[aprssig] APRS-IS: frames bypassing server filter

[Wojtek SP9WPN]

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:

[ig>tx] SR9KFZ-2>APRX29,TCPIP*,qAC,T2POLAND:;SQ9RHX 
*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 
op SQ7PGP KZK TEAM
[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!
[ig>tx] OK8UOF>APMI06,TCPIP*,qAC,T2LONDON::OK8UOF 
: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

-- 
73!
Wojtek SP9WPN