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C-RAN has become a promising scenario to accommodate high-performance services, which provides ubiquitous user coverage and supports real-time cloud computing using cloud BBUs. The interaction between RRH and BBU or resource schedule among BBUs in cloud have become more frequent and complex due to the development of system-scale and user requirements. The heavy-duty interaction can promote the networking demand among RRHs and BBUs, and forces to form elastic optical fiber switching and optical networking according to the characteristics of high bandwidth, low cost, and transparent multi-rate traffic transmission. In such a network, the multiple stratum resources of radio, optical, and BBU processing unit have interwoven with each other, so the traditional architecture cannot efficiently implement the resource optimization and scheduling for the high-level QoS guarantee. In this article, we present a novel C-RoFN architecture for MSRO using software defined networking. The proposed architecture can globally optimize radio frequency, optical spectrum, and BBU processing resources effectively to maximize radio coverage and meet the QoS requirement. The functional modules of C-RoFN architecture, including the core elements of radio, optical, and BBU controllers, are described in detail. The cooperation procedures in multi-layer vertical integration and cross-stratum horizontal merging models are investigated. The overall feasibility and efficiency of the proposed architecture are also experimentally demonstrated on our SDN-enabled testbed with OpenFlow-enabled elastic optical nodes, and compared to cross-stratum optimization strategy in terms of resource occupation and path provisioning latency. Numerical results are given and analyzed based on the testbed. Some future discussions are presented in the conclusion.

The advent of spectrally flexible (a.k.a. elastic) optical networking is widely identified as the next generation optical network solution that permits varying bandwidth demands to be dynamically assigned over flexible spectral containers, targeting optimum use of the available network resources. Additionally, the adoption of the space dimension is identified as a promising solution for the capacity expansion of future networks, while novel spatial-spectral switching solutions show that the flexible networking concept can be further expanded over both the spatial and spectral dimensions. This article provides an overview of the latest developments and possible approaches with respect to flexible optical networking and the emerging benefits that spatially flexible networking approaches can offer. The focus is on the network planning and resource optimization functions, the main network operations related to fragmentation and IP/optical layer integration, and the control plane solutions.

Conventional elastic optical networking, EON, uses elasticity in two domains, time and frequency, to optimize utilization of optical network resources in the presence of fluctuating traffic demand and link quality. Currently, networking exploiting a third domain, space, is the focus of significant research efforts since space-division multiplexing, SDM, has the potential to substantially improve future network capacity and spectral efficiency. This article extends 2D-EON to include elasticity in all three domains: time, frequency, and space. We introduce enabling technologies, architectures, and algorithms for 3D-EONs. Based on sample network topologies, we investigate algorithms for routing, spectrum, spatial mode, and modulation format assignment — RSSMA. In particular, we investigate fragmentation-aware RSSMA and how the constraints in the formation of super-channels in MIMO-based SDM systems can impact the network performance in terms of blocking probability.

The traffic carried by core optical networks as well as the per-channel interface rates required by IP routers are growing at a remarkable pace year after year. This trend is due to the widespread deployment of fixed and wireless broadband access networks, the huge growth of video-based services supported by the Internet, and social media applications, as well as a substantially growing amount of machine-to-machine traffic supporting a variety of data-centric applications. Optical transmission and networking advancements have been able to satisfy this huge traffic growth so far by providing the necessary network infrastructure in a cost- and energy-efficient manner, utilizing to the maximum extent the capabilities of optoelectronic and photonic devices across the available bandwidth of deployed optical fibers. However, as we are rapidly approaching fundamental spectral efficiency limits of single-mode fibers, the scientific and industrial telecommunications community foresees that the growth capabilities of conventional WDM networks operating on a fixed frequency grid in conventional wavelength bands are quite limited.

