Changing attitudes toward energy security and energy conservation have led to the introduction of distributed power systems such as photovoltaic, gas-cogeneration, biomass, water, and wind power generators. The mass installation of distributed energy generators often causes instability in the voltage and frequency of the power grid. Moreover, the power quality of distributed power grids can become degraded when system faults or the activation of highly loaded machines cause rapid changes in power load. To avoid such problems and maintain an acceptable power quality, it is important to detect the source of these rapid changes. To address these issues, next-generation power grids that can detect the fault location have been proposed. Fault location demands accurate time synchronization. Conventional techniques use the Global Positioning System (GPS) and/or IEEE 1588v2 for time synchronization. However, both methods have drawbacks — GPS cannot be used in indoor situations, and the installation cost of IEEE 1588v2 devices is high. In this paper, a time synchronization technique using the broadcast function of an Ethernet Passive Optical Network (EPON) system is proposed. Experiments show that the proposed technique is low-cost and useful for smart grid applications that use time synchronization in EPON-based next-generation power grids.

The Ethernet passive optical network (EPON), which is one of the PON technologies for realizing FTTx (Fiber-To-The-Curb/Home/Office), is a low-cost and high-speed solution to the bottleneck problem that occurs between a backbone network and end users. The EPON is compatible with existing customer devices that are equipped with an Ethernet card. To effectively control frame transmission from optical network units (ONUs) to an optical line termination (OLT), the EPON can use a multi-point control protocol (MPCP) with control functions in addition to the media access control (MAC) protocol function. In this paper, we propose a two-phase cycle dynamic bandwidth allocation (TCDBA) algorithm to increase the channel utilization on the uplink by allowing frame transmissions during computation periods, and combine the TCDBA algorithm with the queue management schemes performed within each ONU, in order to effectively support differentiated services. Additionally, we perform simulations to validate the effectiveness of the proposed algorithm. The results show that the proposed TCDBA algorithm improves the maximum throughput, average transmission delay, and average volume of frames discarded, compared with the existing algorithms. Furthermore, the proposed TCDBA algorithm is able to support differentiated quality of services (QoS).

A fast class-of-service oriented packet scheduling (FCOPS) has a service fairness problem since a credit pool for a service class is initialized at the beginning of a transmission cycle whose starting moment is fixed at a specific ONU. To remedy the service unfairness of FCOPS, we suggest an enhanced class-of-service oriented packet scheduling (ECOPS) that uses a new initialization cycle whose starting moment is fairly distributed to each ONU. Also, ECOPS generates a colorless grant to utilize the resource wastage, when traffic is light and the total sum of grants of an ONU is less than a minimum size. Using simulation, we validate ECOPS as superior to FCOPS in the mean delay and the service fairness.

We suggest a dual thresholds method for the dynamic bandwidth allocation in EPON. In the suggested method, a buffer in ONU has two thresholds and ONU generates a normal request and a greedy request based on the two thresholds. Also, OLT estimates the overall traffic load and grants the greedy request when estimated traffic is light. We study upstream channel resource wastage and show the suggested method decreases the upstream channel resource wastage. Using simulation, we validate the dual thresholds method is superior to the existing methods in the mean delay.

In this paper, we examine the Interleaved Polling with Adaptive Cycle Time (IPACT) that was proposed to control upstream traffic for Gigabit Ethernet-PONs, a promising technology for the Fiber To The Home (FTTH). We analyzed the performance for the gated service and the limited service mathematically. To do this, the IPACT protocol was modeled as a polling system and analyzed by using mean-value analysis technique. The traffic arrival rate λ was divided into three regions, and each region was analyzed separately and merged appropriately by using an interpolation method. The average packet delay, average queue size, and average cycle time of both the gated service and the limited service were obtained through the analysis. In order to evaluate the accuracy of the mathematical analysis, discrete event simulation was performed for the IPACT protocol. Simulation results show the accuracy of the mathematical analysis. The analysis results can be widely used in the design of the FTTH system based on EPON, as the performance results in the present study can be obtained in a rather short time. We can design an appropriate system depending on various traffic conditions by adjusting system parameters, such as the number of users N, the maximum transfer window WMAX, and so on.

We suggest a new minimum credit method for the dynamic bandwidth allocation in EPON. In the suggested method, to eliminate the unused transmission time-slot, each ONU requests no more than a predetermined maximum. We analyze the upstream channel resource wastage when traffic is light. Based on the analysis, we derive a minimum credit that eliminate the upstream channel resource wastage. The OLT estimates a traffic load and grants a minimum credit when the request is smaller than the minimum credit and traffic is light. Using simulation, we show the minimum credit discipline is superior than the existing methods in the mean delay and the frame loss rate.

As an alternative solution to provide the quality of services (QoS) for broadband access over Ethernet Passive Optical Network (EPON), we present the usage of MAC control message for plural class queues and a traffic-class burst-polling based delta dynamic bandwidth allocation (DBA), referred to as TCBP-DDBA, scheme. For better QoS support, the TCBP-DDBA minimizes packet delays and delay variations for expedited forwarding packet and maximizes throughput for assured forwarding and best effort packets. The network resources are efficiently utilized and adaptively allocated to the three traffic classes for the given unbalanced traffic conditions by guaranteeing the requested QoS. Simulation results using OPNET show that the TCBP-DDBA scheme performs well in comparison to the conventional unit-based allocation scheme over the measurement parameters such as: packet delay, packet delay variation, and channel utilization.

A broadband access network is required for supporting the increased Internet data traffic. One of the most cost-effective solutions is the Ethernet Passive Optical Networks (E-PONs) with the efficient bandwidth assignment function by which the upstream bandwidth can be shared among access users. To satisfy the services with heterogeneous QoS characteristics, it is very important to provide QoS guaranteed network access while utilize the bandwidth efficiently. In this paper, a dual DEB-GPS scheduler in E-PON is presented to provide delay-constraint and lossless QoS guarantee to QoS service and maximize the bandwidth to best-effort service. Simulation results show our scheme outperforms the conventional bandwidth allocation scheme in E-PON system.