Disclosed is a method and an apparatus for efficient ACKnowledgmentNonACKnowledgement transmission in order to transmit forward data for multiple layers and support Hybrid Automatic Retransmission reQuest for each layer in a mobile communication system. A positioning protruding surface with a long concave groove is formed in the front side of the containing groove space, and a protruding bar is formed in the relative rear side of the containing groove space. A low pass filter is added to the 2-wire send path to eliminate high frequency noise caused by harmonic reflections of the ISDN-based signals on the 4-wire bus.