Packet data transmitting/ receiving apparatus and method using two sub layer

2 discloses a packet information transmission and reception apparatus and method using the sub-layer. 2 packet information transmission apparatus that uses the sub-layer is compressed the header of the IP packet, it generates the packet information unit PDCP (Packet Data Convergence Protocol) based on the IP packet, the PDCP packet information unit group to a set size at least one PDCP layer portion of reconstructing; And said at least one is connected with the PDCP layer portions and multiplexing the PDCP packet information unit into a MAC (Media Access Control) packet information unit received, demultiplexing the MAC packet information unit in the PDCP packet information unit and, HARQ to perform a MAC layer and includes a transmitting and receiving the MAC packet information unit. PDCP, MAC, HARQ, ARQ.