Low Extra Delay Background Transport (LEDBAT)
RFC 6817
Internet Engineering Task Force (IETF) S. Shalunov
Request for Comments: 6817 G. Hazel
Category: Experimental BitTorrent, Inc.
ISSN: 2070-1721 J. Iyengar
Franklin and Marshall College
M. Kuehlewind
University of Stuttgart
December 2012
Low Extra Delay Background Transport (LEDBAT)
Abstract
Low Extra Delay Background Transport (LEDBAT) is an experimental
delay-based congestion control algorithm that seeks to utilize the
available bandwidth on an end-to-end path while limiting the
consequent increase in queueing delay on that path. LEDBAT uses
changes in one-way delay measurements to limit congestion that the
flow itself induces in the network. LEDBAT is designed for use by
background bulk-transfer applications to be no more aggressive than
standard TCP congestion control (as specified in RFC 5681) and to
yield in the presence of competing flows, thus limiting interference
with the network performance of competing flows.
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/rfc6817.
Shalunov, et al. Experimental [Page 1]
RFC 6817 LEDBAT December 2012
Copyright Notice
Copyright (c) 2012 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
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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.
Shalunov, et al. Experimental [Page 2]
RFC 6817 LEDBAT December 2012
Table of Contents
1. Introduction ....................................................4
1.1. Requirements Notation ......................................4
1.2. Design Goals ...............................................4
1.3. Applicability ..............................................5
2. LEDBAT Congestion Control .......................................6
2.1. Overview ...................................................6
2.2. Preliminaries ..............................................6
2.3. Receiver-Side Operation ....................................7
2.4. Sender-Side Operation ......................................7
2.4.1. An Overview .........................................7
2.4.2. The Complete Sender Algorithm .......................8
2.5. Parameter Values ..........................................11
3. Understanding LEDBAT Mechanisms ................................13
3.1. Delay Estimation ..........................................13
3.1.1. Estimating Base Delay ..............................13
3.1.2. Estimating Queueing Delay ..........................13
3.2. Managing the Congestion Window ............................14
3.2.1. Window Increase: Probing for More Bandwidth ........14
3.2.2. Window Decrease: Responding to Congestion ..........14
3.3. Choosing the Queuing Delay Target .........................15
4. Discussion .....................................................15
4.1. Framing and ACK Frequency Considerations ..................15
4.2. Competing with TCP Flows ..................................15
4.3. Competing with Non-TCP Flows ..............................16
4.4. Fairness among LEDBAT Flows ...............................16
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