Intelligent optical networking for multilayer survivability

In recent years, telecommunication networks have faced explosive (IP) traffic growth. As traffic keeps growing, network reliability gains more and more importance. This article investigates to which extent switched connections and fast connection provisioning, typical for intelligent optical networks (IONs), can be used to provide resilience in an IP-over-optical multilayer network scenario. This solution, based on transport network flexibility, is compared with more traditional static multilayer resilience schemes in terms of cost (capacity) requirements and operational (dis)advantages     

Delivering scalable video with QoS to the home

User satisfaction is a key factor in the success of novel multimedia services. Yet, to enable service providers and network operators to control and maximize the quality (QoS, QoE) of delivered video streams, quite some challenges remain. In this paper, we particularly focus on three of them. First of all, objectively measuring video quality requires appropriate quality metrics and methods of assessing them in a real-time fashion. Secondly, the recent Scalable Video Coding (SVC) format opens opportunities for adapting video to the available (network) resources, yet the appropriate configuration of video encoding as well as real-time streaming adaptation are largely unaddressed research areas. Thirdly, while bandwidth reservation mechanisms in access/core networks do exist, service providers lack a means for guaranteeing QoS in the increasingly complex home networks (which they are not in full control of). In this paper we offer a broad view on these interrelated issues, by presenting the developments originating in a Flemish research project (including proof-of-concept demonstrations). From a developmental perspective, we propose an architecture combining a real-time video quality monitoring platform, on-the-fly adaptation (optimizing the video quality) and QoS reservation in a heterogeneous home network based on UPnP QoS?v3. From a research perspective, we propose a new subjective test procedure that revealed user preference for temporal scalability over quality scalability. In addition, an extensive study on optimizing HD SVC encoding in IPTV scenarios with fluctuating bandwidth showed that under certain bandwidth constraints (prohibiting sufficient fidelity) spatial scalability is a better option than quality scalability.     

Clos lives on in optical packet switching

While the technological evolution since C. Clos's seminal article (see Bell Sys. Tech. J., vol.32, p.406-24, 1953) on multistage switch architectures has been huge, his work and ideas still live on. We discuss node architectures for optical packet switching and show how the multistage approach proposed by Clos can be adopted to solve scalability issues and construct switches with large port counts. As in the old days, the driving factors behind the introduction of multistage concepts also include economic issues: compared to a single-stage architecture, the number of components to realize the switching fabric is reduced.     

Analytical MMAP-Based Bounds for Packet Loss in Optical Packet Switching with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. A crucial issue in packet switched networks is the avoidance of packet losses stemming from contention. In OPS, contention can be solved using a combination of exploitation of the wavelength domain (through wavelength conversion) and buffering. To provide optical buffering, fiber delay lines (FDLs) are used. In this paper, we focus on an optical packet switch with recirculating FDL buffers and wavelength converters. We introduce the Markovian arrival process with marked transitions (MMAP), which has very desirable properties as a traffic model for OPS performance assessment. Using this model, we determine lower and upper bounds for the packet loss rate (PLR) achieved by the aforementioned switch. The calculation of the PLR bounds through matrix analytical methods is repeated for a wide range of traffic conditions, including highly non-uniform traffic, both in space (i.e., packet destinations) and time (bursty traffic). The quality of these bounds is verified through comparison with simulation results.     

The European IST project DAVID: a viable approach toward optical packet switching

In this paper, promising technologies and a network architecture are presented for future optical packet switched networks. The overall network concept is presented and the major choices are highlighted and compared with alternative solutions. Both long and shorter term approaches are considered, as well as both the wide-area network and multiple-area networks parts of the network. The results presented in this paper were developed in the frame of the research project DAVID (Data And Voice Integration over DWDM) project, funded by the European Commission through the IST-framework.     

Routing Strategies to Minimize Packet Loss in an Optical Packet Switched Network with Recirculating FDL Buffers

The major goal of optical packet switching (OPS) is to match switching technology to the huge capacities provided by (D)WDM. We study optical packet switches with recirculating fiber delay line (FDL) buffers. Through simulation, we have assessed the logical performance of a single optical packet router (OPR), focusing on packet loss rate (PLR). By verifying that our scheduling algorithm does not alter the traffic profile characteristics from in- to output, we illustrate how the single node results can be used to assess network-wide performance. We use the capability of assessing end-to-end PLRs to develop network-wide routing algorithms designed to minimize the maximal PLR occurring in the network. In case studies on pan-European networks, we first compare two algorithm variants and thereafter we compare the PLR-based routing algorithm with both load balancing and shortest path routing. While load balancing achieves PLRs that are multiple orders of magnitude lower than shortest path routing, the PLR-based algorithm can reach PLRs up to two orders of magnitude better. The improvement in PLR comes at the price of only a small increase in used bandwidth (a few percent). Subsequently we show that the discussed PLR-based routing algorithm can be easily extended to multiple priorities. By introducing multiple priorities we can keep the loss rates for high priority traffic very low. However, it may lead to an increase of the obtained minimal max-PLR value for low priority traffic. But as we prove this increase to be limited, the cost of introducing multiple priorities is small.     

