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Network Working Group M. Duke Request for Comments: 4614 Boeing Phantom Works Category: Informational R. Braden

                                    USC Information Sciences Institute
                                                               W. Eddy
                                       Verizon Federal Network Systems
                                                            E. Blanton
                                    Purdue University Computer Science
                                                        September 2006
         A Roadmap for Transmission Control Protocol (TCP)
                      Specification Documents

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).


 This document contains a "roadmap" to the Requests for Comments (RFC)
 documents relating to the Internet's Transmission Control Protocol
 (TCP).  This roadmap provides a brief summary of the documents
 defining TCP and various TCP extensions that have accumulated in the
 RFC series.  This serves as a guide and quick reference for both TCP
 implementers and other parties who desire information contained in
 the TCP-related RFCs.

Duke, et al. Informational [Page 1] RFC 4614 TCP Roadmap September 2006

Table of Contents

 1. Introduction ....................................................2
 2. Basic Functionality .............................................4
 3. Recommended Enhancements ........................................6
    3.1. Congestion Control and Loss Recovery Extensions ............7
    3.2. SACK-Based Loss Recovery and Congestion Control ............8
    3.3. Dealing with Forged Segments ...............................9
 4. Experimental Extensions ........................................10
 5. Historic Extensions ............................................13
 6. Support Documents ..............................................14
    6.1. Foundational Works ........................................15
    6.2. Difficult Network Environments ............................16
    6.3. Implementation Advice .....................................19
    6.4. Management Information Bases ..............................20
    6.5. Tools and Tutorials .......................................22
    6.6. Case Studies ..............................................22
 7. Undocumented TCP Features ......................................23
 8. Security Considerations ........................................24
 9. Acknowledgments ................................................24
 10. Informative References ........................................25
    10.1. Basic Functionality ......................................25
    10.2. Recommended Enhancements .................................25
    10.3. Experimental Extensions ..................................26
    10.4. Historic Extensions ......................................27
    10.5. Support Documents ........................................28
    10.6. Informative References Outside the RFC Series ............31

1. Introduction

 A correct and efficient implementation of the Transmission Control
 Protocol (TCP) is a critical part of the software of most Internet
 hosts.  As TCP has evolved over the years, many distinct documents
 have become part of the accepted standard for TCP.  At the same time,
 a large number of more experimental modifications to TCP have also
 been published in the RFC series, along with informational notes,
 case studies, and other advice.
 As an introduction to newcomers and an attempt to organize the
 plethora of information for old hands, this document contains a
 "roadmap" to the TCP-related RFCs.  It provides a brief summary of
 the RFC documents that define TCP.  This should provide guidance to
 implementers on the relevance and significance of the standards-track
 extensions, informational notes, and best current practices that
 relate to TCP.

Duke, et al. Informational [Page 2] RFC 4614 TCP Roadmap September 2006

 This document is not an update of RFC 1122 and is not a rigorous
 standard for what needs to be implemented in TCP.  This document is
 merely an informational roadmap that captures, organizes, and
 summarizes most of the RFC documents that a TCP implementer,
 experimenter, or student should be aware of.  Particular comments or
 broad categorizations that this document makes about individual
 mechanisms and behaviors are not to be taken as definitive, nor
 should the content of this document alone influence implementation
 This roadmap includes a brief description of the contents of each
 TCP-related RFC.  In some cases, we simply supply the abstract or a
 key summary sentence from the text as a terse description.  In
 addition, a letter code after an RFC number indicates its category in
 the RFC series (see BCP 9 [RFC2026] for explanation of these
    S - Standards Track (Proposed Standard, Draft Standard, or
    E - Experimental
    B - Best Current Practice
    I - Informational
 Note that the category of an RFC does not necessarily reflect its
 current relevance.  For instance, RFC 2581 is nearly universally
 deployed although it is only a Proposed Standard.  Similarly, some
 Informational RFCs contain significant technical proposals for
 changing TCP.
 This roadmap is divided into four main sections.  Section 2 lists the
 RFCs that describe absolutely required TCP behaviors for proper
 functioning and interoperability.  Further RFCs that describe
 strongly encouraged, but non-essential, behaviors are listed in
 Section 3.  Experimental extensions that are not yet standard
 practices, but that potentially could be in the future, are described
 in Section 4.
 The reader will probably notice that these three sections are broadly
 equivalent to MUST/SHOULD/MAY specifications (per RFC 2119), and
 although the authors support this intuition, this document is merely
 descriptive; it does not represent a binding standards-track
 position.  Individual implementers still need to examine the
 standards documents themselves to evaluate specific requirement

Duke, et al. Informational [Page 3] RFC 4614 TCP Roadmap September 2006

 A small number of older experimental extensions that have not been
 widely implemented, deployed, and used are noted in Section 5.  Many
 other supporting documents that are relevant to the development,
 implementation, and deployment of TCP are described in Section 6.
 Within each section, RFCs are listed in the chronological order of
 their publication dates.
 A small number of fairly ubiquitous important implementation
 practices that are not currently documented in the RFC series are
 listed in Section 7.

2. Basic Functionality

 A small number of documents compose the core specification of TCP.
 These define the required basic functionalities of TCP's header
 parsing, state machine, congestion control, and retransmission
 timeout computation.  These base specifications must be correctly
 followed for interoperability.
 RFC 793 S: "Transmission Control Protocol", STD 7 (September 1981)
    This is the fundamental TCP specification document [RFC0793].
    Written by Jon Postel as part of the Internet protocol suite's
    core, it describes the TCP packet format, the TCP state machine
    and event processing, and TCP's semantics for data transmission,
    reliability, flow control, multiplexing, and acknowledgment.
    Section 3.6 of RFC 793, describing TCP's handling of the IP
    precedence and security compartment, is mostly irrelevant today.
    RFC 2873 changed the IP precedence handling, and the security
    compartment portion of the API is no longer implemented or used.
    In addition, RFC 793 did not describe any congestion control
    mechanism.  Otherwise, however, the majority of this document
    still accurately describes modern TCPs.  RFC 793 is the last of a
    series of developmental TCP specifications, starting in the
    Internet Experimental Notes (IENs) and continuing in the RFC
 RFC 1122 S: "Requirements for Internet Hosts - Communication Layers"
 (October 1989)
    This document [RFC1122] updates and clarifies RFC 793, fixing some
    specification bugs and oversights.  It also explains some features
    such as keep-alives and Karn's and Jacobson's RTO estimation
    algorithms [KP87][Jac88][JK92].  ICMP interactions are mentioned,
    and some tips are given for efficient implementation.  RFC 1122 is
    an Applicability Statement, listing the various features that
    MUST, SHOULD, MAY, SHOULD NOT, and MUST NOT be present in

