Network Working Group                                            M. Duke
Internet-Draft                                      Boeing Phantom Works
Expires: April 8, July 21, 2005                                         R. Braden
                                      USC Information Sciences Institute
                                                                 W. Eddy
                                                    NASA GRC/Verizon FNS
                                                              E. Blanton
                                                       Purdue University
                                                         October 8, 2004
                                                        January 20, 2005

               A Roadmap for TCP Specification Documents
                     draft-ietf-tcpm-tcp-roadmap-00
                     draft-ietf-tcpm-tcp-roadmap-01

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Copyright Notice

   Copyright (C) The Internet Society (2004). (2005).

Abstract

   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 rough guide and quick reference for both TCP
   implementers and other parties that need help consuming who desire information contained in
   the
   vast cornucopia of TCP-related RFCs.

Table of Contents

   1.  Introduction

   One critical part of an Internet host's software is a . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Basic Functionality  . . . . . . . . . . . . . . . . . . . . .  5
   3.  Standard Enhancements  . . . . . . . . . . . . . . . . . . . .  7
     3.1   Congestion Control and Loss Recovery Extensions  . . . . .  7
     3.2   SACK-based Loss Recovery and Congestion Control  . . . . .  9
     3.3   Dealing with Forged Segments . . . . . . . . . . . . . . .  9
   4.  Experimental Extensions  . . . . . . . . . . . . . . . . . . . 11
   5.  Historic Extensions  . . . . . . . . . . . . . . . . . . . . . 13
   6.  Support Documents  . . . . . . . . . . . . . . . . . . . . . . 15
     6.1   Foundational Works . . . . . . . . . . . . . . . . . . . . 15
     6.2   Difficult Network Environments . . . . . . . . . . . . . . 16
     6.3   Implementation Advice  . . . . . . . . . . . . . . . . . . 18
     6.4   Management Information Bases . . . . . . . . . . . . . . . 19
     6.5   Tools and Tutorials  . . . . . . . . . . . . . . . . . . . 20
     6.6   Case Studies . . . . . . . . . . . . . . . . . . . . . . . 21
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 24
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     9.1   Basic Functionality  . . . . . . . . . . . . . . . . . . . 25
     9.2   Standard Enhancements  . . . . . . . . . . . . . . . . . . 25
     9.3   Experimental Extensions  . . . . . . . . . . . . . . . . . 26
     9.4   Historic Extensions  . . . . . . . . . . . . . . . . . . . 27
     9.5   Support Documents  . . . . . . . . . . . . . . . . . . . . 27
     9.6   Informative References Outside the RFC Series  . . . . . . 30
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
       Intellectual Property and Copyright Statements . . . . . . . . 32

1.  Introduction

   A correct and efficient implementation of the Transmission Control
   Protocol (TCP)
   [RFC0793]. [RFC0793] 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. 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 relevant RFC documents that define TCP.  This can give rough should provide guidance to
   implementers on the relevance and significance of various the standards track
   extensions, informational notes, and best current practices that
   relate to TCP.

   This roadmap includes a brief description of the contents and
   relevance of each
   TCP-related RFC.  In some cases, we simply supply the abstract or some a
   key summary sentence from the text as a terse description.  In
   addition, a letter code after each RFC number indicates its category
   in the RFC series:

      S - Standards Track (Proposed Standard, Draft Standard, or
      Standard)
      E - Experimental
      B - Best Current Practice
      I - Informational

   Note that the category of each an RFC does not necessarily reflect its
   current relevance.  For instance, RFC 2581 is nearly universally
   deployed although it is only a "Proposed Standard". Proposed Standard.  Similarly, some
   "Informational"
   Informational RFCs actually contain significant technical proposals for
   changing TCP.

   This roadmap is divided into four main sections.  Section 2 lists the
   RFCs that form the core describe absolutely required TCP specification.
   Section 3 lists some behaviors for proper
   functioning and interoperability.  Further RFCs that provide suggestions for implementers
   or describe best current practices concerning issues raised by
   particular network environments.
   strongly encouraged, but not essential, behaviors are listed in
   Section 4 lists RFCs 3.  Experimental extensions which are not yet standard
   practices, but potentially could be in the future, are described in
   Section 4.

   The reader probably notices that these three sections are
   experimental broadly
   equivalent to MUST/SHOULD/MAY specifications, and may one day become standards, Section 5 lists some
   deprecated extensions, while the authors
   support this intuition, this document is merely descriptive; it does
   not represent a binding standards track position.  An individual
   implementor still needs to examine the standards documents themselves
   to evaluate specific requirement levels.

   A small number of older experimental extensions which have not caught
   on are noted in Section 6 contains case studies and analysis, 5.  Many other supporting documents that are
   relevant to the development, implementation, and deployment of TCP
   are described in Section 7 provides tips and tools for implementers. 6.  Within each section, RFCs are listed in
   chronological order.

   When this document describes a features as "available in modern
   operating systems", we mean that the feature is at least present in
   widely deployed versions of today's Linux, BSD-derived, and Windows
   operating systems.  Many other specific operating systems are in use
   on the Internet, and feature support varies widely both among them
   and among specific versions of even the few operating systems in the
   above list.  However, if we say a feature is found in "modern
   operating systems", the reader may fairly safely bet that it can at
   least be found in most presently maintained commercial Unix flavors,
   Cisco IOS versions, and various real-time and embedded kernels that
   offer TCP support.

2.  Core Specification  Basic Functionality

   A small number of documents compose the core specification of TCP.
   These can be grouped into the base documents, describing things like define the required basic functionalities of TCP's header format and
   parsing, state machine operation, documents describing machine, congestion control behaviors, and documents that detail SACK use for
   efficient loss recovery.  At this time every conformant TCP
   implementation should implement:

      Base protocol: RFC 793, as extended and clarified by RFC 1122, RFC
      1323, RFC 2873, control, and RFC 2988. retransmission
   timeout computation.  These documents are described in
      Section 2.1
      Congestion control: RFC 2581, RFC 3042, RFC 3168, RFC 3390, and
      RFC 3782.  Section 2.2 discusses these RFCs.
      SACK: RFC 2018, RFC 2883, and RFC 3517 are noted in Section 2.3

   In addition to these core documents, there are a number of standards
   track documents that describe the TCP MIB statistics that are
   required to base specifications must be kept.  These documents are listed in Section 2.4 and
   their history is sketched, as a somewhat complex relationship exists
   between them.

