CUBIC for Fast Long-Distance Networks
RFC 8312

Document Type RFC - Informational (February 2018; Errata)
Last updated 2019-11-15
Replaces draft-zimmermann-tcpm-cubic
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd Yoshifumi Nishida
Shepherd write-up Show (last changed 2017-09-04)
IESG IESG state RFC 8312 (Informational)
Consensus Boilerplate Yes
Telechat date
Responsible AD Mirja K├╝hlewind
Send notices to Yoshifumi Nishida <nishida@sfc.wide.ad.jp>
IANA IANA review state Version Changed - Review Needed
IANA action state No IANA Actions
Internet Engineering Task Force (IETF)                           I. Rhee
Request for Comments: 8312                                          NCSU
Category: Informational                                            L. Xu
ISSN: 2070-1721                                                      UNL
                                                                   S. Ha
                                                                Colorado
                                                           A. Zimmermann

                                                               L. Eggert
                                                        R. Scheffenegger
                                                                  NetApp
                                                           February 2018

                 CUBIC for Fast Long-Distance Networks

Abstract

   CUBIC is an extension to the current TCP standards.  It differs from
   the current TCP standards only in the congestion control algorithm on
   the sender side.  In particular, it uses a cubic function instead of
   a linear window increase function of the current TCP standards to
   improve scalability and stability under fast and long-distance
   networks.  CUBIC and its predecessor algorithm have been adopted as
   defaults by Linux and have been used for many years.  This document
   provides a specification of CUBIC to enable third-party
   implementations and to solicit community feedback through
   experimentation on the performance of CUBIC.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8312.

Rhee, et al.                  Informational                     [Page 1]
RFC 8312                          CUBIC                    February 2018

Copyright Notice

   Copyright (c) 2018 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
   (https://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. Conventions .....................................................3
   3. Design Principles of CUBIC ......................................4
   4. CUBIC Congestion Control ........................................6
      4.1. Window Increase Function ...................................6
      4.2. TCP-Friendly Region ........................................7
      4.3. Concave Region .............................................8
      4.4. Convex Region ..............................................8
      4.5. Multiplicative Decrease ....................................8
      4.6. Fast Convergence ...........................................9
      4.7. Timeout ...................................................10
      4.8. Slow Start ................................................10
   5. Discussion .....................................................10
      5.1. Fairness to Standard TCP ..................................11
      5.2. Using Spare Capacity ......................................13
      5.3. Difficult Environments ....................................13
      5.4. Investigating a Range of Environments .....................13
      5.5. Protection against Congestion Collapse ....................14
      5.6. Fairness within the Alternative Congestion Control
           Algorithm .................................................14
      5.7. Performance with Misbehaving Nodes and Outside Attackers ..14
      5.8. Behavior for Application-Limited Flows ....................14
      5.9. Responses to Sudden or Transient Events ...................14
      5.10. Incremental Deployment ...................................14
   6. Security Considerations ........................................15
   7. IANA Considerations ............................................15
   8. References .....................................................15
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