Duke, et al. Informational [Page 4] RFC 4614 TCP Roadmap September 2006

    standards-conforming TCP implementations.  Unlike a purely
    informational "roadmap", this Applicability Statement is a
    standards document and gives formal rules for implementation.
 RFC 2460 S: "Internet Protocol, Version 6 (IPv6) Specification
 (December 1998)
    This document [RFC2460] is of relevance to TCP because it defines
    how the pseudo-header for TCP's checksum computation is derived
    when 128-bit IPv6 addresses are used instead of 32-bit IPv4
    addresses.  Additionally, RFC 2675 describes TCP changes required
    to support IPv6 jumbograms.
 RFC 2581 S: "TCP Congestion Control" (April 1999)
    Although RFC 793 did not contain any congestion control
    mechanisms, today congestion control is a required component of
    TCP implementations.  This document [RFC2581] defines the current
    versions of Van Jacobson's congestion avoidance and control
    mechanisms for TCP, based on his 1988 SIGCOMM paper [Jac88].  RFC
    2001 was a conceptual precursor that was obsoleted by RFC 2581.
    A number of behaviors that together constitute what the community
    refers to as "Reno TCP" are described in RFC 2581.  The name
    "Reno" comes from the Net/2 release of the 4.3 BSD operating
    system.  This is generally regarded as the least common
    denominator among TCP flavors currently found running on Internet
    hosts.  Reno TCP includes the congestion control features of slow
    start, congestion avoidance, fast retransmit, and fast recovery.
    RFC 1122 mandates the implementation of a congestion control
    mechanism, and RFC 2581 details the currently accepted mechanism.
    RFC 2581 differs slightly from the other documents listed in this
    section, as it does not affect the ability of two TCP endpoints to
    communicate; however, congestion control remains a critical
    component of any widely deployed TCP implementation and is
    required for the avoidance of congestion collapse and to ensure
    fairness among competing flows.
 RFC 2873 S: "TCP Processing of the IPv4 Precedence Field" (June 2000)
    This document [RFC2873] removes from the TCP specification all
    processing of the precedence bits of the TOS byte of the IP
    header.  This resolves a conflict over the use of these bits
    between RFC 793 and Differentiated Services [RFC2474].

Duke, et al. Informational [Page 5] RFC 4614 TCP Roadmap September 2006

 RFC 2988 S: "Computing TCP's Retransmission Timer" (November 2000)
    Abstract: "This document defines the standard algorithm that
    Transmission Control Protocol (TCP) senders are required to use to
    compute and manage their retransmission timer.  It expands on the
    discussion in section of RFC 1122 and upgrades the
    requirement of supporting the algorithm from a SHOULD to a MUST."

3. Recommended Enhancements

 This section describes recommended TCP modifications that improve
 performance and security.  RFCs 1323 and 3168 represent fundamental
 changes to the protocol.  RFC 1323, based on RFCs 1072 and 1185,
 allows better utilization of high bandwidth-delay product paths by
 providing some needed mechanisms for high-rate transfers.  RFC 3168
 describes a change to the Internet's architecture, whereby routers
 signal end-hosts of growing congestion levels and can do so before
 packet losses are forced.  Section 3.1 lists improvements in the
 congestion control and loss recovery mechanisms specified in RFC
 2581.  Section 3.2 describes further refinements that make use of
 selective acknowledgments.  Section 3.3 deals with the problem of
 preventing forged segments.
 RFC 1323 S:  "TCP Extensions for High Performance" (May 1992)
    This document [RFC1323] defines TCP extensions for window scaling,
    timestamps, and protection against wrapped sequence numbers, for
    efficient and safe operation over paths with large bandwidth-delay
    products.  These extensions are commonly found in currently used
    systems; however, they may require manual tuning and
    configuration.  One issue in this specification that is still
    under discussion concerns a modification to the algorithm for
    estimating the mean RTT when timestamps are used.
 RFC 2675 S: "IPv6 Jumbograms" (August 1999)
    IPv6 supports longer datagrams than were allowed in IPv4.  These
    are known as Jumbograms, and use with TCP has necessitated changes
    to the handling of TCP's MSS and Urgent fields (both 16 bits).
    This document [RFC2675] explains those changes.  Although it
    describes changes to basic header semantics, these changes should
    only affect the use of very large segments, such as IPv6
    jumbograms, which are currently rarely used in the general
    Internet.  Supporting the behavior described in this document does
    not affect interoperability with other TCP implementations when
    IPv4 or non-jumbogram IPv6 is used.  This document states that
    jumbograms are to only be used when it can be guaranteed that all

Duke, et al. Informational [Page 6] RFC 4614 TCP Roadmap September 2006

    receiving nodes, including each router in the end-to-end path,
    will support jumbograms.  If even a single node that does not
    support jumbograms is attached to a local network, then no host on
    that network may use jumbograms.  This explains why jumbogram use
    has been rare, and why this document is considered a performance
    optimization and not part of TCP over IPv6's basic functionality.
 RFC 3168 S: "The Addition of Explicit Congestion Notification (ECN)
 to IP" (September 2001)
    This document [RFC3168] defines a means for end hosts to detect
    congestion before congested routers are forced to discard packets.
    Although congestion notification takes place at the IP level, ECN
    requires support at the transport level (e.g., in TCP) to echo the
    bits and adapt the sending rate.  This document updates RFC 793 to
    define two previously unused flag bits in the TCP header for ECN
    support.  RFC 3540 provides a supplementary (experimental) means
    for more secure use of ECN, and RFC 2884 provides some sample
    results from using ECN.

3.1. Congestion Control and Loss Recovery Extensions

 Two of the most important aspects of TCP are its congestion control
 and loss recovery features.  TCP traditionally treats lost packets as
 indicating congestion-related loss, and cannot distinguish between
 congestion-related loss and loss due to transmission errors.  Even
 when ECN is in use, there is a rather intimate coupling between
 congestion control and loss recovery mechanisms.  There are several
 extensions to both features, and more often than not, a particular
 extension applies to both.  In this sub-section, we group
 enhancements to either congestion control, loss recovery, or both,
 which can be performed unilaterally; that is, without negotiating
 support between endpoints.  In the next sub-section, we group the
 extensions that specify or rely on the SACK option, which must be
 negotiated bilaterally.  TCP implementations should include the
 enhancements from both sub-sections so that TCP senders can perform
 well without regard to the feature sets of other hosts they connect
 to.  For example, if SACK use is not successfully negotiated, a host
 should use the NewReno behavior as a fall back.

Duke, et al. Informational [Page 7] RFC 4614 TCP Roadmap September 2006

 RFC 3042 S: "Enhancing TCP's Loss Recovery Using Limited Transmit"
 (January 2001)
    Abstract: "This document proposes Limited Transmit, a new
    Transmission Control Protocol (TCP) mechanism that can be used to
    more effectively recover lost segments when a connection's
    congestion window is small, or when a large number of segments are
    lost in a single transmission window."  [RFC3042] Tests from 2004
    showed that Limited Transmit was deployed in roughly one third of
    the web servers tested [MAF04].
 RFC 3390 S: "Increasing TCP's Initial Window" (October 2002)
    This document [RFC3390] updates RFC 2581 to permit an initial TCP
    window of three or four segments during the slow-start phase,
    depending on the segment size.
 RFC 3782 S: "The NewReno Modification to TCP's Fast Recovery
 Algorithm" (April 2004)
    This document [RFC3782] specifies a modification to the standard
    Reno fast recovery algorithm, whereby a TCP sender can use partial
    acknowledgments to make inferences determining the next segment to
    send in situations where SACK would be helpful but isn't
    available.  Although it is only a slight modification, the NewReno
    behavior can make a significant difference in performance when
    multiple segments are lost from a single window of data.

3.2. SACK-Based Loss Recovery and Congestion Control

 The base TCP specification in RFC 793 provided only a simple
 cumulative acknowledgment mechanism.  However, a selective
 acknowledgment (SACK) mechanism provides performance improvement in
 the presence of multiple packet losses from the same flight, more
 than outweighing the modest increase in complexity.  A TCP should be
 expected to implement SACK; however, SACK is a negotiated option and
 is only used if support is advertised by both sides of a connection.
 RFC 2018 S: "TCP Selective Acknowledgment Options" (October 1996)
    This document [RFC2018] defines the basic selective acknowledgment
    (SACK) mechanism for TCP.
 RFC 2883 S: "An Extension to the Selective Acknowledgement (SACK)
 Option for TCP" (July 2000)
    This document [RFC2883] extends RFC 2018 to cover the case of
    acknowledging duplicate segments.

