SACK-IMMEDIATELY Extension for the Stream Control Transmission Protocol
RFC 7053

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Internet Engineering Task Force (IETF)                         M. Tuexen
Request for Comments: 7053                                  I. Ruengeler
Updates: 4960                           Muenster Univ. of Appl. Sciences
Category: Standards Track                                     R. Stewart
ISSN: 2070-1721                                           Adara Networks
                                                           November 2013

                     SACK-IMMEDIATELY Extension for
                the Stream Control Transmission Protocol

Abstract

   This document updates RFC 4960 by defining a method for the sender of
   a DATA chunk to indicate that the corresponding Selective
   Acknowledgment (SACK) chunk should be sent back immediately and
   should not be delayed.  It is done by specifying a bit in the DATA
   chunk header, called the (I)mmediate bit, which can get set by either
   the Stream Control Transmission Protocol (SCTP) implementation or the
   application using an SCTP stack.  Since unknown flags in chunk
   headers are ignored by SCTP implementations, this extension does not
   introduce any interoperability problems.

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/rfc7053.

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RFC 7053                    SACK-IMMEDIATELY               November 2013

Copyright Notice

   Copyright (c) 2013 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  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  The (I)mmediate Bit in the DATA Chunk Header  . . . . . . . . . 3
   4.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  Triggering at the Application Level . . . . . . . . . . . . 4
     4.2.  Triggering at the SCTP Level  . . . . . . . . . . . . . . . 4
   5.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     5.1.  Sender-Side Considerations  . . . . . . . . . . . . . . . . 5
     5.2.  Receiver Side Considerations  . . . . . . . . . . . . . . . 5
   6.  Interoperability Considerations . . . . . . . . . . . . . . . . 5
   7.  Socket API Considerations . . . . . . . . . . . . . . . . . . . 5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     11.1. Normative References  . . . . . . . . . . . . . . . . . . . 7
     11.2. Informative References  . . . . . . . . . . . . . . . . . . 7

1.  Introduction

   According to [RFC4960], the receiver of a DATA chunk should use
   delayed SACKs.  This delay is completely controlled by the receiver
   of the DATA chunk and remains the default behavior.

   In specific situations, the delaying of SACKs results in reduced
   performance of the protocol:

   1.  If such a situation can be detected by the receiver, the
       corresponding SACK can be sent immediately.  For example,
       [RFC4960] recommends immediately sending the SACK if the receiver
       has detected message loss or message duplication.

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RFC 7053                    SACK-IMMEDIATELY               November 2013

   2.  However, if the situation can only be detected by the sender of
       the DATA chunk, [RFC4960] provides no method of avoiding a delay
       in sending the SACK.  Examples of these situations include ones
       that require interaction with the application (e.g., applications
       using the SCTP_SENDER_DRY_EVENT, see Section 4.1) and ones that
       can be detected by the SCTP stack itself (e.g., closing the