Subject: [P2Prg] CAN

From: Sam Joseph <[email-masked]>
Date: Wed, 19 May 2004 06:38:58 +0900

Hi All,

So I'm just relooking through the DHT papers, and I had one question 
about CAN (Ratnasamy et al., 2001) that was perplexing me slightly.

In CAN keys are mapped onto a 2D or higher space - I'm clear with the 
idea of hashing a value to map onto a 1D space, but I'm not so sure how 
we map keys uniformly onto a 2D space. I can think of several ways to do 
it, but I wondered if there was a standard approach. We can't just use 
the same hash function for each dimension because then there wouldn't be 
a uniform distribution. Possible alternatives seem like splitting the 
original key in half, or using a different function for each dimension.

It also seemed like the overhead of messages required for topology 
maintenance was not analysed in depth, and also that in order for the 
CAN repair algorithms to work the peers seem like they would need to 
maintain additional state beyong just knowing who their neighbours are 
in the space. As I understand it the topology maintenance messages are 
information about a peer and its routing table, broadcast to neighbours 
in the space. When a peer fails, its neighbours have to communicate each 
other - so it seems like they would have to be caching information from 
the topology maintenance messaging ... This probably doesn't affect the 
order of how much state needs to be maintained, but it seemed like 
something that needed to be stated more explicitly.

Anyways, if anyone has any thoughts on these things I'd be very 
interested to hear about it.

Many thanks in advance
CHEERS> SAM

S. Ratnasamy, P. Francis, M. Handley, R. Karp and S. Schenker, “A 
scalable content-addressable network”, Proc. ACM SIGCOMM, 2001

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