Carla Raffaelli

Transparent optical packet switching: the European ACTS KEOPS project approach

This paper reviews the work carried out under the European ACTS KEOPS (KEys to Optical Packet Switching) project, centering on the definition, development and assessment of optical packet switching and routing networks capable of providing transparency to the payload bit rate. The adopted approach uses optical packets of fixed duration with low bit rate headers to facilitate processing at the network/node interfaces. The paper concentrates on the networking concepts developed in the KEOPS project through a description of the implementation issues pertinent to optical packet switching nodes and network/node interfacing blocks, and consideration of the network functionalities provided within the optical packet layer. The implementation, from necessity, relies on advanced optoelectronic components specifically developed within the project, which are also briefly described.

Transparent optical packet switching: network architecture and demonstrators in the KEOPS project

This paper reviews the work carried out in the ACTS KEOPS (Keys to Optical Packet Switching) project, describing the results obtained to date. The main objective of the project is the definition, development, and assessment of optical packet switching and routing networks, capable of providing transparency to the payload bit rate, using optical packets of fixed duration and low bit rate headers in order to enable easier processing at the network/node interfaces. The feasibility of the KEOPS concept is assessed by modeling, laboratory experiments, and testbed implementation of optical packet switching nodes and network/node interfacing blocks, including a fully equipped demonstrator. The demonstration relies on advanced optoelectronic components, developed within the project, which are described.

Exploitation of DWDM for optical packet switching with quality of service guarantees

This paper addresses the problem of building optical packet switches that are able to effectively cope with variable length packet traffic and quality of service management, therefore able to support IP traffic. The paper aims at showing that the availability of dense wavelength division multiplexing is crucial. By suitably exploiting the wavelength dimension a multistage fiber delay line buffer can be implemented, with fine granularity and long delay with an architecture of limited complexity. This is necessary to fulfill the buffering requirements of variable length packets. Furthermore, the wavelength domain is proved to be more effective than the time domain to manage different levels of quality of service. Algorithms are presented that are peculiarly designed for this environment showing that they can effectively differentiate the packet loss probability between three priority classes.

Packet optical networks for high-speed TCP-IP backbones

This article presents a new proposal for TCP-IP backbone implementation based on optical packet switching technology. The proposed network architecture merges the flexibility in resource management of packet switching with the high capacity offered by full optical technology.

Wavelength and time domain exploitation for QoS management in optical packet switches

This paper addresses the problem of congestion resolution and quality of service differentiation in optical packet switching. The paper shows that by designing congestion resolution algorithms that combine the use of the wavelength and the time domain it is possible to significantly reduce information loss phenomena and also to guarantee quality of service differentiation among traffic classes. In particular this is achieved by means of QoS algorithms specifically designed to exploit the characteristics of optical technology. The results are different from the QoS techniques typically implemented in electronic networks. Performance evaluation obtained by simulation shows the influence of the main system parameters on packet loss probability and delay for two service classes.

3-Level Integrated Hybrid Optical Network (3LIHON) to Meet Future QoS Requirements

This paper presents a new hybrid network architecture including different transport technologies to support a wide range of services. In particular the proposed hybrid network provides three service levels, and a possible set of foreseeable services with different QoS needs is mapped into these levels to show the effectiveness of the hybrid networking in managing multi-service requests. In the switching nodes of the network, each service level is associated to a different switching technology, thus optimizing the switch implementation. In the nodes of the network, the service levels are distinguished based on optical encoding techniques, while an output collision stage manages the access to the output wavelengths. Performance studies show the effectiveness of the output collision mechanism.

Multifiber Shared-Per-Wavelength All-Optical Switching: Architectures, Control, and Performance

A new wavelength converter sharing strategy for multifiber optical switches, namely shared-per-wavelength (SPW), which employs wavelength converters with fixed input wavelengths is presented. The aim is to reduce switch costs by using simpler optical components and low complexity space switching matrices. Practical implementations of both the well-known shared-per-node (SPN) and the new SPW schemes are presented, as well as the related scheduling algorithms to manage optical packet forwarding in synchronous scenario. An analytical model to evaluate blocking performance of the SPN architecture is also provided. Results show the accuracy of the model in the range of interest for switch design. The proposed architectures are compared in terms of performance and number of optical components employed. The SPW approach is shown to save a large number of semiconductor optical amplifier gates with respect to the SPN one when the number of fibers per interface is suitably not too high. In these cases, the SPW architecture requires a number of wavelength converters higher than the SPN, but simpler, being their inputs tuned on a single wavelength.

Sharing wavelength converters in multistage optical packet switches

This paper describes a multistage switch based on the broadcast-and-select principle. It implements shared per node wavelength conversion for contention resolution in optical packet-switched networks. A novel scheduling algorithm is proposed to control packet forwarding in synchronous context. An analytical model is provided to calculate the packet loss probability related to the multistage configuration. Results show how the sharing of wavelength converters impacts on node performance, and provide a meaningful support for cost-performance benchmarking studies

Shared-per-wavelength asynchronous optical packet switching: A comparative analysis

This paper compares four different architectures for sharing wavelength converters in asynchronous optical packet switches with variable-length packets. The first two architectures are the well-known shared-per-node (SPN) and shared-per-link (SPL) architectures, while the other two are the shared-per-input-wavelength (SPIW) architecture, recently proposed as an optical switch architecture in synchronous context only, which is extended here to the asynchronous scenario, and an original scheme called shared-per-output-wavelength (SPOW) architecture that we propose in the current article. We introduce novel analytical models to evaluate packet loss probabilities for SPIW and SPOW architectures in asynchronous context based on Markov chains and fixed-point iterations for the particular scenario of Poisson input traffic and exponentially distributed packet lengths. The models also account for unbalanced traffic whose impact is thoroughly studied. These models are validated by comparison with simulations which demonstrate that they are remarkably accurate. In terms of performance, the SPOW scheme provides blocking performance very close to the SPN scheme while maintaining almost the same complexity of the space switch, and employing less expensive wavelength converters. On the other hand, the SPIW scheme allows less complexity in terms of number of optical gates required, while it substantially outperforms the widely accepted SPL scheme. The authors therefore believe that the SPIW and SPOW schemes are promising alternatives to the conventional SPN and SPL schemes for the implementation of next-generation optical packet switching systems.

Photonics in switching: enabling technologies and subsystem design

This paper describes recent research activities and results in the area of photonic switching carried out within the framework of the EU-funded e-Photon/ONe+ network of excellence, Virtual Department on Optical Switching. Technology aspects of photonics in switching and, in particular, recent advances in wavelength conversion, ring resonators, and packet switching and processing subsystems are presented as the building blocks for the implementation of a high-performance router for the next-generation Internet.