Chadi Assi

Dynamic bandwidth allocation for quality-of-service over Ethernet PONs

Ethernet-based passive optical network (EPON) technology is being considered as a promising solution for next-generation broadband access networks due to the convergence of low-cost Ethernet equipment and low-cost fiber infrastructures. A major feature for this new architecture is the use of a shared transmission media between all users; hence, medium access control arbitration mechanisms are essential for the successful implementation of EPON: i.e., to ensure a contention-free transmission and provide end users with equal access to the shared media. We propose to use the multipoint control protocol defined by the IEEE 802.3ah task force to arbitrate the transmission of different users, and we present different dynamic bandwidth allocation (DBA) algorithms to allocate bandwidths effectively and fairly between end users. These DBA algorithms are also augmented to support differentiated services, a crucial requirement for a converged broadband access network with heterogeneous traffic. We show that queueing delays under strict bandwidth allocation algorithms result in an unexpected behavior for certain traffic classes, and we suggest the use of DBA with appropriate local queue management to alleviate this inappropriate behavior. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed protocols.

Disruption-Tolerant Networking: A Comprehensive Survey on Recent Developments and Persisting Challenges

Nowadays, wireless networks are witnessing several deployments in various extreme environments where they suffer from different levels of link disruptions depending on the severity of the operating conditions. In all cases, their operation requirements are differently altered and their performance is negatively affected rendering them heterogeneous by nature. In the open literature, these networks are known as Intermittently Connected Networks (ICNs). The existing Internet protocols fail to operate properly in the context of ICNs, thus raising a variety of new challenging problems that are attracting the attention of the networking research community. Delay-/Disruption-Tolerant Networking emerged as a highly active area of research where networking experts compete in addressing the various ICN problems. Over time, unicast routing, one of the architectural key components common to all ICNs, became an almost independent field of research in which significant efforts continue to be invested. In contrast, network architectural designs, scheduling and forwarding issues dating from the early days of Inter-Planetary Networks (IPNs) have received relatively little attention and accumulate numerous pending challenges. Moreover, the gap caused by the lack of accurate ICN mathematical models is still large irrespective of some of the appreciated seminal works in this direction. This paper sheds the light over the latest advancements in each of the above-mentioned research sectors and highlight pending open issues in each of them.

Fiber-wireless (FiWi) access networks: A survey

This article provides an up-to-date survey of hybrid fiber-wireless (FiWi) access networks that leverage on the respective strengths of optical and wireless technologies and converge them seamlessly. FiWi networks become rapidly mature and give rise to new powerful access network solutions and paradigms. The survey first overviews the state of the art, enabling technologies and future developments of wireless and optical access networks, respectively, paying particular attention to wireless mesh networks and fiber to the home networks. After briefly reviewing some generic integration approaches of EPON and WiMAX networks, several recently proposed FiWi architectures based on different optical network topologies and WiFi technology are described. Finally, technological challenges toward the realization and commercial adoption of future FiWi access networks are identified.

Dynamic Wavelength and Bandwidth Allocation in Hybrid TDM/WDM EPON Networks

We discuss a wavelength-division-multiplexed-based passive-optical-network (PON) architecture that allows for incremental upgrade from single-channel time-division multiple-access PONs in order to provide higher bandwidth in the access network. Various dynamic-wavelength and bandwidth-allocation algorithms (DWBAs) for wave-division multiplexed PON are presented; they exploit both interchannel and intrachannel statistical multiplexing in order to achieve better performance, especially when the load on various channels is not symmetric. Three variants of the DWBA are presented, and their performance is compared. While the first variant incurs larger idle times (and, hence, poor performance), the other two algorithms achieve better but different performance with critical dissimilarities. Our analysis also focuses on the fair assignment of excessive bandwidth in the upstream direction to highly loaded optical network units. We compare the performance of DWBA to another algorithm that relies on static-channel allocation. Furthermore, a study is presented wherein the number of wavelengths increases, and a comparison with interleaved polling with adaptive cycle time is shown. We use extensive simulations throughout this paper

A novel decentralized ethernet-based PON access architecture for provisioning differentiated QoS

