http://www.citeulike.org/user/scottr/article/503372
This is an interesting paper, which is quite recent, and deals with the same kind of issues I am currently looking at. The main crux of the article is that in order to do MAC research we should be using an overlay approach - implementing the MAC in software on top of the existing 802.11 MAC - as it makes it possible to test the MACs in real world environments. The argument for the need for testing MACs in the real world is one that I would like to persue. They also argue that replacing the MAC layer is too costly, and so they present the overlay solution. The MAC they present using this technique allocates timeslots using a distributed algorithm, and increases the total throughput of the system. The paper also outlines some of the current problems with 802.11 in terms of unfairness, etc.
This sounds similar to what I want to do with the Atheros cards, although it does have differences. In this paper, they are essentially doing scheduling of writes to the NIC, but still using 802.11 for framing, addressing, etc. In my system, I would like to run an entirely separate MAC using broadcast 802.11 frames. Obviously this has quite a bit of overhead, but allows cheap deployment of the protocol, and allows us to (mostly) test it in a (mostly) real-world environment. The WAG cards provide us with a way to run the entire MAC on the hardware without 802.11 encapsulation, but that is a very expensive option. More to come on this later.
July 13th, 2006
What have I been up to lately? Well, I’ve been working on implementing a point-to-multipoint wireless MAC protocol. The interesting thing about it is that it was first designed in SDL, then using Dean’s sdl2cpp translator and the WAND Protocol Development Environment (WPDE), I’m able to get it going in actual hardware (using the WAG cards at this point). Eventually, I’ll write a wrapper so that we can deploy it using Atheros based wireless cards - although that’s going to take some hacking. Essentially the last couple of months has been designing the protocol, learning SDL, implementing the protocol in SDL, and then working with Dean to work his WPDE stuff into a useable state. At this point we’ve nearly got the WAG framework working with a simple point-to-point MAC, and once that’s going I’ll be able to get my point-to-multipoint MAC going.
The MAC is based around token-passing, which we hope will help to avoid the hidden-node problem, as it’s being designed with long-distance, rural networks in mind. There is very little overhead due to not having to use interframe spacing, etc. It should be good to see it going.
In the next six or so weeks I have to write a full proposal for my Ph.D, which will involve sorting out exactly what my research is going to be. At the moment it looks like I’ll be continuing to look at wireless MAC protocols, specifically how to deal with packet loss. For example, we would like to see whether it’s feasible to selectively acknowledge portions of a frame, etc, rather than having to re-transmit entire frames. Looking at modelling loss/bit-errors would be a part of this. During this, I will be attempting to argue that to effectively test MAC protocols we need to use real hardware, rather than just relying on simulation results. Hopefully I will be able to use the WAG environment to validate (or invalidate) simulation environments, and possibly come up with better simulation models. Things are still up in the air, and the next few weeks will involve a lot of literature search to try and narrow my focus a bit more.
July 13th, 2006
Thought I’d drop a plug in here for the coolest app I’ve seen in a while, LyX. LyX is a “document processor”, essentially a nice GUI front-end for LaTeX. It’s very very impressive, and also integrates very nicely with BibTeX. Should make writing my upcoming Ph.D proposal quite a bit easier.
July 13th, 2006