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

Steve Dimse steve at dimse.com
Mon Dec 2 07:53:09 CST 2013

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?
> 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 conventional terrestrial path for their outgoing RF traffic, then any local user will suffer QRM from the IGate and the IGating accomplishs nothing, and ISS will also suffer from the added packets on the frequency. If the 2way IGate operator programmed in a path that digipeated INet to RF traffic through ARISS they are violating the policies of the ARISS team and squandering a scarce resource. Having the ARISS gates 1way breaks nothing, because there are no 2way IGates on the frequency.

> 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? 
> 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). 

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!



More information about the aprssig mailing list