Blue (queue management algorithm): Difference between revisions

Revision as of 02:27, 23 December 2010

Revision as of 20:26, 2 January 2011

Line 7:

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.

==Stochastic Fair <span style="font-variant: small-caps;">B'''lue'''</span>== <!--Bolding small cap letters looks MUCH better on Firefox; don't know about other browsers.-->

==Stochastic Fair Blue==

The main flaw of <span style="font-variant: small-caps;">Blue</span>, which it shares with most single-queue queingqueueing disciplines, is that it doesn't distinguish between flows, and treats all flows as a single aggregate. Therefore, a single aggressive flow can push out of the queue packets belonging to other, better behaved, flows.

Stochastic Fair <span style="font-variant: small-caps;">Blue</span> (SFB)<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 In ''|journal=Proc. INFOCOM' 2001''. |year=2001 |month=April |pages=1520–1529 |doi=10.1109/INFCOM.2001.916648 |accessdate=2010-01-02}}</ref> is a stochastically fair variant of blue<span style="font-variant: small-caps;">Blue</span> 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.

Unlike other stochastically fair queuing disciplines, such as SFQ, 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.

<references/>

==References==