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rfc:rfc5783

Internet Research Task Force (IRTF) M. Welzl Request for Comments: 5783 University of Oslo Category: Informational W. Eddy ISSN: 2070-1721 MTI Systems

                                                         February 2010
                Congestion Control in the RFC Series

Abstract

 This document is an informational snapshot taken by the IRTF's
 Internet Congestion Control Research Group (ICCRG) in October 2008.
 It provides a survey of congestion control topics described by
 documents in the RFC series.  This does not modify or update the
 specifications or status of the RFC documents that are discussed.  It
 may be used as a reference or starting point for the future work of
 the research group, especially in noting gaps or open issues in the
 current IETF standards.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for informational purposes.
 This document is a product of the Internet Research Task Force
 (IRTF).  The IRTF publishes the results of Internet-related research
 and development activities.  These results might not be suitable for
 deployment.  This RFC represents the consensus of the Internet
 Congestion Control Research Group of the Internet Research Task Force
 (IRTF).  Documents approved for publication by the IRSG are not a
 candidate for any level of Internet Standard; see Section 2 of RFC
 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5783.

Welzl & Eddy Informational [Page 1] RFC 5783 Congestion Control RFCs February 2010

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Architectural Documents  . . . . . . . . . . . . . . . . . . .  5
 3.  TCP Congestion Control . . . . . . . . . . . . . . . . . . . .  9
 4.  Challenging Link and Path Characteristics  . . . . . . . . . . 10
 5.  End-Host and Router Cooperative Signaling  . . . . . . . . . . 12
   5.1.  Explicit Congestion Notification . . . . . . . . . . . . . 13
   5.2.  Quick-Start  . . . . . . . . . . . . . . . . . . . . . . . 15
 6.  Non-TCP Unicast Congestion Control . . . . . . . . . . . . . . 15
 7.  Multicast Congestion Control . . . . . . . . . . . . . . . . . 18
 8.  Guidance for Developing and Analyzing Congestion Control
     Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 20
 9.  Historic Interest  . . . . . . . . . . . . . . . . . . . . . . 21
 10. Security Considerations  . . . . . . . . . . . . . . . . . . . 22
 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
 12. Informative References . . . . . . . . . . . . . . . . . . . . 22

Welzl & Eddy Informational [Page 2] RFC 5783 Congestion Control RFCs February 2010

1. Introduction

 In this document, we define congestion control as the feedback-based
 adjustment of the rate at which data is sent into the network.
 Congestion control is an indispensable set of principles and
 mechanisms for maintaining the stability of the Internet.  Congestion
 control has been closely associated with TCP since 1988 [Jac88], but
 there has also been a great deal of congestion control work outside
 of TCP (e.g., for real-time multimedia applications, multicast, and
 router-based mechanisms).  Several such proposals have been produced
 within the IETF and published as RFCs, along with RFCs that give
 architectural guidance (e.g., by pointing out the importance of
 performing some form of congestion control).  Several of these
 mechanisms are in use within the Internet.
 When designing a new Internet transport protocol, it is therefore
 important to not only understand how congestion control works in TCP
 but also have a broader understanding of the other congestion control
 RFCs -- some give guidance, some of them describe mechanisms that may
 have a direct influence on a newly designed protocol, and some of
 them may only be "related work" worth knowing about.  The purpose of
 this document is to facilitate and encourage this search for
 knowledge by providing an overview of RFCs related to congestion
 control that have been published thus far.  This document is a
 product of the IRTF's Internet Congestion Control Research Group
 (ICCRG).  It was developed because a strong grasp of the existing
 literature should benefit further ICCRG work.  The ICCRG developed
 consensus on the content of this document during a two-year
 development period based on review comments and ICCRG mailing list
 discussions.  A list of the main review contributors is contained in
 the Acknowledgements section of this document.
 While the ICCRG agreed to the document's production, any opinions
 expressed are the authors' own, and as this document is not an IETF
 publication, it does not update or modify the status of any published
 RFCs.  The format of this document is similar to an annotated
 bibliography.  Although host and router requirements for congestion
 control functions are discussed, this is only an informational
 document and does not contain any formal standards bearing of its
 own.
 Congestion control is a large and active topic, and so the scope of
 this document is limited to published RFCs and a small number of
 current working group drafts.  This allows the document to focus on
 congestion control principles and mechanisms that are among the most
 well-supported, well-accepted, or widely used.  Significant
 contributions to this subject also exist in both the academic
 literature and in the form of Internet-Drafts; however, we exclude

Welzl & Eddy Informational [Page 3] RFC 5783 Congestion Control RFCs February 2010

 these from this study.  In many cases the RFC describing some
 mechanism will contain references to relevant academic publications
 in journals or conference proceedings that presented the research and
 validation of the mechanism.  For instance, RFC 2581 cites Jacobson's
 1988 SIGCOMM paper that has a less standards-oriented but more
 illustrative treatment and explanation of some of the mechanisms in
 RFC 2581.
 The majority of the documents discussed here pertain to end-host-
 based congestion control.  Many network-based mechanisms, such as a
 number of queue management algorithms, do not require any protocol
 exchanges between elements, but merely operate within a single host
 or router.  Thus, network-based congestion control mechanisms have
 often not been described in any RFC, as they generally fall under the
 domain of implementation details that do not influence
 interoperability.
 There are many RFCs related to Quality of Service (QoS), especially
 within the Integrated Services and Differentiated Services frameworks
 [RFC1633] [RFC2475] [RFC2998].  These QoS RFCs themselves deserve a
 similar bibliography to the one that this document provides for
 congestion control.  We specifically do not include the vast amount
 of QoS work into the scope of this document, as it is a full field in
 its own right, and deals with issues that are mostly orthogonal to
 end-host congestion control and router queue management.  Although
 there can certainly be interactions between QoS and congestion
 control mechanisms, scheduling mechanisms used to implement QoS (on
 either a per-flow or an aggregate basis), for instance, can be used
 independently of the end-host congestion control and queue management
 functions also in use.  Similar arguments can be made for traffic-
 shaping, admission control, and other functions that are intended for
 QoS and are only side-notes for congestion control.
 A similar argument can be made for excluding consideration of the
 media access control (MAC) layer protocols used by the links
 throughout a path.  Although the MAC protocols implement various
 forms of resolving contention for shared links (and sometimes offer
 QoS services), these are also distinct from end-to-end congestion
 control.  Furthermore, MAC protocols are not typically discussed in
 the RFC series, but they are defined in outside documents (e.g., IEEE
 standards), since the IETF does not generally work on link layers
 themselves.  Few, if any, of the RFCs that describe mappings of IP
 onto various link layers directly discuss congestion control.
 To organize the subject matter in this document, the content is
 classified into several broad categories.  First, we list documents
 relating to Internet architecture and general architectural concepts
 in Section 2.  Next, the congestion control algorithms used in the

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 TCP transport protocol are discussed in Section 3.  Interactions
 between link properties and mechanisms with the kinds of algorithms
 and heuristics used within end-to-end congestion control are covered
 in Section 4.  One method that has been developed by the IETF (and
 deployed to some extent) for allowing network-based and host-based
 congestion control to interact without dropping packets is the
 subject of Section 5.1.  The congestion control algorithms used by
 unicast transport protocols other than TCP are described in
 Section 6.  Work on congestion control for multicast transports and
 applications is listed in Section 7.  RFCs that give guidance to
 developers of new algorithms are discussed in Section 8.  Finally,
 documents that have historic significance, but perhaps not current
 direct technical application, have been classified into Section 9.
 Note that the use of the term "historic" here has nothing to do with
 the IETF's formal classification of documents as having "Historic"
 status.

