Many media services undergo a varying workload, showing periodic usage patterns or unexpected traffic surges. As cloud and NFV services are increasingly softwarized, they enable a fully dynamic deployment and scaling behaviour. At the same time, there is an increasing need for fast and efficient mechanisms to allocate sufficient resources with the same elasticity, only when they are needed. This requires adequate performance models of the involved services, as well as awareness of those models in the involved orchestration machinery. In this paper we present how a scalable content delivery service can be deployed in a resource- and time-efficient manner, using adaptive machine learning models for performance profiling. We include orchestration mechanisms which are able to act upon the profiled knowledge in a dynamic manner. Using an offline profiled performance model of the service, we are able to optimize the online service orchestration, requiring fewer scaling iterations.

The article describes a numerical approach for Massive MIMO channel modeling that accounts for the effects of electromagnetic coupling between a user and the receiving device. The modeling is performed by a combination of the Finite-Difference Time-Domain and the Ray-Tracing methods, supplemented with a stochastic geometry model of the propagation environment. The influence of user-coupling on the channel properties was studied statistically using the singular value spread and matrix power ratio metrics of the channel correlation matrix. The time-averaged Poynting vector distribution in the near-field of the receiver was evaluated using a realistic human phantom model and the Maximum Ratio Transmission precoding scheme in the downlink. The average enhancement of the time-average Poynting vector magnitude at the receiver location, compared to the surrounding area, was found to be around 10 dB when using 36 antenna elements at the base station. The electromagnetic field exposure of the phantom was assessed in terms of the 10g-average peak-spatial Specific Absorption Rate and compared with the existing public guidelines. Comparison of the EMF and exposure results provides a new perspective on the future regulatory procedures.

The virtualization of compute and network resources enables an unseen flexibility for deploying network services. A wide spectrum of emerging technologies allows an ever-growing range of orchestration possibilities in cloud-based environments. But in this context it remains challenging to rhyme dynamic cloud configurations with deterministic performance. The service operator must somehow map the performance specification in the Service Level Agreement (SLA) to an adequate resource allocation in the virtualized infrastructure. We propose the use of a VNF profile to alleviate this process. This is illustrated by profiling the performance of four example network functions (a virtual router, switch, firewall and cache server) under varying workloads and resource configurations. We then compare several methods to derive a model from the profiled datasets. We select the most accurate method to further train a model which predicts the services' performance, in function of incoming workload and allocated resources. Our presented method can offer the service operator a recommended resource allocation for the targeted service, in function of the targeted performance and maximum workload specified in the SLA. This helps to deploy the softwarized service with an optimal amount of resources to meet the SLA requirements, thereby avoiding unnecessary scaling steps.

In-band full-duplex (FD) wireless communication allows the simultaneous transmission and reception of data at the same frequency band, effectively doubling the spectral efficiency and data rate while reducing the latency. Previously published designs mostly target the self-interference (SI) cancellation in conventional wireless systems. In this paper, we focus on real-time SI cancellation for short-reach wireless FD systems. The superior signal quality of a point-to-point short-reach wireless system, allows the utilization of wideband communications to achieve a high throughput. Besides, in such wireless systems, the impacts of phase noise and nonlinear distortions are largely reduced, easing the SI cancellation. Moreover, the degradation of signal reception quality due to FD operation is experimentally evaluated in different environments. Experimental results of a prototype implementation show that a combination of antenna isolation and digital cancellation can already achieve an overall SI cancellation performance of 72.5 dB over a bandwidth of 123 MHz. This prototype can support a high-data-rate FD communication link of close to 1 Gbps up to 300 cm with an error vector magnitude lower than -26 dB in a typical indoor environment.

The growing demand for flexibility and cost reduction in the telecommunication landscape directs the focus of service development heavily to programmability and softwarization. In the domain of Network Function Virtualization (NFV), one of the goals is to replace dedicated hardware devices (such as switches, routers, firewalls) with software-based network functionalities, showing comparable performance when deployed on common servers. In this paper, we discuss how current VNF implementation and deployment strategies impact the efficient monitoring of their resources. In a multi-tenant, NFV-based ecosystem, different Service Providers deploy VNFs on a shared infrastructure, where the Infrastructure Provider exposes only VNF specific metrics and little information about the physical hosts where the VNFs are eventually orchestrated. Especially in the situation where datacenters are overcommitted, detecting the risk of e.g. CPU starvation is not straight-forward, when no information from the physical host is available. A new monitoring technique is introduced, based on the skewness of the measured probability distribution of the VNF resource consumption. Our measurements show that this metric is a good indicator for the (un)availability of the required CPU resources in the datacenter.

Summary: We present a Cytoscape app for the ISMAGS algorithm, which can enumerate all instances of a motif in a graph, making optimal use of the motif’s symmetries to make the search more efficient. The Cytoscape app provides a handy interface for this algorithm, which allows more efficient network analysis. Availability and Implementation: The Cytoscape app for ISMAGS can be freely downloaded from the Cytoscape App store http://apps.cytoscape.org/apps/ismags. Source code and documentation for ISMAGS are available at https://github.com/biointec/ismags. Source code and documentation for the Cytoscape app are available at https://gitlab.psb.ugent.be/thpar/ISMAGS_Cytoscape. Contacts: [email protected] or [email protected] Supplementary information: Supplementary data are available at Bioinformatics online.

BACKGROUND: Recently, many standalone applications have been proposed to correct sequencing errors in Illumina data. The key idea is that downstream analysis tools such as de novo genome assemblers benefit from a reduced error rate in the input data. Surprisingly, a systematic validation of this assumption using state-of-the-art assembly methods is lacking, even for recently published methods. RESULTS: For twelve recent Illumina error correction tools (EC tools) we evaluated both their ability to correct sequencing errors and their ability to improve de novo genome assembly in terms of contig size and accuracy. CONCLUSIONS: We confirm that most EC tools reduce the number of errors in sequencing data without introducing many new errors. However, we found that many EC tools suffer from poor performance in certain sequence contexts such as regions with low coverage or regions that contain short repeated or low-complexity sequences. Reads overlapping such regions are often ill-corrected in an inconsistent manner, leading to breakpoints in the resulting assemblies that are not present in assemblies obtained from uncorrected data. Resolving this systematic flaw in future EC tools could greatly improve the applicability of such tools.

Resource abstraction aims at enabling flexible allocation of capacity to serve demands by aggregating physical resources taken out of distributed resource pools accessible via dedicated gateways. This paradigm sits at the heart of many networking models including resource virtualization and other cloud computing. In this paper, we show this generic problem can be modeled by combining and extending the Hub Location with the Location Routing Problem, referred to as the Hub-Location Routing Problem (HLRP). A mixed- integer program for the HLRP is proposed and evaluated using representative settings. We compare the results with those obtained when modeling the initial problem as an Location Routing Problem only; hence, obtain a quantitative assessment of the performance tradeoffs between resource abstraction, (al)location and routing.

BACKGROUND: Many algorithms have been developed to infer the topology of gene regulatory networks from gene expression data. These methods typically produce a ranking of links between genes with associated confidence scores, after which a certain threshold is chosen to produce the inferred topology. However, the structural properties of the predicted network do not resemble those typical for a gene regulatory network, as most algorithms only take into account connections found in the data and do not include known graph properties in their inference process. This lowers the prediction accuracy of these methods, limiting their usability in practice. RESULTS: We propose a post-processing algorithm which is applicable to any confidence ranking of regulatory interactions obtained from a network inference method which can use, inter alia, graphlets and several graph-invariant properties to re-rank the links into a more accurate prediction. To demonstrate the potential of our approach, we re-rank predictions of six different state-of-the-art algorithms using three simple network properties as optimization criteria and show that Netter can improve the predictions made on both artificially generated data as well as the DREAM4 and DREAM5 benchmarks. Additionally, the DREAM5 E.coli. community prediction inferred from real expression data is further improved. Furthermore, Netter compares favorably to other post-processing algorithms and is not restricted to correlation-like predictions. Lastly, we demonstrate that the performance increase is robust for a wide range of parameter settings. Netter is available at http://bioinformatics.intec.ugent.be. CONCLUSIONS: Network inference from high-throughput data is a long-standing challenge. In this work, we present Netter, which can further refine network predictions based on a set of user-defined graph properties. Netter is a flexible system which can be applied in unison with any method producing a ranking from omics data. It can be tailored to specific prior knowledge by expert users but can also be applied in general uses cases. Concluding, we believe that Netter is an interesting second step in the network inference process to further increase the quality of prediction.

Real-Time Travel Information (RTTI) for rail commuters is still used inefficiently today and is rarely combined with other knowledge to come to a truly personalised and situation-aware multimodal travelling assistance. It is up to the travellers themselves to look for important info about their trip through static schedules or dedicated non-personalised applications. In a highly dynamic context such as that of public transportation, it would make life easier if one was able to consult the right information at the right time (removing superfluous information), for a variety of multimodal public transportation options, taking into account the context of the person travelling. In this paper we present the LimeDS framework, allowing application developers to rapidly define data workflows from a variety of data sources, deploy these workflows in a scalable and resilient manner and expose results to client applications as REST endpoints. A Proof-of-Concept (PoC) shows how our proposed framework can be used to tie together different open transportation data sources in order to create highly dynamic multimodal travel assistance applications by semantically enriching the data into knowledge, checking for ontological consistency and reason over the resulting knowledge.

A variety of dynamic bandwidth allocation (DBA) algorithms have been proposed to foster the performance of Ethernet passive optical networks (EPONs). These DBA algorithms use packet delay as an important quality of service (QoS) metric. This has led to a significant interest in developing mathematical models for analyzing the delay. These delay models often provide valuable qualitative results and worthwhile insights in understanding the mechanism of the delay and the manner in which it depends upon algorithm characteristics. Up to now, the delay models have been developed under some approximations, e.g., fixed packet sizes, negligible distances between a server and its users, a gated bandwidth assignment method, and Poisson traffic. In this paper, we develop the delay models for more realistic scenarios than the current state-of-the-art, including gated and limited bandwidth assignment methods, Poisson and Pareto traffic, and long-reach PONs in which the distance between the server and the users is significant and hence not negligible. We model different DBA paradigms, such as REPORT after data, REPORT before data, and multi-thread polling. The results from simulation experiments confirm the accuracy of the delay models.

