Showing papers on "Optical Transport Network published in 2015"

Routing and Spectrum Allocation in Elastic Optical Networks: A Tutorial

Abstract: Flexgrid technology is now considered to be a promising solution for future high-speed network design. In this context, we need a tutorial that covers the key aspects of elastic optical networks. This tutorial paper starts with a brief introduction of the elastic optical network and its unique characteristics. The paper then moves to the architecture of the elastic optical network and its operation principle. To complete the discussion of network architecture, this paper focuses on the different node architectures, and compares their performance in terms of scalability and flexibility. Thereafter, this paper reviews and classifies routing and spectrum allocation (RSA) approaches including their pros and cons. Furthermore, various aspects, namely, fragmentation, modulation, quality-of-transmission, traffic grooming, survivability, energy saving, and networking cost related to RSA, are presented. Finally, the paper explores the experimental demonstrations that have tested the functionality of the elastic optical network, and follows that with the research challenges and open issues posed by flexible networks.

NG-PON2 Technology and Standards

Abstract: This paper provides a tutorial overview of the latest generation of passive optical network (PON) technology standards nearing completion in ITU-T. The system is termed NG-PON2 and offers a fiber capacity of 40 Gbit/s by exploiting multiple wavelengths at dense wavelength division multiplexing channel spacing and tunable transceiver technology in the subscriber terminals (ONUs). Here, the focus is on the requirements from network operators that are driving the standards developments and the technology selection prior to standardization. A prestandard view of the main physical layer optical specifications is also given, ahead of final ITU-T approval.

Switching solutions for WDM-SDM optical networks

Abstract: Over the last few decades, network traffic has consistently grown at an exponential rate and was efficiently satisfied using WDM and more efficient coding schemes requiring coherent detection. There is no indication that the network traffic growth trend will cease anytime soon, and we are nearing the day when the capacity of the ubiquitous single-mode fiber will be fully exploited. Space-domain multiplexing (SDM) for high-capacity transmission is the promising solution with the scaling potential to meet future capacity demands. However, there is still a large technological gap between current WDM optical communication system designs and SDM network implementations. In this article we lay the foundation of switching node designs for future WDM-SDM optical networks.

Spectrally and spatially flexible optical network planning and operations

Abstract: 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.

Cellular Underwater Wireless Optical CDMA Network: Performance Analysis and Implementation Concepts

Abstract: In this paper, we introduce and investigate a cellular underwater wireless optical code division multiple-access (OCDMA) network based on optical orthogonal codes (OOC). The structures, principles, and performance of the underwater wireless OCDMA network in various water types are presented. Since underwater wireless optical links are considered for high-bandwidth underwater communications at short ranges, we will place a set of optical base transceiver stations (OBTS) each in the center of a hexagonal cell to cover a larger underwater area. The OBTSs are connected via fiber optic to an optical network controller (ONC) which operates as the core of the network. An integral expression for system error probability is obtained for both uplink and downlink schemes under a specific channel model expressed in this paper, among many channel models in underwater optical communication systems. Furthermore, an experimental prototype of underwater an OCDMA system including the OBTS, ONC, transmitters, and receivers are implemented using field programmable gate arrays (FPGA).

Baseband unit cloud interconnection enabled by flexible grid optical networks with software defined elasticity

Abstract: The evolution toward 5G mobile networks is characterized by supporting higher data rate, excellent end-to-end performance and ubiquitous user-coverage with lower latency, power consumption, and cost. To support this, the RANs are evolving in two important aspects. One aspect is “cloudification,” which is to pool baseband units to be centralized for statistical multiplexing gain. The other aspect is to use advanced optical technologies for digital and analog signal transmission in a cloud-based RAN. In this article, we focus on BBU cloud interconnection with optical layer technologies. Flexible grid optical networks with the enabling technologies are introduced to provide elastic, transparent, and virtualized optical paths between the BBU pools. To improve the elasticity and intelligence of C-RAN, we propose a software defined centralized control plane to coordinate heterogeneous resources from three domains: the BBU domain, radio domain, and optical domain. We report an experimental demonstration of elastic lightpath provision for cloud radio-over-flexible grid optical networks in a software-defined-networking-based testbed.

