Multiflow optical transponder for efficient multilayer optical networking

Elastic optical network (EON) is a promising candidate for the next generation optical transport network because of its high spectrum efficiency and flexible spectrum allocation. However, to migrate from today’s dense wavelength division multiplexing (DWDM) network to EON, optical nodes such as reconfigurable optical add/drop multiplexers (ROADMs) should be replaced with the ones with expensive flexi-grid wavelength selective switches (WSSs). Thus, whether and how today’s optical network will be evolved to EON is still under debate. Meanwhile, with the technical maturity of optical super-channels that transmit bit rates at the level of 1 Tb/s, super-channels are expected to dominate the future optical transport network because of their attractiveness of high spectrum efficiency and superior cost effectiveness. In this paper, we propose a new quasi-coarse wavelength division multiplexing (Quasi-CWDM) optical network architecture that is compatible to today’s WDM network in spectrum operation, while still maintaining the flexibility of adaptation between the bit rate and the transparent reach of an optical super-channel, but not requiring expensive flexi-grid WSSs. Specifically, the Quasi-CWDM optical network employs large fixed frequency grids, whose spacing falls between the traditional CWDM and DWDM, e.g., 200 GHz or 400 GHz. To maintain the flexibility between the bit rate and the transparent reach of an optical super-channel, different modulation formats are chosen according to channel physical distances. To minimize network hardware cost and maximize carried user traffic demand, we develop a mixed integer linear programming (MILP) model and a heuristic algorithm that can efficiently groom upper-layer IP traffic onto the optical layer by optical super-channels. We compare the design based on the Quasi-CWDM network to those based on the DWDM network and the advanced EON. It is found that the proposed Quasi-CWDM network has a much lower hardware cost than the other two types of networks, while achieving spectrum efficiency close to EON.

Content caching is an effective technique that reduces network power consumption by reducing the path between users and requested video content. This paper examines the benefit of caching in an IP over WDM core network with respect to current and future networks. It compares the power savings due to caching in current implementations of optical networks to potential power savings when future optical network features are realized. Future optical core networks are considered with three major power efficiency improvements over current networks. First, network devices are equipped with sleep-mode capabilities where inactive parts of storage devices are put in low-power mode. Second, optical bypass is employed where intermediate IP routers are not engaged in traffic routing. Third, the power consumption of router ports is significantly reduced, consequently reducing the power consumption of transport. The results show that content caching is effective in reducing power consumption under both current and future optical networks, making caching a successful option for video delivery in the future Internet.

Due to widespread applications and rapid development of cloud computing and Internet services, hyperscale data centers have experienced an unprecedented demand for networking. Data center networks are required not only to handle fast-growing traffic, which doubles almost every one to two years, but also to provide high flexibility and availability to support rapidly changing businesses as well. Therefore, hyperscale data center networks have become one of the main drivers for optical interconnect technologies in recent years. In this article, technologies for scaling optical interconnects for inter-data center interconnects (DCIs) are presented. We first describe hyperscale data center network architectures and requirements, as well as the differences between carrier’s optical transport networks and DCI optical networks, with the main focus on metro-DCI and campus-DCI networks. The scale and fast growth rates of DCI networks require innovations not only in data plane technologies but also in control and management planes as well. In data planes, high-capacity flexible coherent technology, pluggable wavelength-division-multiplexing (WDM) optical transponders, including 100G direct-detection four-level pulse-amplitude modulation (PAM4) and coherent 400ZR/800ZR, and flex-grid and disaggregated reconfigurable optical add-drop multiplexer (ROADM) optical networks are described. Control and management planes are an integral part of optical transport networks and crucial for effectively operating DCI networks. We show that standard protocols, data models, and modular design of a software platform are essential to building a scalable open and disaggregated optical network, which is fundamental to enabling high automation and intelligence in an optical network. An example control and management platform is discussed in detail. With current fiber capacity approaching the nonlinear Shannon limit, challenges to further scale DCI networks and some potential technologies to support ever-increasing traffic growth are discussed at the end.

Extending light-trail into elastic optical networks for dynamic traffic grooming

Current optical transport networks provide high bandwidth through the use of advanced WDM technology, but are difficult to adapt to the different statistical patterns and quality of service (QoS) demands of future traffic. There has been much debate whether the use of dynamically reconfigurable optical networks would have a number of advantages in accommodating the needs of future traffic demands. Dynamic networks would eliminate the need for frequent opto-electronic conversion in current networks, and may save resources through higher utilization and fast adaptation. Different architectures have been proposed to address this problem: Wavelength-routed optical networks (WRON), optical burst switching (OBS), and optical packet-switching (with increasing granularity and speed of reconfiguration). In this paper we investigate whether these architectures are suitable (necessary?) to meet the demands of future traffic, using an analysis focusing on both modeling and experimental aspects.

