Subject: Re: [p2prg] New version of the mythbuster-ing draft

From: [email-masked]
Date: Thu, 20 Aug 2009 12:21:25 +0200 (CEST)

Enrico,

I have a few comments.

In Section 3.1:

You should distinguish between "local" cross-domain traffic (a single ISP
and a single torrent) and "global" cross-domain traffic (all ISPs and
214,443 torrents). This is very important because locality may allow to
save a lot of "local" cross-domain traffic in given scenarios without
being beneficial overall. In other words, if it's not possible to save
"global" cross-domain traffic, locality can be *mainly* useless.

"... Simulations and field tests have shown a reduction varying from 20%
to 80%."

If you consider local cross-domain traffic, our experiments with real
distributions of peers per AS actually show that you can save more than
99.5% of "local" Cross-domain traffic and 40% of "global" cross-domain
traffic ([LeBlond], Section 6.3).

"4.  Simulations of the localization approach proposed in [LeBlond]
     run on data collected from crawling of real BitTorrent swarms
     indicate a 40% reduction of cross-domain traffic."

We didn't run simulations but experiments with real BitTorrent clients.

The other works that you cite consider "local" cross-domain traffic so you
shouldn't compare those results with 40% which is for "global"
cross-domain traffic. I would suggest that you either create a subsection
for "global" cross-domain traffic or make this difference very clear. In
any case, you can't compare those numbers directly as they mean something
different.

In Section 3.2:

We have also shown that in the case of severe bottlenecks, BitTorrent with
locality can be more than 200% faster than regular BitTorrent ([LeBlond],
Section 5.3).

In case you didn't have a look at the second version of [LeBlond], here's
the refence:

Stevens Le Blond, Arnaud Legout, Walid Dabbous.
Pushing BitTorrent Locality to the Limit.
Technical Report (inria-00343822, version 2 - 12 May 2009), INRIA,
Sophia Antipolis, May 2009.
http://hal.inria.fr/inria-00343822/en/

Hope this helps.

All the best,
Stevens

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From: Enrico Marocco <[email-masked]>
Date: Thu, 20 Aug 2009 15:07:33 +0200

> traffic ([LeBlond], Section 6.3).

The distinction between observed "local" and "global" cross-domain
traffic reduction is actually fine and definitely worth pointed out. The
section about application performance is already explicit about the fact
that the results of the localization approaches are going to be strictly
dependent on the local network environment, so, besides clarifying the
nature of the numbers in your work, it may be a good idea to explicitly
highlight the expected differences in this section as well. Do you think
you can suggest some text and/or pointers for the Discussion section
about how the effectiveness of the locality strategy relates to the
network conditions? I guess that at the end of the day everything boils
down to the number of peers per AS/ISP, but maybe you've found other
interesting factors that impact too.

> We didn't run simulations but experiments with real BitTorrent clients.

Right, we fixed it somewhere else in the document after Aranud's
comments but did miss this one.

> any case, you can't compare those numbers directly as they mean something

How about replacing the above with the following text?

4.  Experiments with real BitTorrent clients run by researchers a INRIA
    [LeBlond] have shown a 40% reduction in cross-domain traffic on a
    global scale, with local peaks up to the 99.5% in exceptionally
    favorable conditions.

> locality can be more than 200% faster than regular BitTorrent ([LeBlond],

Ok, I'll add the reference there too.

> http://hal.inria.fr/inria-00343822/en/

Sure it does!

-- 
Ciao,
Enrico

---

From: [email-masked]
Date: Fri, 21 Aug 2009 09:07:39 +0200 (CEST)

Enrico,

The savings will indeed have something to do with "the number of peers per
AS" but this can be refined.

To save cross-domain traffic "globally," you need 1) domains to be big
enough so you will have more than one *simultaneous* peer for big torrents
and that 2) the number of big torrents per domain to outweight the number
of small torrents. Even if it's possible to save a lot for big torrents,
that doesn't mean you can save for most torrents, especially because there
are more small torrents than big ones. Fortunately though, big torrents
also generate much more cross-domain traffic than small ones.

As I said during my talk at the last IRTF session, we have found that the
top 1,000 torrents on the 214,443 torrents that we have crawled generated
about half of the "global" cross-domain traffic.

Let me know if this answers your question or if you want me to elaborate
more about this topic. You can also refer the Section 6.3 of our paper
[LeBlond] for more info.

>     global scale, with local peaks up to the 99.5% in exceptionally

That's better but I would add some numbers to make it clear that "global
scale" actually means at the scale of the Internet. "Global" scale could
be interpreted as all torrents (resp. a single torrent) but from the point
of view of a single AS. Something like this:

4. Experiments with real BitTorrent clients and real distributions of peers
   per AS run by researchers at INRIA [LeBlond] have shown that ASes
   with 100 peers or more can save 99.5% of cross-domain traffic
   with high values of locality.

   They have also shown that at a global scale, i.e., 214,443 torrents,
   6,1113,224 unique peers, and 9,605 ASes, high locality can save 40% of
   global inter-AS traffic , i.e., 4.56 Petabytes (PB) on 11.6 PB. This
   result shows that locality would be beneficial at the scale of the
   Internet.

Stevens

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From: Enrico Marocco <[email-masked]>
Date: Fri, 21 Aug 2009 09:51:14 +0200

> more about this topic. You can also refer the Section 6.3 of our paper

Well, this is certainly a useful perspective. What we need now is some
text to reflect it in section 3.1.2; if you want to propose some, that
will be more than welcome. Otherwise we'll figure something out and will
reiterate the discussion on the next version of the document.

>    result shows that locality would be beneficial at the scale of the

Perfect, thanks!

-- 
Ciao,
Enrico