To support data link control in communication systems operating with high-speed transmission systems, various selective repeat protocols have been proposed. In this paper the performance of a selective repeat protocol known as Checkpoint Mode protocol and some of its variations are analyzed. The aim of the analysis is to obtain simple closed-form expressions for the throughput efficiency of the protocol. The approximate results provide insight into the impact of the protocol parameters on its performance. The approximation accuracy is checked with simulations. Numerical examples show the significant performance improvement achieved by the CPM protocols over the go-back-n protocol when used over high-speed terrestrial and satellite links.