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

Steve Dimse steve at dimse.com
Mon Dec 2 10:50:23 CST 2013

On Dec 2, 2013, at 10:46 AM, Pete Loveall AE5PL Lists <hamlists at ametx.com> wrote:

> 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.

Of course. However by definition what is being removed are the duplicates of the message, not the message itself. One copy, the first copy, gets through. However from below I see you are using filtering and not dup checking as the agent here.
> 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.

Yes, but you were saying a message would not get through, so I’m tracing a message packet through the system.

> 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.  

OK the light is slowly peeking into my aging skull. 

The last heard filter is not mentioned in the filter or Igate design and details pages. Where is it explained on aprs-is.org? If I missed it I’m sorry, but it is a key piece of information I either missed or that is absent from the pages. Also I did not see info that filtering is applied based on this last-heard list. From the way you describe it, dup-checking is done on the hubs before the last-heard table is updated. So it isn’t really a last-heard table, but a first-heard table of the most last packet, right?

Does the range filter override this filtering? Yes, I was assuming IGates would use a range filter specifically to be sure they would receive the messages for all stations in that area. You don’t want that, though, do you? You are trying to prevent multiple IGates from sending the same packet on RF, and doing this in the hubs instead of in the IGates. Is that right? I’ll grant you that is a good thing.

You are attempting the defacto routing of messages. Since you cannot directly control the IGates you are trying to route messages by favoring a path to the faster IGate, assuming that the delay will be mostly due to digi delays. Don’t send them the packets you don’t want them to think about transmitting.

So yes, I will concede that 1way gates screw this up. But I’m not happy with it. I always thought the decisions about what IGates would transmit belonged in the local IGate operator’s hands. I don’t think it is appropriate for the APRS-IS to say, in essence “I think you should not transmit this packet so I’m not going to show it to you.” Especially when hardware and software in everyday use (1 way IGates) can result in messages that should be transmitted being filtered.

Steve K4HG

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