MOTIVATION: The accurate discovery and annotation of regulatory elements remains a challenging problem. The growing number of sequenced genomes creates new opportunities for comparative approaches to motif discovery. Putative binding sites are then considered to be functional if they are conserved in orthologous promoter sequences of multiple related species. Existing methods for comparative motif discovery usually rely on pregenerated multiple sequence alignments, which are difficult to obtain for more diverged species such as plants. As a consequence, misaligned regulatory elements often remain undetected. RESULTS: We present a novel algorithm that supports both alignment-free and alignment-based motif discovery in the promoter sequences of related species. Putative motifs are exhaustively enumerated as words over the IUPAC alphabet and screened for conservation using the branch length score. Additionally, a confidence score is established in a genome-wide fashion. In order to take advantage of a cloud computing infrastructure, the MapReduce programming model is adopted. The method is applied to four monocotyledon plant species and it is shown that high-scoring motifs are significantly enriched for open chromatin regions in Oryza sativa and for transcription factor binding sites inferred through protein-binding microarrays in O.sativa and Zea mays. Furthermore, the method is shown to recover experimentally profiled ga2ox1-like KN1 binding sites in Z.mays. AVAILABILITY AND IMPLEMENTATION: BLSSpeller was written in Java. Source code and manual are available at http://bioinformatics.intec.ugent.be/blsspeller CONTACT: [email protected] or [email protected]. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

More and more wireless networks are deployed with overlapping coverage. Especially in the unlicensed bands, we see an increasing density of heterogeneous solutions, with very diverse technologies and application requirements. As a consequence, interference from heterogeneous sources-also called cross-technology interference-is a major problem causing an increase of packet error rate (PER) and decrease of quality of service (QoS), possibly leading to application failure. This issue is apparent, for example, when an IEEE 802.15.4 wireless sensor network coexists with an IEEE 802.11 wireless LAN, which is the focus of this work. One way to alleviate cross-technology interference is to avoid it in the frequency domain by selecting different channels. Different multichannel protocols suitable for frequency-domain interference avoidance have already been proposed in the literature. However, most of these protocols have only been investigated from the perspective of intratechnology interference. Within this work, we create an objective comparison of different candidate channel selection mechanisms based on a new multichannel protocol taxonomy using measurements in a real-life testbed. We assess different metrics for the most suitable mechanism using the same set of measurements as in the comparison study. Finally, we verify the operation of the best channel selection metric in a proof-of-concept implementation running on the testbed.

Abstract Receiver Strength Signal Indication based Wireless Sensor Networks offer a cheap solution for location‐aware applications. For a final breakthrough these systems need fast deployment and easy auto‐configuration. In this study, we use the real‐life iMinds test bed to expand a two‐dimensional localization algorithm to the pseudo third dimension with very low additional computational time. Our experiments show that this fast three‐dimensional algorithm has no outliers and avoids manual calibration. Our algorithm has lower position errors than a maximum likelihood algorithm with a mean square error cost function. Furthermore, with non‐parametric statistical tests, we show that our previously designed two‐dimensional preprocessing performs equally well in pseudo‐three dimensions: the preprocessing reduces the position error in a statistically significant way.Copyright © 2013 John Wiley & Sons, Ltd.

Indoor localization and navigation using wireless sensor networks is still a big challenge if expensive sensor nodes are not involved.Previous research has shown that in a sparse distributed sensor network the error distance is way too high.Even room accuracy can not be guaranteed.In this paper, an easy-to-use generic positioning framework is proposed, which allows users to plug in a single or multiple positioning algorithms.We illustrate the usability of the framework by discussing a new hybrid positioning solution.The combination of a weighted (range-based) and proximity (range-free) algorithm is made.Both solutions separately have an average error distance of 13.5m and 2.5m respectively.The latter result is quite accurate due to the fact that our testbeds are not sparse distributed.Our hybrid algorithm has an average error distance of 2.66m only using a selected set of nodes, simulating a sparse distributed sensor network.All our experiments have been executed in the iMinds testbed: namely at "de Zuiderpoort".These algorithms are also deployed in two real-life environments: "De Vooruit" and "De Vijvers".

In an IPTV environment, different techniques exist to provide faster random access or equivalently, a faster channel switching experience, but none of them provide backward compatibility and limited overhead at the same time. In this paper, a technique is proposed to increase the random access frequency for the High Efficiency Video Coding (HEVC) standard by using a single-loop scalable version of it. This is achieved by encoding an enhancement layer with a higher frequency of random access points compared to the base layer. With this scalable configuration, a backward compatible base stream remains present. The proposed technique requires 12.4% less bitrate compared to sending the fast and slow switching streams in a non-scalable way. Compared to the almost standardized multi-loop scalable extension of HEVC, 5.5% less bitrate is needed on the core of the IPTV network and 12.5% less bitrate on the access network during steady state conditions. Moreover, the multi-loop scalable extension does not provide backward compatibility with legacy HEVC decoders.

As open standards for the Internet of Things gain traction, the current Intranet of Things will evolve to a truly open Internet of Things, where constrained devices are first class citizens of the public Internet. However, the large amount of control over constrained networks offered by today's vertically integrated platforms, becomes even more important in an open IoT considering its promise of direct end-to-end interactions with constrained devices. In this paper a set of challenges is identified for controlling interactions with constrained networks that arise due to their constrained nature and their integration with the public Internet. Furthermore, a number of solutions are presented for overcoming these challenges by means of an intercepting intermediary at the edge of the constrained network.

The Constrained Application Protocol (CoAP) is a new Internet protocol that is currently being standardized. CoAP allows access to the drastically increasing number of smart objects and their sensing resources from virtually anywhere. It is a light-weight protocol designed to cope with the restrictions imposed by the limited resources (CPU, memory, power,...) of many smart objects. Depending on the application, information from individual objects might not be sufficient, reliable, or useful. An application may need to aggregate and/or compare data from a group of objects in order to obtain accurate results. Although multicast may be used to transmit the same request to several objects, multicast communication with smart objects has some disadvantages. Programming individual requests is another solution but lacks flexibility and opportunities for reusability. In this paper we propose a novel CoAP-based approach for communication with a group of resources across multiple smart objects. This approach organizes the group of resources that should be accessed into a new CoAP resource, called an entity, and nicely integrates several important aspects of entity management: creation, validation, usage and manipulation. In order to demonstrate the feasibility of this approach we present an implementation and experimental validation.

OpenFlow decouples the control plane functionality from switches, and embeds it into one or more servers called controllers. One of the challenges of OpenFlow is to deploy a network where control and data traffic are transmitted on the same channel (in-band mode). Implementing such an in-band mode is complex, since switches have to search and establish a path to the controller (bootstrapping) through the other switches in the network. In this paper, we propose a method that facilitates this automatic bootstrapping of switches. In this method, the controller establishes its own control network through the neighbor switches that are connected to it by the OpenFlow protocol. We measure suitability of the proposed method by performing bootstrapping experiments in different types of topologies: linear, ring, star and mesh topologies. The experimental results show that the proposed method allows bootstrapping in a minimal time, which makes it suitable even for a large network.

As embedded networks are evolving to open systems, it's becoming possible to create new applications on top of these existing embedded systems. However, developing new applications can be difficult due to the large diversity of protocols that exist today. In this paper, the authors demonstrate how employing the CoAP protocol can enable rapid application development by re-using well-known principles from the Web development world. Furthermore, we also demonstrate how a number of extensions to CoAP help to lower the barrier for developing applications even further.

RouteFlow provides a way to run routing control platforms (e.g. Quagga) in OpenFlow networks. One of the issues of RouteFlow is that an administrator needs to devote a lot of time (typically 7 hours for 28 switches) in manual configurations. We propose and demonstrate a framework that can automatically configure RouteFlow. For this demonstration, we use an emulated pan-European topology of 28 switches. In the demonstration, we stream a video clip from a server to a remote client, and show that the video clip reaches at the remote client within 4 minutes (including the configuration time). In addition, we show automatic configuration of RouteFlow using a GUI (Graphical User Interface).

MOTIVATION: When genomic data are associated with gene expression data, the resulting expression quantitative trait loci (eQTL) will likely span multiple genes. eQTL prioritization techniques can be used to select the most likely causal gene affecting the expression of a target gene from a list of candidates. As an input, these techniques use physical interaction networks that often contain highly connected genes and unreliable or irrelevant interactions that can interfere with the prioritization process. We present EPSILON, an extendable framework for eQTL prioritization, which mitigates the effect of highly connected genes and unreliable interactions by constructing a local network before a network-based similarity measure is applied to select the true causal gene. RESULTS: We tested the new method on three eQTL datasets derived from yeast data using three different association techniques. A physical interaction network was constructed, and each eQTL in each dataset was prioritized using the EPSILON approach: first, a local network was constructed using a k-trials shortest path algorithm, followed by the calculation of a network-based similarity measure. Three similarity measures were evaluated: random walks, the Laplacian Exponential Diffusion kernel and the Regularized Commute-Time kernel. The aim was to predict knockout interactions from a yeast knockout compendium. EPSILON outperformed two reference prioritization methods, random assignment and shortest path prioritization. Next, we found that using a local network significantly increased prioritization performance in terms of predicted knockout pairs when compared with using exactly the same network similarity measures on the global network, with an average increase in prioritization performance of 8 percentage points (P < 10(-5)). AVAILABILITY: The physical interaction network and the source code (Matlab/C++) of our implementation can be downloaded from http://bioinformatics.intec.ugent.be/epsilon. CONTACT: [email protected], [email protected], [email protected] SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

In order to ensure optimal quality of experience toward end users during video streaming, automatic video quality assessment becomes an important field-of-interest to video service providers. Objective video quality metrics try to estimate perceived quality with high accuracy and in an automated manner. In traditional approaches, these metrics model the complex properties of the human visual system. More recently, however, it has been shown that machine learning approaches can also yield competitive results. In this paper, we present a novel no-reference bitstream-based objective video quality metric that is constructed by genetic programming-based symbolic regression. A key benefit of this approach is that it calculates reliable white-box models that allow us to determine the importance of the parameters. Additionally, these models can provide human insight into the underlying principles of subjective video quality assessment. Numerical results show that perceived quality can be modeled with high accuracy using only parameters extracted from the received video bitstream.

