Re: [tcpm] [tsvwg] [Technical Errata Reported] RFC3782 (6789)
Yoshifumi Nishida <nsd.ietf@gmail.com> Wed, 05 January 2022 09:32 UTC
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From: Yoshifumi Nishida <nsd.ietf@gmail.com>
Date: Wed, 05 Jan 2022 01:32:37 -0800
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To: "Black, David" <David.Black@dell.com>
Cc: RFC Errata System <rfc-editor@rfc-editor.org>, "floyd@acm.org" <floyd@acm.org>, "thomas.r.henderson@boeing.com" <thomas.r.henderson@boeing.com>, "andrei.gurtov@teliasonera.com" <andrei.gurtov@teliasonera.com>, "martin.h.duke@gmail.com" <martin.h.duke@gmail.com>, "Zaheduzzaman.Sarker@ericsson.com" <Zaheduzzaman.Sarker@ericsson.com>, "gorry@erg.abdn.ac.uk" <gorry@erg.abdn.ac.uk>, "wes@mti-systems.com" <wes@mti-systems.com>, "tcpm@ietf.org" <tcpm@ietf.org>, "tsvwg@ietf.org" <tsvwg@ietf.org>, "q645v49v@anonaddy.me" <q645v49v@anonaddy.me>
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Subject: Re: [tcpm] [tsvwg] [Technical Errata Reported] RFC3782 (6789)
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I personally think the errata looks correct, but I would like to see if there're other opinions. But, in any case, it should be for RFC6582 rather than for RFC3782. -- Yoshi On Mon, Jan 3, 2022 at 9:02 AM Black, David <David.Black@dell.com> wrote: > +tcpm, Thanks, --David > > -----Original Message----- > From: RFC Errata System <rfc-editor@rfc-editor.org> > Sent: Sunday, December 19, 2021 3:15 AM > To: floyd@acm.org; thomas.r.henderson@boeing.com; > andrei.gurtov@teliasonera.com; martin.h.duke@gmail.com; > Zaheduzzaman.Sarker@ericsson.com; Black, David; gorry@erg.abdn.ac.uk; > wes@mti-systems.com > Cc: q645v49v@anonaddy.me; tsvwg@ietf.org; rfc-editor@rfc-editor.org > Subject: [Technical Errata Reported] RFC3782 (6789) > > > [EXTERNAL EMAIL] > > The following errata report has been submitted for RFC3782, > "The NewReno Modification to TCP's Fast Recovery Algorithm". > > -------------------------------------- > You may review the report below and at: > > https://urldefense.com/v3/__https://www.rfc-editor.org/errata/eid6789__;!!LpKI!xxWA_mawfGxDiokgZx4JlYDNW_ZS26fWQiKHj4sSE9uTS0HGa1KsqyaqZqDwU0qQ$ > [rfc-editor[.]org] > > -------------------------------------- > Type: Technical > Reported by: Clive Bloom <q645v49v@anonaddy.me> > > Section: 6.1 > > Original Text > ------------- > If the Cumulative Acknowledgement field didn’t cover more than > "recover", check to see if the congestion window is greater than > SMSS bytes and the difference between highest_ack and > prev_highest_ack is at most 4*SMSS bytes. If true, duplicate > ACKs indicate a lost segment (proceed to Step 1A in Section 3). > Otherwise, duplicate ACKs likely result from unnecessary > retransmissions (proceed to Step 1B in Section 3). > > Corrected Text > -------------- > If the Cumulative Acknowledgement field didn’t cover more than > "recover", check to see if the congestion window is greater than > SMSS bytes and the difference between highest_ack and > prev_highest_ack is at most 3*SMSS bytes. If true, duplicate > ACKs indicate a lost segment (proceed to Step 1A in Section 3). > Otherwise, duplicate ACKs likely result from unnecessary > retransmissions (proceed to Step 1B in Section 3). > > Notes > ----- > RFC3782 references to Gur03 and GF04 papers as to the initial sources > of the heuristics both ACK-based and Timestamp-based. Neither of those > papers nor Gur03 nor GF04 defines difference between highest_ack and > previous_highest_ack > of at least 4*SMSS bytes upon receiving the third duplicate ACK as an > indication > of droped retransmitted segment. Instead, section III of GF04 says: > > "The acknowledgment heuristic is based on an observation that if the > TCP sender unnecessarily retransmits at least three adjacent packets, > there will be a jump by at least four segments in a cumulative > acknowledgment field. The sender will have correctly retransmitted at least > one packet, to advance the cumulative acknowledgment field, and > unnecessarily retransmitted at least three more to result in three > duplicate > acknowledgments. Following the advancement of the cumulative acknowledgment > field, the sender stores the value of the previous cumulative > acknowledgment > as prev_highest_ack and stores the latest cumulative acknowledgment as > highest_ack. Upon receiving the third duplicate acknowledgment, > the sender invokes a Fast Retransmit if its congestion window is greater > than one MSS (Maximum Segment Size), and the difference between highest_ack > and prev_highest_ack is at most three MSS." > > According to GF04 if TCP sender in absence of any droped acknowledgments > upon receiving > the third duplicate ACK has difference between highest_ack and > prev_highest ack values > of at most/i.e. no more than 3*SMSS bytes then this is explicite > indication of droped retransmitted > segment and leads TCP sender to invoke Fast Retransmit, but current > description of ACK-based > heuristic in RFC3782 section 6.1 in part of: "if the congestion window is > greater than > SMSS bytes and the difference between highest_ack and > prev_highest_ack is at most 4*SMSS bytes. If true, duplicate > ACKs indicate a lost segment (proceed to Step 1A in Section 3)", makes TCP > sender to treat > difference between highest_ack and prev_highest_ack of 4SMSS bytes upon > receiving 3rd > duplicate ACK as indication of lost retransmitted segment but again > according to GF04 this is NOT so, > and makes TCP sender to invoke Fast Retransmit when in fact those three > duplicate acknowledgments > indicate unnecessarily retransmitted segments and have in their > acknowledgment fields sequence > number which receiver expects to receive next but which sender has NOT > sent yet, so Fast Retransmit > has no point in this case. > > Instructions: > ------------- > This erratum is currently posted as "Reported". If necessary, please > use "Reply All" to discuss whether it should be verified or > rejected. When a decision is reached, the verifying party > can log in to change the status and edit the report, if necessary. > > -------------------------------------- > RFC3782 (draft-ietf-tsvwg-newreno-02) > -------------------------------------- > Title : The NewReno Modification to TCP's Fast Recovery > Algorithm > Publication Date : April 2004 > Author(s) : S. Floyd, T. Henderson, A. Gurtov > Category : PROPOSED STANDARD > Source : Transport Area Working Group > Area : Transport > Stream : IETF > Verifying Party : IESG >
- Re: [tcpm] [Technical Errata Reported] RFC3782 (6… Black, David
- Re: [tcpm] [tsvwg] [Technical Errata Reported] RF… Yoshifumi Nishida