Multi-granularity Optical Cross-connect Research Articles

Design Based Routing with Waveband and Wavelength Assignment in Wavelength Division Multiplexing Networks using Multi-Granular Optical Cross-Connects

In this paper, we extend design based routing (DBR), which is originally proposed for opaque wavelength division mul- tiplexing (WDM) networks without waveband switching (WBS), to transparent WDM networks with WBS. We formulate and solve the corresponding integer linear programming (ILP) prob- lems to facilitate the use of DBR for transparent WDM networks with WBS, referred to as DBR with Waveband and Wavelength Assignment (DBRWWA). The goal of DBRWWA is to minimize the total link cost subject to the constraints on traffic demands and on network resources. DBRWWA guides online routing of dynamic lightpath requests in WDM networks with WBS, where traffic engineered routes are computed offline based on the prior information on traffic demand statistics. We investigate two novel heuristics, called the maximum waveband-wavelength first (MaxWWF) algorithm and the minimum waveband-wavelength first (MinWWF) algorithm, as well as existing first-fit and random-fit algorithms. The proposed heuristics consider all properties of WBS, including waveband and wavelength con- tinuity constraints. We consider end-to-end WBS (ETE-WBS) for lightpath grouping. The online heuristics are combined with shortest path first (SPF) routing, DBR, and DBRWWA to support dynamic traffic. Simulation results show that DBRWWA has on average lower blocking probability compared to DBR, while both DBRWWA and DBR greatly outperform SPF routing in terms of the blocking probability.

Performance analysis of an optical network employing waveband and traffic grooming

This paper analyses an optical network architecture composed by an arrangement of nodes equipped with multi-granular optical cross-connects (MG-OXCs) in addition to the usual optical cross-connects (OXCs). Then, selected network nodes can perform both waveband as well as traffic grooming operations and our goal is to assess the improvement on network performance brought by these additional capabilities. Specifically, the influence of the MG-OXC multi-granularity on the blocking probability is evaluated for 16 classes of service over a network based on the NSFNet topology. A mechanism of fairness in bandwidth capacity is also added to the connection admission control to manage the blocking probabilities of all kind of bandwidth requirements. Comprehensive computational simulation are carried out to compare eight distinct node architectures, showing that an adequate combination of waveband and single-wavelength ports of the MG-OXCs and OXCs allow a more efficient operation of a WDM optical network carrying multi-rate traffic.

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.

Multi-Granular Optical Switching: A Classified Overview for the Past and Future

The wavelength routed network (WRN) accommodates traffic demands by establishing lightpaths along the corresponding routing paths. The wavelength of each lightpath is switched individually by traditional wavelength optical cross-connects (T-OXCs) to transit the traffic. Due to the traffic explosion and the resulted growth in wavelength number, WRNs face a challenge of the increase in node-size (i.e., the port number of a T-OXC) as well as the associated cost and control complexity. As an alternative solution, waveband switching (WBS) is introduced to group multiple wavelengths together as a band or fiber. Whenever possible, the group of wavelengths requires just a single port at a multi-granular optical cross-connect (MG-OXC). One fundamental problem in WBS networks is the routing and wavelength assignment (RWA). With the major goal of minimizing the port numbers in WBS networks, the optimal RWA problem was shown to be NP-Hard. In the literature, various Integer Linear Programming models are proposed to optimally solve a small-size RWA problem, and many heuristic algorithms are proposed to provide a practical solution for the large-scale RWA problem in WBS networks. In this work, we comprehensively review literature studies on waveband switching networks. The topics covered include architecture, RWA problem solving strategies, and future challenges of wavelength conversion, protection, and lightpath rerouting in WBS networks. We aim at presenting a classified view of WBS networks, based on various aspects including the traffic pattern, node and network architecture, grouping policy, and the band configurations. We investigate factors that affect the goal of port reduction and blocking minimization in WBS networks. In addition, we explore several unique features of waveband switching in protection, wavelength conversion and rerouting, along which we point out multiple open challenges in WBS networks that deserve further studies.

