<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div>On 6 Mar 2012, at 07:52, Harald Alvestrand wrote:</div><blockquote type="cite">
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On 03/06/2012 12:32 AM, Colin Perkins wrote:
<blockquote cite="mid:766FE318-7DE3-4481-B3C4-C45F2A94C881@csperkins.org" type="cite">
<pre wrap="">Here's our initial attempt at a "circuit breakers" draft for RTCWeb. Comments welcome - this is very much a straw-man for discussion, rather than a final solution.
Colin
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<pre wrap="">From: <a class="moz-txt-link-abbreviated" href="mailto:internet-drafts@ietf.org">internet-drafts@ietf.org</a>
Subject: I-D Action: draft-perkins-avtcore-rtp-circuit-breakers-00.txt
Date: 5 March 2012 20:17:59 GMT
To: <a class="moz-txt-link-abbreviated" href="mailto:i-d-announce@ietf.org">i-d-announce@ietf.org</a>
Reply-To: <a class="moz-txt-link-abbreviated" href="mailto:internet-drafts@ietf.org">internet-drafts@ietf.org</a>
A New Internet-Draft is available from the on-line Internet-Drafts directories.
Title : RTP Congestion Control: Circuit Breakers for Unicast Sessions
Author(s) : Colin Perkins
Varun Singh
Filename : draft-perkins-avtcore-rtp-circuit-breakers-00.txt
Pages : 14
Date : 2012-03-05
The Real-time Transport Protocol (RTP) is widely used for telephony,
video conferencing, and telepresence applications. These
applications are often used over best-effort UDP/IP networks. If
congestion control is not implemented then network congestion will
deteriorate the user's multimedia experience. This document does not
propose a congestion control algorithm. Instead, it specifies a
minimal set of "circuit-breakers". Circuit-breakers are conditions
under which an RTP flow should cease to transmit media to protect the
network from excessive congestion. It is expected that all RTP
applications running on best-effort networks will be able to run
without triggering these circuit breakers in normal operation.
A URL for this Internet-Draft is:
<a class="moz-txt-link-freetext" href="http://www.ietf.org/internet-drafts/draft-perkins-avtcore-rtp-circuit-breakers-00.txt">http://www.ietf.org/internet-drafts/draft-perkins-avtcore-rtp-circuit-breakers-00.txt</a>
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Thanks for this work!<br>
<br>
A few questions (to make sure I get them noted down):<br>
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Section 4.1:<br>
<br>
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sender of RTP data packets receives two or more consecutive RTCP RR
packets from the same receiver that correspond to its transmission
and have a non-increasing extended highest sequence number received
field, then that sender SHOULD cease transmission.
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If I see RTCP packets with<br>
<br>
1: highest sequence number = 2<br>
2: highest sequence number = 2<br>
3: highest sequence number = 2<br>
<br>
do I cease transmission after packet 3 has arrived, or after packet
2 has arrived?<br>
I *think* the logical time is after packet 3 has arrived, but I'm a
little unsure that the words are<br>
unambiguously saying that; it's not 100% clear to me whether packet
1 is considered included in the set of "non-increasing highest
sequence number".<br></div></blockquote><div><br></div><div>We should clarify. My feeling is that either way would work, depending on how aggressive we want the circuit breaker to be. </div><br><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000">
Section 4.2: Is it reasonable to replace, for the purposes of this
calculation, "an order of magnitude" with "a factor of ten"? (for
those who don't have a physics background, putting text somewhere
that says that an order of magnitude is "somewhere around a factor
of ten" might be appropriate.)<br></div></blockquote><div><br></div><div>Sure, will clarify. </div><br><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000">
We might also want to add the words about doing a dramatically
reduced rate if we can from section 4.1 here, factor it out as a
general statement, or say that it is not appropriate here if it's
not.<br></div></blockquote><div><br></div>Yes.</div><div><br><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000">
Security considerations (missing section): For an end node that
implements this specification, an active attacker can cut the
transmission by faking two RTCP packets that get accepted instead of
the recipient's RTCP packets. This may be worthy of a note, and
pointer to appropriate defenses.<br></div></blockquote><div><br></div>Agreed.</div><div><br><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000">
Good stuff!<br>
<br>
Harald<br>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Arial; font-size: 9px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: 'Lucida Sans Typewriter'; font-size: 9px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: 'Lucida Sans Typewriter'; font-size: 9px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: 'Lucida Sans Typewriter'; font-size: 9px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: 'Lucida Sans Typewriter'; font-size: 9px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div><br class="Apple-interchange-newline"><br class="khtml-block-placeholder"></div><div>-- </div><div></div><div>Colin Perkins</div><div><a href="http://csperkins.org/">http://csperkins.org/</a></div></span></span></span><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline"></span>
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