Orthogonal frequency-division multiplexing (OFDM) is a modulation technology that has been widely adopted in many new and emerging broadband wireless and wireline communication systems. Due to its ...capability to transmit a high-speed data stream using multiple spectral-overlapped lower-speed subcarriers, OFDM technology offers superior advantages of high spectrum efficiency, robustness against inter-carrier and inter-symbol interference, adaptability to server channel conditions, etc. In recent years, there have been intensive studies on optical OFDM (O-OFDM) transmission technologies, and it is considered a promising technology for future ultra-high-speed optical transmission. Based on O-OFDM technology, a novel elastic optical network architecture with immense flexibility and scalability in spectrum allocation and data rate accommodation could be built to support diverse services and the rapid growth of Internet traffic in the future. In this paper, we present a comprehensive survey on OFDM-based elastic optical network technologies, including basic principles of OFDM, O-OFDM technologies, the architectures of OFDM-based elastic core optical networks, and related key enabling technologies. The main advantages and issues of OFDM-based elastic core optical networks that are under research are also discussed.
The concept of elasticity has been proposed in the design of next generation optical networks in tackling the problem of efficient utilization of network resources and increasing traffic demands. The ...elasticity property allows the capacity of lightpaths to best fit the user demands. Even with the elasticity property, there is still a possibility to further improve the resource usage in terms of spectrum or transmitter savings with some techniques developed by research community. The reasoning behind this survey was to emphasize one of them, namely traffic grooming technique, considering the grooming capability at the optical level. Such grooming technique allows the establishment of optical tunnels carrying a several connections in a contiguous block of spectrum without inserting guard bands in between, therefore minimizing the spectrum usage or the number of transmitters. A number of algorithms have been proposed recently in solving this problem including static and dynamic traffic scenario. The objective of the paper is to review, classify and discuss a range of these algorithms in elastic optical networks. The outcomes are expressed as a summar comparison of available algorithms with their main features and objectives. To the best of our knowledge, it is the foremost paper that provides a survey on optical level grooming for elastic optical networks.
The Stop Number Problem arises in the management of a dial-a-ride system served by a fleet of autonomous electric vehicles. In such a system, clients request for a ride from an origin station to a ...destination station, and a fleet of capacitated vehicles must satisfy all requests. The goal is to minimize the number of pick-up/drop-off operations. In this paper we focus on a constrained unitary variant, called Unit Stop Number Problem, where each client requests for a single seat in the vehicles. This variant was recently conjectured to be NP-Hard. In this regard, we show how this problem relates to other problems known in the literature in order to derive some polynomial-time solvable variants. Moreover, we provide a positive answer to the conjecture by showing that the problem is NP-Hard for any fixed capacity greater than or equal to 2, even for the case where the graph of requests is restricted to the class of planar bipartite graphs. Our proof of NP-Hardness also improves the complexity results known in the literature for the related problems identified.
Spectrum elastic optical networks support flexible central frequency and spectrum assignment for lightpaths. When provisioning a new connection in an elastic optical network that allows traffic ...grooming, the control plane has to solve two problems: the electrical-layer routing and optical-layer routing and spectrum assignment (RSA). The electrical-layer routing determines how to route the new connection through a combination of new and existing lightpaths, while the optical-layer RSA decides how to establish new lightpaths under the spectrum-continuity constraint. The flexibility (e.g., bandwidth variability of lightpaths) provided by elastic optical networks makes it suitable for accommodating dynamic traffic. It is important and challenging to exploit the full potential of the flexibility when dealing with the above two problems. In this study, we propose a multi-layer auxiliary graph to jointly solve the electrical-layer routing and optical-layer RSA. Various traffic-grooming policies (objectives) can be achieved by properly adjusting the edge weights in the auxiliary graph. Also, we propose a spectrum reservation scheme that can efficiently utilize the bandwidth variability of lightpaths by reserving bandwidth for non-fully utilized lightpaths and grooming future connections onto them. We show that there is a tradeoff among different traffic-grooming policies, and the spectrum reservation scheme can be easily incorporated into various traffic-grooming policies and lead to a significant reduction in operational expenditure (OPEX) and better spectrum efficiency.
Due to the development of broadband access technologies including FTTx and 5G, the traffic in metro and core networks is forecasted to be more dynamic. To support this dynamicity, flex-grid elastic ...optical networks (EONs) have started to become prolific over the past few years. During the migration from the legacy fixed-grid wavelength division multiplexing optical networks to flex-grid EONs, a transition technology called the fixed/flex-grid optical network has become popular. In such fixed/flex-grid networks, the energy consumption caused by serious capacity mismatch between variable IP traffic and the different optical channel capacities is significantly high to be ignored. In fact, energy-efficient traffic grooming (i.e., to aggregate multiple fine-grained IP flows and map them onto a lightpath) is a challenge in IP-over-fixed/flex-grid optical networks because co-existing fixed-grid and flex-grid nodes have different traffic grooming ability and energy consumption models. To overcome the challenge, we propose an auxiliary-graph-based energy-efficient traffic-grooming ( EETG ) algorithm in IP-over-fixed/flex-grid optical networks for the first time. The construction of an auxiliary graph (AG) model for each connection request is one of the core steps. The well-designed weight-assignment scheme of the AG establishes the relationships between traffic grooming operations and specific energy consumption models. The final traffic grooming operations are undertaken based on the calculated weight-minimized path. The simulation results show that the EETG algorithm achieves 1) the least energy consumption compared with the state-of-the-art traffic grooming algorithms under the non-blocking scenario; and 2) achieves the tradeoff between energy consumption and blocking probability under the blocking scenario.