Dynamic optical networking allows operators to effectively maximize the capacity of their physical infrastructure and cope with the rapid growth rates of the Internet traffic. In the framework of the European DICONET project we proposed and developed a comprehensive solution that utilizes the dynamicity as well as the valuable physical layer information of a reconfigurable WDM core network to provide a smooth transition from the quasi-static networking of today to an intelligent reconfigurable and physical impairment-aware architecture. In this work we discuss the benefits of implementing the DICONET solution and present some of the major achievements of the project that support both the planning and operation phase of a core optical network.

Growing concerns regarding the scalability of current optical networks as well as IP-based networks are driving two important trends. One trend is a shift from the current rigid optical networks to spectrally efficient elastic optical networks with a flexible bandwidth and adaptive channel spacing. The other trend is IP traffic offloading to a lower layer yielding benefits that are potentially cost-effective and power-efficient. This article presents a novel multiflow optical transponder (OTP) that enables more efficient IP optical networking. A multiflow OTP allows client data flows that arrive from a single client interface to be mapped to multiple optical flows. In cooperation with the emerging spectrally efficient elastic optical path networking technology, multiflow OTPs can provide multiple optical connections from a single OTP to multiple OTPs. IP traffic offloading to an elastic optical path layer architecture and the effect of introducing multiflow OTPs (i.e., the potential reduction in the number of router interfaces and considerable potential for cost savings) are discussed. These benefits are brought about by increasing the number of directly connected router pairs while keeping router-to-optical-node interconnections simple. A novel optical virtual private line service based on multiflow OTPs that supports multiple optical connections from a single customer site to multiple customer sites with capacity adjustment is also discussed.

Optical networks are undergoing significant changes, fueled by the exponential growth of traffic due to multimedia services and by the increased uncertainty in predicting the sources of this traffic due to the ever changing models of content providers over the Internet. The change has already begun: simple on-off modulation of signals, which was adequate for bit rates up to 10 Gb/s, has given way to much more sophisticated modulation schemes for 100 Gb/s and beyond. The next bottleneck is the 10-year-old division of the optical spectrum into a fixed "wavelength grid," which will no longer work for 400 Gb/s and above, heralding the need for a more flexible grid. Once both transceivers and switches become flexible, a whole new elastic optical networking paradigm is born. In this article we describe the drivers, building blocks, architecture, and enabling technologies for this new paradigm, as well as early standardization efforts.

In next generation networks, voice, data, and multimedia services will be converged onto a single network platform with increasing complexity and heterogeneity of underlying wireless and optical networking systems. These services should be delivered in the most cost- and resource-efficient manner with ensured user satisfaction. To this end, service providers are now switching the focus from network Quality of Service (QoS) to user Quality of Experience (QoE), which describes the overall performance of a network from the user perspective. High network QoS can, in many cases, result in high QoE, but it cannot assure high QoE. Optimizing end-to-end QoE must consider other contributing factors of QoE such as the application-level QoS, the capability of terminal equipment and customer premises networks, and subjective user factors. This article discusses challenges and a possible solution for optimizing end-to-end QoE in Next Generation Networks.

Integration and full interoperability are challenging areas of research in wide area networks today. A European project, MUPBED, has recently concluded and achieved the main result of integrating and demonstrating technologies and network solutions that enable the operation of future European research infrastructures capable of supporting advanced applications. The achieved results are largely valid for any multidomain network scenario. The test network set up by the project is a prototype multidomain optical network able to provide connectivity on demand services across multiple domains directly driven by the applications. Rather than implementing ex novo a unified control plane and replacing existing equipment, the project approach has been to enable seamless interworking of different control planes by means of ASON/GMPLS and standardized network interfaces. This was done in accomplishment of the project target, which was to test and trial a common migration path toward the future European research network that should be followed by national research and education network operators, together with commercial operators. This article describes the main aspects of the MUPBED experience, which by its own peculiar nature provides deep insight into the most recent evolution of control-plane-enabled optical networking toward multidomain integration. Topics covered by the project and briefly related here include network architecture, applications, protocol and control software development, standardization issues, design, analysis and simulation, testing, measurement, and monitoring.

