Apparatus and method for header decompression

Abstract

In a header decompression apparatus 709 , a header decompressor 703 refers to reference information stored in a reference information manager 707 to decompress a compressed header of a packet received by a packet receiver 704 . An error detector 702 detects a CRC error in the packet with its header decompressed by the packet receiver 704 , and outputs only a correct packet. A successive error counter 705 counts the number of successive errors detected by the error detector 702 . A successive decompression success counter 706 counts the number of decompression successes that successively appear. By referring to these counted numbers, an update request unit 708 transmits an update request to a transmitting side as required. The reference information manager 707 manages the reference information for header decompression. With this structure, the header decompression apparatus can request update of the reference information based on the state of the error.

1. A header decompression apparatus for decompressing a compressed header of a packet for transmission by referring to reference information being the same as reference information referred to for header compression by a transmitting side, said apparatus comprising:
 a packet receiver operable to receive the packet from the transmitting side;   a reference information manager operable to store and manage the reference information;   a header decompressor, operable to carry out header decompression on the received packet by referring to the reference information stored in said reference information manager;   an error detector operable to detect an error in the packet including the decompressed header;   a counter/storage the number operable to count the number of errors detected by said error detector and to store a relationship between the number of error packets and the number of error free packets; and   an update request unit operable to transmit, to the transmitting side, and update request for requesting update information for updating the reference information, when determining, based on the relationship of the packet number stored by said counter/storage, that the reference information stored in said reference information manager should be updated,   wherein when the update information is transmitted from the transmitting side, said reference information manager updates the reference information stored in said reference information manager based on the transmitted update information.   
     
     
       2. The header decompression apparatus according to  claim 1 , wherein counter/storage includes a successive error counter operable to count and store the number of times X a packet having an error detected by said error detector successively appeared and a successive decompression success counter operable to count and store the number of times Y a packet not having an error detected by said error detector successively appeared after counting by said successive error counter is stopped, and
 wherein said update request unit is further operable to determine, based on values of X and Y counted by said counter/storage, whether the reference information stored in said reference information manager should be updated.   
     
     
       3. The header decompression apparatus according to  claim 2 , wherein when X≧Y, said update request unit determines that the reference information stored in said reference information manager should be updated. 
     
     
       4. The header decompression method for decompressing a compressed header of a packet for transmission by referring to stored reference information that is the same as reference information referred to for header compression by a transmitting side, said method comprising:
 receiving the packet from the transmitting side;   carrying out header decompression on the received packet by referring to the stored reference information;   detecting an error in the packet including the decompressed header;   counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets; and   transmitting, to the transmitting side, an update request for requesting update information for updating the reference information, when determining, based on the stored relationship between the number of error packets and the number of error free packets, that the stored reference information should be updated.   
     
     
       5. The header decompression method according to  claim 4 , wherein said counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets includes counting and storing the number of times X a packet having an error detected in said detecting an error successively appeared, and counting and storing the number of times Y a packet not having an error detected in said detecting an error successively appeared after counting and storing the number of times X is stopped, and
 wherein in said transmitting an update request, based on values of X and Y counted in said counting the number of errors detected in said detecting an error and storing a relationship between the number of error free packets, it is determined whether the stored reference information should be updated.   
     
     
       6. The header decompression method according to  claim 5 , wherein in said transmitting an update request, when X≧Y, it is determined that the stored reference information should be updated. 
     
     
       7. A computer-readable recording medium with a program recorded therein, the program being executrd in a computer system for carrying out header decompression of decompressing a compressed header of a packet for transmission by referring to stored reference information that is the same as reference information referred to for header compression by a transmitting side, said program including computer system readable instructions capable of instructing the computer system to implement a method comprising:
 receiving the packet from the transmitting side;   carrying out header decompression on the received packet by referring to the stored reference information;   detecting an error in the packet including the decompressed header;   counting the number of errors detected in said detecting error and storing a relationship between the number of error packets and the number of error free packets; and   transmitting, to the transmitting side, an update request for requesting update information for updating the reference information, when determining, based on the stored relationship between the number of error packets and the number and the number of error free packets, that the stored reference information should be updated.   
     
     
       8. The computer-readable recording medium including computer system readable instructions capable of instructing the computer system to implement the method according to  claim 7 ,
 wherein said counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets includes counting and storing the number of times X a packet having an error detected in said detecting an error successively appeared, and counting and storing the number of times Y a packet not having an error detected in said detecting an error successively appeared after counting and storing the number of times X is stopped, and   wherein in said transmitting an update request, based on values of X and Y counted in said counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets, it is determined whether the stored reference information should be updated.   
     
     
       9. A program executed in a computer system for carrying out header decompression of decompressing a compressed header of a packet for transmission by referrring to reference information the same as reference information referred to for header compression by a transmitting side, said program including computer system readable instructions capable of instructing the computer system to implement the method comprising:
 receiving the packet from the transmitting side;   carrying out header decompression on the received packet by referring to the stored reference information;   detecting an error in the packet including the decompressed header;   counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets; and   transmitting, to the transmitting side, an update request for requesting update information for updating the reference information, when determining, based on the stored relationship between the number of error packets and the number of error free packets, that the stored reference information should be updated.   
     