2. Architectural Documents

 Some documents in this section contain architectural guidance and
 concerns, while others specify congestion-control-related mechanisms
 that are broadly applicable and have impacts on more than a single
 class of congestion control techniques.  Some of these documents are
 direct products of the Internet Architecture Board (IAB), giving
 their guidance on specific aspects of congestion control in the
 Internet.
 RFC 1122: "Requirements for Internet Hosts -- Communication Layers"
    (October 1989)
    [RFC1122] formally mandates that hosts perform congestion control.
    For TCP, several congestion control features are described and
    listed as required elements of conforming implementations, and for
    UDP, RFC 1122 leaves congestion control as an issue for higher-
    layered protocols.  Although sending and reacting to ICMP Source
    Quench packets is no longer recommended [RFC1812] [Gont10], the
    rest of the congestion control guidance in this RFC is still a
    basis for several current practices in TCP implementations.
 RFC 1812: "Requirements for IP Version 4 Routers" (June 1995)
    Numerous issues relevant to router behavior are discussed in
    [RFC1812], and requirements for routers to support are prescribed
    within the document.  Portions of RFC 1812 that are particularly
    relevant to congestion control include the directive that routers
    SHOULD NOT originate ICMP Source Quench messages, discussion of
    precedence in queueing, and Section 5.3.6 titled "Congestion

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    Control" that recommends sizing buffers as a function of the
    product of the bandwidth of the link times the path delay of the
    flows using the link, and advises on the implementation of active
    queue management techniques.
 RFC 1958: "Architectural Principles of the Internet" (June 1996)
    Several guidelines for network systems design that have proven
    useful in the evolution of the Internet are sketched in [RFC1958].
    Congestion control is not specifically mentioned or alluded to,
    but the general principles apply to congestion control.  For
    instance, performing end-to-end functions at end nodes, lack of
    centralized control, heterogeneity, scalability, simplicity,
    avoiding options and parameters, etc., are all valid concerns in
    the design and assessment of congestion control schemes for the
    Internet.
 RFC 2140: "TCP Control Block Interdependence" (April 1997)
    [RFC2140] suggests that TCP connections between the same endpoints
    might share some information, including their congestion control
    state.  To some degree, this is done in practice by a few current
    operating systems; for example, Linux currently has a destination
    cache with this information, but this behavior is not yet formally
    standardized or recognized as a best practice by the IETF.
 RFC 2309: "Recommendations on Queue Management and Congestion
    Avoidance in the Internet" (April 1998)
    [RFC2309] briefly discusses the history of congestion and the
    origin of congestion control in the Internet.  The focus is mainly
    on network- or router-based queue management algorithms.  This RFC
    recommends to test, standardize, and deploy Active Queue
    Management (AQM) in routers; it provides an overview of one such
    mechanism, Random Early Detection (RED), and explains how and why
    AQM mechanisms can improve the performance of the Internet.
    Finally, this document explains the danger of a possible
    "congestion collapse" from unresponsive flows and makes a strong
    recommendation to develop and eventually deploy router mechanisms
    to protect the Internet from such traffic.
    Today, the advice in this document has been followed to some
    extent.  Hardware and software vendors have been receptive, and
    AQM techniques are widely available in many popular dedicated
    commercial router products and even in more general operating

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    systems that are sometimes used as routers.  However, AQM
    techniques may not be enabled in default configurations of these
    systems, and it is often left to users and network engineers to
    enable and configure AQM mechanisms when desired.  In some cases,
    enabling QoS mechanisms on a device also enables AQM mechanisms by
    default.  The number of production routers that actually have
    these AQM features enabled is an open question.
 RFC 2914 (BCP 41): "Congestion Control Principles" (September 2000)
    [RFC2914] is an explanation of the principles of congestion
    control, and the IETF's Best Current Practice for congestion
    control design.  It points out that there are an increasing number
    of applications that do not use TCP, and elaborates on the
    importance of performing congestion control for such traffic in
    order to prevent congestion collapse.  The TCP Reno congestion
    control mechanisms are described as an example of end-to-end
    congestion control within transport protocols.
    SCTP is one example of a non-TCP transport protocol that
    implements congestion control based on these principles.  The
    developments of TFRC [RFC3448] and DCCP [RFC4340] are attempts to
    provide useful tools implementing those principles for
    applications with needs similar to streaming media, where TCP's
    reactions are too fast.  It would be beneficial for users and the
    Internet itself if these carefully designed tools become widely
    deployed in place of other ad hoc schemes that may not be well-
    grounded in the congestion control principles.  This replacement
    process is ongoing and not yet complete.  Appropriate and usable
    congestion control schemes for non-TCP flows continue to be an
    open research area.
 RFC 3124: "The Congestion Manager" (June 2001)
    [RFC3124] specifies the Congestion Manager, an end-system service
    that realizes congestion control on a per-host-pair rather than a
    per-connection basis, which may be a more appropriate way to carry
    out congestion control.  Using the Congestion Manager, multiple
    streams between two hosts (which may include TCP flows) can adapt
    to network congestion in a unified fashion.
    This proposal is related to RFC 2140, discussed above, but with a
    wider scope than TCP.  Because some pieces of its supporting
    architecture have not yet been specified, the Congestion Manager's
    techniques are not commonly used today and have not been widely
    implemented and deployed yet beyond experimental stacks.  Sharing

