[aprssig] APRS-IS: frames bypassing server filter

spam8mybrain spam8mybrain at yahoo.com
Tue Jul 14 19:08:27 EDT 2020

The purpose of the minimal data stream is so your Internet-connected station can function as a transmit-capable I-gate, not just a receive-only I-gate. The minimum packets you receive from the Internet are those intended for stations that your I-gate has delivered to the backbone, under the assumption that your I-gate is one of the nearest stations to send responses back to the RF station. The assumption is, if you can hear them on RF, you can send back to them on RF (and the backbone doesn't understand the concept of I-gates that can't, so you can't turn off such IS->RF traffic).
The backbone sends such packets to all such I-gates that report receiving the RF stations, to ensure a redundant path to get to the RF station. After all, not all I-gates may be capable of transmitting at the time of packet receipt and getting all the way to the RF station (especially if the RF station is mobile and has moved since the last RF->IS-forwarded packet from it).Hope this helps explain this design decision of the backbone servers.Andrew, KA2DDO

-------- Original message --------
From: Wojtek SP9WPN <sp9wpn at gmail.com> 
Date: 7/14/20  18:14  (GMT-05:00) 
To: aprssig at lists.tapr.org 
Subject: Re: [aprssig] APRS-IS: frames bypassing server filter 

W dniu 2020-07-14 o 00:12, Lynn W Deffenbaugh (Mr) wrote:> You will receive packets generated by any station that you have gated > from RF to the APRS-IS for some period of time after you've last gated > one of their packets.  Try matching up the stations you're receiving > with the packets being subsequently received back from the APRS-IS.I'm not sure about this. Most of the stations in question are not heard directly, but only digipeated to me. This shouldn't count, should it?> This is done for several reasons.  One is to give you the opportunity > to gate a "courtesy" posit for the source of any message you may have > gated, but it is also so that your IGate can know if a staiton is > injecting packets directly to the APRS-IS so you don't gate messages > from the -IS to RF for addressed to a station that would have received > them directly on the APRS-IS.Is this true for non-message packets, too? Because I hardly ever see APRS messages in the logs, just beacons and telemetry all the time. If APRS-IS server sends packets downstream only to stop me from uploading the same packets back, it sounds like a weird protocol design...I'd agree with Andrew KA2DDO: it seems there's some "minimal data stream" offered to each Igate (and all IS-connected clients are considered Igates). It probably serves some good purpose, but is not well advertised.Regards,Wojciech-- 73!Wojtek SP9WPN_______________________________________________aprssig mailing listaprssig at lists.tapr.orghttp://lists.tapr.org/mailman/listinfo/aprssig_lists.tapr.org
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