Why have I been quiet for a while? Well most of my entries related to sensor networks are now posted on WSNblog.com instead. WSNBlog.com recently got featured on M2M magazine (although they got some information wrong about us). Some comments on this issue of the M2M magazine: I am keeping an eye out for ArchRock's IPv6 solutions. Lets see how the industry responds to the idea of running IPv6 on sensornets. I recently attended a talk by Bob Metcalf at Cambridge, MA. It seems to me that Bob and Ember believe that they have found the "killer app" in energy management. I wonder how Metcalf's law will scale in that market.

Computer History Museum has this talk by Eric Brewer (UC Berkeley) where he goes over the rise and fall of Inktomi. I highly recommend watching this talk for folks interested in the history of the Internet, case studies of startup companies, insight into the Internet bubble, or technology research in general.

Inktomi was founded in 1996, by Eric and a Berkeley grad student, and went onto the Nasdaq 100 before it was bought by Yahoo! in March 2003. Yahoo search and MSN search are still powered by the Inktomi engine. At one point, Eric actually got a little emotional while talking about Intkomi and I can clearly relate to why.

At the end, he talks about the time when his 10% shares in Inktomi were worth a billion USD and he got interested in doing something for the "third world countries". Eric (along with Umar Saif) is the program co-chair of the NSDR workshop that I am organizing. NSDR'07 is specifically aimed at bringing the benefits of networking technologies to the third world.

Below is the GoogleVideo embedded video of the talk:

Joe Polastre, CTO of Moteiv (one of the co-authors of our recent MAC editorial) recently got featured on Discovery Channel and Science Channel. Below is a YouTube embedded video of the Discovery Channel broadcast. The story was later picked up by CNN as well.

I was a visiting researcher at SICS (Sweden) last fall where I had an amazing time working with Thiemo Voigt and Adam Dunkels. Adam's work on Protothreads recently got accepted at ACM SenSys 2006 and I am listed as a co-author on the paper. SenSys is the premier conference in sensor networks. Much like what SIGCOMM is for networking folks.

"Threads vs. Event-Driven Programming" is an age-old debate in computer systems research. The late Roger Needham (Cambridge) tried to settle this debate with the "duality argument" in 1979 (essentially saying that threads and events are inter-convertible and are the same thing), but the Threads vs. Events remained a hot debatable topic e.g. Ousterhout (creator of the Tcl scripting language) made strong arguments against Threads in his "Why Threads Are A Bad Idea" invited talk at 1996 USENIX Technical Conference. An example of arguments in favour of Threads can be Eric Brewer's (UC Berkeley) "Why Events Are A Bad Idea" HotOS IX (2003) paper.

Protothreads are extremely lightweight stackless threads designed for severely memory constrained systems. One way to think about Protothreads is that they are a proof-of-concept of the 1979 Roger Needham "duality" argument. They are "something in-between" threads and event-driven programming. Maintaining state-machines makes event driven programming hard, but threads take too much memory to make them feasible on memory-constrained systems (e.g. sensor networks). Protothreads reduce/eliminate the need for maintaining explicit state-machines while keeping the memory overhead very low. Protothreads, unlike traditional threads, are stack-less and their memory overhead is very small (only two bytes per protothread).

For more details, read the Protothreads SenSys'06 paper. Also, you can download and use the Protothreads library.

Protothreads are already gaining popularity (checkout the Google hits). Here are a few interesting links:

• Slashdot | Protothreads and Other Wicked C Tricks
• The venerable Jack Ganssle talks about Protothreads in his Embedded Musings
• Framework Lab ported Protothreads to Objective-C
• Protothreads Library 1.3 Released (OSNews)

I found out about Erdős Numbers from my alma mater faculty Arif Zaman, who has done some early work on random number generation. After seeing the list of famous paths to Erdős numbers I got curious about my own Erdős number (if it was not infinite). Let me explain Erdős numbers a little; Paul Erdős is the only person with an Erdos number 0 Anyone who has published a paper with Paul Erdős has Erdős number 1 So, Arif Zaman has an Erdos number 4 because he published a paper with George Marsaglia who published a paper with George P. H. Styan who published a paper with Paul Erdős. The Erdős number is basically a measure of research collaborations taking Paul Erdős as the center. The Erdős Number project found that Fields Medalists and Nobel Prize winners have small Erdős numbers. In other words this shows that the research circles are smaller than what we imagine them to be e.g. Albert Einstein (Physics) has Erdős 2, John Nash (Economics) has Erdős 4, Stephen Hawking (Cosmology) has Erdős 4

The online collaborative distance search page was not so useful in calculating my Erdős number primarily because I am not a Mathematician or a Theoretical Computer Scientist. So I had to manually calculate my Erdős paths and find the limit on the Erdős number (I had to find manual paths to someone recognized by the Erdős project database and reduce the overall path length as much as possible). Here are some paths I found (listing only one example path for each Erdős number):

• Erdős 7 Path: Muneeb Ali ------ Joseph Polastre ------ David Culler [Culler, David E. is recognized as Erdős 5]
• Erdős 6 Path: Muneeb Ali ------ Koen Langendoen ------ Frans Kaashoek [Kaashoek, M. Frans is recognized as Erdős 4]
• Erdős 5 Path: Muneeb Ali ------ Kay Römer ------ Friedemann Mattern [Mattern, Friedemann is recognized as Erdős 3]

So I can say that my Erdős number is 5? What it really means is that from my co-author index on DBLP Bibliography after 5 clicks you should be able to see Paul Erdös. Small world!