Welzl & Eddy Informational [Page 7] RFC 5783 Congestion Control RFCs February 2010

    of congestion and path information between individual connections
    continues to be an open research area with branches in detecting
    shared bottlenecks when using multiple paths, caching of old state
    for faster startup, and sharing of current state and feedback.
 RFC 3426: "General Architectural and Policy Considerations" (November
    2002)
    [RFC3426] lists a number of questions that can be answered for a
    particular technical solution to determine its architectural
    impact and desirability.  These are valid for congestion control
    mechanisms, and end-point congestion management is used as an
    example case-study several times in RFC 3426.  Two salient
    questions that RFC 3426 advises asking about proposed mechanisms
    are why they are needed in addition to existing protocols, and why
    they are needed at a certain layer rather than at other layers.
    These are particularly relevant for congestion control mechanisms
    since several already exist and since they can span network,
    transport, and application layers.
 RFC 3439: "Some Internet Architectural Guidelines and Philosophy"
    (December 2002)
    [RFC3439] supplements RFC 1958.  Simplicity is stressed, as the
    unpredictable results of complexity (due to amplification and
    coupling) are described.  Congestion control issues stemming from
    layering interactions between transport and lower protocols are
    presented, as well as other items relevant to congestion control,
    including asymmetry and the "myth of over-provisioning".
 RFC 3714: "IAB Concerns Regarding Congestion Control for Voice
    Traffic in the Internet" (March 2004)
    [RFC3714] can be seen as a follow-up to the concerns that were
    discussed in RFC 2914.  It expresses the IAB's concern over the
    lack of effective end-to-end congestion control for best-effort
    voice traffic, which is noted as being a current service with
    growing demand.  An example of a VoIP connection between Atlanta,
    Georgia, USA, and Nairobi, Kenya, is given, where a single VoIP
    call consumed more than half of the access link capacity (which is
    normally shared across several different users).  This example is
    used as the basis for further discussion, making it clear that
    using some form of congestion control for VoIP traffic is highly
    recommended.

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3. TCP Congestion Control

 The TCP specifications found in RFC 793 and its predecessors did not
 contain any discussion of using or managing a congestion window.
 Other than a simple retransmission timeout and flow control through
 the advertised receive window, TCP implementations based only on RFC
 793 do not contain congestion control.  As several congestion
 collapse events occurred on the Internet, it was later realized that
 congestion control was needed.  The host requirements in RFC 1122
 require conforming TCP implementations to implement Jacobson's slow
 start and congestion avoidance algorithms (later specified in RFC
 2001 and then RFC 2581).  RFC 1122 also recommends several other
 behaviors that influence congestion control like the Nagle algorithm,
 delayed acknowledgements, Jacobson's retransmission timeout (RTO)
 estimation algorithm, and exponential backoff of the retransmission
 timer.
 Basic TCP congestion control is defined in RFC 2581, with many other
 RFCs that specify ancillary modifications and enhancements.  RFC 2581
 obsoletes the first proposed standard for TCP congestion control in
 RFC 2001.  These two RFCs document the mechanisms that had already
 been in common use by TCP implementations for many years.  The reader
 may refer to the TCP Roadmap [RFC4614] for more information on the
 RFCs that specifically describe TCP congestion control, as this
 material is not replicated here.
 Recently, significant effort has been put into experimental TCP
 congestion control modifications for obtaining high throughput with
 reduced startup and recovery times.  RFCs have been published on some
 of these modifications, including HighSpeed TCP [RFC3649], and
 Limited Slow-Start [RFC3742], but high-rate congestion control
 mechanisms are still considered an open issue in congestion control
 research.  Other schemes have been published as Internet-Drafts or
 have been discussed a little by the IETF, but much of the work in
 this area has not been adopted within the IETF yet, so the majority
 of this work is outside the RFC series and may be discussed in other
 products of the ICCRG.
 At the time of writing, the IETF's TCP Maintenance and Minor
 Extensions (TCPM) Working Group was developing an update to RFC 2581
 to incorporate small changes from other documents and advance TCP
 congestion control mechanisms on the IETF Standards Track.  The
 update also clarifies and revises some points.  These include the
 definition of a duplicate ACK, initial congestion window and slow
 start threshold values, behavior in response to retransmission
 timeouts, the use of the limited transmit mechanism, and security
 with regards to misbehaving receivers that practice ACK division.

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4. Challenging Link and Path Characteristics

 Links with large and/or variable bandwidth-delay products have
 traditionally been problematic for congestion control schemes because
 they can distort the properties of the feedback loop.  Links that
 either expose a high rate of packet losses to the upper layers, or
 use highly-persistent retransmission mechanisms to prevent losses
 also cause problems with some of the standard congestion control
 mechanisms.  The documents in this section discuss challenging link
 characteristics; many of them were written by the Performance
 Implications of Link Characteristics (PILC) Working Group.
 While these documents often refer to specific problems with TCP, the
 link characteristics that they describe can be expected to affect
 other congestion control mechanisms too.  In particular, interactions
 between link properties and TCP congestion control will be shared by
 other protocols that use the similar congestion control behavior,
 such as SCTP [RFC4960] and DCCP with CCID 2 [RFC4341] (see
 Section 6), and should be taken into consideration by designers of
 congestion control mechanisms that utilize the same kind of feedback
 as TCP.
 Some RFCs only make recommendations regarding the implementation and
 configuration of TCP based upon characteristics of special links.  As
 these RFCs are so closely connected to the specification of TCP
 itself, they are not included in this document, but are listed in the
 TCP Roadmap [RFC4614].
 RFC 2488 (BCP 28): "Enhancing TCP Over Satellite Channels using
    Standard Mechanisms" (January 1999)
    The summary of recommendations in [RFC2488] came from the TCP over
    Satellite (TCPSAT) Working Group, whose goal was to identify the
    performance problems that TCP may have over satellite links and
    suggest mitigations.  The document explains several ways that
    existing standards can be applied to improve the performance of
    basic TCP congestion control over paths with characteristics
    similar to those involving satellite links.
 RFC 3135: "Performance Enhancing Proxies Intended to Mitigate Link-
    Related Degradations" (June 2001)
    [RFC3135] is a survey of Performance Enhancing Proxies (PEPs)
    often employed to improve degraded TCP performance caused by
    characteristics of specific link environments, for example, in
    satellite, wireless WAN, and wireless LAN environments.  Different
    types of PEPs are described as well as the mechanisms used to

Welzl & Eddy Informational [Page 10] RFC 5783 Congestion Control RFCs February 2010

    improve performance.  While there is a specific focus on TCP in
    this document, PEPs can operate on any protocol, and the
    performance enhancements that PEPs achieve are often closely
    related to congestion control.
    The use of PEPs has architectural implications as they sometimes
    violate end-to-end assumptions and can add complexity to the inner
    portions of a network.  Certain types of PEPs are commonly used
    today in satellite or long-distance networking because it is
    easier to insert a small number of PEPs near problematic links
    than to upgrade the TCP implementations on all the end hosts that
    might use those links.  One down-side is that their deployment
    raises some issues when introducing new or updated congestion
    control (CC) methods into these deployed networks, since the PEPs
    may be operating with undocumented algorithms, making assumptions
    about the end-host CC behavior, and/or altering packet fields that
    will affect the end-host CC behavior.
 RFC 3150 (BCP 48): "End-to-end Performance Implications of Slow
    Links" (July 2001)
    [RFC3150] makes performance-related recommendations for users of
    network paths that traverse "very low bit-rate" links.  It
    includes a discussion of interactions between such links and TCP
    congestion control.
 RFC 3155 (BCP 50): "End-to-end Performance Implications of Links with
    Errors" (August 2001)
    Under the premise that several types of PEP have undesirable
    implications, [RFC3155] recommends end-to-end alternatives for
    improving TCP performance over paths with error-prone links.
 RFC 3366 (BCP 62): "Advice to link designers on link Automatic Repeat
    reQuest (ARQ)" (August 2002)
    Link-layer ARQ techniques are a popular means to increase the
    robustness of particular links to transmission errors via
    retransmission and acknowledgement mechanisms.  As [RFC3366]
    explains, ARQ techniques on a link can interact poorly with TCP's
    end-to-end congestion control if they lead to additional delay
    variation or reordering.  This RFC gives some advice on limiting
    the extent of these types of problematic interactions.  The proper

