Interleaved Polling with Adaptive Cycle Time (IPACT): A Dynamic Bandwidth Distribution Scheme in an Optical Access Network

The Broadband Passive Optical Network (PON) technology is a promising approach to establish a cost-effective access network. It is intended to provide a simple, low cost, scalable solution capable of delivering broadband access to end users, by passively sharing a single optical fiber transmission system between several packets. While downstream traffic is broadcast to all packets, the access of upstream traffic to the fiber has to be arbitrated in order to avoid collisions. This arbitration mechanism and more generally, bandwidth distribution and QoS Provisioning, have been left to the implementer. Interleaved Polling with Adaptive Cycle Time (IPACT) is one of the earliest proposed schemes for bandwidth distribution in Ethernet PON (EPON) and has been extensively used as a benchmark by many subsequent allocation schemes. In this paper, we propose an analytical model which yields approximate values for mean queue length and mean packet delay in an EPON with the Gated IPACT scheme under the assumption of Poisson arrivals. We show by simulation that the model is remarkably accurate over the whole load range. We use the model to demonstrate that all ONUs experiment performance degradation in case of local overload by some ONUs, thus showing the necessity of correcting somehow the Gated policy in order to avoid this phenomenon.

The deployment of new 5G services and future demands for 6G make it necessary to increase the performance of access networks. This challenge has prompted the development of new standardization proposals for Passive Optical access Networks (PONs) that offer greater bandwidth, greater reach and a higher rate of aggregation of users per fiber, being Time- and Wavelength-Division Multiplexing (TWDM) a promising technological solution for increasing the capacity by up to 40 Gbps by using several wavelengths. This solution introduces tunable transceivers into the Optical Network Units (ONUs) for switching from one wavelength to the other, thus addressing the ever-increasing bandwidth demands in residential broadband and mobile fronthaul networks based on Fiber to the Home (FTTH) technology. This adds complexity and sources of inefficiency, such as the laser tuning time (LTT) delay, which is often ignored when evaluating the performance of Dynamic Bandwidth Allocation (DBA) mechanisms. We present a novel DBA algorithm that dynamically handles the allocation of bandwidth and switches the ONUs’ lasers from one wavelength to the other while taking LTT into consideration. To optimize the packet delay, we introduce a scheduling mechanism that follows the Longest Processing Time first (LPT) scheduling discipline, which is implemented over the Interleaved Polling with Adaptive Cycle Time (IPACT) DBA. We also provide quality of service (QoS) differentiation by introducing the Max-Min Weighted Fair Share Queuing principle (WFQ) into the algorithm. The performance of our algorithm is evaluated through simulations against the original IPACT algorithm, which we have extended to support multi-wavelengths. With the introduction of LPT, we obtain an improved performance of up to 73% reduction in queue delay over IPACT while achieving QoS differentiation with WFQ.

The Ethernet PON (EPON) is viewed by many as an attractive solution to deliver very high-speed broadband access and is widely deployed in some geographical areas. While downstream traffic is broadcast to all customers, the access of upstream traffic to the fiber has to be arbitrated in order to avoid collisions. This arbitration mechanism and more generally, bandwidth distribution and QoS Provisioning, have been left to the implementer. One solution is to enforce static Time Division Multiplexing Access (TDMA) between end-users. This however precludes an efficient usage of resources. Interleaved Polling with Adaptive Cycle Time (IPACT) is one of the earliest proposed schemes for Dynamic Bandwidth Assignment (DBA) in EPON and has been extensively used as a benchmark by many subsequent allocation schemes. In this paper, we first propose an analytical model which yields approximate values for mean queue length and mean packet delay in an EPON using IPACT with Gated Service (GS) scheme under the assumption of heterogeneous Poisson arrivals. We use the model to demonstrate that all users experiment performance degradation in case of local overload, thus showing the necessity of correcting somehow IPACT-GS in order to avoid this phenomenon. This is achieved by designing a control plane for EPON, which includes a priority based DBA together with a framework for enforcing Service Level Agreements (SLAs), and fairly sharing available resources. The proposed framework is easily configured (all the control being centralized at the OLT or in the backbone) while allowing the support of large varieties of services. It is shown to behave more efficiently than other QoS sensitive DBAs in the literature.

