Long-term performance observation of a Free Space Optics link

New bandwidth demanding services for our data networks, especially the Internet, require higher data rates. This ongoing certainty will be an issue accompanying the development of future networks and a certain focus will be kept on this in the next couple of decades. The already available high data rates in the backbone of the Internet have to be made accessible for the end-user. Free space optics (FSO) is a very fast and reliable endorsement to radio links using light to transmit data. Different FSO-systems have been developed at TU Graz in the past years ranging from cheap devices, built with components available on the mass market, to expert systems using components from space technology. Besides other influences, weather and in particular fog has a big impact on the reliability of a FSO link. One of these systems was used in a project to collect long-term performance data over a period of almost three years. This paper shows the results in terms of availability of the optical link used in the conducted project and the influence of fog.