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    balance between end-to-end and link-layer reliability mechanisms
    is still an open research issue that has been explored in many
    academic papers outside the IETF.
 RFC 3449 (BCP 69): "TCP Performance Implications of Network Path
    Asymmetry" (December 2002)
    [RFC3449] describes performance limitations of TCP when the
    capacity of the ACK path is limited.  Several techniques to aid
    TCP in these circumstances are recommended as Best Current
    Practices, particularly ACK congestion control and sender pacing
    are relevant to other non-TCP congestion control schemes, outside
    the scope of this document.  For instance, in the design of the
    Reliable Multicast Transport (RMT) protocols for multicast,
    preventing ACK-implosion at multicast sources can be seen as a
    form of ACK congestion control.
 RFC 3481: "TCP over Second (2.5G) and Third (3G) Generation Wireless
    Networks" (February 2003)
    Among other issues, some mobile data systems exhibit delay spikes,
    handovers, and bandwidth oscillation.  [RFC3481] describes the
    problems that these conditions cause for TCP congestion control
    and how some TCP extensions can be used to mitigate them.
 RFC 3819 (BCP 89): "Advice for Internet Subnetwork Designers" (July
    2004)
    Several issues in link design and optimization for carrying IP
    traffic are discussed in [RFC3819], which recommends Best Current
    Practices.  Many of these principles are motivated by properties
    of TCP, but most of them also apply to other transport-layer
    congestion control techniques as well.

5. End-Host and Router Cooperative Signaling

 Some RFCs define mechanisms that allow routers to add signaling
 information to packets that makes the network's congestion state less
 of a mystery to end-host congestion controllers.  Routers supporting
 these can signal information about the current congestion state to
 flows in-band, providing faster and finer-grained information than
 inference-based methods.  Two examples of this are discussed in this
 section; the first directs sources to slow down in order to avoid
 losses, and the other assists in determining an appropriate starting
 rate for new flows.

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5.1. Explicit Congestion Notification

 Traditionally, under congestion, IP routers enqueue packets until
 some limit is reached, at which point packets are dropped.  TCP, and
 other IETF transport protocols, use a stream of acknowledgements to
 infer these losses and take congestion control action.  This section
 describes a more advanced way to signal congestion to sources before
 packet-dropping is required.
 There are two Explicit Congestion Notification (ECN) bits in the IP
 header that enable an AQM mechanism (see [RFC2309] or Section 2) to
 convey congestion information to endpoints without dropping packets.
 This can significantly reduce the losses experienced by transport
 endpoints if they are responsive to ECN.  While ECN is most
 frequently discussed in the context of TCP (and therefore included in
 the TCP Roadmap [RFC4614]), its applicability is broader, and ECN use
 has also been specified for protocols such as DCCP and SCTP.
 RFC 2481: "A Proposal to add Explicit Congestion Notification (ECN)
    to IP" (January 1999) - Obsoleted by RFC 3168
    [RFC2481] introduced ECN into the RFC series, describing when the
    Congestion Experienced (CE) bit in the IP header should be set in
    routers, and what modifications are needed to TCP to make it ECN-
    capable.  It includes a discussion of issues related to nodes and
    routers that are non-compliant, IPsec tunnels, and dropped or
    corrupted packets, as well as a summary of related work.  Many of
    these issues will also be faced by operators trying to deploy
    other network-based congestion control methods.  RFC 2481 has been
    obsoleted by RFC 3168.
 RFC 2884: "Performance Evaluation of Explicit Congestion Notification
    (ECN) in IP Networks" (July 2000)
    [RFC2884] presents a performance study of ECN as specified in
    [RFC2481] using an implementation on the Linux operating system.
    The experiments focused on ECN for both bulk and transactional
    transfers, showing that there is improvement in throughput over
    TCP without ECN in the case of bulk transfers and substantial
    improvement for transactional transfers.  Studies like this help
    to build the community's confidence that extensions like ECN are
    both safe and valuable.  Similar RFCs helped the community accept
    larger initial windows for TCP [RFC2414] [RFC2415] [RFC2416].

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 RFC 3168: "The Addition of Explicit Congestion Notification (ECN) to
    IP" (September 2001)
    [RFC3168], which obsoletes [RFC2481], specifies the incorporation
    of ECN into TCP and IP.  One notable change in this significantly
    extended specification is the definition of a bit combination that
    was not defined in [RFC2481], which can be used to realize a nonce
    that would prevent a receiver from falsely claiming that there was
    no congestion.  Potential issues related to ECN are discussed at
    length, including those already included in [RFC2481] and
    backwards compatibility with implementations that would follow the
    specification in the obsoleted document.
    ECN, as specified in RFC 3168, is implemented in several popular
    router and end-host platforms.  It is in active use, to at least
    some extent.  Problems with ECN "blackholes" (Internet routers
    misconfigured to discard packets with ECN-capable bits set) were
    discovered when ECN was enabled by default in some end-host
    operating systems.  Fears about the persisting presence of these
    blackholes currently may be keeping ECN from being used by default
    in many end-host operating systems even though it is implemented
    as an option within them.  Some measurements on ECN support and
    usability are available [PF01] [MAF04] [MAF05].
 RFC 3540: "Robust Explicit Congestion Notification (ECN) Signaling
    with Nonces" (June 2003)
    [RFC3540] specifies a nonce mechanism that uses an ECN bit
    combination that is not used in [RFC2481], but that is specified
    in [RFC3168] to allow a one-bit ECN nonce.  This nonce mechanism
    includes a Nonce Sum (NS) field in the TCP header so that senders
    can ensure that ACKs that do not indicate congestion are credible.
    The mechanism improves the robustness of congestion control by
    preventing receivers from exploiting ECN to gain an unfair share
    of network bandwidth.
    This nonce technique is not understood to have been widely
    implemented or deployed, and there has been some discussion as to
    whether the mechanism is really effective or is the best use of
    these bits (see emails to the IETF Transport Area Working Group
    (TSVWG) mailing list, in the thread "ECN nonce snag in TCP ESTATS
    MIB" from December 2006 - January 2007, or [MBJ07]).