Duke, et al. Informational [Page 8] RFC 4614 TCP Roadmap September 2006

 RFC 3517 S: "A Conservative Selective Acknowledgment (SACK)-based
 Loss Recovery Algorithm for TCP" (April 2003)
    This document [RFC3517] describes a relatively sophisticated
    algorithm that a TCP sender can use for loss recovery when SACK
    reports more than one segment lost from a single flight of data.
    Although support for the exchange of SACK information is widely
    implemented, not all implementations use an algorithm as
    sophisticated as that described in RFC 3517.

3.3. Dealing with Forged Segments

 By default, TCP lacks any cryptographic structures to differentiate
 legitimate segments and those spoofed from malicious hosts.  Spoofing
 valid segments requires correctly guessing a number of fields.  The
 documents in this sub-section describe ways to make that guessing
 harder, or to prevent it from being able to affect a connection
 The TCPM working group is currently in progress towards fully
 understanding and defining mechanisms for preventing spoofing attacks
 (including both spoofed TCP segments and ICMP datagrams).  Some of
 the solutions being considered rely on TCP modifications, whereas
 others rely on security at lower layers (like IPsec) for protection.
 RFC 1948 I: "Defending Against Sequence Number Attacks" (May 1996)
    This document [RFC1948] describes the TCP vulnerability that
    allows an attacker to send forged TCP packets, by guessing the
    initial sequence number in the three-way handshake.  Simple
    defenses against exploitation are then described.  Some variation
    is implemented in most currently used operating systems.
 RFC 2385 S: "Protection of BGP Sessions via the TCP MD5 Signature
 Option" (August 1998)
    From document: "This document describes current existing practice
    for securing BGP against certain simple attacks.  It is understood
    to have security weaknesses against concerted attacks.
    This memo describes a TCP extension to enhance security for BGP.
    It defines a new TCP option for carrying an MD5 digest in a TCP
    segment.  This digest acts like a signature for that segment,
    incorporating information known only to the connection end points.
    Since BGP uses TCP as its transport, using this option in the way
    described in this paper significantly reduces the danger from
    certain security attacks on BGP."  [RFC2385]

Duke, et al. Informational [Page 9] RFC 4614 TCP Roadmap September 2006

    TCP MD5 options are currently only used in very limited contexts,
    primarily for defending BGP exchanges between routers.  Some
    deployment notes for those using TCP MD5 are found in the later
    RFC 3562, "Key Management Considerations for the TCP MD5 Signature
    Option" [RFC3562].  RFC 4278 deprecates the use of TCP MD5 outside
    BGP [RFC4278].

4. Experimental Extensions

 The RFCs in this section are still experimental, but they may become
 proposed standards in the future.  At least part of the reason that
 they are still experimental is to gain more wide-scale experience
 with them before a standards track decision is made.  By their
 publication as experimental RFCs, it is hoped that the community of
 TCP researchers will analyze and test the contents of these RFCs.
 Although experimentation is encouraged, there is not yet formal
 consensus that these are fully logical and safe behaviors.  Wide-
 scale deployment of implementations that use these features should be
 well thought-out in terms of consequences.
 RFC 2140 I: "TCP Control Block Interdependence" (April 1997)
    This document [RFC2140] suggests how TCP connections between the
    same endpoints might share information, such as their congestion
    control state.  To some degree, this is done in practice by a few
    operating systems; for example, Linux currently has a destination
    cache.  Although this RFC is technically informational, the
    concepts it describes are in experimental use, so we include it in
    this section.
    A related proposal, the Congestion Manager, is specified in RFC
    3124 [RFC3124].  The idea behind the Congestion Manager, moving
    congestion control outside of individual TCP connections,
    represents a modification to the core of TCP, which supports
    sharing information among TCP connections as well.  Although a
    Proposed Standard, some pieces of the Congestion Manager support
    architecture have not been specified yet, and it has not achieved
    use or implementation beyond experimental stacks, so it is not
    listed among the standard TCP enhancements in this roadmap.
 RFC 2861 E: "TCP Congestion Window Validation" (June 2000)
    This document [RFC2861] suggests reducing the congestion window
    over time when no packets are flowing.  This behavior is more
    aggressive than that specified in RFC 2581, which says that a TCP
    sender SHOULD set its congestion window to the initial window
    after an idle period of an RTO or greater.

Duke, et al. Informational [Page 10] RFC 4614 TCP Roadmap September 2006

 RFC 3465 E: "TCP Congestion Control with Appropriate Byte Counting
 (ABC)" (February 2003)
    This document [RFC3465] suggests that congestion control use the
    number of bytes acknowledged instead of the number of
    acknowledgments received.  This has been implemented in Linux.
    The ABC mechanism behaves differently from the standard method
    when there is not a one-to-one relationship between data segments
    and acknowledgments.  ABC still operates within the accepted
    guidelines, but is more robust to delayed ACKs and ACK-division
 RFC 3522 E: "The Eifel Detection Algorithm for TCP" (April 2003)
    The Eifel detection algorithm [RFC3522] allows a TCP sender to
    detect a posteriori whether it has entered loss recovery
 RFC 3540 E: "Robust Explicit Congestion Notification (ECN) signaling
 with Nonces" (June 2003)
    This document [RFC3540] suggests a modified ECN to address
    security concerns and updates RFC 3168.
 RFC 3649 E: "HighSpeed TCP for Large Congestion Windows" (December
    This document [RFC3649] suggests a modification to TCP's steady-
    state behavior to use very large windows efficiently.
 RFC 3708 E: "Using TCP Duplicate Selective Acknowledgement (DSACKs)
 and Stream Control Transmission Protocol (SCTP) Duplicate
 Transmission Sequence Numbers (TSNs) to Detect Spurious
 Retransmissions" (February 2004)
    Abstract: "TCP and Stream Control Transmission Protocol (SCTP)
    provide notification of duplicate segment receipt through
    Duplicate Selective Acknowledgement (DSACKs) and Duplicate
    Transmission Sequence Number (TSN) notification, respectively.
    This document presents conservative methods of using this
    information to identify unnecessary retransmissions for various
    applications."  [RFC3708]

Duke, et al. Informational [Page 11] RFC 4614 TCP Roadmap September 2006

 RFC 3742 E: "Limited Slow-Start for TCP with Large Congestion
 Windows" (March 2004)
    This document [RFC3742] describes a more conservative slow-start
    behavior to prevent massive packet losses when a connection uses a
    very large window.
 RFC 4015 S: "The Eifel Response Algorithm for TCP" (February 2005)
    This document [RFC4015] describes the response portion of the
    Eifel algorithm, which can be used in conjunction with one of
    several methods of detecting when loss recovery has been
    spuriously entered, such as the Eifel detection algorithm in RFC
    3522, the algorithm in RFC 3708, or F-RTO in RFC 4138.
    Abstract: "Based on an appropriate detection algorithm, the Eifel
    response algorithm provides a way for a TCP sender to respond to a
    detected spurious timeout.  It adapts the retransmission timer to
    avoid further spurious timeouts, and can avoid - depending on the
    detection algorithm - the often unnecessary go-back-N retransmits
    that would otherwise be sent.  In addition, the Eifel response
    algorithm restores the congestion control state in such a way that
    packet bursts are avoided."
    RFC 4015 is itself a Proposed Standard.  The consensus of the TCPM
    working group was to place it in this section of the roadmap
    document due to three factors.
    1.  RFC 4015 operates on the output of a detection algorithm, for
        which there is currently no available mechanism on the
        standards track.
    2.  The working group was not aware of any wide deployment and use
        of RFC 4015.
    3.  The consensus of the working group, after a discussion of the
        known Intellectual Property Rights claims on the techniques
        described in RFC 4015, identified this section of the roadmap
        as an appropriate location.
 RFC 4138 E: "Forward RTO-Recovery (F-RTO): An Algorithm for Detecting
 Spurious Retransmission Timeouts with TCP and the Stream Control
 Transmission Protocol" (August 2005)
    The F-RTO detection algorithm [RFC4138] provides another option
    for inferring spurious retransmission timeouts.  Unlike some
    similar detection methods, F-RTO does not rely on the use of any
    TCP options.

