The requirements of end users on the quality of Internet connection and services is forcing the Internet providersand technical community to propose and introduce new technologies which may react to this demand. The most promising solution in this regard seems to be a passive optical network. There are many standards and recommendations provided by the organizations IEEE and ITU-T, such as EPON, GEPON, G-PON, XG-PON, and newly added NG-PON2 described in the ITU-T G.989 recommendation. Due to the implementation of TWDM mechanism the recommendation describes additionalcontrol messages to manage the whole network. This leads us to a need for a visualization tool which clearly shows control message flows and events between ONU and OLT units for each state. The application, designed by the authors and developed in C# programming language, is mainly focused on education purposes, but could be also useful to skilled industry professionals and in general those who have read the standard but are not fully familiar with the sequence of data flow in NG-PON2.