Welzl & Eddy Informational [Page 14] RFC 5783 Congestion Control RFCs February 2010

5.2. Quick-Start

 RFC 4782: "Quick-Start for TCP and IP" (January 2007)
    Quick-Start provides a way for hosts to ask routers to help them
    select an initial sending rate, and use this rate rather than the
    traditional small initial congestion window and slow-start
    algorithm.  [RFC4782] describes the Quick-Start mechanism and its
    use with TCP.  In addition to discussing the benefits of Quick-
    Start, the document also discusses several limitations of the
    Quick-Start technique with respect to some types of tunnels in use
    over the Internet today and other potential costs of Quick-Start
    including those related to router design.  Analysis of the effects
    of misbehaving entities and appendices containing design rationale
    and related work are also notably present in this RFC.
    Many of the issues discussed in RFC 4782, including router
    architecture, network design / tunnels, and misbehaving agents are
    all challenges relevant to other proposals that try to add router
    assistance into the network.  The consideration of these issues
    can be illustrative for other protocol designers, even if they are
    not interested in Quick-Start itself.

6. Non-TCP Unicast Congestion Control

 In the past, TCP dominated Internet traffic, as it was used for many
 of the popular applications (email, web browsing, file transfer,
 remote login, etc.).  The majority of early congestion control work
 focused on TCP, and the introduction of congestion control into TCP
 alone is often credited with saving the Internet from additional
 congestion collapse events.  Today, TCP has been joined by other
 transport protocols (e.g., custom UDP-based protocols, SCTP, DCCP,
 RTP over UDP [RFC3550], etc.), and so having properly functioning
 congestion control within these other protocols is important for the
 Internet's health (as explained in RFC 3714, for instance, or see the
 discussion of the "congestion control arms race" scenario in RFC
 2914).  Documents that describe unicast congestion control methods
 for non-TCP transport protocols have been grouped into this section.
 RFC 4960: "Stream Control Transmission Protocol" (September 2007)
    SCTP congestion control is very similar to TCP with Selective
    Acknowledgements, but there are some differences, as described in
    Section 7.1 of [RFC4960].  The major difference lies in the fact
    that SCTP supports multihoming, whereas TCP does not.  Thus, SCTP

Welzl & Eddy Informational [Page 15] RFC 5783 Congestion Control RFCs February 2010

    keeps a different set of congestion control parameters for each
    destination address within an association, whereas TCP only keeps
    a single set of congestion control parameters per connection.
 RFC 5348: "TCP Friendly Rate Control (TFRC): Protocol Specification"
    (September 2008)
    [RFC5348], which obsoletes [RFC3448], specifies TCP-Friendly Rate
    Control (TFRC), a rate-based congestion control mechanism for
    unicast flows operating in a best-effort Internet environment
    where flows are competing with standard TCP traffic.  TFRC ensures
    conformance with TCP by continuously calculating the rate that a
    TCP sender would obtain under similar circumstances using a
    slightly simplified version of the TCP Reno throughput equation in
    [PFTK98].  Its sending rate is smoother than the rate of TCP,
    making it suitable for multimedia applications.  TFRC is not a
    wire protocol but rather a mechanism that could, for instance, be
    used within a UDP-based application, in a transport protocol such
    as RTP, or in the context of endpoint congestion management
    [RFC3124].
 RFC 3550: "RTP: A Transport Protocol for Real-Time Applications"
    (July 2003)
    [RFC3550] specifies the real-time transport protocol RTP along
    with its control protocol RTCP.  RTP/RTCP does not prescribe a
    specific congestion control behavior, but it is recommended that
    such a behavior be specified in each RTP profile (which is due to
    the fact that the potential for reducing the sending rate is often
    content dependent in the case of real-time streams).
    Specifically, [RFC3550] states: "For some profiles, it may be
    sufficient to include an applicability statement restricting the
    use of that profile to environments where congestion is avoided by
    engineering.  For other profiles, specific methods such as data
    rate adaptation based on RTCP feedback may be required".
    [RFC4585], which discusses RTCP feedback and adaptation
    mechanisms, points out that RTCP feedback may operate on much
    slower timescales than transport layer feedback mechanisms, and
    that additional mechanisms are therefore required to perform
    proper congestion control.  One way to make use of such additional
    mechanisms is to run RTP over DCCP.

Welzl & Eddy Informational [Page 16] RFC 5783 Congestion Control RFCs February 2010

 RFC 4336: "Problem Statement for the Datagram Congestion Control
    Protocol (DCCP)" (March 2006)
    [RFC4336] provides the motivation leading to the design of DCCP.
    In doing so, other possibilities of implementing similar
    functionality are discussed, including unreliable extensions of
    SCTP, RTP-based congestion control, and providing congestion
    control above or below UDP.
 RFC 4340: "Datagram Congestion Control Protocol" (March 2006)
    [RFC4340] specifies DCCP, the Datagram Congestion Control
    Protocol.  This protocol provides bidirectional unicast
    connections of congestion-controlled unreliable datagrams.  It is
    suitable for applications that can benefit from control over the
    tradeoff between timeliness and reliability.  The core DCCP
    specification does not include a specific congestion control
    behavior; rather, it functions as a framework for such mechanisms,
    which can be selected via the Congestion Control Identifier
    (CCID).
 RFC 4341: "Profile for Datagram Congestion Control Protocol (DCCP)
    Congestion Control ID 2: TCP-like Congestion Control" (March 2006)
    [RFC4341] is the specification of TCP-like congestion control
    within DCCP.  This should be used by senders who would like to
    take advantage of the available bandwidth in an environment with
    rapidly changing conditions, and who are able to adapt to the
    abrupt changes in the congestion window typical of TCP's Additive
    Increase Multiplicative Decrease (AIMD) congestion control.  ECN
    is also supported within RFC 4341.
 RFC 4342: "Profile for Datagram Congestion Control Protocol (DCCP)
    Congestion Control ID 3: TCP-Friendly Rate Control (TFRC)" (March
    2006)
    [RFC4342] is the specification of TFRC congestion control as
    described in [RFC3448] for DCCP.  This should be used by senders
    who want a TCP-friendly sending rate, possibly with Explicit
    Congestion Notification (ECN), while minimizing abrupt rate
    changes.

