Formal Methods for Energy-Efficient EPONs

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.

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.

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 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.

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.

We propose and experimentally demonstrate three novel schemes for upstream access and local area network emulation among customers in a passive optical network using a single reflective semiconductor optical amplifier (RSOA) placed at the customer premises. The first scheme uses the broadband amplified spontaneous emission spectra of the RSOA for the transport of the local area network traffic among the customers, while the second scheme uses the optical carriers delivered to each optical network unit from the central office for the wavelength seeding of the RSOA to facilitate the transport of the local area network traffic. The third scheme describes the self-seeding process of the RSOA with the use of fiber Bragg gratings placed at the optical network unit to facilitate the upstream access and local area network traffic. These schemes for optical layer local area networking among the customers are experimentally demonstrated with more than 2Gbits/s downstream data, 1Gbit/s upstream access traffic, and 1Gbit/s local area network traffic. Moreover, the results of the experiments of all three schemes are compared further and discussed in terms of bandwidth of the local area network traffic, seeding optical power into the reflective semiconductor optical amplifier, and power budget.

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).

The limited scheme with excess distribution (LS-ED), being a superior grant-sizing protocol in terms of average delay minimization while providing fairness and quality of service (QoS) satisfaction in Ethernet passive optical networks (EPONs), has already been deployed in diverse technologies. An analysis of the protocol is of paramount importance for obtaining deeper insight into several network design and deployment aspects. Thus, the primary objective of this paper is to perform a rigorous mathematical analysis of LS-ED, for the first time to the best of our knowledge, with the help of a discrete time Markov chain (DTMC). Owing to the dependency of the grant size of a particular optical network unit (ONU) on the queue length of other ONUs, the exact queuing analysis of this scheme necessitates solving a Markov model of the same dimension as the number of ONUs, which makes the analysis complicated and mathematically intractable. A lower-dimensional valid approximation model may allow us to perform such an analysis. In this paper, for the first time to the best of our knowledge, we present an analysis of the scheme, wherein the system dynamics are captured from the perspective of the scheduler leading to an approximate model. The model aids in obtaining a closed-form expression for the average cycle time and throughput along with closed-form expressions for average buffer occupancy and average delay at low load. Finally, we provide useful design insights for EPONs employing LS-ED.

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.

We address the QoS (Quality of Services) bandwidth reservation and service work scheduling mechanism of how to fairly provide advance quality of service in polling based TDM networks like Ethernet PON (Passive Optical Networks). Unlike existing differentiated QoS supporting schemes, such as SP (Strict Priority) based DBA (Dynamic Bandwidth Allocation) or static work scheduling with min-max theory, proposed service quality pre-engagement (SQP) for prioritized packet scheduling and equal weighted fair bandwidth arbitration (EWF-BA) for fair services among access nodes reflect the dynamically changing service pattern of access node like ONU (Optical Network Unit). The performance results show that the service fairness and QoS are tightly coupled and proposed mechanisms achieve better QoS performances with high fairness and better network performances both in Poisson and Self-similar traffic environment.KeywordsQueue SizeOptical Network UnitAccess NodePassive Optical NetworkDynamic Bandwidth AllocationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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

Energy usage in our networks is increasing rapidly; and to conserve energy, progress has been made in designing energy-efficient passive optical networks, which are being widely deployed for broadband access. Among the various energy-saving techniques, enabling sleep mode in optical network units is a very promising approach. However, the slow transition of power from active mode to sleep mode in an optical network unit, and the relatively large recovery and synchronization time needed during the wakeup process are challenges that need to be addressed. In this regard, we propose a service-level-agreement-based scheduling scheme for passive optical networks in which the optical line terminal can adjust the sleep time and the optical network unit can quit sleep mode for sending high-priority packets. The trade-off in energy savings vs. delay performance is evaluated using simulations under practical power consumption settings.

Chapter 5 - Ranging and Dynamic Bandwidth Allocation

This paper proposes a new scheme for dynamic bandwidth allocation for XG-PON (10-Gbps-capable passive optical network). In the propose scheme, an ONU (optical network unit) does not explicitly report its queue status to an OLT (optical line termination). The OLT monitors the bandwidth usage of each ONU to estimate the queue status of each ONU. The OLT allocates a bandwidth to an ONU when the previous allocated bandwidth was fully used. Also the OLT periodically allocates a probe bandwidth to an ONU to check the queue status of the ONU.