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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 8774: The Quantum Bug</title>
<meta content="Michael Welzl" name="author">
<meta content='
       The age of quantum networking is upon us, and with it comes
"entanglement": a procedure in which a state (i.e., a bit) can be
transferred instantly, with no measurable delay between peers. This will
lead to a perceived round-trip time of zero seconds
on some Internet paths, a capability which was not predicted and so not
included as a possibility in many protocol specifications.
Worse than the millennium bug, this unexpected value is bound to cause
serious Internet failures unless the specifications are fixed in time. 
    ' name="description">
<meta content="xml2rfc 2.41.0" name="generator">
<meta content="Teleportation" name="keyword">
<meta content="Entanglement" name="keyword">
<meta content="0-RTT" name="keyword">
<meta content="8774" name="rfc.number">
<link href="rfc8774.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
  clear: both;
  border-bottom: 1px solid #ddd;
  margin: 0 0 0.5em 0;
  padding: 1em 0 0.5em;
}
.author {
  padding-bottom: 4px;
}
h1 {
  font-size: 26px;
  margin: 1em 0;
}
h2 {
  font-size: 22px;
  margin-top: -20px;  /* provide offset for in-page anchors */
  padding-top: 33px;
}
h3 {
  font-size: 18px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h4 {
  font-size: 16px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h5, h6 {
  font-size: 14px;
}
#n-copyright-notice {
  border-bottom: 1px solid #ddd;
  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
  margin: 0;
}
.alignRight.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
  padding: 0;
}
.alignRight {
  margin: 1em 0;
}
.alignRight > *:first-child {
  border: none;
  margin: 0;
  float: right;
  clear: both;
}
.alignRight > *:nth-child(2) {
  clear: both;
  display: block;
  border: none;
}
svg {
  display: block;
}
.alignCenter.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignCenter.art-text pre {
  padding: 0;
}
.alignCenter {
  margin: 1em 0;
}
.alignCenter > *:first-child {
  border: none;
  /* this isn't optimal, but it's an existence proof.  PrinceXML doesn't
     support flexbox yet.
  */
  display: table;
  margin: 0 auto;
}

/* lists */
ol, ul {
  padding: 0;
  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
  margin-left: 1em;
}
li {
  margin: 0 0 0.25em 0;
}
.ulCompact li {
  margin: 0;
}
ul.empty, .ulEmpty {
  list-style-type: none;
}
ul.empty li, .ulEmpty li {
  margin-top: 0.5em;
}
ul.compact, .ulCompact,
ol.compact, .olCompact {
  line-height: 100%;
  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
  float: left;
  margin-right: 1em;
}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
  margin-bottom: 0em;
}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre, code {
  background-color: #f9f9f9;
  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
  margin: 0.8em 0.4em 0.4em;
}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
    overflow-x: auto;
    max-width: 100%;
    max-width: calc(100% - 22px);
  }
}

/* aside, blockquote */
aside, blockquote {
  margin-left: 0;
  padding: 1.2em 2em;
}
blockquote {
  background-color: #f9f9f9;
  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
  border-radius: 3px;
  margin: 1em 0;
}
cite {
  display: block;
  text-align: right;
  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
}
th {
  text-align: left;
  background-color: #e9e9e9;
}
tr:nth-child(2n+1) > td {
  background-color: #f5f5f5;
}
table caption {
  font-style: italic;
  margin: 0;
  padding: 0;
  text-align: left;
}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
  margin: 0;
}

/* pilcrow */
a.pilcrow {
  color: #666; /* Arlen: AHDJ 2019 */
  text-decoration: none;
  visibility: hidden;
  user-select: none;
  -ms-user-select: none;
  -o-user-select:none;
  -moz-user-select: none;
  -khtml-user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
  }
  a.pilcrow:hover {
    background-color: transparent;
  }
}

/* misc */
hr {
  border: 0;
  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
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</style>
<link href="rfc-local.css" rel="stylesheet" type="text/css">
<link href="https://dx.doi.org/10.17487/rfc8774" rel="alternate">
  <link href="urn:issn:2070-1721" rel="alternate">
  <link href="https://datatracker.ietf.org/doc/draft-welzl-quantumbug-00" rel="prev">
  </head>
<body>