To date, the mainstream ethernet passive optical network (EPON) bandwidth allocation schemes as well as the new IEEE 802.3ah Ethernet in the first mile Task Force specifications have been centralized, relying on a component in the central office [optical line termination (OLT)] to provision upstream traffic. Hence, the OLT is the only device that can arbitrate time-division access to the shared channel. Since the OLT has global knowledge of the state of the entire network, this is a centralized control plane in which the OLT has centralized intelligence. This paper proposes novel distributed EPON architectures, and in the process proves that these distributed networking architectures and the associated bandwidth allocation algorithms and protocols have characteristics that make them far better suited for provisioning quality of service (QoS) schemes necessary for properly handling data, voice, video, and other real-time streaming advanced multimedia services over a single line. Specifically, this paper proposes a novel ethernet over star coupler-based PON architecture that uses a fully distributed time-division multiple-access (TDMA) arbitration scheme. Supported by the decentralized scheme, this paper proposes several QoS-based dynamic bandwidth allocation (DBA) algorithms in which the OLT is excluded from the implementation of the time slot assignment. In contrast with the mainstream centralized EPON architectures that combine priority queuing [intra-optical network unit (ONU) scheduling] with DBA schemes (inter-ONU scheduling), the proposed distributed EPON architecture supports differentiated services through the integration of both scheduling mechanisms at the ONU (intra-ONU scheduling). The introduction of this integration feature that can only be supported by a decentralized architecture provides better QoS guarantees. Furthermore, in addition to the added flexibility and reliability, the overall performance of the proposed decentralized EPON architecture and the associated bandwidth allocation algorithms are shown to be at least as efficient as their centralized counterparts.

Jitter performance in ethernet passive optical networks

Ethernet passive optical networks (EPONs) have emerged as one of the most promising access network technologies. Propelled by rapid price declines in fiber optics and Ethernet components, these architectures combine the latest in optical and electronic advances and are poised to become the dominant means of delivering gigabit broadband connectivity to homes over a unified single platform. As this technology matures, related quality of service (QoS) issues are becoming a key concern. This paper proposes a novel dynamic scheduling algorithm, termed hybrid granting protocol (HGP), to support different QoS in EPON. Specifically, the proposed dynamic scheduling algorithm minimizes packet delay and jitter for delay and delay-variation sensitive traffic (e.g., voice transmissions) by allocating bandwidth in a grant-before-report (GBR) fashion. This considerably improves their performance without degrading QoS guarantees for other service types. Detailed simulation experiments are presented to validate the effectiveness of the proposed algorithm.

On the fairness of dynamic bandwidth allocation schemes in Ethernet passive optical networks

Ethernet passive optical networks (EPONs) technology has emerged as a promising candidate for next-generation broadband access networks. As this technology evolves, the development of efficient dynamic bandwidth allocation (DBA) algorithms has become a key concern. This paper devises and presents the principle and implementation issues of a new robust DBA scheme. This proposed scheme consistently maintains a robust fairness mechanism in the DBA operation. With the better maintained fairness mechanism, network performance is improved; specifically average packet delay and upstream link utilization, as well as inter-ONU statistical bandwidth multiplexing. Detailed simulation experiments are presented to study the performance and to validate the effectiveness of the proposed algorithm.

Smart Microgrids: Optimal Joint Scheduling for Electric Vehicles and Home Appliances

The integration of renewable energy sources and electrical vehicles (EVs) into microgrids is becoming a popular green approach. To reduce greenhouse gas emissions, several incentives are given to use renewable energy sources and EVs. By using EVs as electricity storage and renewable energy sources as distributed generators (DGs), microgrids become more reliable, stable, and cost-effective. In this paper, we propose an optimal centralized scheduling method to jointly control the electricity consumption of home appliances and plug-in EVs as well as to discharge the latter ones when they have excess energy, thereby increasing the reliability and stability of microgrids and giving lower electricity prices to customers. We mathematically formulate the scheduling method as a mixed integer linear programming (MILP) problem and solve it to optimality. We compare the optimal solution to that obtained from a scheduling framework, where EVs do not have discharge capabilities, decentralized charge control using game theory and to a solution obtained from a naive scheduling framework.

Improving Spatial Reuse in Multihop Wireless Networks - A Survey

In multihop wireless ad-hoc networks, the medium access control (MAC) protocol plays a key role in coordinating the access to the shared medium among wireless nodes. Currently, the distributed coordination function (DCF) of the IEEE 802.11 is the dominant MAC protocol for both wireless LANs and wireless multihop ad hoc environment due to its simple implementation and distributed nature. The current access method of the IEEE 802.11 does not make efficient use of the shared channel due to its conservative approach in assessing the level of interference; this in turn affects the spatial reuse of the limited radio resources and highly affect the achieved throughput of a multihop wireless network. This paper surveys various methods that have been proposed in order to enhance the channel utilization by improving the spatial reuse.

A simple dynamic integrated provisioning/protection scheme in IP over WDM networks

This article presents a simple integrated provisioning/protection scheme to dynamically allocate restorable bandwidth guaranteed paths in IP over WDM networks. A guaranteed restorable path implies that a flow of data is successfully routed if both an active path and another alternate link-disjoint path are found at the same time. Unlike the conventional approach, where the IP and WDM layers are not aware of each other, the new scheme takes advantage of the development in generalized multi-protocol label switching (GMPLS) to provide integrated end-to-end survivability by incorporating network state information from both layers (e.g., the cost information in physical links, the bandwidth usage on each lightpath, and intermediate router speed) into protection path allocation. Simulation results are used to evaluate the performance of the new scheme and show that the proposed protection approach can efficiently improve the network utilization, and deliver reliable services.