Energy Efficiency in Ethernet Passive Optical Networks (EPONs): Protocol Design and Performance Evaluation

A survey of dynamic bandwidth allocation algorithms for Ethernet Passive Optical Networks

Energy-efficient passive optical networks (PONs) have gained significant interest since they are estimated to be the largest energy consumers among the wired access networks for the next ten years. In Ethernet PONs (EPONs), the equipment placed at the customer premises, i.e., the optical network units (ONUs), has been shown to be responsible for almost 65% of the total EPON power consumption. Sleep mechanisms, implemented at ONUs’ side, can contribute to the EPONs’ energy-efficiency. However, the tradeoff between energy saving and quality of service (QoS) requirements should be carefully tuned, especially when the downstream transmission is considered, to achieve the desirable results. In this paper, we propose a general framework that exploits formal methods as an approach for EPONs’ energy-efficiency. The idea is to build a holistic model representing both the state machine of the ONU in its details as well as the ONU’s communication with the optical line terminal under EPONs’ specifications. Verification results reveal that, guided by the QoS constraints and considering the transitions’ cost, an “aggressive” policy defining long sleep periods of the 100 ms order can be up to 24.9% beneficial for energy-efficiency compared to a “conservative” policy with sleep periods of the 10 ms order.

In the past few years, Ethernet Passive Optical Networks (EPONs) have rapidly gained large popularity in broadband access networks. However the current standard has no management protocols aiming at reducing power consumption. In this paper, we propose an Energy Management Mechanism (EMM) within the IEEE 802.3ah control scheme. The main idea is to switch Optical Network Units (ONUs) to sleep mode and determine a suitable wakeup time schedule at the Optical Line Terminal (OLT). In the proposed EMM there is a trade-off between maximizing the power saving and guaranteeing the network performance. We compare two types of downstream scheduling schemes, Upstream Centric Scheduling (UCS) and Downstream Centric Scheduling (DCS), which are different in the way they assign 'active' and 'sleep' states to ONUs. Simulation results in terms of energy consumption and queuing delay are shown for the EMM based EPON system.

Ethernet Passive Optical Network (EPON) must be equipped with Operations, Administration and Maintenance(OAM) features. Functions of 802.3ah OAM protocol in EPON system are Link performance monitoring, Fault detection and Fault signaling, Loopback testing. The related five types of OAMPDUs are Variable Request/Response, Information, Event Notification, Loopback Control and Organization Specific. Both OAM functions and OAMPDUs described in detail. The main functions provided by OAM are partitioned into three components: multiplexer, parser and client and control. As a part of our EPON system, the OAM sublayer components has been implemented using FPGA which can manage high speed Non-OAMPDUs and slow protocol at the same time. The OAM sublayer module and implemented its function are designed by using Xilinx PPGA. Not only the hardware block diagram but also the actually circuit are accompanied in detail. The result indicates that the data is the same as the protocol description.

An Ethernet passive optical network (EPON) is an optical access network that allows a higher data rate with low power consumption. To improve energy savings for an EPON, the sleep and doze modes for the optical network units (ONUs) play a pivotal role. Many prediction schemes have been proposed to control these modes. To increase the prediction accuracy, this study proposes an energy-efficient approach that uses a support vector regression (SVR) model. A dynamic bandwidth allocation (DBA) scheme called SVR-DBA is designed to allocate bandwidth to ONUs more efficiently and fairly. To determine the effectiveness of the proposed scheme, simulations are performed. The simulation results show that the proposed scheme decreases energy consumption for ONUs by up to 47% and fulfills the quality-of-service (QoS) requirements in terms of delay, jitter, and packet loss.

Results of the design and performance analysis of two new algorithms for efficient and fair scheduling of variable-length frames in a wavelength division multiplexing (WDM)-passive optical network (PON) under the Stanford University aCCESS-Hybrid PON (SUCCESS-HPON) architecture are reported. The WDM-PON under the SUCCESS-HPON architecture has unique features that have direct impacts on the design of scheduling algorithms. First, an optical line terminal (OLT) uses tunable transmitters and receivers that are shared by all the optical network units (ONUs) served by the OLT to reduce the number of expensive dense WDM (DWDM) transceivers. Second, also for cost reduction, ONUs have no local DWDM light sources but use optical modulators to modulate optical continuous wave (CW) bursts provided by the OLT for upstream transmissions. Therefore, the tunable transmitters at the OLT are used for both upstream and downstream transmissions. To provide efficient bidirectional communications between the OLT and the ONUs and guarantee fairness between upstream and downstream traffic, two scheduling algorithms have been designed: 1) batching earliest departure first (BEDF); and 2) sequential scheduling with schedule-time framing (S/sup 3/F). The BEDF is based on the batch scheduling mode where frames arriving at the OLT during a batch period are stored in virtual output queues (VOQs) and scheduled at the end of the batch period. It improves transmission efficiency by selecting the frame with the earliest departure time from a batch of multiple frames, which optimizes the usage of tunable transmitters in scheduling. Considering the high complexity of the optimization process in BEDF, the S/sup 3/F based on the sequential scheduling mode has also been designed as in the original sequential scheduling algorithm proposed earlier. In S/sup 3/F, the authors use VOQs to provide memory space protection among traffic flows and a granting scheme together with schedule-time framing for both upstream and downstream traffic to reduce framing and guard band overhead. Through extensive simulations under various configurations of the tunable transmitters and receivers, it has been demonstrated that both the BEDF and S/sup 3/F substantially improve the throughput and delay performances over the original sequential scheduling algorithm, while guaranteeing better fairness between upstream and downstream traffic.

