I’ve just had my second exam this semester, I got the grade 11 for my presentation of decidable problems and reductions in DAIMI:dModLog. So this stops my run of 13’s… too bad, but I knew that it was just a matter of time.

Now there’s just the final exam in DAIMI:dDistSik left — I’ve got a week to prepare 16 questions so if I can do three each day then I’ll be fine. That’s it for now, later…

I’m still looking around for a new quiet system to replace my old system. Today I found the SID FutureClient® which is a complete, modern PC built without any fans at all!

The PC is build around a special liquid cooling system which means that it can use a 2.4 GHz Pentium 4 without requiring a fan. The power supply is able to deliver 170 W with an efficiency of over 85%. This means that it will loose 30 W of power as heat to the air when drawing 200 W. The rest is converted from AC to DC and then later turned into heat in the CPU, the harddrives, the RAM etc.

The case is built from aluminium and looks very stylish. It’s so strong that I will be able to put my big Philips 201P10 21″ monitor on top of it.

All very nice… the catch is the price tag: about 2,000 €. That’s a lot of money for a new computer, especially when you don’t get bleeding-edge performance. But then again, such a PC isn’t aimed at people who require the latest hardware to play the latest games, it’s rather aimed at people who are willing to pay that extra to get a completely silent PC.

I guess that if I saw one of these in real life running GNU/Linux, then I would buy it right away — for now I’ll look around a little more. I’ve had my old machine since September 2000, so a month more or less doesn’t make a huge difference. It also seems that I keep finding new interesting quiet products, it’s certainly nice to get an idea of the available options before you go and pay more than 1,500 € for a new machine.

I had my first exam yesterday and it went absolutely fantastic for I got the grade 13. It was an oral exam in Real Analysis, I got a question where I had to talk about the Lebesgue integral of a bounded measurable function over a set of finite measure.

That was a pretty good question, I started by defining the Lebesgue integral of a simple function, and then proceeded by proving that the supremum of integrals of simple functions phi; dominated by a given function f equals the infimum of integrals of dominating simple functions psi; if and only if the function f is measurable. After that we talked about other things until my lecturer and the censor were satisfied and I left the room. They then discussed the grade for what seamed like a very long time… finally Jørgen Vesterstrøm came out and told me the good news.

To put things into proper context, I have to mention that I’m not the only one who got 13 at this exam. Mikkel Krøigård also made it all the way to the top, and so did at least five other, I’ve heard about a total of seven 13’s at this exam alone. But this is because of the way things work at these exams: if you make a performance that’s 98% correct, then they’ll give you 13. And with the exams in mathematics it’s actually possible to do this reliably because we get the list of questions before the exam. It’s also easier to judge people at these exams because the material we present is so objective — there’s no arguing in math, it’s either correct or wrong.

So now I’ll have to get started with the next exam which lies a little more than a week ahead. See you then!

GimpsterDotCom has (again) laid dormant while I’ve had other thing on my mind… Even though I haven’t edited GimpsterDotCom in the last two weeks, there has been some activity. A very friendly person has given the PHP Tutorial a much needed grammar-check and fixed a lot of my bad sentences — thanks a lot! It’s really wonderful to know that there are people out there who want to help make GimpsterDotCom a better place.

I’ve spend the last five days on a DAIMI:dDistSik project together with Mikkel Krøigård. And by “days” I mean from 9:00 to 24:00 (or more) each day.

The project is actually very interesting, we’ve been asked to implement a reliable connection-oriented transport protocol on a very unreliable datagram-based network. Basically, this means that we were asked to implement something like TCP upon something like IP.

So we started out with an enormously ambitious plan: we wanted to have our transport protocol use the same credit based scheme as TCP employs. So we sat down and read RFC:793 titled Transmission Control Protocol (TCP) and started to work on the state-machine that should be the core of the implementation.

But after having worked on this for a full day, we decided that it was too difficult — RFC:793 describes the format of the packets, the states of the sender and receiver and the actions that are to be performed when a packet arrives, but it does so on a somewhat high level.

We switched from the cool, efficient, all-dancing, but complex credit-based flow control mechanism to the terrible inefficient, but simple stop and wait flow control mechanism. The most important difference between the two is that with a credit-based implementation you have more than one packet on it’s way from the sender to the receiver at any given time — with stop and wait you send one packet and then waits until you get an acknowledgment before you send your next packet. As one can imagine, this is a very poor utilization of the available bandwidth.

But because we had started out with dreams about TCP (and we had even started too late with that) we ended up with almost no time at all. And to make things worse, then we somehow managed to implement the supposedly simple stop and wait protocol in a rather tricky way which made it a nightmare to debug. But we also had a huge number of problems with getting Java to do as we wanted. Java is not very well suited to make this kind of low-level programming where you have to fiddle with individual bits in your header. In particular: Java doesn’t have unsigned types and it insists on promoting smaller integral types (bytes and shorts) to 32-bit integers before doing any bit-wise operations on them. That would not be a problem if it were not for the fact that this widening also does sign-extension! That surprised us a couple of times until we got used to manually masking out the bits we wanted before using a variable with a logical operator.

Despite all our problems, we managed to get it to work — we were finished around 22:00 today with the programs and the report. We’ll be allowed to go the exam When the report has been approved. This reminds me: don’t expect to see a lot of changes here for the next month or so, because I’m having my exams now. But if you have something to contribute, then please do — it’s always a nice surprise to see something new here at GimpsterDotCom, something that I didn’t write myself :-) So long!

One of the reasons as to why I haven’t update GimpsterDotCom for a while is, that I suddenly cannot resolve any DNS names?! There’s nothing wrong with my connection to the Internet, I just cannot resolve DNS names to IP addresses. So I haven’t checked my mail for the last five days, and I haven’t looked after GimpsterDotCom until now.

Although I can’t use the Internet, or at least not use any part of it for which I don’t know an IP address, I’ve still been able to utilize my fine broadband LAN connection through the use of FreeNet. Fortunately my FreeNet node knows most of it’s peers through an IP address, so it still works even though the rest of the system doesn’t. That’s pretty cool! I’ve been trying to upload all the eight CDs that make up the latest stable release of [Debian][]. So far I’ve uploaded two CDs, it’s awfully slow and takes an insane amount of RAM. But it’s doable, it just takes time.

So, please bear over with me until I get this DNS thing sorted out.

Update

I’ve now sorted things out again — there’s now two DNS servers for our LAN, 10.2.2.10 and 10.2.2.12, the first of which doesn’t work at the moment. My machine has a permanent IP address, so I’m not using DHCP and therefore I didn’t discover the change automatically, which left my computer without a working DNS server.

I’ve just emptied my mgeisler@mgeisler.net mailbox and I’ll come back to you as soon as possible. There were 400 mails waiting for me, but the vast majority of these are either SPAM (which TMDA “reads” for me) or traffic from the various mailinglists I follow.

But it’s good to be back on the Internet! :-)