[aprssig] are write-only APRS-IS clients valid?

Pete Loveall AE5PL Lists hamlists at ametx.com
Mon Dec 2 09:46:57 CST 2013

I did explain it, you just didn't understand the explanation so here goes again...

Your statement "Dupe elimination means eliminating dups, not eliminating messages." is incorrect because messages are packets just like any other packet and, therefore, they are subject to dupe elimination as well.  So, start with that understanding that messages are handled as any other packet in the backend of the APRS-IS server.

The second place where you have a misunderstanding is with the statement "still send downstream messages to that callsign because the RF station's position falls within the IGate filter footprint".  There are multiple errors in this statement.  First, the server doesn't "send downstream messages to that callsign" because it passes packets, period.  On most limited feed ports, the server also maintains a "last heard" list for the connection so it can also pass message packets and associated posit packets that are addressed to stations gated to the server by the connected client.  Second, your statement assumes 1) the station transmitted an accurate posit and 2) the IGate is using a range or area filter and 3) the station falls within that range or area filter and 4) a range or area filter has any effect on what message packets are passed to a client.  All 4 or any 1 of them can be false and your method of determining a valid message packet for the client will fail.  Not only that, #4 assumes that a range or area filter has anything to do with how message packets are passed to the client; they don't (see prior statement for how that determination is made).

In the environment where the IGate is either integral with a server or sits behind a server with an upstream connection to a limited feed port (very common configuration), the upstream server may not see packets gated to APRS-IS by the IGate because that integral/local downstream server received the packet from the RX-only IGate before processing the local IGate's gated packet and the local IGate's gated packet is eliminated as a dupe and not passed to the upstream server.

Again, bottom line is the RX-only IGate is incapable of messaging (receive only) and may interfere with ability for messaging by bidirectional IGates with an integral server or local server on a limited feed.  RX-only IGates serve no useful function as most modern-day clients can connect to both RF and APRS-IS without gating.  If there is a need for gating, then make it bidirectional.

Also, this conversation is regarding standard terrestrial gating, not SatGates.  Hope this helps.


Pete Loveall AE5PL
pete at ae5pl dot net

> -----Original Message-----
> From: Steve Dimse
> Sent: Monday, December 02, 2013 9:22 AM
> So by going to the bottom line you are saying you aren't going to explain it
> other than to say it happens? If this is real, and I'm even more skeptical now
> that you seem so reluctant to explain it, why won't you explain it? You've
> been right when I've been wrong before, I value your insight, and I'm asking
> you to explain exactly how this happens. If you can't or won't explain it, do
> you think I should just take your word for it?
> Dupe elimination means eliminating dups, not eliminating messages. So a
> packet originating with a one-way station get to an upstream server first. The
> upstream server still has a position report for the RF station, and it will still
> send downstream messages to that callsign because the RF station's position
> falls within the IGate filter footprint. I just don't see how it can block a
> message from getting to the IGate. So will you explain it in detail to me and
> the rest of the sig, or are we just to trust you, just because?
> This isn't an academic exercise. Every client program I've seen allows one-
> way gating, and furthermore it will always be possible by turning off TX
> Enable, not connecting a PTT line, or by using a scanner to feed a TNC. So
> please, I'm asking as nicely as I can, convince me this is a real problem.

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