The invention is to use the ability of a switching fabric to set a congestion
indicator bit in a segment if any queue through which the segment passes is filled
above a lower threshold. The output linecard monitors the field of the congestion
indicator bit as it receives segments from the switching fabric. The output linecard
periodically calculates the ratio of segments having the congestion bit set to
all segments routed to a particular port. The periodically calculated ratio is
used as an input parameter to a Random Early Detection (RED) algorithm. The RED
algorithm selects a packet for the output linecard to drop, by use of a random
selection method. The destination computer then does not receive the packet. The
random selection of packets to drop has the effect of helping to prevent undesirable
network synchronization of transmission of replacement packets. With adaptive source
computers, the network device then does not reach a congested state, thereby maintaining
optimum throughput for the computer network. When an ATM switching fabric is used
with ATM cells for the segments, then the Explicit Forward Congestion Indication
Field (EFCI bit) of a data cell is used to mark a data cell which has passed through
a queue which is filled above a lower threshold level. Data cells arriving at the
output line card with the EFCI bit set are then counted, and this count is used
in the periodic calculation of the ratio used as input to the RED algorithm.