A new multi-granularity grooming algorithm based on traffic partition in IP over WDM networks

Currently, the required bandwidth of IP-level users tends to be diversity, i.e., coarse-granularity demands and small-granularity demands. Employing traffic grooming or waveband switching (WS) only may results in several traffic-diversity problems in wavelength routed networks (WRNs) or WaveBand Switching (WBS) networks. In order to solve the traffic-diversity problems in IP over WDM networks, an identified multi-granularity optical cross-connect (MG-OXC) with supporting traffic partition is devised in this paper. In this node structure, one traffic partition module is used to check the type of demand. Followed by our proposed traffic partition based grooming policy (TPGP), if the currently-arriving IP-level user is small-granularity demand, it will be processed by traffic grooming, otherwise processed by waveband switching. Then, we propose a new multi-granularity grooming algorithm based on integrated grooming auxiliary graph (MG-IGAG). The IGAG includes a wavelength integrated auxiliary graph (WIAG) and a waveband integrated auxiliary graph (BIAG) to groom small-granularity and coarse-granularity demands, respectively. Simulation results show that compared to previous WS algorithms and multi-granularity grooming algorithms followed by integrated grooming policy (IGP), MG-IGAG not only performs traffic grooming and waveband switching together, but also solves the traffic-diversity problems effectively, especially for port savings.

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.

Performance analysis of dedicated protection and shared protection for waveband switching based on multi-granularity optical cross-connect

In order to save the switching ports and the cost of Multi-Granularity Optical Cross-Connect (MG-OXC), the waveband switching technique was proposed to groom multiple wavelength-level traffic to a few waveband tunnels to be switched by a few switching ports in MG-OXC. At the same time, protection for fibers is very important to ensure the service continuity since each wavelength carries a lot of traffic. Although existing works have addressed the waveband switching protection, most of them separately considered only the dedicated protection or shared protection in static demand scenario and did not deeply analyze and compare the dedicated protection and shared protection in dynamic demand scenario. Therefore, in this paper, we deeply study the consumptions of wavelengths in fibers and ports in MG-OXCs for Waveband Shared Protection (WSP) and Waveband Dedicated Protection (WDP) in dynamic demand scenario, and propose the port-cost calculation and update methods based on a new waveband layered auxiliary graph that is developed based on MG-OXC structure. In simulations, we compare WSP, WDP, traditional end-to-end waveband shared protection and traditional end-to-end waveband dedicated protection. Simulation results show that the shared protection has smaller port-cost, better wavelength utilization efficiency and lower blocking probability than the dedicated protection with the same waveband switching policy, and the sub-path waveband switching has bigger port-cost, better wavelength utilization efficiency and lower blocking probability than the end-to-end waveband switching with the same backup wavelength assignment policy.

Multi-Granular Waveband Assignment and Protection in WDM Networks

Waveband switching (WBS) is introduced to group multiple wavelengths together as a band or fiber and switch the group using a single port whenever possible. Instead of using the traditional optical cross-connects (T-OXCs), WBS networks employ multi-granular optical cross-connects (MG-OXCs) to switch the traffic at different granularities. In this work, we first briefly review and discuss the development in MG-OXC architecture design, routing and wavelength assignment algorithms, and protection schemes in WBS networks. Then two new schemes are proposed to solve the waveband assignment problem and waveband protection problem. In the first scheme, we demonstrate that factors such as bypass traffic and node degree can affect the waveband switching efficiency. A new hierarchical waveband assignment (HWA) algorithm is then proposed to effectively take these wavebanding factors into consideration for saving ports. In the second scheme, we introduce the concept of band-segment and explore band-segment based protection schemes to achieve the goal of port reduction, the sharing of resources and survivability in WBS networks. Our simulations show that the proposed HWA scheme outperforms a representative approach, namely balanced path routing with heavy-traffic first waveband assignment (BPHT), by up to 18% in terms of port reduction. For the first time, our study demonstrates that protection and the sharing of resources can be achieved without sacrificing port saving when the proposed concept of band-segment is efficiently adopted in WBS networks.