2.1  Base Protocol correctly
   followed for interoperability.

   RFC 0793 793 S: "Transmission Control Protocol", STD 7 (Sep 81) (September 1981)

      This is the fundamental TCP specification document. 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 acknowledgement.
      Although

      Section 3.6 of RFC 793, describing TCP's handling of the IP
      precedence and security compartment portions are compartment, is mostly irrelevant today, 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 acurately describes modern TCPs.  [RFC0793]  RFC 1122 S: "Requirements for Internet Hosts - Communication Layers"
   (Oct 89)

      This 793 is the last of a
      series of developmental TCP specifications, starting from IENs and
      continuing in the RFC series.

   RFC 1122 S: "Requirements for Internet Hosts - Communication Layers"
   (October 1989)

      This document [RFC1122] updates and clarifies RFC 793; 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 [karn][vj88]. [Karn][VJ88].  ICMP interactions are mentioned and some
      tips are given for efficient implementation.  RFC 1122 lists is an
      Applicability Statement, listing the various features that MUST,
      SHOULD, MAY, SHOULD NOT, and MUST NOT be present in
      standards-conforming TCP implementations.  [RFC1122]

   RFC 1323 2147 S: "TCP Extensions for High Performance" and UDP over IPv6 Jumbograms" (May 92) 1997)

      IPv6's support for longer datagrams than were allowed in IPv4,
      necessitated some changes to the way that TCP's MSS and Urgent
      fields (both 16 bits) are treated.

   RFC 2460 S: "Internet Protocol, Version 6 (IPv6) Specification
   (December 1998)

      This document introduces window scaling, timestamps, and
      protection against wrapped sequence numbers [RFC2460] makes a slight update to the way the
      pseudo-header for efficient checksum computation is derived, defining the
      process for IPv6 in addition to the previous practice for IPv4.

   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 safe
      operation over paths with large bandwidth-delay products.  These control
      mechanisms for TCP, based on his 1988 SIGCOMM paper [VJ88].  RFC
      2001 was a conceptual precursor that was obsoleted by RFC 2581.

      A number of behaviors that together comprise what the community
      refers to as "Reno TCP", are all commonly found described in modern RFC 2581.  The name
      "Reno" comes from the Net/2 release of the 4.3 BSD operating systems; however, they
      may require manual tuning
      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 configuration.  There are some
      corner cases in this specification that are still under
      discussion.  [RFC1323] fast recovery.

   RFC 2873 S: "TCP Processing of the IPv4 Precendence Field" (Jun 00) (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 Diff-Serv.  [RFC2873] Differentiated Services.

   RFC 2988 S: "Computing TCP's Retransmission Timer" (Nov 00) (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 4.2.3.1 of RFC 1122 and upgrades the
      requirement of supporting the algorithm from a SHOULD to a MUST."
      [RFC2988]

2.2  Congestion Control

   RFC 2581 S: "TCP Congestion Control" (Apr 99)

3.  Standard Enhancements

   This document defines the current versions of Van Jacobson's
      congestion avoidance section describes recommended TCP modifications that improve
   performance and control mechanisms for TCP, security.  RFCs 1323 and 3168 represent fundamental
   changes to the protocol.  RFC 1323, based on his
      1988 SIGCOMM paper [vj88].  [RFC2581] RFCs 1072 and 1185,
   allows better utilization of high bandwidth-delay product paths by
   providing some needed mechanisms for high-rate transfers.  RFC 3042 S: "Enhancing TCP's Loss Recovery Using Limited Transmit"
   (Jan 01)

      Abstract: "This document proposes 3168
   describes a new Transmission Control
      Protocol (TCP) mechanism that can be used change to more effectively
      recover lost segments when a connection's the Internet's architecture, where 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 acknowledgements.  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 is
      small, or when a scaling,
      timestamps, and protection against wrapped sequence numbers, for
      efficient and safe operation over paths with large number of segments bandwidth-delay
      products.  These extensions are lost commonly found in a single
      transmission window." [RFC3042] currently-used
      systems; however, they may require manual tuning and
      configuration.  Some "corner cases" in this specification are
      still under discussion.

   RFC 3168 S: "The Addition of Explicit Congestion Notification (ECN)
   to IP" (Sep 01) (September 2001)

      This document [RFC3168] defines a means of detecting congestion
      without resorting to packet loss.  Although congestion
      notification takes place at the IP level, ECN requires support is required 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.  [RFC3168] header for ECN support.
      RFC 3390 S: "Increasing TCP'S Initial Window" (Oct 02)

      This document permits 3540 provides a TCP to supplementary (experimental) means for making
      ECN use an initial window larger that
      one packet during in the slow-start phase, updating RFC 2581.
      [RFC3390] more secure, and RFC 3782 S: "The NewReno Modification to TCP's Fast 2884 provides some sample results
      from using ECN.

3.1  Congestion Control and Loss Recovery
   Algorithm" (Apr 04)

      This document specifies a slight modification to Extensions

   Two of the standard Reno
      fast recovery algorithm, whereby a most important aspects of TCP sender can use partial
      acknowledgements are its congestion control
   and loss recovery features.  Since TCP traditionally (in the absence
   of ECN) uses losses to make inferences determining infer congestion, 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 - without negotiating
   support between endpoints.  In the next segment
      to send in situations where sub-section, we group the
   extensions which specify or rely on the SACK would option, whose use must
   be helpful, but isn't
      available.  [RFC3782]

2.3  SACK-based Loss Recovery

   RFC 2018 S: "TCP Selective Acknowledgement Options" (Oct 96)

      This document defines negotiated bilaterally.  TCP implementations should include the sective acknowledgement (SACK)
      mechanism, providing more fine-grained acknowledgement information
      than
   enhancements from both sub-sections so that they can perform well
   without regard to the basic cummulative acknowledgement mechanism.  Exchange feature sets of other hosts they connect to.
   For example, if SACK information use is widely implemented in modern operating
      systems.  [RFC2018]

   RFC 2883 S: "An Extension to the Selective Acknowledgement (SACK)
   Option for TCP" (Jul 00)

      This document extends RFC 2018 to cover not successfully negotiated, a TCP should
   use the case of acknowledging
      duplicate packets.  [RFC2883] NewReno behavior as a fall-back.

