Re: [p2pi] Information in an ALTO protocol

On Sep 15, 2008, at 7:09 AM, Ye WANG wrote:
> We have seen many studies on video streaming applications that  
> prefer higher-uplink-bandwidth peers.  I certainly agree with you  
> that the system may somehow get 'blocked' if all clients naively  
> select the highest-uplink peer to be parents.

Better yet, if this is taken literally, the system turns client/ 
server: the peers with absolute highest uplinks form the server bank  
and nobody else uploads anything.  This, of course, dramatically  
reduces swarm efficiency and thus download rates.

If done as a preference, the effect is not as extreme, but still a  
move in the same counterproductive direction.

> Analysis based on a fluid model of P2P file sharing system indicates  
> that bandwidth matching can help improve average file download rate.

I'd like to understand this better.  I understand the effect with more  
linear response -- bigger uplink now means proportionally higher  
uplinks of your peers, which means higher download rate, linearly.  I  
don't yet see why capacity matching will improve average rate.

Anyway -- the sublinear response is consciously designed and desirable  
-- with it, high-capacity peers still have an incentive to contribute,  
while a majority of peers see improved outcomes.  Think of a log(rate)  
utility function -- 50% better outcomes for 10 typical peers are worth  
30% worse outcome for 1 unusually well-provisioned peer.

Making the response more linear will improve the outcomes of a few  
very well-off peers at the expense of a large number of typical ones.   
I do not yet see why it is desirable.

--
Stanislav Shalunov