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[ NNSquad ] Re: Comments on NNSquad Purpose
- To: Brett Glass <email@example.com>
- Subject: [ NNSquad ] Re: Comments on NNSquad Purpose
- From: Phil Karn <firstname.lastname@example.org>
- Date: Fri, 16 Nov 2007 03:21:59 -0800
- Cc: email@example.com
Brett Glass wrote:
It's not how BitTorrent works. With BitTorrent, you have to send at
least as much as you receive, so the total bandwidth each client uses
is at least doubled. BitTorrent is designed to offload bandwidth
demand, and possibly speed up the transfer, by co-opting bandwidth
from other ISPs bandwidth. It does not conserve bandwidth; in fact,
it wastes it because there is no opportunity for caching as there is
I think you should take a closer look at how Bit Torrent really works.
Read its design documents, experiment with it and observe it in action
instead of leaping to conclusions based on misconceptions.
If you set up a Bit Torrent seed, i.e., a node with a full copy of a
file to be shared, and other nodes want that file, they will establish
ad-hoc connections to each other and to the seed. They tell each other
which pieces of the file they have and begin exchanging those pieces
among themselves until everyone has the whole file.
An important feature of the algorithm is that peers place priority on
getting the "scarcest" pieces of a file, i.e., those pieces with the
fewest total copies in the swarm. Obviously there has to be at least one
copy of every piece somewhere in the swarm, i.e., at the seed, or the
transfer cannot succeed.
Whenever the seed sends a piece, at least two copies of it then exist in
the swarm. It has become less scarce than the pieces the seed has yet to
send to anyone, so the peers become much more likely to ask the seed for
pieces it has yet to send to anyone.
The effect is that the seed tends to send only one copy of each piece
and the peers tend to share it among themselves instead of each asking
the seed for their own copies. This makes much better use of the seed's
limited upstream bandwidth.
Isn't this better for the seed's ISP than to ban Bit Torrent and force
him to send a full copy to each and every recipient?
It's certainly possible for Bit Torrent seeds to send out multiple
copies. A new peer might arrive, grab a complete copy, and then
disappear before it has repaid its debt by passing on a full copy to
someone else. The user might do this himself, or his misguided ISP might
be interfering with the protocol. Either way, the effect is to shift the
burden back to the original seeder and to any additional seeders.
Bit Torrent is actually quite cacheable. The ISPs merely set up Bit
Torrent nodes of their own. Because they will have a fast outbound
capability, peers will prefer to receive from them than from peers or
seeds on user access links. If each ISP sets up a Bit Torrent node of
its own, this will have the further beneficial effect of minimizing the
traffic between those ISPs.
I'm sure that the Bit Torrent folks would be quite happy to work with
the ISPs to build a special purpose Bit Torrent package optimized for
caching purposes, e.g., by automatically participating in every torrent
it sees. It has also been suggested that the Bit Torrent folks would be
willing to work with the ISPs on peer selection algorithms that minimize
their costs. This will require information from the ISPs and, of course,
a cooperative rather than an adversary attitude.
Another way that the ISPs could make Bit Torrent more efficient is to
(finally) implement IP multicasting. Without it, a sort of "packet
conservation law" exists; for someone to receive a data packet, someone
else has to send it. With IP multicasting, one data packet sent up a
slow DSL or cable access link could be duplicated and sent to multiple
receivers in such a way that usage of ISP resources is minimized.
Without multicasting or other assistance from the ISPs, users have no
choice but to transmit every data packet themselves over their own slow
uplinks. The ISPs have no one to blame but themselves for this
Very few people would send out baby pictures via BitTorrent. By far,
the absolutely overwhelming majority of BitTorrent traffic is pirated
music, video, movies, and software.
That may be true, but it is still not 100%. 100% of my own Bit Torrent
traffic is entirely legal, and I strongly resent the implication that I
"must" be engaging in piracy simply because of the protocol I choose to
move my material.
I'm a service provider who is trying to make sure my customers get
good service. My customers want me to prioritize real time traffic
and de-prioritize non-interactive traffic such as file downloads.
What's more, they don't want my upstream pipes to be congested by
Fine. I'd like to help you, because I'd like to have good service too. I
think the same is probably true for most of your customers. This is best
accomplished with a cooperative relationship between the users and the
ISPs, not an adversary one. I've already given several examples of how
this cooperation could substantially reduce the ISP resources that file
sharing with Bit Torrent would consume.
Actually, some of our pipes ARE smaller upstream than downstream.
(These are the ones that feed our Web cache.) However, as I've
already mentioned, BitTorrent at least doubles the load, because it
requires you to transmit as much as you receive. And you can cache
FTP. You can't cache BitTorrent.
And are you aware of the safe harbor provisions of the DMCA?
Frankly, I don't care if I can manage to get off the hook. I don't
have deep pockets. If I'm sued, I'm already screwed.
My advice, then, is to stay out of the ISP business. That is the only
way you can be sure of not being sued.
No. Because you still will be attempting to hog and monopolize
bandwidth. That's still abusive behavior.
If you don't want me to "hog" and "monopolize" your bandwidth, then I
suggest that you build your own personal dedicated network and not sell
it to anyone. I'm reminded of the South Park episode in which Eric
Cartman bought his own personal amusement park.
When you go into the network service business, your customers have the
right to expect to use it. That's why they pay you. There certainly
should be a good faith give-and-take to maximize the value of your
network to your customers while minimizing your costs. Your customers
should be aware that most of the resources they use are shared with each
other, and that their behavior patterns may affect the performance of
the network as seen by the other users. And it is perfectly reasonable
for you to discard excess traffic from some users when it is necessary
to give a minimum grade of service to other users.
But it is NOT reasonable for you to make, by fiat, value judgments about
the relative importance of your customers' traffic based on their
selection of protocols, or unsupported assumptions about the legality or
illegality of their transactions. That is, quite frankly, outside your
You *should* give your customers the hooks they need to mark their
traffic according to the importance that *they* (not you) place on it,
and you should use these hooks as advice when deciding what traffic to
discard when it is necessary to maintain a minimum grade of service to
In sum, I simply cannot understand how such a hostile, adversary
situation has arisen given that there are many workable technical
measures that can alleviate the situation to everyone's benefit. I am
hoping that education and discussion can lead to a productive outcome.