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ZL3AI > APRDIG 29.09.03 18:09l 149 Lines 6356 Bytes #999 (0) @ WW
BID : 2020-ZL3AI
Read: GUEST
Subj: TAPR Digest, Sep 26, 5/7
Path: DB0FHN<DB0RGB<DB0MRW<DB0FOR<DB0SIF<DB0EA<DB0RES<ON0AR<ZL2BAU<ZL3VML
Sent: 030928/2019Z @:ZL3VML.#80.NZL.OC #:9242 [Chch-NZ] FBB7.00i $:2020-ZL3AI
From: ZL3AI@ZL3VML.#80.NZL.OC
To : APRDIG@WW
Subject: Re: Part 2/2 -Re: Take Control - oh let's just go backwards
From: Henk de Groot <henk.de.groot@hetnet.nl>
Date: Fri, 26 Sep 2003 23:31:06 +0200
X-Message-Number: 28
Hello Steve,
At 13:28 26-9-03 -0400, Steve Jones wrote:
>Henk can correct me if I'm wrong but Digined inspects the contents of the
>packet and if it hasn't changed from the last time it digi'd it then it
>discards it.
Correct. But this is the short story, the finer details are more complicated.
DIGI_NED discriminates between direct and indirect packets. Direct packets
are always digipeated, even if the originator call and contents are the
same as an earlier packet. So in the local coverage area of the digi, users
force transmission of a packet by the digi if the digi receives the packet
directly from the originator. Dupe checking is only done for packets that
already digipeated at least once.
DIGI_NED has two settings how long to "remember" a packet for dupe
checking. There is one setting that is meant for specific types of packets,
its based on the first character of the payload. In the configuration file
you can specify for which characters this setting shall be applied. Default
this setting is applied to packets starting with characters ":", "?" and
"~", i.e. APRS messages, APRS queries and UIview messages. These packets
are in the default setting remembered 10 seconds. All other packets are
remembered much longer, in the default setting 300 seconds (5 minutes).
Since dupe checking is only applied to indirect packets a setting of 1740
(29 minutes) only affects duplicate packets that come from outside the
coverage area, there is no service degradation for stations in the area
covered by the digipeater.
These are just details but thery are important to provide optimal
communication within the area covered by the digi and to leave the power
with the users in the served area.
>If my digi digi's a wide3-3 packet and then another digi sends it back as
>wide3-2, my digi will not repeat it. Cuts down on traffic.
This is also what any Kantronics TNC should do. In DIGI_NED this however
works for any packet, not only for WIDEn-N type calls but also for WIDE
etc. So even WIDE,WIDE,WIDE,WIDE will not create a loop, even is call
substitution is not applied.
Kind regards,
Henk.
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Subject: Re: Part 2/2 -Re: Take Control - oh let's just go backwards
From: Henk de Groot <henk.de.groot@hetnet.nl>
Date: Fri, 26 Sep 2003 23:58:58 +0200
X-Message-Number: 29
Hello David,
At 12:48 26-9-03 -0500, you wrote:
>>Dupe, dupe, dupe. The same packet repeated by the same digi multiple times
>>is a dupe. If the content hasn't changed then why repeat it?
>
>So if I'm sitting still, I disappear?
No, the first time the packet is received it is remembered and a timeout
timer is started. If the same packet is received again and the digi still
remembers the first packet the new one is ignored. When the timeout timer
elapses the digi forgets the packet. If after that the same packet is
received, the digi doesn't know that it is the same packet anymore and it
is treated as a first time packet.
Default DIGI_NED remembers packets 5 minutes. If you send the same packet
with a 1 minute rate then:
Packet at t=0 min is digipeated and remembered, timeout 5 min
Packet at t=1 min is ignored, data timeout in 4 min
Packet at t=2 min is ignored, data timeout in 3 min
Packet at t=3 min is ignored, data timeout in 2 min
Packet at t=4 min is ignored, data timeout in 1 min
Packet at t=5 min data timeout reached, remembered data is discarded,
packet is digipeated and remembered, timeout 5 min
Packet at t=6 min is ignored, data timeout in 4 min
So the answer is: you will not disappear but the update rate will be once
every 5 (or 6 if the timing is not exact) minutes. 5 minutes should not be
a problem, the APRS specification assumes a 10 minute net-cycle time; this
is well within that timing.
If your stations is mobile your packet will be different each time and you
will get a new position every minute.
If you use a timeout of 29 minutes static data is digipeated once every 29
minutes (once every 30 minutes in practice if the originator sends the
static data every 5 or 10 minutes).
I hope this is clear, kind regards,
Henk.
P.S. note what I wrote in another message, dire-------------------------------------
Subject: APRS Grass growing...
From: Bob Bruninga <bruninga@usna.edu>
Date: Fri, 26 Sep 2003 18:30:12 -0400 (EDT)
X-Message-Number: 32
On Fri, 26 Sep 2003, Roger Grady wrote:
>... Why should home-stations be allowed to generate as much data on the
>network as a moving station when every packet is the same?
They dont. They generate only 3% as much load (only one posit in 30
minutes compared to 1 per minute from a high-rate mobile)...
>By using a 30 minute dupe period, a fixed station will not get digi'd
>more than once every 30 minutes. A moving station, whose packet changes
>every time, will not be seen as a dupe and will get digi'd.
Violates the KISS principle and gains nothing. Already a home station is
only transmitting once every 30 minutes. Why get the digi involved in it?
Besides the purpose of a HOME station Beacon is not necessrily so much as
to show us his non-changing position, but more so to indicate that he
still has power, and is participating in the NET. That is how HAM radio
emergency and special event traffic nets work. The various participating
stations check in now and then to indicate that they are still avaliable
to handle traffic. WIthout this, no one in the net knows who is
available or what constitutes the net.
What I would like to see for local area ACTIVE networks involved in an
event, emergency, skywarn, or whatever is that the client software detects
the presence of an operator (mouse movement or keyboard activity) and then
ups from the 30 minute rate to the ACTIVE status of the local 10 minute
net cycle rate (with a direct packet).
This better fullfills the need for knowing "who" is actively participating
in the LOCAL net (under active conditions), and who is just letting the
APRS grass grow.
Bob, WB4APR.
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