<script src="https://www.rfc-editor.org/js/metadata.min.js"></script>
<table class="ears">
<thead><tr>
<td class="left">RFC 8774</td>
<td class="center">The Quantum Bug</td>
<td class="right">April 2020</td>
</tr></thead>
<tfoot><tr>
<td class="left">Welzl</td>
<td class="center">Informational</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Independent Submission</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc8774" class="eref">8774</a></dd>
<dt class="label-category">Category:</dt>
<dd class="category">Informational</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2020-04-01" class="published">1 April 2020</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Author:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">M. Welzl</div>
<div class="org">University of Oslo</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8774</h1>
<h1 id="title">The Quantum Bug</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">The age of quantum networking is upon us, and with it comes
"entanglement": a procedure in which a state (i.e., a bit) can be
transferred instantly, with no measurable delay between peers. This will
lead to a perceived round-trip time of zero seconds
on some Internet paths, a capability which was not predicted and so not
included as a possibility in many protocol specifications.
Worse than the millennium bug, this unexpected value is bound to cause
serious Internet failures unless the specifications are fixed in time.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This document is not an Internet Standards Track specification; it is
            published for informational purposes.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This is a contribution to the RFC Series, independently of any
            other RFC stream.  The RFC Editor has chosen to publish this
            document at its discretion and makes no statement about its value
            for implementation or deployment.  Documents approved for
            publication by the RFC Editor are not candidates for any level of
            Internet Standard; see Section 2 of RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc8774">https://www.rfc-editor.org/info/rfc8774</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2020 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1"><a href="#section-2" class="xref">2</a>.  <a href="#name-protocols-and-protocol-mech" class="xref">Protocols and Protocol Mechanisms That Will Fail</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.2.2.1">
                <p id="section-toc.1-1.2.2.1.1"><a href="#section-2.1" class="xref">2.1</a>.  <a href="#name-ledbat" class="xref">LEDBAT</a><a href="#section-toc.1-1.2.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.2">
                <p id="section-toc.1-1.2.2.2.1"><a href="#section-2.2" class="xref">2.2</a>.  <a href="#name-multipath-tcp-mptcp" class="xref">Multipath TCP (MPTCP)</a><a href="#section-toc.1-1.2.2.2.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.2.2.3">
                <p id="section-toc.1-1.2.2.3.1"><a href="#section-2.3" class="xref">2.3</a>.  <a href="#name-rtp-circuit-breakers" class="xref">RTP Circuit Breakers</a><a href="#section-toc.1-1.2.2.3.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-what-can-be-done" class="xref">What can be done?</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-conclusion" class="xref">Conclusion</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-references" class="xref">References</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
<ul class="toc ulEmpty">
<li class="toc ulEmpty" id="section-toc.1-1.7.2.1">
                <p id="section-toc.1-1.7.2.1.1"><a href="#section-7.1" class="xref">7.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.7.2.1.1" class="pilcrow">¶</a></p>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.7.2.2">
                <p id="section-toc.1-1.7.2.2.1"><a href="#section-7.2" class="xref">7.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.7.2.2.1" class="pilcrow">¶</a></p>
</li>
</ul>
</li>
<li class="toc ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-authors-address" class="xref">Author's Address</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
</ul>
</nav>
</section>
</div>
<div id="sec-intro">
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1"><span>[<a href="#RFC6921" class="xref">RFC6921</a>]</span> discusses faster-than-light
      communication, where packets arrive before they are sent. 
