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A Survey of Lower-than-Best-Effort Transport Protocols
RFC 6297

Internet Engineering Task Force (IETF)                          M. Welzl
Request for Comments: 6297                            University of Oslo
Category: Informational                                           D. Ros
ISSN: 2070-1721                                    IT / Telecom Bretagne
                                                               June 2011

         A Survey of Lower-than-Best-Effort Transport Protocols

Abstract

   This document provides a survey of transport protocols that are
   designed to have a smaller bandwidth and/or delay impact on standard
   TCP than standard TCP itself when they share a bottleneck with it.
   Such protocols could be used for delay-insensitive "background"
   traffic, as they provide what is sometimes called a "less than" (or
   "lower than") best-effort service.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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/rfc6297.

Copyright Notice

   Copyright (c) 2011 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.

Welzl & Ros                   Informational                     [Page 1]
RFC 6297                  LBE Transport Survey                 June 2011

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Delay-Based Transport Protocols  . . . . . . . . . . . . . . .  3
     2.1.  Accuracy of Delay-Based Congestion Predictors  . . . . . .  6
     2.2.  Potential Issues with Delay-Based Congestion Control
           for LBE Transport  . . . . . . . . . . . . . . . . . . . .  7
   3.  Non-Delay-Based Transport Protocols  . . . . . . . . . . . . .  8
   4.  Upper-Layer Approaches . . . . . . . . . . . . . . . . . . . .  8
     4.1.  Receiver-Oriented, Flow-Control-Based Approaches . . . . .  9
   5.  Network-Assisted Approaches  . . . . . . . . . . . . . . . . . 10
   6.  LEDBAT Considerations  . . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 12

1.  Introduction

   This document presents a brief survey of proposals to attain a Less-
   than-Best-Effort (LBE) service by means of end-host mechanisms.  We
   loosely define an LBE service as a service which results in smaller
   bandwidth and/or delay impact on standard TCP than standard TCP
   itself, when sharing a bottleneck with it.  We refer to systems that
   are designed to provide this service as LBE systems.  With the
   exception of TCP Vegas, which we present for historical reasons, we
   exclude systems that have been noted to exhibit LBE behavior under
   some circumstances but were not designed for this purpose (e.g.,
   RAPID [Kon09]).

   Generally, LBE behavior can be achieved by reacting to queue growth
   earlier than standard TCP would or by changing the congestion-
   avoidance behavior of TCP without utilizing any additional implicit
   feedback.  It is therefore assumed that readers are familiar with TCP
   congestion control [RFC5681].  Some mechanisms achieve an LBE
   behavior without modifying transport-protocol standards (e.g., by
   changing the receiver window of standard TCP), whereas others
   leverage network-level mechanisms at the transport layer for LBE
   purposes.  According to this classification, solutions have been
   categorized in this document as delay-based transport protocols, non-
   delay-based transport protocols, upper-layer approaches, and network-
   assisted approaches.  Some of the schemes in the first two categories

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