Re: [P2Prg] CORE subgroup problem statement

[Luca Caviglione <luca.caviglione at cnit.it>]

Hi Arnaud ...

Quoting Arnaud Legout <Arnaud.Legout at sophia.inria.fr>:

> Hi Luca,

> > <LC>
> > I would not start a flame about "terminology" :-). However, hybrid
> > protocol is something I don't like in this context. In fact, I used
> > "architectural", rather than protocol. So, I think there are not
> > errors in defying BitTorrent as an hybrid architecture. Actually,
> > there are two architectural flavors overlapped: centralized, from "a
> > content localization point of view" and p2p for the swarm.
> > Hybrid Protocol suggests functionalities and does not lead to a better
> > understanding of "how the architecture is arranged".
> > </LC>
> <AL>
> I don't agree. When you classify architectures as structured and
> unstructured, hybrid should mean that you have a combination of
> structured and unstructured.
> Otherwise, hybrid is for everything you don't know how to classify.
> "Other" would have been a better name, but still a weak classification.

I do agree here. Other is a better name and also a weak classification. However,
I think that correct classification (better, the one I would prefer) must rely
on architectures, rather than functionalities.

> It is not correct to classify some protocol based on their localization
> architecture and some other protocols based on their content replication
> architecture,
> without making a clear distinction in the taxonomy.
> If you consider BitTorrent to be an hybrid architecture because there is
> a central content localization and p2p file replication, then
> any other P2P protocol should be hybrid. Instead, using your taxonomy BT
> should be considered as centralized.

Actually, BitTorrent is a superposition of two protocols. The BT-Tracker
protocol and the BT protocol for the swarm. Then, the protocols reflect the
architecture where they act. However, this is my perspective and it doesn't
mean it is the best one or better than others.

>
> I do not believe I am raising a flame about terminology.

Yes, sorry. I was suggesting (for my answer) that it is not solely a debate for
"terms".

> I simply want to point out that the way P2P is considered for now is
> content localization oriented.
> This is only one side of P2P, and content localization and content
> replication should be uncorrelated.
> BitTorrent, which is undoubtedly the most efficient general purpose P2P
> protocol, cannot be classified
> using the current taxonomy.
> Thus, this taxonomy do not cover all the P2P architectures.
> </AL>
> >
> >>
> >> From my point of view, a better taxonomy for P2P is:
> >> *Content Localization
> >>  -Structured
> >>  -Unstructured
> >>  -Centralized
> >>  -Hybrid (?)
> >> *Content delivery
> >>  -Parallel download
> >>  -File splitting  (swarming)
> >>  -Piece selection
> >>  -Peer selection
> > <LC>
> > In my opinion, what you suggest is somewhat misleading. I mean,
> > parallel download, file-splitting, piece selection... are techniques
> > for delivering a file over a network and are not strictly related with
> > p2p. The only requirement is that content is replicated among several
> > entities.
> > Then with your taxonomy, I can describe as p2p "GetRight", the FTP
> > client for Windows. With GetRight you can set mirrors and concurrently
> > download from different FTP servers. Ok, this is an exasperation of
> > the concept, but I think that architectures must be separated from
> > peculiar tricks.
> > </LC>
> <AL>
> I am not sure it is possible to abstract the architecture from the
> technique..Unstructured is not specific to P2P as well. Multicast has
> been using this kind of architectures and techniques (flooding,
> expanding ring search, etc.) for a long time.

I partially agree. However, I think that the first step, in order to produce a
taxonomy, is to separate causes with effects. You can use swarming, hording (or
flooding and expanding ring) since the architectural blueprints allow such
techniques.

> Structured is not specific to P2P as well, unless you mean
> Structured=DHT, but in this case you are no more making a distinction
> between architecture
> and technique.
> Using the current taxonomy you can already classify protocols that are
> not P2P.
>
> You are right that my taxonomy is technique oriented rather architecture
> oriented.
> For all the P2P protocols I know, structured means DHT, and unstructured
> means flooding, expanding ring search, random walk, etc.
> I would really prefer a taxonomy using DHT, flooding, expanding ring
> search, etc. than structured and unstructured.

For me, structured means that there is an enforcement in the organization of
peers. Having the peers forced to arrange in a ring (as an example) allows to
exploit some search strategies. On the contrary, having peers connected
randomly, brings you in the case where you don't know where the content is. So
you must flood or something else.


> </AL>
> >> This taxonomy must be refined, but at least, it takes into account
> >> both content localization and content delivery.
> >> With this taxonomy, BitTorrent can now be correctly classified:
> >> Content Localization: centralized
> >> Content Delivery: Parallel download, File splitting, rarest first
> >> piece selection, choke algorithm peer selection.
> >
> > <LC>
> > I think you did not classified BitTorrent. You are only listing some
> > techniques used for achieving a better efficiency on the networked
> > environment.
> > </LC>
> When you classify Chord as structured, don't you mean it is a DHT? Do
> you have an example of structured P2P architecture that is not a DHT?
>
>  From my point of view, DHT is at the same semantic level than piece
> selection, and Chord is at the same semantic level than rarest first.

This is an interesting point.

> I don't know which definition of structured and unstructured
> architecture you consider, but the one presented in [1] is technique
> dependent and vague.
> Structured is for DHT, unstructured is for other localization techniques.
>

...and probably is there the main knot. For me, unstructured and structured is
how "the peers are organized" and not related to localization techniques. I
mean, if I am going crazy, I can use a flood based technique selecting randomly
peers in Chord's finger tables (and probably I can patent this as the useless
search system ever).

> Regards,
> Arnaud.

Regards,
Luca


>
>
> [1] Lua et al. "A Survey and Comparison of Peer-to-Peer Overlay Network
> Schemes" IEEE Communication s survey and tutorial, March 2004
>
>
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