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5. Historic Extensions

 The RFCs listed here define extensions that have thus far failed to
 arouse substantial interest from implementers, or that were found to
 be defective for general use.
 RFC 1106 "TCP Big Window and NAK Options" (June 1989): found
    This RFC [RFC1106] defined an alternative to the Window Scale
    option for using large windows and described the "negative
    acknowledgement" or NAK option.  There is a comparison of NAK and
    SACK methods, and early discussion of TCP over satellite issues.
    RFC 1110 explains some problems with the approaches described in
    RFC 1106.  The options described in this document have not been
    adopted by the larger community, although NAKs are used in the
    SCPS-TP adaptation of TCP for satellite and spacecraft use,
    developed by the Consultative Committee for Space Data Systems
 RFC 1110 "A Problem with the TCP Big Window Option" (August 1989):
 deprecates RFC 1106
    Abstract: "The TCP Big Window option discussed in RFC 1106 will
    not work properly in an Internet environment which has both a high
    bandwidth * delay product and the possibility of disordering and
    duplicating packets.  In such networks, the window size must not
    be increased without a similar increase in the sequence number
    space.  Therefore, a different approach to big windows should be
    taken in the Internet."  [RFC1110]
 RFC 1146 E "TCP Alternate Checksum Options" (March 1990): lack of
    This document [RFC1146] defined more robust TCP checksums than the
    16-bit ones-complement in use today.  A typographical error in RFC
    1145 is fixed in RFC 1146; otherwise, the documents are the same.
 RFC 1263 "TCP Extensions Considered Harmful" (October 1991) - lack of
    This document [RFC1263] argues against "backwards compatible" TCP
    extensions.  Specifically mentioned are several TCP enhancements
    that have been successful, including timestamps, window scaling,
    PAWS, and SACK.  RFC 1263 presents an alternative approach called
    "protocol evolution", whereby several evolutionary versions of TCP
    would exist on hosts.  These distinct TCP versions would represent
    upgrades to each other and could be header-incompatible.

Duke, et al. Informational [Page 13] RFC 4614 TCP Roadmap September 2006

    Interoperability would be provided by having a virtualization
    layer select the right TCP version for a particular connection.
    This idea did not catch on with the community, although the type
    of extensions RFC 1263 specifically targeted as harmful did become
 RFC 1379 I "Extending TCP for Transactions -- Concepts" (November
 1992): found defective
    See RFC 1644.
 RFC 1644 E "T/TCP -- TCP Extensions for Transactions Functional
 Specification" (July 1994): found defective
    The inventors of TCP believed that cached connection state could
    have been used to eliminate TCP's 3-way handshake, to support
    two-packet request/response exchanges.  RFCs 1379 [RFC1379] and
    1644 [RFC1644] show that this is far from simple.  Furthermore,
    T/TCP floundered on the ease of denial-of-service attacks that can
    result.  One idea pioneered by T/TCP lives on in RFC 2140, in the
    sharing of state across connections.
 RFC 1693 E "An Extension to TCP: Partial Order Service" (November
 1994): lack of interest
    This document [RFC1693] defines a TCP extension for applications
    that do not care about the order in which application-layer
    objects are received.  Examples are multimedia and database
    applications.  In practice, these applications either accept the
    possible performance loss because of TCP's strict ordering or use
    more specialized transport protocols.

6. Support Documents

 This section contains several classes of documents that do not
 necessarily define current protocol behaviors, but that are
 nevertheless of interest to TCP implementers.  Section 6.1 describes
 several foundational RFCs that give modern readers a better
 understanding of the principles underlying TCP's behaviors and
 development over the years.  The documents listed in Section 6.2
 provide advice on using TCP in various types of network situations
 that pose challenges above those of typical wired links.  Some
 implementation notes can be found in Section 6.3.  The TCP Management
 Information Bases are described in Section 6.4.  RFCs that describe
 tools for testing and debugging TCP implementations or that contain
 high-level tutorials on the protocol are listed Section 6.5, and
 Section 6.6 lists a number of case studies that have explored TCP

Duke, et al. Informational [Page 14] RFC 4614 TCP Roadmap September 2006

6.1. Foundational Works

 The documents listed in this section contain information that is
 largely duplicated by the standards documents previously discussed.
 However, some of them contain a greater depth of problem statement
 explanation or other context.  Particularly, RFCs 813 - 817 (known as
 the "Dave Clark Five") describe some early problems and solutions
 (RFC 815 only describes the reassembly of IP fragments and is not
 included in this TCP roadmap).
 RFC 813: "Window and Acknowledgement Strategy in TCP" (July 1982)
    This document [RFC0813] contains an early discussion of Silly
    Window Syndrome and its avoidance and motivates and describes the
    use of delayed acknowledgments.
 RFC 814: "Name, Addresses, Ports, and Routes" (July 1982)
    Suggestions and guidance for the design of tables and algorithms
    to keep track of various identifiers within a TCP/IP
    implementation are provided by this document [RFC0814].
 RFC 816: "Fault Isolation and Recovery" (July 1982)
    In this document [RFC0816], TCP's response to indications of
    network error conditions such as timeouts or received ICMP
    messages is discussed.
 RFC 817: "Modularity and Efficiency in Protocol Implementation" (July
    This document [RFC0817] contains implementation suggestions that
    are general and not TCP specific.  However, they have been used to
    develop TCP implementations and to describe some performance
    implications of the interactions between various layers in the
    Internet stack.
 RFC 872: "TCP-ON-A-LAN" (September 1982)
    Conclusion: "The sometimes-expressed fear that using TCP on a
    local net is a bad idea is unfounded."  [RFC0872]
 RFC 896: "Congestion Control in IP/TCP Internetworks" (January 1984)
    This document  [RFC0896] contains some early experiences with
    congestion collapse and some initial thoughts on how to avoid it
    using congestion control in TCP.

Duke, et al. Informational [Page 15] RFC 4614 TCP Roadmap September 2006

 RFC 964: "Some Problems with the Specification of the Military
 Standard Transmission Control Protocol" (November 1985)
    This document [RFC0964] points out several specification bugs in
    the US Military's MIL-STD-1778 document, which was intended as a
    successor to RFC 793.  This serves to remind us of the difficulty
    in specification writing (even when we work from existing
 RFC 1072: "TCP Extensions for Long-Delay Paths" (October 1988)
    This document [RFC1072] contains early explanations of the
    mechanisms that were later described by RFCs 1323 and 2018, which
    obsolete it.
 RFC 1185: "TCP Extension for High-Speed Paths" (October 1990)
    This document [RFC1185] builds on RFC 1072 to describe more
    advanced strategies for dealing with sequence number wrapping and
    detecting duplicates from earlier connections.  This document was
    obsoleted by RFC 1323.
 RFC 2914 B: "Congestion Control Principles" (September 2000)
    This document [RFC2914] motivates the use of end-to-end congestion
    control for preventing congestion collapse and providing fairness
    to TCP.

