Metro-access Optical Network Research Articles

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.

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.

Fair Resource Allocation Based on User Satisfaction in Multi-OLT Virtual Passive Optical Network

In this paper, a fair resource allocation mechanism based on user satisfaction in multiple optical line terminal (multi-OLT) virtual passive optical network (VPON) is proposed. By introducing user satisfaction functions, the satisfaction of users can be quantified. By presenting multi-OLT VPON in metro-access optical network (MAON), different priority services can be effectively handled separately. Based on user satisfaction, a fair resource allocation mechanism called double fair dynamic bandwidth allocation scheme (DFDBAS) is proposed. DFDBAS is a combination of two algorithms: wavelength fair allocation (WFA) algorithm and timeslot fair allocation (TFA) algorithm. In TFA algorithm, max-min fairness (MMF) algorithm is presented to allocate bandwidth for high priority service and Lagrange multiplier method is implemented to allocate bandwidth for low priority service. By implementing DFDBAS, not only user delay satisfaction can be improved, but also user bandwidth satisfaction can increase. By the simulation and analysis, the effectiveness of the proposed algorithms is demonstrated. Compared with modified limited service (LS) algorithm, DFDBAS makes both delay satisfaction and bandwidth satisfaction increase by at least 30% when the load is greater than 1.

Tg‐minimised bandwidth‐allocated scheme for multi‐subsystem‐based VPON in metro‐access optical network

Here, Tg-minimised bandwidth-allocated scheme is proposed for VPON supporting joint scheduling of multiple subsystems in metro-access optical network. To minimise guard time (Tg) in WDM-PON and TDM-PON, the Tg-transferred mechanism is introduced. To reduce the number of Tg in OFDM-PON, the subcarrier allocation algorithm based on the minimum number of Tg is proposed. To effectively utilise the network bandwidth resources, the bandwidth allocation based on matrix model is established. To increase the utilisation of wavelength, a dynamic-wavelength allocation mechanism is proposed. Finally, by the simulation, the effectiveness of Tg-minimised bandwidth-allocated scheme is demonstrated. Compared with other schemes, this scheme has at least 3% bandwidth utilisation improvement and lower average delay.

Proposal for an SDN-Like Innovative Metro-Access Optical Network Architecture

Today, telecommunication operators are facing an epochal challenge due to the need of higher reconfigurability, flexibility, and dynamicity for their networks. In the latest years, this necessity has been addressed by the introduction of Software-Defined Networking (SDN), mainly in the fields of data centers and core networks. The present work introduces a unified metro-access optical network architecture based on some features inspired by SDN models. The essential aim is to enable bandwidth shared among different passive optical networks (PONs) in order to achieve higher adaptability to increasingly migratory and volatile traffic patterns. Even if the present work is mainly focused on the architecture, several hints for specific implementation of the network nodes are detailed as well in order to demonstrate its feasibility. Several numerical simulations have been performed to assess the performance of the proposed solution both about physical effects and about quality of service. Bit error ratio degradation due to physical impairments has been evaluated and traffic congestion has been estimated in terms of burst loss probability and average throughput.

Grid Architecture of a Metro-Access Optical Network to Support Discretionary Peer-to-Peer Intracommunication and Intercommunication Between ONUs

Direct communication between optical network units (ONUs) is an important function in metro-access optical networks. In this paper, a grid architecture supporting the intracommunication and intercommunication between ONUs is proposed. By employing an arrayed waveguide grating (AWG) and coarse wavelength division multiplexer in a remote node, not only can the intracommunication between ONUs within one WDM passive optical network (PON) be realized, but the intercommunication between ONUs belonging to different WDM-PONs can also be supported. By allocating one specific wavelength to the ONU to transmit direct communication signals and utilizing the periodic assignment property of the AWG, discretionary peer-to-peer direct communication between ONUs can be achieved. By adopting a grid topology and expanding module, the network can not only realize multiple-fault protection but also carry out online expansion. Both the scalability and the reliability of the network can be improved. Finally, the performance analyses and the simulations verify the feasibility of the proposed architecture.

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.

