Routing in an AWG-Based Optical Packet Switch

For the next generation of the optical internet, focus is now moving from circuit switched networks, which occupy a wavelength continuously regardless of the demand at that time, towards optical packet/burst switching. By only occupying a wavelength when data is to be transmitted, a more efficient utilization of bandwidth in optical fibers is strived for. As bandwidth in fibers keeps increasing, the bottleneck of the optical network is now moving towards the switching node, since evolution of electronic routers cannot follow the speed of bandwidth increase. Thus a key component in these novel networks is the optical node. Through this node we want to switch traffic very fast and reliably, preferably transparent. Lack of efficient and practically realizable optical buffer, however, makes migration from electronic routers to optical routers a non-straightforward transition. In most optical nodes payload traffic can be switched transparently, whilst control information (e.g., in a header, on a control channel) is still converted to the electronic domain in every node, since optical processing is far from mature. In this paper we present a possible architecture for such a node, array waveguide gratings and all-optical tuneable wavelength converters. The concept of this switch is explained and the node is evaluated in terms of loss rate. We will see that an inherent problem of this switch is its internal blocking. This drawback can be greatly overcome by using an intelligent and efficient wavelength assignment algorithm within the node. Simulation of slotted operation will give some numerical results.     

Scheduling Algorithms for a Slotted Packet Switch with either Fixed or Variable Length Packets

We address the problem of congestion resolution in optical packet switching (OPS). We consider a fairly generic all-optical packet switch architecture with a feedback optical buffer constituted of fiber delay lines (FDL). Two alternatives of switching granularity are addressed for a switch operating in a slotted transfer mode: switching at the slot level (i.e., fixed length packets of a single slot) or at the burst level (variable length packets that are integer multiples of the slot length). For both cases, we show that in spite of the limited queuing resources, acceptable performance in terms of packet loss can be achieved for reasonable hardware resources with an appropriate design of the time/wavelength scheduling algorithms. Depending on the switching units (slots or bursts), an adapted scheduling algorithm needs to be deployed to exploit the bandwidth and buffer resources most efficiently.     

On dimensioning optical grids and the impact of scheduling

When deploying Grid infrastructure, the problem of dimensioning arises: how many servers to provide, where to place them, and which network to install for interconnecting server sites and users generating Grid jobs? In contrast to classical optical network design problems, it is typical of optical Grids that the destination of traffic (jobs) is not known beforehand. This leads to so-called anycast routing of jobs. For network dimensioning, this implies the absence of a clearly defined (source, destination)-based traffic matrix, since only the origin of Grid jobs (and their data) is known, but not their destination. The latter depends not only on the state of Grid resources, including network, storage, and computational resources, but also the Grid scheduling algorithm used. We present a phased solution approach to dimension all these resources, and use it to evaluate various scheduling algorithms in two European network case studies. Results show that the Grid scheduling algorithm has a substantial impact on the required network capacity. This capacity can be minimized by appropriately choosing a (reasonably small) number of server site locations: an optimal balance can be found, in between the single server site case requiring a lot of network traffic to this single location, and an overly fragmented distribution of server capacity over too many sites without much statistical multiplexing opportunities, and hence a relatively large probability of not finding free servers at nearby sites.     

Improving the utilization factor of a PEM electrolyzer powered by a 15 MW PV park by combining wind power and battery storage – Feasibility study

So far, the biggest photovoltaic park in Belgium has been injecting all its energy into the electric distribution grid through a power purchase agreement with an electricity supplier. Due to decreasing and volatile wholesale electricity prices, the industrial partners/owners of the photovoltaic park are considering hydrogen storage in an attempt to increase the value proposition of their renewable energy installation. A major objective of the present work is to show how the utilization factor of the electrolyzer is affected by the design of the power supply system when the latter consists only of renewable energy sources instead of using the electric grid. Different hybrid designs were developed, by combining the existing photovoltaic source with wind power and state-of-the-art energy storage technologies (Vanadium Redox Flow or Lithium NMC). Finally, four scenarios were investigated, all considering a 1 MW PEM electrolyzer: A) 15 MW PV, B) 15 MW PV, 2MW Wind, C) 15 MW PV, 2 MW Wind, Battery, D) 15 MW PV, 15 MW Wind. The utilization factor was found as follows, for each scenario respectively: A) 41,5%, B) 65,5%, C) 66,0–86,0%, D) 82,0%. Furthermore, the analysis was extended to include economic evaluations (i.e. payback period, accumulated profit), specifically concerning scenario B and C. The results of this study lead to a number of conclusions such as: i) The utilization of the electrolyzer is limited when its power supply is intermittent. ii) Compared to PV, wind power makes larger contribution to the increase of the utilization factor, iii) 100% utilization can be achieved only if an energy storage system co-exists. iv) With a utilization factor at 65,5% scenario B can deliver a payback period in less than 8 years, if hydrogen is sold above 5€/kg. An analytic overview of all conclusions is presented in the last section of the paper.     

Analysis of an anycast based overlay system for scalable service discovery and execution

Support for anycast in the IP network layer allows one source node to contact a single member out of a group of destination nodes configured with the same IP address. Due to the stateless nature of the IP protocol, subsequent packets from the same source node targeted at the same anycast group may arrive at different group members. Consequently, native IP anycast cannot be applied directly to support distributed session-based services. For this reason, an anycast overlay architecture combining the transparency offered by native anycast with support for stateful communications has been proposed. In this paper, we investigate the operational impact of deploying this overlay architecture. Performance evaluation of a data plane prototype implementation for an anycast overlay node shows that high throughput and small latency can be achieved. Additionally, we show how threshold-based update triggering, in combination with an appropriate inter-proxy update strategy, delivers control plane accuracy with minimal network overhead.     

