Experimental WDM Packet Networks for Metro Applications: the RingO and Wonder Projects A. Bianciotto, A. Carena, V. De Feo, J. Finochietto, R. Gaudino, F. Neri, C. Piglione and P. Poggiolini PhotonLab and LIPAR Advanced Laboratories Dipartimento di Elettronica, Politecnico di Torino C.so Duca degli Abruzzi 24, 10129, Torino, Italy E-mail: [lastname]@mail.tlc.polito.it Tel. +39.011.5644172 Fax +39.011.5644099 Abstract This paper presents the activities carried out at Politecnico di Torino, Italy, on an advanced ring-based WDM optical packet network suitable for a high-capacity metro environment. We present two alternative architectural designs, and elaborate on the effectiveness of optical with respect to electronic technologies, trying to identify an optimal mix of the two technologies [1]. The first presented architecture refers to a research project called RingO, which ended in 2002, while the second one refers to the current ongoing project Wonder. Both projects are funded by the Italian Ministry for Education and Research (MIUR). We present the design and prototyping of a simple but efficient access control protocol, based upon the equiv- alence 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. The main contribution of the 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. I. Introduction Metropolitan area networks are one of the best arenas for an early penetration of ad- vanced optical technologies. Indeed, their large traffic dynamism requires packet switching to efficiently use the available resources; their high capacity requirements justifies WDM use; and their limited geographical distances lowers the impact of fiber transmission impair- ments. From a research view point, designing innovative architectures for metro networks often means finding cost-effective combinations of optical and electronic technologies, and new networking paradigms that better suit the constraints dictated by available photonic components and subsystems. Our research groups at Politecnico di Torino, Italy, have designed and prototyped network architectures for metro applications, taking an approach based upon optical packets, but limiting optical complexity to a minimum, and trying to use only commercially available components. To best exploit the advantages of available technologies, the bulk of raw data is kept in the optical domain, while more complex network control functions are mostly implemented in the electronic domain. Likewise, neither distributed resource allocation nor contention resolution is performed in the optical domain, thereby taking a radically different perspective with respect to traditional electronic packet-switched architectures. In this paper we introduce the rationale and design of two research projects focused on optical network for metro application. The first presented architecture refers to a research project called RingO (Ring Optical) [2], which ended in 2002, while the second one refers to