Priority-based mode transformation algorithm in a multisystem-based virtual passive optical network

With the development of passive optical network, different standards will occur in the same network topology. Virtualization technology is a preferable solution for multi-standard coexistence. In this paper, priority-based mode transformation algorithm is proposed for cross-standard bandwidth management in multisystem-based virtual passive optical network (VPON) in metro-access optical network (MAON). It is aimed to improve the fairness between priority services as well as the utilization of network resources. According to service lever agreement (SLA), priority services are divided into three categories: Expedited Forwarding (EF), Assured Forwarding (AF) and Best Effort (BE). For the first time, a model transformation scenario that requires consideration of priority is analyzed. Under the model transformation scenario, multi-dimension 0/1 knapsack models of the priority-based mode transformation algorithm are established. By solving the model, an optimal combination of ONUs for mode transformation can be found. Finally, the simulation shows that the priority-based mode transformation algorithm and the single ONU mode transformation algorithm differ in the amount of each service’s transformation bandwidth. It further demonstrates the contribution of the proposed algorithm in fairness.

A novel WDM-MAN enabling cross-regional reconfiguration and comprehensive protection based on tangent-ring

Abstract A reconfigurable and reliable wavelength division multiplexing (WDM) metro-access optical network architecture is proposed in this paper. With the establishment of one optical transmitter in the optical network unit (ONU) and the reuse of optical distribution network, three kinds of reconfigurable WDM optical networks can be successfully built to achieve efficient inter and intra PON communication in the physical layer. With the adoption of multiple topologies based on single ring, four-level protections of feeder and distribution fibers can be achieved. With the creative design of flexible distribution node (FDN), the transmission wavelengths in the central office can be not only transmitted to the express ONUs connected straight with FDN, but also routed to the indirect ONUs hung in the remote node. Finally, large capacity, high reliability, low cost and great transmission performances at 10 Gbps and 2.5 Gbps data rate are obtained via analyses and simulation

Two-stage bandwidth-allocated algorithm for multi-subsystem-based VPON in metro-access optical network

In the metro-access optical network, a two-stage bandwidth-allocated algorithm is proposed for the multi-subsystem-based virtual passive optical network (VPON) that can achieve the syncretism of multiple systems such as time division multiplexing-PON, wavelength division multiplexing-PON and orthogonal frequency division multiplexing-PON. In this paper, the bandwidth is allocated in two stages. The first-stage allocation is designed to improve the admission probability of new VPONs by allocating bandwidth to all new VPONs followed by original VPONs. Meanwhile, to avoid the bandwidth being monopolized by the new VPONs, the bandwidth allocated to each VPON is no more than its guaranteed bandwidth. Therefore, the whole fairness can be guaranteed. The second-stage allocation is used to promote the bandwidth-utilized ratio by assigning the remaining bandwidth to VPONs whose demand is not fully met in the first stage. With the two-stage allocation, not only the admission probability can be improved, but also the bandwidth-utilized ratio can be promoted. MATLAB is used to evaluate the performance of proposed algorithm according to admission probability of new VPONs and bandwidth-utilized ratio.

Cost-effective ROADM design to maximize the Traffic Load Capacity of u-DWDM coherent metro-access networks

The current constant growing in traffic demands caused by the popularization of cloud services, mobile and social networks is requiring architectural changes at the underlying networks so as to provide a more highly dynamic connectivity. Cost-effective and energy efficient solutions are also required in flexible network subsystems in order to make available future sustainable networks. In this context, a novel cost-effective and energy-efficient solution DWDM ROADM (D-ROADM) node design has been recently considered to enable optical Metro-Access networks convergence. In this paper, we assess the D-ROADM capabilities in a dynamic ultra-Dense Wavelength Multiplexing (u-DWDM) coherent Ring Network scenario. In particular, the metric Blocking Bandwidth Probability (BBP) vs. Traffic Load Capacity (TLC) has been considered. Our numerical evaluations show that the performance penalty of cost-effective D-ROADM based networks could be reduced to 35% for 62.5 GHz DWDM channels when compared to WSS-based ROADMs.

