[aprssig] are write-only APRS-IS clients valid?

Pete Loveall AE5PL Lists hamlists at ametx.com
Mon Dec 2 08:58:09 CST 2013

See below...

> -----Original Message-----
> From: Steve Dimse
> Sent: Monday, December 02, 2013 7:53 AM
> On Dec 2, 2013, at 7:58 AM, Pete Loveall AE5PL Lists <hamlists at ametx.com>
> wrote:
> > Tom, you are correct.  RX-only IGates break the -current- intent of APRS-IS:
> to interconnect amateur radio APRS RF networks.  They break this intent
> because they do not support messaging.  They also can break messaging for
> nearby bidirectional IGates using filtered feeds from the upstream server.
> The reason this last fact is true is because of dupe elimination present in
> APRS-IS servers.  If the RX-only IGate is quicker at getting packets to APRS-IS,
> the upstream server of the bidirectional IGate may never see packets gated
> by the bidirectional IGate.  Therefore, the bidirectional IGate will never see
> messages for APRS stations it sees on RF.
> Huh? I don't get this at all. Say the 2way IGate runs its audio into the TNC
> through a ten second loop filter so that the packet sent by the rx-only IGate
> has fully propagated through the APRS-IS before the the 2way sees it on the
> TNC serial port. This is an exaggeration of the scenario you are taking about,
> right? The two-way IGate should certainly have a filter wide enough that
> allows messages to the RF user to pass through the filter. So a message to
> the RF user will appear at on the internet side of the two-way IGate. The
> 2way will still have heard the RF user on the RF port regardless of the delay,
> and assuming it is within two hops will have identified the RF user as a local
> station, and therefore the message will be IGated. If there is something I'm
> missing that can cause this would you please explain better?

You are correct, you don't understand how an APRS-IS server dupe elimination works or how a limited feed from a server works.  Bottom line: if the server that the bidirectional IGate is connected to sees the packet from the RX-only IGate before it sees the packet from the bidirectional IGate and the bidirectional IGate's server is connected to a filtered port (common combined server/IGate configuration), the upstream server will not pass messages destined for the station the bidirectional IGate just tried to gate.  Messaging is busted in either case with a RX-only IGate and the proverbial "I never see an ack but I can see my packets on aprs.fi" complaint is made.

> > The statements of Steve "An rx only IGate is better than no IGate in almost
> all cases." and "If nothing else, all ARISS IGates should be receive only." are
> invalid because they do break messaging, even for bidirectional IGates.
> ARISS is simplex, and ARISS IGates must be one way. If they are 2way with a

Ok, I misread your second statement.  You are correct, SatGates must be receive-only and were not addressed by anyone other than you before.  My statement was regarding APRS-IS which is what your first statement was regarding and that was invalid.

> > Unlike "fill-in" digipeaters which provide RF coverage for areas that are
> dead spots to local wide-area digipeaters, IGates normally depend on local
> wide-area digipeaters for their "ears".  A receive-only IGate provides no
> added coverage and can interfere with the proper operation of a
> bidirectional IGate.
> That assumes you have a mature situation with an IGate every one or
> digipeaters away. Some of us do not live in that situation. Some people live in
> areas with no IGates. Would you argue they should be denied the ability to
> send their traffic to the internet just because they do not wish to take the
> risk to their licenses of implementing two way messaging over an unsecured
> system?

No, it assumes the primary nature of modern-day APRS-IS to interconnect amateur radio APRS RF networks.  No one is denying anyone anything.  Everyone has the right to operate their station the best way they see fit within the laws of their country.  I am stating that RX-only IGates break APRS messaging in more ways than your limited understanding and I am stating that RX-only IGates do not serve the amateur radio community using APRS-IS.  If someone is so concerned about the lack of security on APRS-IS and don't want to run a bidirectional IGate but need to have their posits seen by non-amateurs on the Internet, maybe they should think of using a different free tracking service for their broadcast communications directed towards non-amateurs (also illegal in the US).

> > I highly discourage receive-only IGates as they break APRS messaging to
> the RF area they cover.  If your belief that APRS-IS solely exists to support
> database servers providing tracking services, the RX-only IGates are fine.
> However, if you believe that APRS-IS is to support and interconnect amateur
> radio RF networks, RX-only IGates are not fine.
> Other than for ARISS where they are mandatory, I agree that a 2way is better
> than a 1way IGate, and there is no need for tens or hundreds, but multiple
> receivers do provide diversity reception. I remain skeptical that a one-way
> IGate can interfere with two way messaging. I want you to explain that
> better, if that really is true I might change my opinion (but only on terrestrial
> APRS, ARISS MUST be 1way).

Again, I have explained it many times and if you still don't understand how dupe elimination in servers can affect IGates receiving limited feeds from the servers, I recommend you visit www.aprs-is.net and learn more about the modern-day network.

> One more good reason for one way IGates. It is much easier for a 1way IGate
> to simply click a box to become a two-way when the usual IGate goes down
> due to emergency or other causes. A 1way IGate will have more experience
> in the operation of the sofftware than someone that has never tried to set
> up an IGate. We should still at least give lip service to being an emergency
> and training service!

Again, lack of understanding of modern-day clients.  It is just as easy to click to boxes to make that client gate to/from RF at all.  Most GUI clients allow connection to RF and to APRS-IS without gating between them.  Not a good reason to run an IGate that if left on due to an evacuation could further break the emergency communications you want it to support.  Best to be not IGating at all than be a receive-only IGate (SatGates are not included in this statement).


Pete Loveall AE5PL
pete at ae5pl dot net

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