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
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document authors. All rights reserved.
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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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