In an on/off-keying atmospheric optical communication system, index of refraction turbulence and PAT (pointing, acquisition and tracking) instabilities create strong and very slow fading compared to the usually used high data-rates. With this channel behavior, forward error correction can only work effectively if the codeword-length is longer than the mean duration of fade. Therefore packet-layer coding is a favorable way to implement a code with codewords longer than typical fading events. A code validation platform based on Ethernet transmission technology and packet-layer coding using UDP packets was built up to prove the performance of packet-layer coding. In this paper a demonstrator setup as well as results from a free-space transmission experiment are presented.