Re: [tsvwg] Fwd: New Version Notification for draft-eggert-tsvwg-rfc5405bis-00.txt
Greg Shepherd <gjshep@gmail.com> Mon, 16 June 2014 20:45 UTC
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Date: Mon, 16 Jun 2014 13:45:44 -0700
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From: Greg Shepherd <gjshep@gmail.com>
To: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Subject: Re: [tsvwg] Fwd: New Version Notification for draft-eggert-tsvwg-rfc5405bis-00.txt
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On Mon, Jun 16, 2014 at 1:31 PM, <gorry@erg.abdn.ac.uk> wrote: > So, basically, ALC doesn't mention RTT, but NORM does. Both of these > react on larger time scales than TCP would have reacted to the same > congestion event. So if we remove RTT is this OK: > > Section 4.1: > Congestion control mechanisms for multicast may operate on longer > timescales than for unicast (especially where group members have > widely different path delays). Appropriate methods are particularly > important for any multicast session were all or part of the multicast > distribution tree spans an access network (e.g., a home gateway). > Again, this is topology dependent. It may also operate on much shorter timescales. Greg > Gorry > > > On Mon, Jun 16, 2014 at 1:12 PM, <gorry@erg.abdn.ac.uk> wrote: > > > >> In-line > >> > >> > Inline: > >> > > >> > On Mon, Jun 16, 2014 at 12:34 PM, <gorry@erg.abdn.ac.uk> wrote: > >> > > >> >> See-in-line > >> >> > On Mon, Jun 16, 2014 at 11:33 AM, <gorry@erg.abdn.ac.uk> wrote: > >> >> > > >> >> >> I'll respond on the RTT query - since I wrote that section. > >> >> >> > >> >> >> I'm, not sure what you are saying, are you saying there are > >> methods > >> >> that > >> >> >> determine how to respond to congestion that take less than one > >> RTT, > >> >> or > >> >> >> simply the group RTT isn't an issue - maybe I'd see better with an > >> >> >> example? > >> >> > > >> >> > > >> >> > Right, the whole concept of RTT is irrelevant here since there is > >> no > >> >> > message round trip from receiver to source and back. The CC > >> >> determination > >> >> > (channel selection/combination) is determined by the application > >> >> without > >> >> > upstream signaling at all. That was the point of the last sentence > >> in > >> >> the > >> >> > previous paragraph which came from section 2.1 of my > >> >> > draft draft-shepherd-multicast-udp-guidelines-01.txt > >> >> > > >> >> I had some doubt about that part: Let me see if I can explain what I > >> am > >> >> thinking: > >> >> > >> >> - For example, using ALC, I'd have expected loss due to congestion at > >> a > >> >> bottleneck to result in each receiver downstream of the bottleneck > >> in > >> >> reducing the group membership for the higher-rate streams, but the > >> >> required rate reduction takes a little while to propagate up the > >> (PIM) > >> >> multicast distribution tree, and the source only ceases when there > >> are > >> >> no > >> >> further subscriptions (or timeout). > >> >> > >> > > >> > We're already gone off track here; RTT is just a measure of time. It > >> > doesn't itself directly refer to any form of CC. Join latency is not > >> RTT. > >> > WEBRC coined the term MRTT in an attempt to tie join-latency to the > >> > concept > >> > of RTT as it applies to CC. > >> > > >> I don't agree - even though there may be no "RTT timer", the largest > >> round > >> trip time of any receiver in the ALC group is still the parameter that > >> controls the responsiveness of the CC mechanism. > > > > > > Almost right.. It's not any round trip time. It's join/leave latency. I'm > > not arguing the mechanism, I'm arguing the term. We need to be clear - > > there is not control RTT like TCP here. > > > > > >> > > >> >> Whatever, ALC would take at least a RTT to the furthest receiver > >> (with > >> >> loss) that has subscribed to the group, before the source has a > >> chance > >> >> to > >> >> reduce the load on the bottleneck. > >> >> > >> > > >> > I don't believe ALC sources change rates at all. There is a rate/group > >> > profile which the receiver application side selects. > >> > > >> I should have been clearer, the rate at which the source injects traffic > >> into the congested bottleneck queue. The rate at which the ALC source > >> feeds this queue varies as the subscription to higher-rate groups > >> subside. > > > > > > Sure, but this is a topology dependency and no application will be able > to > > respond to where congestion occurs, only if/when they see congestion > > directly. Just like TCP - it has no clue where congestion occurs. It just > > reacts to local detection. > > > > Greg > > > > > >> > > >> >> I know you could also immediately react to loss (aka NORM), but then > >> >> that > >> >> would prevent heterogenous operation where one part of the group can > >> >> receive faster than others. This reaction is more conservative from a > >> CC > >> >> viewpoint > >> > > >> > > >> > ..which goes into the description of various CC mechanisms and departs > >> > from > >> > any applicability of RTT. > >> > > >> > Greg > >> > > >> > >> > >> Gorry > >> > > >> >> > >> >> Gorry > >> >> > >> >> > Greg > >> >> > > >> >> > > >> >> > > >> >> >> > >> >> >> Gorry > >> >> >> > >> >> >> > >> >> >> > Thanks