   RFC 3517 3042 S: "A Conservative Selective Acknowledgement (SACK)-based "Enhancing TCP's Loss Recovery Algorithm for TCP" (Apr 03)

      This Using Limited Transmit"
   (January 2001)

      Abstract: "This document describes proposes [Limited Transmit,] a TCP loss recovery algorithm which uses
      available SACK information new
      Transmission Control Protocol (TCP) mechanism that can be used to intelligently
      more effectively recover lost segments when more than
      one segment a connection's
      congestion window is lost from small, or when a single flight of data.  While support
      for the exchange large number of SACK information is widely implemented, not
      all implementations use an algorithm as sophisticated as that
      described segments are
      lost in a single transmission window." [RFC3042]

   RFC 3517.  [RFC3517]

2.4 3390 S: "Increasing TCP'S Initial Window" (October 2002)

      This document [RFC3390] updates RFC 2581 to permit an initial TCP
      window larger that one packet during in the slow-start phase.

   RFC 3782 S: "The NewReno Modification to TCP's Fast Recovery
   Algorithm" (April 2004)

      This document [RFC3782] specifies a slight modification to the
      standard Reno fast recovery algorithm, whereby a TCP MIBs sender can
      use partial acknowledgements to make inferences determining the
      next segment to send in situations where SACK would be helpful,
      but isn't available.

   Work in progress: The first MIB module defined Eifel Response Algorithm for use with SNMP (in RFC 1066 TCP (Internet
   Draft name: draft-ietf-tsvwg-tcp-eifel-response)

      At the time of this writing, work on this document (from authors
      Reiner Ludwig and its
   update, RFC 1156) Andrei Gurtov) had stabilized within the
      Transport Area Working Group, and the document was a single monolithic MIB module, called MIB-I.
   This evolved over time planned to be MIB-II (RFC 1213).  It then became
   apparent that having
      become a single monolithic MIB module Proposed Standard, pending IESG review, but was not scalable,
   given yet a
      part of the number and breadth RFC series.  This document describes the response
      portion of MIB data definitions that needed to the Eifel algorithm, which can be included.  Thus, additional MIB modules were defined, and those
   parts used in conjunction
      with one of MIB-II which needed to evolve were split off.  Eventually,
   the remaining parts several methods of MIB-II were also split off, with detecting when loss recovery has
      been spuriously entered, such as the
   TCP-specific part being documented Eifel detection algorithm in
      RFC 2012. 3522, the algorithm in RFC 2012 is 3708, or F-RTO.

      Abstract: "Based on an appropriate detection algorithm, the primary document that implementers should presently
   be concerned with Eifel
      response algorithm provides a way for MIB-II.  If implementers desire a TCP sender to support
   MIB-I, then RFC 1156 is respond to a
      detected spurious timeout.  It adapts the document retransmission timer to refer to, although it has
   been obsoleted by
      avoid further spurious timeouts, and can avoid - depending on the MIB-II specification in RFC 1213.  Although a
   standards track document, RFC 2452 is considered a historic mistake
   by
      detection algorithm - the MIB community, as it is based on often unnecessary go-back-N retransmits
      that would otherwise be sent.  In addition, the idea of parallel IPv4 and
   IPv6 structures.  The community has decided Eifel response
      algorithm restores the congestion control state in such a way that while new structures
      packet bursts are needed to accomodate IPv6, a single generic structure for both
   IPv4 avoided."

3.2  SACK-based Loss Recovery and IPv6 addresses, to aid Congestion Control

   The base TCP specification in definition, implementation, and
   transition between IPv4 and IPv6. RFC 1156 S: "Management Information Base for Network Management 793 provided only a simple
   cumulative acknowledgment mechanism.  However, a selective
   acknowledgment (SACK) mechanism provides significant performance
   improvement in the presence of
   TCP/IP-based Internets" (May 90)

      This document describes packet losses, more than outweighing
   the required MIB fields for modest increase in complexity.  A TCP
      implementations, with minor corrections should be expected to
   implement SACK, however SACK is a negotiated option and no technical changes
      from RFC 1066, which it obsoletes.  This is the standards track
      document for MIB-I.  [RFC1156] only used
   if support is advertised by both sides of a connection.

   RFC 2012 2018 S: "SNMPv2 Management Information Base for the Transmission
   Control Protocol using SMIv2" (Nov 96) "TCP Selective Acknowledgement Options" (October 1996)

      This document [RFC2018] defines the TCP MIB, updating RFC 1213.[RFC2012] basic selective
      acknowledgement (SACK) mechanism for TCP.

   RFC 2452 2883 S: "IP Version 6 Management Information Base for "An Extension to the
   Transmission Control Protocol" (Dec 98) Selective Acknowledgement (SACK)
   Option for TCP" (July 2000)

      This document augments [RFC2883] extends RFC 2012 by adding an IPv6-specific
      connection table.  The rest 2018 to cover the case of 2012 holds for any IP version.
      ((Shouldn't 2452 "Update" 2012 ?)) [RFC2452]

3.  Special Cases and Implementation Hints
      acknowledging duplicate packets.

   RFC 1144 3517 S: "Compressing TCP/IP headers for low-speed serial links"
   (Feb 90) "A Conservative Selective Acknowledgement (SACK)-based
   Loss Recovery Algorithm for TCP" (April 2003)

      This document contains Van Jacobson's classic specification [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
      TCP/IP header compression.  It is notable data.
      While support for its elegance 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
      clarity.  [RFC1144] 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 prevent it from being able to negatively impact a
   connection.

