Compelling features such as low power consumption and low complexity make LoRaWAN one of the most promising technologies to provide long-range connectivity to resource-constrained devices. However, LoRaWAN suffers from limited scalability since it uses an Aloha-based protocol for accessing the channel that causes a huge amount of frame collisions when the number of devices (or the network load) is high. This paper presents LFS-CSMA, a new medium access control mechanism that enhances the scalability of LoRaWAN networks by just combining the well-known slotted Aloha and CSMA schemes in a novel manner. With LFS-CSMA, longer frames are transmitted earlier within a given timeslot. Thus, devices with short frames to be transmitted can check the channel availability before sending them and avoid collisions if they detect an ongoing transmission. Performance results show that LFS-CSMA causes far less collisions than traditional MAC mechanisms, thus improving the scalability of LoRaWAN networks significantly.

This paper studies two issues related with the use of distributed control for modular power converters based on the use of single-phase power units, namely intelligent Power Electronics Building Block (iPEBB) for power conversion in hybrid DC/AC microgrids. Some issues related to the distributed control are studied in this paper. Homopolar injection for PWM generation becomes more difficult, since each distributed controller calculates (and knows) only its control action. A possible solution is provided, based on the calculation of this homopolar injection by the central controller at 1 kHz. Synchronization with the grid becomes more difficult too, because each controller acts independently, without communication with the other ones (only with the central controller). Two alternatives are studied for this synchronization angle calculation: calculation in the central controller at central control frequency (1 kHz) or in each module at distributed control frequency (10 kHz).

Optical Burst Switching is efficient for bursty traffic but also weak in guaranteeing the delivery of real-time traffic. In this paper, we propose to enhance OBS with an OCS-like feature by providing each source-destination pair with a wavelength sharable home circuit. These wavelength sharable home circuits not only provide guaranteed bandwidth for in-profile traffic to different destinations from the same source, but also allow out-of-profile traffic between any source and destination to be statistically multiplexed. The proposed OBS enhancement approach, called Labeled OBS with Home circuits or LOBS-H, is shown, through both analysis and simulations, to require less resources (e.g., wavelengths) than OCS in order to provide the same bandwidth guarantee service, or to result in a better loss and/or delay performance with the same amount of resources.

Contrary to Optical Circuit Switching (OCS), Optical Burst Switching (OBS) is efficient for bursty traffic but also weak in guaranteeing the delivery of real-time traffic. We have proposed an OBS enhancement approach, called Labeled OBS with Home Circuits or LOBS-HC, which provides each source-destination pair with a wavelength sharable home circuit for the real-time traffic, so it can guarantee lossless transmission with a short delay. In previous works, we have shown that LOBS-HC requires less resources and provides a better QoS to the real-time traffic than OCS, since it does statistical multiplexing. Here, we extend the study of LOBS-HC. First, we study a few possible design choices in LOBS-HC. Then we evaluate its performance under not only real-time traffic, but also best-effort traffic. Finally, we analyze the effects of the switching speed and the burst size on the performance.

In this paper, we propose probabilistic splitting of a packet stream at the edge routers as the basic method to provide end-to-end proportional QoS to packet flows carried through an OBS network, in terms of loss probability. We argue that the only requirement that the optical transport infrastructure has to satisfy is the support for two internal burst classes with wide separation between their respective service levels. Under this condition, we show how quantifiable end-to-end per-flow guarantees can be attained without diminishing network resource usage. The scheme is analyzed theoretically and evaluated through numerical simulations, both in regular topologies (ring networks) and in a mesh network. Our results suggest that a layered approach to the problem of end-to-end QoS provisioning can be very effective when a proportional service model is offered, and that the research on sophisticated scheduling algorithms at the optical switches could be too narrow-focused for that purpose.

With the increasing popularity of multimedia applications, video data represents a large portion of the traffic in modern networks. Consequently, adequate models of video traffic, characterized by a high burstiness and a strong positive correlation, are very important for the performance evaluation of network architectures and protocols. This paper presents a new model for traffic with persistent correlations based on the M/G/infin process. We use a new discrete distribution for the service time of the M/G/infin queueing system, flexible enough to give rise to a wide range of correlation structures of the resulting M/G/infin process in a parsimonious way. The corresponding simulation model is easy to initialize in steady state. Moreover, as the distribution has subexponential decay, we can apply a highly efficient and flexible generator of synthetic traces of the M/G/infin process. As an example, we analyze the capabilities of our model for capturing the empirical distribution and correlation structure of VBR MPEG video traffic.

This paper addresses the provision of proportional differentiated services to an arbitrary number of traffic classes in terms of the class packet loss probability measured between the ingress node and the egress node of an OBS network. Our solution relies on a key idea: OBS networks consist of bufferless nodes and can therefore be regarded as a whole like a one-hop bufferless subnetwork characterized by a collection of loss probabilities computable with simple, approximate circuit switching models. Consequently, we believe it is possible to attain packet loss proportionality merely using a simple stochastic algorithm to assemble two classes of bursts, provided there exists some form of internal relative differentiation such that one of the burst classes has a much lower loss probability than the other. In order to evaluate the algorithm accuracy in attaining the proportionality, we present an analytical study of two idealized scenarios (a single link and a multi-node symmetrical network), including the effect caused by the flow dynamics of the traffic received at the ingress nodes. Our results show that, despite its simplicity, this approach is able to provide the desired proportionality over a wide range of operating conditions.

One of the more challenging research issues in the context of assured forwarding (AF) is the fair distribution of bandwidth among aggregates sharing the same AF class. Several studies have shown that the number of microflows in aggregates, the round trip time, the mean packet size and the TCP/UDP interaction are the key factors in the throughput obtained by the competing aggregates. Dynamic RIO (DRIO) is an interesting RIO technique suggested to improve assurances among heterogeneous flows in AF-based services. In this paper, we propose applying DRIO to aggregated traffic instead of the individual flows. Working at the aggregate level not only makes DRIO more appropriate to be used in AF networks, but also improves scalability substantially. In addition, we also mitigate some unfairness issues found in the original scheme. Several simulation experiments have been conducted to verify that the proposed improvements allow DRIO to fulfill fairness requirements more satisfactorily.