths (LSPs) called OCDM-LSPs, and OCDM-LSP switching can be implemented in the optical domain. To improve the network flexibility for an OCDM-LSP provisioning, two kinds of switches enabling hybrid optical code (OC)-wavelength conversion are designed. Simulation results indicate that a blocking probability reduction of 2 orders can be obtained by deploying only five OCs to a single wavelength. Furthermore, compared with time-division-multiplexing LSP (TDM-LSP), owing to the asynchronous accessibility and the OC conversion, OCDM-LSPs have been shown to permit a simpler switch architecture and achieve better blocking performance than TDM-LSPs.

Framework for waveband switching in multigranular optical networks: part I-multigranular cross-connect architectures [Invited

Feature Issue on Waveband Switching, Routing, and GroomingOptical networks using wavelength-division multiplexing (WDM) are the foremost solution to the ever-increasing traffic in the Internet backbone. Rapid advances in WDM technology will enable each fiber to carry hundreds or even a thousand wavelengths (using dense-WDM, or DWDM, and ultra-DWDM) of traffic. This, coupled with worldwide fiber deployment, will bring about a tremendous increase in the size of the optical cross-connects, i.e., the number of ports of the wavelength switching elements. Waveband switching (WBS), wherein wavelengths are grouped into bands and switched as a single entity, can reduce the cost and control complexity of switching nodes by minimizing the port count. This paper presents a detailed study on recent advances and open research issues in WBS networks. In this study, we investigate in detail the architecture for various WBS cross-connects and compare them in terms of the number of ports and complexity and also in terms of how flexible they are in adjusting to dynamic traffic. We outline various techniques for grouping wavelengths into bands for the purpose of WBS and show how traditional wavelength routing is different from waveband routing and why techniques developed for wavelength-routed networks (WRNs) cannot be simply applied to WBS networks. We also outline how traffic grooming of subwavelength traffic can be done in WBS networks. In part II of this study [Cao , submitted to J. Opt. Netw.], we study the effect of wavelength conversion on the performance of WBS networks with reconfigurable MG-OXCs. We present an algorithm for waveband grouping in wavelength-convertible networks and evaluate its performance. We also investigate issues related to survivability in WBS networks and show how waveband and wavelength conversion can be used to recover from failures in WBS networks.

A Lagrangean Relaxation-Based Approach for Routing and Wavelength Assignment in Multigranularity Optical WDM Networks

Optical wavelength-division multiplexed (WDM) networks often include optical cross-connects with multigranularity switching capability, such as switching on a single lambda, a waveband, or an entire fiber basis. In addition, it has been shown that routing and wavelength assignment (RWA) in an arbitrary mesh WDM network is an NP-complete problem. In this paper, we propose an efficient approximation approach, called Lagrangean relaxation with heuristics (LRH), aimed to resolve RWA in multigranularity WDM networks particularly with lambda and fiber switches. The task is first formulated as a combinatorial optimization problem in which the bottleneck link utilization is to be minimized. The LRH approach performs constraint relaxation and derives a lower-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LRH approach employs a new heuristic algorithm to arrive at a near-optimal upper-bound solution. With lower and upper bounds, we conduct a performance study on LRH with respect to accuracy and convergence speed under different parameter settings. We further draw comparisons between LRH and an existing practical approach via experiments over randomly generated and several well-known large sized networks. Numerical results demonstrate that LRH outperforms the existing approach in both accuracy and computational time complexity, particularly for larger sized networks.

Dynamic routing and wavelength assignment for two-stage multi-granularity WDM optical networks

Multi-granularity optical cross-connect (MG-OXC) has been proposed to reduce the complexity and size of optical switch. This paper studies dynamic routing and wavelength assignment (RWA) algorithm for WDM optical networks consisting of MG-OXCs. We present an online adaptive routing algorithm to solve this problem. Simulation results show that for a two-stage multi-granularity optical network, the fiber-tunnel topology can greatly affect the blocking probability. To further improve the network performance, a fiber-tunnel topology optimization algorithm is proposed, and simulation results show that the blocking probability can be drastically reduced after fiber-tunnel topology reconfiguration.

Traffic engineering in multigranularity heterogeneous optical WDM mesh networks through dynamic traffic grooming

In this article we investigate the problem of efficiently provisioning connections of different bandwidth granularities in a heterogeneous WDM mesh network through dynamic traffic grooming schemes under traffic engineering principles. Due to the huge amount of traffic a WDM backbone network can support and the large geographic area it can cover, constructing and upgrading such an optical WDM network can be costly. Hence, it is extremely important for network operators to apply traffic engineering strategies to cost-effectively support different bandwidth granularity services using only the appropriate amount of network resources. This requires an optical WDM network to have multigranularity switching capability, and such a network tends to be a multivendor heterogeneous network. However, WDM network heterogeneity increases the difficulty and challenge of efficient traffic provisioning. In this article we present different TE issues that need to be carefully considered in such an optical WDM network, and propose possible solutions and extensions for the generalized multiprotocol label switching optical network control plane. We extend an existing generic graph model to perform efficient traffic grooming and achieve different TE objectives through simple shortest path computation algorithms. We show that our approach is very practical and very suitable for traffic engineering in a heterogeneous multigranularity optical WDM mesh network.