6.2. Difficult Network Environments

 As the internetworking field has explored wireless, satellite,
 cellular telephone, and other kinds of link-layer technologies, a
 large body of work has built up on enhancing TCP performance for such
 links.  The RFCs listed in this section describe some of these more
 challenging network environments and how TCP interacts with them.
 RFC 2488 B: "Enhancing TCP Over Satellite Channels using Standard
 Mechanisms" (January 1999)
    From abstract: "While TCP works over satellite channels there are
    several IETF standardized mechanisms that enable TCP to more
    effectively utilize the available capacity of the network path.
    This document outlines some of these TCP mitigations.  At this
    time, all mitigations discussed in this document are IETF
    standards track mechanisms (or are compliant with IETF
    standards)."  [RFC2488]

Duke, et al. Informational [Page 16] RFC 4614 TCP Roadmap September 2006

 RFC 2757 I: "Long Thin Networks" (January 2000)
    Several methods of improving TCP performance over long thin
    networks, such as geosynchronous satellite links, are discussed in
    this document [RFC2757].  A particular set of TCP options is
    developed that should work well in such environments and be safe
    to use in the global Internet.  The implications of such
    environments have been further discussed in RFC 3150 and RFC 3155,
    and these documents should be preferred where there is overlap
    between them and RFC 2757.
 RFC 2760 I: "Ongoing TCP Research Related to Satellites" (February
    This document [RFC2760] discusses the advantages and disadvantages
    of several different experimental means of improving TCP
    performance over long-delay or error-prone paths.  These include
    T/TCP, larger initial windows, byte counting, delayed
    acknowledgments, slow start thresholds, NewReno and SACK-based
    loss recovery, FACK [MM96], ECN, various corruption-detection
    mechanisms, congestion avoidance changes for fairness, use of
    multiple parallel flows, pacing, header compression, state
    sharing, and ACK congestion control, filtering, and
    reconstruction.  Although RFC 2488 looks at standard extensions,
    this document focuses on more experimental means of performance
 RFC 3135 I: "Performance Enhancing Proxies Intended to Mitigate
 Link-Related Degradations" (June 2001)
    From abstract: "This document 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 Performance Enhancing Proxies
    are described as well as the mechanisms used to improve
    performance."  [RFC3135]

Duke, et al. Informational [Page 17] RFC 4614 TCP Roadmap September 2006

 RFC 3150 B: "End-to-end Performance Implications of Slow Links" (July
    From abstract: "This document makes performance-related
    recommendations for users of network paths that traverse "very low
    bit-rate" links....This recommendation may be useful in any
    network where hosts can saturate available bandwidth, but the
    design space for this recommendation explicitly includes
    connections that traverse 56 Kb/second modem links or 4.8 Kb/
    second wireless access links - both of which are widely deployed."
 RFC 3155 B: "End-to-end Performance Implications of Links with
 Errors" (August 2001)
    From abstract: "This document discusses the specific TCP
    mechanisms that are problematic in environments with high
    uncorrected error rates, and discusses what can be done to
    mitigate the problems without introducing intermediate devices
    into the connection."  [RFC3155]
 RFC 3366 "Advice to link designers on link Automatic Repeat reQuest
 (ARQ)" (August 2002)
    From abstract: "This document provides advice to the designers of
    digital communication equipment and link-layer protocols employing
    link-layer Automatic Repeat reQuest (ARQ) techniques.  This
    document presumes that the designers wish to support Internet
    protocols, but may be unfamiliar with the architecture of the
    Internet and with the implications of their design choices for the
    performance and efficiency of Internet traffic carried over their
    links."  [RFC3366]
 RFC 3449 B: "TCP Performance Implications of Network Path Asymmetry"
 (December 2002)
    From abstract: "This document describes TCP performance problems
    that arise because of asymmetric effects.  These problems arise in
    several access networks, including bandwidth-asymmetric networks
    and packet radio subnetworks, for different underlying reasons.
    However, the end result on TCP performance is the same in both
    cases: performance often degrades significantly because of
    imperfection and variability in the ACK feedback from the receiver
    to the sender.
    The document details several mitigations to these effects, which
    have either been proposed or evaluated in the literature, or are
    currently deployed in networks."  [RFC3449]

Duke, et al. Informational [Page 18] RFC 4614 TCP Roadmap September 2006

 RFC 3481 B: "TCP over Second (2.5G) and Third (3G) Generation
 Wireless Networks" (February 2003)
    From abstract: "This document describes a profile for optimizing
    TCP to adapt so that it handles paths including second (2.5G) and
    third (3G) generation wireless networks."  [RFC3481]
 RFC 3819 B: "Advice for Internet Subnetwork Designers" (July 2004)
    This document [RFC3819] describes how TCP performance can be
    negatively affected by some particular lower-layer behaviors and
    provides guidance in designing lower-layer networks and protocols
    to be amicable to TCP.

6.3. Implementation Advice

 RFC 879: "The TCP Maximum Segment Size and Related Topics" (November
    Abstract: "This memo discusses the TCP Maximum Segment Size Option
    and related topics.  The purposes is to clarify some aspects of
    TCP and its interaction with IP.  This memo is a clarification to
    the TCP specification, and contains information that may be
    considered as 'advice to implementers'."  [RFC0879]
 RFC 1071: "Computing the Internet Checksum" (September 1988)
    This document [RFC1071] lists a number of implementation
    techniques for efficiently computing the Internet checksum (used
    by TCP).
 RFC 1624 I: "Computation of the Internet Checksum via Incremental
 Update" (May 1994)
    Incrementally updating the Internet checksum is useful to routers
    in updating IP checksums.  Some middleboxes that alter TCP headers
    may also be able to update the TCP checksum incrementally.  This
    document [RFC1624] expands upon the explanation of the incremental
    update procedure in RFC 1071.
 RFC 1936 I: "Implementing the Internet Checksum in Hardware" (April
    This document [RFC1936] describes the motivation for implementing
    the Internet checksum in hardware, rather than in software, and
    provides an implementation example.

Duke, et al. Informational [Page 19] RFC 4614 TCP Roadmap September 2006

 RFC 2525 I: "Known TCP Implementation Problems" (March 1999)
    From abstract: "This memo catalogs a number of known TCP
    implementation problems.  The goal in doing so is to improve
    conditions in the existing Internet by enhancing the quality of
    current TCP/IP implementations."  [RFC2525]
 RFC 2923 I: "TCP Problems with Path MTU Discovery" (September 2000)
    From abstract: "This memo catalogs several known Transmission
    Control Protocol (TCP) implementation problems dealing with Path
    Maximum Transmission Unit Discovery (PMTUD), including the long-
    standing black hole problem, stretch acknowlegements (ACKs) due to
    confusion between Maximum Segment Size (MSS) and segment size, and
    MSS advertisement based on PMTU."  [RFC2923]
 RFC 3360 B: "Inappropriate TCP Resets Considered Harmful" (August
    This document [RFC3360] is a plea that firewall vendors not send
    gratuitous TCP RST (Reset) packets when unassigned TCP header bits
    are used.  This practice prevents desirable extension and
    evolution of the protocol and thus is potentially harmful to the
    future of the Internet.
 RFC 3493 I: "Basic Socket Interface Extensions for IPv6" (February
    This document [RFC3493] describes the de facto standard sockets
    API for programming with TCP.  This API is implemented nearly
    ubiquitously in modern operating systems and programming