     
       10. The program including computer system readable instructions capable of instructing the computer system to implement the method according to  claim 9 ,
 wherein said counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets includes counting and storing the number of times X a packet having an error detected in said detecting an error successively appeared, and packet not having an error detected in said detecting an error successively appeared after counting and storing the number of times X is stopped, and   wherein in said transmitting an update request, based on values of X and Y counted in said counting the number of errors detected in said detecting an error and storing a relationship between the number of error packets and the number of error free packets, it is determined whether the stored reference information should be updated.   
     
     
       11. A header decompression apparatus for decompressing a compressed header of a packet by referring to reference information, the apparatus comprising:
 a reference information manager for storing and managing the reference information;   a header decompressor for carrying out header decompression by referring to the reference information stored in the reference information manager;   an error detector for detecting an error in the packet including the header decompressed by the header decompressor;   a counter for counting a number R of packets having an error detected by the error detector from among a last W packets decompressed by the header decompressor, and storing a relationship between the number R of packets having an error and a number of error free packets, wherein (i) the stored relationship is the number R, (ii) W is an integer, and (iii) R is an integer; and   an update request unit for determining that the reference information stored in the reference information manager has an error based on the number R stored by the counter.   
     
     
       12. The header decompression apparatus according to claim 11, wherein the update request unit determines that the reference information stored in the reference information manager has an error when R is equal to or more than a threshold value. 
     
     
       13. The header decompression apparatus according to claim 12, wherein the threshold value is determined based on W. 
     
     
       14. The header decompression apparatus according to claim 11, wherein the error detector utilizes CRC to detect an error in a packet including a header decompressed by the header decompressor. 
     
     
       15. The header decompression apparatus according to claim 11, wherein when the update request unit determines that the reference information has an error, the update request unit transmits an update request for requesting update of the reference information stored in the reference information manager. 
     
     
       16. The header decompression apparatus according to claim 11, wherein when the update request unit determines that the reference information has an error, the update request unit transmits a NACK for requesting update of the reference information stored in the reference information manager. 
     
     
       17. A header decompression method for decompressing a compressed header of a packet by referring to reference information, the method comprising:
 carrying out header decompression by referring to the reference information;   detecting an error in the packet including the header decompressed in the carrying out header decompression;   counting a number R of packets having an error detected in the detecting from among a last W packets decompressed in the carrying out of header decompression, and storing a relationship between the number R of packets having an error and a number of error free packets, wherein (i) the stored relationship is the number R, (ii) W is an integer, and (iii) R is an integer; and   determining that the reference information has an error based on the stored number R.   
     
     
       18. The header decompression method according to claim 17, wherein the determining determines that the reference information has an error when R is equal to or more than a threshold value. 
     
     
       19. The header decompression method according to claim 18, wherein the threshold value is determined based on W. 
     
     
       20. The header decompression method according to claim 17, wherein the detecting utilizes CRC to detect an error in a packet including a header decompressed in the carrying out header decompression. 
     
     
       21. The header decompression method according to claim 17, wherein transmitting an update request for requesting update of the reference information, when it is determined that the reference information has an error in the determining. 
     
     
       22. The header decompression method according to claim 17, wherein transmitting a NACK for requesting update of the reference information, when it is determined that the reference information has an error in the determining. 
     
     
       23. A header decompression apparatus for decompressing a compressed header of a packet by referring to reference information, the apparatus comprising:
 a reference information manager for storing and managing the reference information;   a header decompressor for carrying out header decompression by referring to the reference information stored in the reference information manager;   an error detector for detecting an error in the packet including the header decompressed by the header decompressor;   a counter for counting a number R of packets having an error detected by the error detector from among a last W packets decompressed by the header decompressor, and storing a relationship between the number R of packets having an error and a number of error free packets, wherein (i) the stored relationship is the number R, (ii) W is an integer, and (iii) R is an integer; and   an update request unit for transmitting an update request for requesting update of the reference information stored in the reference information manager based on the number R stored by the counter.   
     
     
       24. The header decompression apparatus according to claim 23, wherein the update request unit transmits an update request when R is equal to or more than a threshold value. 
     
     
       25. The header decompression apparatus according to claim 24, wherein the threshold value is determined based on W. 
     
     
       26. A header decompression method for decompressing a compressed header of a packet by referring to reference information, the method comprising:
 carrying out header decompression by referring to the reference information;   detecting an error in the packet including the header decompressed in the carrying out header decompression;   counting a number R of packets having an error detected in the detecting from among a last W packets decompressed in the carrying out of header decompression, and storing a relationship between the number R of packets having an error and a number of error free packets, wherein (i) the stored relationship is the number R, (ii) W is an integer, and (iii) R is an integer; and   transmitting an update request for requesting update of the reference information based on the stored number R.   
     
     
       27. A header decompression method according to claim 26, wherein the transmitting transmits the update request when R is equal to or more than a threshold value. 
     
     
       28. A header decompression method according to claim 27, wherein the threshold value is determined based on W.