Adopting the pay-as-you-grow approach to upgrade passive optical network (PON) facilities by WDM technology insures the smoothness of the upgrade, and also results in the coexistence of wavelength-fixed/tunable optical network units (ONUs) in WDM/TDM PONs. Dynamic bandwidth allocation (DBA) is the key to support such coexistence of heterogeneous ONUs. Thus, DBA is also the key to support the smooth evolution of PONs. To more fairly coordinate the bandwidth allocation among the coexisting heterogeneous ONUs, a differentiated grant sizing (DGS) scheme is proposed. In DGS, not only the fairness between the wavelength-fixed/tunable ONUs but also the fairness between the lightly/heavily loaded ONUs is taken into account. To further carry out load balancing among wavelengths, a grant scheduling scheme is also proposed to cooperate with the grant sizing scheme. In the grant scheduling scheme, a measure of the ONUs’ flexibility is given, and then the least flexible job first rule (LFJF) is adopted for joint wavelength and time-slot assignment. Finally, to demonstrate the effectiveness of the proposed algorithm, a series of comparative analyses is conducted based on simulation experiments.

The potential for sharing infrastructure costs between a large number of customers and the high data rates allowed by optical fibres make passive optical networks (PONs) an attractive solution to the problem of upgrading current copper-based access networks. Optically-amplified, long reach, time division multiple access (TDMA) PONs or 'SuperPONs' offer the potential to further reduce bandwidth transport costs by enabling the direct connection of access networks and inner core networks, thereby eliminating the costs of the outer core/metro backhaul network. The use of dense wavelength division multiplexing (DWDM) could also allow sharing the same feeder fibre and PON head end equipment between a number of such TDMA SuperPONs, each working at different ITU-grid wavelengths. However, a cost effective access solution should employ a customer optical network unit (ONU), which is independent of the PON wavelength, or colorless, in order to reduce the high inventory and deployment costs of using expensive, wavelength-specified sources at the customer. In this paper we demonstrate for the first time the use of a monolithically-integrated, electroabsorption modulator-semiconductor optical amplifiers (EAM-SOAs) as a colorless ONU in a high performance DWDM SuperPON system. These compact devices offer the potential for low-cost optoelectronic integration with other ONU components together with the ability to modulate at rates up to 10Gbps and beyond. We have used this approach to investigate the feasibility of supporting up to 17 SuperPONs from a single feeder fibre and PON head end, each of 100km-reach accommodating 512 users at 2.5Gb/s or 128 at 10Gb/s.

On solving the access network bottleneck problem (usually known as the last mile problem), Ethernet passive optical network (EPON) is paid a great many attentions. Many works have been done on TDMA-based EPON system. Architecture of a WDM-based EPON system is proposed in this paper. The proposed system consists of one OLT, 1:32 Splitter/combiner, 32 ONUs and a Network Management System (NMS). The OLT includes a Service Node Interface (SNI), an Ethernet switch, an ODN Interface and a Network Management agent, while the ONU includes a User Side Interface (USI), an Ethernet Frame Forwarding, an ODN Interface and a Network Management agent. The downstream data are broadcast from the OLT to all ONUs with 1.25Gbps of line speed. Each ONU send the upstream data encapsulated in Ethernet frames up to OLT with specific wavelength and the 125Mbps of line speed. The upstream signals from all ONUs are aggregated to one fiber by the 1:32 combiner. When the aggregated stream arrives at the OLT, it is de-multiplexed and converted into 32 pairs of signals for more processing. As a result, all ONUs can send data to the OLT simultaneously. Experimental results show that our WDM-based EPON system works well.