      While it is amusing to entertain the possibility of time travel, we have
      to accept the cold facts: time travel will never work (or it would
      already have been used). Quantum networking,
      however, is an entirely different matter -- commercial products are
      already available, and quantum networks will without a doubt become the
      prevalent Internet link-layer technology across the globe within the
      next five to ten years.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">With the help of entanglement, implemented in quantum repeaters,
      quantum networks can transfer information faster than ever before: a
      state can be transmitted over a long distance instantly, with no delay.
      This is so cool that it is also called (and, by some, mistaken
      for) teleportation. If a path between a sender and a receiver is fully
      quantum-ized, the measured one-way delay (OWD) will be zero. What's
      more, assuming that there are blazing fast quantum computers involved on
      both ends, the processing time will be well below anything measurable;
      hence, even the round-trip time (RTT) will be zero in these
      scenarios.<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">In today's Internet, only very few protocols are prepared for such
      "0-RTT" situations (e.g., TCP with "TCP Fast Open" (TFO) <span>[<a href="#RFC7413" class="xref">RFC7413</a>]</span>, TLS 1.3 <span>[<a href="#RFC8446" class="xref">RFC8446</a>]</span>, and QUIC <span>[<a href="#I-D.ietf-quic-transport" class="xref">QUIC-TRANS</a>]</span>). Many others will fail in interesting ways; we coin
      the term "Quantum Bug" for such failures. In the following section, we
      will discuss some examples of Quantum Bugs.<a href="#section-1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Problems">
<section id="section-2">
      <h2 id="name-protocols-and-protocol-mech">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-protocols-and-protocol-mech" class="section-name selfRef">Protocols and Protocol Mechanisms That Will Fail</a>
      </h2>
<p id="section-2-1">The number of protocols and protocol mechanisms that
                will fail in the face of a zero RTT is too large to
                report here; we are truly
                heading towards something close to an Internet meltdown. We
 can only provide some guidance to those who hunt for the
 Quantum Bug, by discussing examples of specification mistakes
 that will need to be fixed.<a href="#section-2-1" class="pilcrow">¶</a></p>
<div id="LEDBAT">
<section id="section-2.1">
        <h3 id="name-ledbat">
<a href="#section-2.1" class="section-number selfRef">2.1. </a><a href="#name-ledbat" class="section-name selfRef">LEDBAT</a>
        </h3>
<p id="section-2.1-1">The Low Extra Delay Background Transfer (LEDBAT) congestion control
 mechanism <span>[<a href="#RFC6817" class="xref">RFC6817</a>]</span> is a very
 interesting failure case: designed to "get out of the way" of other
 traffic; it will end up sending as fast as possible. Specifically,
 when the algorithm described in <span><a href="https://www.rfc-editor.org/rfc/rfc6817#section-2.4.2" class="relref">Section 2.4.2</a> of [<a href="#RFC6817" class="xref">RFC6817</a>]</span> obtains a delay
 sample, it updates a list of base delays that will all become 0
 and current delays that will also all become 0. It calculates
 a queuing delay as the difference between the current delay and the
 base delay (resulting in 0) and keeps increasing the Congestion Window
 (cwnd) until the queuing delay reaches a predefined parameter value
 TARGET (100 milliseconds or less).<a href="#section-2.1-1" class="pilcrow">¶</a></p>
<p id="section-2.1-2">A TARGET value of 100 milliseconds will never be reached, because
 the queuing delay does not grow when the sender increases its cwnd;
 this means that LEDBAT would endlessly increase its cwnd, limited only
 by the number of bits that are used to represent cwnd. However, given
 that TARGET=0 is also allowed, this parameter choice may seem to be a
 way out. Always staying at the target means that the sender would
 maintain its initial cwnd, which should be set to 2. This may seem
 like a small number, but remember that cwnd is the number of bytes
 that can be transmitted per RTT (which is 0). Thus, irrespective of
 the TARGET value, the sender will send data as fast as it can.<a href="#section-2.1-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="TCP-MPTCP">
<section id="section-2.2">
        <h3 id="name-multipath-tcp-mptcp">
<a href="#section-2.2" class="section-number selfRef">2.2. </a><a href="#name-multipath-tcp-mptcp" class="section-name selfRef">Multipath TCP (MPTCP)</a>
        </h3>
<p id="section-2.2-1">The coupled congestion control mechanism proposed for MPTCP in