The evolution toward grid and cloud computing as observed for over a decennium illustrates the crucial role played by (optical) networks in supporting today's applications. In this paper, we start from an overview of the challenging applications in both academic (further referred to as scientific), enterprise (business) and nonprofessional user (consumer) domains. They pose novel challenges, calling for efficient interworking of IT resources, for both processing and storage, as well as the network that interconnects them and provides access to their users. We outline those novel applications' requirements, including sheer performance attributes (which will determine the quality as perceived by end users of the cloud applications), as well as the ability to adapt to changing demands (usually referred to as elasticity) and possible failures (i.e., resilience). In outlining the foundational concepts that provide the building blocks for grid/cloud solutions that meet the stringent application requirements we highlight, a prominent role is played by optical networking. The pieces of the solution studied in this respect span the optical transport layer as well as mechanisms located in higher layers (e.g., anycast routing, virtualization) and their interworking (e.g., through appropriate control plane extensions and middleware). Based on this study, we conclude by identifying challenges and research opportunities that can enable future-proof optical cloud systems (e.g., pushing the virtualization paradigms to optical networks).

In a future 'internet of things', an increasing number of every-day objects are connected with each other. Nowadays, connectivity between these devices is supported by assigning each device to an existing (wireless) network. However, these networks do not take into account the individual needs of these devices, even though all these devices are very different in terms of application requirements and hardware capabilities. Moreover, multiple existing networks are often configured independent from each other without any interaction. As an alternative, this paper proposes and discusses a methodology that more efficiently supports network cooperation between heterogeneous devices. The paper argues for autonomously created communities of similar devices, that are able to negotiate with different co-located communities to further optimize their network performance. Different communities engage in cooperation by activating network service, but only when the end result is beneficial for all involved communities. In this paper, the concepts and advantages of this approach are discussed. In addition, a methodology is explored that is able to realize these concepts. Finally, based on this methodology, possible network solutions are presented, remaining challenges are listed and future research opportunities are identified.

This paper is aiming at facilitating the energy-efficient operation of an integrated optical network and IT infrastructure. In this context we propose an energy-efficient routing algorithm for provisioning of IT services that originate from specific source sites and which need to be executed by suitable IT resources (e.g. data centers). The routing approach followed is anycast, since the requirement for the IT services is the delivery of results, while the exact location of the execution of the job can be freely chosen. In this scenario, energy efficiency is achieved by identifying the least energy consuming IT and network resources required to support the services, enabling the switching off of any unused network and IT resources. Our results show significant energy savings that can reach up to 55% compared to energy-unaware schemes, depending on the granularity with which a data center is able to switch on/off servers.

Software Defined Networking is a networking paradigm which allows network operators to manage networking elements using software running on an external server. This is accomplished by a split in the architecture between the forwarding element and the control element. Two technologies which allow this split for packet networks are For CES and Openflow. We present energy efficiency and resilience aspects of carrier grade networks which can be met by Openflow. We implement flow restoration and run extensive experiments in an emulated carrier grade network. We show that Openflow can restore traffic quite fast, but its dependency on a centralized controller means that it will be hard to achieve 50 ms restoration in large networks serving many flows. In order to achieve 50 ms recovery, protection will be required in carrier grade networks.

We demonstrate machine learning augmented Open Shortest Path First (OSPF) routing which infers Shared Risk Groups (SRG) from link failure history. For an initial link failure matching an SRG, it predicts subsequent link state advertisements corresponding with that SRG, improving convergence and recovery times during multiple network failures.

In this paper we propose a new random channel access protocol to reduce the channel access delay in a multichannel orthogonal frequency division multiple access (OFDMA) wireless networks. In particular, we propose a two dimensional random walk through time and frequency domain slots simultaneously to reduce the random channel access delay for the IEEE 802.16e-2005 based WiMAX media access control (MAC) protocol. We prove through simulation that our proposed scheme improves upon the existing random channel access mechanism with truncated binary back-off, currently implemented in WiMAX. We demonstrated that with our proposed channel access mechanism, a mobile node with real time traffic requirements will have minimum service disruption due to the reduced delay in the initial ranging and the bandwidth request phase while changing rooms.

Abstract Summary: Network motifs in integrated molecular networks represent functional relationships between distinct data types. They aggregate to form dense topological structures corresponding to functional modules which cannot be detected by traditional graph clustering algorithms. We developed CyClus3D, a Cytoscape plugin for clustering composite three-node network motifs using a 3D spectral clustering algorithm. Availability: Via the Cytoscape plugin manager or http://bioinformatics.psb.ugent.be/software/details/CyClus3D. Contact: [email protected] Supplementary Information: Supplementary data are available at Bioinformatics online.

MOTIVATION: Many comparative genomics studies rely on the correct identification of homologous genomic regions using accurate alignment tools. In such case, the alphabet of the input sequences consists of complete genes, rather than nucleotides or amino acids. As optimal multiple sequence alignment is computationally impractical, a progressive alignment strategy is often employed. However, such an approach is susceptible to the propagation of alignment errors in early pairwise alignment steps, especially when dealing with strongly diverged genomic regions. In this article, we present a novel accurate and efficient greedy, graph-based algorithm for the alignment of multiple homologous genomic segments, represented as ordered gene lists. RESULTS: Based on provable properties of the graph structure, several heuristics are developed to resolve local alignment conflicts that occur due to gene duplication and/or rearrangement events on the different genomic segments. The performance of the algorithm is assessed by comparing the alignment results of homologous genomic segments in Arabidopsis thaliana to those obtained by using both a progressive alignment method and an earlier graph-based implementation. Especially for datasets that contain strongly diverged segments, the proposed method achieves a substantially higher alignment accuracy, and proves to be sufficiently fast for large datasets including a few dozens of eukaryotic genomes. AVAILABILITY: http://bioinformatics.psb.ugent.be/software. The algorithm is implemented as a part of the i-ADHoRe 3.0 package.

The use of semantic technology has recently witnessed a huge increase. One of the areas in which this technology is being used increasingly more often is that of context-aware agents. However, the use of ontologies in general and reasoning in particular can rapidly become resource intensive. Certainly if the data set, called the A-Box, used by these agents grows considerably over time. Moreover, in order to create context-aware applications, taking into account a wide range of different data sets and context parameters, agents have to be provided to expose that data. The collaboration between the agents in the system is necessary to correlate the information and augment the intelligence and added value of the context-aware agents. Therefore, there is a need to have a distributed approach by means of a service-platform, where the different agents in a context-aware environment can collaborate. The main focus of this article is on the research on the design of a service-platform for semantic ontology-based context-aware collaboration. The platform architecture to allow the collaboration and scheduling, together with the associated algorithms, will be presented. The engineering and implementation details will be highlighted. By means of detailed UML sequence diagrams, we will present the workflow and collaboration between the different modules in the platform. Additionally, supporting developments, such as the meta-ontology and our ontology generator, OTAGen, will be presented. Furthermore, we will detail how the platform can operate in an autonomous way, taking into account the changing context of the agents in the platform.

A large number of intelligent components for managing the Future Internet have been proposed recently or are currently being investigated. However, before these network components can be deployed in real-life networks, they need to be thoroughly validated through realistic and large scale experiments. Testbed facilities provide a means to set up large scale network topologies but offer only a limited functionality in managing the deployment of the experiment itself. In this paper, we propose a management framework which automates the configuration and management of network experiments. The framework focuses on the emulation of user behaviour, to obtain realistic network conditions, and features several mechanisms that allow to reduce the experiments' size both temporally (in shorter simulation time) as spatially (with fewer physical nodes).

In this paper, we use machine learning technique at the routers to study the link state protocol data to predict the existence of shared risk link groups (SRLG) in the network. In particular, we use the correlation between different link state updates (LSUs) issued by different network nodes (routers) upon failure. The concerned network router then runs a novel Bayesian network based statistical learning process to learn about the possible existence of SRLGs. The decision of this online learning is transferred to the routing information base (RIB) so that it can accordingly modify the routing table for the entire SRLG upon failure detection of one of the candidate node of that particular SRLG and hence reduce the protection switching time.

For Mobile WiMAX, data rate and throughput figures are often presented in literature. However, the used calculation methods and the influence of the packet size on the data rate are often unclear. Therefore, we develop a new method in order to obtain more precise data rate figures at the MAC (Medium Access Control) layer. In this paper the common physical data rate and MAC data rate calculation method are first examined. Next, the new MAC data rate calculation method is presented. They are applied to the official set of Mobile WiMAX parameters. Our method is able to differentiate for different packet sizes and provides a prediction of the MAC layer throughput.

As the adoption of the Service Oriented Architecture paradigm has dramatically increased over the past few years, proper coordination of loosely coupled services becomes an important issue when building state-of-the-art applications. This coordination is typically organized through orchestration (requiring a central coordinating entity) or through choreographies. While the latter approach allows for a fully distributed coordination, the need also arises for a distributed conformance check, ensuring that each participant of the choreography behaves according to the general choreography. In this paper, a formalism is presented to ensure this conformance at design time, with possible extensions to deploy time and to runtime conformance checking. This formalism is referred to as the piX-model and it will be shown that the approach taken is inherently less complex, both in time and space, than the conventional π-calculus-based approach, whilst offering the same conformance guarantees. This gain in performance allows for a small design turnaround time, and also opens the avenue to runtime conformance checking by resource constrained devices.

