APRS-IS data not posting on APRS.fi

[Robert Bratton]

Like a switch; a few days ago about half of my normal iGate traffic ceased to show up on APRS.fi.  The missing data, unpublished by APRS.fi, does show up on findu.com and APRS.link.  My assumption that there is only one (1) output data stream from the APRS-IS network must be wrong?  I would appreciate any comments.  Thanks, Bob W4TTU.

[Heikki Hannikainen]

On Fri, 3 Nov 2017, Robert Bratton wrote:

> Like a switch; a few days ago about half of my normal iGate traffic
> ceased to show up on APRS.fi.  The missing data, unpublished by APRS.fi,
> does show up on findu.com and APRS.link. 

Hi, could you point to some specific example data that is missing? It's
easier to look for any issue if there is a concrete example: what is
missing, where, what are you expecting to see vs. what you are seeing
instead. Thanks!

> My assumption that there is
> only one (1) output data stream from the APRS-IS network must be wrong? 
> I would appreciate any comments.

There should be, but a few times the APRS-IS has been bugging a bit and
providing incomplete data to some clients.

- Hessu

[Bob W4TTU]

Hessu,

Thank you for responding.  Please look at the raw APRS-IS data for N3KTX-1, as posted on APRS.fi for the last 24 hours.

(2017-11-07 to 2017-11-08 12:00-12:00 hrs UTC)  You will not see any entries with my call, W4TTU.  Now look at the APRS-IS

raw data entries for N3KTX-1 as posted on APRS.link and Findu.com for the same 24 hour window.  Multiple W4TTU entries

are posted on both sites.

The disparity in reporting, as it relates to my iGate, is not isolated to any one station, there are others.

73 Bob, W4TTU 

[Heikki Hannikainen]

Hi,

Just to clarify, I'm not sure if I understood you right:

- You're in fact *not* saying that there are packets sent by N3KTX-1 that
are missing from aprs.fi? aprs.fi is not missing data from N3KTX-1?

- You're saying that the packets from N3KTX-1 no longer go via the W4TTU
igate to aprs.fi, but via other igates instead? And sometimes via W4TTU to
some other web services?

If so, then yes, you have slightly misunderstood how the APRS-IS operates.
The APRS-IS network tries to make sure that the unique packets from
N3KTX-1 get through (once). It does not in any way try to make sure that
all igates would be credited or attributed in any fair manner; it's
simply not a design criteria or feature of the APRS-IS. It just tries to
get the packets through.

Each APRS-IS server has a duplicate packet filter of it's own, and
depending on where you connect to the APRS-IS to get the packets, you
might get the packet via one igate, or some other, depending on which path
is the quickest between the transmitting station and your APRS-IS client
(or aprs.fi).

So, more than slightly simplified: if your igate is connected to APRS-IS
server named A, and then another igate is connected to APRS-IS server B,
and both of the igates hear the same packet from station X. Both igates
send the packet to the servers. If aprs.fi would be connected to A, it
might get the packet first from your igate, and if it would be connected
to B, it might get it first from the other igate.

Of course it's more complicated than this; the Internet latencies between
each of the igates, and the servers, and aprs.fi, are in the ranges of few
tens or hundreds of milliseconds and the paths taken by the packets are
more complex. Here's an old but still-valid blog post describing how
aprs.fi gets the packets:

http://blog.aprs.fi/2012/05/aprsfi-connected-directly-to-aprs2net.html

If some packets that were sent by N3KTX-1 are in fact missing from
aprs.fi, then that's more of a problem; please point out the missing
packets if there are some.

If your igate is not getting credited by aprs.fi as much, it's just a sign
of a good situation: your area has good igate coverage and a lot of
redundancy! Even if one or two igates are broken for some reason, there's
still some path for packets.


On Wed, 8 Nov 2017, Bob W4TTU wrote:

> Hessu,Thank you for responding.  Please look at the raw APRS-IS data for N3KTX-1, as posted on APRS.fi for the last 24 hours.

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- Hessu

[Matthew Chambers]

This puts not am uncommon occurrence. When I lived in Tucson Az, a friend and I built a digipeater/igate up on Keystone Peak (7k ft AMSL) that was connected directly into the internet backbone of a major ISP there. We were gating mobiles in Albuquerque and getting credit on APRS.fi. It wasn't that the igates in Albuquerque weren't working, it was that we had a faster internet connection. Reality was that our super digi didn't really benefit the local network and eventually was turned off.

Matthew Chambers, CBT, NR0Q

Director - Macon County Office Of Emergency Management 

Firefighter - Atlanta Volunteer Fire Department 

M Chambers Communications Engineering LLC
Contract Broadcast Engineer & 2-Way Radio Sales & Service

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  - Hessu

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