Controlled Delay Active Queue Management
AQM K. Nichols
Internet-Draft Pollere, Inc.
Intended status: Informational V. Jacobson
Expires: June 3, 2016 A. McGregor, ed.
J. Iyengar, ed.
December 1, 2015
Controlled Delay Active Queue Management
This document describes a general framework called CoDel (Controlled
Delay) [CODEL2012] that controls bufferbloat-generated excess delay
in modern networking environments. CoDel consists of an estimator, a
setpoint, and a control loop. It requires no configuration in normal
Internet deployments. CoDel comprises some major technical
innovations and has been made available as open source so that the
framework can be applied by the community to a range of problems. It
has been implemented in Linux (and available in the Linux
distribution) and deployed in some networks at the consumer edge. In
addition, the framework has been successfully applied in other ways.
Note: Code Components extracted from this document must include the
license as included with the code in Section 5.
Status of This Memo
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 3, 2016.
Nichols, et al. Expires June 3, 2016 [Page 1]
Internet-Draft CoDel December 2015
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The need for queue management has been evident for decades. The
"persistently full buffer" problem has been discussed in the IETF
community since the early 80's [RFC896]. The IRTF's End-to-End
Working Group called for the deployment of active queue management
(AQM) to solve the problem in 1998 [RFC2309]. Despite this
awareness, the problem has only gotten worse as Moore's Law growth in
memory density fueled an exponential increase in buffer pool size.
Efforts to deploy AQM have been frustrated by difficult configuration
and negative impact on network utilization. This problem, recently
christened "bufferbloat", [TSV2011] [BB2011] has become increasingly
important throughout the Internet but particularly at the consumer
edge. Recently, queue management has become more critical due to
increased consumer use of the Internet, mixing large video
transactions with time-critical VoIP and gaming. Gettys [TSV2011,
BB2011] has been instrumental in publicizing the problem and the
measurement work [CHARB2007, NATAL2010] and coining the term
bufferbloat. Large content distributors such as Google have observed
that bufferbloat is ubiquitous and adversely affects performance for
many users. The solution is an effective AQM that remediates
bufferbloat at a bottleneck while "doing no harm" at hops where
buffers are not bloated.
The development and deployment of effective active queue management
has been hampered by persistent misconceptions about the cause and
meaning of packet queues in network buffers. Network buffers exist
to absorb the packet bursts that occur naturally in statistically
multiplexed networks. Buffers helpfully absorb the queues created by
such reasonable packet network behavior as short-term mismatches in
traffic arrival and departure rates that arise from upstream resource
contention, transport conversation startup transients and/or changes
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