Interleaved polling with adaptive cycle time (IPACT) has great significance in the Ethernet passive optical network (EPON), which is regarded as one of the best choices for next generation access networks. In this paper, we propose an estimation-based scheme, IPACT with grant estimation (IPACT-GE), to improve the performance of the IPACT. By estimating the amount of new packets arriving in one polling cycles and granting transmission windows to ONUs based on the estimation, the proposed scheme can provide a shorter waiting delay for the packets and less buffer occupancy than those of the IPACT scheme at the light traffic load so that the light load penalty could be greatly mitigated when combined with the strict priority queue (SPQ) mechanism to provide the differentiated services

In this paper a particular passive optical network based on the Ethernet framing is investigated considering a typical tree-based topology. User stations are managed for upstream data transmissions by means of a polling algorithm which has also to support a dynamic bandwidth management. Here the Interleaved polling with adaptive cycle time (IPACT) algorithm is investigated and evaluated through simulation, exploiting the ns simulation tool. Different scheduling disciplines which the IPACT may employ are evaluated in terms of bandwidth distribution, cycle times and queue lengths.

An uplink access scheme for the Ethernet passive optical network (EPON), called broadcast polling (BP), has been proposed. In the BP scheme, the optical line terminal (OLT) knows all optical network units' (ONUs) bandwidth requirements before allocating bandwidth to them, and only one gate message is used to inform all ONUs of their bandwidth grant information in every cycle. Compared with interleaved polling with adaptive cycle time (IPACT)--an important access scheme--BP can adopt more- sophisticated bandwidth-allocation algorithms so that it can better support the service-level agreement (SLA). Based on packet-delay analysis for the BP scheme, a simple bandwidth-allocation algorithm aiming to provide three different service levels to customers has been designed. The simulation results show that the algorithm works well. In fact, more-sophisticated algorithms can be designed on the basis of the BP scheme to support more-sophisticated SLAs.

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.

Explosion of data and mass availability of Internet connections around the globe had created huge bandwidth requirements for bandwidth hungry applications. Despite the technological advances in the core and their ability to transport, still much work has to be done in the access networks in order to be able to let the broadband traffic be transmitted transparently. Current solutions for access networks do not provide a concrete solution for the famous last mile problem. In this review we will investigate optical access networks as viable solutions to the ongoing problems in the access networks. Further we will study physical and technological limitations with the current state-of-the-art optical technology. We will address the optical access networks promises in responding to these shortcomings. We will thoroughly study passive optical networks (PONs), reviewing different type of PONs considering their benefits and limitations. We will conclude our study with comparison of these current solutions.

Today, tremendous pressure falls on the local networks to provide customers with access to the global telecom infrastructure. To ease this pressure, various versions of broadband access networks have been developed. Among them, the optical access networks provide the most promising immediate and future solution to the access problem. These optical access networks are mostly implemented today in the form of passive optical networks (PONs). This paper analyzes the quality of service (QoS) provided by the PONs. We start with an introduction to the principle of PON operation, the architectures, topologies, protocols and standards, design issues, and network management and services. Through this introduction, we consider provisioning such QoS parameters as bandwidth allocation, delay (response) time, security, and availability. We also discuss PON lifeline service and survivability and compare the QoS provisioning in ATM-based and Ethernet-based PONs

Ethernet passive optical networks (EPONs) have emerged as the one of the most promising candidates for next-generation access networks. These new architectures couple low-cost optics with advanced edge electronics to offer vastly improved scalability over competing digital subscriber line and cable modem offerings. This paper proposes several novel architectural enhancements for EPON, which will help increase the viability of optical access over a broader range of subscriber access scenarios. Specifically, this paper proposes a two-stage EPON architecture that allows more end-users to share an optical line terminal link, and enables longer access reach/distances (beyond the usual 25 km distance). In addition, a new dynamic bandwidth allocation (DBA) algorithm is proposed to effectively allocate bandwidths between end users. This DBA algorithm can support differentiated services in a network with heterogeneous traffic. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed architecture and algorithms.

