Subject: [p2prg] Fwd: I-D Action:draft-irtf-p2prg-alto-survey-01.txt

From: stefano previdi <[email-masked]>
Date: Tue, 15 Dec 2009 11:31:04 +0100

Folks,

the authors have submitted an updated version of alto-survey draft.
Please, bring to the list your comments and we'll proceed with the
publication process.

Thanks.

s.

Begin forwarded message:

> From: [email-masked]
> Date: December 11, 2009 4:30:02 PM GMT+01:00
> To: [email-masked]
> Subject: I-D Action:draft-irtf-p2prg-alto-survey-01.txt
> Reply-To: [email-masked]
>
> A New Internet-Draft is available from the on-line Internet-Drafts  
> directories.
>
> 	Title           : A Survey on Research on the Application-Layer  
> Traffic Optimization (ALTO) Problem
> 	Author(s)       : I. Rimac, et al.
> 	Filename        : draft-irtf-p2prg-alto-survey-01.txt
> 	Pages           : 17
> 	Date            : 2009-12-11
>
> A significant part of the Internet traffic today is generated by
> peer-to-peer (P2P) applications used traditionally for file-sharing,
> and more recently for real-time communications and live media
> streaming.  Such applications discover a route to each other through
> an overlay network with little knowledge of the underlying network
> topology.  As a result, they may choose peers based on information
> deduced from empirical measurements, which can lead to suboptimal
> choices.  This document, a product of the P2P Research Group,
> presents a survey of existing literature on discovering and using
> network topology information for application-layer traffic
> optimization.
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-irtf-p2prg-alto- 
> survey-01.txt
>
> Internet-Drafts are also available by anonymous FTP at:
> ftp://ftp.ietf.org/internet-drafts/
>
> Below is the data which will enable a MIME compliant mail reader
> implementation to automatically retrieve the ASCII version of the
> Internet-Draft.
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> or ftp://ftp.ietf.org/ietf/1shadow-sites.txt

---

From: Arnaud Legout <[email-masked]>
Date: Tue, 15 Dec 2009 12:22:55 +0100

Hi,

I believe that our work on "Pushing BitTorrent Locality to the Limit" 
http://hal.inria.fr/inria-00343822/en/
is highly relevant to ALTO.
Whereas we do not propose a new architecture, we perform a thorough 
large scale evaluation using real world
data of the impact of locality. In particular, we answer two important 
questions for ALTO.

First, how much traffic can be kept local without adversely impacting 
peers? Whatever the ALTO architecture is,
it will impact the structure of the overlay interconnecting peers.
We go much further than previous work on the understanding of the impact 
of locality on the structure of that overlay.
In addition, reducing the amount of traffic that is kept local in order 
to prevent partitions (thus a loss of performance for peers)
is the solution adopted by P4P and Ono. We introduce a simple mechanism 
(that is backward compatible) to prevent partitions
and show that the traffic reduction on specific links can be 
dramatically reduced by keeping more traffic local without adversely
impacting peers. Those kind of mechanisms are very important because 
they enable to reap full benefits from the information
provided by ALTO.

Second, what would be the benefit of a locality policy at the Internet 
scale?
We show using a real world crawl of a large fraction of the all 
BitTorrent peers that the benefit from deploying
a locality policy today would be a reduction of 40% on inter-AS links. 
To the best of our knowledge, the work closer to ours is
the one of P4P. However, they only consider one torrent and one AS. 
Whereas the P4P field tests are successfully used to support the relevance
of the P4P architecture, they cannot be used to support the relevance of 
a locality policy at the scale of the Internet. But that last
point fundamental for the ALTO justification. A classical
argument (that we often faced before performing the large scale 
BitTorrent measurement) is that at the scale of the Internet
the benefit of a locality policy will be negligible because there is on 
average one or a few peers per AS. We show that even if
it is true that there is on average few peers per AS, the reduction of 
traffic on inter-AS links that can be achieved using a locality
policy is still high at the Internet scale. Thus we believe that this is 
the first large scale measurement that strongly support the relevance of the
ALTO effort.

Finally, we do not claim that inter-AS links are always the right links 
on which to perform traffic reduction, but that it is a reasonable first
level approximation.