Advanced modulation formats for 400-Gbps short-reach optical inter-connection

Abstract: Besides the long-haul optical networks covering over thousands of kilometers for backbone transmission, short reach optical networks (SR-ONs) are widely deployed in metro-area for aggregation and accessing. The SR-ONs include the metro optical transport networks (Metro-OTN), optical access networks or other optical inter-connection systems with even shorter distance. As predicted, the growing bandwidth demanding from SR-ONs will be much more than that from the long-haul optical networks in the near future. Besides, there are tremendous amounts of optical terminals and end-users in SR-ONs compared with the long-haul transmission systems and thus will induce large cost and huge energy consumption. So, the power and cost efficiency should be the key consideration for SR-ONs besides the transmission performance. To improve the power and cost efficiency in SR-ONs, advanced modulations and detection techniques based on low power, low cost and integrated optical modulators should be utilized. In this paper, different advanced modulation formats have been discussed. 56Gbps PAM4, 112Gbps poly-binary and 100Gbps DMT that can be used to realize 400-Gbps SR-ONs for different applications have also been demonstrated respectively. In addition, low-cost and low-power opto-electronic components suitable for SR-ONs, the impairments induced by all kinds of defects and bandwidth limitation of opto-electronic components and the corresponding compensation techniques based on DSP algorithms have also been discussed in the experiments.

CSO: cross stratum optimization for optical as a service

Abstract: Data center interconnection with elastic optical networks is a promising scenario to meet the high burstiness and high-bandwidth requirements of services. Many data center services require lower delay and higher availability with end-to-end guaranteed QoS, which involves both application and transport network resources. However, in the current mode of operation, the control of elastic optical networks and data centers is separately deployed. Enabling even limited interworking among these separated control systems requires the adoption of complex and inelastic interfaces among the various networks, and this solution is not efficient enough to provide the required QoS. In this article, we present a novel cross stratum optimization (CSO) architecture in elastic data center optical interconnection. The proposed architecture can allow global optimization and control across elastic optical transport network and data center application stratum heterogeneous resources to meet the QoS requirement with the objective of optical as a service (OaaS). The functional modules of CSO architecture, including the core elements of application and transport controllers, are described in detail. The cooperation procedure in CSO-based service provisioning and cross stratum service resilience modes is investigated. The overall feasibility and efficiency of the proposed architecture is also experimentally demonstrated on our OaaS testbed with four OpenFlow-enabled elastic optical nodes, and compared to MFA, ALB, and CSO-DGLB service provisioning schemes in terms of path setup/release/adjustment latency, blocking probability, and resource occupation rate. Numerical results are given and analyzed based on the testbed. Some future discussion and exploration issues are presented in the conclusion.

Optical interconnects at the top of the rack for energy-efficient data centers

Abstract: The growing popularity of cloud and multimedia services is dramatically increasing the traffic volume that each data center needs to handle. This is driving the demand for highly scalable, flexible, and energy-efficient networks inside data centers, in particular for the edge tier, which requires a large number of interconnects and consumes the dominant part of the overall power. Optical fiber communication is widely recognized as the highest energy- and cost-efficient technique to offer ultra-large capacity for telecommunication networks. It has also been considered as a promising transmission technology for future data center applications. Taking into account the characteristics of the traffic generated by the servers, such as locality, multicast, dynamicity, and burstiness, the emphasis of the research on data center networks has to be put on architectures that leverage optical transport to the greatest possible extent. However, no feasible solution based on optical switching is available so far for handling the data center traffic at the edge tier. Therefore, apart from conventional optical switching, we investigate a completely different paradigm, passive optical interconnects, and aim to explore the possibility for optical interconnects at the top of the rack. In this article, we present three major types of passive optical interconnects and carry out a performance assessment with respect to the ability to host data center traffic, scalability, optical power budget, complexity of the required interface, cost, and energy consumption. Our results have verified that the investigated passive optical interconnects can achieve a significant reduction of power consumption and maintain cost at a similar level compared to its electronic counterpart. Furthermore, several research directions on passive optical interconnects have been pointed out for future green data centers.