As the variety in network service platforms and end user devices grows rapidly, content providers must constantly adapt their production system to support these new technologies. In this paper, we present a middleware platform for deploying highly interactive (television) applications over a diverse collection of networks and end user devices. As the user interface of such interactive applications may vary depending on the capabilities of the different target devices, our middleware uses UIML for the description of generic user interfaces. Our middleware platform also provides a pluggable support for new networks. A factor that highly complicates the design is the need for strict synchronization between an interactive application and video or audio data that is broadcasted. In order to support a maximum of functionality, downloadable application logic is used to provide the interactive services. As a test case, an evaluation setup was built, targeting both set-top boxes and mobile phones.

Deflection routing is a much-studied contention resolution technique in the context of Optical Burst/Packet Switching networks, as it promises to improve burst blocking performance and may reduce or even eliminate buffer requirements. An OBS-based Grid is frequently based on anycast routing, which h

In this paper we discuss the impact of proactive routing in comparison with a reactive routing approach in an environment where multiple communication technologies are used simultaneously. Therefore the Virtual Private Ad Hoc Networking platform will be introduced and used. A simulation environment is created and used to illustrate the outcomes with a simple scenario. Although many papers have been published comparing proactive and reactive routing protocols, this paper focusses on the impact on the VPAN platform with its two-level hierarchical architecture and nodes joining and leaving clusters.

Wireless sensor networks consist of several hundredths of simple sensing devices, equipped with a radio. They are typically used for monitoring and automation purposes of large areas. Due to their simplicity, these networks quickly run out of energy, and often have problems regarding scalability and available bandwidth. To solve these issues, current research is mostly limited to the addition of extra sinks to the network, or the use of gateways to request sensor data over the Internet. In this paper, we explore how wireless sensor networks can be combined with wireless mesh networks to obtain a more optimized solution. The mesh network can be used to connect separate sensor networks, to connect sensor nodes with a monitoring platform, or as a scalable backbone for sensor to sensor communication. Additionally, we give an overview of the advantages and disadvantages of existing interconnection techniques between wireless and mesh networks, and propose several new interconnection strategies. Finally, we identify remaining challenges, upon which future research can be based.

DSL aggregation networks are evolving to the standard platform for the delivery of multimedia services such as television and network based personal video recording. These multimedia services introduce large challenges for network operators as they are sensitive to packet loss. Therefore, admission control mechanisms are required to avoid congestion caused by allowing too many sessions. However, as multimedia services are often bursty it is not possible to reserve a fixed amount of bandwidth in the network since this policy will lead to either over-admittance or under-admittance. Recently, the IETF Pre-Congestion Notification (PCN) Working Group, proposed a measurement based admission control mechanism, where the network load is measured at each node and sessions are allowed or blocked at the edge of the network. In this paper, we extend and evaluate the PCN mechanism: we propose a new measurement algorithm for PCN, based on bandwidth metering, and determine the configuration guidelines for the parameters of both the original token bucket based approach and the novel algorithm for different network conditions and traffic types. More specifically, we study PCN's applicability on protecting VBR video services, which is currently not studied in the PCN Working Group. Furthermore, we characterise the gain of PCN in comparison to a centralised admission control mechanism.

Massively online virtual environments (MOVEs) have been gaining popularity for several years. Today, these complex networked applications are serving thousands of clients simultaneously. However, these MOVEs are typically hosted on specialized server clusters and rely on internal knowledge of the services to optimize the load balancing. This makes running MOVEs an expensive undertaking as it cannot be outsourced to third party hosting providers. This paper details two integer linear programming approaches to optimize the MOVE deployment through load balancing and minimizing the delay experienced by the end-users. Optimization includes assigning MOVE components to resources and replication of components to increase the scalability. One approach assuming full application knowledge of a dedicated MOVE and one with no internal knowledge and geared toward a generic MOVE hosting platform. For both cases an optimizing heuristic is evaluated and the obtained results are compared.

A generic and self-managing service hosting infrastructure, provides a means to offer a large variety of services to users across the Internet. Such an infrastructure provides mechanisms to automatically allocate resources to services, discover the location of these services, and route client requests to a suitable service instance. In this paper we propose a dynamic and latency-aware algorithm for assigning resources to services. Additionally, the proposed service hosting architecture and its protocols to support the service placement algorithm, are described in detail. Extensive simulations were performed to compare the solution of our latency-aware algorithm to the latency-unaware variant, in terms of system efficiency and scalability.

In this paper we introduce the Virtual Private Ad Hoc Networking platform as an integrated solution for emergency communication and applications. This platform creates a virtual logical self-organizing network on top of existing network technologies reducing complexity and facilitating immediate availability. The architecture and its features will be explained in detail and matched against the specific communication needs of emergency applications.

The xStreamer intends to be a flexible and modular open source streamer. The selection of current open source streamers which support both video and audio is limited, with VLC Media Player, Darwin Streaming Server and Helix DNA Server being the foremost solutions. The xStreamer distinguishes itself by providing a modularity that goes beyond the mere modular programming offered by the current open source solutions and that manifests itself in how the user controls and configures the streamer.

In thin client computing, applications are executed on a network server instead of on the user terminal. Since the amount of processing at the terminal is reduced, thin clients are potentially energy efficient devices. However, a network connection between client and server is required for the transmission of user input and display updates. The energy needed for this intense network communication might undo or even exceed the power savings achieved by the reduction in client-side processing. In this paper, we present experimental results on power efficiency of the wireless platform on the thin client in case of thin client traffic. The discussion is focused on VNC-RFB, a widespread thin client protocol, over an IEEE 802.11 link in three typical user scenarios. The results indicate that a cross-layer approach between application and wireless link layer could potentially lead to important power savings.

A grid is a distributed computational and storage environment often composed of heterogeneous autonomously managed subsystems. As a result, varying resource availability becomes commonplace, often resulting in loss and delay of executing jobs. To ensure good grid performance, fault tolerance should be taken into account. Commonly utilized techniques for providing fault tolerance in distributed systems are periodic job checkpointing and replication. While very robust, both techniques can delay job execution if inappropriate checkpointing intervals and replica numbers are chosen. This paper introduces several heuristics that dynamically adapt the above mentioned parameters based on information on grid status to provide high job throughput in the presence of failure while reducing the system overhead. Furthermore, a novel fault-tolerant algorithm combining checkpointing and replication is presented. The proposed methods are evaluated in a newly developed grid simulation environment dynamic scheduling in distributed environments (DSiDE), which allows for easy modeling of dynamic system and job behavior. Simulations are run employing workload and system parameters derived from logs that were collected from several large-scale parallel production systems. Experiments have shown that adaptive approaches can considerably improve system performance, while the preference for one of the solutions depends on particular system characteristics, such as load, job submission patterns, and failure frequency.

Nowadays, many telecom operators are reluctant to roll out a new fiber to the home (FTTH) infrastructure, as they are put off by the high investment costs. Inspired by several local FTTH initiatives, especially in Western Europe, this paper considers an FTTH rollout by a local community. We show that clearly different economics play a part in case a community would roll out the FTTH infrastructure, and we give also an indication of some required conditions to obtain a feasible FTTH rollout. To get realistic results, the techno-economic study has been applied on a municipality network in the city of Ghent, located in Belgium. We have performed a cost/benefit analysis, and different rollout schemes are compared to each other. As the introduction of a new technology involves a lot of uncertainties, it is of great importance to determine the most influencing parameters. For that purpose, we have executed a detailed sensitivity analysis, which also provide us with a general forecast of the outcome of the considered case study.

To cope with ever-increasing traffic demands in transport networks, all-optical switching is currently perceived as a potential solution to remove bottlenecks caused by optoelectronic conversions. An effective realization of this concept must support a wide range of traffic patterns, while remaining feasible to construct and deploy both in an economical and practical sense. In this paper, we propose the use of multi-granular optical cross-connects (MG-OXC), which support switching on both the wavelength and sub-wavelength level. To this end, the MG-OXCs are equipped with cheap, highly scalable slow switching fabrics, as well as a small number of expensive fast switching ports. The main goal of this work is to motivate the use of multi-granular switching, as this can reduce total network installation costs. To this end, we introduce an Integer Linear Programming model, and our evaluation demonstrates that multi-granular optical switching can be a cost-effective solution on the network level, in comparison to slow only or fast only approaches. Furthermore, we can achieve reduced costs of individual OXC nodes, which allows us to minimize scalability problems corresponding to emerging fast switching fabrics.

In this paper, the focus is on how context information can be efficiently modeled with an ontology. This ontology can than be used by reasoning algorithms which are based on this context information. This is illustrated with a use case which studies the evolution from a place oriented to a person oriented nurse call system. An ontology was designed which holds the necessary context information. A nurse call algorithm that uses this information was constructed. The CASP Context framework was extended to implement the use case. This framework is bases on an OSGi framework. Rules are formulated to implement the algorithm. OWL was applied to integrate the ontology into the framework. A Web Service interface was designed which allows to insert new information into the Knowledge Base or extract information from it. At last a simulation was set up to show the advantages of the person oriented approach. The results of a performance study are shown as well.

On the one hand, agent-based software platforms are commonly used these days, while on the other hand Semantic Web technologies are also maturing. It is obvious that the combination of these two technologies can bring added value through the creation of Semantic Agent-based frameworks. However, it is also known that these Semantic Web technologies, and the reasoning on ontologies in particular, can rapidly become resource intensive. In order to get a clear view on this problem, we have developed OTAGen, a highly tunable tool to generate customized ontologies and corresponding queries. The generated ontologies can then be used to evaluate at design-time the performance of the Semantic Agent-based platform as a function of the number of ontologies, users and queries.

Nowadays, wireless sensor and actuator networks are a hot issue because they can enable the Internet of things at little expense. Research activities mainly focus on one aspect of these networks (e.g. energy consumption) neglecting others (e.g. latency, scalability). Aspects like energy reduction, scalability, quality-of-service, and reliability are key requirements in our envisaged heterogeneous applications for sensor and actuator networks in commercial/residential buildings consisting of 1000+ nodes. In this paper, a stack which meets these requirements is proposed. We found that simulations only are not sufficient when developing WSAN solutions. We showed that it is possible to combine low-power with low-latency on large-scale QoS-aware networks.

