This enables or disables Weighted Random Early Drop, WRED, for this QoS rule, the mechanism that randomly drops packets as the queue approaches full rather than waiting until it's completely full. Enabling WRED on a rule carrying TCP traffic, such as ftp or http, lets TCP's congestion-control algorithms back off gradually as random early drops occur, avoiding the 'tail drop' cliff where a suddenly-full queue drops many packets from many flows at once and causes synchronized retransmit storms. For example, enabling WRED on a bulk-data QoS rule during a congested period spreads packet loss thinly across many FTP sessions instead of stalling all of them simultaneously when the queue hits 100% full.