Subject: [p2prg] Mythbustering P2P traffic localization

From: Enrico Marocco <[email-masked]>
Date: Thu, 26 Feb 2009 16:50:09 +0100

Hello folks,

we have just submitted a draft that tries to summarize many discussions
about possible effects (and side-effects) of P2P traffic localization:
http://www.ietf.org/internet-drafts/draft-marocco-p2prg-mythbustering-00.txt

The document is very early and the conclusions may be controversial; any
comments, feedback and contributions to improve it will be greatly
appreciated.

Apologies for cross-posting, I'm sending this email to all the lists
where some of the discussions happened; please consider addressing any
follow-up to p2prg only.

-- 
Ciao,
Enrico

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From: zooko <[email-masked]>
Date: Thu, 26 Feb 2009 11:07:05 -0700

On Feb 26, 2009, at 8:50 AM, Enrico Marocco wrote:

> Apologies for cross-posting, I'm sending this email to all the  
> lists where some of the discussions happened; please consider  
> addressing any follow-up to p2prg only.

Hey, I didn't know about p2prg.  Cool.  I'm now subscribing.

Regards,

Zooko
---
Tahoe, the Least-Authority Filesystem -- http://allmydata.org
store your data: $10/month -- http://allmydata.com/?tracking=zsig

---

From: Arnaud Legout <[email-masked]>
Date: Fri, 27 Feb 2009 11:44:23 +0100

[Should we limit the cross posting? I believe sending this thread to 4 
mailing lists is too much
(may be this is because I am subscribed to all four)]

Hi,

here is some feeback based on what we did in [Le Blond].

section 3
We show that we can achieve much higher savings than 80% of reduction. 
The direct implication of this
result is that you can still achieve significant savings with few peers 
per ISP (per torrent).

section 4
we explain the relation between peers download completion time and 
network congestion.
With large enough network congestion you can significantly improve the 
peers download completion time.
Therefore, it is likely that the different gains shown by field 
experiments report different level of congestion
of the underlying network during the experiments.

section 8.1
you write that we did simulations. We did not, we did experiments with 
real BitTorrent clients.

section 8.2
it is not clear what you mean in "as shown in [Le Blond], the right 
balance of randomness and
  locality depends on the P2P algorithm". We did not explore several P2P 
protocols, but only BitTorrent.
We show that BT is extremely robust to high locality (as long as there 
is enough randomness within each ISP).
We cannot conclude for any other P2P protocol.

"On the other hand, P2P systems not adopting the tit-for-tat approach
  (e.g. the eDonkey network) should not be damaged by locality-based"
It is not clear to me. Peer selection (tit-for-tat like choking algo in 
BT) is not the only one factor of efficiency, there is also piece 
diversity.
Edonkey/emule also use rarest first (but a less efficient peer selection 
algorithm). Therefore, as locality adversely impact
piece diversity, my bet is that Edonkey/emule will suffer from locality.

Regards,
Arnaud.

Enrico Marocco wrote:
> ------------------------------------------------------------------------
>
> _______________________________________________
> p2prg mailing list
> [email-masked]
> http://www.irtf.org/mailman/listinfo/p2prg
>   

-- 
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: "Vijay K. Gurbani" <[email-masked]>
Date: Fri, 27 Feb 2009 12:18:18 -0600

Arnaud Legout wrote:
> [Should we limit the cross posting? I believe sending this thread to
> 4 mailing lists is too much (may be this is because I am subscribed
> to all four)]

[... I took p2pi off; I suspect that a lot of this discussion is
  pertinent to p2p-hackers.  Unless I hear from that list's moderator
  otherwise we can continue to include them (many from p2p-hackers
  may not be subscribed to the IETF lists.) ...]

First off, thanks for reading the draft.

Next ...

> section 3 We show that we can achieve much higher savings than 80% of
> reduction. [...]

OK; noted.

> section 4 we explain the relation between peers download completion
> time and network congestion. [...]

Similarly noted; thanks.

> section 8.1 you write that we did simulations. We did not, we did
> experiments with real BitTorrent clients.

OK, we will correct that.

> section 8.2 it is not clear what you mean in "as shown in [Le Blond],
> the right balance of randomness and locality depends on the P2P
> algorithm". We did not explore several P2P protocols, but only
> BitTorrent. We show that BT is extremely robust to high locality (as
> long as there is enough randomness within each ISP). We cannot
> conclude for any other P2P protocol.

Sure; we will correct and restrict the offending text accordingly.

> It is not clear to me. Peer selection (tit-for-tat like choking algo
> in BT) is not the only one factor of efficiency, there is also piece
> diversity. Edonkey/emule also use rarest first (but a less efficient
> peer selection algorithm). Therefore, as locality adversely impact 

OK; we had clearly not considered piece diversity here.

Thanks, Arnaud.

- vijay
-- 
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60566 (USA)
Email: vkg@{alcatel-lucent.com,bell-labs.com,acm.org}
Web:   http://ect.bell-labs.com/who/vkg/

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From: Song Haibin <[email-masked]>
Date: Sat, 28 Feb 2009 15:47:41 +0800

Hi Arnaud,

>We cannot conclude for any other P2P protocol.

I guess if locality will weaken a swarm depends on in which proportion the
pieces of the resource the local peers have; and the balance of the cotent
pieces distribution among these local peers.

>piece diversity, my bet is that Edonkey/emule will suffer from locality.

What do you mean with "less efficient" by saying "Edonkey/emule also use
rarest first (but a less efficient peer selection algorithm)"?

Regards,
Song Haibin

---

From: Arnaud Legout <[email-masked]>
Date: Sat, 28 Feb 2009 22:58:16 +0100

> rarest first (but a less efficient peer selection algorithm)"?

The peer selection algorithm of a P2P protocol is a tradeoff between 
maximizing
the efficiency (in terms of download completion time, or upload 
utilization of leechers) and fostering
persistency of seeds (and of the torrent).

BT with its choking algorithm clearly fosters the efficiency of the 
torrent. The peer selection algorithm of Emule
fosters persistency. You are served by a peer when you are the first one 
in its waiting queue. You place is the queue is mainly of function of 
the time
you spent in the queue and your upload contribution. I believe this 
upload contribution and the rarest first piece selection was added to emule
based on BT experience in order to improve its efficiency, but the main 
focus of emule is still to keep peers as long as possible in the swarm 
in order
to improve the persistency of contents.

Regards,
Arnaud.