[freenet-support] Question about handling churn in FreeNet

[Nawfal Abbassi Saber]

Hi FreeNet,

I'm doing a research about peer to peer file storage systems and i would
like to know if the system FreeNet has some mechanisms to deal with churn.

Cordially

Nawfal.
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Re: [freenet-support] Question about handling churn in FreeNet

[Bert Massop]

On Wed, Jan 6, 2016 at 10:59 AM, Nawfal Abbassi Saber
 wrote:
> Hi FreeNet,
>
> I'm doing a research about peer to peer file storage systems and i would
> like to know if the system FreeNet has some mechanisms to deal with churn.
>

Short answer: yes, Freenet has mechanisms to deal with network churn


I suppose you'd also like to learn something about those mechanism, so
let me introduce you to the basic concepts.

Most files on Freenet are stored with several layers of redundancy.
1. On the lowest level, for large files, Freenet uses segmentation
with forward error correction to keep entire files available when some
of their segments are unavailable on the network.
2. Freenet nodes store newly inserted data they consider to match
their own location closely enough, so a single segment may end up
stored on multiple nodes.
3. When a segment is retrieved, it will be cached by most of the nodes
that relay the data to the requester.
4. After a large file is retrieved, some if its non-retrievable
segments may with probability be recalculated and re-inserted by the
requester, further restoring the reliability of the file.

As for request routing, Freenet maintains a small-world network
topology that allows for efficient routing. This topology can be
maintained even under the presence of network churn. How this works
depends on the particular mode of operation of Freenet, e.g. opennet
vs. darknet, but it boils down to path folding and location swapping
strategies.

For more information, especially on the ongoing work of maintaining
the network topology, please refer to the literature presented on the
Freenet website [0].

Kind regards,
Bert

[0]: https://freenetproject.org/about.html#papers
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