RFC 3522 (rfc3522) - Page 1 of 14

The Eifel Detection Algorithm for TCP

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Network Working Group                                          R. Ludwig
Request for Comments: 3522                                      M. Meyer
Category: Experimental                                 Ericsson Research
                                                              April 2003

                 The Eifel Detection Algorithm for TCP

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.


   The Eifel detection algorithm allows a TCP sender to detect a
   posteriori whether it has entered loss recovery unnecessarily.  It
   requires that the TCP Timestamps option defined in RFC 1323 be
   enabled for a connection.  The Eifel detection algorithm makes use of
   the fact that the TCP Timestamps option eliminates the retransmission
   ambiguity in TCP.  Based on the timestamp of the first acceptable ACK
   that arrives during loss recovery, it decides whether loss recovery
   was entered unnecessarily.  The Eifel detection algorithm provides a
   basis for future TCP enhancements.  This includes response algorithms
   to back out of loss recovery by restoring a TCP sender's congestion
   control state.


   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [RFC 2119].

   We refer to the first-time transmission of an octet as the 'original
   transmit'.  A subsequent transmission of the same octet is referred
   to as a 'retransmit'.  In most cases, this terminology can likewise
   be applied to data segments as opposed to octets.  However, with
   repacketization, a segment can contain both first-time transmissions
   and retransmissions of octets.  In that case, this terminology is
   only consistent when applied to octets.  For the Eifel detection
   algorithm, this makes no difference as it also operates correctly
   when repacketization occurs.

Ludwig & Meyer                Experimental

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