All-optical label swapping (AOLS) forms a key technology towards the implementation of all-optical packet switching nodes (AOPS) for the future optical Internet. The capital expenditures of the deployment of AOLS increases with the size of the label spaces (i.e. the number of used labels), since a special optical device is needed for each recognized label on every node. Label space sizes are affected by the way in which demands are routed. For instance, while shortest-path routing leads to the usage of fewer labels but high link utilization, minimum interference routing leads to the opposite. This paper studies all-optical label stacking (AOLStack), which is an extension of the AOLS architecture. AOLStack aims at reducing label spaces while easing the compromise with link utilization. In this paper, an integer lineal program is proposed with the objective of analyzing the softening of the aforementioned trade-off due to AOLStack. Furthermore, a heuristic aiming at finding good solutions in polynomial-time is proposed as well. Simulation results show that AOLStack either a) reduces the label spaces with a low increase in the link utilization or, similarly, b) uses better the residual bandwidth to decrease the number of labels even more.

In this paper we present a cross layer topology preserving channel selection protocol for a two interface wireless mesh network. The presented protocol is a cluster driven channel selection protocol, preserving a single interface to maintain connectivity and using the other interface to participate in small clusters. The clusters are organized by an independent set clustering algorithm, in which the cluster head dictates the operating channel for the local cluster. We show that the channel selection algorithm doubles the capacity for both a regular grid and a random topology.

More and more, multimedia services are being accessed via fixed and mobile networks. These services are typically much more sensitive to packet loss, delay and/or congestion than traditional services. In particular, multimedia data is often time critical and, as a result, network issues are not well tolerated and significantly deteriorate the userpsilas quality of experience (QoE). We therefore propose a QoE optimization platform that is able to mitigate problems that might occur at any location in the delivery path from service provider to customer. More specifically, the distributed architecture supports overlay routing to circumvent erratic parts of the network core. In addition, it comprises proxy components that realize last mile optimization through automatic bandwidth management and the application of processing on multimedia flows. In this paper we introduce a transcoding service for this proxy component which enables the transformation of H.264/AVC video flows to an arbitrary bit rate. Through representative experimental results, we illustrate how this addition enhances the QoE optimization capabilities of the proposed platform by allowing the proxy component to compute more flexible and effective bandwidth distributions.

This paper describes extensive research in the field of the Multipoint Control Protocol (MPCP) for the Ethernet Passive Optical Network (EPON). More in particular the dynamic bandwidth allocation (DBA) algorithm IPACT (Interleaved Polling with Adaptive Cycle Time) is analytically modeled. The main focus has been on analyzing cycle times and packet delay in detail. The analysis starts from a simple traffic model with Poisson arrival rates, symmetric load and fixed packet size. Based on the obtained insights, more general cases with asymmetric traffic load, packet size distribution, self-similar traffic and differentiated services are further elaborated.

Grid computing aims to realize a high-performance computing environment, while increasing the usage efficiency of installed resources. This puts considerable constraints on the network technology, and ultimately has led to the development of Grids over optical networks. In this paper, we investigate the fundamental question of how to optimize the performance of such Grid networks. We start with an analysis of different architectural approaches (and their respective technological choices) to integrate Grid computing with optical networks. This results in models and algorithms to design optical Grid networks, and we show the importance to combine both dimensioning (offline) and scheduling (online) in the design phase of such systems. Finally, the concept of anycast routing is introduced and motivated. Both exact and heuristic algorithms are proposed, and their performance in terms of blocking probability and latency is presented.

In this paper we present a protocol performing on demand distributed channel selection in multi channel, multi interface wireless mesh networks, based on the exchange of control messages. The link based channel reservation happens almost instantly when data traffic is sent through the network, and does not require long-term traffic profiles or measurements. The protocol is both simulated and implemented using the IEEE 802.11 b/g protocol. We show that in a raster topology, the protocol successfully optimizes the local spectrum usage at 87% of the nodes, and that globally, an equal amount of links is allocated to each of the channels used for the transport of data packets.

In order to deliver intelligent context-aware services (e.g. notifications of nearby points of interest), location based services are getting a lot of interest. However, deploying these services efficiently is currently hampered by the lack of enabling platforms, especially platforms taking advantage of easy service composition and flexible management. In this paper we detail the design of pCASE, a platform for enabling context aware services. This platform allows easy deployment in both home and business premises and flexible management of complex services taking into account context information such as location and presence. A use case is presented: an intelligent call redirection service which dynamically (re)routes communication sessions depending on the location, occupation and social networks of users.

Notwithstanding IP anycast's introduction in Internet standards dates back to 1993 and its more recent adoption in IPv6 standards, its use in production environments is limited to date. This is mainly because native IP anycast lacks routing scalability and does not support session-based communications, thereby limiting its applicability to single request-response services such as DNS. For this reason, we propose a transparent anycast overlay architecture that retains the strengths of native anycast and neutralizes above-mentioned limitations. The resulting proxy infrastructure unleashes the power of anycast by opening up new opportunities for transparent distributed service provisioning. Taking into account user demands, available resources, network overhead and anycast infrastructure costs, we provide near- optimal heuristics for the placement of proxy nodes and dimensioning the infrastructure in large networks. We show that even modest overlay infrastructures, consisting of a small number of proxy routers, provide an effective stateful anycast solution where the detour via the proxy routers is negligible in terms of extra network load. Furthermore, simulation results illustrate that server state aggregation in the proxy nodes lessens control plane overhead, which contributes significantly to service robustness.

Wireless body area networks (WBANs) form a new and interesting area in the world of remote health monitoring. An important concern in such networks is the communication between the sensors. This communication needs to be energy efficient and highly reliable while keeping delays low. Mobility also has to be supported as the nodes are positioned on different parts of the body that move with regard to each other. In this paper, we present a new cross-layer communication protocol for WBANs: CICADA or Cascading Information retrieval by Controlling Access with Distributed slot Assignment. The protocol sets up a network tree in a distributed manner. This tree structure is subsequently used to guarantee collision free access to the medium and to route data towards the sink. The paper analyzes CICADA and shows simulation results. The protocol offers low delay and good resilience to mobility. The energy usage is low as the nodes can sleep in slots where they are not transmitting or receiving.

Nowadays on-board wireless broadband connectivity in mass transport vehicles, like trains and light rails, are being trialed around the world. These solutions depend on existing mobile network or satellite coverage to maintain a broadband Internet connection to these vehicles. However these technologies lack coverage in underground areas or tunnels, and an alternative "gap filler" technology is needed to keep the train connected. In this paper we discuss the architecture and design of a WLAN based gap filler network solution for rail vehicles, which is able to provide a reliable broadband connection, even at high speed.

An important current topic is the provisioning of multimedia services to users in fast moving vehicules (e.g., trains or cars). As an example, the focus of the paper is on services to train-users. Different important open challenges will be highlighted. First, an overview of current architectures for network connectivity to trains is presented. An Ethernet-based solution with moving tunnels is detailed. Next, the business case of delivering video services to train users is introduced and critically assessed. A dependable video provisioning service is detailed, together with an overview of the practical deployment of the service.

As the popularity of resource-constrained devices such as hand-held computers increases, a new network service off loading complex processing tasks towards computational resources located in the access- or core network, sounds very promising. In a consumer-oriented environment, characterized by a large diversity in connected devices, a transparent network-based request processing strategy offers a clear flexibility advantage, as the installation and configuration of extra software components on all client devices can be avoided. In this work, this is achieved by linking computational resources to an any cast group, which allows intermediate router nodes to decide upon the target server. It is shown in the paper that the anycast routing problem can be reduced to unicast routing. Consequently, unicast multiple constraints routing algorithms can be applied to compute an optimal path based on several server selection criteria, including server load, path delay, path cost, etc. For this purpose, we envision the SAMCRA algorithm. A new evaluation ordering strategy for previously computed sub-paths is introduced, which guarantees optimality for the complete SAMCRA path between source and destination. Simulation results show that an effective distribution of the job scheduling requests over the available resources can be achieved by applying the described algorithm.

While the Java programming language and the J2EE platform are increasingly popular for implementing business logic on backend platforms, new emerging Java technologies such as JAIN SLEE and SIP Servlet are focusing on the development of low latency Java applications. As J2EE mainly focuses on enterprise applications with complex long lasting transactions, this technology is considered unsuitable for applications with low latency and high throughput characteristics. This paper compares these telecom oriented Java technologies to J2EE both in terms of functionality and through a detailed performance evaluation. JVM performance tuning has been studied as well and is explained in the paper. We performed a SIP proxy benchmark with strict low latency requirements of which the results are presented. Furthermore, design guidelines for J2EE applications are discussed to optimize for low latency behavior together with an interpretation of the obtained performance results.

More and more, content providers offer multimedia services such as Internet TV, multimedia conferencing and online gaming to their customers. These services are characterized by their high sensitivity to network delay and a multicast nature. An overlay network allows for supporting QoS by making reservations in the underlying networks and for multicasting the multimedia streams towards their targets at the overlay layer, without requiring multicast support from the underlying networks. This paper outlines the architecture of a dynamic QoS enabled multicast overlay network and also introduces a set of algorithms to determine an overlay distribution tree that connects a multimedia server to a number of clients. The algorithms construct a tree with a bounded end-to-end delay and minimize the bandwidth that is used. These algorithms are evaluated in terms of bandwidth cost, overlay cost and end-to-end delay. We show that one of our heuristics finds overlay multicast trees that approximate the optimal result in terms of cost and that have a small diameter and a low average delay.

