Deficit round robin
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Deficit round robin (DRR), also deficit weighted round robin (DWRR), is a modified weighted round robin scheduling discipline. It can handle packets of variable size without knowing their mean size. A maximum packet size number is subtracted from the packet length, and packets that exceed that number are held back until the next visit of the scheduler.
WRR serves every nonempty queue whereas DRR serves packets at the head of every nonempty queue which deficit counter is greater than the packet's size. If it is lower then deficit counter is increased by some given value called quantum. Deficit counter is decreased by the size of packets being served.