On Thursday 10 April 2008 19:14, Michael Rogers wrote: > Colin Davis wrote: > > It seems like some sort of "in network" solution, such as a variation of > > a tit-for-tat measurement.. Inserting file A with 100X redundancy is > > approximately the same as inserting file B which is 100X the size.. If > > we enforce fairness on accepting traffic unless they've "earned" it, a > > user can then decide how to "spend" that bandwidth.. One mostly lossy > > 10M file, or 10X redundancy on your 1M file. > > In principle I think this is a great idea. In practice I've spent a lot > of time working on tit-for-tat-ish incentive mechanisms for multi-hop > networks, without much success. That probably just means I should find > another line of work, but it might also mean the problem is harder than > it looks.
This is interesting. We will eventually need some form of tit for tat, won't we? Not necessarily in inserts, IIRC we talked about it as a way to prevent an attacker flooding opennet with spam requests/inserts? It's something we've talked about for a long time anyway... > > In a single-hop network such as BitTorrent, the value provided by a > neighbouring node is directly related to how much it spends on you: if > it spends 1MB of bandwidth uploading to you, you receive 1MB of data (or > some fixed fraction of 1MB, allowing for overhead), all of which is > directly useful to you. That makes it easy to design strategies that > reward cooperative neighbours and punish uncooperative neighbours. (It > turns out that TFT isn't actually a very good strategy in this context, > but the point is that good strategies can be found.) > > But in a multi-hop network the relationship between cost and benefit is > more complicated: assuming all nodes allocate bandwidth to cooperative > neighbours, if you receive a request from neighbour A, should you > forward it to neighbour B? First, will you get a response or will you > spend the bandwidth and have nothing to show for it? Second, if you get > a response and return it to A, will the cooperation you earn from A be > worth more than the cooperation previously earned from B and spent on > A's request? > > I've been banging my head against this problem for a while, and I can't > come up with a model where it makes sense for selfish nodes to forward > requests. It makes sense to answer requests locally if you can, to earn > cooperation from your neighbours, but it doesn't make sense to forward > them. Unfortunately if everyone behaves like that, the network doesn't > function. > > Doubtless someone else can solve this problem, but at this stage I'm > just hoping they won't solve it before my thesis is written up. ;-) > > Cheers, > Michael -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 189 bytes Desc: not available URL: <https://emu.freenetproject.org/pipermail/tech/attachments/20080410/a3dcc1ca/attachment.pgp>