Data-centric optical networks and their survivability

The explosive growth of data traffic-for example, due to the popularity of the Internet-poses important emerging network requirements on today's telecommunication networks. This paper describes how core networks will evolve to optical transport networks (OTNs), which are optimized for the transport of data traffic, resulting in an IP-directly-over-OTN paradigm. Special attention is paid to the survivability of such data-centric optical networks. This becomes increasingly crucial since more and more traffic is multiplexed onto a single fiber (e.g., 160×10 Gb/s), implying that a single cable cut can affect incredible large traffic volumes. In particular, this paper is tackling multilayer survivability problems, since a data-centric optical network consists of at least an IP and optical layer. In practice, this means that the questions "in which layer or layers should survivability be provided?" and "if multiple layers are chosen for this purpose, then how should this functionality in these layers be coordinated?" have to be answered. In addition to a theoretical study, some case studies are presented in order to illustrate the relevance of the described issues and to help in strategic planning decisions. Two case studies are studying the problem from a capacity viewpoint. Another case study presents simulations from a timing/throughput performance viewpoint     

Transparent resource sharing framework for internet services on handheld devices

Handheld devices have limited processing power and a short battery lifetime. As a result, computationally intensive applications cannot run appropriately or cause the device to run out of battery too early. Additionally, Internet-based service providers targeting these mobile devices lack information to estimate the remaining battery autonomy and have no view on the availability of idle resources in the neighborhood of the handheld device. These battery-related issues create an opportunity for Internet providers to broaden their role and start managing energy aspects of battery-driven mobile devices inside the home. In this paper, we propose an energy-aware resource-sharing framework that enables Internet access providers to delegate (a part of) a client application from a handheld device to idle resources in the LAN, in a transparent way for the end-user. The key component is the resource sharing service, hosted on the LAN gateway, which can be remotely queried and managed by the Internet access provider. The service includes a battery model to predict the remaining battery lifetime. We describe the concept of resource-sharing-as-a-service that allows users of handheld devices to subscribe to the resource sharing service. In a proof-of-concept, we evaluate the delay to offload a client application to an idle computer and study the impact on battery autonomy as a function of the CPU cycles that can be offloaded.     

Using topology information for quality‐aware Peer‐to‐Peer multilayer video streaming

Due to increasing bandwidth capacities, the Internet has become a viable transport medium for a (live) video. Often, delivery of video streams relies on the client–server paradigm and therefore exhibits limited scalability. The Peer‐to‐Peer (P2P) network model is an attractive and scalable candidate to stream video content to end users. However, these P2P frameworks typically operate in a network agnostic mode. Introducing network topology information into these P2P frameworks offers opportunities to enhance the performance. In this paper, we introduce a model to include network information when streaming a (multilayered) video in P2P frameworks. An important metric for video stream providers is the content quality perceived by end users. The optimization studied here aims at maximizing the number of users receiving a high quality video. The paper addresses the optimization problem seen from the stream provider's viewpoint, having access to network topology information. An exact optimization approach is presented for benchmarking purposes and a heuristic approach to cope with realistic network sizes. In addition, we present an approach to decide the deployment location of peering functionality. The results show that our strategy significantly decreases the fraction of destinations receiving only the base layer, and by introducing extra peering functionality, network capacities are used more efficiently. Copyright © 2015 John Wiley & Sons, Ltd.     

Benchmarking and viability assessment of optical packet switching for metro networks

Optical packet switching (OPS) has been proposed as a strong candidate for future metro networks. This paper assesses the viability of an OPS-based ring architecture as proposed within the research project DAVID (Data And Voice Integration on DWDM), funded by the European Commission through the Information Society Technologies (IST) framework. Its feasibility is discussed from a physical-layer point of view, and its limitations in size are explored. Through dimensioning studies, we show that the proposed OPS architecture is competitive with respect to alternative metropolitan area network (MAN) approaches, including synchronous digital hierarchy, resilient packet rings (RPR), and star-based Ethernet. Finally, the proposed OPS architectures are discussed from a logical performance point of view, and a high-quality scheduling algorithm to control the packet-switching operations in the rings is explained.     

Influence of GMPLS Recovery Mechanisms on TCP Performance

Optical networks based on wavelength-division-multiplexing (WDM) techniques are very likely to be omnipresent in future telecommunication networks. Those networks are deployed in order to face the steady growth of traffic, which is for a large part Internet related. In the resulting IP-over-WDM scenario, TCP/IP constitutes an important fraction of the traffic transported over these networks. As IP networks are becoming increasingly mission-critical, it is of the utmost importance that these networks (and hence the supporting transport networks) be able to recover quickly from failures such as cable breaks or equipment outages. To that end, several IP-over-WDM network scenarios and corresponding protection and restoration strategies have been devised. It is clear that some trade-offs will have to be made in order to choose an appropriate strategy. In this paper, we investigate the effects of such recovery actions on the behavior of TCP, being the ubiquitous protocol used by today's network users. We examine the influence of different parameters such as the speed of recovery actions, changing length of the routes followed by the client data (TCP flows), changes in available bandwidth, etc. Thereby, we focus on what the TCP end-users care about, i.e., the number of bytes transported end-to-end within a certain time interval.