   RFC 1948 I: "Defending Against Sequence Number Attacks" (May 96)

      The sequence number guessing 1996)

      This document [RFC1948] describes the TCP vulnerability is described in
      this document based upon
      guessing sequence numbers and means for defending it from exploitation are
      discussed in as well as defenses against this document.
      exploit.  Some variation is implemented in most
      modern currently-used
      operating systems.  [RFC1948]

   RFC 2140 I: "TCP Control Block Interdependence" (Apr 97)

      This document suggests how TCP connections between 2385 S: "Protection of BGP Sessions via the same
      endpoints might share information, such as their congestion
      control state.  To some degree, this is done in TCP MD5 Signature
   Option" (August 1998)

      From document: "This document describes currrent existing practice by
      for securing BGP against certain simple attacks.  It is understood
      to have security weaknesses against concerted attacks.

      This memo describes a few
      modern operating systems.  [RFC2140]

   RFC 2488 B: "Enhancing TCP Over Satellite Channels using Standard
   Mechanisms" (Jan 99)

      From abstract: "While extension to enhance security for BGP.
      It defines a new TCP works over satellite channels there are
      several IETF standardized mechanisms that enable option for carrying an MD5 [RFC1321] digest
      in a TCP segment.  This digest acts like a signature for that
      segment, incorporating information known only to more
      effectively utilize the available capacity of the network path.
      This document outlines some of these connection
      end points.  Since BGP uses TCP mitigations.  At this
      time, all mitigations discussed as its transport, using this
      option in the way described in this document paper significantly reduces
      the danger from certain security attacks on BGP." [RFC2385]

      TCP MD5 options are IETF
      standards track mechanisms (or currently only used in very limited contexts,
      primarily for defending BGP exchanges between routers.  Some
      deployment notes for those using TCP MD5 are compliant with IETF
      standards)." [RFC2488] found in the later
      RFC 2525 I: "Known 3562, "Key Management Considerations for the TCP Implementation Problems" (Mar 99)

      From abstract: "This memo catalogs a number MD5 Signature
      Option" [RFC3562].

   Work in progress: Transmission Control Protocol Security
   Considerations (Internet Draft name: draft-ietf-tcpm-tcpsecure)

      At the time of known this writing, the TCP
      implementation problems.  The goal in doing so Maintenance and Minor
      Extensions Working Group is to improve
      conditions in the existing Internet producing a document (edited by enhancing the quality of
      current TCP/IP implementations." [RFC2525]

   RFC 3360 B: "Inappropriate Mitesh
      Dalal) which describes a challenge-response mechanism for securing
      TCP Resets Considered Harmful" (Aug 02) against spoofed control segments.  This document is a plea to firewall vendors not expected
      to send gratuitous
      TCP RST (Reset) packets when unassigned TCP header bits become an RFC in the near future.

4.  Experimental Extensions

   The RFCs in this section are used.
      This practice prevents desirable extension and evolution still experimental, but may become
   proposed standards in the future.  At least part of the
      protocol and hence reason that
   they are still experimental is inimical to the future of the Internet.
      [RFC3360] gain more wide-scale experience
   with them before making a standards track decision.

   RFC 3449 B: 2140 I: "TCP Performance Implications of Network Path Asymmetry"
   (Dec 02)

      From abstract: "This Control Block Interdependence" (April 1997)

      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 [RFC2140] suggests how TCP performance is connections between the
      same endpoints might share information, such as their congestion
      control state.  To some degree, this is done in both
      cases: performance often degrades significantly because of
      imperfection and variability in practice by a few
      operating systems; for example, Linux has a destination cache.

      A related proposal, the ACK feedback from Congestion Manager, is specified in RFC
      3124 [RFC3124].  The idea behind the receiver Congestion Manager, moving
      congestion control outside of individual TCP connections,
      represents a modification to the sender.  The document details several mitigations to these
      effects, which core of TCP.  Although a Proposed
      Standard, some pieces of the Congestion Manager support
      architecture have either not been proposed or evaluated in the
      literature, or are currently deployed in networks." [RFC3449]

   RFC 3481 B: "TCP over Second (2.5G) specified yet, and Third (3G) Generation
   Wireless Networks" (Feb 03)

      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 3493 I: "Basic Socket Interface Extensions for IPv6" (Feb 03)

      This document describes the de facto standard sockets API for
      programming with TCP, which is implemented nearly ubiquitously in
      modern operating systems and programming languages.  [RFC3493]

4.  Experimental TCP Extensions

   These documents may one day join the standards track, but they are
   currently has not recommended for implementation. achieved
      use or implementation beyond experimental stacks.

   RFC 2861 E: "TCP Congestion Window Validation" (Jun 00)

      Decaying (June 2000)

      This document [RFC2861] suggests reducing the congestion window if it hasn't been recently
      utilized.  [RFC2861]
      over time when no packets are flowing.

   RFC 3465 E: "TCP Congestion Control with Appropriate Byte Counting
   (ABC)" (Feb 03)

      Congestion (February 2003)

      This document [RFC3465] suggests that congestion control using use the
      number of bytes acknowledged rather than the number of
      acknowledgements received.  Implemented  This has been implemented in Linux.
      [RFC3465]
      The ABC mechanism behaves differently than the standard means when
      there is not a one-to-one relationship between data segments and
      acknowledgements.  ABC still operates within the accepted
      guidelines, but is more robust to delayed ACKs and ACK-division
      [Savage].

   RFC 3522 E: "The Eifel Detection Algorithm for TCP" (Apr 03)

      Use of (April 2003)

      This document [RFC3522] suggests using timestamps to detect
      spurious timeouts.  [RFC3522]

   RFC 3540 E: "Robust Explicit Congestion Notification (ECN) signaling
   with Nonces" (Jun 03)

      Modified (June 2003)

      This document [RFC3540] suggests a modified ECN to address
      security concerns.  [RFC3540] concerns, and updates RFC 3168.

