[aprssig] APRS-IS: frames bypassing server filter

Lynn W Deffenbaugh (Mr) KJ4ERJ at arrl.net
Mon Jul 13 18:12:05 EDT 2020

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.

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.

There may be other reasons for packets coming to your IGate, but they 
escape me at the moment.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 7/13/2020 5:56 PM, Wojtek SP9WPN wrote:
> Hello everybody,
> I'm running a simple APRS-IS receiver (using direwolf). It uses a 
> metered GSM connection, so I try to control costs by reducing amount 
> of unnecessary or redundant data.
> As I have no possibility to Tx from this location, it is an obvious 
> step to stop any frames being sent from APRS-IS server to my client 
> (they will never be forwarded to RF). But here the problem appears: 
> I've tried setting different server-side filters without any success. 
> It seems that some frames always reach me despite applied filtering 
> (mostly these are same stations all the time). I've tried different 
> tier2 servers, both aprsc and javAPRS - no difference. This is short 
> sample what I get in logs:
> *111111z5108.47N/01701.74E-PHG3360 Damian
> [ig>tx] 
> SR7NSI>BEACON,TCPIP*,qAC,T2POLAND:;438.825-S*121515z5135.96N/01841.68ErC077 
> -760 SR7SI op SQ7PGP
> [ig>tx] 
> SR7NSI>APNW01,TCPIP*,qAC,T2POLAND:@121515z5135.60N/01844.02E#432,500MHz 
> [ig>tx] SQ9NKH-9>APK101,SR9POD*,WIDE1*,W2-1,qAR,SR9NSK::SQ7LQU-9 :73!{Q
> [ig>tx] SQ9NKH-9>PP0PP0,SR9POD*,WIDE1*,W2-1,qAR,SR9NSK:'vX<0x1c>l 
> <0x1c>>/]"3r}op.Lukasz 73!
> :PARM.Vin,Rx1h,EffTot,Eff1h,Temp,O1,O2,O3,O4,I1,I2,I3,I4
> I know that my station is supposed to transmit messages to any station 
> which was heard previously, but these are not messages - mostly 
> telemetry and beacons. I can't find any common factor in these frames, 
> but there are not completely random (most of the are from SP, OK, OL, 
> but occasionally some from I or S5 appear, so there's some 
> geographical connection). I've tried to find the reason or rule which 
> causes them to be sent, but no luck. Even on Polish APRS forum people 
> are surprised I'm getting lots of frames having set eg. b/SP9WPN-1 
> filter.
> Could somebody with extent knowledge of APRS-IS shed some light on 
> this? Even if I can't ultimately block those frames, it would be great 
> to understand why they are forwarded from server to my station. Right 
> now it's a mystery for me.
> Best Regards,
> Wojtek

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