Microwave link for transparent protection of optical access networks F. Ferreira 1,2 , S. Pato 1,2 , J. Pedro 1,3 , H. Silva 2 1 Nokia Siemens Networks Portugal S.A., Amadora, Portugal Tel: +351 21 4242076, Fax: +351 21 4242082, E-mail: filipe.ferreira@nsn.com 2 Instituto de Telecomunicações, DEEC-UC, Pólo II, Coimbra, Portugal 3 Instituto de Telecomunicações, Instituto Superior Técnico, Lisboa, Portugal This paper presents a novel design for a microwave link to circumvent failures (e.g., fibre cuts) in fixed optical access networks. Among its most distinctive features, the proposed scheme is transparent to the modulation formats employed in the fixed access network, enabling it to be used with diverse access systems at the expense of minimal modifications. Moreover, protection to failures is attained in a cost-effective way, when compared with the utilization of existing wireless protection mechanisms or with the installation of new ducts to establish redundant fibre paths. 1. Introduction The increasing capacity of optical access networks and the foreseen diversity of customer requirements will drive the demand for selective protection schemes to ensure survivability to network failures to a sub-set of premium customers, which require and are willing to afford this added feature. Protection becomes especially important in high capacity systems supporting end-users with critical applications, such as Passive Optical Networks (PONs) serving business customers. The survivability to failures may be critical in dense urban areas, where a large number of users requiring all-time connectivity are located. The growing demand for high quality-of-service and network availability, together with the network capacity increase, enhances the devastating consequences, in terms of loss of data and the consequent loss of revenue caused by a single failure. In such scenario, a simple fibre cut, whose probability of occurrence is non-negligible, may severely degrade the services provided to end-users. The impact of these disruptive events can be minimized by deploying recovery/protection mechanisms, which are common in metropolitan networks, in access networks. Typically, PON systems are deployed without a priori planning for protection mechanisms, such as fibre or components duplication. When such systems are intended to serve demanding end-users, which require survivability to single failures, in a very dense area, the duplication of fibre may become impractical due to high capital expenditures (e.g., from installing new fibres or new ducts). Hence, the availability of alternative methods for providing survivability to premium network users without incurring very high costs is important for access network operators. The solution presented in this paper aims to provide a method, based on a microwave link [1], to guarantee the survivability of such access networks in the most cost-effective way possible and also guaranteeing transparency to all types of traffic carried by the network.