   RFC 3649 E: "HighSpeed TCP for Large Congestion Windows" (Dec 03)

      A modification to TCP's steady state (December
   2003)

      This document [RFC3649] suggests a modification to TCP's
      steady-state behavior in order to efficiently use very large windows is described in windows.

   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 document.
      information to identify unnecessary retransmissions for various
      applications." [RFC3708]

   RFC 3742 E: "Limited Slow-Start for TCP with Large Congestion
   Windows" (Mar 04) (March 2004)

      This document [RFC3742] describes a more conservative slow-start behavoir
      behavior to prevent massive amounts of loss packet losses when connections use a connection uses a
      very large
      windows.  [RFC3742]

5.  Deprecated window.

   Work in progress: Forward RTO-Recovery (F-RTO): An Algorithm for
   Detecting Spurious Retransmission Timeouts with TCP and SCTP
   (Internet Draft name: draft-ietf-tcpm-frto)

      The F-RTO detection algorithm provides another option for
      inferring spurious retransmission timeouts.  At the time of this
      writing, the TCP Maintenance and Minor Extensions Working Group
      had completed a document describing F-RTO (by Pasi Sarolahti and
      Markku Kojo), and planned to make this an Experimental part of the
      RFC series, pending IESG review.

5.  Historic Extensions

   The RFCs listed here define extensions that have thus far failed to
   arouse substantial interest, or were found to be defective.

   RFC 1106 "TCP Big Window and NAK Options" (June 1989)

      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.
      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, developed by the Consultive Committee for Space
      Data Systems (CCSDS).

   RFC 1110 "A Problem with the TCP Big Window Option" (August 1989)

      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" (Mar 90) (March 1990)

      This document [RFC1146] defined a mechanism for using more robust TCP checksums other than the
      16-bit ones-complement, which might be more robust.
      [RFC1146] ones-complement in use today.  A typographical error in RFC 1379 I "Extending TCP for Transactions -- Concepts" (Nov 92)

      See
      1145 is fixed in RFC 1644.  [RFC1379] 1146, otherwise the documents are the same.

   RFC 1644 E "T/TCP -- TCP 1263 "TCP Extensions for Transactions Considered Harmful" (October 1991)

      This interesting 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.  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, while the type of extensions RFC 1263 specifically
      targeted as harmful did become popular.

   RFC 1379 I "Extending TCP for Transactions -- Concepts" (November
   1992)

      See RFC 1644.

   RFC 1644 E "T/TCP -- TCP Extensions for Transactions Functional
   Specification" (Jul 94) (July 1994)

      The inventors of T/TCP TCP believed that cached connection state could
      be
      have been used to eliminate TCP's 3-way handshake, to support single-
      packet
      two-packet request/response exchanges.  RFCs 1379 [RFC1379] and
      1644 [RFC1644] show that
      it this is far from simple.  Furthermore,
      T/TCP floundered on the ease of denial-of-service attacks that can
      result.  [RFC1644]

   RFC 1693 E "An Extension to TCP: Partial Order Service" (Nov 94) (November
   1994)

      This document [RFC1693] defines a TCP extension for applications where
      that do not care about the order that application layer in which application-layer
      objects are received in is relatively
      unimportant, citing received.  Examples are multimedia and database applications as
      examples.
      applications.  In practice, these applications either made due with accept the mismatch
      possible performance loss because of standard TCP for their goals, TCP's strict ordering, or used other
      they use more specialized transport protocols.  [RFC1693]

6.  Case Studies and Protocol Analysis

   RFC 1337 I: "TIME-WAIT Assassination Hazards in TCP" (May 92)  Support Documents

   This document points out a problem with acting on received reset
      segments while in the TIME-WAIT state.  The main reccommendation
      is section contains several classes of documents that hosts in TIME-WAIT ignore resets.  [RFC1337]

   RFC 2415 I: "Simulation Studies do not
   necessarily define current protocol behaviors, but are nevertheless
   of Increased Initial interest to TCP Window Size"
   (Sep 98)

      Results implementors.  Section 6.1 describes several
   foundational RFCs that give modern readers a better understanding of some simulations
   the principles underlying TCP's behaviors and development over the
   years.  The documents listed in Section 6.2 provide advice on using
   TCP initial windows greater than
      1 segment are presented in this document.  The analysis indicates various types of network situations that user-perceived performance pose challenges above
   those of typical wired links.  Some implementation notes can be improved by increasing the
      initial window to 3 segments.  [RFC2415] 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 contain high-level tutorials on the protocol
   are listed Section 6.5, while Section 6.6 lists a number of case
   studies that have explored TCP performance.

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 here).

   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 acknowledgements.

   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.

   RFC 817: "Modularity and Efficiency in Protocol Implementation" (July
   1982)

      This document [RFC0817] contains implementation suggestions that
      are general and not TCP-specific.  However they have been used to
      develop TCP implementations and 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.

   RFC 964: "Some Problems with the Specification of the Military
   Standard Transmission Control Protocol" (November 1985)

      This document [RFC0964] was prepared by the US Military to define
      TCP in greater detail than RFC 793.  A few serious specification
      bugs are detailed in RFC 964, reminding us of the difficulty in
      specification writing (even when working from existing
      documents!).

   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]

   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.

   RFC 2760 I: "Ongoing TCP Research Related to Satellites" (February
   2000)

      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
      acknowledgements, slow start thresholds, NewReno and SACK-based
      loss recovery, FACK [FACK], 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.  While RFC 2488 looks at standard extensions, this
      document focuses on more experimental means of performance
      enhancement.

   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]

   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]

   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 impacted 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
   1983)

      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 2416 2525 I: "When "Known TCP Starts Up With Four Packets Into Only Three
   Buffers" (Sep 98) 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
   2002)

      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 hence is inimical to the future of
      the Internet.

   RFC 3493 I: "Basic Socket Interface Extensions for IPv6" (February
   2003)

      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
      languages.

