Method and apparatus for header compression

A header decompression apparatus for decompressing a header of a received packet by referring to reference information that is also included in a transmitting side, said apparatus comprising:

• reference information management means for storing and managing said reference information;
• packet receiving means for receiving the packet with update information selectively added thereto for updating said reference information;
• packet decompression means, provided with the packet received by said packet receiving means, for updating said reference information by using said update information, and decompressing the header of the packet by referring to said reference information;
• packet transmission means for transmitting an ACK packet indicating that said reference information has been correctly updated or a NACK packet for requesting transmission of said update information when a header decompression error occurs in said packet decompression means;
• mode determination means for switching the operation mode of the transmitting side to a reliable mode where, after updating the reference information of the transmitting side, the transmitting side continuously adds said update information until receiving the ACK packet, and to an optimistic mode where the transmitting side adds said update information when the reference information of the transmitting side is updated and whenever receiving the NACK packet;
• and
• mode notification means for notifying the transmitting side of said operation mode selected by said mode determination means, wherein
• said mode determination means counts the number of header decompression errors that occurred by a unit time X in said packet decompression means, and, when said operation mode is the optimistic mode and said number is larger than a predetermined value Y, said mode determination means switches said operation mode to the reliable mode, and when said operation mode is the reliable mode and said number is smaller than a predetermined value Z, said mode determination means switches said operation mode to the optimistic mode.

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:

• reference information management means for storing and managing said reference information;
• packet compression means for compressing the header of the packet in a specified operation mode by referring to said reference information, and selectively adding, to the compressed packet, update information for updating the reference information at the receiving side;
• packet transmission means for transmitting the packet compressed by said packet compression means;
• packet receiving means for receiving 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;
• delay time measuring means for measuring a roundtrip delay time with respect to the receiving side by transmitting and receiving a packet to and from the receiving side;
• and
• mode determination means for switching the operation mode of said packet compression means to a reliable mode where, after the reference information of the header compression apparatus is updated, said packet compression means continuously adds said update information until the ACK packet is received, and an optimistic mode where said packet compression means adds said update information when the reference information of the transmitting side is updated and whenever receiving the NACK packet, wherein
• said mode determination means receives, by a unit time X, said roundtrip delay time from said delay time measuring means, and switches said operation mode to the reliable mode when said operation mode is the optimistic mode and said roundtrip delay time is smaller than a predetermined value Y, and to the optimistic mode when said operation mode is the reliable mode and said roundtrip delay time is larger than a predetermined value Z.

A header decompression apparatus for decompressing a header of a received packet by referring to reference information that is also included in a transmitting side, said apparatus comprising:

• reference information management means for storing and managing said reference information;
• packet receiving means for receiving the packet with update information selectively added thereto for updating said reference information;
• packet decompression means, provided with the packet received by said packet receiving means, for updating said reference information by using said update information, and decompressing the header of the packet by referring to said reference information;
• packet transmission means for transmitting an ACK packet indicating that said reference information has been correctly updated or a NACK packet for requesting transmission of said update information when a header decompression error occurs in said packet decompression means;
• delay time measuring means for measuring a roundtrip delay time with respect to the transmitting side by transmitting and receiving a packet to and from the transmitting side;
• mode determination means for switching the operation mode of the transmitting side to a reliable mode where, after updating the reference information of the transmitting side, the transmitting side continuously adds said update information until receiving the ACK packet, and to an optimistic mode where the transmitting side adds said update information when the reference information of the transmitting side is updated and whenever receiving the NACK packet;
• and
• mode notification means for notifying the transmitting side of said operation mode selected by said mode determination means, wherein
• said mode determination means receives, by a unit time X, said roundtrip delay time from said delay time measuring means, and switches said operation mode to the reliable mode when said operation mode is the optimistic mode and said roundtrip delay time is smaller than a predetermined value Y, and to the optimistic mode when said operation mode is the reliable mode and said roundtrip delay time is larger than a predetermined value Z.

