Patent ID: 8208474

Claim:
A method for transmitting a packet by a transmission apparatus in a mobile communication system, the method comprising: allocating a short sequence number for an initial transmission using some bits from among bits of a full sequence number for expressing a sequence number of the packet, and setting a first flag indicating use of the short sequence number; inserting the short sequence number and the first flag into the packet, and transmitting the packet with the short sequence number and the first flag inserted therein to a receiving side; before the allocation of the short sequence number, determining whether there is a loss of ‘n’ previously-transmitted consecutive packets where ‘n’ denotes an integer; if there is the loss of the ‘n’ previously-transmitted packets, allocating the full sequence number for expressing the sequence number of the packet, and setting a second flag indicating use of the full sequence number; and inserting the full sequence number and the second flag into the packet, and transmitting the packet with the full sequence number and the second flag inserted therein to the receiving side.