Archive for February, 2007

IP Datagrams on Avian Carriers

Wednesday, February 28th, 2007

From a recent article: Scientists with the Robot Engineering Technology Research Center of east China’s Shandong University of Science and Technology say they implanted micro electrodes in the brain of a pigeon so they can command it to fly right or left or up or down.

How does this relate to networks? There is a RFC standard (RFC 1149) on using pigeons to carry IP datagrams.

(And if you are really interested in the absurd, look at this article on similar work on sharks!)

2 meetings: one on Security & the other on Enterpise

Thursday, February 22nd, 2007

Recently, I’ve been at two interesting meetings:

1st: Post-grad student club meeting of the Centre for Security and Crime Science (CSCS). It’s a nice opportunity to network with UCL students and faculty members who are interested in security. I was amazed at the number of projects dealing with sensors of which I’ve never heard a word :-) The club will host some very interesting talks.

2nd: UCL Enterprise Society. Great talk by Sumit – CEO of Kuluvalley. The talk was a Lessig style one – for each slide he had either one huge text sentence or one big image (here is an example). Cool stuff!

Anonymous Nicknames vs. Real Identities in Reputation Systems

Friday, February 9th, 2007

“MySpace has been talking to eBay for several months about ways they could partner on what MySpace calls “peer commerce,” according to people familiar with the matter. The idea is to let MySpace users buy and sell items from each other using eBay’s online-commerce technology and its PayPal payment system, these people said. MySpace users would be able to post items for sale on their profiles, and their eBay auctions would be automatically updated, according to one person close to the discussion”.

Buy, cell, hold

Friday, February 9th, 2007

(From The Economist) The technology revolution may be coming to poor countries via the mobile phone, not the personal computer, as it did in rich ones. … TradeNet, a software company based in Accra, Ghana, will unveil a simple sort of eBay for agricultural products across a dozen countries in west Africa. It lets buyers and sellers indicate what they are after and their contact information, which is sent to all relevant subscribers as an SMS text message in one of four languages. Interested parties can then reach others directly to do a deal.

Trust propagation and the origins of PageRank

Wednesday, February 7th, 2007

Since Matteo’s seminar about neighbourhood maps a couple of months ago I’ve been wondering whether PageRank could be applied to a local view of a social network to calculate trust scores. (This might be useful in the new darknet version of Freenet, for example.) One of the Freenet developers pointed out that PageRank is patented, but Wikipedia showed that using eigenvector centrality to calculate the importance of nodes isn’t a new idea.

After following a few references it turns out that the idea of propagating trust/status/etc across a graph dates back to at least 1953 [1]. Pinski and Narin [2] suggested normalising each node’s output by dividing the output on each outgoing edge by the node’s outdegree. Geller [3] pointed out that their model was equivalent to a Markov chain: the scores assigned to the nodes followed the Markov chain’s stationary distribution. In other words, propagating trust/status/etc with normalisation at each node is equivalent to taking random walks from random starting points and counting how many times you end up at each node.

The only difference between Geller’s model and PageRank is the damping factor: in PageRank you continue your random walk with probability d or jump to a random node with probability 1-d. (Incidentally, when the algorithm’s described this way rather than in terms of a transition matrix, it’s easy to see how you could implement it on a web spider.)

[1] L. Katz, “A new status index derived from sociometric analysis,” Psychometrika 18 (1953), pp. 39-43. (PDF)
[2] G. Pinski and F. Narin, “Citation influence for journal aggregates of scientific publications: Theory, with application to the literature of physics,” Information Processing and Management 12 (1976), pp. 297-312. (PDF)
[3] N. Geller, “On the citation influence method of Pinski and Narin,” Information Processing and Management 14 (1978), pp. 93-95. (PDF)