This paper discusses an efficient implementation of the multiplexing protocol H.223, which is an important part of 3G-324M protocol stack required for 3G mobile multimedia communications. Our implementation of the protocol aims to support the multi-point video conferencing with the capability of transmitting/receiving multiple video/audio streams simultaneously. Conference managements such as admission and audio channel scheduling are also discussed. As a result, the implementation improves efficiency and makes the conference more convenient to set up and operate. Our prototype system is stable and its performance is satisfactory.