[ax25-layer2] General Concept Conglomeration

[Jeff King]

On Fri, 16 Sep 2005 08:52:47 -0500, Jason Winningham wrote:

>Is there really enough difference between Bell 202 and MSK to matter
>at layer 2?

No, but that is like saying is their really enough difference between  FM and SSB to matter with the sound coming out of your speaker. Your looking at a 10+db hit between MSK and a typically misadjusted Bell 202 UI frame transmitter on APRS.

Layer one is where the rubber meets the road. If it is flawed, everything above suffers. FEC also must be done beneath AX.25 to be effective as well, and it would offer considerable improvement on UI frames,in particular in a APRS mobile environment with fast flutter. 

And yes, I realize the official statement is this list is "not APRS centrentric" but one only need look at the influx of APRS players to see that is the primary interest. And there is nothing wrong with that, in particular since that is heaviest use of UI frame AX.25. But if one wants quantum improvement, one must be honest with oneself. It also would help the focus, which I assume is APRS NSR, or no source routing. I read the paper Pete listed and it seems interesting to me. I'd focus on that first as it seems it could offer some benefit.


>I don't think we can ignore the fact that, in order for any
>resulting specification to be useful, we must take into account the
>ability to _implement_ that specification. 

Right, and off the shelf embedded Linux could do that NOW, cheap and easy.. Alot has happened since 1984 and we shouldn't hobble ourselves with 1984 class processors. 

>I personally don't think
>that something _requiring_ a full PC to implement is viable, because
>of power consumption.

If your using a free throw away computer, yes your right. But there are embedded intel class Linux PC's that run with less power consumption then those 1984 TNC's. And I might add at less then half the cost of that 1984 TNC (and that isn't even adjusting for inflation!!)

http://www.soekris.com/  ~ 7 watts
http://www.pcengines.ch/wrap.htm  ~3-5 watts

And then of course their are the Linux OS ARM processors, which can take it even lower. Both the NLUS and WRT54G both run Linux athough a sound card interface might be problematical. Of course, there are $140 class ARM boards that run Linux out of the box, and sound cards do work with them. About 2 watts.

And as for Itsy bitsy pics, please look at the MX-COM link I posted. MSK and FEC all on one chip and quite happy to talk to a PIC.



-Jeff