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'''Blue''' is a [[scheduling discipline]] for the [[network scheduler]] developed by graduate student Wu-chang Feng for Professor [[Kang G. Shin]] at the [[University of Michigan]] and others at the [[Thomas J. Watson Research Center]] of [[IBM]] in 1999.<ref name="mich">{{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 |date=April 1999 |url=http://www.eecs.umich.edu/techreports/cse/99/CSE-TR-387-99.pdf |publisher= University of Michigan |journal= Computer Science Technical Report |issue=CSE–TR–387–99 |accessdate= June 8, 2013 }}</ref>
==Functioning==
==Stochastic Fair Blue==▼
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>i</sub>'', and whenever the queue is empty, ''p'' is decreased by a constant ''p<sub>d</sub> < p<sub>i</sub>''.
If the mix of traffic on the interface does not change, ''p'' will slowly converge to a value that keeps the queue within its bounds with full link utilization.
The main flaw of Blue, which it shares with most single-queue queing 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.▼
▲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>{{Cite book|author1=Wu-Chang Feng |author2=Dilip D. Kandlur |author3=Debanjan Saha |author4=Kang G. Shin |title=Proceedings IEEE INFOCOM 2001. Conference on Computer Communications. Twentieth Annual Joint Conference of the IEEE Computer and Communications Society (Cat. No.01CH37213) |chapter=Stochastic fair blue: A queue management algorithm for enforcing fairness |url=http://www.thefengs.com/wuchang/blue/41_2.PDF |date=April 2001 |pages=1520–1529 |doi=10.1109/INFCOM.2001.916648 |accessdate= June 8, 2013 |volume=3|isbn=978-0-7803-7016-6 |citeseerx=10.1.1.11.4235 |s2cid=5902623 }}</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 [[
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===
==References==▼
Many scheduling 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 in 2009 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>{{Cite book |author1=Changwang Zhang |author2=Jianping Yin |author3=Zhiping Cai |name-list-style=amp |url= http://sites.google.com/site/cwzhangres/home/files/RSFBaResilientStochasticFairBluealgorithmagainstspoofingDDoSattacks.pdf |title= RSFB: a Resilient Stochastic Fair Blue algorithm against spoofing DDoS attacks |journal= International Symposium on Communication and Information Technology |year= 2009 |pages= 1566–1567 |isbn= 978-1-4244-4521-9 |accessdate= June 8, 2013 }} [http://portal.acm.org/citation.cfm?id=1789954.1790341 Abstract]</ref>
==Implementations==
An implementation of Blue is part of [[ALTQ]], the [[network scheduler]] for BSD Unix.<ref>{{Cite web |title= Blue |work= Web page |author= Wu-chang Feng |url= http://www.thefengs.com/wuchang/blue/ |accessdate= June 8, 2013 }}</ref>
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>
▲==References==
{{Reflist}}
[[Category:Packets (information technology)]]
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