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.

Multi-Granular Optical Cross-Connect: Design, Analysis, and Demonstration

A fundamental issue in all-optical switching is to offer efficient and cost-effective transport services for a wide range of bandwidth granularities. This paper presents multi-granular optical cross-connect (MG-OXC) architectures that combine slow (ms regime) and fast (ns regime) switch elements, in order to support optical circuit switching (OCS), optical burst switching (OBS), and even optical packet switching (OPS). The MG-OXC architectures are designed to provide a cost-effective approach, while offering the flexibility and reconfigurability to deal with dynamic requirements of different applications. All proposed MG-OXC designs are analyzed and compared in terms of dimensionality, flexibility/reconfigurability, and scalability. Furthermore, node level simulations are conducted to evaluate the performance of MG-OXCs under different traffic regimes. Finally, the feasibility of the proposed architectures is demonstrated on an application-aware, multi-bit-rate (10 and 40 Gbps), end-to-end OBS testbed.

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.

Analytical models of blocking probability for multi-granularity cross-connect-based optical networks

Multi-granularity optical cross-connect (MG-OXC)-based optical network is a promising optical network architecture as it is capable of flexible switching at different granularity levels. In MG-OXC-based optical networks, wavelength conversion (WC) capability and the number of usable add/drop ports of the nodes are two key factors affecting its performance. Two analytical models of blocking probability for MG-OXC-based optical networks both without WC capability and with sparse WC capability are proposed, exploiting Erlang's loss formula and birth–death process. Based on the models and simulation, the impact of WC capability and the number of add/drop ports on the blocking probability are investigated. Three kinds of granularities (i.e. fibre, waveband and wavelength) are considered in MG-OXC nodes to reduce the complexity and size of switch fabric. Both the analytical and simulation results are given on two network topologies under dynamic traffic patterns. Simulation results show that the proposed models are accurate and effective for the analysis of blocking probability in MG-OXC-based optical networks.

A novel dynamic RWA algorithm with intelligent granularity regulation in multi-granular all-optical networks

With the great advances of DWDM technology, optical cross-connects have to deal with much more wavelengths. Accordingly, the size of optical cross-connects become larger and larger; also the management cost is much higher. To simplify the architecture of cross-connects for low-complexity maintenance, waveband switching (WBS) in conjunction with several optical cross-connect architectures have been proposed and attracted much attention recently. The main concept of WBS is to group multiple wavelengths into a single waveband and what it concerns includes cross-connect cost and port count reduction. In this paper, we investigate the dynamic RWA problem (MG_DRWA) in WBS networks comprising of all-optical switches based on a cost-effective multi-granular optical cross-connect (MG-OXC) architecture. With this reconfigurable architecture, an optical cross-connect can switch at either fiber level, waveband level, or wavelength level according to its configuration. In order to effectively accommodate dynamic traffic demand, we propose a new MG_DRWA algorithm. Numerical results reveal that the proposed algorithm can achieve significantly better blocking performance as compared to a previously proposed algorithm named MILB under various traffic loads.

Waveband Switching for Dynamic Traffic Demands in Multigranular Optical Networks

Waveband switching (WBS) in conjunction with multigranular optical cross-connect (MG-OXC) architectures can reduce the cost and complexity of OXCs. In this paper, we study the performance of different MG-OXC architectures under dynamic traffic. In the case with online incremental traffic, we compare two MG-OXC architectures in terms of the blocking probability of new lightpath requests and study the impact of port counts and traffic loads. We develop an online Integer Linear Programming model (On-ILP), which minimizes the number of used ports and the request blocking probability, given a fixed number of wavelengths and MG-OXC architecture. The On-ILP optimizes the routing of new lightpaths so as to maximize lightpath grouping and reduce the port count given that existing traffic cannot be rearranged. We also propose a new efficient heuristic algorithm, called Maximum Overlap Ratio (MOR) to satisfy incremental traffic and compare it with the On-ILP, first-fit, and random-fit algorithms. Our results and analysis indicate that using WBS with MG-OXCs can reduce the size (and, hence, the cost) of switching fabrics compared to using ordinary OXCs. Based on the results and observations in the incremental traffic case, we further study the performance of a particular MG-OXC architecture under fully dynamic or fluctuating traffic. Our simulations show that the proposed heuristic algorithm waveband assignment with path graph, which groups wavelengths to bands and uses wavelength converters efficiently under fluctuating traffic, significantly out-performs other heuristic algorithms.