To improve efficiency in setting up and operation of IP-over-WDM (IPoWDM) network, the network can be designed by minimizing either the capital expenditure (CapEx) or the operational expenditure ...(OpEx) in the planning phase. However, the CapEx-aware designed network may differ from the OpEx-aware designed network. Thus, Capex and OpEx need to be considered together to develop an expenditure-efficient network for a given planning period. Lightpath bypass and traffic grooming techniques help to minimize the required line card number in the core IP router. We design an expenditure (i.e., CapEx and OpEx put together for a given planning period) efficient IPoWDM network. We also review the effect of lightpath bypass and traffic grooming in the design. To design IPoWDM networks, we develop an optimization model and auxiliary-matrix-based heuristics to reduce the network’s total expenditure. The proposed methods judiciously deploy the network equipment at different places to reduce the total expenses and provide solutions for traffic grooming and placement of regenerators. We assume a realistic network framework where the bidirectional WDM equipment has finite transparent reach limit. The performance analysis shows that the multi-hop bypass approach provides more expenditure-efficient networks compared with the direct bypass and the non-bypass methods.
Traffic grooming (TG) has been proposed in two ways as electrical and optical grooming to efficiently utilize spectrum and transponders due to omitting guard bands between adjacent lightpaths and ...establishing multiple independent lightpaths with the same sliceable bandwidth variable transponder (SBVT) in Elastic Optical Networks (EON). In this paper, cooperation of electrical and optical TG is developed as minimized utilization of spectrum or transponder using integer linear programming (ILP) model under static traffic scenario and our proposed corresponding heuristic LMAG algorithm. Electrical and optical grooming are coordinated with each other to construct an auxiliary graph (AG) and establish connection requests under dynamic traffic scenario using the LMAG algorithm. The multipath routing (MR) as an effective defragmentation method, adaptive modulation as effective technique in reducing bandwidth requirement of connection request, and load balancing as an appropriate routing method are employed in AG construction with coordination of electrical and optical TG. Various traffic grooming policies (TGP) by properly adjusting the edge weights are proposed to achieve significant performance improvements in blocking ratio (BR), spectrum and transponder (TP) utilization, and energy consumption in EON.
•New mathematical and linearization models for the network design problem with traffic grooming (NDGP).•A twist based neighborhood structure as well as a fast evaluation technique for NDGP.•A ...matheuristic algorithm by embedding (integer) linear programming within a metaheuristic.•The NDGP is converted into a satisfaction problem by solving a series of k-NDG problems.•Our matheuristic performs favorably in comparison with the state-of-the-art algorithms for NDGP.
This paper addresses a network design and traffic grooming problem arising in optical telecommunication networks that are based on wavelength division multiplexing. Given a set of nodes and a set of traffic demands between these nodes, the network design and traffic grooming problem (NDGP) consists of installing a minimum number of lightpaths between the nodes and of routing the demand on the lightpaths while respecting capacity constraints. We introduce a new mathematical formulation of the NDGP as well as a hybrid algorithm capable of finding high quality solutions in short computing times. The proposed algorithm uses linear and mixed integer programming as slave methods and embeds them within a tabu search procedure. Computational results and comparisons with an existing method from the literature show the effectiveness of the proposed algorithm. Further analyses also show the efficiency of the neighborhood structure and of its evaluation technique.
Traffic grooming has evolved to present some new features in sliceable bandwidth-variable transponder enabled elastic optical networks (SBVT-EON). One of the new features is "optical traffic ...grooming," in which multiple optical flows from/to different sources/destinations can be groomed onto a sliceable transponder. When establishing a new connection request in SBVT-EON, a key problem is how to coordinate electrical and optical traffic grooming. In this study, we propose a three-layered auxiliary graph (AG) model to address mixed-electrical-optical grooming under dynamic traffic scenario. By adjusting the edge weights of AG, we can achieve various traffic-grooming policies for different purposes. Also, we propose two spectrum reservation schemes that can efficiently utilize the capacity of a transponder. We compare different traffic-grooming policies under two spectrum reservation schemes, and a tradeoff is shown to exist among the policies. We also evaluate their performances for different network topologies with different resource provisions.
The management of multilayer networks is often a complex task, since each layer is typically independently operated and maintained, and there is a lack of shared network resource knowledge between ...layers. In this work, we have illustrated that Ant Colony Optimization (ACO) algorithms can be a suitable solution for coordinated management of disjoint IP and optical layers with limited or no visibility between the control planes of each layer. ACO algorithms are used to achieve fully-distributed multilayer routing policies in IP-over-optical networks. Simulations have demonstrated that ACO-based policies can achieve lower levels of blocking probability and higher levels of restorability for IP connections compared to fixed-alternate routing policies in almost all cases. This better performance is achieved with only small increases in the connection setup and restoration times, and without requiring a significant amount of communication overhead.
•Ant-based algorithms allow for distributed routing in IP/MLPS over optical networks.•Only local information is used in ant-based routing to avoid scalability issues.•Crankback is used to improve the setup and recovery of connections.•Setup latencies and network control overhead are kept at a reasonable level.•A comprehensive evaluation of different metrics in each network layer is presented.
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