I hope those comments will help.

Arnaud.

---

From: Enrico Marocco <[email-masked]>
Date: Thu, 17 Dec 2009 11:50:56 +0100

Hi Arnoud,

the work you mention is actually relevant to ALTO, but I'm not sure how
to fit it in the survey part of the draft (that, in fact, is about
proposed solutions). However, it deals with a relevant issue we did not
mention, so what about adding the following text in a subsection of
section 4?

4.6.  Negative impact of over-localization

   The literature presented in Section 2 show that certain level of
   locality-awareness in the peer selection process of P2P algorithms is
   usually beneficial to the application performance.  However, it seems
   reasonable to expect that an excessive impact of localization on such
   a process (to the detriment of randomness) will cause partitioning in
   overlay networks that will negatively affect the performance
   experienced by the users, especially in networks with lower density
   of peers.

   Finding the right balance between localization and randomness in peer
   selection is an open issue and, at the time of writing, it seems that
   different applications have different levels of tolerance and should
   be addressed separately.  Le Blond et al. [LeBlond] have studied the
   specific case of BitTorrent, proposing a simple mechanism to prevent
   partitioning in the overlay, yet reaching high levels of cross-domain
   traffic reduction without adversely impacting peers.

I'd rather avoid the details of how much traffic could be reduced
according to your experience, as that's not really the goal of this
document (it is actually mythbusting draft's goal). WDYT?

Enrico

Arnaud Legout wrote:
> p2prg mailing list
> [email-masked]
> http://www.irtf.org/mailman/listinfo/p2prg

---

From: Arnaud Legout <[email-masked]>
Date: Thu, 17 Dec 2009 14:07:56 +0100

Hi,

I am fine with the text you propose, except that I would remove the sentence
"especially in networks with lower density of peers." I believe that it 
is actually the opposite.
When there is a low density of peers, the locality policy will have few 
impact on the overlay
interconnecting peers.
Find below a revised text.

You are right that my points better fit into the mythbusting draft.
I will send you a proposition of text in a separate email.

Thanks,
Arnaud.

   The literature presented in Section 2 shows that a certain level of
   locality-awareness in the peer selection process of P2P algorithms is
   usually beneficial to the application performance.  However, an 
   excessive localization of the traffic might cause partitioning in 
   the overlay interconnecting peers, which will negatively affect 
   the performance experienced by the peers.

   Finding the right balance between localization and randomness in peer
   selection is an open issue. At the time of writing, it seems that
   different applications have different levels of tolerance and should
   be addressed separately.  Le Blond et al. [LeBlond] have studied the
   specific case of BitTorrent, proposing a simple mechanism to prevent
   partitioning in the overlay, yet reaching a high level of cross-domain
   traffic reduction without adversely impacting peers.

-- 
Arnaud Legout, Ph.D.

INRIA Sophia Antipolis - Planète  Phone : 00.33.4.92.38.78.15
2004 route des lucioles - BP 93   Fax   : 00.33.4.92.38.79.78
06902 Sophia Antipolis CEDEX      E-mail: [email-masked]
FRANCE                            Web   : http://www-sop.inria.fr/planete/Arnaud.Legout/index.html

---

From: Enrico Marocco <[email-masked]>
Date: Thu, 17 Dec 2009 14:12:51 +0100

Ok, we'll integrate the text in an update that will be out soon.

Enrico

---

From: Ivica Rimac <[email-masked]>
Date: Thu, 17 Dec 2009 09:07:42 -0800

Hi Arnaud, Enrico,

regarding the impact on low-density vs. higher-density local swarms, it
depends on how localization is implemented. If it is a strict
localization, where the neighbor list could be truncated, than
lower-density swarms would suffer. On the other hand, for the de facto
standard approach of prioritization and substitution of peers
localization wouldn't have to much impact on small local swarms. Thus, I 
agree with Arnaud's suggestion to remove this subsentence.

Thanks,
   Ivica

---

From: Enrico Marocco <[email-masked]>
Date: Mon, 21 Dec 2009 17:23:37 +0100

The agreed text is now in
http://www.ietf.org/id/draft-irtf-p2prg-alto-survey-02.txt

Enrico