We consider the problem of scheduling the transmission of packets in an input-queued switch. In order to achieve maximum throughput, scheduling algorithms usually employ the queue length as a parameter for determining the priority to serve a given queue. In this work, we propose a novel scheme to optimize the performance of a preexisting scheduler. Our main idea is to assist the scheduling decision, considering "messagesâ rather than queue lengths. Such messages are obtained by running an iterative parallel algorithm, inspired by a rigorous belief-propagation approach. We demonstrate that belief-propagation-assisted scheduling is able to boost the performance of a given scheduler, reaching almost optimal throughput, even under critical traffic scenarios.

Optical switching fabrics (OSF) are gaining interest because they promise to satisfy the higher information densities demanded by each successive generation of high-end routers and switches. Silicon microring resonators (MRR) can be employed to perform switching operations directly in the optical domain. However, similarly to other devices used to build all-optical switching fabrics, such as Arrayed Waveguide Gratings (AWG), MRR-based switching fabrics might show a limited scalability in terms of port count due to the crosstalk accumulation caused by the spatial wavelengths reuse. We consider an OSF built on a Wavelength-Routing-Matrix (WRM) based on MRRs, we highlight its scalability issues and we propose a new design as well as two different strategies to limit the wavelength spatial reuse.

Today, the permutation of circuits in the Main Distribution Frames (MDF), which connect the subscriber lines to POTS and to DSLAMs, is still operated manually. However, new market regulations, allowing subscribers to change network operator frequently, and the new schemes to concentrate active ADSL users into few DSLAMs during off-peak hours, adopted by network operators to reduce the energy consumption in the access network (and the related operational costs), require more advanced, reliable and faster mechanisms than human operations. Indeed, Automated MDFs (AMDF) have recently become available on the market to provide cheap and almost real-time circuit switching. Even if grounded on more than 50 years of research activities on architectures for circuit switching, the considered scenario is quite peculiar and offers new interesting technical challenges, since classical multistage strictly non-blocking networks are too expensive for the number of required ports (sometimes very large, exceeding 100,000), and rearrangeable multistage networks can interrupt temporarily active circuits, affecting in a indefinite way the performance of ADSL lines. For these reasons, we propose the design of AMDFs based on recently proposed non-interruptive rearrangeable (NIR) networks and show how to optimize the routing control to minimize the setup time of a circuit. Finally, our findings are relevant both for the theory of multistage interconnection networks, and for those companies producing, engineering and operating large AMDFs.

Optical switching fabrics are gaining interest as in multi Terabit switching devices; the advantages over their electronic equivalents are mainly their information density and power consumption. Arrayed Waveguide Gratings (AWGs) are promising optical devices proposed by the academic and industrial community to build optical switching fabrics. Because of their wavelength routing property, AWGs allow wavelength reuse over different ports introducing in-band crosstalk which strongly limits scalability of AWG-based backplanes. However, this effect can be mitigated or even completely avoided by means of proper scheduling algorithms. In this paper, we present several modified scheduling algorithms which limit the effect of coherent crosstalk in AWG-based switching fabrics and achieve good performance in terms of throughput and delay.

Input-queued (IQ) switches are one of the reference architectures for the design of high-speed packet switches. Classical results in this field refer to the scenario in which the whole switch transfers the packets in a synchronous fashion, in phase with a sequence of fixed-size timeslots, selected to transport a minimum-size packet. However, for switches with large number of ports and high bandwidth, maintaining an accurate global synchronization and transferring all the packets in a synchronous fashion is becoming more and more challenging. Furthermore, variable size packets (as in the traffic present in the Internet) require rather complex segmentation and reassembly processes and some switching capacity is lost due to partial filling of timeslots. Thus, we consider a switch able to natively transfer packets in an asynchronous fashion thanks to a simple and distributed packet scheduler. We investigate the performance of asynchronous IQ switches and show that, despite their simplicity, their performance are comparable or even better than those of synchronous switches. These partly unexpected results highlight the great potentiality of the asynchronous approach for the design of high-performance switches.

Interconnection networks must transport an always increasing information density and connect a rising number of processing units. Electronic technologies have been able to sustain the traffic growth rate, but are getting close to their physical limits. In this context, optical interconnection networks are becoming progressively more attractive, especially because new photonic devices can be directly integrated in CMOS technology. Indeed, interest in microring resonators as switching components is rising, but their usability in full optical interconnection architectures is still limited by their physical characteristics. Indeed, differently from classical devices used for switching, switching elements based on microring resonators exhibit asymmetric power losses depending on the output ports input signals are directed to. In this paper, we study classical interconnection architectures such as crossbar, Benes and Clos networks exploiting microring resonators as building blocks. Since classical interconnection networks lack either scalability or complexity, we propose two new architectures to improve performance of microring based interconnection networks while keeping a reasonable complexity.

Passive optical networks (PONs) represent a step forward in "first mile" networks; indeed, by using optical technologies, PONs can transfer a large amount of data, and by being completely passive, they reduce management costs and failure probabilities. Access network is logically a point-to-multipoint network and the tree topology emerged as the winning solution; however, it naturally lacks protection capability and requires local traffic to be processed by the optical line terminal. In this paper, we present WONDER, a novel PON architecture based on a folded bus topology, which offers fault resilience and efficient local traffic support, and we discuss WONDER strengths and weaknesses.

Designing switching architectures for network routers and switches needs to consider limits imposed by the electronic technology, like small bandwidth x distance factors, power density constraints, energy consumption and dissipation issues. Introducing optical technologies to implement switching functions can overcome several of the current design limits. We propose a cost-effective architecture implementing an optical switch without any need for optoelectronic conversion within the switching fabric. We further propose a distributed scheduling scheme, based on an extension of the Fasnet protocol, and we compare it to classical centralized scheduling algorithms, showing that a distributed scheduler can provide performance comparable to the ones offered by more complex centralized schedulers.

We focus on metropolitan area networks operating in packet mode and exploiting a single-hop wavelength division multiplexing (WDM) architecture. First, we briefly describe a specific slotted WDM optical network, based on a folded bus topology. Then, we address the fairness problem arising in this architecture and propose an extension of the MetaRing protocol to a WDM scenario. Two possible strategies are defined and analyzed. Finally, we show that both fair access and high aggregate network throughput can be achieved by properly handling node access through all WDM channels.

Single-hop wavelength division multiplexing (WDM) ring networks operating in packet mode are a promising architecture for the design of innovate metropolitan area networks. They allow a cost-effective design, with a good combination of optical and electronic technologies, while supporting features like restoration and reconfiguration that are essential in any metropolitan scenario. In this article, we address the fairness problem in a slotted WDM optical network. We introduce the multi-fasnet fairness protocol, we discuss its limitations and we propose an extension, based on a dynamic strategy, that achieves high aggregate network throughput, throughput fairness, and bounded and fair access delays.