This paper deals with design of a database for capturing and saving frames transmitted in downstream direction over gigabit passive optical network (GPON). This kind of system uses optical transfer over passive optical networks and therefore the architecture of network is different than Ethernet technology. The useful payload is encapsulated in GEM frames by using the gigabit encapsulation method. In this article, we describe basic principles of passive optical networks and a database model for saving GPON frames in the downstream direction captured by the field programmable gate array (FPGA) card. Next, the fundamental scripts for analysing physical layer operation, admission and maintenance (PLOAM) messages are discussed. Finally, a developed Python tool for advanced analysis is shown.