Jorge M. Finochietto

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.

Click vs. Linux: two efficient open-source IP network stacks for software routers

Software routers based on off-the-shelf hardware and open-source operating systems are gaining more and more momentum. The reasons are manifold: first, personal computer (PC) hardware is broadly available at low cost; second, large-scale production and the huge market spur the manufacturers to closely track the improvements made available by Moores Law; third, open-source software leaves the freedom to study the source code, learn from it, modify it to improve the performance, and tailor its operation to ones own needs. In this paper we focus only on the data plane performance and compare the default Linux IP stack with the Click modular IP stack in terms of the forwarding throughput. The results are surprising and show that a high-end PC is easily able to fit into the multi-Gigabit-per-second routing segment, for a price much lower than commercial routers.

Can Simple Optical Switching Fabrics Scale to Terabit per Second Switch Capacities

The design of fabrics for terabit packet switches and routers needs to consider the limitations imposed by electronic technologies. In particular, attention has to be paid to information density and to power consumption and dissipation, as well as to power supply and footprint requirements. Optical technologies can overcome some of these limitations. We analyze the use of optical fabrics to interconnect line cards in terabit packet switches and routers. For this purpose, single-plane and multiplane optical interconnection architectures are proposed that exploit wavelength agility at line cards to implement the required switching functionality. The physical-layer scalability and feasibility of these architectures are studied by using realistic models, mostly based on the characteristics of commercially available optoelectronic devices. As a result, the considered architectures can be characterized in terms of power budget and signal-to-noise ratio, enabling the computation of the maximum achievable port count and aggregate switching capacity. Our results show that aggregate capacities of the order of a few terabits per second are possible in very simple optical switching fabrics and that the multiplane architectures permit a complexity trade-off between the wavelength and space domains, making the overall design more feasible.

Simple Optical Fabrics for Scalable Terabit Packet Switches

The design of fabrics for Terabit packet switches and routers needs to consider the limitations imposed by the electronic technology; in particular, more and more attention has to be paid to information density and to power consumption and dissipation, as well as to power supply and footprint requirements. These issues make more difficult to package a packet switch in one single rack of equipment; thus, optical links start being used to interconnect the line cards with the switching fabric. In this paper, we consider optical interconnection architectures that exploit wavelength agility at line cards to control switching decisions. The actual feasibility and physical layer scalability of this approach is analyzed by considering different optical fabric alternatives to interconnect the line cards. The main contribution of the paper is the characterization of these optical fabrics in terms of their power budget, and the analysis of the port count and of the aggregate bandwidth offered by these architectures to build Terabit packet switches.

A 40nm CMOS single-chip 50Gb/s DP-QPSK/BPSK transceiver with electronic dispersion compensation for coherent optical channels

Optical communication technology in long-haul and metropolitan links is experiencing a transition to coherent techniques and high spectral efficiency modulation formats such as dual-polarization (DP) QPSK, DP-QAM and OFDM. The combination of coherent demodulation and DSP allows costly optical signal-processing hardware used to compensate fiber optic impairments such as chromatic dispersion (CD) and polarization-mode dispersion (PMD) to be replaced by DSP-based techniques [1]. Economic large-scale deployment of coherent systems requires the integration of the optical transceiver functions in CMOS technology.

Multistage Switching Architectures for Software Routers

Software routers based on personal computer (PC) architectures are becoming an important alternative to proprietary and expensive network devices. However, software routers suffer from many limitations of the PC architecture, including, among others, limited bus and central processing unit (CPU) bandwidth, high memory access latency, limited scalability in terms of number of network interface cards, and lack of resilience mechanisms. Multistage PC-based architectures can be an interesting alternative since they permit us to i) increase the performance of single- software routers, ii) scale router size, iii) distribute packet-manipulation and control functionality, iv) recover from single-component failures, and v) incrementally upgrade router performance. We propose a specific multistage architecture, exploiting PC-based routers as switching elements, to build a high-speed, large-size, scalable, and reliable software router. A small-scale prototype of the multistage router is currently up and running in our labs, and performance evaluation is under way.

Open-Source PC-Based software routers: a viable approach to high-performance packet switching

We consider IP routers based on off-the-shelf personal computer (PC) hardware running the Linux open-source operating system. The choice of building IP routers with off-the-shelf hardware stems from the wide availability of documentation, the low cost associated with large-scale production, and the continuous evolution driven by the market. On the other hand, open-source software provides the opportunity to easily modify the router operation so as to suit every need. The main contribution of the paper is the analysis of the performance bottlenecks of PC-based open-source software routers and the evaluation of the solutions currently available to overcome them.

Design challenges in contact plans for disruption-tolerant satellite networks

During the past 20 years, space communications technologies have shown limited progress in comparison to Internet-based networks on Earth. However, a brand new working group of the IETF with focus on DTN promises to extend todays Internet boundaries to embrace disruptive communications such as those seen in space networks. Nevertheless, several challenges need to be overcome before operative DTNs can be deployed in orbit. We analyze the state of the art of effective design, planning, and implementation of the forthcoming network communications opportunities (contacts). To this end, different modeling techniques, system constraints, selection criteria, and methods are reviewed and compared. Finally, we discuss the increasing complexity of considering routing and traffic information to enrich the planning procedure, yielding the need to implement a contact plan computation element to support space DTN operation.

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.

Routing-aware fair contact plan design for predictable delay tolerant networks

Delay tolerant networks (DTNs) have become a promising solution for extending Internet boundaries to challenged environments such as satellite constellations. In this context, strategies to exploit scarce communication opportunities, while still considering device and application constraints, are still to be investigated to enable the actual deployment of these networks. In particular, the Contact Graph Routing (CGR) scheme has been proposed as it takes advantage of the contact plan, which comprises all future contacts among nodes. However, resource constraints can forbid the totality of these contacts to belong to the contact plan; thus, only those which together meet an overall goal shall be selected. In this article, we consider the problem of designing a contact plan that can provide fairness in link assignment and minimal all-to-all route delay; therefore, achieving equal contact opportunities while favoring end-to-end traffic latency. We formalize this by means of a multi-objective optimization model that can be computationally intractable for large topologies; thus, heuristic algorithms are proposed to compute the contact plan in practice. Finally, we analyze general results from these routines and discuss how they can used to provision valuable contact plans for real networks.