Chiara Piglione

PIE: A lightweight control scheme to address the bufferbloat problem

Bufferbloat is a phenomenon where excess buffers in the network cause high latency and jitter. As more and more interactive applications (e.g. voice over IP, real time video conferencing and financial transactions) run in the Internet, high latency and jitter degrade application performance. There is a pressing need to design intelligent queue management schemes that can control latency and jitter; and hence provide desirable quality of service to users. We present here a lightweight design, PIE (Proportional Integral controller Enhanced), that can effectively control the average queueing latency to a reference value. The design does not require per-packet extra processing, so it incurs very small overhead and is simple to implement in both hardware and software. In addition, the design parameters are self-tuning, and hence PIE is robust and optimized for various network scenarios. Simulation results, theoretical analysis and Linux testbed results show that PIE can ensure low latency and achieve high link utilization under various congestion situations.

RingO: an experimental WDM optical packet network for metro applications

This paper presents Ring Optical Network (RingO), a wavelength-division-multiplexing (WDM), ring-based, optical packet network suitable for a high-capacity metro environment. We present three alternative architectural designs and elaborate on the effectiveness of optic with respect to electronic technologies, trying to identify an optimal mix. We present the design and prototyping of a simple but efficient access control protocol, based upon the equivalence of the proposed network architecture with input-buffering packet switches. We discuss the problem of node allocation to WDM channels, which can be viewed as a particular optical network design problem. We, finally, briefly illustrate the fault protection properties of the RingO architecture. The main contribution of this paper is the identification and experimental validation of an innovative optical network architecture, which is feasible and cost effective with technologies available today, and can be a valid alternative to more consolidated solutions in metro applications.

On the number of input queues to efficiently support multicast traffic in input queued switches

The paper studies the design of IQ cell-based switch architectures with a reduced number of queues at input ports to support multicast traffic delivery. The design involves the definition of a queueing policy (to select how and where to enqueue packets) and of a scheduling policy (to select when and from which queue to transfer packets, satisfying the transmission constraints given by the switching fabric). The possible tradeoffs between performance figures, queueing policies and scheduling algorithms, are discussed. Clever design can lead to non-negligible performance gains; thus, several queuing policies and scheduling algorithms are examined by simulation. The main contributions of the paper are the following. First, it is shown that a small number of queues is sufficient to obtain good switch performance under typical traffic patterns. Second, multicast traffic patterns difficult to schedule are obtained by concentrating the load over few input ports, while keeping the output port load high. Third, the scheduling algorithm is shown to have a deeper impact on the switch performance than the queuing policy. Fourth, queueing policies that balance the load among all the available queues are shown to perform better than queuing policies based on other criteria. Finally, a novel greedy scheduling policy that improves switch performance is presented.

Measurement-based reconfiguration in optical ring metro networks

Single-hop wavelength division multiplexing (WDM) optical ring networks operating in packet mode are one of the most promising architectures for the design of innovative metropolitan network (metro) architectures. They permit 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 metro scenario. In this article, we address the tunability requirements that lead to an effective resource usage and permit reconfiguration in optical WDM metros. We introduce reconfiguration algorithms that, on the basis of traffic measurements, adapt the network configuration to traffic demands to optimize performance. Using a specific network architecture as a reference case, the paper aims at the broader goal of showing which are the advantages fostered by innovative network designs exploiting the features of optical technologies.

Practical algorithms for multicast support in input queued switches

This paper deals with multicast flow support in NtimesN input queued switch architectures. A practical approach to support multicast traffic is presented, assuming that O(N) queues are available at each input port. The focus is on dynamic queueing policies, where, at each input port, multicast flows are assigned to one among the available queues when flows become active: flows are assigned to queues according to switch queue status and, possibly, to flow information. We discuss queueing assignments, scheduling algorithms and flow activity definition models. We explain why dynamic queueing disciplines may outperform static policies, and we show that, even in the most favorable conditions for static policies, they provide comparable performance

OPN03-1: Multi-Fasnet Protocol: Short-Term Fairness Control in WDM Slotted MANs

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.

Fair uni- and multicasting in a ring metro WDM network

Packet-switched wavelength-division multiplexing (WDM) ring networks have been extensively studied as solutions to the increasing amount of traffic in metropolitan area networks, which is widely expected to be a mix of unicast and multicast traffic. We study the fairness between unicasting and multicasting in slotted packet-switched WDM ring networks that employ a tunable transmitter and fixed tuned receiver at each node and a posteriori buffer selection. We find that single-step longest-queue (LQ) buffer selection generally results in unfairness between unicasting and multicasting or a fixed relative priority for multicast versus unicast traffic. We propose and evaluate dual-step buffer selection policies that achieve fairness and allow for a range of relative priorities of multicast versus unicast traffic.

Performance evaluation of large capacity broadcast-and-select optical crossconnects

Abstract In this work, two bufferless high capacity broadcast-and-select optical switching node architectures are presented and their performance is evaluated. The architectures are modular permitting the expansion from basic to complex structures by adding new blocks/components in a gradual way, enhancing at the same time the corresponding network functionality. The blocking performance is assessed and scheduling algorithms are proposed to solve contention for a single node. Finally, physical layer modeling is carried out in order to investigate node scalability and node cascadeability. Overall, the proposed solutions are offering modularity, transparency to switching technology, graceful evolution and high performance at an affordable cost.

Optical switching nodes: architectures and performance

We propose and describe four optical buffer-less switching node architectures studied in the European Network of Excellence e-Photon/ONe. We consider two possible switching scenarios: data at inputs may require either an output fiber (fiber to fiber switching) or an output fiber and a specific wavelength (wavelength to wavelength switching). We first describe the four architectures; then, we propose both heuristic and optimal algorithms to solve contention among data at inputs, and study their loss performance. Although the modeling refers to synchronous fixed-size data units, most of the observations and results hold also when considering the proposed architectures as optical cross-connects for circuit-mode operations.

Cost and performance trade-offs in reconfiguration strategies for WDM networks

In this paper we study the problem of receiver allocation in WDM single-hop optical networks under dynamically changing traffic. Instead of focusing only on performance optimization, we wish to take into account both network performance and reconfiguration cost reduction. We first formalize the receiver allocation problem as a multi-criteria ILP. Then, we define Pareto-optimal solutions to solve the problem. The number and characteristics of Pareto-optimal solutions is studied to assess the problem significance. Finally, we propose different reconfiguration schemes that may guide the choice of network administrators among efficient solutions for the re-allocation problem.