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Making TCP More Robust to Long Connectivity Disruptions (TCP-LCD)
RFC 6069

Document type: RFC - Experimental (December 2010; No errata)
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 6069 (Experimental)
Responsible AD: Lars Eggert
Send notices to: tcpm-chairs@tools.ietf.org, draft-ietf-tcpm-tcp-lcd@tools.ietf.org

Internet Engineering Task Force (IETF)                     A. Zimmermann
Request for Comments: 6069                                  A. Hannemann
Category: Experimental                            RWTH Aachen University
ISSN: 2070-1721                                            December 2010

   Making TCP More Robust to Long Connectivity Disruptions (TCP-LCD)

Abstract

   Disruptions in end-to-end path connectivity, which last longer than
   one retransmission timeout, cause suboptimal TCP performance.  The
   reason for this performance degradation is that TCP interprets
   segment loss induced by long connectivity disruptions as a sign of
   congestion, resulting in repeated retransmission timer backoffs.
   This, in turn, leads to a delayed detection of the re-establishment
   of the connection since TCP waits for the next retransmission timeout
   before it attempts a retransmission.

   This document proposes an algorithm to make TCP more robust to long
   connectivity disruptions (TCP-LCD).  It describes how standard ICMP
   messages can be exploited during timeout-based loss recovery to
   disambiguate true congestion loss from non-congestion loss caused by
   connectivity disruptions.  Moreover, a reversion strategy of the
   retransmission timer is specified that enables a more prompt
   detection of whether or not the connectivity to a previously
   disconnected peer node has been restored.  TCP-LCD is a TCP sender-
   only modification that effectively improves TCP performance in the
   case of connectivity disruptions.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This document is a product of the Internet Engineering
   Task Force (IETF).  It represents the consensus of the IETF
   community.  It has received public review and has been approved for
   publication by the Internet Engineering Steering Group (IESG).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6069.

Zimmermann & Hannemann        Experimental                      [Page 1]
RFC 6069             Making TCP More Robust to LCDs        December 2010

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Connectivity Disruption Indication ..............................5
   4. Connectivity Disruption Reaction ................................7
      4.1. Basic Idea .................................................7
      4.2. Algorithm Details ..........................................8
   5. Discussion of TCP-LCD ..........................................11
      5.1. Retransmission Ambiguity ..................................12
      5.2. Wrapped Sequence Numbers ..................................12
      5.3. Packet Duplication ........................................13
      5.4. Probing Frequency .........................................14
      5.5. Reaction during Connection Establishment ..................14
      5.6. Reaction in Steady-State ..................................14
   6. Dissolving Ambiguity Issues Using the TCP Timestamps Option ....15
   7. Interoperability Issues ........................................17
      7.1. Detection of TCP Connection Failures ......................17
      7.2. Explicit Congestion Notification (ECN) ....................17
      7.3. TCP-LCD and IP Tunnels ....................................17
   8. Related Work ...................................................18
   9. Security Considerations ........................................19
   10. Acknowledgments ...............................................20
   11. References ....................................................20
      11.1. Normative References .....................................20

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