6.4. Management Information Bases

 The first MIB module defined for use with Simple Network Management
 Protocol (SNMP) (in RFC 1066 and its update, RFC 1156) was a single
 monolithic MIB module, called MIB-I.  This evolved over time to be
 MIB-II (RFC 1213).  It then became apparent that having a single
 monolithic MIB module was not scalable, given the number and breadth
 of MIB data definitions that needed to be included.  Thus, additional
 MIB modules were defined, and those parts of MIB-II that needed to
 evolve were split off.  Eventually, the remaining parts of MIB-II
 were also split off, the TCP-specific part being documented in RFC

Duke, et al. Informational [Page 20] RFC 4614 TCP Roadmap September 2006

 RFC 2012 was obsoleted by RFC 4022, which is the primary TCP MIB
 document today.  MIB-I, defined in RFC 1156, has been obsoleted by
 the MIB-II specification in RFC 1213.  For current TCP implementers,
 RFC 4022 should be supported.
 RFC 1066: "Management Information Base for Network Management of
 TCP/IP-based Internets" (August 1988)
    This document [RFC1066] was the description of the TCP MIB.  It
    was obsoleted by RFC 1156.
 RFC 1156 S: "Management Information Base for Network Management of
 TCP/IP-based Internets" (May 1990)
    This document [RFC1156] describes the required MIB fields for TCP
    implementations, with minor corrections and no technical changes
    from RFC 1066, which it obsoletes.  This is the standards track
    document for MIB-I.
 RFC 1213 S: "Management Information Base for Network Management of
 TCP/IP-based Internets: MIB-II" (March 1991)
    This document [RFC1213] describes the second version of the MIB in
    a monolithic form.  RFC 2012 updates this document by splitting
    out the TCP-specific portions.
 RFC 2012 S: "SNMPv2 Management Information Base for the Transmission
 Control Protocol using SMIv2" (November 1996)
    This document [RFC2012] defined the TCP MIB, in an update to RFC
    1213.  It is now obsoleted by RFC 4022.
 RFC 2452 S: "IP Version 6 Management Information Base for the
 Transmission Control Protocol" (December 1998)
    This document [RFC2452] augments RFC 2012 by adding an IPv6-
    specific connection table.  The rest of 2012 holds for any IP
    version.  RFC 2012 is now obsoleted by RFC 4022.
    Although it is a standards track document, RFC 2452 is considered
    a historic mistake by the MIB community, as it is based on the
    idea of parallel IPv4 and IPv6 structures.  Although IPv6 requires
    new structures, the community has decided to define a single
    generic structure for both IPv4 and IPv6.  This will aid in
    definition, implementation, and transition between IPv4 and IPv6.

Duke, et al. Informational [Page 21] RFC 4614 TCP Roadmap September 2006

 RFC 4022 S: "Management Information Base for the Transmission Control
 Protocol (TCP)" (March 2005)
    This document [RFC4022] obsoletes RFC 2012 and RFC 2452 and
    specifies the current standard for the TCP MIB that should be

6.5. Tools and Tutorials

 RFC 1180 I: "TCP/IP Tutorial" (January 1991)
    This document [RFC1180] is an extremely brief overview of the
    TCP/IP protocol suite as a whole.  It gives some explanation as to
    how and where TCP fits in.
 RFC 1470 I: "FYI on a Network Management Tool Catalog: Tools for
 Monitoring and Debugging TCP/IP Internets and Interconnected Devices"
 (June 1993)
    A few of the tools that this document [RFC1470] describes are
    still maintained and in use today; for example, ttcp and tcpdump.
    However, many of the tools described do not relate specifically to
    TCP and are no longer used or easily available.
 RFC 2398 I: "Some Testing Tools for TCP Implementors" (August 1998)
    This document [RFC2398] describes a number of TCP packet
    generation and analysis tools.  Although some of these tools are
    no longer readily available or widely used, for the most part they
    are still relevant and usable.

6.6. Case Studies

 RFC 1337 I: "TIME-WAIT Assassination Hazards in TCP" (May 1992)
    This document [RFC1337] points out a problem with acting on
    received reset segments while one is in the TIME-WAIT state.  The
    main recommendation is that hosts in TIME-WAIT ignore resets.
    This recommendation might not currently be widely implemented.
 RFC 2415 I: "Simulation Studies of Increased Initial TCP Window Size"
 (September 1998)
    This document [RFC2415] presents results of some simulations using
    TCP initial windows greater than 1 segment.  The analysis
    indicates that user-perceived performance can be improved by
    increasing the initial window to 3 segments.

Duke, et al. Informational [Page 22] RFC 4614 TCP Roadmap September 2006

 RFC 2416 I: "When TCP Starts Up With Four Packets Into Only Three
 Buffers" (September 1998)
    This document [RFC2416] uses simulation results to clear up some
    concerns about using an initial window of 4 segments when the
    network path has less provisioning.
 RFC 2884 I: "Performance Evaluation of Explicit Congestion
 Notification (ECN) in IP Networks" (July 2000)
    This document [RFC2884] describes experimental results that show
    some improvements to the performance of both short- and long-lived
    connections due to ECN.

7. Undocumented TCP Features

 There are a few important implementation tactics for the TCP that
 have not yet been described in any RFC.  Although this roadmap is
 primarily concerned with mapping the TCP RFCs, this section is
 included because an implementer needs to be aware of these important
 SYN Cookies
    A mechanism known as "SYN cookies" is widely used to thwart TCP
    SYN flooding attacks, in which an attacker sends a flood of SYNs
    to a victim but fails to complete the 3-way handshake.  The result
    is exhaustion of resources at the server.  The SYN cookie
    mechanism allows the server to return a cleverly chosen initial
    sequence number that has all the required state for the secure
    completion of the handshake.  Then the server can avoid saving
    connection state during the 3-way handshake and thus survive a SYN
    flooding attack.
    A web search for "SYN cookies" will reveal a number of useful
    descriptions of this mechanism, although there is currently no RFC
    on the matter.
 Header Prediction
    Header prediction is a trick to speed up the processing of
    segments.  Van Jacobson and Mike Karels developed the technique in
    the late 1980s.  The basic idea is that some processing time can
    be saved when most of a segment's fields can be predicted from
    previous segments.  A good description of this was sent to the
    TCP-IP mailing list by Van Jacobson on March 9, 1988:

Duke, et al. Informational [Page 23] RFC 4614 TCP Roadmap September 2006

       Quite a bit of the speedup comes from an algorithm that we
       ('we' refers to collaborator Mike Karels and myself) are
       calling "header prediction".  The idea is that if you're in the
       middle of a bulk data transfer and have just seen a packet, you
       know what the next packet is going to look like:  It will look
       just like the current packet with either the sequence number or
       ack number updated (depending on whether you're the sender or
       receiver).  Combining this with the "Use hints" epigram from
       Butler Lampson's classic "Epigrams for System Designers", you
       start to think of the tcp state (rcv.nxt, snd.una, etc.) as
       "hints" about what the next packet should look like.
       If you arrange those "hints" so they match the layout of a tcp
       packet header, it takes a single 14-byte compare to see if your
       prediction is correct (3 longword compares to pick up the send
       & ack sequence numbers, header length, flags and window, plus a
       short compare on the length).  If the prediction is correct,
       there's a single test on the length to see if you're the sender
       or receiver followed by the appropriate processing.  E.g., if
       the length is non-zero (you're the receiver), checksum and
       append the data to the socket buffer then wake any process
       that's sleeping on the buffer.  Update rcv.nxt by the length of
       this packet (this updates your "prediction" of the next
       packet).  Check if you can handle another packet the same size
       as the current one.  If not, set one of the unused flag bits in
       your header prediction to guarantee that the prediction will
       fail on the next packet and force you to go through full
       protocol processing.  Otherwise, you're done with this packet.
       So, the *total* tcp protocol processing, exclusive of
       checksumming, is on the order of 6 compares and an add.

