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Average delay is a poor metric of quality in a CSMA/CA system

Monday, December 13, 2010 Posted by

Many works show the average delay of for instance an IEEE 802.11p system which uses CSMA/CA. While varying parameters such as number of nodes, supplied traffic per node and the like the average delays are provided. Though averages always provide nice indications for variates which are normally distributed, they are prone to misinterpretation in case the underlying variable is exponentially distributed (or otherwise long-tailed). Therefore, it is always a good idea to also provide a histrogram which enables estimation of the probability density function. These provide good insight and a ground to start from when we want to calculate, for instance, the maximum delay in 90% of the cases. Though a maximum cannot always be derived (or it is very large, cluttering figures) a properly binned (or distretised) histogram is an intuitive way to convey a notion of the delay. Read the rest of this entry »

Attacks by “Anonymous” WikiLeaks proponents not anonymous

Friday, December 10, 2010 Posted by

For a number of days the websites of MasterCard, Visa, PayPal and others are attacked by a group of WikiLeaks supporters (hacktivist). Although the group calls itself “Anonymous”, researchers at the DACS group of the University of Twente (UT), the Netherlands, discovered that these hacktivists are easy traceable, and therefore anything but anonymous. The LOIC (Low Orbit Ion Cannon) software, which is used by the hacktivists, was analyzed by UT researchers, who concluded that the attacks generated by this tool are relatively simple and unveil the identity of the attacker. If hacktivists use this tool directly from their own machines, instead of via anonymization networks such as Tor, the Internet address of the attacker is included in every Internet message being transmitted. In the tools no sophisticated techniques are used, such as IP-spoofing, in which the source address of others is used, or reflected attacks, in which attacks go via third party systems. The current attack technique can therefore be compared to overwhelming someone with letters, but putting your address at the back of the envelop. In addition, hacktivists may not be aware that international data retention laws require that commercial Internet providers store data regarding Internet usage for at least 6 months. This means that hacktivists can still be traced easily after the attacks are over.

A complete report about that can be downloaded from this link.

source: http://www.utwente.nl/ewi/dacs/news/archive/2010/wikileaks.doc/

Inventum HK100B – King of Coffee

Friday, November 19, 2010 Posted by

Een nieuw huis, en wat is een leuker geschenk van je familie dan een koffiezetapparaat? Na uitvoerig rondkijken (en niet in de laatste plaats op basis van de smaak van de koffie!) kreeg ik een Inventum HK100B. Spoedig bleek dat dit apparaat met recht de naam “King of Coffee” draagt!
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(K)Ubuntu 10.10: No Sound!

Sunday, October 31, 2010 Posted by

I had a perfectly working system of Kubuntu 10.4, but after the dist upgrade yesterday, sound does not work anymore! Read how we solve this… Read the rest of this entry »

ING Zakelijk – alleen op werkdagen

Sunday, October 24, 2010 Posted by

ING Zakelijk – voorheen Postbank Zakelijk – heeft een website voor internetbankieren. Superhandig, welke bank heeft dat tegenwoordig niet? Maar de ING heeft iets wat andere banken niet hebben: regelmatige storing (en dus volledig niet werken van de website), met name in de weekenden. Read the rest of this entry »