Re: [p2pi] draft-livingood-woundy-p4p-experiences-02 posted

Comments below.

- Laird Popkin, CTO, Pando Networks
  mobile: 646/465-0570

----- Original Message -----
From: "Richard Woundy" <Richard_Woundy@cable.comcast.com>
To: "Reinaldo Penno" <rpenno@juniper.net>, p2pi@ietf.org
Cc: "Richard Woundy" <Richard_Woundy@cable.comcast.com>, "Jason Livingood" <Jason_Livingood@cable.comcast.com>
Sent: Wednesday, November 5, 2008 5:29:45 PM (GMT-0500) America/New_York
Subject: Re: [p2pi] draft-livingood-woundy-p4p-experiences-02 posted

Reinaldo,

I can answer the easy questions. We will need some assistance from Pando
(and Yale) for some of the other ones.

>What was the file size in those experiments?

21 megabytes. From section 2: "Pando distributed a special 21 MB
licensed video file as in order to measure the effectiveness of P4P
iTrackers."

The performance benefit of P4P is that peers much more rapidly find good peers. Over time random peer discovery will also find good peers, and "catch up" in performance. This can take a very long time, however. For example, in a swarm of 100,000 peers, let's look at how long it would take to find the closest peer. If you perform a test transfer with one random peer a second (i.e. typical BitTorrent client behavior), it would take 100,000 seconds to probe 50% of the swarm, meaning that in 28 hours you would have a 50% chance of probing the closest peer. With P4P guidance, you would have a very high chance of probing that closest peer on your first announce. Admittedly this simplifies the network interaction somewhat, but I think that you see the impact of P4P guidance.

For very large downloads, random peer assignment would catch up to P4P in transfer rate, but the random peer download would always be slower by the "ramp up" time. Of course, the cost to ISP would be (on average) less, even when the performance is the same, which seems beneficial as well.

>How long would it take to download the file in the three different
scenarios? I know that more consumed bandwidth in access might lead one
to conclude that file was downloaded faster...

To clarify, most of the raw data (download speed and Internet
peering/transit traffic volumes) were collected by Pando Networks from
their P2P clients, not collected by Comcast across its links. So my
assumption is that the Pando client used the content size (21 MB), and
divided by the download time to get the speed.

LP: Pando's client can capture extended logging, which we enabled for this test. This captures the source and destination IP address of all p2p transfers, the number of bytes transferred, and the start and end timestamps. This gives a precise measurement of the data flow in the network, allowing us to compute not only data transfer volumes but also data flow rates at each point in time. We also capture the times of the start and completion of every download, as well as the average transfer rate observed by the client for the download. As you can imagine, this allowed us to perform extensive analysis of the data flow and the user experience in the network.

>Was the file already seeded in Comcast's network? More specifically,
how
was file propagation done?

Any seeding happened outside of Comcast's network, and outside of
Comcast's control. That's really a question for Pando.

LP: Pando served the data from an origin server external to Comcast's network. This server served about 10 copies of the file, after which all transfers (about 1m downloads) were performed purely p2p.

>Was PEX, DHT and others enabled in the clients?

Pando would know whether PEX was enabled. It would be safe to assume
that with respect to this trial, DHT was NOT enabled, since Pando
supplied the tracker. (The pTracker in the draft is a tracker operated
by Pando.)

LP: Pando starts with tracker-provided peers, then uses peer exchange to discover additional peers. Thus, the starting peers were provided with P4P guidance (90% P4P guidance, 10% random), then later peers discover the entire swarm via either additional announces or peer exchange. What we found is that because the initial P4P-guided peers were quite fast, the later peers did not reduce data localization much, though we believe that it is important for the p2p mesh to be well connected over time so that the swarm remains resilient (and to compensate for cases where P4P cannot provide good guidance).

>Was local peer discovery enabled in the clients?

Pando would know.

LP: Yes, Pando preferentially connects peers on a LAN before internet peers. We don't use multi-cast for this, as we've found other methods that work more generally.

>BTW, can broadcast/multicast peer discovery work in Cable networks?