A novel tangent-ring TWDM metro-access optical network featuring reconfiguration and reliability

In this paper, we propose a novel tangent-ring TWDM metro-access network providing flexible reconfiguration and high reliability. With the innovate design of flexible distribution node (FDN) and distributed control mechanism (DCM), three kinds of reconfigurable TWDM-PONs can be built to achieve efficient intra and inter ONU direct communication by reusing optical distribution network (ODN). In addition, three-level protections covering both feeder and distribution fibers are also separately supported by the use of optical switches and natural advantage of single-fiber tangent ring topology. Moreover, with the use of simplified RN* and ONU*, the proposed network can upgrade smoothly and achieve pay-as-you grow. The network capacity, OSNR, cost and transmission performances are also studied, which suggests that this network has a good performance.

Performance of highly connected photonic switching lossless metro-access optical networks

The present work analyzes the performance of photonic switching networks, optical packet switching (OPS) and optical burst switching (OBS), in mesh topology of different sizes and configurations. The “lossless” photonic switching node is based on a semiconductor optical amplifier, demonstrated and validated with experimental results on optical power gain, noise figure, and spectral range. The network performance was evaluated through computer simulations based on parameters such as average number of hops, optical packet loss fraction, and optical transport delay (Am). The combination of these elements leads to a consistent account of performance, in terms of network traffic and packet delivery for OPS and OBS metropolitan networks. Results show that a combination of highly connected mesh topologies having an ingress e-buffer present high efficiency and throughput, with very low packet loss and low latency, ensuring fast data delivery to the final receiver.

Allocation of spectral and spatial modes in multidimensional metro-access optical networks

Introduction of spatial division multiplexing (SDM) has added a new dimension in an effort to increase optical fiber channel capacity. At the same time, it can also be explored as an advanced optical networking tool. In this paper, we have investigated the resource allocation to end-users in multidimensional networking structure with plurality of spectral and spatial modes actively deployed in different networking segments. This presents a more comprehensive method as compared to the common practice where the segments of optical network are analyzed independently since the interaction between network hierarchies is included into consideration. We explored the possible transparency from the metro/core network to the optical access network, analyzed the potential bottlenecks from the network architecture perspective, and identified an optimized network structure. In our considerations, the viability of optical grooming through the entire hierarchical all-optical network is investigated by evaluating the effective utilization and spectral efficiency of the network architecture.

Cost-Effective DWDM ROADM Design for Flexible Sustainable Optical Metro–Access Networks

Architectural changes are required for the underlying networks to support the expected Internet data traffic volume growth caused by the popularization of cloud services, 5G-based services, and social networks, to provide a highly dynamic connectivity. Cost-effective and energy-efficient solutions for flexible network subsystems are required to provide future sustainable networks. In this paper, we present a cost-effective dense wavelength division multiplexing (DWDM) reconfigurable optical add/drop multiplexer (ROADM) design enabling optical metro–access networks convergence. The cost-effective DWDM ROADM capabilities also have been assessed in an ultradense wavelength multiplexing (u-DWDM) ring network scenario. In particular, achievable network throughput has been considered.

SOA Based Photonic Integrated WDM Cross-Connects for Optical Metro-Access Networks

We present a novel optical metro node architecture that exploits the Wavelength Division Multiplexing (WDM) optical cross-connect nodes for interconnecting network elements, as well as computing and storage resources. The photonic WDM cross-connect node based on semiconductor optical amplifiers (SOA) allows switching data signals in wavelength, space, and time for fully exploiting statistical multiplexing. The advantages of using an SOA to realize the WDM cross-connect switch in terms of transparency, switching speed, photonic integrated amplification for loss-less operation, and gain equalization are verified experimentally. The experimental assessment of a 4 × 4 photonic integrated WDM cross-connect confirmed the capability of the cross-connect chip to switch the WDM signal in space and wavelength. Experimental results show lossless operation, low cross-talk <−30 dB, and dynamically switch within few nanoseconds. Moreover, the operation of the cross-connect switch with multiple WDM channels and diverse modulation formats is also investigated and reported. Error-free operation with less than a 2 dB power penalty for a single channel, as well as WDM input operation, has been measured for multiple 10/20/40 Gb/s NRZ-OOK, 20 Gb/s PAM4, and data-rate adaptive DMT traffic. Compensation of the losses indicates that the modular architecture could scale to a larger number of ports.