Torus-Topology Data Center Network Based on Optical Packet/Agile Circuit Switching with Intelligent Flow Management

Abstract: We review our work on an intra-data center (DC) network based on co-deployment of optical packet switching (OPS) and optical circuit switching (OCS), conducted within the framework of a five-year-long national R&D program in Japan (∼March 2016). For the starter, preceding works relevant to optical switching technologies in intra-DC networks are briefly reviewed. Next, we present the architecture of our torus-topology OPS and agile OCS intra-DC network, together with a new flow management concept, where instantaneous optical path on-demand, so-called Express Path is established. Then, our hybrid optoelectronic packet router (HOPR), which handles 100 Gbps (25 Gbps × 4-wavelength) optical packets and its enabling device and sub-system technologies are presented. The HOPR aims at a high energy-efficiency of 0.09 [W/Gbps] and low-latency of 100 ns regime. Next, we provide the contention resolution strategies in the OPS and agile OCS network and present the performance analysis with the simulation results. It is followed by the discussions on the power consumption of intra-DC networks. We compare the power consumption and the throughput of a conventional fat-tree topology with the N -dimensional torus topology. Finally, for further power saving, we propose a new scheme, which shuts off HOPR buffers according to the server operation status.

Joint defragmentation of optical spectrum and IT resources in elastic optical datacenter interconnections

Abstract: With its agile spectrum management in the optical layer, the flexible-grid elastic optical network can become a promising physical infrastructure to efficiently support the highly dynamic traffic in future datacenter interconnections (DCIs). While the resulting elastic optical DCIs (EO-DCIs) need to serve requests that not only require bandwidth resources on fiber links but also require multidimensional IT resources in the DCs, multidimensional resource fragmentation can occur during dynamic network operations and deteriorate the network performance. To address this issue, this paper investigates the problem of joint defragmentation (DF) for the spectrum and IT resources in EO-DCIs. Specifically, we reoptimize the allocations of multidimensional resources jointly with complexity-controlled network reconfigurations. For the DFoperation, we first study the request selection process and propose a joint selection strategy that can perform the spectrum- and IT-oriented selections adaptively according to the network status. Then, we formulate a mixed integer linear programming model and design several heuristics to tackle the problem of network reconfiguration in the joint DF. The proposed algorithms are evaluated with extensive simulations. Simulation results demonstrate that the proposed joint DF algorithms can significantly reduce the blocking probability in EO-DCIs by consolidating the spectrum and IT resource usages effectively.

3D elastic optical networking in the temporal, spectral, and spatial domains

Abstract: 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.

Heterogeneous space-division multiplexing and joint wavelength switching demonstration

Abstract: We demonstrate a six spatial-mode, wavelength-routing network interoperable with few-mode, coupled-multi-core, and single-mode fiber spans using a custom 57-port wavelength-selective switch configured for joint-switching of spatial-superchannels.

Security-Enhanced OFDM-PON Using Hybrid Chaotic System

Abstract: A dual-field encryption scheme of an orthogonal frequency division multiplexing passive optical network (OFDM-PON) is proposed based on analog–digital hybrid chaotic system. In our scheme, the downstream data are encrypted in optical field, and the upstream data are encrypted in electrical field. The hybrid chaotic system circumvents the security vulnerabilities of both analog and digital chaos, e.g., the periodicity of digital chaos is masked by the analog one, and the time delay signature of the analog system is concealed by injecting digital chaos. Meanwhile, the key space dimension of the system is enlarged. Simulation results show both the feasibility and security of the proposed OFDM-PON system.

Transport Network Orchestration for End-to-End Multilayer Provisioning Across Heterogeneous SDN/OpenFlow and GMPLS/PCE Control Domains

Abstract: A multidomain optical transport network composed of heterogeneous optical transport technologies (e.g., flexi/fixed-grid optical circuit switching and optical packet switching) and control plane technologies (e.g., centralized OpenFlow or distributed GMPLS) does not naturally interoperate, and a network orchestration mechanism is required. A network orchestrator allows the composition of end-to-end network service provisioning across multidomain optical networks comprising different transport and control plane technologies. Software-defined networking (SDN) is a key technology to address this requirement, since the separation of control and data planes makes the SDN a suitable candidate for end-to-end provisioning service orchestration across multiple domains with heterogeneous control and transport technologies. This paper presents two different network orchestration's architectures based on the application-based network operations (ABNO) which is being defined by IETF based on standard building blocks. Then, we experimentally assesses in the international testbed of the STRAUSS project, an ABNO-based network orchestrator for end-to-end multi-layer (OPS and Flexi-grid OCS) and multidomain provisioning across heterogeneous control domains (SDN/OpenFlow and GMPLS/Stateful PCE) employing dynamic domain abstraction based on virtual node aggregation.

