[tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-17.txt

internet-drafts@ietf.org Mon, 07 March 2022 23:17 UTC

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Subject: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-17.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-17.txt
	Pages           : 60
	Date            : 2022-03-07

   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 updates the original ECN
   specification to specify 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, updating
   BCP 69 with respect to ACK filtering.

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