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ZL3AI > APRDIG 18.05.04 20:13l 255 Lines 9730 Bytes #999 (0) @ WW
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From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Kenwood d700a not reconizing my fixed station
From: "john gravely" <jkb3hia@aol.com>
Date: Mon, 3 May 2004 16:22:24
X-Message-Number: 44
Help! Does anyone know why my d700a will not reconize my (home) fixed
station in its list of heard stations? I do see my fixed stations beacon
text if monitoring packets (pmon). Several local hams have the same set-up
as I, they recieve their home stations no problem. I am using the d700a
mobile and I'm running UI-Veiw at the fixed station. My fixed station is
using my call kb3hia, and the d700a mobile is kb3hia-9.If anyone can help
please post or e-mail me direct at kb3hia@arrl.net. Thank You 73
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Subject: Re: Attn: Armchair Lawyers
From: Jeff King <jeff@aerodata.net>
Date: Mon, 03 May 2004 16:24:17 -0500 (CDT)
X-Message-Number: 45
Quoting Steve Dimse <k4hg@tapr.org>:
>On 5/3/04 at 3:18 PM Jeff King <jeff@aerodata.net> sent:
>
>>Again, then what mode should 144.39 APRS be operated under then? Pure
>Aloha or
>>CSMA? That is the defining question.
>
>Who said it was pure anything?
But a properly designed network, designed to good amateur standards, should
not be mixed. As such, the expectation of a standard channel access method
is a given, and will help amateur comply with 97.101. The fact that it is
not pure, does not release one from their requirements to follow FCC
regulations. In other words, you can't have it both ways. It is one way or
the other, warts, pimples and shortcomings not withstanding.
>You've been here long enough to know APRS is a
>pyramid of pragmatic kludges built on top of one another.
I'm well aware of it. But just because other people won't do things right
doesn't mean the next guy shouldn't.
>I'd say one of the good ones is it lets one use common sense
To me, it is common sense to listen first before I transmit and make every
effort I can to reduce collisions on the channel. But that is just me.
>to solve questions like what is good amateur practice in APRS, as Bob
>has stated, and not resort to an academic discussion as you have done...
Problem is, packet radio is based on these "academic discussions", as the
whole field of packet radio got its start at the University of Hawaii in
the 1970's.
Channel access schemes are fundemental here, and need to be defined.
So what is it?
1. Is 144.39 mhz APRS based on a aloha model? (as you seem to suggest earlier)
2. Is 144.39 mhz APRS based on a CSMA model? (as I thought it was)
3. Some new creation? ("pyramid of pragmatic kludges" method, as you suggest
now)
Knowing the channel access scheme is fundemental to layer one of packet radio.
Now, even though I basically agree with your analysis of the sitution, my
feeling here is we as amateur radio operators need to aspire to higher
technical ideals, and in general err on the side of the caution. That is
why I won't do something that way "just because everyone else is" and
further, I tend to err on the side of caution when it comes to FCC rule
compliance.
But that is my opinion.
I suggest to those that are concerned they seek professional advice on rule
compliance as your not getting it on the APRS-SIG so far.
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Subject: Re: Slotted ALOHA
From: David VanHorn <dvanhorn@cedar.net>
Date: Mon, 03 May 2004 17:11:04 -0500
X-Message-Number: 46
At 04:44 PM 5/3/2004 -0400, Sadowski, Allan wrote:
>It was interesting to see Jeff's post on ALOHA vs CSMA... in particular
>since its been a while since I read Andrew Tannenbaums book that talks
>at length on ALOHA protocol.
>
>Of note in the wiki link... is that SLOTTED ALOHA is twice as efficient
>as pure ALOHA - claims of 36% channel efficiency.. and multiple posts
>here on the sig in the (relatively) distant past
I talked to Norm about slotted aloha back in '84 or thereabouts.
We were looking at it for networked CC terminals.
It's pretty effective, given how simple it is.
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Subject: Re: Attn: Armchair Lawyers
From: "Robert Bruninga" <bruninga@usna.edu>
Date: Mon, 03 May 2004 18:38:43 -0400
X-Message-Number: 47
>>>Jeff King <jeff@aerodata.net> 5/3/04 5:24:17 PM >>>
>But a properly designed network, designed to good amateur
>standards, should not be mixed. As such, the expectation
>of a standard channel access method is a given, and
>will help the amateur comply with 97.101.