This article takes a broad look at a variety of optical network technologies that have been developed over the past two decades and comments on why some were successful in the real world while others have yet to make it beyond research laboratories or paper publications. We describe each technology briefly and then offer possible explanations for its rapid or slow adoption by the industry

It is now evident to the research community that local computational resources cannot keep up in an economical way with the demands generated by some users/applications. Therefore, distributed computing and the concept of a computational grid are now emerging. Novel transport network concepts are needed to support such visions, and high-speed intelligent optical networking may be the required infrastructure that will enable global grids. Emerging utility grid applications like business continuity and disaster recovery have strong requirements on the dynamic optical networks connecting the distributed grid resources. Supporting grid networking with an intelligent optical network (ION) infrastructure will allow utility grid applications the necessary flexibility with the required QoS (e.g., high bandwidth, reliability, limited delay). Emerging QoS requirements, such as scalable recovery time, highly depend on the ION's signaling architecture. This article gives simple analytical models for the implementation options of optical control plane signaling, shows simulation models for different resilience strategies, and offers some illustrative numerical comparisons to support the aforementioned efforts. This research area is also discussed, among others, in the European research project Multi-Partner European Testbeds for Research Networking (MUPBED).

This article describes deployments of the JumpStart architecture and protocols in several ultra-high-performance optical networking testbeds. JumpStart interoperates with a variety of commercial optical switching gear, and supports operator-, user-, application-, and protocol-initiated ultra-fast lightpath provisioning. We briefly describe JumpStart's data and control plane architectures, and the functionality and performance of its edge and core components. We summarize results from JumpStart testbed demonstrations supporting ultra-fast lightpath provisioning for grids, high-performance file transfers, low-latency zero-jitter interactive visualization, and optical transport using optical burst switching.

The Internet transport infrastructure is evolving toward a model of high-speed routers interconnected by intelligent optical networks. In this article we review current optical networking architectures and describe a new concept proposed in A. Gumaste and I. Chlamtac [2003]: light-trails. We develop light-trails as a novel and amenable control and management solution to address IP-centric communication problems at the optical layer. We implement a testbed to demonstrate light-trail feasibility. We also present three medium access control protocols for light-trails and evaluate their performance. The goal of light-trails and our solution is to combine commercially available components with emerging network technologies to provide a transparent, reliable, and highly scalable communication network.

The introduction of affordable broadband services and applications will drive the next phase of deployment of optical networks. Research on optical networks and related photonics technologies, which has been a key element of the European Union's Research Programs over the past 15 years, has evolved in line with industry and market developments, and will continue, with a strong focus on broadband, in the Information Society Technologies (IST) priority of the new Framework Six Program. The infrastructure to deliver "broadband for all" is seen as the key future direction for optical networking, and the key growth market for industry.

In March, optical communications and networking professionals from around the world will once again convene in Los Angeles for an exciting week of networking, high-quality science and a world-class exposition at the Optical Fiber Communication Conference (OFC) and the National Fiber Optic Engineers Conference (NFOEC). With hundreds of peer-reviewed technical and invited presentations on topics including flexible grid technology, gigabit FTTx networks, "green" networking, and datacenters, as well as an exhibit hall with more than 500 leading optical communication companies and so much more; this year's event promises to uphold the tradition of excellence participants have come to expect over the last 37 years.

In recent years, telecommunication networks have faced explosive (IP) traffic growth. As traffic keeps growing, network reliability gains more and more importance. This article investigates to which extent switched connections and fast connection provisioning, typical for intelligent optical networks (IONs), can be used to provide resilience in an IP-over-optical multilayer network scenario. This solution, based on transport network flexibility, is compared with more traditional static multilayer resilience schemes in terms of cost (capacity) requirements and operational (dis)advantages.

