Steve Dimse K4HG wrote:
> On 3/30/99 3:49 PM Jeff King ([EMAIL PROTECTED]) wrote:
> >
> >You stated earlier that "There is no need for areas outside of propagation
> >range to be on the same frequency". You also stated that "the 144.39
> >allocation is for North America".
> >
> The message I responded to was from an Austrailian ham, complaining that
> 144.39 was in their weak signal band, even though it is not within the
> weak signal band in the US.
So the statement "There is no need for areas outside of propagation
range to be on the same frequency" is not true within North America?
>
> >Correct me if I am wrong, but typical VHF coverage ranges are line
> >of sight, not continent wide.
> >
> Yes, but the idea is that each digi is within line of sight of each
> other, forming a continuous network. That there are holes is inevitable,
> but the goal is still one single link. Right now you can drive from
> Atlanta to Boston without ever being out of range of a digipeater and
> internet gateway on 144.39.
Shades of 145.01, and this is a *technically* sound network design? Hey,
shouldn't South America be on 144.39 also? (a line of digipeaters down
Central America)... or maybe we could float some digipeaters on some buoys in
the Atlantic... maybe put a single frequency digipeater on a 1000 foot tower..
> >So tell me why you think a continent wide frequency allocation is
> >not *technically* unsound as you stated?
> >
> I did not state a continent wide frequency allocation was unsound. I said
> a worldwide allocation was unnecessary. Big difference!
I've asked the question twice, and twice you didn't answer it. It is your
opinion that a _single_ frequency, continent wide 'network' is
*technically* sound? Note that politically expedient and technically
sound are not the same thing.
> >You might want to consider the "145.01mhz" bbs network in the
> >late 1980's to put this in perspective. (except in APRS's case it is
> >worse).
> >
> APRS is completely different from a BBS system.
The underlay issues are EXACTLY the same. Your explaining a application
to me, this is a level one through level 3-4 issue. At best, the APRS 'network'
appears as a pure aloha implementation, much as the 145.01mhz bbs network
appeared. Channel effiencecies are very poor when heavily loaded. This
is not good network design.
You might want to refer to some of the article written in PSR back in the
later 80's, early 90's that went over some of these issues. Tom Clark wrote
a number of them.
While I understand why things were done the way they were when APRS
was first conceived, its time to step back and stop putting band aids on it.
Stop being so defensive about APRS. Granted it works and is impressive,
and you certainly have done alot with it, that doesn't mean it couldn't be
improved. I hope more can be done to make AAVL (Amateur AVL) a
open standard within the Linux community. I think the PIC-ET project
is a good chance to scrape the present APRS protocol and come up with
something that works a bit better, at least in the lower layers (and it likely
wouldn't affect your applications much). Just because the registered
APRS authors do it a certain way doesn't mean innovation should be stifled.
And, BTW, I have absolutely no problem at all with someone making money
off their labors.
While to a certain degree I see the need for 144.39 for legacy systems and/or
a calling frequency, there is no reason local fixed users, and local travelers
should be on it. And in no way shape or form should it be used as a "network"
due to hidden terminal issues and other factors. That's why I brought up 145.01,
these issues were beat to death in the late 1980's. The physics haven't changed
just
because you call it APRS.
So here are a few things I have considered for Amateur AVL (AAVL):
A real addressable connection less protocol (to much overhead with AX.25)
Simple FEC (so a PIC could deal with it)
Broadcast rate adjustable for speed (faster doing 60mph, slower doing 20mph)
A control channel (maybe 144.39??) to tell users about local lans and for
handoffs for mobiles going between LAN's.
Buffering POSITS received on the LAN channel to be sent in one transmission on
the hand-off and/or backbone channel
Obviously there could be alot more, but you get the idea.
What I see happening with APRS on a single frequency is it being a victim of its
own 'success', much as the BBS network on 145.01 was. You can either keep
applying the band aids or consider some of those issues now.
-Jeff
