Patent ID: 7024490

Claim:
A header compression method for compressing and transmitting, by using predetermined timestamp calculation information, a packet including transmission data and a header in which a timestamp is included in a system where transmission and reception ends share the same timestamp calculation information for header compression and decompression, the header compression method comprising: deriving timestamp calculation information dt(i) which is used to calculate a timestamp of a packet i (where i is a positive integer) to be compressed; storing the timestamp calculation information dt(i) in a history record as timestamp calculation information which has been so far transmitted; keeping track of tracked timestamp calculation information which is used for header compression; comparing the tracked timestamp calculation information and the timestamp calculation information dt(i) with each other, and when the tracked timestamp calculation information and the timestamp calculation information dt(i) are the same, compressing the timestamp of the packet i by using the tracked timestamp calculation information, and transmitting a resultant header carrying no timestamp; and determining, when the tracked timestamp calculation information and the timestamp calculation information dt(i) are not the same in said comparing, by referring to the history record, whether or not to update the tracked timestamp calculation information to the timestamp calculation information dt(i) to transmit a resultant header carrying the timestamp, if updated, together with an update signal.