A recent important evolution in broadband access network design is the deployment of IP aware access network elements, which allow to introduce access network services beyond basic triple-play. The focus of this paper is on the management of time-shifted television (tsTV), an IPTV service which allows for watching the broadcast content at real-time or with a (small) time shift. An architecture for a large-scale tsTV service deployment is presented, using co-operating transparent diskless proxy caches in broadband access networks, with an implementation based on the IETF's real-time streaming protocol (RTSP). Caching algorithms have been designed to take into account content popularity and distance metrics. The algorithms make use of the sliding window concept and calculate the optimal trade-off between bandwidth usage efficiency and storage cost. A prototype implementation of a transparent tsTV proxy is presented and evaluated through performance measurements.

Recent advances in optical networking technology have moved the state-of-the-art from manually installed fiber connections to fully automatic switched lightpaths. Multilayer Traffic Engineering (MTE) in an IP-over-Optical network allows to leverage rapid lightpath setup/teardown as a cross-layer traffic engineering technique. It enables on-the-fly reconfiguration of the IP layer logical topology and up/downgrade of the capacity of IP links. Together with classical IP layer routing techniques, MTE intelligently solves problems such as IP layer congestion and packet loss and it may optimize optical layer capacity usage and total network throughput. In this, the rate at which MTE can make adjustments to the network is limited by technology and stability concerns. We present some example MTE techniques and discuss how the timing parameters of these mechanisms impact perceived network performance.

When we examine today's internet architecture, we notice that the IP layer network is divided into multiple domains, managed by different service providers, operating different architectures, providing different services, handling different business strategies. In order to provide survivable inter-domain connections, to ensure connectivity in case of the most prevalent failures, different strategies can be followed. In this paper, we present some multidomain resilience schemes for a single optical backbone network interconnecting different IP domains. We then present a quantitative study of the network capacity required, in a specific pan-European backbone network.

Today, the Belgian research network GIGANET, managed by BELNET, consists of two star-shaped structures, centralized in Brussels, from where data transmission lines depart to national PoPs (point-of-presence), which are located all over the country. Local universities, colleges and other research institutions connect to their nearest PoP. Current capacity is way below predictions for the near future, thus the network needs to be scaled up dramatically. Also, there is a new demand for securely connecting distant institutions, due to several associations between them. We studied the optimal design of the future next-generation network GIGANET2, choosing a new topology, predicting future capacity demands and taking into account real pricing information obtained from telecom companies and optical hardware vendors. The study consisted of involved optimization efforts, and large-scale comparisons of optical hardware and available fiber infrastructure. This work resulted in the design of a physical optical ring topology, together with three network scenarios which are subject to different bandwidth, reliability and cost considerations, closely matching the institutions' requirements. This paper presents the final results of the study.

A current important trend is the introduction of new services in the access and aggregation network, close to the end user. A major opportunity for such service enabled access networks is providing users with fast and reliable storage, allowing them to transparently access and share their digital media library anytime, anywhere, while guaranteeing data retention. An important issue in deploying such a service is where to put the storage servers, in order to minimize deployment cost without sacrificing performance. This paper presents and evaluates two algorithms for solving the storage server placement problem, minimizing the deployment cost while guaranteeing a low delay for accessing the digital media libraries from any access node. The base algorithm, referred to as SSPA (storage server placement algorithm), assumes the access and aggregation network has unlimited bandwidth. SSPA provides a lower bound on the required number of servers, respecting a maximum delay constraint. The extended algorithm, SSPA, solves the storage server placement problem, respecting both a maximum delay constraint and bandwidth constraints of the network links. It will be shown that the algorithms produce close to optimal results relatively fast

Wireless body area networks (WBANs) have gained a lot of interest in the world of medical monitoring. Current implementations generally use a large single hop network to connect all sensors to a personal server. However recent research pointed out that multihop networks are more energy-efficient and even necessary when applied near the human body with inherent severe propagation loss. In this paper we present a slotted multihop approach to medium access control and routing in wireless body area networks, the wireless autonomous spanning tree protocol or WASP. It uses crosslayer techniques to achieve efficient distributed coordination of the separated wireless links. Traffic in the network is controlled by setting up a spanning tree and by broadcasting scheme messages over it that are used both by the parent and the children of each node in the tree. We analyze the performance of WASP and show the simulation results

The increasing use of wireless networks and the popularity of multimedia applications, leads to the need of Quality of Service support in a mobile IP-based environment. In [1], we investigated the reasons for path changes in the access network and we presented a framework to support these path changes regardless their cause and to avoid router inconsistencies. In this paper, the performance of this framework is thoroughly evaluated. To this end, we added the functionality of the framework to our Q-MEHROM handoff scheme [2]. However, the ideas and results presented in this paper are not restricted to this micromobility protocol. The performance with and without the defined functionalities is compared and tested under different network topologies, in terms of received service, packet loss and end-to-end delay.

Content distribution networks (CDN) have been increasingly used to deliver bandwidth-intensive multimedia content to a large amount of users. In a CDN, the content is replicated from the origin server to so-called surrogate servers in order to improve the quality of service experienced by the end-users and decrease the network load. However, despite the promising concept, current centralized and distributed CDN architectures lack placement and retrieval algorithms that are both scalable and provide a close to optimal placement. In this article, we propose a novel replica placement algorithm called COCOA (cooperative cost optimization algorithm), suited for a self-organizing hybrid CDN architecture. Our results show that COCOA achieves a performance comparable to the less scalable centralized algorithms, while maintaining the benefits of distributed approaches. Contrary to the more common off-line content replication and management strategies, on-line replication in a self-optimizing CDN puts an additional strain on the network. We explore techniques to control this traffic and study its implications on the performance of the CDN. Because in a CDN content is replicated to geographically distributed surrogate servers, one of the main benefits is its ability to recover from network failures and increase the availability of content during flash crowds. As illustrated in this article, we succeed in making the CDN more robust by effectively reducing the convergence time of the network after the occurrence of such disruptive events

As Massively Multiplayer Online Games enjoy a huge popularity and are played by tens of thousands of players simultaneously, an efficient software architecture is needed to cope with the dynamically changing loads at the server side. In this paper we discuss a novel way to support this kind of application by dividing the virtual world into several parts, called microcells. Every server is assigned a number of microcells and by dynamically redeploying these microcells when the load in a region of the world suddenly increases, the platform is able to adapt to changing load distributions. The software architecture for this system is described and we also provide some evaluation results that indicate the performance of our platform.

Despite the growing popularity and advantages of thin-client systems, they still have some important shortcomings. Current thin-client systems are ideally suited to be used with classic office-applications but as soon as multimedia and 3D gaming applications are used they require a large amount of bandwidth and processing power. Furthermore, most of these applications heavily rely on the Graphical Processing Unit (GPU). Due to the architectural design of thin-client systems, they cannot profit from the GPU resulting in slow performance and bad image quality. In this paper, we propose a thin-client system which addresses these problems: we introduce a realtime desktopstreamer using a videocodec to stream the graphical output of applications after GPU-processing to a thin-client device, capable of decoding a videostream. We compare this approach to a number of popular classic thin-client systems in terms of bandwidth, delay and image quality. The outcome is an architecture for a hybrid protocol, which can dynamically switch between a classic thin-client protocol and realtime desktopstreaming.

Due to natural disasters or intentional attacks, large parts of our telecommunication network can be destroyed. The setup of a wireless shadow network can restore the damaged network connectivity. This paper investigates the need for a network layer solution to integrate such a wireless shadow network with the wired network. It presents the combination of the micromobility protocols MEHROM and mobile IP regional registration as an efficient solution to support terminal mobility. The proposed solution is evaluated in terms of control overhead, required storage and calculation capacity, and functional complexity

Handoffs between access points in a distributed IEEE 802.11 wireless LAN network for vehicular users can be a source of considerable packet loss. This severely degrades the visual quality of streaming video applications. In this paper we introduce the architecture of an Ethernet soft switch, which tries to preserve the quality of high bit rate streaming video upon each handoff, even if only limited resources are available access points. We have evaluated its performance in a test bed implementation for MPEG-2, MPEG-4 and H.264 video-on-demand and have compared it to the standard IEEE 802.11F-IAPP approach

To efficiently support the highly dynamic traffic patterns of the current Internet in large-scale switches, we propose a new hybrid optical network design: Overspill Routing In Optical Networks (ORION). By taking advantage of the reduced (electronic) processing requirements of all-optical wavelength switching, the electronic bottleneck is relieved. At the same time, ORION achieves a level of statistical multiplexing comparable to the more traditional point to point WDM solutions, circumventing the bandwidth inefficiencies of all-optical wavelength switched networks, caused by dynamic traffic patterns. The result is a true hybrid optical network design, forming a bridge between these two switching concepts. In this paper the generic concept of ORION is described. An example node design, based on current advanced optical technologies, is described in detail. The ORION concept is also evaluated, comparing it with its two composing technologies, optical wavelength switching and point to point WDM, as well as a third, more trivial, hybrid one, through several case studies

In the domain of digital video coding, new technologies and solutions are emerging in a fast pace, targeting the needs of the evolving multimedia landscape. One of the questions that arises is how to assess these different video coding technologies in terms of compression efficiency. In this paper, several compression schemes are compared by means of peak signal-to-noise ratio (PSNR) and just noticeable difference (JND). The codecs examined are XviD 0.9.1 (conform to the MPEG-4 Visual Simple Profile), DivX 5.1 (implementing the MPEG-4 Visual Advanced Simple Profile), Windows Media Video 9, MC-EZBC and H.264/AVC AHM 2.0 (version JM 6.1 of the reference software, extended with rate control). The latter plays a key role in this comparison because the H.264/AVC standard can be considered as the de facto benchmark in the field of digital video coding. The obtained results show that H.264/AVC AHM 2.0 outperforms current proprietary and standards-based implementations in almost all cases. Another observation is that the choice of a particular quality metric can influence general statements about the relation between the different codecs.