 <span>[<a href="#RFC6356" class="xref">RFC6356</a>]</span> requires calculating a value
 called "alpha". Equation 2 in <span>[<a href="#RFC6356" class="xref">RFC6356</a>]</span>
        contains a term where a value called "cwnd_i" is divided by the square
        of the RTT, and another term where this value is divided by the
        RTT. Enough said.<a href="#section-2.2-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="CircuitBreakers">
<section id="section-2.3">
        <h3 id="name-rtp-circuit-breakers">
<a href="#section-2.3" class="section-number selfRef">2.3. </a><a href="#name-rtp-circuit-breakers" class="section-name selfRef">RTP Circuit Breakers</a>
        </h3>
<p id="section-2.3-1">The RTP Circuit Breakers <span>[<a href="#RFC8083" class="xref">RFC8083</a>]</span>
 require calculation of a well-known equation which yields the
 throughput of a TCP connection:<a href="#section-2.3-1" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-2.3-2">
<pre>
                          s
X = -------------------------------------------------------------
  Tr*sqrt(2*b*p/3)+(t_RTO * (3*sqrt(3*b*p/8) * p * (1+32*p*p)))</pre><a href="#section-2.3-2" class="pilcrow">¶</a>
</div>
<p id="section-2.3-3">
            where Tr is the RTT and t_RTO is the retransmission timeout of TCP
     (we don't need to care about the other variables). As we will
     discuss in <a href="#Solution" class="xref">Section 3</a>, t_RTO is
     lower-bounded with 1 second; therefore, it saves us from a
     division by zero. However, there is also a simplified version
     of this equation:<a href="#section-2.3-3" class="pilcrow">¶</a></p>
<div class="artwork art-text alignLeft" id="section-2.3-4">
<pre>
          s
X = ----------------
    Tr*sqrt(2*b*p/3)</pre><a href="#section-2.3-4" class="pilcrow">¶</a>
</div>
<p id="section-2.3-5">Unfortunately, <span>[<a href="#RFC8083" class="xref">RFC8083</a>]</span> states:
 "It is RECOMMENDED that this simplified throughput equation be used 
        since the reduction in accuracy is small, and it is much simpler to
        calculate than the full equation." Due to this simplification, many 
        multimedia applications will crash.<a href="#section-2.3-5" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="Solution">
<section id="section-3">
      <h2 id="name-what-can-be-done">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-what-can-be-done" class="section-name selfRef">What can be done?</a>
      </h2>
<p id="section-3-1">Fear not: when everything else fails, TCP will still work.
      Its retransmission timeout is lower-bounded by 1 second <span>[<a href="#RFC6298" class="xref">RFC6298</a>]</span>. Moreover, while its cwnd may grow up to the maximum storable number, data
      transmission is limited by the Receiver Window (rwnd). This means that
      flow control will save TCP from failing.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">From this, we can learn two simple rules: lower-bound any values
      calculated from the RTT (and, obviously, do not divide by the RTT), and
      use flow control. Specifications will need to be updated by fixing all
      RTT-based calculations and introducing flow control everywhere. For example,
      UDP will have to be extended with a receiver window, e.g., as a UDP
      option <span>[<a href="#I-D.ietf-tsvwg-udp-options" class="xref">UDP-OPT</a>]</span>.<a href="#section-3-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="conclusion">
<section id="section-4">
      <h2 id="name-conclusion">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-conclusion" class="section-name selfRef">Conclusion</a>
      </h2>
<p id="section-4-1">We are in trouble, and there is only one way out: develop a
      comprehensive list of all RFCs containing "0-RTT" mistakes (taking <span>[<a href="#RFC2626" class="xref">RFC2626</a>]</span> as a guideline), and update all
      code. This needs to happen fast, the clock is ticking. Luckily, if we
      are too slow, we will still be able to use TCP to access the
      specifications. With DNS over TCP <span>[<a href="#RFC7766" class="xref">RFC7766</a>]</span>, name resolution to find the server containing the
      specifications should also work.<a href="#section-4-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="IANA">
<section id="section-5">
      <h2 id="name-iana-considerations">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-5-1">This document has no IANA actions.<a href="#section-5-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Security">
<section id="section-6">
      <h2 id="name-security-considerations">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-6-1">Flow control must be used on 0-RTT paths, or else an
            attacker can completely overwhelm a sender with data
            in a denial-of-service (DoS) attack within an instant.
