[aprssig] APRS-IS q construct / (server?) reject messages "qAO" related to foreign call sign

Jörg Schultze-Lutter joerg.schultze.lutter at gmail.com
Wed Aug 4 03:36:06 EDT 2021

tl;dr: I think that an Austrian call sign causes unintended message
interferences with APRS-IS and several APRS bots - including mine. I
haven't seen this behavior in the past and I don't believe that there is a
general design flaw with my program. Please advise.


I am the author of an APRS bot which started its life in January as a
functional clone of KI6WJP's WXBOT (my program was written from scratch,
though). The bot uses its own TOCALL identifier (
http://aprs.org/aprs11/tocalls.txt). Raw APRS messages can be accessed
here:  https://aprs.fi/?c=raw&call=MPAD&limit=1000&view=normal

Over the past few days, I noticed that there was a decline in the number of
messages that I was able to receive from my bot via *radio* transmission.
Based on the analysis of the message flow, it looks to me as if my bot and
others are affected by an Austrian call sign (OE3XWJ-11) which results in
the intermittent generation of qAO reject messages that are broadcasted in
response to the user's original requests to our bots. This issue only
affects messages with message ID's - unconfirmed messages are not affected.
I would like to get some clarification on how to remedy this issue on my
end (if possible).

Message exchange examples follow. Note that all reject messages use the
generic "APRS" ToCall identifier which makes me assume that they were all
generated by the APRS-IS server itself.

1 - message exchange:  APRS-IS to APRS-IS (via an IOS app)
2021-08-03 07:29:54 CEST: DF1JSL-10>APSK21,TCPIP*,qAC,T2GYOR::MPAD
2021-08-03 07:29:55 CEST: MPAD>APMPAD,TCPIP*,qAC,T2UKRAINE::DF1JSL-10:ack2
2021-08-03 07:29:55 CEST: MPAD>APRS,qAO,OE3XWJ-11::DF1JSL-10:rej2
DW6761 03-Aug-21 11C 136deg Spd 0.0km/h Gust 0.0km/h Hum 94%{OO
2021-08-03 07:30:08 CEST: MPAD>APMPAD,TCPIP*,qAC,T2UKRAINE::DF1JSL-10:Pres
1014.3mb Rain(cm) 1h=0.0, 24h=0.0, mn=0.0{OP
2021-08-03 07:30:02 CEST: DF1JSL-10>APSK21,TCPIP*,qAC,T2GYOR::MPAD
2021-08-03 07:30:02 CEST: DF1JSL-10>APRS,qAO,OE3XWJ-11::OE3BCB-1 :rejOO
2021-08-03 07:30:08 CEST: DF1JSL-10>APRS,qAO,OE3XWJ-11::MPAD     :rejOP
2021-08-03 07:30:08 CEST: DF1JSL-10>APSK21,TCPIP*,qAC,T2GYOR::MPAD

2 - message exchange: radio to APRS-IS (via FTM-400XDE)
2021-08-03 08:20:08 CEST:
DF1JSL-1>APY400,WIDE1-1,WIDE2-1,qAR,DB0BI-10::MPAD     :cwop{41
2021-08-03 08:20:08 CEST: MPAD>APRS,qAO,OE3XWJ-11::DF1JSL-1 :rej41
2021-08-03 08:20:09 CEST: MPAD>APMPAD,TCPIP*,qAC,T2UKRAINE::DF1JSL-1 :ack41
EW6958 03-Aug-21 11C 23deg Spd 0.0km/h Gust 3.2km/h Hum 95%{OT
2021-08-03 08:20:22 CEST: MPAD>APMPAD,TCPIP*,qAC,T2UKRAINE::DF1JSL-1 :Pres
1014.0mb Rain(cm) 1h=0.0, 24h=0.10, mn=0.0{OU
2021-08-03 08:20:16 CEST: DF1JSL-1>APRS,qAO,OE3XWJ-11::MPAD     :rejOT
2021-08-03 08:20:22 CEST: DF1JSL-1>APRS,qAO,OE3XWJ-11::MPAD     :rejOU
2021-08-03 08:20:35 CEST:
DF1JSL-1>APY400,WIDE1-1,WIDE2-1,qAR,DB0BI-10::MPAD     :ackOU

Additional example traffic from the other affected bots' logs can be found
at the end of this email.

