Re: [SAM] [irsg] IRSG review for draft-irtf-samrg-sam-baseline-protocol-02

Michael Welzl <> Wed, 01 May 2013 09:38 UTC

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Subject: Re: [SAM] [irsg] IRSG review for draft-irtf-samrg-sam-baseline-protocol-02
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One (non-blocking) question: why is this intended as Informational, and not Experimental? The latter would seem more appropriate to me.


On Apr 28, 2013, at 10:00 AM, Thomas C. Schmidt <> wrote:

> Hi Michael,
> this means a "ready to publish" vote?
> Viele Grüße
> Thomas
> On 28.04.2013 07:23, Michael Welzl wrote:
>> Hi,
>> I just noticed that somehow, irsg and samrg were dropped from the list
>> of recipients of this response, sorry
>> Begin forwarded message:
>>> *From: *Michael Welzl < <>>
>>> *Subject: **Re: [irsg] IRSG review for
>>> draft-irtf-samrg-sam-baseline-protocol-02*
>>> *Date: *April 24, 2013 4:06:17 PM GMT+02:00
>>> *To: *Dr Mario Kolberg < <>>
>>> *Cc: *sam < <>>, John Buford
>>> < <>>
>>> Hi,
>>> In line:
>>> On 22. apr. 2013, at 12:36, Dr Mario Kolberg wrote:
>>>> Hi Michael and All,
>>>> please find below our response to the IRSG review by Michael Welzl.
>>>> Best wishes,
>>>> Mario & John
>>>>> General higher-level comments:
>>>>> 1) I found parts of the document very hard to read, sometimes
>>>>> wondered if this is really necessary.
>>>> The document is intended for an audience which does have a technical
>>>> background in the area of application layer multicasting and peer to
>>>> peer overlay protocols.  We would expect readers unfamiliar with the
>>>> area to first go to more basic material. Perhaps many comments in the
>>>> review stem from the fact that the reviewer doesn’t have this
>>>> familiarity. To help readers to get a better understanding we have
>>>> added references to introductory and background material as a
>>>> starting point:
>>>> J. Buford, H. Yu, E. K. Lua P2P Networking and Applications. Morgan
>>>> Kaufman 2009 (Ch 9 Peercasting and Overlay Multicasting).
>>>> M. Kolberg. Employing Multicast in P2P Networks, in: Handbook of
>>>> Peer-to-Peer Networking. (Ed. X. Shen, H. Yu, J. Buford, M. Akon).
>>>> J. Buford and H. Yu. Peer-to-Peer Overlay Multicast, in: Encyclopedia
>>>> of Wireless and Mobile Communications. 2008.
>>> Good!
>>> I would like to mention that, while I know very little about
>>> application layer multicast, I do have some (outdated) P2P knowledge.
>>> It's not really my field, but I have done a little bit of work on it
>>> and also taught a lecture about it a few years ago (which even
>>> contained a brief overview of Scribe, IIRC). So that made me think,
>>> someone like me should at least be able to make some sense of the
>>> document - within certain limits of course, as I know nothing about
>>> RELOAD, for example.
>>>>> 2) In particular, P2PCast appears to be a rather complex algorithm
>>>>> which is "sort of" described here... I doubt that the description in
>>>>> the document will help most readers to really fully understand
>>>>> P2PCast, and I  wonder, is it necessary for this doc to try to
>>>>> really explain the algorithm (when, in doing so, it can really only
>>>>> go half-way anyway)? e.g., wouldn't it suffice to just keep the
>>>>> "Overview" (section 9.1) but then point to [P2PCAST] for further
>>>>> details, and just list the necessary facts? e.g., the JOIN procedure
>>>>> - do we have to know all these details here, isn't it enough to e.g.
>>>>> list the reorganisation messages by name and say that they're used
>>>>> in accordance with [P2PCAST]?
>>>> The ID is written for a technical audience which is presumed to be
>>>> knowledgeable about RELOAD and P2P overlays and has somefamiliarity
>>>> with multicasting at the application layer. We provide summaries of
>>>> P2PCAST and SCRIBE since these two algorithms are well known in the
>>>> ALM research community, and are each representative of an important
>>>> class of ALM algorithms.  If the reader needs more background, then
>>>> they can go to thereference papers and find it there.
>>>> In our opinion, the inclusion of the essential features about each
>>>> algorithm is useful and should be in the ID.  The level of
>>>> detaildescribes  “Scribe-like” and “P2PCast-like” algorithms, and not
>>>> only Scribe and P2PCAST.  Since the protocol we define is intended to
>>>> support a large variety of such algorithms.
>>>> This is done in other in other IDs and RFCs.   For example, please
>>>> take a look at section 10 of the RELOAD ID which gives detailed
>>>> information about the Chord algorithm, but yet omits Chord details
>>>> which one would find in the original papers from MIT. If your
>>>> comments were followed, this Chord material should be removed from
>>>> RELOAD spec.      Likewise see this id produced by the PPSP WG
>>>> draft-ietf-ppsp-survey-04.  There are lots of other examples where
>>>> important previously existing algorithms are summarized in an ID.
