[tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-15.txt

internet-drafts@ietf.org Mon, 12 July 2021 21:48 UTC

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Subject: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-15.txt
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A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the TCP Maintenance and Minor Extensions WG of the IETF.

        Title           : More Accurate ECN Feedback in TCP
        Authors         : Bob Briscoe
                          Mirja Kühlewind
                          Richard Scheffenegger
	Filename        : draft-ietf-tcpm-accurate-ecn-15.txt
	Pages           : 59
	Date            : 2021-07-12

   Explicit Congestion Notification (ECN) is a mechanism where network
   nodes can mark IP packets instead of dropping them to indicate
   incipient congestion to the end-points.  Receivers with an ECN-
   capable transport protocol feed back this information to the sender.
   ECN was originally specified for TCP in such a way that only one
   feedback signal can be transmitted per Round-Trip Time (RTT).  Recent
   new TCP mechanisms like Congestion Exposure (ConEx), Data Center TCP
   (DCTCP) or Low Latency Low Loss Scalable Throughput (L4S) need more
   accurate ECN feedback information whenever more than one marking is
   received in one RTT.  This document specifies a scheme to provide
   more than one feedback signal per RTT in the TCP header.  Given TCP
   header space is scarce, it allocates a reserved header bit previously
   assigned to the ECN-Nonce.  It also overloads the two existing ECN
   flags in the TCP header.  The resulting extra space is exploited to
   feed back the IP-ECN field received during the 3-way handshake as
   well.  Supplementary feedback information can optionally be provided
   in a new TCP option, which is never used on the TCP SYN.  The
   document also specifies the treatment of this updated TCP wire
   protocol by middleboxes.

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