Metro-access Network Research Articles

Photonic WDM switches architecture for multi-band optical networks

Addressing the capacity, low cost, and low power challenges of 6G distribution networks, this paper proposes and demonstrates a multi-band optical metro-access network architecture employing semiconductor optical amplifier (SOA)-based wavelength division multiplexing (WDM) switches as low-cost and low-power multi-band optical add-drop multiplexers (MB-OADMs) to extend the capacity beyond C-band limits. We implemented and evaluated the performance of an SOA-based MB-OADM prototype in the C- and O-bands including the network reconfigurability, the node scalability, and the capability to support high-capacity transmission. Experimental results show that the MB-OADM-based network maintains high optical signal-to-noise ratio (OSNR) values up to 35.38 dB in the C-band and 33.56 dB in the O-band over 100 km across five nodes with a 20 km linkspan in between (a total of 100 km) without additional optical amplifiers at 25 Gbps. This work also assesses the MB-OADM-based network scalability in terms of nodes and data rate. Results indicated that the architecture supports cascading through nine C-band nodes over 45 km with a 3.6 dB power penalty at 25 Gbps for a bit error rate (BER) of 10−6 and through four O-band nodes with a 3 dB penalty at 25 Gbps for a BER of 10−6, maintaining nearly uniform power levels across channels at a BER under the FEC threshold. It successfully demonstrates PAM-4 at 50 Gbps and 100 Gbps data rate transmission operation crossing four nodes over a 4 km distance, with 2 dB and 2.4 dB power penalty at a BER of 10−3 in the C-band and 1.85 dB and 2.2 dB power penalty at a BER of 10−3 in the O-band, respectively.

Architecture for low-cost and highly flexible metro-access networks using SOA-based OADM nodes and digital subcarrier multiplexing with power loading.

Metro-access networks exploiting wavelength division multiplexing (WDM) to cope with the ever-growing bandwidth demands are sensitive to cost and need to be fast-configurable to meet the requirements of many new network services. Optical add-drop multiplexers (OADMs) are a key component in enabling fast dynamic wavelength allocation and optimization. In this Letter, we propose and demonstrate, to our knowledge, a novel architecture for high-performance metro-access networks that utilizes semiconductor optical amplifier (SOA)-based OADM nodes, digital subcarrier multiplexing (DSCM), low-cost direct detection receivers, and power loading techniques, which makes the designed metro-access network cost-effective, fast reconfigurable, and flexible for bandwidth allocation on demand. Through a proof-of-concept experiment, we have successfully demonstrated a prototype horseshoe optical network consisting of up to four SOA-based OADM nodes at 40 Gb/s per wavelength channel by leveraging the proposed scheme. The flexible bandwidth allocation and dynamic add and drop operations have also been achieved in an emulated WDM optical network. All results indicate the great scalability and flexibility of the proposed architecture.

A High-Capacity Optical Metro Access Network: Efficiently Recovering Fiber Failures with Robust Switching and Centralized Optical Line Terminal.

This study proposes and presents a new central office (CO) for the optical metro access network (OMAN) with an affordable and distinctive switching system. The CO's foundation is built upon a novel optical multicarrier (OMC) generation technique. This technique provides numerous frequency carriers that are characterized by a high tone-to-noise ratio (TNR) of 40 dB and minimal amplitude excursions. The purpose is to accommodate multiple users at the optical network unit side in the optical metropolitan area network (OMAN). The OMC generation is achieved through a cascaded configuration involving a single phase and two Mach Zehnder modulators without incorporating optical or electrical amplifiers or filters. The proposed OMC is installed in the CO of the OMAN to support the 1.2 Tbps downlink and 600 Gbps uplink transmission, with practical bit error rate (BER) ranges from 10-3 to 10-13 for the downlink and 10-6 to 10-14 for the uplink transmission. Furthermore, in the OMAN's context, optical fiber failure is a main issue. Therefore, we have proposed a possible solution for ensuring uninterrupted communication without any disturbance in various scenarios of main optical fiber failures. This demonstrates how this novel CO can rapidly recover transmission failures through robust switching a and centralized OLT. The proposed system is intended to provide users with a reliable and affordable service while maintaining high-quality transmission rates.

