Blue (queue management algorithm)

Blue^[1] is an Active Queue Management algorithm. Like RED, it operates by randomly dropping or ECN-marking packets in a router's queue before it overflows. Unlike RED, however, it requires little or no tuning on the part of the network administrator.

Operation of Blue

A Blue queue maintains a drop/mark probability p, and drops/marks packets with probability p as they enter the queue. Whenever the queue overflows, p is increased by a small constant p_d, and whenever the queue is empty, p is decreased by a constant p_i<p_d.

Assuming the mix of traffic on the interface doesn't change, p will slowly converge to a value that keeps the queue within its bounds with full link utilisation.

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References

1. W. Feng, D. Kandlur, D. Saha, K. Shin. Blue: A New Class of Active Queue Management Algorithms. U. Michigan CSE-TR-387-99, April 1999.

External links

• Wu-chang Feng's page about Blue and SFB.
• An implementation of SFB for the Linux kernel.