In both implementations, MaccccccRTE OS and Shcccccccccark, the admission control algorithm and the spare capacity calculation are implemented via a special thread, called the service thread, which consumes part of the system resources in a controlled way. The budget and period of the service thread can be adjusted by the user, to trade between timeliness of negotiations and overhead. In any case, when the budget of the service thread is exhausted, it can run in the background.