            Flow control will need to be added to protocols that do
            not currently have it, such as UDP or ICMP.
                IPv6 will not save us.<a href="#section-6-1" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-7">
      <h2 id="name-references">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-7.1">
        <h3 id="name-normative-references">
<a href="#section-7.1" class="section-number selfRef">7.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC2626">[RFC2626]</dt>
<dd>
<span class="refAuthor">Nesser II, P.</span>, <span class="refTitle">"The Internet and the Millennium Problem (Year 2000)"</span>, <span class="seriesInfo">RFC 2626</span>, <span class="seriesInfo">DOI 10.17487/RFC2626</span>, <time datetime="1999-06">June 1999</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2626">https://www.rfc-editor.org/info/rfc2626</a>&gt;</span>. </dd>
<dt id="RFC6921">[RFC6921]</dt>
<dd>
<span class="refAuthor">Hinden, R.</span>, <span class="refTitle">"Design Considerations for Faster-Than-Light (FTL) Communication"</span>, <span class="seriesInfo">RFC 6921</span>, <span class="seriesInfo">DOI 10.17487/RFC6921</span>, <time datetime="2013-04">April 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6921">https://www.rfc-editor.org/info/rfc6921</a>&gt;</span>. </dd>
</dl>
</section>
<section id="section-7.2">
        <h3 id="name-informative-references">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="I-D.ietf-quic-transport">[QUIC-TRANS]</dt>
<dd>
<span class="refAuthor">Iyengar, J.</span><span class="refAuthor"> and M. Thomson</span>, <span class="refTitle">"QUIC: A UDP-Based Multiplexed and Secure Transport"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-quic-transport-27</span>, <time datetime="2020-02-21">21 February 2020</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-ietf-quic-transport-27">https://tools.ietf.org/html/draft-ietf-quic-transport-27</a>&gt;</span>. </dd>
<dt id="RFC6298">[RFC6298]</dt>
<dd>
<span class="refAuthor">Paxson, V.</span><span class="refAuthor">, Allman, M.</span><span class="refAuthor">, Chu, J.</span><span class="refAuthor">, and M. Sargent</span>, <span class="refTitle">"Computing TCP's Retransmission Timer"</span>, <span class="seriesInfo">RFC 6298</span>, <span class="seriesInfo">DOI 10.17487/RFC6298</span>, <time datetime="2011-06">June 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6298">https://www.rfc-editor.org/info/rfc6298</a>&gt;</span>. </dd>
<dt id="RFC6356">[RFC6356]</dt>
<dd>
<span class="refAuthor">Raiciu, C.</span><span class="refAuthor">, Handley, M.</span><span class="refAuthor">, and D. Wischik</span>, <span class="refTitle">"Coupled Congestion Control for Multipath Transport Protocols"</span>, <span class="seriesInfo">RFC 6356</span>, <span class="seriesInfo">DOI 10.17487/RFC6356</span>, <time datetime="2011-10">October 2011</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6356">https://www.rfc-editor.org/info/rfc6356</a>&gt;</span>. </dd>
<dt id="RFC6817">[RFC6817]</dt>
<dd>
<span class="refAuthor">Shalunov, S.</span><span class="refAuthor">, Hazel, G.</span><span class="refAuthor">, Iyengar, J.</span><span class="refAuthor">, and M. Kuehlewind</span>, <span class="refTitle">"Low Extra Delay Background Transport (LEDBAT)"</span>, <span class="seriesInfo">RFC 6817</span>, <span class="seriesInfo">DOI 10.17487/RFC6817</span>, <time datetime="2012-12">December 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6817">https://www.rfc-editor.org/info/rfc6817</a>&gt;</span>. </dd>
