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'''Blue''' is
==Functioning==
▲'''Blue''' is an [[active queue management]] algorithm. Like [[random early detection]] (RED), it operates by randomly dropping or marking packet with [[explicit congestion notification]] 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.<ref>{{Cite journal |title=BLUE: A New Class of Active Queue Management Algorithms |author1=Wu-chang Feng |author2=Dilip D. Kandlur |author3=Debanjan Saha |author4=Kang G. Shin |year=1999 |month=April |url=http://www.eecs.umich.edu/techreports/cse/99/CSE-TR-387-99.pdf |journal=U. Michigan Computer Science Technical Report |issue=CSE–TR–387–99 |accessdate= June 8, 2013 }}</ref>
Like [[random early detection]] (RED), Blue operates by randomly dropping or marking packet with [[explicit congestion notification]] mark before the transmit buffer of the [[network interface controller]] overflows. Unlike RED, however, it requires little or no tuning to be performed by the network administrator. 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<sub>
===Stochastic fair 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<sub>d</sub>'', and whenever the queue is empty, ''p'' is decreased by a constant ''p<sub>i</sub><p<sub>d</sub>''.
The main flaw of Blue, which it shares with most single-queue
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>{{
▲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 Blue==
▲The main flaw of Blue, which it shares with most single-queue queueing disciplines, is that it does not 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 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=Proc. INFOCOM 2001 |year=2001 |month=April |pages=1520–1529 |doi=10.1109/INFCOM.2001.916648 |accessdate=2010-01-02 |volume=3}}</ref>
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.▼
▲Unlike other stochastically fair queuing disciplines, such as SFQ ([[Stochastic Fairness Queuing]]), 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.
===Resilient stochastic fair Blue===
▲Active queue management (AQM) algorithms, including the fairness-aimed ones, are notably vulnerable to spoofing [[distributed denial-of-service]] (DDoS) attacks. A Resilient Stochastic Fair Blue (RSFB) algorithm was proposed against spoofing DDoS attacks. The basic idea behind RSFB is to record the responsive normal TCP flows and rescue their dropped packets. RSFB algorithm is effective in preserving the TCP throughput in the presence of spoofing DDoS attacks.<ref name=RSFB>Changwang Zhang, Jianping Yin, and Zhiping Cai, [http://sites.google.com/site/cwzhangres/home/files/RSFBaResilientStochasticFairBluealgorithmagainstspoofingDDoSattacks.pdf?attredirects=0 RSFB: a Resilient Stochastic Fair Blue algorithm against spoofing DDoS attacks], in International Symposium on Communication and Information Technology (ISCIT), 2009. [http://portal.acm.org/citation.cfm?id=1789954.1790341 Ref]</ref>
==Implementations==
An implementation of Blue is part of [[ALTQ]], the
An implementation of SFB for [[Linux]] was included in the [[Linux kernel]] in version 2.6.39.<ref>[http://kernelnewbies.org/Linux_2_6_39#head-87ffd4407af29460251c521e0228fe0ac9219d4b Kernel Newbies - Linux 2.6.39 - Networking]</ref><ref>{{cite web |url=https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/tree/net/sched/sch_sfb.c |title=SFB Linux kernel network scheduler module |publisher=[[kernel.org]] |accessdate=2013-09-07}}</ref><ref>{{Cite web |title= Stochastic Fair Blue for the Linux kernel |author= Juliusz Chroboczek |url= http://www.pps.univ-paris-diderot.fr/~jch/software/sfb/ |accessdate= June 8, 2013 }}</ref>
▲An implementation of Blue is part of [[ALTQ]], the alternative AQM framework for BSD Unix.<ref>[http://www.thefengs.com/wuchang/blue/ BLUE]</ref>
==References==
{{Reflist}}
[[Category:Packets (information technology)]]
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