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TCP and Stream Control Transmission Protocol (SCTP) RTO Restart (RFC7765) Disclosure Number: IPCOM000245136D
Original Publication Date: 2016-Feb-01
Included in the Prior Art Database: 2016-Feb-12
Document File: 30 page(s) / 35K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

P. Hurtig: AUTHOR [+3]


TCP and SCTP use two almost identical mechanisms to detect and recover from data loss, specified in [RFC6298] and [RFC5681] for TCP and [RFC4960] for SCTP. First, if transmitted data is not acknowledged within a certain amount of time, a retransmission timeout (RTO) occurs and the data is retransmitted. While the RTO is based on measured round-trip times (RTTs) between the sender and receiver, it also has a conservative lower bound of 1 second to ensure that delayed data are not mistaken as lost. Second, when a sender receives duplicate acknowledgments or similar information via selective acknowledgments, the fast retransmit algorithm suspects data loss and can trigger a retransmission. Duplicate (and selective) acknowledgments are generated by a receiver when data arrives out of order. As both data loss and data reordering cause out-of-order arrival, fast retransmit waits for three out-of-order notifications before considering the corresponding data as lost. In some situations, however, the amount of outstanding data is not enough to trigger three such acknowledgments, and the sender must rely on lengthy RTOs for loss recovery.

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Internet Engineering Task Force (IETF)                         P. Hurtig Request for Comments: 7765                                  A. Brunstrom Category: Experimental                               Karlstad University ISSN: 2070-1721                                               A. Petlund                                            Simula Research Laboratory AS                                                                 M. Welzl                                                       University of Oslo                                                            February 2016

     TCP and Stream Control Transmission Protocol (SCTP) RTO Restart


   This document describes a modified sender-side algorithm for managing    the TCP and Stream Control Transmission Protocol (SCTP)    retransmission timers that provides faster loss recovery when there    is a small amount of outstanding data for a connection.  The    modification, RTO Restart (RTOR), allows the transport to restart its    retransmission timer using a smaller timeout duration, so that the    effective retransmission timeout (RTO) becomes more aggressive in    situations where fast retransmit cannot be used.  This enables faster    loss detection and recovery for connections that are short lived or    application limited.

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

Hurtig, et al.                Experimental                      [Page 1]
 RFC 7765                TCP and SCTP RTO Restart           February 2016

 Copyright Notice

   Copyright (c) 2016 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  ...