A signal impairment-aware scheme for next-gen flexible spectrum in 10 Gb/s VCSEL metro-access optical fibre networks

We experimentally characterized and optimized link performance of a multi-node flexible spectrum network. The cheap and low power consuming and wavelength tunable vertical cavity surface-emitting lasers (VCSELs) have been used to create colourless and wavelength selective flexible transmitters to enable up to 10Gb/s per channel/wavelength signals. With a −3.8dBm VCSEL optical power and chromatic dispersion mitigation, a 25km multi-node network has been experimentally demonstrated with a transmission penalty range of 0.2–3.2dB. Moreover, an impairment-aware mathematical model has been created to predict signal continuity for crosstalk and dispersion penalties for a hop-to-hop signal transmission and a bit error-rate (BER) evaluation at the 10-9 threshold level. This study is vital for creating routing and network algorithms for the next-generation optical fibre networks.

Mode transformation and united control mechanism supporting wavelength division multiplexing Ethernet passive optical network and orthogonal frequency division multiplexing passive optical network in multi‐subsystem‐based virtual passive optical network

In this study, mode transformation and united control mechanism for multiple subsystems in metro-access optical network (MAON) are proposed to realise multi-subsystem-based virtual passive optical network. By combing the characteristics of multi-point control protocols (MPCPs) of wavelength division multiplexing Ethernet passive optical network (WDM-EPON) and orthogonal frequency division multiplexing passive optical network (OFDM-PON), a unified MPCP (U-MPCP) is proposed. Based on the U-MPCP, flexible control node and central node are constructed to achieve asynchronous unified control of multiple subsystems. By designing new control frames, the mode transformation between two subsystems (WDM-EPON and OFDM-PON) can be carried out. It can not only finish the flexible transformation of optical network unit's (ONU's) working modes but also make the MAON have the backward compatibility to the existing access technologies. By creating transformation algorithm of ONU's working modes, the transmission delay of over-load subsystem can be effectively reduced when ONU meets the condition of the mode transformation and finishes the transformation. Finally, by simulation, the effectiveness of the proposed scheme is demonstrated.

(Box-filling-model)-based ONU schedule algorithm and bandwidth-requirement-based ONU transfer mechanism for multi-subsystem-based VPONs’ management in metro-access optical network

Abstract ONU schedule algorithm and ONU transfer mechanism for multi-subsystem-based VPONs’ management is proposed in this paper. To avoid frequent wavelength switch and realize high system stability, ONU schedule algorithm is presented for wavelength allocation by introducing box-filling model. At the same time, judgement mechanism is designed to filter wavelength-increased request caused by slight bandwidth fluctuation of VPON. To share remained bandwidth among VPONs, ONU transfer mechanism is put forward according to flexible wavelength routing. To manage wavelength resource of entire network and wavelength requirement from VPONs, information-managed matrix model is constructed. Finally, the effectiveness of the proposed scheme is demonstrated by simulation and analysis.

GPON-and-EPON transmission based on multi-standard OLT management structure for VPON in metro-access optical network

Based on multi-standard OLT management structure, this paper realizes supporting GPON and EPON simultaneously in metro-access optical network. To adjust VPON structure dynamically, virtual access mechanism is established. To support two different standards, compatible multi-standard management structure for VPONs is proposed. It can also manage dynamic connection between ONU and OLT. To transmit GPON and EPON frames in the same wavelength, this paper proposes shared bandwidth algorithm to allocate bandwidth to GPON and EPON sub-networks fairly. This algorithm can prevent bandwidth monopoly from high load sub-network, when load of one sub-network is much higher than that of the other. To further balance QoS demands for ONUs, different class services will acquire bandwidth by priority. Finally, the simulation results demonstrate a good performance of the mechanism and algorithm.