A header compression method of compressing a header of a packet to be transmitted by referring to reference information that is also included in a receiving side, said method comprising:

• a packet compression step of compressing the header of the packet in a specified operation mode by referring to said reference information stored, and selectively adding, to the compressed packet, update information for updating the reference information at the receiving side;
• a packet transmission step of transmitting the packet compressed in said packet compression step;
• a packet receiving step of receiving 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 step of switching the operation mode of said packet compression step to a reliable mode where, after said reference information is updated, said update information is continuously added until the ACK packet is received, and to an optimistic mode where said update information is added when said reference information is updated and whenever the NACK packet is received, wherein
• in said mode determination step, 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 operation mode is switched 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 operation mode is switched to the optimistic mode.

A header decompression method of decompressing a header of a received packet by referring to reference information that is also included in a transmitting side, said method comprising:

• a packet receiving step of receiving the packet with update information selectively added thereto for updating said reference information stored;
• a packet decompression step, provided with the packet received in said packet receiving step, for updating said reference information by using said update information, and decompressing the header of the packet by referring to said reference information;
• a packet transmission step of transmitting an ACK packet indicating that said reference information has been correctly updated or a NACK packet for requesting transmission of said update information when a header decompression error occurs in said packet decompression step;
• a mode determination step of switching the operation mode of the transmitting side to a reliable mode where, after updating the reference information of the transmitting side, the transmitting side continuously adds said update information until receiving the ACK packet, and to an optimistic mode where the transmitting side adds said update information when the reference information of the transmitting side is updated and whenever receiving the NACK packet;
• and
• a mode notification step of notifying the transmitting side of said operation mode selected in said mode determination step, wherein
• in said mode determination step, the number of header decompression errors that occurred by a unit time X in said packet decompression step is counted and, when said operation mode is the optimistic mode and said number is larger than a predetermined value Y, said operation mode is switched to the reliable mode, and when said operation mode is the reliable mode and said number is smaller than a predetermined value Z, said operation mode is switched to the optimistic mode.

A header compression method of compressing a header of a packet to be transmitted by referring to reference information that is also included in a receiving side, said method comprising:

• a packet compression step of compressing the header of the packet in a specified operation mode by referring to said reference information stored, and selectively adding, to the compressed packet, update information for updating the reference information at the receiving side;
• a packet transmission step of transmitting the packet compressed in said packet compression step;
• a packet receiving step of receiving 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;
• a delay time measuring step of measuring a roundtrip delay time with respect to the receiving side by transmitting and receiving a packet to and from the receiving side;
• and
• a mode determination step of switching the operation mode of said packet compression step to a reliable mode where, after the reference information to be referred to is updated, said update information is continuously added until the ACK packet is received, and to an optimistic mode where said update information is added when the reference information is updated and whenever the NACK packet is received, wherein
• in said mode determination step, said roundtrip delay time measured by a unit time X in said delay time measuring step is provided and, when said operation mode is the optimistic mode and said roundtrip delay time is smaller than a predetermined value Y, said operation mode is switched to the reliable mode, and when said operation mode is the reliable mode and said roundtrip delay time is larger than a predetermined value Z, said operation mode is switched to the optimistic mode.

A header decompression method of decompressing a header of a received packet by referring to reference information that is also included in a transmitting side, said method comprising:

• a packet receiving step of receiving the packet with update information selectively added thereto for updating said reference information stored;
• a packet decompression step of, provided with the packet received in said packet receiving step, updating said update information by using said update information, and decompressing the header of the packet by referring to said reference information;
• a packet transmission step of transmitting an ACK packet indicating that said reference information has been correctly updated or a NACK packet for requesting transmission of said update information when a header decompression error occurs in said packet decompression step;
• a delay time measuring step of measuring a roundtrip delay time with respect to the transmitting side by transmitting and receiving a packet to and from the transmitting side;
• a mode determination step of switching the operation mode of the transmitting side to a reliable mode where, after updating the reference information of the transmitting side, the transmitting side continuously adds said update information until receiving the ACK packet, and to an optimistic mode where the transmitting side adds said update information when the reference information of the transmitting side is updated and whenever receiving the NACK packet;
• and
• a mode notification step of notifying the transmitting side of said operation mode selected in said mode determination step, wherein
• in said mode determination step, said roundtrip delay time measured by a unit time X in said delay time measuring step is received, and said operation mode is switched to the reliable mode when said operation mode is the optimistic mode and said roundtrip delay time is smaller than a predetermined value Y, and to the optimistic mode when said operation mode is the reliable mode and said roundtrip delay time is larger than a predetermined value Z.