Protection in elastic optical networks

Abstract: In this article, we analyze gains resulting from the use of EON architectures with special focus on transportation of cloud-ready and content-oriented traffic in the context of network resilience. EONs are a promising approach for future optical transport networks and, apart from improving the network spectral efficiency, bring such new capabilities as squeezed protection, which reduces resource requirements in failure scenarios. In the introductory part, we present a background on new network services based on cloud computing and content orientation paradigms, EON architectures, and their survivability mechanisms. Next, we show the impact of disasters on EON performance. To support the discussion, in the evaluation part we provide simulation results to compare survivable EONs and wavelength-switching optical networks, estimate the efficiency of different survivable EON schemes supporting cloud- and content-oriented traffic, and assess the robustness of EONs to disasters.

Rethinking Optical Transport to Pave the Way for 5G and the Networked Society

Abstract: The fifth generation of mobile networks (5G) is the next major phase of mobile telecommunications, which will provide the foundation for the Networked Society. To support 5G, transport will need to cater for a wide range of service requirements. It will need to support emerging 5G radio systems in terms of higher capacity and increasing number of cell sites. It must also cater for increasing need for radio interference coordination between sites as well as cost effective radio access network deployment models, and provide a flexible platform for sharing of resources where different actors through transport application programming interfaces have access to network resources and diverse transport services. In this paper, we summarize the key defining factors for 5G transport and outline a concept for programmable transport based on WDM and exploiting emerging optical devices enabled by integrated photonics.

Time-division-multiplexed few-mode passive optical network.

Abstract: We demonstrate the first few-mode-fiber based passive optical network, effectively utilizing mode multiplexing to eliminate combining loss for upstream traffic. Error-free performance has been achieved for 20-km low-crosstalk 3-mode transmission in a commercial GPON system carrying live Ethernet traffic. The alternative approach of low modal group delay is also analyzed with simulation results over 10 modes.

Transmission media for an SDM-based optical communication system

Abstract: Space-division multiplexing technology is an attractive candidate for overcoming a potential future “capacity crunch” in optical networks based on conventional single-mode fiber. Transmission media for SDM optical communication systems can be designed based on both single-and multi-core concepts. This article investigates the potential of various SDM transmission media.

Next-generation optical access networks for C-RAN

Abstract: This paper reviews the required specifications to optical fronthaul links for C-RAN and presents key technologies of optical transmissions and a CPRI data compression for next-generation optical access networks.

Reconfigurable 100 Gb/s silicon photonic network-on-chip [invited]

Abstract: Optical interconnects have the potential to realize a scalable intra- and inter-chip communication infrastructure. They can meet the large bandwidth capacity and stringent latency requirements in a power-efficient fashion. Integration of photonics on silicon provides a path to a low-cost and highly scalable platform for this application. Here, we report an intra-chip 10 × 10 Gb/s optical link based on a large-scale silicon photonic integrated circuit with 72 functional elements. Furthermore, the optical circuit is reconfigurable as a 10 × 10 switch or a broadcasting network. This demonstration verifies the feasibility of implementing a compact high-capacity wavelength division multiplexing interconnect on a chip, which also enables many new advanced optic network functionalities on a chip scale.

Constrained interleaving for 5G wireless and optical transport networks

Abstract: The present invention provides a design framework that is used to develop new types of constrained turbo block convolutional (CTBC) codes that have higher performance than was previously attainable. The design framework is applied to design both random and deterministic constrained interleavers. Vectorizable deterministic constrained interleavers are developed and used to design parallel architectures for real time SISO decoding of CTBC codes. A new signal mapping technique called constrained interleaved coded modulation (CICM) is also developed. CICM is then used to develop rate matching, spatial modulation, and MIMO modulation subsystems to be used with CTBC codes and other types of codes. By way of example, embodiments are primarily provided for improved 5G LTE and optical transport network (OTN) communication systems.

SDN-Based Network Orchestration of Variable-Capacity Optical Packet Switching Network Over Programmable Flexi-Grid Elastic Optical Path Network

Abstract: A multidomain and multitechnology optical network orchestration is demonstrated in an international testbed located in Japan, the U.K., and Spain. The application-based network operations architecture is proposed as a carrier software-defined network solution for provisioning end-to-end optical transport services through a multidomain multitechnology network scenario, consisting of a 46–108 Gb/s variable-capacity OpenFlow-capable optical packet switching network and a programmable, flexi-grid elastic optical path network.

