This paper studies an adaptive CDMA/PRMA protocol for satellite LEO systems. The new protocol is called S-CDMA/PRMA (Satellite-Code Division Multiple Access / Packet Reservation Multiple Access). The goal is to integrate several types of traffic (voice, file transfer and web) on the channel. This leads to service multiplexing and resource allocation study. New permission probability control functions are defined to give priority to voice users in order to guarantee its QoS. As a first step we propose an analytical model for voice and file transfer data to calculate their performance. As web traffic is very complicated to be studied analytically, we studied it by simulation. A simulation multiplexing several traffic types is also presented. The essential performance parameters are the loss probability for voice users and the waiting time for data users.