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<div class="moz-cite-prefix">On 12/2/2013 8:17 PM, Lee Bengston
wrote:<br>
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<blockquote
cite="mid:CAPF_JSJVpyX+zZESt+MbmuHG9cCZsE8ZwB5MdhUAUpY-zbhpTA@mail.gmail.com"
type="cite">
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<div class="gmail_default"
style="font-family:verdana,sans-serif;font-size:small">Yes,
the heard list should give the IGate the necessary
packets, but what about the ability of the IGate to
determine if a station heard on RF is also directly
connected to the Internet/APRS-IS? With no range filter
(or a very small range filter), wouldn't that create the
possibility of gating a message via RF addressed to a
station heard on RF that is also connected to the
Internet? Or would the IS server take care of this by not
sending the message to IGates that have gated RF beacons
from the message recipient - instead only send the message
to the addressee?</div>
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<br>
The APRS-IS server(s) not only send messages addressed to the heard
list stations, but also any posits for those heard stations as
well. This allows the IGate to determine #4 in (from
<a class="moz-txt-link-freetext" href="http://www.aprs-is.net/IGateDetails.aspx">http://www.aprs-is.net/IGateDetails.aspx</a>, emphasis mine):<br>
<br>
<blockquote type="cite">
<p> Gate message packets and associated posits to RF if all of the
following are true: </p>
<ol>
<li>the receiving station has been heard within range within a
predefined time period (range defined as digi hops, distance,
or both). </li>
<li>the sending station has not been heard via RF within a
predefined time period (packets gated from the Internet by
other stations are excluded from this test). </li>
<li>the sending station does not have TCPXX, NOGATE, or RFONLY
in the header. </li>
<li>the receiving station has<b> not </b>been heard via the
Internet within a predefined time period.<br>
A station is said to be heard via the Internet if <b>packets
from the station contain TCPIP* or TCPXX* in the header</b>
or if gated (3rd-party) packets are seen on RF gated by the
station and containing TCPIP or TCPXX in the 3rd-party header
(in other words, the station is seen on RF as being an IGate).
</li>
</ol>
</blockquote>
<br>
To provide for the determination of #4, my understanding (and
observation) is that the APRS-IS servers forward any packets sourced
by the heard stations to the IGate client on the filter port. This
is why IGates with no filters will STILL receive packets from the
APRS-IS that are NOT intended to be transmitted to RF, but provide
visibility for the IGate to make local gating decisions.<br>
<br>
There's (at least) one IGate implementation out there (don't
remember which one) that blindly transmits 3rd party packets via RF
for every packet received from the APRS-IS server. In my
understanding, this is not proper as the APRS-IS servers forward
information-providing packets not intended for transmission, but
instead rely on local IGate intelligence to determine which packets
should actually be gated from -IS to RF.<br>
<br>
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32<br>
<br>
<br>
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32<br>
<br>
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