Optical access networks are beginning to be deployed at the edge of the optical backbone network to support access by the high-end users that drive increased bandwidth demands. This development in the applications of optical networking poses new challenges in the areas of medium access, topology design, and network management. In particular, since optical access networks carry high volumes of critical traffic, the level of reliability and robustness traditionally reserved for core applications must be implemented in access networks. We survey access network architectures and outline the issues associated with providing reliability for these architectures. In the area of architecture design, two main approaches emerge. The first considers dedicated optical access networks, such as stars or folded buses, to implement optical access LANs and MANs. The second is overlay architectures, which use existing network infrastructure. Overlay architectures seek to replicate, on a smaller scale, logical topologies akin to those of backbone networks, or may instead create architectures specifically designed for access purposes.

This article first discusses how advances in networking architectures and protocols can complement advances in optical communications research to increase the overall value of optical networks by enabling more applications. A review of existing optical networking solutions is then provided along with a classification of different types of optical networks. Finally, we show how single-hop and multihop wavelength-routed networks can be used efficiently for fast end-to-end file transfers when these networks are equipped with a hardware-implementable signaling protocol, a routing protocol, and a simple transport protocol.

In this new millennium, the most valuable commodity will be information, as seen by the surge in demand for faster access technologies such as cable modems, xDSL, and wireless data. The tremendous growth in data traffic, particularly that associated with the Internet, is changing the way it is carried over public and private networks. Together with the rapid advances in optical networking technology and the spawning of a new category of wavelength services stimulated by new high-speed data requirements, this is dramatically changing network architectures and the relationship between network service providers and their customers. Incumbent carrier globalization and new carrier entry require support for a broader set of business models and range of service interfaces. The growth and expansion of networks imply a greater need for more scalable solutions and more automation for network maintenance. An intelligent optical core optimized for service optical networking, the services optical network, needs to take the best aspects of both the transport and data networking domains to meet the above needs. This article focuses on architecting the services optical network to meet the challenges of optical data networking, and includes a snapshot of supporting standardization activities.

The explosion of the Internet has brought about an acute need for broadband communications, which can only be filled with optical networking. This in turn has resulted in an unprecedented interest in optical micro-electromechanical systems. Since the early days of fiber optics, it has been recognized that micro-optics was a fertile ground for the applications of MEMS. MEMS-based products offer substantial cost and performance advantages for optical networking applications in the area of switching fabrics, variable attenuators, tunable lasers, and other devices. This article provides a review of various types of MEMS technologies for optical networking applications.

This article summarizes the present state of optical networking, how we got to this point, and what needs to be done to complete the job. The point of departure is an assumed future two-level structure in which the transport is by means of steadily growing interconnected all-optical islands of transparency, while the remainder of the communication layers are based on IP, both levels being managed by an MPLS-based control plane. After reviewing why such networks are becoming inevitable, a review is given of the various optical layer technology and architecture bottlenecks that have had to be solved. Issues that remain center on increasing the number of channels and reducing the technology costs.

Several new technological advancements have extended the capabilities of the basic broadband passive optical network (B-PON) described in the ITU-T standard G.983.1. This article describes three of these new technologies: wavelength division multiplexing (WDM), dynamic bandwidth assignment, and survivable networking. These additions to the B-PON family of solutions increase its utility by increasing its raw capacity, its efficiency, and its reliability, respectively. A description is also given of the next wave of innovations that will further extend the B-PON.

Previous advances in WDM technology are now beginning to shift the focus more toward optical networking and network-level issues. Providing survivability at the optical layer is inherently attractive, but whether it makes practical sense, given similar mechanisms that are already available at the higher layers, poses serious challenges and raises many questions. Today's core network architecture model has functional overlap among its layers, contains outdated functionality, and is too slow to scale. If IP can be mapped directly onto the WDM layer, some of the unnecessary network layers can be eliminated, opening up new possibilities for developing a simple and integrated-protection/restoration scheme that can be coordinated at both the IP and WDM layers. This article presents an overview of existing optical protection/restoration schemes. Then we present a novel mesh-based hybrid optical protection scheme that utilizes multifiber physical links along with a hierarchical OXC structure. An overview of the envisioned IP-centric DWDM-based optical data network architecture is then presented. The basis of how to implement a more direct IP standard-based approach for closer and efficient IP-WDM integration is also discussed. Finally, we articulate a view of how to provide a joint protection/restoration scheme that is coordinated at both the IP and WDM layers.