Welzl & Eddy Informational [Page 17] RFC 5783 Congestion Control RFCs February 2010

7. Multicast Congestion Control

 In the IETF, congestion control for multicast (one-to-many)
 communication has primarily been tackled in the Reliable Multicast
 Transport (RMT) Working Group.  Except for [RFC2357] and [RFC3208],
 all the documents in this section were written by this group.  Since
 a "one size fits all" protocol cannot meet the requirements of all
 possible applications in this space, the approach taken is a modular
 one, consisting of "protocol cores" and "building blocks".  Multiple
 congestion control building blocks have been defined, providing both
 sender-driven and receiver-driven congestion control methods that
 differ widely in their assumptions and behavior.
 RFC 2357: "IETF Criteria for Evaluating Reliable Multicast Transport
    and Application Protocols" (June 1998)
    Some early multicast content dissemination proposals did not
    incorporate proper congestion control; this is pointed out as
    being a severe mistake in [RFC2357], as large-scale multicast
    applications have the potential to do vast congestion-related
    damage.  This document clearly makes the case that congestion
    control mechanisms should be developed and incorporated into
    multicast content dissemination protocols intended for use over
    the Internet.
 RFC 2887: "The Reliable Multicast Design Space for Bulk Data
    Transfer" (August 2000)
    Several classes of potential congestion control schemes for
    single-sender multicast protocols are briefly sketched as
    possibilities, but no specific protocols are developed or selected
    in [RFC2887].
 RFC 3048: "Reliable Multicast Transport Building Blocks for One-to-
    Many Bulk-Data Transfer" (January 2001)
    [RFC3048] discusses the building block approach to RMT protocols
    and mentions that several different congestion control building
    blocks may be required in order to deal with different situations.
    Some of the possible interactions between building blocks for
    congestion control and those for Forward Error Correction (FEC),
    acknowledgement, and group management are also mentioned.

Welzl & Eddy Informational [Page 18] RFC 5783 Congestion Control RFCs February 2010

 RFC 3208: "PGM Reliable Transport Protocol Specification" (December
    2001)
    Pragmatic General Multicast (PGM) is a reliable multicast
    transport protocol for applications that require ordered or
    unordered, duplicate-free, multicast data delivery from multiple
    sources to multiple receivers.  As discussed in [RFC3208]'s
    Appendix B, a PGM protocol source can request congestion control
    feedback from both network elements (routers) and receivers (end
    hosts).  These reports can indicate the load on the worst link in
    a particular path, or the load on the worst path.  The actual
    procedure used in response to this feedback is not part of RFC
    3208, but the notion of using multicast routers to assist in
    congestion control is significant.
 RFC 3450: "Asynchronous Layered Coding (ALC) Protocol Instantiation"
    (December 2002)
    [RFC3450] specifies ALC, a rough header format using the RMT
    building blocks, that can be used by multicast content
    dissemination protocols.  ALC is intended to use a multi-rate
    congestion control building block, where the sender does not
    require any feedback, but where multiple multicast groups with
    different transmission rates are available within and ALC session,
    and receivers control their rates by joining or leaving groups.
 RFC 3738: "Wave and Equation Based Rate Control (WEBRC) Building
    Block" (April 2004)
    The WEBRC mechanism defined in [RFC3738] is a receiver-driven form
    of congestion control, where each receiver in a multicast group
    can determine the individual rate at which packets are delivered
    to it.  WEBRC senders create a base channel for control
    information and several multicast channels for data transmission
    that each send packets at a varying rate in the form of a wave.
    The receivers dynamically join and leave channels at chosen points
    within the wave of sending rates to obtain the desired overall
    receive rate based on an equation using the estimated loss
    probability and round-trip time within an epoch.  WEBRC is
    compatible for use within ALC.

Welzl & Eddy Informational [Page 19] RFC 5783 Congestion Control RFCs February 2010

 RFC 4654: "TCP-Friendly Multicast Congestion Control (TFMCC):
    Protocol Specification" (August 2006)
    TFMCC, as described in [RFC4654], is a sender-driven congestion
    control mechanism, where the received rate for the entire
    multicast group is determined by the worst-connected receiver.
    TFMCC builds upon TFRC, but scales down the feedback to prevent
    ACK-implosion effects by having receivers suppress their feedback
    unless they perceive it to be the worst among the reception group.

8. Guidance for Developing and Analyzing Congestion Control Techniques

 Some recently published RFCs discuss the properties of congestion
 control protocols that are "safe" for Internet deployment, as well as
 how to measure the properties of congestion control mechanisms and
 transport protocols.  These documents are particularly relevant to
 the ICCRG as some of the group's activities involve reviewing
 congestion control proposals that have been brought to the IETF for
 publication (see
 http://www.ietf.org/iesg/statement/congestion-control.html).
 RFC 5033 (BCP 133): "Specifying New Congestion Control Algorithms"
    (August 2007)
    The concurrent development of multiple TCP modifications for high-
    rate use and the deployments of these modifications on the
    Internet prompted [RFC5033] to be written.  RFC 5033 comes from
    the Transport Area Working Group (TSVWG), and gives guidance on
    the classes of Experimental RFC that can be published to document
    algorithms that are either encouraged for investigation on the
    Internet, and those that are only encouraged for experimentation
    in less-critical environments.  It has been described as a list of
    things for people to think about when creating new congestion
    control techniques that they are planning to widely deploy.
 RFC 5166: "Metrics for the Evaluation of Congestion Control
    Mechanisms" (March 2008)
    The IRTF Transport Modeling Research Group (TMRG) produced
    [RFC5166] to describe the set of metrics and related tradeoffs
    between metrics that can be used to compare, contrast, and
    evaluate congestion control techniques.  This RFC gives an
    overview of many such metrics, and gives references to their
    detailed descriptions.

Welzl & Eddy Informational [Page 20] RFC 5783 Congestion Control RFCs February 2010

9. Historic Interest

 Early in the RFC series, there are many documents that represent an
 author's thoughts on a subject or brief summaries from measurement
 and experimentation, rather than the result of a long formal IETF
 process.  Some of the RFCs listed in this section have this
 distinction.
 RFC 889: "Internet Delay Experiments" (December 1983)
    Based on reported measurement experiments, changes to the TCP
    retransmission timeout (RTO) calculation are suggested in
    [RFC0889].  It is noted that the original TCP RTO calculation
    leads to congestion when a delay spike occurs because it takes too
    long for the RTO to adapt, leading to superfluous retransmissions.
 RFC 896: "Congestion Control in IP/TCP Internetworks" (January 1984)
    [RFC0896] is the first document known to the authors where the
    term "congestion collapse" was used.  Here, it refers to the
    stable state that was observed when a sudden load on the net
    caused the round-trip time to rise faster than the sending hosts
    measured round-trip time could be updated.  Two problems are
    discussed: the "small-packet problem" (now commonly known by the
    name "silly window syndrome") and the "source-quench problem",
    which is about inappropriately deciding when to send and how to
    react to ICMP Source Quench messages.  Solutions for these
    problems are presented.
 RFC 970: "On Packet Switches with Infinite Storage" (December 1985)
    Using a thought experiment based on a router with infinite
    buffering capacity, [RFC0970] develops a different kind of
    congestion collapse scenario, where few useful packet
    transmissions occur due to the queue being longer than the time-
    to-live of the packets within it.  As described in RFC 970, this
    scenario was also demonstrated using real equipment by the author.
    The document also includes discussion of game-theoretic analysis
    of congestion control and obtaining fairness between behaving and
    non-behaving flows, by focusing on the order of scheduling packets
    within the buffer rather than the actual allocation of buffer
    space between flows.