Performance assessment of multiband OADM in metro-access network for converged Xhaul traffic

Performance assessment of multiband OADM in metro-access network for converged Xhaul traffic

Efficient optical fiber communication in the metro access domain based on an optical multicarrier source

AbstractThis paper proposes an efficient optical fiber communication scheme for an optical metro access network (OMAN) based on an optical multicarrier (OMC) generator. The central office (CO)'s foundation is a novel, cost‐effective OMC‐generating technique. The OMC is designed from a pulsed laser source and three cascaded electro‐optic modulators (EOMs) driven by an amplified RF source of 20 GHz signal that has generated more than 60 frequencies with excellent tone‐to‐noise ratio (TNR) ~ 40 dB and amplitude excursions from zero to 3 dB. The conventional CO is replaced with a cost‐effective OMC‐based source with an effective switching mechanism, which is necessary and equally important to be handled reliably. The downstream data of 20 Gbps per carrier is transmitted using a duo‐binary coding scheme. Six remote nodes (RNs) supported by the suggested OMC source, at each RN 10 optical network units (ONUs), can be deployed having distance laps of 5 km between the RNs, the distance between the RNs and the ONUs is kept at 2 km, the ONUs were tested w.r.t the bit error rate (BER) and the power penalties for the proposed transmissions. The BER for different fiber lengths from 5 to 25 km at various RNs and ONUs ranges were calculated and demonstrated from 1e−3 to 1e−13, showing the feasibility of the proposed OMAN.

Optimal design of cost-effective OXC and ROADM nodes to maximize the throughput of mesh-based u-DWDM metro-access networks

Optimal design of cost-effective OXC and ROADM nodes to maximize the throughput of mesh-based u-DWDM metro-access networks

Reconfigurable photonic integrated transmitter for metro-access networks

A reconfigurable photonic integrated transmitter, enabling dynamic resource allocation in the metro-access network, is proposed. The device consists of a multicarrier sliceable bandwidth variable transmitter (MC-SBVT) realized in indium phosphide and a silicon-nitride-based optical cross-connect (OXC). The proposed architecture delivers full flexibility in terms of the choice of data format/bandwidth, channel spacing, and wavelength assignment. The functional design of the MC-SBVT and OXC as well as their practical realization are discussed. Preliminary characterization results of the photonic-integrated-circuit-based MC-SBVT, demonstrating the reconfigurability of the device, are also presented.

Precise path computation based on functional block-based disaggregation for future heterogeneous access-metro networks

Emerging 5G/6G mobile services are intended to cover a broad range of use cases, including applications requiring high bandwidth, low latency, and/or high reliability. To meet these diverse requirements, various optical network technologies and architectures, including optical node structures, transmission technologies, and virtualization technologies, have been extensively investigated. These novel technologies will be integrated to form a platform of future optical access-metro networks that support various mobile services. Such an optical access-metro platform will comprise heterogeneous node structures based on various optical functional blocks (e.g., wavelength selective switches, optical splitters, or arrayed waveguide gratings). To realize a versatile optical access-metro platform, a network resource management system that can universally handle heterogeneous node structures is indispensable. This study investigates the applicability of a functional block-based disaggregation (FBD) approach to such a resource-management system. Here, the previously proposed FBD model is extended to incorporate latency aware path computation. The results demonstrated that the FBD model could be successfully used with heterogeneous network structures, including both passive and switchable optical nodes. The precise path computation capability of the model was also demonstrated, and the scalability of the computation time was quantitatively evaluated in a parallel processing environment. Precise path computation can effectively consider both intra- and inter-node fiber connection lengths, which are useful for handling latency requirements based on an accurate representation of the propagation delay.

Disaggregation for Energy Efficient Fog in Future 6G Networks

We study the benefits of adopting server disaggregation in the fog computing tier by evaluating energy efficient placement of interactive apps in a future (6G) fog network. Using a mixed integer linear programming (MILP) model, we compare the adoption of traditional server (TS) and disaggregated server (DS) architectures in a fog network that comprises selected fog sites. We also propose a heuristic for energy efficient and delay aware placement of interactive fog apps in a fog network which effectively mimics the MILP model formulated in this paper. Compared to a non-federated fog computing layer, federation of selected fog computing sites over the metro-access network enables significant reductions of the total fog computing power consumption (TFPC). Relative to the use of TSs in the fog network, the adoption of DSs improves the energy efficiency of the fog network and enables up to 18% reduction in TFPC. To minimize response time, more instances of interactive fog apps are provisioned in a fog network that is implemented over a network topology with high delay penalty. Our result also shows that the proximity of metro-central offices and radio cell sites to geo-distributed users makes them important fog sites for provisioning delay-sensitive fog applications.