Based on http://www.aprs-is.net/q.aspx, my conclusion is as follows:

1) My call sign  (DF1JSL) sends a message to my MPAD APRS bot.
2) The APRS-IS server network generates a reject message (qAO, FROMCALL
does not match login) that is associated with call sign OE3XWJ-11 and sends
that reject back to my call sign DF1JSL-xx.
3) The original request to my bot still traverses through the APRS-IS
network and therefore gets picked up by my bot.  Similar to WXBOT and its
clones, my bot does not take ack/req requests into consideration.
4) Additionally: As the reject msg from the APRS-IS server was sent to the
sender's call sign (DF1JSL..), my bot would never have seen it anyway. So
it will honor the user's request and process it.
5) The bot generates an ack message, processes the user's initial query and
sends the response messages back to the user via APRS-IS.

What I don't understand is the constant association of each reject message
with that Austrian call sign. Regardless of the content that I send to my
bot - it aways triggers a reject which is always associated with the same
Austrian call sign. As several other bots also seem to be affected, I doubt
that this is a general design flaw with all of our bots.

It also looks to me that from time to time, any bot response received via
*radio* can sometimes experience long/very long delays between sending the
request and receiving the response. This might be related to the "reject"
responses which _may_ prevent the response message to be broadcasted via
radio - or the radio itselfs rejects the message after receiving the 'rej'.
Everything I SEND to my bot via radio or APRS-IS is usually received by the
bot without any delay, though.

Is there any way for my bot to detect and remedy this situation? As
mentioned earlier, the reject message gets returned to the original sender
(and *not* to my bot) so that message will not pass my bot's APRS-IS
message filter (g/MPAD). Disabling the APRS-IS filters, having a look at
the whole traffic and detecting the reject message cannot be the answer.
What is the best cause of action for such a case?

.... or did I just misinterpret the whole thing and this is normal
behavior? :-)

Thanks for taking the time to read this.

73's from Germany

Additional examples which make the "Austrian reject pattern" obvious. Every
reject message is associated with OE3XWJ-11.

from WXBOT

2021-08-02 19:03:40 CEST: N0ISU-9>APY400,WIDE1-1,WIDE2-1,qAR,W0RAY::WXBOT
 :friday {01
2021-08-02 19:03:40 CEST: WXBOT>APRS,qAS,KI6WJP::N0ISU-9  :ack01
2021-08-02 19:03:40 CEST: WXBOT>APRS,qAO,OE3XWJ-11::N0ISU-9  :rej01
2021-08-02 19:03:46 CEST: WXBOT>APRS,qAS,KI6WJP::N0ISU-9  :Waukee IA.
Friday,Sunny High 87{UX

from WXYO (WXBOT clone)

2021-08-01 23:18:29 CEST: WXYO>APRS,qAO,OE3XWJ-11::YO9JAZ-9 :rej3
2021-08-01 23:18:29 CEST: WXYO>APRS,qAS,YO8SDE-1::YO9JAZ-9 :ack3
2021-08-01 23:18:36 CEST: WXYO>APRS,qAS,YO8SDE-1::YO9JAZ-9 :Targoviste in h
clear sky T:23.83C,W28 at 3.18,H44,P1009hPa,rain 0mm,c{GQ

from WA1GOV-10 (not even a WXBOT clone)

2021-08-01 23:42:38 CEST: WA1GOV-10>APRS,qAO,OE3XWJ-11::YO9JAZ-9 :rej1
2021-08-01 23:42:38 CEST: WA1GOV-10>APX217,TCPIP*,qAC,T2USANE::YO9JAZ-9
2021-08-01 23:43:05 CEST: WA1GOV-10>APX217,TCPIP*,qAC,T2QUEBEC::YO9JAZ-9
:ISS over KN43GS AOS 02Aug21 10:01 UTC AZ 169 MaxEL/AZ 6/128
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