Blue (queue management algorithm): Difference between revisions

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===Stochastic fair Blue===

The main flaw of Blue, which it shares with most single-queue queueing[[queuing disciplinesdiscipline]]s, is that it does not distinguish between [[Traffic flow (computer networking)|traffic flows]], but treats all flows as a single aggregate. Therefore, a single aggressive flow can push packets out of the queue belonging to other, better behaved, flows.

Stochastic fair Blue (SFB) is a stochastically fair variant of Blue which hashes flows and maintains a different mark/drop probability for each hash value. Assuming no hash collisions, SFB is able to provide a fair share of buffer space for every flow. In the presence of hash collisions, SFB is only stochastically fair.<ref>{{Citation |author1=Wu-Chang Feng |author2=Dilip D. Kandlur |author3=Debanjan Saha |author4=Kang G. Shin |title=Stochastic Fair Blue: an algorithm for enforcing fairness |url=http://www.thefengs.com/wuchang/blue/41_2.PDF |journal=Proceedings of INFOCOM 2001 |date=April 2001 |pages=1520–1529 |doi=10.1109/INFCOM.2001.916648 |accessdate= June 8, 2013 |volume=3}}</ref>

Unlike other stochastically fair queuing disciplines, such as SFQ ([[Stochastic Fairness QueueingQueuing]]), SFB can be implemented using a [[bloom filter]] rather than a [[hash table]], which dramatically reduces its storage requirements when the number of flows is large.

When a flow's drop/mark probability reaches 1, the flow has been shown to not react to congestion indications from the network. Such an inelastic flow is put in a "[[penalty box]]", and rate-limited.