Lars. Much of this text is taken directly from my > >> previous > >> >> >> > draft, draft-shepherd-multicast-udp. Can you please add me to > >> the > >> >> >> authors > >> >> >> > list of this draft? > >> >> >> > > >> >> >> > Content notes: > >> >> >> > > >> >> >> > Section 4.1: > >> >> >> > > >> >> >> > Congestion control mechanisms for multicast may operate on > >> longer > >> >> >> > timescales than for unicast (e.g., due to the higher group > >> RTT > >> >> of a > >> >> >> > heterogeneous group); appropriate methods are particularly > >> for > >> >> any > >> >> >> > multicast session were all or part of the multicast > >> distribution > >> >> >> tree > >> >> >> > spans an access network (e.g., a home gateway). > >> >> >> > > >> >> >> > > >> >> >> > The above isn't relevant for application based CC mechanism. In > >> >> fact, > >> >> >> an > >> >> >> > application-based mechanism may often operate faster than any > >> RTT > >> >> >> > dependent > >> >> >> > mechanism. I think we should either remove this paragraph > >> entirely > >> >> or > >> >> >> > restructure it to make the point that application based CC > >> operates > >> >> >> > without > >> >> >> > dependency on RTT. > >> >> >> > > >> >> >> > Greg > >> >> >> > > >> >> >> > > >> >> >> > On Mon, Jun 16, 2014 at 1:50 AM, Eggert, Lars <lars@netapp.com> > >> >> wrote: > >> >> >> > > >> >> >> >> Hi, > >> >> >> >> > >> >> >> >> Gorry and me have started to put together an update to RFC5405 > >> in > >> >> >> light > >> >> >> >> of > >> >> >> >> the recent discussions. Comments welcome. > >> >> >> >> > >> >> >> >> Lars > >> >> >> >> > >> >> >> >> > >> >> >> >> Begin forwarded message: > >> >> >> >> > >> >> >> >> > From: <internet-drafts@ietf.org> > >> >> >> >> > Subject: New Version Notification for > >> >> >> >> draft-eggert-tsvwg-rfc5405bis-00.txt > >> >> >> >> > Date: June 14, 2014 at 12:14:42 GMT+2 > >> >> >> >> > To: Lars Eggert <lars@netapp.com>, Godred Fairhurst < > >> >> >> >> gorry@erg.abdn.ac.uk>, Gorry Fairhurst <gorry@erg.abdn.ac.uk>, > >> >> Lars > >> >> >> >> Eggert <lars@netapp.com> > >> >> >> >> > > >> >> >> >> > > >> >> >> >> > A new version of I-D, draft-eggert-tsvwg-rfc5405bis-00.txt > >> >> >> >> > has been successfully submitted by Lars Eggert and posted to > >> the > >> >> >> >> > IETF repository. > >> >> >> >> > > >> >> >> >> > Name: draft-eggert-tsvwg-rfc5405bis > >> >> >> >> > Revision: 00 > >> >> >> >> > Title: UDP Usage Guidelines > >> >> >> >> > Document date: 2014-06-14 > >> >> >> >> > Group: Individual Submission > >> >> >> >> > Pages: 36 > >> >> >> >> > URL: > >> >> >> >> > >> >> >> > >> >> > >> > http://www.ietf.org/internet-drafts/draft-eggert-tsvwg-rfc5405bis-00.txt > >> >> >> >> > Status: > >> >> >> >> > https://datatracker.ietf.org/doc/draft-eggert-tsvwg-rfc5405bis/ > >> >> >> >> > Htmlized: > >> >> >> >> http://tools.ietf.org/html/draft-eggert-tsvwg-rfc5405bis-00 > >> >> >> >> > > >> >> >> >> > > >> >> >> >> > Abstract: > >> >> >> >> > The User Datagram Protocol (UDP) provides a minimal > >> >> >> message-passing > >> >> >> >> > transport that has no inherent congestion control > >> mechanisms. > >> >> >> >> > Because congestion control is critical to the stable > >> operation > >> >> of > >> >> >> >> the > >> >> >> >> > Internet, applications and other protocols that choose to > >> use > >> >> UDP > >> >> >> as > >> >> >> >> > an Internet transport must employ mechanisms to prevent > >> >> >> congestion > >> >> >> >> > collapse and to establish some degree of fairness with > >> >> concurrent > >> >> >> >> > traffic. They may also need to implement additional > >> >> mechanisms, > >> >> >> >> > depending on how they use UDP. > >> >> >> >> > > >> >> >> >> > This document provides guidelines on the use of UDP for the > >> >> >> >> designers > >> >> >> >> > of applications, tunnels and other protocols that use UDP. > >> >> >> >> > Congestion control guidelines are a primary focus, but the > >> >> >> document > >> >> >> >> > also provides guidance on other topics, including message > >> >> sizes, > >> >> >> >> > reliability, checksums, and middlebox traversal. > >> >> >> >> > > >> >> >> >> > If published as an RFC, this document will obsolete > >> RFC5405. > >> >> >> >> > > >> >> >> >> > > >> >> >> >> > > >> >> >> >> > > >> >> >> >> > Please note that it may take a couple of minutes from the > >> time > >> >> of > >> >> >> >> submission > >> >> >> >> > until the htmlized version and diff are available at > >> >> >> tools.ietf.org. > >> >> >> >> > > >> >> >> >> > The IETF Secretariat > >> >> >> >> > > >> >> >> >> > >> >> >> >> > >> >> >> > > >> >> >> > >> >> >> > >> >> >> > >> >> > > >> >> > >> >> > >> >> > >> > > >> > >> > >> > > > > >
- [tsvwg] Fwd: New Version Notification for draft-e… Eggert, Lars
- [tsvwg] [Fwd: Re: Fwd: New Version Notification f… gorry
- Re: [tsvwg] Fwd: New Version Notification for dra… gorry
- Re: [tsvwg] Fwd: New Version Notification for dra… gorry
- Re: [tsvwg] Fwd: New Version Notification for dra… Greg Shepherd
- Re: [tsvwg] Fwd: New Version Notification for dra… gorry
- Re: [tsvwg] Fwd: New Version Notification for dra… Greg Shepherd
- Re: [tsvwg] Fwd: New Version Notification for dra… gorry
- Re: [tsvwg] Fwd: New Version Notification for dra… Greg Shepherd