Welzl & Eddy Informational [Page 21] RFC 5783 Congestion Control RFCs February 2010

 RFC 1016: "Something a Host Could Do with Source Quench: The Source
    Quench Introduced Delay (SQuID)" (July 1987)
    [RFC1016] outlines a rate-based congestion control mechanism where
    end-hosts use Source Quench packets from routers to adjust their
    sending rates.  RFC 1016 also suggests sending congestion
    notifications before queues are actually full, at a rate that
    increases with the current queue occupancy.  This strategy has
    been used in several other AQM mechanisms, notably RED [FJ93].
 RFC 1254: "Gateway Congestion Control Survey" (August 1991)
    [RFC1254] is a survey of congestion control approaches in routers
    that first discusses general congestion control performance goals
    (such as fairness), and then elaborates on the use of Source
    Quench messages (which are now discouraged, as they have been
    found ineffective), Random Drop (which would now be called "Active
    Queue Management"), Congestion Indication (DEC Bit; an early form
    of ECN), "Selective Feedback Congestion Indication" (one
    particular method for applying ECN), and Fair Queuing.  Finally,
    end-system congestion control policies are discussed, including
    Jacobson's well-known algorithms [Jac88] and their predecessor --
    "CUTE" [Jain86].

10. Security Considerations

 This document introduces no new security considerations.  Each RFC
 listed in this document discusses the security considerations of the
 specification it contains.

11. Acknowledgements

 Several participants in the ICCRG contributed useful comments in the
 development of this document, including Rex Buddenberg, Mitchell
 Erblichs, Lachlan Andrew, Sally Floyd, Stephen Farrell, Gorry
 Fairhurst, Lars Eggert, Mark Allman, and Juergen Schoenwaelder.

12. Informative References

 [FJ93]     Floyd, S. and V. Jacobson, "Random Early Detection
            Gateways for Congestion Avoidance", IEEE/ACM Transactions
            on Networking, volume 1, number 4, August 1993.
 [Gont10]   Gont, F., "ICMP attacks against TCP", Work in Progress,
            January 2010.

Welzl & Eddy Informational [Page 22] RFC 5783 Congestion Control RFCs February 2010

 [Jac88]    Jacobson, V., "Congestion Avoidance and Control",
            Proceedings of ACM SIGCOMM 1988, in ACM Computer
            Communication Review, 18 (4), pp. 314-329.
 [Jain86]   Jain, R., "A Timeout-Based Congestion Control Scheme for
            Window Flow-Controlled Networks", IEEE Journal on Selected
            Areas in Communications, volume 4, number 7, October 1986.
 [MAF04]    Medina, A., Allman, M., and S. Floyd, "Measuring
            Interactions Between Transport Protocols and Middleboxes",
            Proceedings of the Internet Measurement Conference 2004,
            August 2004.
 [MAF05]    Medina, A., Allman, M., and S. Floyd, "Measuring the
            Evolution of Transport Protocols in the Internet", ACM
            Computer Communications Review, volume 35, issue 2,
            April 2005.
 [MBJ07]    Moncaster, T., Briscoe, B., and A. Jacquet, "A TCP Test to
            Allow Senders to Identify Receiver Non-Compliance", Work
            in Progress, November 2007.
 [PF01]     Padhye, J. and S. Floyd, "On Inferring TCP Behavior",
            Proceedings of ACM SIGCOMM 2001, August 2001.
 [PFTK98]   Padhye, J., Firoiu, V., Towsley, D., and J. Kurose,
            "Modeling TCP Throughput: A Simple Model and its Empirical
            Validation", Proceedings of ACM SIGCOMM 1998.
 [RFC0889]  Mills, D., "Internet delay experiments", RFC 889,
            December 1983.
 [RFC0896]  Nagle, J., "Congestion control in IP/TCP internetworks",
            RFC 896, January 1984.
 [RFC0970]  Nagle, J., "On packet switches with infinite storage",
            RFC 970, December 1985.
 [RFC1016]  Prue, W. and J. Postel, "Something a host could do with
            source quench: The Source Quench Introduced Delay
            (SQuID)", RFC 1016, July 1987.
 [RFC1122]  Braden, R., "Requirements for Internet Hosts -
            Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC1254]  Mankin, A. and K. Ramakrishnan, "Gateway Congestion
            Control Survey", RFC 1254, August 1991.

Welzl & Eddy Informational [Page 23] RFC 5783 Congestion Control RFCs February 2010

 [RFC1633]  Braden, B., Clark, D., and S. Shenker, "Integrated
            Services in the Internet Architecture: an Overview",
            RFC 1633, June 1994.
 [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers",
            RFC 1812, June 1995.
 [RFC1958]  Carpenter, B., "Architectural Principles of the Internet",
            RFC 1958, June 1996.
 [RFC2001]  Stevens, W., "TCP Slow Start, Congestion Avoidance, Fast
            Retransmit, and Fast Recovery Algorithms", RFC 2001,
            January 1997.
 [RFC2140]  Touch, J., "TCP Control Block Interdependence", RFC 2140,
            April 1997.
 [RFC2309]  Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering,
            S., Estrin, D., Floyd, S., Jacobson, V., Minshall, G.,
            Partridge, C., Peterson, L., Ramakrishnan, K., Shenker,
            S., Wroclawski, J., and L. Zhang, "Recommendations on
            Queue Management and Congestion Avoidance in the
            Internet", RFC 2309, April 1998.
 [RFC2357]  Mankin, A., Romanov, A., Bradner, S., and V. Paxson, "IETF
            Criteria for Evaluating Reliable Multicast Transport and
            Application Protocols", RFC 2357, June 1998.
 [RFC2414]  Allman, M., Floyd, S., and C. Partridge, "Increasing TCP's
            Initial Window", RFC 2414, September 1998.
 [RFC2415]  Poduri, K., "Simulation Studies of Increased Initial TCP
            Window Size", RFC 2415, September 1998.
 [RFC2416]  Shepard, T. and C. Partridge, "When TCP Starts Up With
            Four Packets Into Only Three Buffers", RFC 2416,
            September 1998.
 [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
            and W. Weiss, "An Architecture for Differentiated
            Services", RFC 2475, December 1998.
 [RFC2481]  Ramakrishnan, K. and S. Floyd, "A Proposal to add Explicit
            Congestion Notification (ECN) to IP", RFC 2481,
            January 1999.

