Patent ID: 6661811
Filing Date: 2003-12-09
Classification: H04J,H04L,H04N,H04Q

Abstract:
A method of correcting timing errors when transmitting isochronous data through a packet based communication network in which at least some of the data packets contain timestamps which indicate to a receiver the time at which the data should be processed, the method comprising:a) inserting transmission timestamps in isochronous data packets which relate to an absolute time as defined by a transmission clock and which are to be transmitted over a transmission network, b) receiving the data packets and detecting and temporally recording the transmission timestamps therein, c) providing a receiver clock which is synchronised in frequency but not necessarily in absolute time with the transmission clock, d) storing the absolute time of the receiver clock when the first packet containing a transmission timestamp is received, e) adding a given time offset to the stored receiver clock time, the offset being greater than or equal to the maximum variation in time between successive received data packets, to define the output time of the first of the received data packets f) subtracting the value of the transmission timestamp in the first received data packet from the transmission timestamp in each subsequently received data packet, and g) adding the difference between the transmission timestamp of the present data packet and the transmission timestamp of the first data packet to the output time of the first data packet to define the output time of the present packet.