Patent ID: 6870854

Claim:
A method of controlling transfer of packets at a packet switching system that has a buffer, wherein each of the packets has a header portion and a data portion, the header portion having identifier that indicates priority for packet transferring, the method comprising: providing a first packet discard threshold for packets with higher priority; providing a second packet discard threshold for packets with lower priority, the first packet discard threshold being higher than the second packet discard threshold; counting the number of packets held in the buffer; counting the number of packets with higher priority held in the buffer; counting the number of packets with lower priority held in the buffer; judging congestion level of the buffer based on the counted the number of packets held in the buffer; discarding packets with higher priority if the number of the packets with higher priority counted is larger than the first packet discard threshold, discarding packets with lower priority if the number of the packets with lower priority counted is larger than the second packet discard threshold, charging the first packet discard threshold and the second packet discard threshold if the congestion level changes, wherein the changed packet discard threshold for packets with higher priority is higher than the changed packet discard threshold for packets with lower priority.