In a hybrid PON/xDSL access network, multiple customer premise equipment (CPE) nodes connect over individual digital subscriber lines (DSLs) to a drop-point device. The drop-point device, which is typically reverse powered from the customer, is co-located with an optical network unit (ONU) of the passive optical network (PON). We demonstrate that the drop-point experiences very high buffer occupancies when no flow control or standard Ethernet PAUSE frame flow control is employed. In order to reduce the buffer occupancies in the drop-point, we introduce two gated flow control protocols that extend the polling-based PON medium access control to the DSL segments between the CPEs and the ONUs. We analyze the timing of the gated flow control mechanisms to specify the latest possible time instant when CPEs can start the DSL upstream transmissions so that the ONU can forward the upstream transmissions at the full PON upstream transmission bit rate. Through extensive simulations for a wide range of bursty traffic models, we find that the gated flow control mechanisms, specifically, the ONU and CPE grant sizing policies, enable effective control of the maximum drop-point buffer occupancies.

In this paper, we study the performance of multi-tier integrated fiber-wireless (FiWi) smart grid communications infrastructures based on low cost, simple, and reliable next-generation passive optical network (PON) with quality-of-service (QoS) enabled wireless local area networks (WLANs) in terms of capacity, latency, and reliability. We study the coexistence of human-to-human (H2H), e.g., triple-play traffic and machine-to-machine (M2M) traffic originating from wireless sensors operating on a wide range of possible configurations. Our analysis enables the quantification of the maximum achievable data rates of both event- and time-driven wireless sensors without violating given upper delay limits of H2H traffic. By using experimental measurements of real-world smart grid applications, we investigate the impact of variable H2H traffic loads on the sensor end-to-end delay performance. The obtained results show that a conventional Ethernet PON may cause a bottleneck and increase the delay for both H2H and M2M traffic. In contrast, by using a 10 G-EPON or wavelength division multiplexing (WDM) PON, the bottleneck arises in the wireless network. Furthermore, we study the interplay between time- and event-driven nodes and show that the theoretical upper bound of time-driven sensors decreases linearly as a function of the number of sensors, whereas with event-driven sensors, the upper bound decrease is nonlinear and more pronounced.

Current Gigabit-class passive optical networks (PONs) evolve into next-generation PONs, whereby high-speed 10+ Gb/s time division multiplexing (TDM) and long-reach wavelength-broadcasting/routing wavelength division multiplexing (WDM) PONs are promising near-term candidates. On the other hand, next-generation wireless local area networks (WLANs) based on frame aggregation techniques will leverage physical-layer enhancements, giving rise to Gigabit-class very high throughput (VHT) WLANs. In this paper, we develop an analytical framework for evaluating the capacity and delay performance of a wide range of routing algorithms in converged fiber-wireless (FiWi) broadband access networks based on different next-generation PONs and a Gigabit-class multiradio multichannel WLAN-mesh front end. Our framework is very flexible and incorporates arbitrary frame size distributions, traffic matrices, optical/wireless propagation delays, data rates, and fiber faults. We verify the accuracy of our probabilistic analysis by means of simulation for the wireless and wireless-optical-wireless operation modes of various FiWi network architectures under peer-to-peer, upstream, uniform, and nonuniform traffic scenarios. The results indicate that our proposed optimized FiWi routing algorithm (OFRA) outperforms minimum (wireless) hop and delay routing in terms of throughput for balanced and unbalanced traffic loads, at the expense of a slightly increased mean delay at small to medium traffic loads.

Toward the vision of complete fixed-mobile convergence, a plethora of wireless, integrated optical-wireless, multipath, and energy-aware routing algorithms were proposed for legacy EPON/WLAN-mesh based bimodal fiber-wireless (FiWi) broadband access networks. In this paper, we present the first comprehensive analytical framework for providing deeper insights into the capacity and delay performance of routing algorithms in next-generation FiWi networks based on emerging powerful optical and wireless technologies such as long-reach 10+ Gb/s TDM/WDM PONs and Gigabit-class VHT WLANs.

We introduce a convenient notational framework for Dynamic Bandwidth Allocation (DBA) algorithms in Ethernet Passive Optical Networks (EPONs) that uses the three principal axes of grant scheduling framework, grant sizing, and grant scheduling policy. We conduct comprehensive stability limit and packet delay investigations to determine which components have the strongest impact on these measures. We find that the grant sizing has the strongest impact on the delay and the combined grant scheduling framework and policy have the strongest impact on the stability limit. Further, we find that among the wide set of DBA algorithms we examined the shortest propagation delay first grant scheduling policy coupled with the limited with excess distribution grant sizing provides both the lowest delay and highest stability limit. The performance of shortest propagation delay first grant scheduling policy coupled with the limited with excess distribution grant sizing exceeds that of the online scheduling framework with limited grant sizing.

Building on the Ethernet Passive Optical Network (EPON) and Gigabit PON (GPON) standards, Next-Generation (NG) PONs (i) provide increased data rates, split ratios, wavelengths counts, and fiber lengths, as well as (ii) allow for all-optical integration of access and metro networks. In this paper we provide a comprehensive probabilistic analysis of the capacity (maximum mean packet throughput) and packet delay of subnetworks that can be used to form NG-PONs. Our analysis can cover a wide range of NG-PONs through taking the minimum capacity of the subnetworks forming the NG-PON and weighing the packet delays of the subnetworks. Our numerical and simulation results indicate that our analysis quite accurately characterizes the throughput-delay performance of EPON/GPON tree networks, including networks upgraded with higher data rates and wavelength counts. Our analysis also characterizes the trade-offs and bottlenecks when integrating EPON/GPON tree networks across a metro area with a ring, a Passive Star Coupler (PSC), or an Arrayed Waveguide Grating (AWG) for uniform and non-uniform traffic. To the best of our knowledge, the presented analysis is the first to consider multiple PONs interconnected via a metro network.

Due to the geographic distribution of its subscribers, Ethernet Passive Optical Networks (EPONs) have typically varying propagation delays between the Optical Network Units (ONUs) and the Optical Line Terminal (OLT). In this paper, we consider EPONs with an offline scheduling framework, which enables Quality-of-Service mechanisms by collecting bandwidth requests from all ONUs before the OLT makes dynamic bandwidth allocations for transmissions on the shared ONUs-to- OLT upstream channel. We propose and evaluate the Shortest Propagation Delay (SPD) first scheduling policy which sequences the ONUs' upstream transmissions in increasing order of the ONUs' propagation delays, i.e., the upstream transmission of the ONU with the smallest propagation delay is scheduled first. We formally analyze the competitiveness of SPD first scheduling and find that it achieves very close to optimal performance. We characterize the stability limit for Gated and Limited grant sizing in conjunction with SPD grant scheduling. We evaluate the cycle length and packet delay with SPD scheduling through probabilistic analysis and simulations and find significant reductions in packet delay with SPD first scheduling in EPONs with heterogeneous propagation delays, especially when Limited grant sizing is employed.