6.4  Management Information Bases

   The first MIB module defined for use with SNMP (in RFC 1066 and its
   update, RFC 1156) was a single monolithic MIB module, called MIB-I.
   This document uses simulation results evolved over time to clear up some concerns
      about using an initial window 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 4 segments when MIB data definitions that needed to
   be included.  Thus, additional MIB modules were defined, and those
   parts of MIB-II which needed to evolve were split off.  Eventually,
   the network path remaining parts of MIB-II were also split off, with the
   TCP-specific part being documented in RFC 2012.

   RFC 2012 is the primary document for MIB-II.  MIB-I, defined in RFC
   1156, has less provisioning.  [RFC2416] been obsoleted by the MIB-II specification in RFC 2760 I: "Ongoing TCP Research Related 1213
   (updated by 2012).  Work is in progress, at the time of this writing,
   on a document that incorporates IPv6 and updates and obsoletes RFC
   2012 (currently in the form of draft-ietf-ipv6-rfc2012-update, edited
   by Rajiv Raghunarayan, under submission to Satellites" (Feb 00) the IESG as a Proposed
   Standard).

   RFC 1066: "Management Information Base for Network Management of
   TCP/IP-based Internets" (August 1988)

      This document discusses [RFC1066] was the advantages and disadvantages of
      several different experimental means description of improving the TCP performance
      over long-delay or error-prone paths.  These include: T/TCP,
      larger initial windows, byte counting, delayed acknowledgements,
      slow start thresholds, NewReno and SACK-based loss recovery, FACK
      [FACK], ECN, various corruption-detection mechanisms, congestion
      avoidance changes MIB.  It
      was obsoleted by RFC 1156.

   RFC 1156 S: "Management Information Base for fairness, use Network Management of multiple parallel flows,
      pacing, header compression, state sharing, and ACK congestion
      control, filtering,
   TCP/IP-based Internets" (May 1990)

      This document [RFC1156] describes the required MIB fields for TCP
      implementations, with minor corrections and reconstruction.  [RFC2760] no technical changes
      from RFC 2884 I: "Performance Evaluation 1066, which it obsoletes.  This is the standards track
      document for MIB-I.

   RFC 1213 S: "Management Information Base for Network Management of Explicit Congestion
   Notification (ECN) in IP Networks" (Jul 00)
   TCP/IP-based Internets: MIB-II" (March 1991)

      This document [RFC1213] describes experimental results that show some
      improvements to the performance second version of both short and long-lived
      connections due to ECN.  [RFC2884] the MIB in
      a monolithic form.  RFC 2914 B: "Congestion Control Principles" (Sep 00)

      The use of end-to-end congestion control for preventing congestion
      collapse and providing fairness to TCP is motivated by 2012 updates this
      document.  [RFC2914] document by splitting
      out the TCP-specific portions.

   RFC 2923 I: "TCP Problems with Path MTU Discovery" (Sep 00)

      From abstract: "This memo catalogs several known 2012 S: "SNMPv2 Management Information Base for the Transmission
   Control Protocol (TCP) implementation problems dealing with Path
      Maximum Transmission Unit Discovery (PMTUD), including using SMIv2" (November 1996)

      This document [RFC2012] defines 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] TCP MIB, updating RFC 2963 I: "A Rate Adaptive Shaper 1213.

   RFC 2452 S: "IP Version 6 Management Information Base for Differentiated Services" (Oct
   2000) the
   Transmission Control Protocol" (December 1998)

      This document describes how TCP performance can be improved in
      diffserv networks using rate adaptive shapers and color markers.
      [RFC2963] [RFC2452] augments RFC 3135 I: "Performance Enhancing Proxies Intended to Mitigate
   Link-Related Degradations" (Jun 01)

      From abstract: "This document 2012 by adding an
      IPv6-specific connection table.  The rest of 2012 holds for any IP
      version.

      Although it is a survey of Performance Enhancing
      Proxies (PEPs) often employed to improve degraded TCP performance
      caused standards track document, RFC 2452 is considered
      a historic mistake by characteristics the MIB community, as it is based on the
      idea of specific link environments, for
      example, in satellite, wireless WAN, parallel IPv4 and wireless LAN
      environments.  Different types of Performance Enhancing Proxies
      are described as well as IPv6 structures.  Although IPv6 requires
      new structures, the mechanisms used community has decided to improve
      performance."  [RFC3135]

7. define a single
      generic structure for both IPv4 and IPv6.  This will aid in
      definition, implementation, and transition between IPv4 and IPv6.

6.5  Tools and Tutorials
   RFC 1180 I: "TCP/IP Tutorial" (Jan 91) (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.  [RFC1180]

   RFC 1470 I: "FYI on a Network Management Tool Catalog: Tools for
   Monitoring and Debugging TCP/IP Internets and Interconnected Devices"
   (Jun 93)
   (June 1993)

      A few of the tools that this document [RFC1470] describes are
      still maintained and in use today, such as for example ttcp and tcpdump, however, tcpdump.
      However, many of the tools described do not related relate specifically to
      TCP and are no longer used or easily available.  [RFC1470]

   RFC 2398 I: "Some Testing Tools for TCP Implementors" (Aug 98)

      A number of TCP packet generation and analysis tools are described
      in this document.  While some of these tools are no longer readily
      available or widely used, for the most part they are still
      relevant and useable.  [RFC2398]

8.  Historical

   The documents listed in this section contain information that is
   largely duplicated by the standards documents in Section 2, however
   some of them contain a greater depth of problem statement
   explanation, or other historical context.

   RFC 813: "Window and Acknowledgement Strategy in TCP" (July 82) (August 1998)

      This document contains an early discussion of Silly Window
      Syndrome and its avoidance, and motivates and  [RFC2398] describes the use of
      delayed acknowledgements.  [RFC0813]

   RFC 817: "Modularity and Efficiency in Protocol Implementation" (July
   82)

      The suggestions for implementation in this document are general
      and not TCP-specific, however they have been used to develop TCP
      implementations and describe some performance implications of the
      interactions between various layers in the Internet stack.
      [RFC0817]

   RFC 876: "The TCP Maximum Segment Size and Related Topics" (Nov 83)

      Abstract: This memo discusses the TCP Maximum Segment Size Option
      and related topics.  The purposes is to clarify some aspects a number of TCP packet
      generation and its interaction with IP.  This memo is a clarification to analysis tools.  While some of these tools are no
      longer readily available or widely used, for the TCP specification, most part they
      are still relevant and contains information that may be
      considered as "advice to implementers".  [RFC0876] useable.

