Sébastien Rumley

JAVOBS: A Flexible Simulator for OBS Network Architectures

Since the OBS paradigm has become a potential candidate to cope with the needs of the future all optical networks, it has really caught the attention from both academia and industry worldwide. In this direction, OBS networks have been investigated under many different scenarios comprising numerous architectures and strategies. This heterogeneous context encouraged the development of various simulation tools. In this paper we present our novel Java-based OBS network simulator called JAVOBS. We discuss its architecture, study its performance and provide some exemplary results that point out its remarkable flexibility. This flexibility should permit an easy integration of upcoming new network protocol designs but also support changing and evolving research goals.

Multi-agent Approach to Electrical Distribution Networks Control

A new approach to the configuration and operation of electrical distribution networks is proposed. Traditionally, the medium-voltage part of the electrical grid is operated in a centralised and static manner. In the context of electric sector deregulation and electric market liberalisation, the pertinence of this central organisation is no longer ensured. This paper presents an alternative approach based on a multi-agent system, implementing a distributed control algorithm. Concepts used in communication networks have been applied and adapted to the electrical supply system.

Cost aware design of translucent WDM transport networks

Fully-transparent DWDM networks working at 10 Gb/s or more have limited reach. At these high rates, only translucent networks able to fully regenerate the signal when needed can be used to implement long haul transport networks. Since signal regeneration and regenerator placement can be done in many ways, an effective design procedure will target the overall cost minimization. In this paper, we propose three regenerator placement procedures. Two of them minimise the number of regeneration nodes, whereas the third method minimises the total number of regenerators. Moreover, we present an economic model aimed to evaluate and compare the overall cost of these procedures. We show how to choose the optimum regenerator placement method according to regeneration type and associated costs.

A performance survey on deflection routing techniques for OBS networks

In this paper, we present a survey comparing different deflection routing based techniques applied to optical burst switching (OBS) networks. For such study we consider the E-OBS architecture proposed in [1] which is an advantageous solution for OBS networks since routing decision can be taken freely inside the network without constraints on the length of the path. Under this environment, several effective routing strategies proposed in the literature are applied, namely deflection routing, reflection routing, reflection-deflection routing and multi-topology routing. The aim of this study is to analyse all these techniques considering both asynchronous and synchronous burst arrivals and compare their benefits. Moreover, we focus on a quasi-synchronous burst arrival case (with bursts not perfectly aligned) and analyse the trade-off between performance and alignment.

Flexible simulators for oBS network architectures

Since the OBS paradigm has become a potential candidate to cope with the needs of the future all optical networks, it has really caught the attention from both academia and industry worldwide. In this direction, OBS networks have been investigated under many different scenarios comprising numerous architectures and strategies. This heterogeneous context encourages the development of flexible simulation tools. These tools should permit both an easy integration of any possible new network protocol design and a rapid adaptation to different performance target goals. In this paper, we present two OBS network simulators, namely, a C-based simulator (ADOBS) and our novel Java-based simulator (JAVOBS). We compare their performances and we provide some exemplary results that point out remarkable flexibility that can be achieved with the JAVOBS simulator.

Multilayer Description of Large Scale Communication Networks

Data exchanges between various modules and tools raise interfacing difficulties in a multilayer environment. This aspect may become particularly critical in a distributed context.

Resource utilisation analysis in WDM backbone networks

Circuit-switched backbone networks are appealing especially due to their low switching cost. However, some of their links may be poorly utilised with respect to the available capacity. Grooming can be used to improve this utilisation: optically switched lightpaths are groomed in fibres using WDM, and flows are groomed in lightpaths using TDM. However, grooming require more transmission resources if lightpaths/flows are not following the shortest-path and take detours. It can thus be counterproductive. In this paper, we propose an approach detailing the resource utilisation at two levels: lightpaths and fibres. Assuming a practical network layout, our approach measures the impact of the fibre and lightpath granularities and of the wavelength continuity constraint on the link utilisation. It also analyses to which extent detours consume resources. We apply this resource utilisation analysis to a set of layouts provided by a heuristic. Numerical results show how our approach can be used to further improve a layout or a heuristic.

Performance overview of the quasi-synchronous operation mode in optical burst switching (OBS) networks

Optical burst switching (OBS) is able to operate under both asynchronous and synchronous burst departures. Although the asynchronous approach is generally assumed in OBS owing to its simplicity and low technical requirements, it has been shown that performance improvements, in terms of the overall burst loss probability, can be achieved under synchronous operation. Moreover, when effective contention resolution mechanisms are applied, such improvements are significant. Since perfect synchronization is not a viable solution, we propose a novel operation mode with relaxed technical requirements, the quasi-synchronous (QS) operation. In this paper, the performance of the QS operation mode is evaluated by an exact analytic expression, assuming a Poisson burst arrival process and a single-wavelength scenario. This mathematical analysis is completed with numerical results that validate its accuracy. Furthermore, we tackle the issue of not having well-aligned clock information between network nodes by proposing a novel re-synchronization mechanism for OBS networks. Finally, a performance study of the QS operation under different deflection routing techniques is presented. The results show that our novel QS approach achieves significant performance benefits with respect to the asynchronous operation while avoiding the architectural complexity of the synchronous scheme.

Feedback Based Load Balancing, Deflection Routing and Admission Control in OBS Networks

The Optical Burst Switching (OBS) paradigm allows statistical multiplexing directly at the optical layer. Thus, OBS networks are suited to carry traffic demands varying in either the short or long term. Due to the lack of buffering, burst contention due to short term variations can only be mitigated through deflection routing. For longer term variations, higher order mechanisms such as dynamic flow-balancing or flow shaping are generally proposed. In this paper, a unified scheme, based on a feedback mechanism combined with deflection routing and admission control is introduced to handle all types of traffic variations. The use of only one single scheme simplifies the architecture of OBS networks and enhances its flexibility. The validity of our technique is supported by simulation results.

Adaptive burst admission and forwarding in OBS networks

This paper addresses the problem of controlling the performance of optical burst switching (OBS) networks in presence of non-stationary traffic demands. We propose a joint burst admission control and forwarding mechanism that operates in core nodes. This mechanism dynamically adapts its behaviour according to the feedback messages received from other nodes. By not forwarding certain bursts not complying with given requirements, an admission control is implicitly made. Moreover, by forwarding bursts to appropriately selected nodes, traffic balancing is achieved. The advantageous effects of the proposed mechanism can additionally be amplified by granting extra offset time to the burst. The benefits provided by this mechanism are supported by numerical results.