Mobile communication networks can provide various types of services, such as voice, data, video, and multimedia as they evolve toward 3G networks. To increase the efficiency of limited resources in the UTRAN Iub interface, AAL2/ATM link transmission schemes with multiplexing have been introduced. As an all-IP based network technology develops, the AAL2/ATM link transmission schemes will be replaced by IP based link transmission schemes in future to reduce large protocol overheads. Accordingly, CIP, LIPE and PPPmux have been proposed in 3GPP standards. In this paper, we describe a link transmission model in the UTRAN Iub interface and evaluate the performance of ATM based and IP based link transmission schemes in terms of link efficiency and average link transmission delay. Simulation results show that the IP based transmission schemes perform better than the ATM based transmission scheme as the number of users increases.