6.6  Case Studies

   RFC 896: "Congestion Control 1337 I: "TIME-WAIT Assassination Hazards in IP/TCP Internetworks" (Jan 84) TCP" (May 1992)

      This document contains some early experiences [RFC1337] points out a problem with congestion
      collapse and some initial thoughts acting on how to avoid it using
      congestion control
      received reset segments while in TCP.  [RFC0896]

   RFC 964: "Some Problems with the Specification of the Military
   Standard Transmission Control Protocol" (Nov 85) TIME-WAIT state.  The US Military wrote their own document defining TCP in addition
      to RFC 793.  A few serious specification bugs are detailed in RFC
      964, reminding us of the difficulty main
      recemmendation is that hosts in specification writing (even
      when working from existing documents!).  [RFC0964] TIME-WAIT ignore resets.

   RFC 1066: "Management Information Base for Network Management 2415 I: "Simulation Studies of
   TCP/IP-based Internets" (Aug 88) Increased Initial TCP Window Size"
   (September 1998)

      This was the first document describing the TCP MIB.  It is
      obsoleted by RFC 1156.  [RFC1066]

   RFC 1072: "TCP Extensions for Long-Delay Paths" (Oct 88)

      Early explanations [RFC2415] presents results of the mechanisms some simulations using
      TCP initial windows greater than 1 segment.  The analysis
      indicates that were later described user-perceived performance can be improved by
      RFCs 1323 and 2018 are found in this document.  [RFC1072]
      increasing the initial window to 3 segments.

   RFC 1185: "TCP Extension for High-Speed Paths" (Oct 90)

      More advanced strategies for dealing with sequence number wrapping
      and detecting duplicates from earlier connections are outlined in
      this 2416 I: "When TCP Starts Up With Four Packets Into Only Three
   Buffers" (September 1998)

      This document that builds on RFC 1072.  [RFC1185] [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 1213 S: "Management Information Base for Network Management 2884 I: "Performance Evaluation of
   TCP/IP-based Internets: MIB-II" (Mar 91) Explicit Congestion
   Notification (ECN) in IP Networks" (July 2000)

      This document [RFC2884] describes experimental results that show
      some improvements to the second version performance of the MIB in a
      monolithic form.  RFC 2012 updates this document, by splitting out
      the TCP-specific portions.  [RFC1213]

9. both short and long-lived
      connections due to ECN.

7.  Security Considerations

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

10.

8.  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.  We thank Joe Touch and Touch, Reiner Ludwig Ludwig, and Pekka Savola 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.

11.

9.  References

11.1  Core Specification

9.1  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.

   [RFC1156]  McCloghrie, K.

   [RFC2147]  Borman, D., "TCP and M. Rose, "Management Information Base
              for network management of TCP/IP-based internets", UDP over IPv6 Jumbograms", RFC
              1156, 2147,
              May 1990. 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC2581]  Allman, M., Paxson, V. and W. Stevens, "TCP Congestion
              Control", RFC 2581, April 1999.

   [RFC2873]  Xiao, X., Hannan, A., Paxson, V. and E. Crabbe, "TCP
              Processing of the IPv4 Precedence Field", RFC 2873, June
              2000.

   [RFC2988]  Paxson, V. and M. Allman, "Computing TCP's Retransmission
              Timer", RFC 2988, November 2000.

9.2  Standard Enhancements

   [RFC1323]  Jacobson, V., Braden, B. and D. Borman, "TCP Extensions
              for High Performance", RFC 1323, May 1992.

   [RFC2012]  McCloghrie, K., "SNMPv2 Management Information Base for
              the Transmission Control Protocol using SMIv2",

   [RFC1948]  Bellovin, S., "Defending Against Sequence Number Attacks",
              RFC 2012,
              November 1948, May 1996.

   [RFC2018]  Mathis, M., Mahdavi, J., Floyd, S. and A. Romanow, "TCP
              Selective Acknowledgment Options", RFC 2018, October 1996.

   [RFC2452]  Daniele, M., "IP Version 6 Management Information Base for
              the Transmission Control Protocol", RFC 2452, December
              1998.

   [RFC2581]  Allman, M., Paxson, V. and W. Stevens, and A. Romanow, "TCP Congestion
              Control",
              Selective Acknowledgment Options", RFC 2581, April 1999.

   [RFC2873]  Xiao, X., Hannan, 2018, October 1996.

   [RFC2385]  Heffernan, A., Paxson, V. and E. Crabbe, "TCP
              Processing "Protection of BGP Sessions via the IPv4 Precedence Field", TCP MD5
              Signature Option", RFC 2873, June
              2000. 2385, August 1998.

   [RFC2883]  Floyd, S., Mahdavi, J., Mathis, M. and M. Podolsky, "An
              Extension to the Selective Acknowledgement (SACK) Option
              for TCP", RFC 2883, July 2000.

   [RFC2988]  Paxson, V. and M. Allman, "Computing TCP's Retransmission
              Timer", RFC 2988, November 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.

11.2  Special Cases and Implementation Hints

   [RFC1144]  Jacobson, V., "Compressing TCP/IP headers for low-speed
              serial links", RFC 1144, February 1990.

   [RFC1948]  Bellovin, S., "Defending Against Sequence Number Attacks",
              RFC 1948, May 1996.

9.3  Experimental Extensions

   [RFC2140]  Touch, J., "TCP Control Block Interdependence", RFC 2140,
              April 1997.

   [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., Dawson, S., Fenner, W., Griner, J., Heavens,
              I., Lahey, K., Semke, J. and B. Volz, "Known TCP
              Implementation Problems", RFC 2525, March 1999.

