[freenet-dev] Alpha, Darknet routing, et al.

[Robert Hailey]

On Feb 4, 2008, at 7:24 PM, Michael Rogers wrote:

> Matthew Toseland wrote:
>> Swapping creates this problem. Or does it? Could you perhaps do  
>> some simulations of two networks of different sizes weakly linked  
>> and show whether they get independant location spaces, or whether  
>> swapping tries to put one of them within the global keyspace for  
>> the other?
>
> Here's a quick simulation that shows that two weakly-connected  
> subnets move into separate regions of the key space. Each subnet has  
> an ideal Kleinberg topology and starts out uniformly distributed  
> across the whole key space, and there are also a few random links  
> between the subnets - this is meant to represent what would happen  
> if you created a few links between two mature networks, or between a  
> real network and a Sybil network.
>
> I couldn't be bothered to do a nice GUI so the output is just a  
> series of histograms: on each line the key space is divided into 20  
> regions, and each column shows the number of nodes from the first  
> subnet in that region. Initially there are roughly 50 nodes in each  
> region, but swapping causes the subnets to segregate so that  
> eventually most regions are almost exclusively occupied by one  
> subnet or the other.
>
> It's kind of interesting to compare this with "white flight" in  
> sociology...
>
> Cheers,
> Michael

For a "quick simulation", I think this is an excellent demonstration!  
However, I think that there are two major errors.

First, there is an equal chance of nodes from either network swapping.  
In the freenet network (since swapping is done through the network) it  
is not equal (if for no other cause than the scarce links between the  
two networks). More on this below.

Second, it looks like you forgot to actually make any connections  
between the two networks; without the stress points (plus the fact of  
equal weighting on swaps), it is no wonder the nodes flee so quickly!

Once I added the joins to the two networks on your sim, I noticed that  
the networks would "bunchup", but not split the keyspace. However, I'm  
not sure the lack-of-keyspace-split helps either side of the argument  
as these swaps are are applied to stable/mature networks to begin  
with. What this demonstrates is more the merging of two large networks  
(e.g. freenet-china and freenet-usa finally get linked up), and that  
they maintain there keyspace.

Speculating about the swap probability...

ASSUMING that the keyspace would be split (i.e. as the networks grow  
up together) [which I still don't think is the case], then as the  
probability of swapping becomes equal the two networks occupy the same  
key space (as Michael's supplied simulator). However, surely as the  
probability of swapping (between the two networks) approaches zero  
they overlap the keyspace. Actually, it is well before zero...  
logically it is that small probability of randomizing the location  
after the swap (new locations entering the network at the same rate  
they leave).

I've quite enjoyed playing around with this, particularly tracking  
particular nodes in the network to see if I could catch the two  
networks rotating to match each other, but also varying probabilities  
of swaps across the networks.

--
Robert Hailey

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