Yumiko Senoo

Dynamic-load-balancing algorithm suppressing the number of wavelength reallocations for λ-tunable WDM/TDM-PON

We propose a dynamic-load-balancing algorithm that is derived using Jains fairness index. Simulation results show that the proposed algorithm can distribute traffic loads among PON-branches quite fairly with a very small number of wavelength reallocations compared with a round-robin approach.

512-ONU real-time dynamic load balancing with few wavelength reallocations in 40 Gbps λ-tunable WDM/TDM-PON [Invited]

The wavelength (λ)-tunable wavelength-division multiplexing/time-division multiplexing passive optical network (WDM/TDM-PON) can distribute traffic loads fairly by dynamically reallocating a certain number of optical network units (ONUs) from highly loaded optical subscriber units (OSUs) to lightly loaded OSUs. This reallocation can be executed by hitless λ-tuning. However, hitless λ-tuning causes delays or fluctuations in traffic. To reduce these penalties, the number of wavelength reallocations should be suppressed. Thus, we proposed a dynamic-load-balancing (DLB) algorithm that can distribute traffic loads among OSUs with few wavelength reallocations. However, no demonstration of the proposed DLB algorithm had been conducted up to now, and the impact of the reallocation frequency on the average latency remained unevaluated. In this paper, we demonstrate the DLB algorithm in a 40-Gbps λ-tunable WDM/TDM-PON. The demonstrations confirm that our DLB algorithm can distribute 512-ONU traffic loads fairly among 4 OSUs in real time with fewer reallocation frequencies compared to the conventional round-robin algorithm, and little impact on average latency, with various input traffic rates.

Wavelength router for energy efficient photonic aggregation with large-scale λ-tunable WDM/TDM-PON

This paper proposes a wavelength router configuration with large aggregation ratio for lambda (λ)-tunable wavelength-division-multiplexing / time-division-multiplexing passive optical network (WDM/TDM-PON). With this router, the aggregation functions of layer-2 switches (L2SWs) in the conventional access networks are moved into the PON; photonic aggregation. Therefore, L2SWs are no longer required, which lowers power consumptions in the central office. Our wavelength router comprises cyclic arrayed-waveguide gratings (AWGs), two-stage power splitters that work for wavelength-routing and aggregating the traffics from different PON branches, respectively. Optical amplifiers are placed in parallel between each stage of power splitters to compensate for the insertion losses of this router itself, and the number of optical amplifiers is proportional to that of splitting ratios of power splitters on the optical subscriber unit (OSU) side. When the total aggregation ratio of the router is fixed, the allowable combination of the splitting ratios of each stage is decided to fulfill the loss budget requirements. Based on theoretical analysis clarifying the allowable combinations, we decide the router configuration with the lowest power consumption and estimate the impact of the photonic aggregation on the power consumption in the central office.

Novel Automatic Service Restoration Technique by Using Self-Reconfiguration of Network Resources for a Disaster-struck Metro-Access Network

This paper shows the concept of the elastic lambda aggregation network (EλAN) that will achieve an elastic common access infrastructure for the metro-access network. It proposes a service restoration technique that uses optical path switching and intercentral office handover for EλAN to recover from disasters. The feasibility of the proposed service restoration technique is successfully demonstrated for the first time by using a prototype testbed of a metro-access network. By applying both orthogonal frequency division multiplexing and adaptive modulation, the system automatically changes the transmission parameters (modulation level, the number of subcarriers, and symbol rate) according to the service requirements and conditions of the optical distribution network, such as the links end-to-end optical loss, in order to achieve accommodate multiple services. In the experiment, an optical network unit in a faulted system automatically reconnected within 10 s to another office 20-km away with the same throughput.

First-time Demonstration of Automatic Service Restoration by Using Inter-Central-Office OLT handover and Optical Path Switching in Metro-Access Network

The first demonstration of the service restoration technique for metro-access networks successfully shows that ONU accommodated by the disaster-stricken central office is automatically reconnected within 10 sec to another office 20-km away with the same throughput as before disaster.

Fairness-aware dynamic sub-carrier allocation in distance-adaptive modulation OFDMA-PON for elastic lambda aggregation networks

In this paper, fairness-aware dynamic subcarrier allocation (DSA) in a distance-adaptive modulation orthogonal frequency division multiple access passive optical network (OFDMA-PON) is proposed and experimentally demonstrated for elastic lambda aggregation networks (EXANs). By applying the distance-adaptive modulation function to OFDMA-PONs, the system can change the transmission parameters (modulation level and symbol rate) for each user according to the users end-to-end optical loss, which will yield additional bits. Meanwhile, by applying our proposed DSA algorithm, which allocates sub-carriers to users based on transmission parameters and traffic demands, the additional bits can be shared by all users in a fair manner regardless of a users end-to-end optical loss. This paper conducts a real-time demonstration using an optical coherent OFDMA transceiver and a medium-access control board. The experiments confirm that our algorithm can greatly improve fairness in terms of frame loss rate among users compared to fixed sub-carrier allocation.

Hitless λ-tuning sequence to reduce tuning delay in λ-tunable WDM/TDM-PON

In wavelength (λ)-tunable wavelength-division-multiplexing/time-division-multiplexing passive optical networks (WDM/TDM-PONs), an optical line terminal (OLT) directs optical network units (ONUs) to change wavelengths to achieve functions such as load balancing or power saving. This demands λ-tuning without any data-frame loss, i.e., hitless λ-tuning. In addition, there is a need to increase the dynamic bandwidth allocation cycle period (DBA-p) to expand scalability as regards the splitting ratio or fiber reach. Unfortunately, with a large DBA-p, more buffer memory is needed in the OLTs or ONUs to cover the tuning delay demanded by the conventional hitless λ-tuning sequence, which requires a message exchange between the OLT and the ONU after λ-tuning. In this paper, we propose a novel hitless λ-tuning sequence to reduce the tuning delay. With the proposed sequence, the completion of λ-tuning is decided by calculation, and the buffers for upstream and downstream transmissions are released according to the calculation, instead of the message exchange. Experiments confirm that the proposed sequence can tune the wavelength of the ONUs transceiver without any data-frame losses for multiple measurements. Each measurement includes 300 λ-tuning operations. Additionally, it is shown that, when the DBA cycle is 4 ms, the tuning delay and buffer memory for upstream transmission can be reduced by 98% and 50%, respectively, while those for downstream transmission can be reduced by 86% and 86%, respectively, compared to the conventional sequence. We also show that the maximum upstream throughput is not degraded.

Optical path protection with FEC switching in WDM/TDM-PON for ring access networks

We propose and demonstrate an optical path protection that offers FEC switching function for WDM/TDM-PON with ring topology. A system demonstration confirms proposed automatic wavelength and FEC switching enables a 30km difference of redundant optical path in ring access networks.