The evolution of the Ethernet passive optical network (EPON) to the enhanced 10G-EPON standard looks poised to maintain its position as the leading fiber to the home technology worldwide. Fair bandwidth allocation will be a challenge in the near future in plants where 1G and 10G customer premises equipment coexists. In this paper we propose a distributed algorithm, distributed dynamic scheduling for EPON (DDSPON), to dynamically allocate the bandwidth requested by the user equipment with quality of service (QoS) constraints. The proposed algorithm is scalable and simple to re-configure, which facilitates a smoother transition from legacy 1G to 10G networks. By using the DDSPON, enhanced optical network units (ONUs) will take full advantage of the 10 Gb/s rate while legacy 1G ONUs maintain their service level agreement; as a result, the individual performance is maximized for both groups of ONUs. We also present an analytical model to evaluate the algorithm performance in a coexistent 1G/10G network. Finally, we also illustrate the enhancement of the DDSPON to provision the QoS to different services under the DiffServ architecture. Analysis and simulation results validate the effectiveness of the proposed mechanisms.

We investigate FTTX (Fiber-to-the Home/Premises/Curb) Passive Optical Networks (PON) for the deployment of broadband access networks such that the opportunities of optical fiber enabled technologies as well as of passive switching equipment can be exploited. We focus on designing the best possible architectures of hybrid FTTX PONs, which embraces both TDM and WDM technology. Advantages of hybrid PONs are twofold: they can (i) offer increased data rate to each user by employing WDM technology, (ii) provide flexible bandwidth utilization by employing TDM technology. We propose a novel network design optimization scheme for greenfield deployment of a set of hybrid PONs. For a given geographical location of an optical line terminal (OLT), a set of optical network units (ONUs) and their corresponding aggregated traffic demand, our proposed optimization scheme determines the design and dimensioning of the most economical set of hybrid PON networks while satisfying unicast/multicast traffic demands and taking into account the signal attenuation constraints. Computational experiments have been conducted on a set of up to 512 ONUs in order to evaluate the performance of the proposed scheme.

Next-generation passive optical network (PON) has been widely considered as a cost-effective broadband access technology. With the ever-increasing power saving concern, energy efficiency has been an important issue for its operations. In this paper, we present a novel sleep time sizing and scheduling framework that satisfies power efficient bandwidth allocation in PONs. We consider the downstream links from an optical line terminal (OLT) to an optical network unit (ONU). The ONU has two classes of traffic, control and data. Control traffic are delay intolerant with higher priority than the data traffic. Closed form model for average ONU sleeping time and end-to-end data traffic delay are presented and evaluated. Our framework decouples the dependency between ONU sleeping time and the QoS of the traffic.

Wavelength division multiplexing/time division multiplexing (WDM/TDM) passive optical networks (PON) is being viewed as a promising solution for delivering multiple services and applications. The hybrid WDM / TDM PON uses the wavelength and bandwidth allocation strategy to control the distribution of the wavelength channels in the uplink direction, so that it can ensure the high bandwidth requirements of multiple Optical Network Units (ONUs) while improving the wavelength resource utilization. Through the investigation of the presented dynamic bandwidth allocation algorithms, these algorithms can't satisfy the requirements of different levels of service very well while adapting to the structural characteristics of mixed WDM / TDM PON system. This paper introduces a novel wavelength and bandwidth allocation algorithm to efficiently utilize the bandwidth and support QoS (Quality of Service) guarantees in WDM/TDM PON. Two priority based polling subcycles are introduced in order to increase system efficiency and improve system performance. The fixed priority polling subcycle and dynamic priority polling subcycle follow different principles to implement wavelength and bandwidth allocation according to the priority of different levels of service. A simulation was conducted to study the performance of the priority based polling in dynamic resource allocation algorithm in WDM/TDM PON. The results show that the performance of delay-sensitive services is greatly improved without degrading QoS guarantees for other services. Compared with the traditional dynamic bandwidth allocation algorithms, this algorithm can meet bandwidth needs of different priority traffic class, achieve low loss rate performance, and ensure real-time of high priority traffic class in terms of overall traffic on the network.

An FEC scheme combined with weighted scheduling to reduce multicast packet loss in IPTV over PON

Passive optical networks (PONs) are thought to be the next step in the development of access networks and providing broadband access in the ¿last mile¿ area. Ethernet PON (EPON) gains the most attention from the researchers as it offers highly flexible and cost effective solution. In this paper we propose two high level scheduler algorithms inside the optical line terminal (OLT) and optical network units (ONU). In the proposed dynamic bandwidth allocation (DBA) algorithm, the OLT allocates the bandwidth to the ONUs in proportion to the weight associated with the excess bandwidth available, while the ONU preferentially allocates its bandwidth to queues with a strict or non strict priority order. The algorithms provide dynamic bandwidth allocation and separate the burden of queue management fairly between the customer and the network. This led to less complicated and more intelligent equipment has been used on the customer's premises. We show the results of simulations to validate the effectiveness of algorithms presented and to provide quality of service (QoS) for triple play real time services in Ethernet passive optical networks (EPONs).