8. Security Considerations

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

9. Acknowledgments

 This document grew out of a discussion on the end2end-interest
 mailing list, the public list of the End-to-End Research Group of the
 IRTF, and continued development under the IETF's TCP Maintenance and
 Minor Extensions (TCPM) working group.  We thank Joe Touch, Reiner
 Ludwig, Pekka Savola, Gorry Fairhurst, and Sally Floyd for their
 contributions, in particular.  The chairs of the TCPM working group,
 Mark Allman and Ted Faber, have been instrumental in the development
 of this document.  Keith McCloghrie provided some useful notes and
 clarification on the various MIB-related RFCs.

Duke, et al. Informational [Page 24] RFC 4614 TCP Roadmap September 2006

10. Informative References

10.1. Basic Functionality

 [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
            793, September 1981.
 [RFC1122]  Braden, R., "Requirements for Internet Hosts -
            Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
            3", BCP 9, RFC 2026, October 1996.
 [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, December 1998.
 [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
            "Definition of the Differentiated Services Field (DS
            Field) in the IPv4 and IPv6 Headers", RFC 2474, December
 [RFC2581]  Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
            Control", RFC 2581, April 1999.
 [RFC2675]  Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
            RFC 2675, August 1999.
 [RFC2873]  Xiao, X., Hannan, A., Paxson, V., and E. Crabbe, "TCP
            Processing of the IPv4 Precedence Field", RFC 2873, June
 [RFC2988]  Paxson, V. and M. Allman, "Computing TCP's Retransmission
            Timer", RFC 2988, November 2000.

10.2. Recommended Enhancements

 [RFC1323]  Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
            for High Performance", RFC 1323, May 1992.
 [RFC1948]  Bellovin, S., "Defending Against Sequence Number Attacks",
            RFC 1948, May 1996.
 [RFC2018]  Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
            Selective Acknowledgment Options", RFC 2018, October 1996.
 [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
            Signature Option", RFC 2385, August 1998.

Duke, et al. Informational [Page 25] RFC 4614 TCP Roadmap September 2006

 [RFC2883]  Floyd, S., Mahdavi, J., Mathis, M., and M. Podolsky, "An
            Extension to the Selective Acknowledgement (SACK) Option
            for TCP", RFC 2883, July 2000.
 [RFC3042]  Allman, M., Balakrishnan, H., and S. Floyd, "Enhancing
            TCP's Loss Recovery Using Limited Transmit", RFC 3042,
            January 2001.
 [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
            of Explicit Congestion Notification (ECN) to IP", RFC
            3168, September 2001.
 [RFC3390]  Allman, M., Floyd, S., and C. Partridge, "Increasing TCP's
            Initial Window", RFC 3390, October 2002.
 [RFC3517]  Blanton, E., Allman, M., Fall, K., and L. Wang, "A
            Conservative Selective Acknowledgment (SACK)-based Loss
            Recovery Algorithm for TCP", RFC 3517, April 2003.
 [RFC3562]  Leech, M., "Key Management Considerations for the TCP MD5
            Signature Option", RFC 3562, July 2003.
 [RFC3782]  Floyd, S., Henderson, T., and A. Gurtov, "The NewReno
            Modification to TCP's Fast Recovery Algorithm", RFC 3782,
            April 2004.
 [RFC4015]  Ludwig, R. and A. Gurtov, "The Eifel Response Algorithm
            for TCP", RFC 4015, February 2005.
 [RFC4278]  Bellovin, S. and A. Zinin, "Standards Maturity Variance
            Regarding the TCP MD5 Signature Option (RFC 2385) and the
            BGP-4 Specification", RFC 4278, January 2006.

10.3. Experimental Extensions

 [RFC2140]  Touch, J., "TCP Control Block Interdependence", RFC 2140,
            April 1997.
 [RFC2861]  Handley, M., Padhye, J., and S. Floyd, "TCP Congestion
            Window Validation", RFC 2861, June 2000.
 [RFC3124]  Balakrishnan, H. and S. Seshan, "The Congestion Manager",
            RFC 3124, June 2001.
 [RFC3465]  Allman, M., "TCP Congestion Control with Appropriate Byte
            Counting (ABC)", RFC 3465, February 2003.

Duke, et al. Informational [Page 26] RFC 4614 TCP Roadmap September 2006

 [RFC3522]  Ludwig, R. and M. Meyer, "The Eifel Detection Algorithm
            for TCP", RFC 3522, April 2003.
 [RFC3540]  Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
            Congestion Notification (ECN) Signaling with Nonces", RFC
            3540, June 2003.
 [RFC3649]  Floyd, S., "HighSpeed TCP for Large Congestion Windows",
            RFC 3649, December 2003.
 [RFC3708]  Blanton, E. and M. Allman, "Using TCP Duplicate Selective
            Acknowledgement (DSACKs) and Stream Control Transmission
            Protocol (SCTP) Duplicate Transmission Sequence Numbers
            (TSNs) to Detect Spurious Retransmissions", RFC 3708,
            February 2004.
 [RFC3742]  Floyd, S., "Limited Slow-Start for TCP with Large
            Congestion Windows", RFC 3742, March 2004.
 [RFC4138]  Sarolahti, P. and M. Kojo, "Forward RTO-Recovery (F-RTO):
            An Algorithm for Detecting Spurious Retransmission
            Timeouts with TCP and the Stream Control Transmission
            Protocol (SCTP)", RFC 4138, August 2005.

10.4. Historic Extensions

 [RFC1106]  Fox, R., "TCP big window and NAK options", RFC 1106, June
 [RFC1110]  McKenzie, A., "Problem with the TCP big window option",
            RFC 1110, August 1989.
 [RFC1146]  Zweig, J. and C. Partridge, "TCP alternate checksum
            options", RFC 1146, March 1990.
 [RFC1263]  O'Malley, S. and L. Peterson, "TCP Extensions Considered
            Harmful", RFC 1263, October 1991.
 [RFC1379]  Braden, R., "Extending TCP for Transactions -- Concepts",
            RFC 1379, November 1992.
 [RFC1644]  Braden, R., "T/TCP -- TCP Extensions for Transactions
            Functional Specification", RFC 1644, July 1994.
 [RFC1693]  Connolly, T., Amer, P., and P. Conrad, "An Extension to
            TCP : Partial Order Service", RFC 1693, November 1994.