Experimental Assessment of Automatic Optical Metro Edge Computing Network for Beyond 5G Applications and Network Service Composition

The upcoming 5G and beyond 5G heterogeneous applications with different quality of service (QoS) will impose strict latency, bandwidth, and flexibility requirements on optical metro access networks. Conventional cloud computing is gradually unable to fulfill the application requirements, especially on latency due to the distance causing propagation and networking delay. Therefore, the edge computing that distributed in metro access networks is promising to serve the applications with the requirements of ultra-low latency. As the resources of edge computing nodes are restricted and light compared with cloud data centers (DC), it is significant to manage across multiple edge computing nodes to enable joint allocation of the distributed resources. To address this issue, the optical metro network infrastructure should be flexible on the data plane and able to interact with the control and orchestration plane to automatically adapt to the communication requirements of multiple edge computing nodes. Related works have been focused on the simulation and numerical study. In this paper, an experimental testbed of a flexible optical metro access network including hardware and software components is built, and the performance is validated with real server traffic. The presented network system is based on the field-programmable gate array (FPGA), and hardware adapted open source network management and telemetry tools. Different from the commercial electrical switches, FPGA is fully programmable making it able to flexibly forward and monitor the traffic, in the meantime, to dynamically control the optical devices according to the feedback from the control plane. By exploiting dynamic software defined networking (SDN) control and network service orchestration, the proposed network is able to establish capacity adapted network slices for edge computing connections. Successful telemetry-assisted dynamic network service chain (NSC) generation, automatic bandwidth resources assignment, and QoS protection are demonstrated.

Retraction Note to: Power Budget Analysis of an Ultra-Dense Coherent MB-OFDM WDM Metro-Access Networks

The power budget (PB) of an ultra-dense wavelength division multiplexing virtual-carrier helped coherent-detection multi-band orthogonal frequency division which multiplexes metro-access network with 10.7 Gb/s per client and per band, with groups divided by 3.125 GHz, is surveyed numerically, for channel spacings of 12.5 GHz and 25 GHz. In the light of the findings, the PB ranges between 14.8 and 20.5 dB. It was found that the minimum PB, on one hand, enables an optical distribution network (ODN) splitting ratio of 16 with standard single mode fiber (SSMF) reach of 13 km. The maximum PB, on the other hand, enables an ODN splitting ratio of 64 with SSMF reach of 12 km.

Highly Reliable Metro-Access Network Based on a Dual-Fiber Ring Architecture and Optimized Protection Mechanisms

Network reliability is very important for the next generation of optical networks. In this paper, a highly reliable protection mechanism, which integrates the approaches of optical protection and microwave protection, is proposed for metro-access optical networks based on the wavelength division multiplexing (WDM) technique. By designing a scheme for the convergence of optical and wireless access and cooperating with designed remote nodes (RNs), not only can access for both wired and wireless service be provided simultaneously in each optical network unit (ONU) but also microwave protection can be realized when a failure occurs in a distribution segment. By developing a novel optical switch module (OSM) to cooperate with the dual-fiber ring structure, flexible switching can be achieved to protect against multiple types of failures in the feeder segment, including single-fiber faults, dual-fiber faults and multifiber faults. Based on the above structure, the influence of Rayleigh backscattering (RB) noise can be mitigated when the network is operating under all operating scenarios except for an inner-fiber fault. To further mitigate the influence of noise, optimization for upstream transmission performance is implemented by configuring a reflective semiconductor optical amplifier (RSOA). Furthermore, the feasibility of the overall scheme is verified through experiments and simulations under different operating conditions. The results show that the proposed mechanisms can achieve acceptable bit error rate performance and quality of service (QoS) metrics while also offering various advantages, including high reliability, large scale, and a relatively low cost.

