context: Federalism is one of the entrenched constitutional principles of Germany. According to the German constitution (called Grundgesetz or in English Basic Law), some topics, such as foreign affairs and defense, are the exclusive responsibility of the federation (i.e., the federal level), while others fall under the shared authority of the states and the federation; the states retain residual legislative authority for all other areas, including "culture", which in Germany includes not only topics such as financial promotion of arts and sciences, but also most forms of education and job training. Though international relations including international treaties are primarily the responsibility of the federal level, the constituent states have certain limited powers in this area: in matters that affect them directly, the states defend their interests at the federal level through the Bundesrat (literally Federal Council, the upper house of the German Federal Parliament) and in areas where they have legislative authority they have limited powers to conclude international treaties "with the consent of the federal government".
question: কিসের মাধ্যমে ফেডারেল পর্যায়ে রাষ্ট্রগুলো তাদের স্বার্থ রক্ষা করে?
answers: the Bundesrat