>>> Well. I'm not sure if the cases you compare here really are comparable
>>> - the Chord text in the RELOAD ID is much longer, for a (it seems to
>>> me) much simpler algorithm, and a survey is really a different case, I
>>> think - its overall intention is different from a document like this
>>> one. But I see your point about trying to convey the essential
>>> features right here, and if you feel the text explains the essential
>>> bits and is helpful, I'll trust you on this one, given my lack of
>>> expertise in application-layer multicast.
>>>>> 3) Another source of confusion: the Scribe algorithm description has
>>>>> some pseudocode that I wasn't able to parse (maybe it refers to
>>>>> RELOAD things?) Not all functions there seem to clearly relate to
>>>>> messages that were described earlier. Even more confusing, the
>>>>> P2PCast algorithm description doesn't have these pseudocode
>>>>> snippets, so the whole thing appears inconsistent. Should it be
>>>>> everywhere? Should it be removed? If it stays, some explanations are
>>>>> needed. It can't be up to the reader to guess what e.g.
>>>>> "invokeMessageHandler" does, right?? (section 8.7). In this
>>>>> particular section, I would also expect the text and/or pseudocode
>>>>> to somehow draw a relationship to "push" (listed in fig. 3), but
>>>>> that's not there... so what is this?
>>>> We agree that this pseudocode is more general and applies to both
>>>> algorithms. To avoid duplication, we have moved it from Section 8 to
>>>> the relevant subsections in Section 7.
>>> Fine.
>>>>> 4) Structure: even if the two algorithms are only a part of the
>>>>> whole thing you define, the text going with them feels a bit like
>>>>> "we've set the stage, now we apply it - the messages you heard about
>>>>> before are used like this & that with this & that algorithm". That's
>>>>> fine! But it also gives the reader the feeling of that being "part
>>>>> 2", i.e. I think it should be at the end, if that makes sense.
>>>> Yes the algorithms are an application of the material in earlier
>>>> sections, but we don't agree that moving it to the end will help the
>>>> understanding of the draft.
>>> Fine.
>>>>> 5) I also think that it would be better to move the examples
>>>>> (section 12) to where you introduce the messages, the flow of which
>>>>> they illustrate. First I have to imagine what an "INVITE" message
>>>>> flow could look like, then I get complicated explanations of how
>>>>> INVITE is applied in an algorithm that I can't fully understand from
>>>>> this text anyway, and THEN I get a nice example illustrating an
>>>>> INVITE message flow... that's not very helpful for the reader I
>>>>> think.  e.g., when I read 7.2.3, I wondered why the "peer_id" of the
>>>>> source peer is even needed in the struct. By looking at the example,
>>>>> this would have become clear to me.
>>>> The document is not meant to be a tutorial, hence the examples are
>>>> not first.  The examples follow the definition of the messages sothat
>>>> the message use is illustrated.  If we moved the examples first, then
>>>> some other reviewer could then say … why are the examplesshown before
>>>> the protocol messages are defined? It is not the purpose of the ID to
>>>> bootstrap the reader into basic knowledge of ALM and Peer to Peer
>>>> messaging.
>>> Fine.
>>>>> 6) Speaking of the examples, what's the point of showing more peers
>>>>> than you actually use in the example? Okay, I can understand that
>>>>> perhaps you wanted to have the same number for all of them, but then
>>>>> you could still remove P3 because it seems that you never use P3 for
>>>>> anything in any of the examples.
>>>> We added these peers is to illustrate that 1) not all the peers in
>>>> the overlay have to be part of each ALM connection, and 2) the
>>>> overlay could have an arbitrary number of peers.
>>> Well, even a total P2P nut like myself understands that
>>> without even seeing P3, but whatever  :-)
>>>>> 7) Nits:
>>>>> IANA Considerations: are you sure that there is nothing? e.g., how
>>>>> would a new algorithm code be assigned?   (section 11.4)
>>>>> - btw, why is the section called "Algorithm Codes" but then the text
>>>>> talks about "Algorithm Types" ?
>>>> There are no IANA considerations since this is to be an informational
>>>> RFC.
>>> Ah, ok, sure -
>>>>> 8) Some references (CASTRO2003, P2PCAST) need a space (I mean, " ")
>>>>> after their first appearance.
>>>>> cut.....
>>>> All these edits have been done and version 03 has been submitted.
>>> Fine, thanks!
>>> Cheers,
>>> Michael
>> _______________________________________________
>> SAM mailing list
> -- 
> Prof. Dr. Thomas C. Schmidt
> ° Hamburg University of Applied Sciences                   Berliner Tor 7 °
> ° Dept. Informatik, Internet Technologies Group    20099 Hamburg, Germany °
> °                   Fon: +49-40-42875-8452 °
> °    Fax: +49-40-42875-8409 °