Do you mean something like this:
http://bittorrent.org/beps/bep_0026.html?

If so, peer discovery probably would not work over the typical last mile
cable network. Maybe I'm wrong, but I see this protocol as intended for
peer discovery within one's home network / LAN / WiFi network, not over
a cable network.

>So, were clients allowed to become seeders to the outside of Comcast's
network?

Yes, they were.

As a related item, look closely at section 4.2. The amount of aggregate
uploaded data from Comcast clients (per swarm) was about 140,000 MB. The
amount of aggregate downloaded data from Comcast clients (per swarm) was
about 60,000 MB or so. So the typical Comcast client uploaded more than
twice the amount of data that it downloaded. 

>How much of the swarm was within Comcast and outside?

Most of the swarm was outside of Comcast. Unfortunately I don't have
access to the size of the global swarm, but I would guess that Comcast
clients represented no more than 15% of the swarm, and maybe as little
as 5%. Those guesses are based on the behavior of the random swarm, e.g.
Comcast clients uploaded to non-Comcast clients 94% of the time in the
random swarm.

-- Rich

-----Original Message-----
From: p2pi-bounces@ietf.org [mailto:p2pi-bounces@ietf.org] On Behalf Of
Reinaldo Penno
Sent: Wednesday, November 05, 2008 11:23 AM
To: Livingood, Jason; p2pi@ietf.org
Subject: Re: [p2pi] draft-livingood-woundy-p4p-experiences-02 posted

Hello Jason/Rich,

This is such an interesting draft. I'm surprised there are no questions
about it. Maybe everybody else is part of P4P one way or another and I'm
not
in the 'in' crowd (;-) so I have questions.

* What was the file size in those experiments? Some post long ago said
the
file size in some P4P experiments was really small, as opposed to the
top
100 torrents where the file size is ~1Gb. I was curious what is the
optimization payback in terms of download time for large files as
opposed
small files. 

* How long would it take to download the file in the three different
scenarios? I know that more consumed bandwidth in access might lead one
to
conclude that file was downloaded faster but I'm not sure this is a
straightforward conclusion.

* Was the file already seeded in Comcast's network? More specifically,
how
was file propagation done? All clients started from scratch and had to
start
pulling the file from some other side of the world and then exchanging
pieces? This is mainly due to the discussion in 4.2.

* Was PEX, DHT and others enabled in the clients?

* Was local peer discovery enabled in the clients? BTW, can
broadcast/multicast peer discovery work in Cable networks?

* If more clients finish downloading faster and become seeders you would
think that for popular content Comcast's upstream bandwidth would
increase
due to the number of seeder in its network. So, were clients allowed to
become seeders to the outside of Comcast's network? How much of the
swarm
was within Comcast and outside?

Thanks,

Reinaldo

On 11/3/08 12:49 PM, "Livingood, Jason"
<Jason_Livingood@cable.comcast.com>
wrote:

> For some reason the URL was cut to two lines - trying again:
> 
>
http://www.ietf.org/internet-drafts/draft-livingood-woundy-p4p-experienc
> es-02.txt
> 
> 
> 
>> -----Original Message-----
>> From: p2pi-bounces@ietf.org [mailto:p2pi-bounces@ietf.org] On
>> Behalf Of Livingood, Jason
>> Sent: Monday, November 03, 2008 3:35 PM
>> To: p2pi@ietf.org
>> Subject: [p2pi] draft-livingood-woundy-p4p-experiences-02 posted
>> 
>> A draft at
>> http://www.ietf.org/internet-drafts/draft-livingood-woundy-p4p
>> -experienc
>> es-02.txt may be of interest to folks that have been
>> interested in P2Pi and ALTO.  We have requested time on the
>> ALTO agenda at IETF 73 to present this.
>> 
>> Regards
>> Jason
>> _______________________________________________
>> p2pi mailing list
>> p2pi@ietf.org
>> https://www.ietf.org/mailman/listinfo/p2pi
>> 
> _______________________________________________
> p2pi mailing list
> p2pi@ietf.org
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