Linked by Thom Holwerda on Wed 8th Feb 2012 23:15 UTC
Internet & Networking "While the file-sharing ecosystem is currently filled with uncertainty and doubt, researchers at Delft University of Technology continue to work on their decentralized BitTorrent network. Their Tribler client doesn't require torrent sites to find or download content, as it is based on pure peer-to-peer communication. 'The only way to take it down is to take the Internet down,' the lead researcher says." In a way, the efforts by Hollywood and the corrupt US Congress is actually increasing the resiliency of peer-to-peer technology. Karma.
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RE: "pure" P2P
by Alfman on Thu 9th Feb 2012 03:51 UTC in reply to ""pure" P2P"
Alfman
Member since:
2011-01-28

"Pure P2P" systems need to be boot strapped somehow.
Once bootstrapped with some initial peers, the network can expand by itself to learn new peers. As long as enough peers are online, the network has a very good chance to recover itself.

The old freenet network was an example of this type of design. However the fact that the network exchanged peer information to repair and optimize the network implies that an attacker can join the network and build a list of peers over time. This enabled one to get IPs of peers in the network, which was considered a security problem in regimes like china where the simple fact of running an anti-censorship technology can land someone in trouble.

They developed a new freenet protocol and called it the "dark net". The principal difference is that this protocol does not exchange peers, and the user must enter "trusted" peers manually. This has/had so many obvious scalability problems that it was a terrible idea from the get-go in my opinion, but it was supposed to allow peers to operate with much better confidence that no one outside the trusted peers would know that they're part of the network. So, the state wouldn't have a way to identify peers by simply joining the network.


In practice, the freenet darknet between anonymous users is practically useless because users go to a clear IRC channel to exchange peer lists, which is far less secure than the previous freenet since it leaks even more information than before. And it tends to create very long if not completely broken routes between members who exchange peer information in the IRC channels at different times.


I'd be interested in hearing anyone else's take on this subject.

Reply Parent Score: 4

RE[2]: "pure" P2P
by galvanash on Thu 9th Feb 2012 06:47 in reply to "RE: "pure" P2P"
galvanash Member since:
2006-01-25

In practice, the freenet darknet between anonymous users is practically useless because users go to a clear IRC channel to exchange peer lists, which is far less secure than the previous freenet since it leaks even more information than before. And it tends to create very long if not completely broken routes between members who exchange peer information in the IRC channels at different times.


I'd be interested in hearing anyone else's take on this subject.


Darknets for file sharing are simply trust networks - they are only as trustworthy as the people you let into them. As such, it is all rather pointless to me, since they eventually succumb to their own popularity - once you reach the point that you no longer know everyone you can no longer trust it.

Its fine to a point for a small group of peers who actually do know each other - but then you never really gain the advantages you have with large P2P networks (namely diverse content and multiple seeders to speed up downloads).

Tribler does not seem to even try to behave like a darknet. There is no address anonymity as far as I can see - it is simply decentralized. You would of course need a few "superpeers" to bootstrap things, but once it got going it would be self-maintaining. That is the point I think - not address anonymity. It's not really anything like Freenet, where anonymity is actually the primary goal.

Reply Parent Score: 3

RE[3]: "pure" P2P
by Alfman on Thu 9th Feb 2012 11:15 in reply to "RE[2]: "pure" P2P"
Alfman Member since:
2011-01-28

galvanash,

"That is the point I think - not address anonymity. It's not really anything like Freenet, where anonymity is actually the primary goal."

Yes, I was trying to highlight the two different levels of anonymity using freenet as an example. A decentralized P2P network shouldn't be a "darknet" if it's to be scalable. However it's still possible to protect the privacy of the traffic so third parties don't know what's being transfered between known peers.

Reply Parent Score: 2

RE[2]: "pure" P2P
by Valhalla on Fri 10th Feb 2012 03:13 in reply to "RE: "pure" P2P"
Valhalla Member since:
2006-01-24

Yes, I find this interesting aswell, particularly the decentralized bit. I read up on the p2p methodologies a while back with torrents, e2dk, direct connect being examples of centralized networks and kademlia, DHT (partly), winny, share, being examples of decentralized networks.

Centralized networks relies on a server which provides vital information neccesary for file sharing, this is quite efficient but also has a huge vulnerability as the network is totally dependant on these servers operating and if they go down, so does the network functionality.

Decentralized networks are those where each peer take on part of the burden handled entirely by a server in a centralized setting and therefore has no central point of functionality, leading to a network where it can lose any peer and still continue to function as before.

From a network robustness standpoint it's obvious that decentralized networks are better, but there are as always other factors, such as efficency. A single purpose server in a centralized setting is more efficient in spreading necessary information to peers than it a decentralized network where more bandwidth use/cpu use is required for relaying the same information.

Other areas where centralized networks can be more attractive is how they can be community/interest targeted, and often with their own set of rules pertaining to how much peers must upload in contrast with how much they are allowed to download.

Then we have anonymity, popular networks such as bittorrent and ed2k/kademlia have no anonymity to speak of, the closest thing is protocol obfuscation but that is targeted entirely at preventing isp-throttling.

