Sender RTT Estimate Option for the Datagram Congestion Control Protocol (DCCP)
RFC 6323

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Internet Engineering Task Force (IETF)                         G. Renker
Request for Comments: 6323                                  G. Fairhurst
Updates: 4342, 5622                               University of Aberdeen
Category: Standards Track                                      July 2011
ISSN: 2070-1721

                       Sender RTT Estimate Option
          for the Datagram Congestion Control Protocol (DCCP)

Abstract

   This document specifies an update to the round-trip time (RTT)
   estimation algorithm used for TFRC (TCP-Friendly Rate Control)
   congestion control by the Datagram Congestion Control Protocol
   (DCCP).  It updates specifications for the CCID-3 and CCID-4
   Congestion Control IDs of DCCP.

   The update addresses parameter-estimation problems occurring with
   TFRC-based DCCP congestion control.  It uses a recommendation made in
   the original TFRC specification to avoid the inherent problems of
   receiver-based RTT sampling, by utilising higher-accuracy RTT samples
   already available at the sender.

   It is integrated into the feature set of DCCP as an end-to-end
   negotiable extension.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in 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/rfc6323.

Renker & Fairhurst           Standards Track                    [Page 1]
RFC 6323           Sender RTT Estimate Option for DCCP         July 2011

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.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Problems Caused by Sampling the RTT at the Receiver  . . . . .  4
     2.1.  List of Problems Encountered with a Real Implementation  .  4
     2.2.  Other Areas Affected by the RTT Sampling Problems  . . . .  5
       2.2.1.  Measured Receive Rate X_recv . . . . . . . . . . . . .  6
       2.2.2.  Disambiguation and Accuracy of Loss Intervals  . . . .  6
       2.2.3.  Determining Quiescence . . . . . . . . . . . . . . . .  6
       2.2.4.  Practical Considerations . . . . . . . . . . . . . . .  7
   3.  Specification  . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  7
     3.2.  Options and Features . . . . . . . . . . . . . . . . . . .  7
       3.2.1.  RTT Estimate Option  . . . . . . . . . . . . . . . . .  7
       3.2.2.  Send RTT Estimate Feature  . . . . . . . . . . . . . .  9
     3.3.  Basic Usage  . . . . . . . . . . . . . . . . . . . . . . .  9
     3.4.  Receiver Robustness Measures . . . . . . . . . . . . . . . 10
   4.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  Option Types . . . . . . . . . . . . . . . . . . . . . . . 11
     5.2.  Feature Numbers  . . . . . . . . . . . . . . . . . . . . . 12
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 12

Renker & Fairhurst           Standards Track                    [Page 2]
RFC 6323           Sender RTT Estimate Option for DCCP         July 2011

1.  Introduction

   The Datagram Congestion Control Protocol (DCCP) [RFC4340] is a
   transport protocol for connection-oriented, unreliable, and
   congestion-controlled datagram delivery.  In DCCP, an application has
   a choice of congestion control mechanisms, each specified by a
   Congestion Control Identifier (CCID; [RFC4340], Section 10).

   This document defines a Standards-Track update to the sender and
   receiver sides of two rate-based DCCP congestion control IDs: CCID-3
   [RFC4342] and the Experimental CCID-4 variant [RFC5622].

   Both CCIDs are based on the principles of TCP-Friendly Rate Control
   (TFRC) [RFC5348], which performs rate-based congestion control.  Its