On 3/30/99 5:21 PM Jeff King ([EMAIL PROTECTED]) wrote:
>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?
>
All of North America is within propagation range of another point. Yes,
if North America were two islands separated by 500 miles, then the two
halves could be on two separate frequencies.
>>
>> >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,
Yes, it is a sound design, for this application. If we were supporting a
bunch of BBSes and users, it would not be. The one-to-many paradigm of
APRS is different. A car drives from Atlanta to Boston, and the operator
never needs to change frequency. Since APRS uses generic aliases like
WIDE and RELAY, the user never needs to modify his unproto path. There is
much more to the design of APRS RF network, like the WIDEn-n algorith,
callsign substitution, and TRACE digis that are far beyond the scope of
this list.
The take home message is this isn't a BBS network--the data, protocol,
and user needs and expectations are different. It works well with the
present levels of use. Yes, if APRS suddenly tripled it's users, there
would be problems. But that isn't happening...
>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..
>
We have one at 1000 feet to the south of Miami, so we have most of the
Straits of Florida covered. Add a couple in Cuba, the Caymans, and a few
oil rig or floaters and we'll be golden, HI! Seriously, if building such
a network were a realistic goal, then yes indeed, any South American APRS
nets that form ought to be on 144.39. I don't think that is a very likely
scenario though!
>> >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.
>
I'm sorry, but even now when I read the statement "*not technically*
unsound as you stated" it sounds like you are quoting me saying it is
unsound. Using double negatives often leads to confusion. I wasn't
evading your question, I didn't understand what you were asking.
Yes, I believe that the APRS network on a single frequency is sound. This
isn't a theoretical opinion. There are many hundreds of APRS digis, now
virtually all on 144.39, and it works well! If I were building a
nationwide network for BBS, TCP, or other point to point use, then I
would say putting it on a single frequency would indeed be unsound. APRS
isn't BBS!
>> >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.
>
I disagree, the issues are not the same. In a BBS system, there are one
or a few users connected to a BBS. Each packet must be received intact,
and is of little or no interest to other users. One user's data is
another's QRM. In APRS, it is no big deal if a position packet gets
dropped...you'll get the next one, and all data is of interest.
>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.
>
Please give me some specific references for papers dealing with
one-to-many networking, I'd love to read 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.
>
I don't see any innovation being stifled. If you have something that
works better, it will get adopted. That is what happened with my APRServe
system, and numerous other examples over the years. But you gotta build
the better mousetrap before people will switch to it!
>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)
The whole point of APRS is that it isn't addressable. Everybody gets
everything. If I need to address who is going to see my position report,
then that is a very different system than the present APRS.
>Simple FEC (so a PIC could deal with it)
Sure, this would be nice. There are much better modulation methods than
AX-25. Of course, you are talking about replacing or upgrading many
thousands of TNCs.
>Broadcast rate adjustable for speed (faster doing 60mph, slower doing 20mph)
This can be done right now in the Pic-E, no need to wait for a new
protocol.
>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
>
What I see here are plans for a needlessly complex network. You are
talking about multiple radios at every digi site, and two radios in every
tracked vehicle, one for control and another tunable at the command of
the control station, or perhaps alternate the radio between the control
and local freq. Computer tunable mobile radios aren't common or cheap.
Sounds like you are going after a gnat with a cruise missle. It'll work,
and it'll make a really cool bang, but sometimes simple is better.
>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.
IMHO, there is no area where there is a true shortage of bandwidth, those
areas that have congestion problems deal with it through peer pressure
promoting shorter unproto paths and longer transmit intervals. Better
placement of digipeaters, and more advanced digi software have a lot of
potential as well. The APRServe network also has an impact, it means
people use shorter paths and still converse and be tracked by far away
stations. So there are lots of BandAids that can be used.
>You can either keep
>applying the band aids or consider some of those issues now.
>
Well, I'm willing to discuss any of your ideas. I'd maintain though that
anything that would be successful needs to be compatible with what is
already out there. You will run into a lot of resistance if you tell all
300-odd digi owners that they need to spend $1000 upgrading their system!
If you had a few tens of millions of dollars, and were designing a
nationwide tracking system, you certainly could do a much better job than
APRS. This is an amateur system, and there are real limitations on the
complexity and finacial outlay hams will tolerate. Every time you double
the cost or complexity, you probably cut the number of interested hams by
two-thirds.
Steve K4HG
