This was a slow week. I didn’t get much done in terms of programming and I also took a short vacation a couple of days to clear my head.

Some late breaking news about Android: Google Android phones make debut.

Estimated time used for the project the past week: 30 hours

The Java Magical Service

JMS is like a magical service. Inject a message about a certain topic into a JMS system and other people, who are interested in the same topic, can read the message as well. Maybe not too much magic, but it does work. JMS has basically two types of message channels:

  • Topics – used by publish/subscribe (pub/sub) where the communication can be many-to-many.
  • Queues – used for point-to-point communication.

In both cases the sender and receiver can be decoupled in terms of both space, time and synchronization as described by Eugster et al. in The Many Faces of Publish/Subscribe. JMS also has a hierarchical topic-based publish/subscribe model which is easy to get into. I’ve been working with Apache MQ to implement a simple JMS based publish/subscribe system. The server part of the system is almost functional, but I haven’t started on the mobile client code yet. I’m not quite satisfied with the way the server system processes all the incoming events because the business logic is spread out into several listener classes. My current goal is to find a more convenient way to arrange the logic so that it will be easier to set different policies for the system. I’ll also start writing some code for Android and find out how easy it is to get Android to talk to a JMS based system. Maybe I’ll have to use one of the alternative transports that Apache MQ provides to make it easier.

I’ve done some checking on IEEE 802.1Q and 802.1p (which is rumored to be defined in 802.1G) in regards to the router that might be used in a practical implementation of this system. 802.1p is essentially a standard for providing QoS at the MAC level. It defines eight different traffic classes which are used by 802.1Q. 802.1Q is the Virtual Bridged Local Area Networks (VLAN) standard. In this standard the IEEE has defined a framework called the Generic Attribute Registration Protocol (GARP) for switches and bridges to work with different types of attribute values. GARP is in turn used by a VLAN management protocol called GARP VLAN Registration Protocol (GVRP) which enables you to manage how VLAN configurations are propagated throughout a network of switches (Cisco has a similar proprietary protocol called VTP).

What seems to be the case is that GVRP can only be used to manage switches when there are several connected in a network. According to this article by HP it looks like the first switch must be manually configured. I’m not entirely sure about the technical details, but from what I can tell it doesn’t seem to align with our needs of just configuring one switch and getting it to forward Internet traffic.

Estimated time used for the project the past week: 40 hours

Progress report for the past week

I’ve read a lot about about messaging systems, JMS and how they relate to publish-subscribe, but I think I need to start programming to get a feel for what it really is about. The Enterprise Integration Patterns book that I’m borrowing has kept me busy most of the week. I’ve also drawn a few other models for the system with different level of abstraction. You can view the new models in this PDF: Location-based event system models.

I’ve checked out Apache MQ and is seems like something I can use. It supports lots of different transport protocols for message exchange and the configuration doesn’t seem to be too tricky. It also supports JMS 1.1 which is the latest version of JMS. I also tested Git a bit and I’ve decided to start using it on this project. At the surface it doesn’t seem to be very much different from Subversion, which I’m used to, but the fact that you can commit to a local repository/index is a big bonus. I look forward to explore the distributed features in Git.

Estimated time used for the project the past week: 38 hours

Progress report so far

So far I’ve read a lot of literature about location-based/aware systems and also a few things about publish-subscribe based event systems. The architecture of the system I intend to design is shown as part of a set of slided I made a while ago. I found a way to make the architecture more generic by using a publish-subscribe based system on the home server. Check these PDF files for the original and the new slides.

The original slides were based on the assumption that the mobile phone already knew the status of the alarm system. That isn’t very realistic so the new slides makes use of an event driven system (publish-subscribe) to make the phone aware of the alarm system status. The correct order to read the slides would be to first look at the new slides and then the process continues in the original slides.

I’ve also tried out the Android SDK and written a few small applications to understand how it works. Since there might be better mobile phone frameworks/platforms that can be used I’ve also done some research into other related frameworks/platforms. The disadvantage of Android is obviously that it doesn’t have any supported phones on the market yet, but on the other hand it’s a quite powerful platform compared to some of the others which are already in the hands of consumers.

I estimate that I’ve used about 40 hours on the project the last 7 days. It’s probably a bit more than 100 if you count from when I began and till now. I’ve also put together a project plan which is nice to have.

Progress report for week 51

The DECS project report is complete and has been delivered for evaluation. The report can also be downloaded from the link below. I’ll also add some work units to the BOINC server soon, so that people can try it out.

If you happen to need software for plotting I highly recommend gnuplot. I also tried R for a few hours, but that is a chapter in my life I would rather forget. gnuplot lets me do exactly what I needed in a few simple steps, which is more than I can say about R. It might be because the documentation for gnuplot is so exellent or because there are so many good tutorials, but I managed to whip up a couple of graphs in no time at all. If you want some work done, and you want it done now then gnuplot is your friend.

BTW, this is probably the last DECS progress report as well. At least on this website. At least for now :)

Jan Magne,
Over and out

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.

Progress report for week 50

A new draft of the report is complete. This time all the chapters are in place and all the “??” references has been eliminated.

The following is a list of modifications made to chapter 1 and 2:

  • Fixed typos and minor word and sentence bugs.
  • Moved first paragraph of Section 2.1 to Chapter 1.
  • Added reason for redifining ‘one’ to ‘non-zero’ (disambiguation) in second paragraph of Section 2.1.
  • Added reduced and identical matrix disambiguation in Section 2.1.
  • Fixed notation ambiguity at the end of Section 2.1.
  • Added a bit about backtracking in the third paragraph of Section 2.2.
  • DeKnuthified some of the content.
  • Added formal definition of exact cover to section 2.1. (Does it confuse more than it helps?)
  • Added some information and a couple of illustrations about n-queens to the introduction.
  • Added n-queens example with primary and secondary columns in Section 2.1.1. It also makes use of the formal exact cover definition.

Pluss the addition of the chapters about implementation, testing and simulation and the conclusion.

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.

Progress report for week 49

The report is comming along nicely. It is currently undergoing revision and is expected to be done by the deadline the 20. December.

Inspired by a comment by Hein Meling I put together some notes on how the Dancing Links algorithm could be made non-recursive (read: neither recursive nor iterative). It was more of a side comment from his side, but I’m prone to fall for nerd sniping so this is nothing new.

The BOINC server for the project is now available for the public. It’s not really production ready yet, but take a look if you’re interested.

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.

Progress report for week 48

Lots and lots and lots and lots of work on the report :)

The report is coming along nicely. A draft of the first two chapters is available here. I only added the beginning as that is more or less stabilized. The rest of the report is still undergoing some significant changes so I choose not to include those chapters yet. There are some “??” references which didn’t resolve because the sections they refer to are not included. For the moment you can just ignore them.

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.

Progress report for week 45 – 47


For the most part I’ve been busy with other things like exam reading and a few projects. However, last week I got back to writing on the report so I’m back in business.

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.

Progress report for week 44

Not much happened this week either. I’m finishing a couple of projects this week before I finally can get back to work on DECS.

I got a C on the Petri net model and simulation report of DECS that I mentioned in week 42. The reason given was that the model did not take into account the possibility of deadlocks and resource starvation.

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.