Patent ID: 6889261

Claim:
A header compression apparatus for compressing a header of a packet to be transmitted by referring to reference information that is also included in a receiving side, said apparatus comprising: a reference information manager operable to store and manage said reference information; a packet compressor operable to compress the header of the packet in a specified operation mode by referring to said reference information, and to selectively add to the compressed packet, update information for updating the reference information at the receiving side; a packet transmitter operable to transmit the packet compressed by said packet compressor; a packet receiver operable to receive an ACK packet indicating that the reference information at the receiving side has been correctly updated or a NACK packet for requesting transmission of said update information due to a header decompression error that occurred at the receiving side; and a mode determination unit operable to switch the operation mode of said packet compressor to a reliable mode where, after the reference information of the header compression apparatus is updated, said packet compressor continuously adds said update information until the ACK packet is received, and to an optimistic mode where said packet compressor adds said update information when the reference information of the header compression apparatus is updated and whenever receiving the NACK packet, wherein when said operation mode is the optimistic mode and the number of NACK packets received by a unit time X is larger than a predetermined value Y, said mode determination unit switches said operation mode to the reliable mode, and when said operation mode is the reliable mode and the number of ACK packets received by the unit time X is larger than a predetermined value Z, said mode determination means switches said operation mode to the optimistic mode.