We challenge current thinking about IP over WDM by outlining a path to optical data networking that includes multiple data networking protocols coupled with a protocol-neutral optical networking infrastructure. Included is a discussion of the diversity of data networking protocols and network architectures for optical data networking.

A pan-European transport network must cope with enormous traffic inflation by introducing appropriate network solutions. WDM technology is the solution adopted by GTS, driven by capacity requirements, infrastructure availability, flexibility, and cost. The deployment of this new technology presents specific technical issues, but more important, it lays the foundation of future optical networking. We describe the motives underlying the deployment of WDM technology in the long-haul and short-haul areas of GTS's operational transport network. Next, after presenting the use of WDM as the multiservice platform for SDH and IP overlay networks as well as native WDM services, we focus on the design of SDH-over-WDM and IP-over-WDM networks. Finally, we discuss future WDM networking and management requirements to better serve the needs of a pan-European carrier such as GTS.

This article reports a review of the most significant issues related to network architectures and technologies which will enable the realization of future optical Internet networks. The design of such networks has to take into consideration the peculiar characteristics of Internet traffic. Several architectures have been proposed to provide optical networking solutions, based on wavelength-division multiplexing and compatible with the IP world. These architectures are presented briefly, and the main advantages and drawbacks are discussed. Furthermore, advanced network architectures are reported. In particular, two network paradigms are illustrated and discussed: the optical transparent packet network and optical burst switching. Finally, the key technologies are illustrated.

The rapid pace of development in both Internet applications and emerging optical technologies is bringing about fundamental changes in networking philosophies. Key trends are the emergence of dynamic wavelength provisioning and a corresponding reduction in wavelength provisioning timescales. As this transition continues, the current use of the wavelength-routing paradigm for carrying bursty Internet traffic will likely suffer from various shortcomings associated with circuit-switched networks. Meanwhile, optical packet switching technology is still facing significant cost and technological hurdles. Optical burst switching, or OBS, which represents a balance between circuit and packet switching, has opened up some exciting new dimensions in optical networking. This article describes the OBS paradigm, and also proposes the use of labeled OBS, or LOBS, as a natural control and provisioning solution under the ubiquitous IP multiprotocol label switching framework.

A pan-European carriers' carrier network, like other carrier networks, must cope with the enormous traffic inflation by introducing appropriate network solutions. WDM technology is the solution adopted by GTS Carrier Services' Trans European Network unit (TEN, formerly known as Hermes Europe Railtel), driven by bandwidth requirements, infrastructure limitations, flexibility, and cost. The introduction of such new technology presents specific technical issues, although it lays the foundation of future optical networking. Network outages are an important concern since, by using WDM, tens of gigabits of data are transported on each fiber. On one hand, traffic interruption is avoided as much as possible through secure fiber routings, cable protection, high design and equipment standards, and security. On the other hand, network protection techniques are used to limit the impact on services when inevitable outages occur. We explain the role of the different technologies in TEN's network. We concentrate on WDM and optical networking where optical channels are used to interconnect the equipment used by the different technologies. We focus on optical network protection techniques and illustrate that a clear requirement exists for this. We also emphasize interworking issues that come into play when multiple technologies are combined in the same network. It is not the intent to discuss only future requirements, but also to explain how the different aspects are currently implemented in TEN's operational network.