In this PhD dissertation multi-rate models are examined for the performance analysis of telecommunication networks through mathematical analysis and simulation. Particular emphasis is given to optical networks. The main goal is the development of analytical models for the calculation of network performance metrics, such as blocking probabilities, transmission delay and utilization of the common channel. The proposed analytical models are distinguished according to the network technologies. Three different technologies are considered: A) Wavelength routed optical networks. B) Optical access networks. C) Wireless Internet access networks. Multi-rate loss models are proposed for the performance evaluation of wavelength routed optical networks. Firstly, the case of a single link is considered and then a mesh all-optical network is examined. In addition, analytical models are proposed for Optical Packet Switching (OPS) networks, for the case of an all-optical OPS switch and of an OPS mesh network. Multi-rate analytical models are proposed for the evaluation of the performance of Passive Optical Networks (PONs) implementing different multiple access methods. For the case of Time Division Multiple Access (TDMA) the Ethernet PON is studied, which supports multiple service-classes. Regarding the Wavelength Division Multiplexing (WDM) PONs a hybrid WDM-TDMA PON is considered and the call-level performance is evaluated. Calls are distinguished by their arrival process, which can be random or quasi random, by their bandwidth requirements, which can be fixed of elastic and by their behavior during their service, which can be calls of fixed transmission rate or calls that alternate between ON and OFF periods. Finally multi-rate loss models are proposed for the case of Optical Code Division Multiple Access (OCDMA) PONs that take into account the user activity and the presence of additive noise in the transmission channel. For the performance analysis of wireless Internet access networks analytical models are proposed, which implement the IEEE 802.11 protocol or the IEEE 802.11e protocol. The proposed analysis calculated the saturation throughput and the end-to-end packet delay as a function of the Medium Access Control (MAC) delay and the queueing delay. In all cases the accuracy of the proposed models is validated through simulation.

In order to share access infrastructure between mobile and access network, integration of wireless services on optical access network with Radio over Fibre (RoF) technologies is a potential solution for operators. In this paper, we propose an overlay Universal Mobile Telecommunication System (UMTS) or third generation (3G) signal transmission on a Gigabit Passive Optical Network. Main advantages of this transmission scheme are the use of only one laser to feed the signal and one photodiode to receive it. A trade-off between extinction ratio and laser linearity has been found and the penalty induced by the 3G signal overlay is small. We demonstrate a 1x32 PON over 20km, which can distribute UMTS signal for remote base station, and binary signal at 1.25Gbit/s for others users.

Radio over Fibre (RoF) technology provides distribution of broadband signals to base station using an optical access network. This technology reduces the complexity at base station. On the other hand, giga bit passive optical network (GPON) has gained much of the interest in today's network due to its high data rate (1.2 GHz-2.4 GHz), simplicity, flexibility and low costs. The combination of GPON with RoF technology provides high capacity and high data rate solution. This paper provides characterization of RoF GPON by various simulations performed on OPTSIM software. The statistical analysis of simulation results are based on received signal strength and eye pattern obtained for various modulation schemes at different distances.

It is well known that optical access networks are able to provide high data rates over long distances and to a reasonable number of users. Security and privacy are always a challenge for public accessible network infrastructures. Especially in time-division multiplexing passive optical networks (TDM-PONs), in which the downstream signal is broadcasted to all users connected via the same wavelength channel in a shared fiber link, privacy can be a critical concern. Although encryption at the application layer can provide a high level of security, this can be achieved only if the encryption key distribution is perfectly save. On the other hand, encryption on the physical layer such as quantum cryptography or, more precisely, quantum key distribution (QKD) is a very promising approach to achieve secure communication. However, there remain several issues that have to be solved before the quantum cryptography reaches the maturity level needed for a cost effective implementation in practical networks. In this paper, we address quantum key distribution (QKD) over passive optical access networks, which is an enabling technology required to cost efficiently deploy practical quantum encrypted data communication in the access area. We study different methods to integrate QKD systems in conventional optical access networks and quantitatively evaluate their suitability for a potential implementation.

This article describes Ethernet passive optical networks, an emerging local subscriber access architecture that combines low-cost point-to-multipoint fiber infrastructure with Ethernet. EPONs are designed to carry Ethernet frames at standard Ethernet rates. An EPON uses a single trunk fiber that extends from a central office to a passive optical splitter, which then fans out to multiple optical drop fibers connected to subscriber nodes. Other than the end terminating equipment, no component in the network requires electrical power, hence the term passive. Local carriers have long been interested in passive optical networks for the benefits they offer: minimal fiber infrastructure and no powering requirement in the outside plant. With Ethernet now emerging as the protocol of choice for carrying IP traffic in metro and access networks, EPON has emerged as a potential optimized architecture for fiber to the building and fiber to the home.