[ax25-layer2] line in the sand revisited

[Jeff King]

Your right Scott, layer one involves more then just modems, it also involves channel access methods as well as the radio itself. The german DAMA method, which I believe was mention here, is a polling system, and can greatly improve efficiency. Karn's MACA method, is a layer one channel access method (which by the way, was "borrowed" by 802.11b as RTS/CTS). Even reducing the digipeater lengths, as pete is suggesting, ultimately translates to a level one decision, as it reduces the footprint of the RF signal, and as such reduces the number of hidden terminals. Even something simple, like slotted aloha, would greatly improve things (and easy and transparent to do on APRS since ya' all have GPS'es).

I'm sorry to keep beating on layer one to everyone, but in the real world, it is where we can reap the most benefit and we can develop at layer two and three without giving it any thought. In most amateur applications, layer one is seriously flawed, from APRS all the way to Winlink Pactor3 (which doesn't listen for other modes before transmitting). Radio ultimately means layer one, and as radio amateurs, we need to pay attention to it. We can't bury our sand in it and hope our gee whiz layer 2/3 implementation will fix it. They all work hand in hand.

BTW, as an aside, the ARRL HSMM is doing some testing of wide bandwidth digtail modes using NVIS propagation on 80 meters. Doing some testing later this afternoon if your interested. Contact me off SIG. Also, I have a 80 meter warbler and will be looking into modifying its passband so interested in hearing your feedback on it.



On Fri, 16 Sep 2005 09:31:35 -0700, scott at opentrac.org wrote:

>I'd certainly like to improve the layer 1 situation as well.  If
>we're just talking about switching to MSK or something that wouldn't
>be a big impact on layer 2, but I'd imagine that something like the
>multi-channel PSK31 SSB mode I was talking about would require some
>serious redesign of layer 2 if you've got some kind of coordination
>of channel access.
>
>As an aside, what really interests me about that sort of mode is the
>ability to build an automated traffic handling system that'd work
>with a compact, inexpensive transceiver like the PSK80 warbler.