Optimal design for survivable backbones with end-to-end and subpath wavebanding

We deal with the optimal design of a survivable optical mesh network supporting end-to-end and subpath waveband switching (WBS) in order to compare various WBS schemes according to a given cost function. An integer linear programming formulation is proposed to minimize the global network cost, which is expressed in terms of port cost, fiber cost, and propagation delay cost. We assume a single-layer multigranularity optical cross-connect (MG-OXC) node with a variable number of incoming fibers and a fixed number of wavelengths per waveband. The results show that on our case-study networks WBS with joint end-to-end and subpath wavebanding guarantees a gain of up to 22% and 85% in port number and global network costs, respectively. © 2006 Optical Society of America OCIS codes: 000.1200, 060.0060.

Performance Evaluation and Experiment of a Configuration Algorithm for Three-Stage Multi-Granularity Optical Cross-Connects

We study the configuration issue of three-stage multi-granularity optical cross-connects (MG-OXC) for the dynamic traffic model in all-optical networks. From the single node point of view, we propose a configuration algorithm to configure different granularity cross-connects for arrival sub-requests with different traffic types and bandwidths. The performance of the configuration algorithm is evaluated by simulation and, furthermore, is validated by experiment based on our flexible Multi-functional Optical Switching Testbed (MOST).

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.

Waveband switching networks with limited wavelength conversion

We study reconfigurable multi-granular optical cross-connects (MG-OXCs) in waveband switching networks with limited wavelength conversion and propose a heuristic algorithm to minimize the number of used wavelength converters while reducing the blocking probability.

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.

A study of waveband switching with multilayer multigranular optical cross-connects

Waveband switching (WBS) has attracted attention from the optical networking industry for its practical importance in reducing port count, the associated control complexity, and cost of optical cross-connects (OXCs). However, WBS-related problems of theoretical interest have not been addressed thoroughly by the research community and many issues are still wide open. In particular, WBS is different from wavelength routing and, thus, techniques developed for wavelength-routed networks (including for example, those for traffic grooming) cannot be directly applied to effectively address WBS-related problems. In this paper, we first develop an integer linear programming (ILP) model, which for a given set of lightpath requests, determines the routes and assigns wavelengths to the lightpaths so as to minimize the number of ports needed. Since the optimal WBS problem of minimizing the port count in WBS networks contains an instance of routing and wavelength assignment (RWA), which is NP-complete, we adopt a powerful waveband assignment strategy and develop an efficient heuristic algorithm called balanced path routing with heavy-traffic first waveband assignment (BPHT). Both the ILP and the heuristic algorithm can handle the case with multiple fibers per link. We conduct a comprehensive evaluation of the benefits of WBS through detailed analysis and simulations. For small networks, our results indicate that the performance of the BPHT heuristic is close to that achievable by using the ILP model and, hence verifying its near-optimality. We show that for larger networks, BPHT can perform better than its variation called balanced traffic routing with maximum-hop first waveband assignment and much better than another heuristic based on optimal (but waveband oblivious) RWA that minimizes wavelength resources. We also show that WBS using BPHT is even more beneficial in multifiber networks than in single-fiber networks in terms of reducing the port count. Our analytical and simulation results provide valuable insights into the effect of wavelength band granularity, as well as the tradeoffs between the wavelength-hop and the port count required in WBS networks.