The Dutch rail infrastructure manager – Prorail – utilizes simulation to perform research in a number of areas of railtransport.One area that is of particular interest is that of the analysis of Dynamic Traffic Management (DTM) of trains. The aim of DTM is to manage plan/timetable deviations from daily train operations effectively in order to improve overall performance of the train service. To perform this analysis two existing (legacy) systems, FRISO and TMS, have been connected via the High Level Architecture (HLA). FRISO is a train simulator that is used to investigate rail transport in the area of several (tens of) kilometers. TMS is a further development of the controller system COMBINE and is an advanced traffic control system that is used to predict and minimize route conflicts between trains in order to improve efficiency, reliability and quality in rail transport. Analysis involves the execution of stochastic (Monte Carlo) simulation, for which conservative Time Management is a critical issue. This paper focuses on the design of the TMS-FRISO federation, the federation agreements made, the lessons learned in making both legacy systems HLA enabled and possible future improvements. Within this project TNO provided distributed simulation expertise and HLA software tools, like the TNO-RTI and the RCI middleware with code generator.