ZusammenfassungEnergy efficiency is important for optical networks in terms of scalability, low-cost operation, and sustainability. At the same time, optical networks play an important role in enabling energy efficiency for the Internet as a whole and for information and communication technologies more generally. Understanding energy in the context of optical networks begins with an understanding of the constituent components and equipment that make up an optical network and how their energy use is evolving over time. The network architecture, describing how these parts are put together and operated, will also have a considerable impact on the energy efficiency of optical networks. This impact can be modeled and understood in different ways. Perhaps the largest energy impact, however, comes from including optical networks in cross-layer design and survivability strategies. These aspects of energy-efficient optical network design are examined, along with issues related to mobile and optical network convergence, nonlinear optics and optical processing, and computer and optical network cross-optimization. An introduction to resources for recommendations and guidance from standards bodies and other organizations on the energy efficiency of optical networks is also provided.

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

Objectives: The current technologies of wavelength routing and allocation of available for WDM networks are no longer applicable in Elastic Optical Networks (EON), since all their connections are allocated in a fixed manner, as provided for ITU. Therefore, the topic concerning routing and allocation of resources in EON is relevant given the growth projected in web traffic. This survey includes the evolution, main characteristics, and the process of routing and allocation of wavelengths required by EON. Methodology: The processes of allocation of sub-wavelengths and those of super-wavelengths are presented, as well as the multiple storage for different transmission rates and the principle of spectral contiguity. The process of routing and allocation taking OFMD into account is explained. Findings: In this study, we present a survey with routing and allocation techniques of wavelengths that improve the spectral efficiency of EON. Application/Improvements: This survey provides a wide knowledge on the methods to improve the spectral efficiency in EON. Such efficiency can promote an advance in new routing and allocation techniques for the optical transport networks. Keywords: Elastic Optical Networks, EON, Optical Networks, Routing, WDM

Radio access network (RAN) cost savings are expected in future cloud RAN (C-RAN). In contrast to traditional distributed RAN architectures, in C-RAN, remote radio heads (RRHs) from different sites can share baseband processing resources from virtualized baseband unit pools placed in a few central locations (COs). Due to the stringent requirements of the several interfaces needed in C-RAN, optical networks have been proposed to support C-RAN. One of the key elements that needs to be considered are optical transponders. Specifically, sliceable bandwidthvariable transponders (SBVTs) have recently shown many advantages for core optical transport networks. In this paper, we study the connectivity requirements of C-RAN applications and conclude that dynamicity, fine granularity, and elasticity are needed. However, there is no SBVT implementation that supports those requirements, and thus, we propose and assess an SBVTarchitecture based on dynamic optical arbitrary generation/measurement. We consider different long-term evolution-advanced configurations and study the impact of the centralization level in terms of the capital expense and operating expense. An optimization problem is modeled to decide which COs should be equipped and which equipment, including transponders, needs to be installed. The results show noticeable cost savings from installing the proposed SBVTs compared to installing fixed transponders. Finally, compared to the maximum centralization level, remarkable cost savings are shown when a lower level of centralization is considered.

With the fast development of various applications, the demand for network bandwidth has been increasing significantly during the past decade. Although the WDM (wavelength-division multiplexing) technology has already provided high bandwidth using parallel wavelength channels, the overall network spectrum efficiency is however severely discounted by the fixed grid definition and standard rate transmission. The short-term solution to increase capacity is by introducing hardware enabling elastic optical networking (EON), which is intrinsically related to flexible-grid channel allocation; and the longer-term solution involves extending the fiber capacity by space division multiplexing (SDM) based on new types of fibers supporting multiple cores, multiple elements, few LP modes or even modes carrying Orbital Angular Momentum (OAM). Moreover, for short-term evolution, it may not be economically viable to make a one-time complete upgrade to full flexible-grid technology on the entire network, which means, before the current optical transport network capacity is exhausted, the current fixed-grid network could be maximally kept operational during the migration to preserve the already-made investment. In this talk, a series of topics will be discussed, such as the network architecture with co-existing fixed-grid and flexible-grid technologies, migration strategies evolving from fixed-grid to flexible-grid, SDM based Reconfigurable Optical Add/Drop Multiplexers (ROADMs), as well as networking aspects of routing and spectrum resource allocation when considering spectral/spatial switching.

