TCP and Stream Control Transmission Protocol (SCTP) RTO Restart
RFC 7765

Approval announcement
Draft of message to be sent after approval:

From: The IESG <>
To: "IETF-Announce" <>
Cc:,,,, "The IESG" <>,,
Subject: Document Action: 'TCP and SCTP RTO Restart' to Experimental RFC (draft-ietf-tcpm-rtorestart-10.txt)

The IESG has approved the following document:
- 'TCP and SCTP RTO Restart'
  (draft-ietf-tcpm-rtorestart-10.txt) as Experimental RFC

This document is the product of the TCP Maintenance and Minor Extensions
Working Group.

The IESG contact persons are Spencer Dawkins and Martin Stiemerling.

A URL of this Internet Draft is:

Technical Summary

This document describes a modified sender-side algorithm for managing 
the TCP and 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 so that the effective 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.

Working Group Summary

It is the consensus of the TCPM working group to document this 
alternative algorithm, given the potential performance benefit. The work 
has mostly been driven by the authors, but the document has been 
reviewed in detail by several experts and the content has been modified 
accordingly. Performance experiments in simulations and testbeds have 
been performed and published by the authors and the experimental results 
have been reviewed in several TCPM meetings. At the time of writing, 
there is only limited deployment experience. 

Two issues have been discussed extensively in the working group. First, 
any reduction of the retransmission timeout duration inherently comes 
along with a risk of negative impact on TCP performance, e.g. in mobile 
networks with highly variable RTT. The current understanding is that 
this risk is low and that the algorithm is conservative and relatively 
robust, but further experimentation has to confirm this. Second, the 
Linux operation system uses the "Tail Loss Probe" method discussed in 
Section 6, which is similar but more complex. This method was not 
adopted in TCPM since it depends on FACK error recovery method, which 
has not been standardizes so far.

Document Quality

This document was also last called in TSVWG, since it specifies an 
algorithm that can be applied both to TCP and SCTP. As a result of WGLC 
comments the applicability to SCTP has been better explained, including 
the SCTP API. One issue is that TCP and SCTP use slightly different 
terminology for comparable concepts. In order to keep the document 
simple, it was decided not to add another, duplicated description of the 
algorithm using SCTP terminology.


The document shepherd is Michael Scharf <michael.scharf@alcatel->. The responsible Area Director is Martin Stiemerling