Platform for real-time subjective assessment of interactive multimedia applications

With the advent of cloud computing and remote execution of interactive applications, there is a need for evaluating the Quality of Experience (QoE) and the influence on this QoE of network condition variations, media encoding parameter settings and related optimization algorithms. However, current QoE assessment focuses mainly on audiovisual quality in non-interactive applications, such as video-on-demand services. On the other hand, where experiments aim to quantify interactive quality, the focus is typically targeted at games, using an ad-hoc test setup to assess the impact of network variations on the playing experience. In this paper, we present a novel platform enabling the assessment of a broad range of interactive applications (e.g., thin client remote desktop systems, remotely rendered engineering applications, games). Dynamic reconfiguration of media encoding and decoding is built into the system, to allow dynamic adaptation of the media encoding to the network conditions and the application characteristics. Evaluating the influence of these automatic adaptations is a key asset of our approach. A range of possible use cases is discussed, as well as a performance study of our implementation, showing that the platform we built is capable of highly controllable subjective user assessment. Furthermore, we present results obtained by applying the platform for a subjective evaluation of an interactive multimedia application. Specifically, the influence of visual quality and frame rate on interactive QoE has been assessed for a remotely executed race game.     

MPLS Recovery Mechanisms for IP-over-WDM Networks

Due to the fast increase of Internet traffic and the enormous bandwidth potential of all-optical transport networks based on wavelength division multiplexing, an IP-over-WDM network scenario is likely to be widespread in future communication networks. At the same time, IP networks are becoming more and more mission-critical. Hence, it is of paramount importance for IP-over-WDM networks to be able to recover quickly from frequently occurring network failures. This paper explains how multi-protocol label switching (both electrical and optical) recovery mechanisms can be important to reach that goal. Moreover, a novel MPLS recovery mechanism called fast topology-driven constrained-based rerouting is presented. Different MPLS recovery mechanisms are compared to each other. Special attention hereby goes to the additional capacity that is required to recover from frequently occurring failures.     

Creation and evaluation of large keyphrase extraction collections with multiple opinions

While several automatic keyphrase extraction (AKE) techniques have been developed and analyzed, there is little consensus on the definition of the task and a lack of overview of the effectiveness of different techniques. Proper evaluation of keyphrase extraction requires large test collections with multiple opinions, currently not available for research. In this paper, we (i) present a set of test collections derived from various sources with multiple annotations (which we also refer to as opinions in the remained of the paper) for each document, (ii) systematically evaluate keyphrase extraction using several supervised and unsupervised AKE techniques, (iii) and experimentally analyze the effects of disagreement on AKE evaluation. Our newly created set of test collections spans different types of topical content from general news and magazines, and is annotated with multiple annotations per article by a large annotator panel. Our annotator study shows that for a given document there seems to be a large disagreement on the preferred keyphrases, suggesting the need for multiple opinions per document. A first systematic evaluation of ranking and classification of keyphrases using both unsupervised and supervised AKE techniques on the test collections shows a superior effectiveness of supervised models, even for a low annotation effort and with basic positional and frequency features, and highlights the importance of a suitable keyphrase candidate generation approach. We also study the influence of multiple opinions, training data and document length on evaluation of keyphrase extraction. Our new test collection for keyphrase extraction is one of the largest of its kind and will be made available to stimulate future work to improve reliable evaluation of new keyphrase extractors.     

OMUS: an optimized multimedia service for the home environment

Media content in home environments is often scattered across multiple devices in the home network. As both the available multimedia devices in the home (e.g., smartphones, tablets, laptops, game consoles, etc.) and the available content (video and audio) is increasing, interconnecting desired content with available devices is becoming harder and home users are experiencing difficulties in selecting interesting content for their current context. In this paper, we start with an analysis of the home environment by means of a user study. Information handling problems are identified and requirements for a home information system formulated. To meet these requirements we propose the OMUS home information system which includes an optimized content aggregation framework, a hybrid group-based contextual recommender system, and an overall web-based user interface making both content and recommendations available for all devices across the home network. For the group recommendations we introduced distinct weights for each user and showed that by varying the weights, the coverage (i.e., items that can be returned by the recommender) considerably increases. Also the addition of genre filter functionality was proven to further boost the coverage. The OMUS system was evaluated by means of focus groups and by qualitative and quantitative performance assessment of individual parts of the system. The modularity of internal components and limited imposed hardware requirements implies flexibility as to how the OMUS system can be deployed (ranging from e.g., embedded in hardware devices or more software services based).