Jeff, this is rediculuous. This would require:
1) All users to live on a FLAT Earth
2) All users to never be more than 5 miles apart
3) All users to have the same antenna height
-OR-
4) all digipeaters to be full duplex requiring trash can
sized cavaties at great expense.
5) AND rquring TWO frequencies
6) AND requiring us to be up in the repeater part
of the band where a national frequency pair
decdicated to APRS would be absolutely
impossible.
>The fact that it is not pure, does not release one from
>their requirements to follow FCC regulations. In
>other words, you can't have it both ways. It is one way
>or the other, warts, pimples and shortcomings not
>withstanding.
Not true. Best practice means just that. Best practice for the situation.
And the situation is not PURE CSMA in fact, the only stations on 144.39
that are even remotely CSMA are the digis, all the rest are almost pure
ALOHA with respect to avoiding any collisions to others.
>So what is it?
>
>1. Is 144.39 mhz APRS based on a aloha model? (as you seem to suggest
earlier)
>2. Is 144.39 mhz APRS based on a CSMA model? (as I thought it was)
>Knowing the channel access scheme is fundemental to layer one of
packet radio.
Yes, that is why you seem to fail to understand the situation. Most of the
users on 144.39 cannot hear each other and so they definately are not CSMA
for the purpose of avoiding colisions with other users.
Its a well known fact of geometry and not living on a flat earth.
de Wb4APR, Bob
...
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Subject: Re: Attn: Armchair Lawyers
From: Jeff King <jeff@aerodata.net>
Date: Mon, 03 May 2004 17:57:57 -0500 (CDT)
X-Message-Number: 49
Quoting Robert Bruninga <bruninga@usna.edu>:
>Jeff, this is rediculuous. This would require:
No it wouldn't. All it would require is your define a common channel access
method that everyone use. Yes, I know it is not perfect, but it is better
then "undefined" which seems to be what you are saying.
>Not true. Best practice means just that. Best practice
>for the situation. And the situation is not PURE CSMA
>in fact, the only stations on 144.39 that are even remotely
>CSMA are the digis, all the rest are almost pure ALOHA
>with respect to avoiding any collisions to others.
Your talking about the aggragete of what is on 144.39mhz, and I do not
disgree with your assement. But that is not the question.
What method should each individial user approach the network? Should they
throw away the CSMA signal or should the use it? That is the difference
between a CSMA network and a Aloha network. The fact, that in the aggrigate
of all stations, the CSMA model starts to approach the aloha method is not
relevent to 97.101. 97.101 defines what the individial does.
>>So what is it?
>>
>>1. Is 144.39 mhz APRS based on a aloha model? (as you seem to suggest
>earlier)
>>2. Is 144.39 mhz APRS based on a CSMA model? (as I thought it was)
>>Knowing the channel access scheme is fundemental to layer one of
>packet radio.
>
>Yes, that is why you seem to fail to understand the
>situation.
No, I don't.
>Most of the users on 144.39 cannot hear
>each other and so they definately are not CSMA for
>the purpose of avoiding colisions with other users.
Again, Bob, we are not talking about the aggrigate, we are talking about
97.101, which defines individial behavior. The fact that the model, as a
whole, starts to fail, is not relevent to the question.
And that question is, what model is APRS based on so INDIVIDIAL stations
can follow that model.
It is either CSMA or Aloha. Can't have it both ways as I've never seen a
CSMA input on a tracker that is indeterminant. It is either hooked up
(CSMA), or it is not hooked up (ALOHA). This decision has ABSOLUTELY
NOTHING TO DO with the fact some APRS networks are poorly engineering
and/or overextended. It is a DEFINITION of the method a individial tracker
uses, NOT the definition of the network as a whole.
Make your mind up so we can bring this thread to a close.
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Subject: Re: Attn: Armchair Lawyers
From: David VanHorn <dvanhorn@cedar.net>
Date: Mon, 03 May 2004 18:01:55 -0500
X-Message-Number: 50
>Its a well known fact of geometry and not living on a flat earth.
>
>de Wb4APR, Bob
Sometimes it helps.
There was a system that never quite made it for Satellite based CC
terminals, that used the fact that the earth is more or less spherical.
The idea was that the sat, in geo, would send a ping, and all the terminals
that could hear it, if they had traffic, would respond. The data rate was
so fast that the wavefront spreading out across the earth, from the point
directly below the satellite, caused basically a parabola of replies to be
launched. The receiver on the sat then had most of them spread out in
time, and those that collided simply re transmitted on the next ping.
Spatial aloha, of sorts, but I digress.
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