Welzl & Eddy Informational [Page 24] RFC 5783 Congestion Control RFCs February 2010

 [RFC2488]  Allman, M., Glover, D., and L. Sanchez, "Enhancing TCP
            Over Satellite Channels using Standard Mechanisms",
            BCP 28, RFC 2488, January 1999.
 [RFC2581]  Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
            Control", RFC 2581, April 1999.
 [RFC2884]  Hadi Salim, J. and U. Ahmed, "Performance Evaluation of
            Explicit Congestion Notification (ECN) in IP Networks",
            RFC 2884, July 2000.
 [RFC2887]  Handley, M., Floyd, S., Whetten, B., Kermode, R.,
            Vicisano, L., and M. Luby, "The Reliable Multicast Design
            Space for Bulk Data Transfer", RFC 2887, August 2000.
 [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41,
            RFC 2914, September 2000.
 [RFC2998]  Bernet, Y., Ford, P., Yavatkar, R., Baker, F., Zhang, L.,
            Speer, M., Braden, R., Davie, B., Wroclawski, J., and E.
            Felstaine, "A Framework for Integrated Services Operation
            over Diffserv Networks", RFC 2998, November 2000.
 [RFC3048]  Whetten, B., Vicisano, L., Kermode, R., Handley, M.,
            Floyd, S., and M. Luby, "Reliable Multicast Transport
            Building Blocks for One-to-Many Bulk-Data Transfer",
            RFC 3048, January 2001.
 [RFC3124]  Balakrishnan, H. and S. Seshan, "The Congestion Manager",
            RFC 3124, June 2001.
 [RFC3135]  Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
            Shelby, "Performance Enhancing Proxies Intended to
            Mitigate Link-Related Degradations", RFC 3135, June 2001.
 [RFC3150]  Dawkins, S., Montenegro, G., Kojo, M., and V. Magret,
            "End-to-end Performance Implications of Slow Links",
            BCP 48, RFC 3150, July 2001.
 [RFC3155]  Dawkins, S., Montenegro, G., Kojo, M., Magret, V., and N.
            Vaidya, "End-to-end Performance Implications of Links with
            Errors", BCP 50, RFC 3155, August 2001.
 [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
            of Explicit Congestion Notification (ECN) to IP",
            RFC 3168, September 2001.

Welzl & Eddy Informational [Page 25] RFC 5783 Congestion Control RFCs February 2010

 [RFC3208]  Speakman, T., Crowcroft, J., Gemmell, J., Farinacci, D.,
            Lin, S., Leshchiner, D., Luby, M., Montgomery, T., Rizzo,
            L., Tweedly, A., Bhaskar, N., Edmonstone, R.,
            Sumanasekera, R., and L. Vicisano, "PGM Reliable Transport
            Protocol Specification", RFC 3208, December 2001.
 [RFC3366]  Fairhurst, G. and L. Wood, "Advice to link designers on
            link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
            August 2002.
 [RFC3426]  Floyd, S., "General Architectural and Policy
            Considerations", RFC 3426, November 2002.
 [RFC3439]  Bush, R. and D. Meyer, "Some Internet Architectural
            Guidelines and Philosophy", RFC 3439, December 2002.
 [RFC3448]  Handley, M., Floyd, S., Padhye, J., and J. Widmer, "TCP
            Friendly Rate Control (TFRC): Protocol Specification",
            RFC 3448, January 2003.
 [RFC3449]  Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.
            Sooriyabandara, "TCP Performance Implications of Network
            Path Asymmetry", BCP 69, RFC 3449, December 2002.
 [RFC3450]  Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., and J.
            Crowcroft, "Asynchronous Layered Coding (ALC) Protocol
            Instantiation", RFC 3450, December 2002.
 [RFC3481]  Inamura, H., Montenegro, G., Ludwig, R., Gurtov, A., and
            F. Khafizov, "TCP over Second (2.5G) and Third (3G)
            Generation Wireless Networks", BCP 71, RFC 3481,
            February 2003.
 [RFC3540]  Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
            Congestion Notification (ECN) Signaling with Nonces",
            RFC 3540, June 2003.
 [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
            Jacobson, "RTP: A Transport Protocol for Real-Time
            Applications", STD 64, RFC 3550, July 2003.
 [RFC3649]  Floyd, S., "HighSpeed TCP for Large Congestion Windows",
            RFC 3649, December 2003.
 [RFC3714]  Floyd, S. and J. Kempf, "IAB Concerns Regarding Congestion
            Control for Voice Traffic in the Internet", RFC 3714,
            March 2004.

Welzl & Eddy Informational [Page 26] RFC 5783 Congestion Control RFCs February 2010

 [RFC3738]  Luby, M. and V. Goyal, "Wave and Equation Based Rate
            Control (WEBRC) Building Block", RFC 3738, April 2004.
 [RFC3742]  Floyd, S., "Limited Slow-Start for TCP with Large
            Congestion Windows", RFC 3742, March 2004.
 [RFC3819]  Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
            Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
            Wood, "Advice for Internet Subnetwork Designers", BCP 89,
            RFC 3819, July 2004.
 [RFC4336]  Floyd, S., Handley, M., and E. Kohler, "Problem Statement
            for the Datagram Congestion Control Protocol (DCCP)",
            RFC 4336, March 2006.
 [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
            Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
 [RFC4341]  Floyd, S. and E. Kohler, "Profile for Datagram Congestion
            Control Protocol (DCCP) Congestion Control ID 2: TCP-like
            Congestion Control", RFC 4341, March 2006.
 [RFC4342]  Floyd, S., Kohler, E., and J. Padhye, "Profile for
            Datagram Congestion Control Protocol (DCCP) Congestion
            Control ID 3: TCP-Friendly Rate Control (TFRC)", RFC 4342,
            March 2006.
 [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
            "Extended RTP Profile for Real-time Transport Control
            Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
            July 2006.
 [RFC4614]  Duke, M., Braden, R., Eddy, W., and E. Blanton, "A Roadmap
            for Transmission Control Protocol (TCP) Specification
            Documents", RFC 4614, September 2006.
 [RFC4654]  Widmer, J. and M. Handley, "TCP-Friendly Multicast
            Congestion Control (TFMCC): Protocol Specification",
            RFC 4654, August 2006.
 [RFC4782]  Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
            Start for TCP and IP", RFC 4782, January 2007.
 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
            RFC 4960, September 2007.
 [RFC5033]  Floyd, S. and M. Allman, "Specifying New Congestion
            Control Algorithms", BCP 133, RFC 5033, August 2007.

Welzl & Eddy Informational [Page 27] RFC 5783 Congestion Control RFCs February 2010

 [RFC5166]  Floyd, S., "Metrics for the Evaluation of Congestion
            Control Mechanisms", RFC 5166, March 2008.
 [RFC5348]  Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
            Friendly Rate Control (TFRC): Protocol Specification",
            RFC 5348, September 2008.

Authors' Addresses

 Michael Welzl
 University of Oslo
 Department of Informatics
 PO Box 1080 Blindern
 N-0316 Oslo, Norway
 Phone: +47 22 85 24 20
 EMail: michawe@ifi.uio.no
 Wesley M. Eddy
 MTI Systems
 NASA Glenn Research Center
 21000 Brookpark Rd, MS 500-ASRC
 Cleveland, OH  44135
 Phone: (216) 433-6682
 EMail: wes@mti-systems.com

Welzl & Eddy Informational [Page 28]

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