The performance of RFID anti-collision protocols that are based on framed ALOHA depends on a transmission scheme that controls access to the shared channel. In this paper, we outline the characteristics of the RFID domain that impact the performance of such transmission schemes and compare four different transmission strategies. A novel technique introduced in this paper that recursively estimates the backlog on a slot-by-slot basis exhibits a superior performance in our simulations. The results also illustrate that our implementation of the Q algorithm proposed in [2] only performs well, if the frame size changes are restricted to incremental updates.