Re: [Mobopts] [IRSG] review of draft-irtf-mobopts-mmcastv6-ps-06.txt
Craig Partridge <craig@aland.bbn.com> Fri, 10 April 2009 17:21 UTC
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To: "Thomas C. Schmidt" <schmidt@informatik.haw-hamburg.de>
In-Reply-To: Your message of "Sat, 28 Mar 2009 01:32:17 PDT." <49CDE091.7070705@informatik.haw-hamburg.de>
Date: Fri, 10 Apr 2009 13:22:03 -0400
From: Craig Partridge <craig@aland.bbn.com>
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Cc: Rajeev Koodli <rajeev_koodli@yahoo.com>, irsg@ISI.EDU, Craig Partridge <craig@aland.bbn.com>, mobopts@irtf.org
Subject: Re: [Mobopts] [IRSG] review of draft-irtf-mobopts-mmcastv6-ps-06.txt
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All sounds right from my perspective (sorry for delay -- I was on vacation). In message <49CDE091.7070705@informatik.haw-hamburg.de>, "Thomas C. Schmidt" wr ites: >Dear Craig, > >many thanks again for your review. > >We have now discussed and overlooked things, and are ready to answer: >please see comments inline. > > >> --- On *Tue, 3/24/09, Craig Partridge /<craig@aland.bbn.com>/* wrote: >> >> >> From: Craig Partridge <craig@aland.bbn.com> >> Subject: [IRSG] review of draft-irtf-mobopts-mmcastv6-ps-06.txt >> To: irsg@ISI.EDU >> Date: Tuesday, March 24, 2009, 9:22 AM >> >> >> I had two almost contradictory views after reviewing the document. >> >> The first view is that it is very well-informed and presents a lot of >> complex information well. The second view is that it seems lost -- that >> it doesn't know what it is trying to do and where it is going. >> > >This is in a sense quite right: We are trying to comprehensively explore >the problem space and to present all relevant aspects of the somewhat >intricate issues. The idea was to write a general reference document >that summarizes 'all there is to think about' in its corresponding contexts. > >In this sense, the document is not going into a particular direction, >that's right. > >> So, I'm comfortable seeing it published -- I think some folks will find >> it useful, but have some suggestions for how it could be improved to >> work >> as a roadmap for research/thinking about the problem of multicast >> mobility in wireless (which I think is what it aspires to be). >> >> Comments: >> >> * First, the draft should be more explicit that its focus is >> on multicast IPv6 mobility in WIRELESS environments. You can read >> the early part of the draft and think you might be involved >> in worrying about someone unplugging from one wired network >> and plugging >> into wired network. Particular odd is that Figure 1 clearly >> envisions wireless edge networks (single and multihop) yet never >> says wireless anywhere in the text around it.. >> >> (Example -- "wireless" appears in the abstract but then not >> again until page 8...) >> > >Yes, you are right: one should not forget about the obvious. > >We added explicit statements in the introduction to link to the wireless >domain. > >> * The document appears to be seeking to define a set of constraints >> within which a solution must appear. I took the step of >> capitalizing >> every MUST/MUST NOT and SHOULD/SHOULD NOT in the document and >> when you >> do that the document is clearly a half-thought-out requirements >> document. I suspect the authors would be surprised at >> themselves if >> they undertook the experiment. >> > >We repeated your experiment and questioned all these occurrences. In >quite a number of cases we reworded, in particular the "must/must not" >terms. > >In general the document does not make use of normative terms in the >sense of RFC 2119, so there are repeated occurrences where "should" is >just used as an English word, in particular like "should preferably do ...". > >There are a couple of instances, where requirements drop out of other >sources. Some originate for instance from normative aspects of existing >standards (e.g., "must respect scoping restrictions"), some are just >logical consequences of technical arguments given beforehand (e.g., >"source must provide address transparency"). The latter are not meant as >requirements for specific protocols, but as conclusions "if we want to >achieve this, we have to do the other". > >> I mention it because I often reacted that the document was setting >> requirements in one spot but not another and I wondered why. >> >Actually, we tried to keep the solution space as open as possible by >avoiding any evitable constraint in argumentation. > >> * in section 2.1, "jointly support unicast and multicast" -- why >> not broadcast and anycast as well? (esp. as broadcast is >> near universal in wireless and anycast apparently matters) >> >:-) The issue we discuss is multicast and thereby assume, a unicast >routing is present. Broadcast, I suspect, is not exactly an issue, as it >may be viewed as a special case of multicast (can at least be emulated >by multicast). >Anycast matters, yes, but it is not required to implement multicast. So >adding anycast mobility aspects to the document would probably just >confuse the reader, or am I wrong? > > >> * in section 2.2.1, 2nd bullet, why would we enable multicast in >> a network but ban a particular multicast group from circulation? >> (Needs some more explanation here about why this happens -- it is >> a surprising restriction not mentioned earlier). >> >We added a clarifying remark. >A limited group allowance is not rare these days for administrative >reasons. A typical example are IPTV deployments, where providers offer >(allow for) a certain collection of groups (TV channels) they >(contractually) support. Other IPTV multicast groups they do not support >(allow) in their networks. So by changing a provider on handover, one >may enter a domain without the group previously under subscription. > >> * 2.2.2 uses the word "n-casting" in a context where it is clear >> the draft things n-casting is evil, but n-casting is never defined >> anywhere in the document. >> >We added an explanation. > >By the way: this is not meant to say n-casting is evil - the document >just recalls known issues. > >> * 2.4 "Facing deployment complexity, it is desirable that any >> solution for >> mobile multicast SHOULD leave routing protocosl unchanged". [Note >> I capitalized SHOULD to point out the restriction here]. Why >> is this >> desired? If we found a routing approach that worked better >> for all >> environments and supported multicast, wouldn't we prefer that? >> > > From a technical and research perspective we completely agree: We would >much rather design an elegant routing protocol than fiddle with proxy >functions. However, this is a pure deployment argument. Given the >experiences with slow, limited multicast deployment today, it appears >much more promising to propose solutions that only require adding some >'boxes' at the wireless edges and leave the routing core untouched. >Otherwise, we assume, a timely deployment is hardly to expect. > >> * 4.1 -- never mentions that wireless is inherently a broadcast >> medium >> and that there may be opportunities to exploit this feature. >> Especially for receivers, an inherently multicast medium makes it >> easier to rejoin groups (if the group is already live, you can >> immediately listen in). >> >Yes, again this is one of the obvious to be mentioned in the beginning >of section 4. We added this. > >I hope we got all your comments and hints right. > >Best regards, > >Thomas > >-- > >Prof. Dr. Thomas C. Schmidt >° Hamburg University of Applied Sciences Berliner Tor 7 ° >° Dept. Informatik, Internet Technologies Group 20099 Hamburg, Germany ° >° http://www.haw-hamburg.de/inet Fon: +49-40-42875-8452 ° >° http://www.informatik.haw-hamburg.de/~schmidt Fax: +49-40-42875-8409 °
- Re: [Mobopts] [IRSG] review of draft-irtf-mobopts… Rajeev Koodli
- Re: [Mobopts] [IRSG] review of draft-irtf-mobopts… Thomas C. Schmidt
- Re: [Mobopts] [IRSG] review of draft-irtf-mobopts… Thomas C. Schmidt
- Re: [Mobopts] [IRSG] review of draft-irtf-mobopts… Craig Partridge
- Re: [Mobopts] [IRSG] review of draft-irtf-mobopts… Thomas C. Schmidt