DC-biased optical OFDM for IM/DD passive optical network systems

Abstract: In the context of access networks, orthogonal frequency division multiplexing (OFDM) has been extensively studied for fiber-based optical communications. A DC-biased optical OFDM (DCO-OFDM) scheme (where no real constellation or Hermitian symmetry constraint is used), is proposed and explored for the first time, to the best of our knowledge, in an intensity modulated and direct detected (IM/DD) passive optical network (PON). In this paper, an analysis of the peak-to-average-power ratio and a discussion of the algorithm complexity are investigated. By means of numerical simulation in 12 Gb/s next-generation (NG)-PON1 OFDM with a split ratio of 1:64 users and 35 km reach, the new DCO-OFDM method is shown to achieve the same performance as the well-known conventional DCO-OFDM but with less computational complexity (gain of almost 54.3% on the required operations per bit). As a result, the new DCO-OFDM seems very interesting and a good candidate for NG-PON cost-sensitive applications, considering the implementation of real-time demonstrators including digital modulators and demodulators based on digital signal processing or a field-programmable gate array (FPGA).

OPMDC: Architecture Design and Implementation of a New Optical Pyramid Data Center Network

Abstract: In this paper, we propose a novel optical pyramid data center network architecture (OPMDC), achieving scalable and high bandwidth, low latency, and reduced power consumption and wiring complexity. Based on an incremental and modular design, a full-scale OPMDC is built on three types of WSS-based optical switching nodes in three tiers. These optical nodes are recursively interconnected according to a pyramid structure parameterized by the number of nodes ( B ) at the base. Such a pyramid-based topology facilitates horizontal mesh connections that are tailored to achieve flexible optical packet-based transport. To this aim, we design a wavelength scheduling algorithm, called most-contentious-first, augmented with source and destination relay and aggregation (SDRA) via the horizontal mesh connections in the source and destination pods. Simulation results show that employing SDRA results in a vast improvement of throughput from 42.5% to 87.9% at full load, at a cost of no more than two additional hops of latency. Further, we present our OPMDC ( $B = 7$ ) prototype and provide performance assessment and the measurements of packet latency. Finally, experimental results show that after travelling the longest possible path with six optical nodes in OPMDC, the signal suffers no accumulated distortion and noise from the cascades of WSS and EDFA modules.

Introduction of spectrally and spatially flexible optical networks

Abstract: Given the introduction of coherent 100G systems has provided enough fiber capacity to meet data traffic growth in the near term, enhancing network efficiency will be service providers' high priority. Adding flexibility at the optical layer is a key step to increasing network efficiency, and both spectral and spatial functionality will be considered in next generation optical networks along with advanced network management to effectively harness the new capabilities.

AMO-FBMC for Asynchronous Heterogeneous Signal Integrated Optical Transmission

Abstract: Orthogonal frequency-division multiplexing (OFDM) is susceptible to multiple access interference and synchronization errors due to sidelobes, which hinder the integration of various applications and multiple access in OFDM-based optical transmission. In this letter, an adaptively modulated optical filter bank multicarrier with offset quadrature amplitude modulation-based sidelobe suppression is proposed in a wired/wireless converged optical network. We experimentally verified both the improvements in signal performance and spectral efficiency compared with OFDM in a multisender-supported optical network after a 50-km transmission.

Transport Network Function Virtualization

Abstract: In this paper, we present a network function virtualization (NFV) architecture to deploy different virtualized network functions (VNF) on an optical transport network. NFV concepts do not only apply to data plane functions (i.e., packet processing or forwarding), but also to control plane functions, such as path computation. First, we focus on the IT and network resources that are virtualized to provide the required VNFs. Second, we provide an example of VNF on top of the virtualized infrastructure, by proposing a path computation element (PCE) architecture to deploy a PCE by means of NFV. The instances of the virtualized PCE are deployed on demand, but they are perceived as a single-network element. We present the benefits of such approach by providing experimental validation.

Network planning strategies for next-generation flexible optical networks [invited]

Abstract: Using well-established results on nonlinear propagation modeling in coherent optical links, two different approaches for network planning are addressed and compared in terms of performance maximization and robustness to dynamic changes in the network, one based on maximization of the margin in the optical signal-to-noise ratio, the other on minimization of the pre-forward-error-correction bit error rate (BER). We show that, in pure coherent optical networks, the planning strategy that best supports the dynamic evolution of the network is the design aimed at BER minimization. A closed-form formula for the maximum reach (in terms of number of spans and loss budget) of each interface is analytically derived, which is a useful tool for the evaluation of the overall network cost for a desired traffic capacity.