In this paper, we propose the use of a distributed service management architecture for state-of-the-art service-enabled grids. The architecture is capable of performing automated resource and network bandwidth partitioning based on registered grid resource properties and monitored grid service demand. A main characteristic is that it enables the use of different service priority schemes and allows for policy-based differentiation between local and foreign service offerings. Resource and network bandwidth partitioning algorithms are introduced and their performance is evaluated on a sample grid topology using NSGrid, an ns-2 based grid simulator. Our results show that the use of this Service Management Architecture improves resource efficiency, simplifies schedule making decisions, reduces the overall complexity of managing the grid system, and at the same time improves grid service QoS support (with regard to job response times) by automatically making grid resource and network service reservations prior to scheduling.

Design of aggregation networks for delivering multimedia services to fast moving users is an interesting topic. Research has already been devoted to the dimensioning taking into account the movement of the users. However, the effects of packet loss and packet reordering when switching paths have not been taken into account before. This paper presents a design method that aims at minimizing packet loss and packet reordering in the dimensioning and routing process. Consequently, various routing techniques are presented and their performance is thoroughly compared. The results show that for some routing strategies only a slight extra installation cost is required for guaranteeing minimal packet loss and reordering. Deployment of routing schemes in Ethernet networks requires mapping of the calculated routes on different spanning tree instances. A path aggregation algorithm is presented that forms a minimal set of spanning tree instances out of a set of routing paths.

The increasing use of wireless networks and the popularity of multimedia applications, leads to the need of QoS (quality of service) support in a mobile IP-based environment. This paper considers the reservation of resources in the micromobility scenario. The reasons for path changes in the access network are investigated. Based upon this, we present the functionality that should be present in the different access network elements to support path changes regardless their cause and to avoid router inconsistencies. For the simulations we added this functionality to our previously developed Q-MEHROM handoff scheme (L. Peters et al., 2005). However, the ideas and results presented in this paper are not restricted to this micromobility protocol

In this paper, the focus is on the management aspects for delivery of multimedia services to fast moving users (e.g., users in trains, cars or airplanes). The considered network architecture consists of two parts: an aggregation network part and an access network part. We designed a management system for the aggregation network. The main functionalities of this management system are: (i) pre-configuration of the QoS (quality of service) tunnels, based on the results of the network capacity planning process, (ii) activation of the QoS tunnels when required and (iii) tunnel reconfiguration when the activated tunnels are insufficient to carry the instantaneous demand or in case of other failures. The main difference with existing management systems is that it is designed to deal with the rapidly moving nature of the traffic conditions and the generation of triggers for tunnel activations or reconfigurations. The management system focuses on multimedia service delivery to trains through high speed Ethernet aggregation networks. An extended GVRP (GARP (generic attribute registration protocol) VLAN registration protocol) and a new GARP protocol (G2RP) were designed and implemented as protocols for the automatic tunnel pre-configuration and activation, respectively. The management system makes use of optimization algorithms for network dimensioning and tunnel path determination. These algorithms are described in detail and their evaluation results are compared for a basic train scenario. Finally, measurement results on the performance of the designed protocols for tunnel pre-configuration and activation, are presented in detail.

Currently, a lot of research has been devoted to (i) content distribution, (ii) traffic engineering, (iii) network monitoring and (iv) service enabling platforms. However, the integration of these four individual concepts in a single platform has not yet been studied in enough detail. In this paper we present an architecture for such a robust content delivery service. The combination of both distributed replication of videos and multi-source traffic engineering tackles specific problems such as congested network parts, overloaded servers and the occurrence of flash crowds. Contrary to most existing systems, the content placement and retrieval algorithms in the presented CDN obtain precise network state information from an integrated monitoring system, allowing even a higher efficiency. To validate the performance of the CDN, an exact placement ILP formulation and various RPA heuristics are implemented and simulated.

With the deployment of broadband Internet access, a new set of applications that is becoming more and more popular are highly interactive services such as online gaming. When the delay experienced in an online game passes a certain threshold, the quality of service (QoS) degrades enormously, as a result the clients are no longer satisfied and might decide to leave the game or to cancel the subscription. Thus, delay is critical to the success of this type of service. Network delay is a result of the way the data is distributed between the players. In this paper we propose the use of a set of game servers. These servers not only play the role of a traditional game server but also form an overlay network which can be used as an application layer routing infrastructure, allowing us to route along low delay paths and thereby increasing the QoS of the game. We study algorithms that determine the ideal location of the servers in a network and look at the performance of the resulting overlay networks in terms of end-to-end delay and the relationship between the number of servers in the overlay network and the offered QoS. We also compare our distributed architecture with both a single server and a peer-to-peer architecture.

With the currently emerging trials for Internet solutions on the train, it is a matter of time before best-effort Internet on the train becomes a reality. However, designing the aggregation network which transports data from fast moving users to service providers, requires extended research because an aggregation network responsible for the reliable transport of broadband multimedia traffic has not been studied before. We propose a flexible recovery strategy for Ethernet networks with dynamic VLANs. It is shown that fast recovery can be achieved in aggregation networks if standard Ethernet protocols are adjusted to co-operate with the fast and efficient link probe mechanism. Additionally a cost-effective design method is presented for networks of realistic size which aims at combining requirements of the commuters (such as end-to-end delay variations) with reliability constraints

Distributed systems often use a form of communication middleware to cope with different forms of heterogeneity, including geographical spreading of the components, different programming languages and platform architectures, etc. The middleware, of course, impact the architecture and the performance of the system. This paper presents a model transformation framework to automatically include the architectural impact and the overhead incurred by using a middleware layer between several system components. Using this framework, architects can model the system in a middleware-independent fashion. Accurate, middleware-aware models can then be obtained automatically using a middleware model repository. The actual transformation algorithm is presented in more detail. The resulting models can be used to obtain performance models of the system. From those performance models, early indications of the system performance can be extracted.

New networking paradigms try to combine packet switching and circuit switching, keeping the best of both worlds and getting rid of the drawbacks. One promising technology is overspill routing in optical networks (ORION). In this paper we develop a control technique to set up LSPs in this novel network environment. It is based on the GMPLS paradigm and needs no extra control messages.

An ad hoc network is an autonomous system of heterogeneous, mobile nodes that communicate with each other over wireless links. Routing protocols for these networks are inherently based on broadcasting control information and are therefore very bandwidth consuming. In order to limit the amount of routing information that has to be stored and maintained by the individual nodes, the technique of clustering is used. The network is partitioned into nonoverlapping sub networks, referred to as clusters, and one cluster node, the clusterhead, will take a leading role in the dissemination of control information. In this paper we approach the problem of finding an optimal partition that explicitly takes into account the heterogeneity of the network, as an integer linear programming (ILP) problem. In a second phase we have developed a new heuristic that approximates our ILP solution that is used in our clustering algorithm. It is shown that this heuristic tends to be more stable than existing clustering techniques that are solely based on ID number and/or connectivity and that do not take into account the heterogeneity of the network.

A major opportunity for IP network operators to increase the revenue stream generated by their network is a closer and faster integration of services into the IP broadband network. However, with this integration come responsibilities concerning the quality, availability and continuity of these services, which are much harder to fulfil than the requirements for the current IP data traffic. SONAR (service-oriented networking using adaptive resource control) is a network management and operations platform designed to drive a DiffServ/MPLS network so that these responsibilities can be met. In this paper we discuss and evaluate the architecture and algorithms that are the basis for this platform. The architecture decomposes the network management problem in two components: a centralised path computation and a distributed tunnel management. Finally this hybrid on line/off line adaptive traffic engineering approach is evaluated in an modified NS-2 simulator environment.

This paper describes the design of a novel tunnel set-up mechanism for Ethernet access networks. The establishment of VLAN-based tunnels is realised with a "scoped refresh" extension of the GVRP standard. For the distribution of QoS-related reservation parameters, a new GARP-based protocol (G2RP) is developed with a closed loop design for updating the reservation parameters and hop-by-hop admission control. Both protocols are implemented on a Linux test bed using the click modular router. Extensive performance evaluations were performed. The results are compared with Linux implementations of the other tunnel set-up mechanisms.

The combination of mobile IP with frequent handovers results in high handoff latencies and control overhead in the core network. Micromobility protocols like cellular IP. Hawaii and MIPv4 regional registration were developed to avoid these problems, supporting local mobility within one IP domain. Hereby, tree access topologies were considered to evaluate the protocol performance A. Campbell et al., (2000) (2002) although meshed topologies are desired for reasons of robustness against link failures and load balancing L. Peters et al., (2003). The mentioned micromobility protocols do not use the extra links or result in a bad performance in terms of end-to-end delay. This paper proposes a new micromobility protocol for random access topologies. During handoff a router in the access network detects if it has the function of cross-over node. Hereby, control traffic is concentrated near the involved access routers, while optimal paths in the access network are achieved. The basic concept of the protocol is presented and the handoff performance is compared to other micromobility protocols.

Active networking is one of the suggested technologies to introduce additional intelligence and programmability in the network and its services. In this paper, the use of active networking to support advanced multicast services providing media transcoding inside the network is investigated. In the multicast service different versions of the streamed data are made available and customers can select a specific version according to their wishes or their capabilities. Based on the active networking facilities of the underlying framework the different versions of the streamed data can be created inside the network, through transformations or transcodings of the original data. Both design and performance issues of the detailed service are discussed. A new multicast tree set-up protocol, taking into account the required transcodings, is introduced. A number of different strategies are discussed optimizing the location of the transcodings as well as the use of bandwidth in the network, while considering the availability of sufficient processing power in the nodes. The performance analysis is done for a voice stream multicast service, addressing the efficiency of the tree set-up strategies, the optimization of network resource utilization, the use of processing power for transcodings, and the resulting quality of streamed voice signals after multiple transcodings.

Traffic grooming in networks employing WDM is gaining attention due to the difference between the bandwidth requirements of the traffic demands coming from the client layer and the capacity of a wavelength in an optical transport network (OTN). In this paper an algorithm for efficient traffic grooming in a multi-layer IP/MPLS-over-meshed OTN scenario is presented. It allows designing the IP/MPLS logical topology best suited to deal with the offered traffic pattern, taking into account the unidirectional and maybe asymmetric character of IP traffic. This multi-layer traffic grooming algorithm is based on the idea of charging the IP/MPLS layer for the capacity it consumes in the optical layer. In order to assess its performance, a comparison with other grooming approaches is made. The results show that our method allows for serious savings in the overall network design cost. It also allows for a gradual capacity installation in the network, thus spreading the installation cost.