Lossless Photonic Integrated Add-Drop Switch Node for Metro-Access Networks

We assess the performance of a modular photonic integrated circuit (PIC) for space and time optical switching as an optical add-drop node for metro-access network applications. The PIC based on semiconductor optical amplifier (SOA) technology enables the implementation of compact, low cost and lossless add-dropping through fast optical switching. Data integrity measurements demonstrate error-free switching operation with less than 1 dB and 2.5 dB power penalty for 10 Gb/s and 40 Gb/s NRZ OOK optical signal, respectively. The dynamic control of the SOA based optical gates by the switch controller permits the power equalization of the switched channels. The experimental results also demonstrate dynamic forwarding, dropping and multicasting operation for a packetized 10 Gb/s NRZ OOK optical signal. The transparency of the SOA technology towards the optical signal’s data rate allows to avoid costly and power consuming dedicated interfaces at the add-drop node and open a path towards efficient statistical multiplexing.

Performance assessment of a fast optical add-drop multiplexer-based metro access network with edge computing

Next-generation metro access nodes with edge computing need to be redesigned to co-allocate advanced optical technologies, computing, and storage resources to support the upcoming multiple applications in 5G. In this paper, we present a novel metro access edge computing node based on a fast optical add-drop multiplexer with submicrosecond reconfiguration and control for low-latency operation. We investigate the network performance, the location of the edge computing nodes, and the computing resources dimensioning and utilization in order to fulfill the stringent latency requirement in 5G networks. Network function virtualization and network slicing have been considered in the model to emulate the realistic network operation. Optimization of the network, node location, and computing resources in terms of latency and packet loss ratio is numerically investigated via the OMNeT++ simulator under three different types of 5G applications (Massive Internet of Things, content delivery network, and loss-sensitive traffic). Considering a typical metro access network topology with 20 nodes covering a population of around 1 million, numerical results show that less than 200 µs latency is guaranteed for 5G network applications by deploying more than 6 edge computing nodes with 80 servers for each node.

Three-dimensional grid architecture supporting discretionary direct communication among optical network units in metro-access networks

In this paper, a three-dimensional grid architecture supporting discretionary direct communication among optical network units (ONUs) is proposed. By setting up one $N \times N\hspace{3pt}$N×N arrayed waveguide grating (AWG) and two coarse wavelength division multiplexers in the remote node (RN), the optimal path selection of discretionary direct communication among ONUs can be carried out. At the same time, the construction of the RN is simple. By combining with a three-band wavelength allocation, downstream and upstream signals as well as direct-communication signals can be simultaneously transmitted. By utilizing a four-level protection mechanism, three kinds of optical fiber fault protection (i.e., feeder fiber fault protection, distribution fiber fault protection, and interconnecting fiber fault protection) can be achieved. Besides, both the scalability and the reliability of the network can be greatly improved. Finally, the feasibility of the proposed architecture is demonstrated by the simulation experiment.

RETRACTED ARTICLE: Power Budget Analysis of an Ultra-Dense Coherent MB-OFDM WDM Metro-Access Networks

The power budget (PB) of an ultra-dense wavelength division multiplexing virtual-carrier helped coherent-detection multi-band orthogonal frequency division which multiplexes metro-access network with 10.7 Gb/s per client and per band, with groups divided by 3.125 GHz, is surveyed numerically, for channel spacings of 12.5 GHz and 25 GHz. In the light of the findings, the PB ranges between 14.8 and 20.5 dB. It was found that the minimum PB, on one hand, enables an optical distribution network (ODN) splitting ratio of 16 with standard single mode fiber (SSMF) reach of 13 km. The maximum PB, on the other hand, enables an ODN splitting ratio of 64 with SSMF reach of 12 km.

