[aprssig] Help explaining packets

[AE5PL Lists]

You are seeing three effects: the first is basically a preemptive acking
introduced very long ago by APRSDos which causes two acks, relatively
close together, to be sent with the hope that one of the two acks will
get through preventing a retransmission.  The second effect is simply
multiple digipeats.

Finally, and I think the source of your concern, is the gating to RF of
your packet when the sending station has, in all likelihood, been heard
on RF by the IGate.  IGate implementations vary all over the place.  In
this instance, the IGate is UI-View (APU25N) which _apparently_ is
gating to RF regardless of whether it hears the sending station on RF.
As development has ceased on UI-View, this will probably never be
corrected.

The basic criteria used within javAPRSIGate (adjunct to javAPRSSrvr) for
gating messages to RF is:

The receiving station has been heard on RF within X hops in the last T
minutes.
The receiving station has not been heard directly on APRS-IS (TCPIP in
the Internet path) in the last T minutes (prevents APRS-IS only
messaging from QRMing RF).
The sending station has not been heard on RF in the last T minutes
(prevents gating to RF when the receiving station can probably hear the
sending station on RF).

There are some further options, but these three criteria are the most
critical.  X hops is sysop-defined as different areas of the world have
different requirements.  T minutes defaults to 30 minutes as mobiles
will have normally moved on or been shut off if 30 minutes have passed
since the station was last heard.  But, again, this is sysop-defined for
specific area conditions.

All IGate software implement some variation of these criteria, but each
author has the option to include/exclude any or all of them as IGates
have been developed with no defined specification.

73,

Pete Loveall AE5PL
mailto:pete at ae5pl.net 

> -----Original Message-----
> From: David L. Martin
> Posted At: Monday, May 09, 2005 8:35 PM
> Subject: [aprssig] Help explaining packets
> 
> I send out a ping to W2MER, here is what I send and receive:
> ---------------------
> W2MER>APW261,KB2EAR-1,WIDE::W0SNJ    :ack09}
> W2MER>APW261,KB2EAR-1,WIDE::W0SNJ    :ack09}
> W2MER>APW261,KB2EAR-1,WIDE::W0SNJ    :ack09}
> W2MER>APW261,KB2EAR-1*,WIDE::W0SNJ    :ack09}
> W2MER>APW261,KB2EAR-1*,WIDE::W0SNJ    :ack09}
> W2MER>APW261,KB2EAR-1*,WIDE::W0SNJ    :ack09}
> W2MER>APW261,KB2EAR-1,KB2TSV-15*::W0SNJ    :ack09}
> W2KB>APU25N,KB2EAR-1*,WIDE3-2:}W0SNJ>APX150,TCPIP,W2KB*::W2MER
> :PING1,PING1, PING1{09}