[tcpm] [Technical Errata Reported] RFC9438 (7806)
RFC Errata System <rfc-editor@rfc-editor.org> Fri, 09 February 2024 16:06 UTC
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Subject: [tcpm] [Technical Errata Reported] RFC9438 (7806)
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The following errata report has been submitted for RFC9438, "CUBIC for Fast and Long-Distance Networks". -------------------------------------- You may review the report below and at: https://www.rfc-editor.org/errata/eid7806 -------------------------------------- Type: Technical Reported by: Richard Scheffenegger <rs.ietf@gmx.at> Section: 4.1.2 Original Text ------------- * cwndprior: Size of cwnd in segments at the time of setting ssthresh most recently, either upon exiting the first slow start or just before cwnd was reduced in the last congestion event. Corrected Text -------------- * cwndprior: Flight Size as defined in RFC5681 in segments at the time of setting ssthresh most recently, either upon exiting the first slow start or just before cwnd was reduced in the last congestion event. Notes ----- The implicit assumption appears to be, that only singular, isolated events happen during a cubic congestion control response. However, it is not uncommon that multiple events, such as loss, loss recovery initiation, followed by one or more RTOs happen. In many implementations, cwnd only properly tracks Flight Size while no loss recovery is going on. RFC5681 made it clear, that adjustments to ssthresh should be based off of the (estimated) Flightsize. Similarly, it appears prudent to observe Flight Size and not a potentially adjusted cwnd value here. The observed effect of deriving cwnd_prior directly from cwnd, and not Flight Size is a deflated value for ssthresh, earlier transition from slow-start to congestion avoidance, and less rapid resumption of reasonable bandwidth after e.g. a burst loss event followed by a RTO. RFC5681 section 7 has this to say around setting ssthresh: The treatment of ssthresh on retransmission timeout was clarified. In particular, ssthresh must be set to half the FlightSize on the first retransmission of a given segment and then is held constant on subsequent retransmissions of the same segment. Instructions: ------------- This erratum is currently posted as "Reported". (If it is spam, it will be removed shortly by the RFC Production Center.) Please use "Reply All" to discuss whether it should be verified or rejected. When a decision is reached, the verifying party will log in to change the status and edit the report, if necessary. -------------------------------------- RFC9438 (draft-ietf-tcpm-rfc8312bis-15) -------------------------------------- Title : CUBIC for Fast and Long-Distance Networks Publication Date : August 2023 Author(s) : L. Xu, S. Ha, I. Rhee, V. Goel, L. Eggert, Ed. Category : PROPOSED STANDARD Source : TCP Maintenance and Minor Extensions Area : Transport Stream : IETF Verifying Party : IESG
- [tcpm] [Technical Errata Reported] RFC9438 (7806) RFC Errata System