The reason why the demand for anonymity has been low is because there's a very slim chance of legal reprecussions while using networks like bittorrent today, and also that anonymity measures 'waste' bandwidth.

I found it very interesting that in Japan, where online copyright breaches are much more likely to cause legal problems the two major p2p applications (Winny, Share) are built from the ground up to be anonymous.

Obviously there's no real anonymity given that you need to expose your ip address in order to join any p2p network, however the difficulty in proving what an ip downloaded is what these 'anonymous' networks are based upon. Both Winny and Share require the user to allocate a large chunk of hd space as an encrypted buffer not only for the data they are interested in, but also data they will be relaying from one peer to another. It's this relaying of data which obfuscates the source->destination ip addresses and makes it very hard to prove who downloaded what from who'm. Naturally this makes for a less efficient network, as not only do each user need to spend their bandwidth on what they want, but also on relaying lots of data they have no interest in.

It will be interesting to see whether these types of pseudo-anonymous networks will start to rise in use here aswell if we end up with harder anti-piracy measures resulting in more resources being spent on identifying and prosecuting online piracy.

Oops, became a bit longwinded ;)

Reply Parent Score: 3

RE[3]: "pure" P2P
by Alfman on Fri 10th Feb 2012 06:03 in reply to "RE[2]: "pure" P2P"
Alfman Member since:
2011-01-28

Valhalla,

I didn't know about the Japanese P2P differences. Different motivations will yield different solutions.

Yes, any network that intends to obfuscate the IP addresses is going to be inherently inefficient. That seems somewhat unsolvable, at least without the cooperation of the ISPs. If they routinely reassigned IP addresses and didn't keep records, that would achieve the desired anonymity, but of course they don't do that.


"A single purpose server in a centralized setting is more efficient in spreading necessary information to peers than it a decentralized network where more bandwidth use/cpu use is required for relaying the same information."

I actually disagree, a P2P medium (one which is designed for efficiency mind you, and hasn't been subjected to other compromises) should be more efficient than a centralized system. However, as I haven't actually analyzed the problem before, I'd like to do so now.

Let's say there are 2M viewers watching an hour long television program. The entire program is 500MB. 1M watching it live, the other 1M watch it later on demand.

The required bandwidth for one instance is about 1.2Mbps. The aggregate across 1M active viewers becomes 1.2Tbps during the live broadcast. Of course, you'll have to distribute this across many different data centers, but that's a boatload of trucks traveling through our tubes.

Now consider an optimized P2P network taking the form of a tree where peers can also download from one or two upstream peers.

Obviously there's a whole spectrum of peer bandwidth possibilities, but to keep the example simple: assume 500K have enough upstream bandwidth for one other peer, 250k have enough upstream bandwidth for two other peers, 250k have no upstream bandwidth for any peers.

Lets say the entire broadcast is originated from a single 10Mbps node which supports 8 direct downstream peers, lets call this level 0. For optimal topology peers with the best connections connect first.


Level 1 has 8 peers, 8 total
Level 2 has 16 peers, 24 total
Level 3 has 32 peers, 56 total
Level 4 has 64 peers, 120 total
Level 5 has 128 peers, 248 total
Level 6 has 256 peers, 504 total
Level 7 has 512 peers, 1016 total
Level 8 has 1024 peers, 2040 total
Level 9 has 2048 peers, 4088 total
Level 10 has 4096 peers, 8184 total
Level 11 has 8192 peers, 16376 total
Level 12 has 16384 peers, 32760 total
Level 13 has 32768 peers, 65528 total
Level 14 has 65536 peers, 131064 total
Level 15 has 131072 peers, 262136 total
On level 15, 118936 can support two downstream peers, 12136 support only one
Level 16 has 250008 peers, 512144 total
Level 17 has 250008 peers, 762152 total
On level 17, 237856 can support one downstream peer, 12152 support none
Level 18 has 237848 peers, 1M total


Assuming a pessimistic latency of 500ms per level, those on level 18 have a latency of 9s, which could be considered good or bad, however considering the the initial 10mbps uplink, I think it's great. And assuming these streams are being recorded, they would also be sufficient to send the files to the folks who watch the program later on demand.

I see my estimates for video bandwidth are way too high, looking at the bandwidth used for youtube streams, even the HD videos are only 450kbps, so factoring the smaller load on peers, the tree fanout above would be much greater than the binary division I've illustrated, making the tree half as deep, however I leave it as is.

A real streaming network would have to account for dynamic conditions, less ideal topologies, and fault tolerance, however I think my numbers were pessimistic enough to leave some wiggle room too. Large broadcasters would have more initial distribution points anyways.

To tie this all back into the discussion of efficiency, not only does P2P significantly lower the burden for the distributer, but having peers transferring amongst each other inside ISP networks off the internet backbone helps too. This should probably be factored into the protocol.


I envision a P2P set-top box one day that works just like this. If my neighbor's box has a show I want, my box will just download it from his. On the other hand, services running on the edge of the networks is probably the opposite of what companies like ms & google want, since they make more money being centralized gatekeepers. I believe that if the media conglomerates weren't holding us back, we'd already have the technology to build far better content distribution systems than the industry has been willing to do.



"Oops, became a bit longwinded ;) "

Also guilty, but I love CS topics!

Reply Parent Score: 2