   [RFC3360]  Floyd, S., "Inappropriate TCP Resets Considered Harmful",
              BCP 60, RFC 3360, 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
              2003.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J. and W.
              Stevens, "Basic Socket Interface Extensions for IPv6", RFC
              3493, February 2003.

11.3  Experimental TCP Extensions

   [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.

   [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.

11.4  Deprecated

9.4  Historic Extensions

   [RFC1106]  Fox, R., "TCP big window and NAK options", RFC 1106, June
              1989.

   [RFC1110]  McKenzie, A., "Problem with the TCP Extensions 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, B., "Extending TCP for Transactions -- Concepts",
              RFC 1379, November 1992.

   [RFC1644]  Braden, B., "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.

11.5  Case Studies

9.5  Support Documents

   [RFC0813]  Clark, D., "Window and Protocol Analysis 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
              1982.

   [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.

   [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.

   [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, B., "TIME-WAIT Assassination Hazards in TCP", RFC
              1337, May 1992.
              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", RFC 1470, June
              1993.

   [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., "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.

   [RFC2452]  Daniele, M., "IP Version 6 Management Information Base for
              the Transmission Control Protocol", RFC 2452, December
              1998.

   [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.

   [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.

   [RFC2963]  Bonaventure, O. and S. De Cnodder, "A Rate Adaptive Shaper
              for Differentiated Services", RFC 2963, October 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.

11.6  Tools and Tutorials

   [RFC1180]  Socolofsky, T. and C. Kale, "TCP/IP tutorial", RFC 1180,
              January 1991.

   [RFC1470]  Enger, R. and J. Reynolds, "FYI on a Network Management
              Tool Catalog: Tools for Monitoring and Debugging TCP/IP
              Internets and Interconnected Devices", RFC 1470, June
              1993.

   [RFC2151]  Kessler, G. and S. Shepard, "A Primer On Internet and
              TCP/IP Tools and Utilities", RFC 2151, June 1997.

   [RFC2398]  Parker, S. and C. Schmechel, "Some Testing Tools for TCP
              Implementors", RFC 2398, August 1998.

11.7  Historical

   [RFC0813]  Clark, D., "Window and Acknowledgement Strategy in TCP",
              RFC 813, July 1982.

   [RFC0817]  Clark, D., "Modularity and efficiency Notification (ECN) in protocol
              implementation", IP Networks",
              RFC 817, 2884, July 1982.

   [RFC0876]  Smallberg, D., "Survey of SMTP implementations", 2000.

   [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41, RFC 876,
              2914, September 1983.

   [RFC0896]  Nagle, J., "Congestion control in IP/TCP internetworks", 2000.

   [RFC2923]  Lahey, K., "TCP Problems with Path MTU Discovery", RFC 896, January 1984.

   [RFC0964]  Sidhu, D.
              2923, September 2000.

   [RFC3135]  Border, J., Kojo, M., Griner, J., Montenegro, G. and T. Blumer, "Some problems with the
              specification of the Military Standard Transmission
              Control Protocol", Z.
              Shelby, "Performance Enhancing Proxies Intended to
              Mitigate Link-Related Degradations", RFC 964, November 1985.

   [RFC1066]  McCloghrie, K. 3135, June 2001.

   [RFC3360]  Floyd, S., "Inappropriate TCP Resets Considered Harmful",
              BCP 60, RFC 3360, August 2002.

   [RFC3449]  Balakrishnan, H., Padmanabhan, V., Fairhurst, G. and M. Rose, "Management Information Base
              for network management
              Sooriyabandara, "TCP Performance Implications of TCP/IP-based internets", Network
              Path Asymmetry", BCP 69, RFC
              1066, August 1988.

   [RFC1072]  Jacobson, V. 3449, December 2002.

   [RFC3481]  Inamura, H., Montenegro, G., Ludwig, R., Gurtov, A. and R. Braden, F.
              Khafizov, "TCP extensions for long-delay
              paths", over Second (2.5G) and Third (3G)
              Generation Wireless Networks", BCP 71, RFC 1072, October 1988.

   [RFC1185]  Jacobson, V., Braden, B. 3481, February
              2003.

   [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J. and L. Zhang, "TCP Extension W.
              Stevens, "Basic Socket Interface Extensions for
              High-Speed Paths", IPv6", RFC 1185, October 1990.

   [RFC1213]  McCloghrie, K.
              3493, February 2003.

   [RFC3819]  Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
              Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J. and M. Rose, "Management Information Base L.
              Wood, "Advice for Network Management of TCP/IP-based internets:MIB-II",
              STD 17, Internet Subnetwork Designers", BCP 89,
              RFC 1213, March 1991.

11.8 3819, July 2004.

9.6  Informative References Ouside Outside the RFC Series

   [FACK]    Mathis, M. and J. Mahdavi, "Forward Acknowledgement:
             Refining TCP Congestion Control", ACM SIGCOMM, August 1996.

   [karn]

   [Karn]    Karn, P. and C. Partridge, "Round Trip Time Estimation",
             ACM SIGCOMM, August 1987.

   [vj88]

   [Savage]  Savage, S., Cardwell, N., Wetherall, D. and T. Anderson,
             "TCP Congestion Control with a Misbehaving Receiver", ACM
             Computer Communication Review 29 (5), October 1999.

   [VJ88]    Jacobson, V., "Congestion Avoidance and Control", ACM
             SIGCOMM, August 1988.

Authors' Addresses

   Martin Duke
   Boeing Phantom Works
   PO Box 3707, MC 3W-51
   Seattle, WA  98124-2207

   Phone: 253-657-8203
   EMail: mduke26@comcast.net

   Robert Braden
   USC Information Sciences Institute
   Marina del Rey, CA  90292-6695

   Phone: 310-448-9173
   EMail: braden@isi.edu

   Wesley M. Eddy
   NASA GRC/Verizon FNS

   EMail: weddy@grc.nasa.gov
   Ethan Blanton
   Purdue University

   EMail: eblanton@cs.purdue.edu

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