Moving the Network to the Cloud: The Cloud Central Office Revolution and Its Implications for the Optical Layer

SDN and NFV have recently changed the way we operate networks. By decoupling control and data plane operations and virtualising their components, they have opened up new frontiers towards reducing network ownership costs and improving usability and efficiency. Recently, their applicability has moved towards public telecommunications networks, with concepts such as the cloud-CO that have pioneered its use in access and metro networks: an idea that has quickly attracted the interest of network operators. By merging mobile, residential and enterprise services into a common framework, built around commoditised data centre types of architectures, future embodiments of this CO virtualisation concept could achieve significant capital and operational cost savings, while providing customised network experience to high-capacity and low-latency future applications. This tutorial provides an overview of the various frameworks and architectures outlining current network disaggregation trends that are leading to the virtualisation/cloudification of central offices. It also provides insight on the virtualisation of the access-metro network, showcasing new software functionalities like the virtual \ac{DBA} mechanisms for \acp{PON}. In addition, we explore how it can bring together different network technologies to enable convergence of mobile and optical access networks and pave the way for the integration of disaggregated ROADM networks. Finally, this paper discusses some of the open challenges towards the realisation of networks capable of delivering guaranteed performance, while sharing resources across multiple operators and services.

Dual-Fiber-Ring Architecture Supporting Discretionary Peer-to-Peer Intra-Communication and Bidirectional Inter-communication in Metro-Access Network

Direct communication among optical network units (ONUs) is very significant for next-generation optical networks. In this paper, a metro-access optical network architecture supporting intra-communication and inter-communication is proposed based on dual-fiber ring topology. By adopting two tunable fiber Bragg gratings and one arrayed waveguide grating in the remote node, direct peer-to-peer communication of ONUs can be achieved. By designing the architecture to provide inter-communication in two opposite transmission directions, not only the efficiency and flexibility of inter-communication can be guaranteed depending on the shortest transmission path, but also the inter-communication can be supported even if a dual-fiber fault occurs. By allocating three wavelengths to one ONU, not only the intra-communication and inter-communication for one ONU can be carried out simultaneously, but also the inter-communication for different ONUs can be realized simultaneously. By using a dual-fiber ring structure, both the scale and the reliability can be improved. Because the network capacity and scale are relatively large, the relative construction-and-maintenance cost of the network is low. The availability of the proposal can be verified via the performance analyses and the simulations.

A Review of DSP-Based Enabling Technologies for Cloud Access Networks

Optical access networks, metro networks and mobile data networks are facing rapidly evolving demands, not only is it essential to satisfy the unyielding need for increased user bandwidths, but future networks must also support the growing wide variation in traffic dynamics and characteristics, due to various emerging technologies, such as cloud-based services, the Internet-of-Things (IoT) and 5G mobile systems, and due to growing trends, such as the proliferation of mobile devices and the rapidly increasing popularity of video-on-demand services. To be cost-effective and commercially sustainable, future optical networks must offer features, such as, dynamic reconfigurability, highly efficient use of network resources, elastic bandwidth provisioning with fine granularity, network sliceabilty and software defined networking (SDN). To meet these requirements Cloud Access Networks (CANs) are proposed which require a number of flexible, adaptive and reconfigurable networking elements. By exploiting digital signal processing (DSP) we have proposed a digital orthogonal filter-based multiplexing technique to implement CANs with multiplexed, independent optical channels at the wavelength, sub-wavelength, and orthogonal sub-band levels. This paper reviews the overall CAN concept, the operating principles of the various CAN network elements and presents an overview of the research work we have undertaken in order to validate the feasibility of the proposed technologies which includes real-time DSP-based demonstrations.

Group protection and LAN service scheme utilizing flexible modularization and high efficiency for metro‐access network

SummaryIn this paper, a reliable scheme based on star topology is proposed by introducing group protection. Depending on interconnecting fibers, all optical network units (ONUs) are divided into some groups and each group contains 2 ONUs. Through these groups, the network can not only realize efficient transmission of local area network service between adjacent ONUs but also provide mutual protection for ONUs in a group when distribution fibers happen to faults. By using the backup pathway, the network can further provide protections for feeder fibers when they fall in faults. With the help of the optical tunable receiver in ONU, dynamic bandwidth allocation algorithm is also supported to realize flexible bandwidth allocation in 1 group. By the subtly design, the network can realize passivity (there are no active devices in remote nodes), modularization, and scalability. By utilizing amplitude modulation, differential phase shift keying modulation and reflective semiconductor optical amplifier technology, wavelength triple reuse is also achieved. Finally, the results of simulation and performance analysis demonstrate the feasibility of the architecture.