The definition of standards for optical networking is a new work item for the International Telecommunication Union (ITU) 1997-2000 Study Period. The authors provide a brief overview of this nascent standards development effort, with a specific focus on key issues currently under discussion that, when resolved, will have far-reaching impact on the ultimate realization of "optical networking".

This article examines the complex issues surrounding deployment of wavelength-division multiplexing technology in the local exchange network. It discusses demand, economics, technology advantages/disadvantages, saleability, operations, interoperability, and optical networking. The emphasis is on economics and manageability. After a review of these issues, the article looks forward to the optical network in a multi-vendor interoperable environment and to the continuing evolution of standards that will expedite the deployment of optical networking technology.

For decades, TDM has been the fundamental basis for adding capacity to digital telecommunications networks. Suddenly emerging in the past two years WDM has emerged as an important and widely deployed complement to TDM. In fact, sales of systems based on the new technology have risen to over a billion dollars at breathtaking speed. The author addresses the factors that propelled WDM to the forefront of telecommunications technologies, and looks at the immediate future, with WDM pushing into new areas of telecommunications networks, and emerging as the basis of logical optical networking.

The development of the information society will require the introduction of high-capacity transport networks with high performance and low cost. There are currently two ACTS (Advanced Communications Technologies and Services program launched by the European Commission) projects addressing specifically the problem of trans-European optical transport networks using WDM (wavelength division multiplexing). Important issues addressed are the high capacity transmission on existing fiber infrastructure and the introduction of flexibility in the network through the use of optical cross-connects. If these networks become a reality, they could drastically change the evolution of both telecommunication and computer networking because of their transparency and the abundance of inexpensive bandwidth.

We revisit the topic of optical layer protection from a motivation and deployment perspective. We first discuss the changes that have occurred in optical networking in general and the implications for protection. We then discuss scenarios where optical protection makes sense, recognizing that other fast protection schemes at the client layer provide viable alternatives in certain cases. Our conclusion is that optical protection makes sense for metro networks, as long as they are based on simple dedicated schemes. When it gets to more complex shared ring and mesh protection, we believe that OEO-based schemes are more viable, whether crossconnect-based or packet-switch-based.

Optical networking is attracting a large amount of interest, particularly for local access and increasingly for long-haul, or core, network applications. However, optical networks are essentially analog, and with this return to analog transmission there are a number of issues that need to be understood and overcome if the concept of an optical transport layer is to become a reality. The Multi-Wavelength Transport Network (MWTN) within the European RACE II research program is studying the potential for optical networking in a managed network environment. This article outlines the MWTN networking concept and the comprehensive experimental test bed developed within the project. Communication networks are poised, awaiting the broadband revolution. Telecommunication, computer, and broadcast entertainment market places are converging with multimedia-based future services providing the drive and focus. In such an information-intensive future, customers will demand high-performance service with an agreed and measurable quality at the lowest cost. Furthermore, they will expect a common interface to all services. From a customer's perspective, the role of the network, the terminal equipment and the computer based multimedia application will be virtually indistinguishable. The synchronous digital hierarchy (SDH) and asynchronous transfer mode (ATM) techniques are at the forefront of the move toward these future communication networks. >

The global optical communications industry continues to show progress in all segments from access to core networks. Fiber-based broadband access network deployments have been slow and steady with service provider attention currently focused on recent developments and new technologies for higher bandwidth copper-based broadband access. Service providers have continued their deployments, globally, of high-speed (100G and beyond) transport networks, and have been participating in field trials of 400G optical transport network equipment and systems. Since the beginning of 2013, there have been more focus and attention on network functions virtualization (NFV) and software-defined networking (SDN) to provide service providers with the tools for more effective operation and management of optical communications networks.

In this issue, we wish to inform our readers of an important change. After a long and successful service as OCS (Optical Communications Series) editor, Hideo Kuwahara has departed to start his term as the president of the IEEE Photonics Society in January of this year. We take this opportunity to express our deep appreciation for his dedicated service to the OCS and wish him well in his new role as IEEE Photonics Society President.