Optical packet/burst switching is considered a promising technique to improve the performance of optical networks. Key components in these technologies are the optical switching nodes. Some of these node architectures suffer from internal blocking. Synchronous operation allows overcoming most of the problems introduced by this internal blocking. However, in asynchronous networks internal blocking can have a more pronounced effect. In this paper, we propose a windowing technique to improve the performance of internally blocking optical switching nodes in asynchronous operation. Simulations will show significant improvements can be made.

In this paper, we address the design and implementation of a generic and scalable platform for efficient management of computational resources. The developed platform is called the Intelligent Agent Platform. Its architecture is based on middleware technology in order to ensure easy distribution of the software components between the participating workstations and to exploit advanced software techniques. The computational tasks are referred to as agents, defined as software components that are capable of executing particular algorithms on input data. The platform offers advanced features such as transparent task management, load balancing, run time compilation of agent code and task migration and is therefore denoted by the adjective "Intelligent". The architecture of the platform will be outlined from a computational point of view and each component will be described in detail. Furthermore, some important design issues of the platform are covered and a performance evaluation is presented.

The growing widespread use of advanced multimedia and interactive real-time applications is setting forth new challenges such as end-to-end quality-of-service (QoS) and broadband Internet access. The high bandwidth needs are pushing fiber closer and closer to the home, and as such WDM (wavelength division multiplexing) seems ideally suited to be used in the broadband access feeder network which interconnects the Internet core networks and the last mile networks. In the HARMONICS project (Hybrid Access Reconfigurable Multi-wavelength Optical Networks for IP-based Communication Services), a novel DWDM (dense wavelength division multiplexing) based optical access feeder network is investigated. This feeder network transports IP, guarantees QoS and can feed various last mile networks, stimulating the convergence of access networks. VDSL and Hiperlan/2 are studied within the project as last mile access networks. To support end-to-end QoS, a distributed CORBA-based generic network management framework is being developed as part of the project. This paper elaborates on the framework which is aligned with TINA, although adapted to be more consistent and applicable. End-to-end QoS is based on Differentiated Services (DiffServ) at layer 3, various QoS supporting technologies at layer 2 and QoS mappings between both layers.

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/spl times/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.

We address the design of a generic and scalable platform for cluster computing. The architecture of the platform is based on middleware technology in order to ensure easy distribution of the software components along the participating workstations and to exploit advanced communication techniques, such as event notification and object registration. The computational tasks are referred to as intelligent agents, which are software agents that are capable of executing particular algorithms on input data. The developed platform offers advanced features such as transparent load balancing, task scheduling, run time compilation of agent code and migration of tasks. The architecture of the platform is outlined from a computational point of view and each component is described in detail. Furthermore, the engineering aspects of the platform are covered. In addition, a sample scenario for computational tasks in the area of telecommunication network design and management is described.

When voice traffic is transported over a packet-based network, a number of conditions different from the ones in the traditional circuit-switched network will have an influence on the quality of the speech signal as perceived by the users. In particular, distortion of the voice signal due to delay jitter and partial loss of signal caused by packet loss will have an important impact. Therefore, in order to determine the influence of delay jitter and packet loss on the perceived quality, an objective speech quality assessment system, called DSLA, is used to predict the mean opinion score for voice connections, which are set up on a test-bed, subject to artificially introduced network conditions. A decomposition of the voice degradation is made into different parts, due to sampling, digitization, encoding/decoding, packet loss and delay jitter, respectively. It is found that delay jitter has a devastating influence on the perceived quality, when no dejittering buffer is used. However, when the received signal is dejittered, the degradation due to jitter is similar to the one caused by packet loss.

In this paper we address the design of a generic and scalable architecture for connection management and SLA (service level agreement) monitoring of VPNs (virtual private networks). Layer-based design ensures that the architecture is independent of the network technology. Use of advanced software techniques such as run time compilation and intelligent agents allow easy integration of new monitoring and routing algorithms. The architecture offers advanced features such as VPN edge device capability matching, XML-based SLS (service level specification) language, load balancing of computational tasks, and programmable components. The architecture is compliant with the TINA (telecommunication information network architecture) recommendations and its implementation is based on CORBA (common object request broker architecture). In addition, a sample VPN setup and monitoring scenario will be detailed.

In this paper we envisage the issue of quality of service (QoS) management for multimedia services as an end to end QoS discovery problem. With this perception as a basis, we designed and implemented a layered QoS management architecture which handles QoS from the user's perspective, as well as from the end system's and the network's perspective. The architecture is decomposed into three layers. First there is the QoS specification, presentation and parameterization layer at which an end user is able to specify his/her QoS requirements in a comprehensible and qualitative way, and at which these QoS requirements are translated into parameterized terminal capabilities. Secondly, there is the QoS matching and negotiation layer at which the parameterized QoS capabilities of different terminal end systems are marched and compared in order to search for a QoS equilibrium. Finally, there is the QoS implementation layer which implements the resolved QoS equilibrium in the network and in the terminals. This generic architecture, which allows a de-abstraction of user defined QoS, has been implemented in the context of a CORBA based TINA platform.

In this paper we address the design and implementation aspects of a generic architecture for the NML (network management layer). The focus in this paper will be on SNMP manageable ADSL/ATM networks. SNMP (simple network management protocol) is a standardized protocol which is supported by almost all current computer network devices. The architecture is compliant with the TINA (Telecommunication Information Network Architecture) recommendations and is implemented based on the CORBA (Common Object Request Broker Architecture) standard. During the design and implementation process, a lot of effort has been devoted to the performance, robustness, persistence and consistence of the distributed software under various load and fault scenarios. The most suitable distributed software techniques, like object transactions, concurrency control, event notification and naming service were used and thoroughly tested on their usability. It is also indicated how the core of the described architecture can be extended towards next-generation IP-based networks.

In this paper, we address the problem of the end-to-end management of a heterogeneous public network. In the case study, the access part of the network is based on the ADSL technology for the provisioning of high-speed IP over ATM to the customer and consists of ADSL network elements and ATM access switches. The core of the network is ATM-based and provides connectivity to retailers, which in this case are Internet service providers (ISP). We give an insight into the technological approach which consists of building a distributed platform, based on CORBA, that integrates existing element and network management systems and provides an end-to-end configuration, performance and fault management solution. The architecture of a generic resource adapter for SNMP devices as well as an automated SNMP-to-IDL mapping method are detailed.

In this paper routing, planning of working capacity, rerouting, and planning of spare capacity in wavelength division multiplexing (WDM) networks are investigated. Integer linear programming (ILP) and simulated annealing (SA) are used as solution techniques. A complex cost model is presented. The spare capacity assignment is optimized with respect to three restoration strategies. The benefit of wavelength conversion, the choice of the fiber line system, and the influence of cost parameter values are discussed, with respect to the different restoration strategies and solution techniques. Wavelength conversion is found to be of limited importance, whereas tunability at the end points of the connections has substantial benefits.

The European ACTS project optical pan-European network (OPEN) aims at assessing the feasibility of an optical pan-European overlay network, interconnecting major European cities by means of a mesh of high-capacity optical fiber links, cross-connected through transparent photonic nodes. Both the transmission links and the routing network elements rely on wavelength division multiplexing (WDM) all-optical technologies, such as wavelength translation. This paper presents results obtained in the following domains covered within the project: network topology considerations (optimization and dimensioning); network physical layer simulation; fabrications of packaged functional modules based on advanced optoelectronic devices; laboratory demonstrations of N/spl times/10 Gb/s transmission and routing; feasibility of an optical time division multiplexing/WDM (OTDM/WDM) interface; and the field implementation of a 4/spl times/4 multiwavelength crossconnect prototype, featuring all-optical space and wavelength routing. This implementation was realized in two cross-border field trials, one conducted between Norway and Denmark and the other between France and Belgium. The final results of the Norway to Denmark field trials are presented, featuring the successful cascade of three wavelength-translating optical crossconnects (OXCs), along with the transmission over 1000 km of a mix of standard/submarine cable links for four channels at 2.5 Gb/s.

For restoration in the case of single link failures in meshed networks several strategies can be considered: link restoration, path restoration and path restoration with link-disjunct route. In terms of spare capacity requirement path restoration is found to be most attractive. These results are obtained by using two general optimisation techniques (simulated annealing and integer linear programming). Both techniques have each their own features; their applicability depends on the size and type of the problem. Application to WDM fibre networks is discussed.

The main purpose of this paper is to present a novel generic configuration to protect traffic against gateway failures. A gateway comprises the network resources interconnecting neighbouring sub-networks. The issue of gateway failures is relevant to both public as well as private networks where traffic may cross multiple sub-networks operated by different organisations. The proposed configuration is simple and requires only minimal co-ordination. The configuration is applied to a mesh-mesh and a ring-mesh structured ATM layer network.

The paper first discusses the interworking between survivable sub-networks in transport networks. It then presents a novel generic interworking configuration to protect gateways between survivable sub-networks. A gateway comprises the network resources interconnecting neighbouring survivable sub-networks. The issue of gateway failures is relevant to both public as well as private networks where traffic may cross multiple sub-networks operated by different organisations. The proposed configuration is simple, achieves fast recovery of any single failure and requires only minimal coordination. The configuration has been simulated for a mesh-mesh and a ring-mesh structured survivable ATM layer network.

We discuss the wavelength requirement for optical networks based on wavelength-division multiplexing (WDM). A mathematical model, to represent the routing and wavelength assignment in optical networks with or without wavelength conversion, is described, and metrics are defined to express the performance. A new heuristic for routing and wavelength assignment is proposed and compared with the Dijkstra algorithm and with a solution based on integer linear programming. The different techniques are applied to a variety of network examples with different traffic loads.