Duke, et al. Informational [Page 27] RFC 4614 TCP Roadmap September 2006

10.5. Support Documents

 [RFC0813]  Clark, D., "Window and Acknowledgement Strategy in TCP",
            RFC 813, July 1982.
 [RFC0814]  Clark, D., "Name, addresses, ports, and routes", RFC 814,
            July 1982.
 [RFC0816]  Clark, D., "Fault isolation and recovery", RFC 816, July
 [RFC0817]  Clark, D., "Modularity and efficiency in protocol
            implementation", RFC 817, July 1982.
 [RFC0872]  Padlipsky, M., "TCP-on-a-LAN", RFC 872, September 1982.
 [RFC0879]  Postel, J., "TCP maximum segment size and related topics",
            RFC 879, November 1983.
 [RFC0896]  Nagle, J., "Congestion control in IP/TCP internetworks",
            RFC 896, January 1984.
 [RFC0964]  Sidhu, D. and T. Blumer, "Some problems with the
            specification of the Military Standard Transmission
            Control Protocol", RFC 964, November 1985.
 [RFC1066]  McCloghrie, K. and M. Rose, "Management Information Base
            for Network Management of TCP/IP-based internets", RFC
            1066, August 1988.
 [RFC1071]  Braden, R., Borman, D., and C. Partridge, "Computing the
            Internet checksum", RFC 1071, September 1988.
 [RFC1072]  Jacobson, V. and R. Braden, "TCP extensions for long-delay
            paths", RFC 1072, October 1988.
 [RFC1156]  McCloghrie, K. and M. Rose, "Management Information Base
            for network management of TCP/IP-based internets", RFC
            1156, May 1990.
 [RFC1180]  Socolofsky, T. and C. Kale, "TCP/IP tutorial", RFC 1180,
            January 1991.
 [RFC1185]  Jacobson, V., Braden, B., and L. Zhang, "TCP Extension for
            High-Speed Paths", RFC 1185, October 1990.

Duke, et al. Informational [Page 28] RFC 4614 TCP Roadmap September 2006

 [RFC1213]  McCloghrie, K. and M. Rose, "Management Information Base
            for Network Management of TCP/IP-based internets: MIB-II",
            STD 17, RFC 1213, March 1991.
 [RFC1337]  Braden, R., "TIME-WAIT Assassination Hazards in TCP", RFC
            1337, May 1992.
 [RFC1470]  Enger, R. and J. Reynolds, "FYI on a Network Management
            Tool Catalog: Tools for Monitoring and Debugging TCP/IP
            Internets and Interconnected Devices", FYI 2, RFC 1470,
            June 1993.
 [RFC1624]  Rijsinghani, A., "Computation of the Internet Checksum via
            Incremental Update", RFC 1624, May 1994.
 [RFC1936]  Touch, J. and B. Parham, "Implementing the Internet
            Checksum in Hardware", RFC 1936, April 1996.
 [RFC2012]  McCloghrie, K., "SNMPv2 Management Information Base for
            the Transmission Control Protocol using SMIv2", RFC 2012,
            November 1996.
 [RFC2398]  Parker, S. and C. Schmechel, "Some Testing Tools for TCP
            Implementors", RFC 2398, August 1998.
 [RFC2415]  Poduri, K. and K. Nichols, "Simulation Studies of
            Increased Initial TCP Window Size", RFC 2415, September
 [RFC2416]  Shepard, T. and C. Partridge, "When TCP Starts Up With
            Four Packets Into Only Three Buffers", RFC 2416, September
 [RFC2452]  Daniele, M., "IP Version 6 Management Information Base for
            the Transmission Control Protocol", RFC 2452, December
 [RFC2488]  Allman, M., Glover, D., and L. Sanchez, "Enhancing TCP
            Over Satellite Channels using Standard Mechanisms", BCP
            28, RFC 2488, January 1999.
 [RFC2525]  Paxson, V., Allman, M., Dawson, S., Fenner, W., Griner,
            J., Heavens, I., Lahey, K., Semke, J., and B. Volz, "Known
            TCP Implementation Problems", RFC 2525, March 1999.
 [RFC2757]  Montenegro, G., Dawkins, S., Kojo, M., Magret, V., and N.
            Vaidya, "Long Thin Networks", RFC 2757, January 2000.

Duke, et al. Informational [Page 29] RFC 4614 TCP Roadmap September 2006

 [RFC2760]  Allman, M., Dawkins, S., Glover, D., Griner, J., Tran, D.,
            Henderson, T., Heidemann, J., Touch, J., Kruse, H.,
            Ostermann, S., Scott, K., and J. Semke, "Ongoing TCP
            Research Related to Satellites", RFC 2760, February 2000.
 [RFC2884]  Hadi Salim, J. and U. Ahmed, "Performance Evaluation of
            Explicit Congestion Notification (ECN) in IP Networks",
            RFC 2884, July 2000.
 [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41, RFC
            2914, September 2000.
 [RFC2923]  Lahey, K., "TCP Problems with Path MTU Discovery", RFC
            2923, September 2000.
 [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.
 [RFC3360]  Floyd, S., "Inappropriate TCP Resets Considered Harmful",
            BCP 60, RFC 3360, August 2002.
 [RFC3366]  Fairhurst, G. and L. Wood, "Advice to link designers on
            link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
            August 2002.
 [RFC3449]  Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.
            Sooriyabandara, "TCP Performance Implications of Network
            Path Asymmetry", BCP 69, RFC 3449, 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
 [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
            Stevens, "Basic Socket Interface Extensions for IPv6", RFC
            3493, February 2003.

Duke, et al. Informational [Page 30] RFC 4614 TCP Roadmap September 2006

 [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.
 [RFC4022]  Raghunarayan, R., "Management Information Base for the
            Transmission Control Protocol (TCP)", RFC 4022, March

10.6. Informative References Outside the RFC Series

 [JK92]     Jacobson, V. and M. Karels, "Congestion Avoidance and
            Control", This paper is a revised version of [Jac88], that
            includes an additional appendix.  This paper has not been
            traditionally published, but is currently available at
 [Jac88]    Jacobson, V., "Congestion Avoidance and Control", ACM
            SIGCOMM 1988 Proceedings, in ACM Computer Communication
            Review, 18 (4), pp. 314-329, August 1988.
 [KP87]     Karn, P. and C. Partridge, "Round Trip Time Estimation",
            ACM SIGCOMM 1987 Proceedings, in ACM Computer
            Communication Review, 17 (5), pp. 2-7, August 1987
 [MAF04]    Medina, A., Allman, M., and S. Floyd, "Measuring the
            Evolution of Transport Protocols in the Internet", ACM
            Computer Communication Review, 35 (2), April 2005.
 [MM96]     Mathis, M. and J. Mahdavi, "Forward Acknowledgement:
            Refining TCP Congestion Control", ACM SIGCOMM 1996
            Proceedings, in ACM Computer Communication Review 26 (4),
            pp. 281-292, October 1996.
 [SCWA99]   Savage, S., Cardwell, N., Wetherall, D., and T. Anderson,
            "TCP Congestion Control with a Misbehaving Receiver", ACM
            Computer Communication Review, 29 (5), pp. 71-78, October

Duke, et al. Informational [Page 31] RFC 4614 TCP Roadmap September 2006

Authors' Addresses

 Martin H. Duke
 The Boeing Company
 PO Box 3707, MC 7L-49
 Seattle, WA  98124-2207
 Phone: 425-373-2852
 Robert Braden
 USC Information Sciences Institute
 Marina del Rey, CA  90292-6695
 Phone: 310-448-9173
 Wesley M. Eddy
 Verizon Federal Network Systems
 21000 Brookpark Rd, MS 54-5
 Cleveland, OH  44135
 Phone: 216-433-6682
 Ethan Blanton
 Purdue University Computer Science
 250 N. University St.
 West Lafayette, IN  47907

Duke, et al. Informational [Page 32] RFC 4614 TCP Roadmap September 2006

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Duke, et al. Informational [Page 33]

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