Abstract: A method of transmitting PDCP (Packet Data Convergence Protocol) status reports, is performed by a mobile terminal by receiving, from an upper layer, a request for PDCP (Packet Data Convergence Protocol) re-establishment; detecting whether there are any out-of-sequence PDCP SDUs (service data units) stored; and if there is at least one out-of-sequence PDCP SDU stored, allocating a bitmap field of length in bits equal to the number of PDCP SNs from and not including the first out-of-sequence PDCP SDU up to and including a last out-of-sequence PDCP SDU.