<dt id="RFC7413">[RFC7413]</dt>
<dd>
<span class="refAuthor">Cheng, Y.</span><span class="refAuthor">, Chu, J.</span><span class="refAuthor">, Radhakrishnan, S.</span><span class="refAuthor">, and A. Jain</span>, <span class="refTitle">"TCP Fast Open"</span>, <span class="seriesInfo">RFC 7413</span>, <span class="seriesInfo">DOI 10.17487/RFC7413</span>, <time datetime="2014-12">December 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7413">https://www.rfc-editor.org/info/rfc7413</a>&gt;</span>. </dd>
<dt id="RFC7766">[RFC7766]</dt>
<dd>
<span class="refAuthor">Dickinson, J.</span><span class="refAuthor">, Dickinson, S.</span><span class="refAuthor">, Bellis, R.</span><span class="refAuthor">, Mankin, A.</span><span class="refAuthor">, and D. Wessels</span>, <span class="refTitle">"DNS Transport over TCP - Implementation Requirements"</span>, <span class="seriesInfo">RFC 7766</span>, <span class="seriesInfo">DOI 10.17487/RFC7766</span>, <time datetime="2016-03">March 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7766">https://www.rfc-editor.org/info/rfc7766</a>&gt;</span>. </dd>
<dt id="RFC8083">[RFC8083]</dt>
<dd>
<span class="refAuthor">Perkins, C.</span><span class="refAuthor"> and V. Singh</span>, <span class="refTitle">"Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions"</span>, <span class="seriesInfo">RFC 8083</span>, <span class="seriesInfo">DOI 10.17487/RFC8083</span>, <time datetime="2017-03">March 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8083">https://www.rfc-editor.org/info/rfc8083</a>&gt;</span>. </dd>
<dt id="RFC8446">[RFC8446]</dt>
<dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.3"</span>, <span class="seriesInfo">RFC 8446</span>, <span class="seriesInfo">DOI 10.17487/RFC8446</span>, <time datetime="2018-08">August 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8446">https://www.rfc-editor.org/info/rfc8446</a>&gt;</span>. </dd>
<dt id="I-D.ietf-tsvwg-udp-options">[UDP-OPT]</dt>
<dd>
<span class="refAuthor">Touch, J.</span>, <span class="refTitle">"Transport Options for UDP"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-tsvwg-udp-options-08</span>, <time datetime="2019-09-12">12 September 2019</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-ietf-tsvwg-udp-options-08">https://tools.ietf.org/html/draft-ietf-tsvwg-udp-options-08</a>&gt;</span>. </dd>
</dl>
</section>
</section>
<div id="authors-addresses">
<section id="section-appendix.a">
      <h2 id="name-authors-address">
<a href="#name-authors-address" class="section-name selfRef">Author's Address</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Michael Welzl</span></div>
<div dir="auto" class="left"><span class="org">University of Oslo</span></div>
<div dir="auto" class="left"><span class="street-address">PO Box 1080 Blindern</span></div>
<div dir="auto" class="left">
<span class="postal-code">N-0316</span> <span class="locality">Oslo</span>
</div>
<div dir="auto" class="left"><span class="country-name">Norway</span></div>
<div class="tel">
<span>Phone:</span>
<a href="tel:+47%2022%2085%2024%2020" class="tel">+47 22 85 24 20</a>
</div>
<div class="email">
<span>Email:</span>
<a href="mailto:michawe@ifi.uio.no" class="email">michawe@ifi.uio.no</a>
</div>
</address>
</section>
</div>
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