Study and Analysis of Routing and Spectrum Allocation (RSA) and Routing, Modulation and Spectrum Allocation (RMSA) Algorithms in Elastic Optical Networks (EONs)

The sustained growth of data traffic volume calls for an introduction of an efficient and scalable transport platform for links of 100 Gb/s and beyond in the future optical network. In this article, after briefly reviewing the existing major technology options, we propose a novel, spectrum- efficient, and scalable optical transport network architecture called SLICE. The SLICE architecture enables sub-wavelength, superwavelength, and multiple-rate data traffic accommodation in a highly spectrum-efficient manner, thereby providing a fractional bandwidth service. Dynamic bandwidth variation of elastic optical paths provides network operators with new business opportunities offering cost-effective and highly available connectivity services through time-dependent bandwidth sharing, energy-efficient network operation, and highly survivable restoration with bandwidth squeezing. We also discuss an optical orthogonal frequency-division multiplexing-based flexible-rate transponder and a bandwidth-variable wavelength cross-connect as the enabling technologies of SLICE concept. Finally, we present the performance evaluation and technical challenges that arise in this new network architecture.

This book presents an in-depth deliberation on optical networks in four parts, capturing the past, present, and ensuing developments in the field. Part I has two chapters presenting an overview of optical networks and the enabling technologies. Part II has three chapters dealing with the single-wavelength optical networks: optical LANs/MANs, optical access networks using passive optical network architecture, SONET/SDH, optical transport network and resilient packet ring. Part III consists of four chapters on WDM-based optical networks, including WDM-based local/metropolitan networks (LANs/MANs) using single and multihop architectures over passive-star couplers, WDM/TWDM access networks as an extension of PONs with WDM transmission, WDM metro ring networks covering circuit-switched (using point-to-point WDM and wavelength-routed transmission) plus packet-switched architectures and WDM long-haul backbone networks presenting the offline and online design methodologies using wavelength-routed transmission. Part IV deals with some selected topics in six chapters. The first deals with transmission impairments and power-consumption issues in optical networks, while the next three chapters deal with the survivable optical networks, network control and management techniques, including GMPLS, ASON, and SDN/SDON, and datacenter networks using electrical, optical, and hybrid switching techniques. The final two chapters present elastic optical networks using flexible grid for better utilization of the optical-fiber spectrum and optical packet and burst-switched networks. The three appendices present the basics of the linear programming techniques, noise processes encountered in the optical communication systems, and the fundamentals of queuing theory and its applications in telecommunication networks. (238 words)

As power grids and optical interconnection networks are interdependent, the reliabilities of the optical networks are critical issues in power systems. The optical networks hold prominent performance including wide bandwidth, low loss, strong anti‐interference capability, high fidelity, and reliable performance. They are regarded as promising alternatives to electrical networks for parallel processing. This paper is aimed at taking the first step in understanding the communication efficiencies of optical networks. For that purpose, on optical networks, we propose a series of novel notions including communication pattern, r‐communication graph, reduced diameter, enhanced connectivity, r‐diameter, and r‐connectivity. Using these notions, we determine that the r‐diameter and r‐connectivity of the optical n‐dimensional hypercube network are ⌈n/r⌉ and , respectively. Since the parameter r is variable, we can adjust different values of r on the basis of the wavelength resources and load of the optical networks, achieving enhanced communication efficiencies of these networks. Compared with the electric n‐dimensional hypercube network, the proposed communication pattern on the optical hypercube network not only reduces the maximum communication delay of the conventional electrical hypercube significantly but also improves its fault tolerance remarkably.

In the past few decades, the architecture of optical networks has undergone significant evolution, from the earliest wavelength-division multiplexing (WDM) optical networks to elastic optical networks (EONs) and later to space-division multiplexing (SDM) EONs, to address the continuous growth of Internet traffic. By 2024, Pbps-level optical networks are expected, far exceeding the capacity limit of single-mode fibers. The massive SDM era is on the horizon. In this context, a newly designed architecture for optical networks called the spatial channel network (SCN) architecture, which achieves high cost efficiency by means of practical hierarchical optical cross-connects, has recently been proposed. However, the evolution of optical network architectures will simultaneously present challenges related to network optimization. For instance, with the evolution from WDM optical networks to EONs, the kernel network optimization problem was transformed from the routing and wavelength assignment (RWA) problem into the routing and spectrum assignment (RSA) problem due to the additionally introduced constraint of spectrum contiguity. Similarly, specially designed algorithms are also expected to be essential for addressing the network optimization problem in SCNs. In this paper, we define this new problem as the routing, spatial channel, and spectrum assignment (RSCSA) problem. We propose an integer linear programming (ILP) model and a heuristic algorithm to solve the RSCSA problem. We examine the performance of the proposed approaches via simulation experiments. The results show that both proposed approaches are effective in finding the optimal solutions or solutions close to the lower bounds. To the best of our knowledge, this is the first work to focus on the network optimization problem in SCNs.