Assessment of physical impairments in a DWDM ring network based on optical packet switching M. A. Losada 1 , A. Lopez 1 , I. Garces 1 ,J .A. Lazaro 2 1 GTF, Aragón Institute of Engineering Research (i3A), University of Zaragoza, Zaragoza, Spain Tel: +34 976762373, Fax: +34 976762111, E-mail: alosada@unizar.es , aliclope@unizar.es , ngarces@unizar.es 2 Broadband and Optical Communications Group, Walqa, University of Zaragoza, Huesca, Spain Tel: +34 974 21 5481, E-mail: jalazaro@unizar.es In this work, we study the physical effects over a multiple-access unidirectional ring network with a DWDM wavelength scheme based on optical packet switching. In our proposal, each node in the ring is identified by a combination of wavelength and numerical address and can transmit data in any wavelength, but receive data only in its assigned wavelength. Packets dropped by the node are routed using an optical switch according to their address, without optoelectronic conversion. We introduce physical impairments in this network, making the necessary modifications in the node design to minimize the restrictions they impose. 1. Introduction Metropolitan networks have been attracting much attention as they impose a bandwidth bottleneck between the local access networks and the backbone. The deployed circuit-switched SONET/SDH rings are relatively inefficient for dynamic traffic and, although several approaches to adapt circuit-switched techniques to data traffic are in the standardization stage, many efforts are oriented to the design of packet-switched techniques combined to WDM to increase bandwidth. These later techniques are particularly promising, but they are still in an early stage. A complete classification and description of different proposals to WDM metropolitan rings can be found in [1]. Most of these approaches are based on wavelength sharing among different channels in a unidirectional all-optical fiber ring, while they differ in the node design, with either tunable transmitters or receivers and in the medium access control (MAC) protocols. In our approach, each node is equipped with a fixed receiver and a transmitter array to allow insertion in any of the rings wavelength, and with an optical switch. This later feature introduces true optical layer functionality into the ring architecture as there is no need for conversion to the electronic domain until it reaches its final destination, and it can be viable as commercial switching times have decreased up to 100ns [2]. In fact, recent results obtained from the simulation of a 10Gbps ring showed that this network is able to support high traffic loads and a great number of nodes [3]. However, the physical viability of the proposed network has not been assessed up to this point. Our node design requires optical components which impose power