A recent algorithm of Modiano selects packet In this paper we modify the algorithm of Modiano so that the sizes in a selective repeat ARQ protocol based on the proposed scheme adapts between one of only two preacknowledgement history of the most recently transmitted specified packet sizes. Our analysis follows closely the packets. In this paper we modify this algorithm so that analysis of [5], but in the process we also provide a simplified the choice of packet size is restricted to one of two presolution to equation (8) in [5]. The rest of the paper is