APRS on RF from your computer network

Enable Server Ports.  Those three words have baffled me for years. It's a menu item, under Interface, on Xastir and I've been wondering what it does for a while.  I had searched the Internet before without a positive result but last night I hit gold.

Okay, maybe not gold but I did hit the online version of the Xastir man page (who reads the man pages anyway?).  On the man page it clearly calls out how to interact with this switch:

Enable these ports on this menu: "Interface->Enable Server

TCP:2023 Bidirectional TCP port for clients to connect
to. Requires login if client will be transmitting.

UDP:2023 Unidirectional UDP input port for clients to inject
packets. See the documentation for the format.

Hmm, this would make it seem I could share out my RF APRS connection with other APRS clients on my LAN.  Bingo!  A quick modification to iptables and setting up my APRSdroid software to connect to my APRS computer yielded APRS stations coming across the radio showing up directly on my phone!  Nice!  I was using a TCP connection so I am able to [STRIKEOUT:transmit and] receive on my Android device using the TNC and radio upstairs in my shack.

WG3K>APX204,K3CAL-1,WIDE2-1:}WG3K-5>APDR13,TCPIP,WG3K*:=3841.14N/07632.08W$202/005/A==-00052 CALV ARES EC WL2K-1

Where is this useful?

This would be extremely useful anywhere you have multiple APRS clients but only a single RF connection (and who wants ten different APRS stations at a single location?).  Think EOCs where you have multiple stations setup.  Each station could have their own APRS client where they could monitor the status of other stations, update resources, and send and receive messages.

For sharing situational awareness information this is great as well. Using a UDP connection, several APRS clients could be connected to Xastir as "read-only".  Think the big situational awareness screens or information screens for bike races and marathons.

TCPIP Troubles

If there were a downside to this implementation it's that it doesn't appear these stations will show up on the Internet.  [STRIKEOUT:That TCPIP in the packet stream should tell any I-gate that the packet has already come across the APRS-IS and shouldn't be passed.  This isn't a problem if all your stations you want to communicate with are on RF but if some are coming across another TCP/IP network... well, there will likely be problems.  I haven't tested if this affects incoming packets marked as TCPIP but it's on my list.]

Update: 2016-03-27 @ 1812z

After discussing what I was seeing with some Xastir developers I realized that what I was seeing was expected.  The feature was designed to have a master computer on the APRS network with other clients hanging off that master that were getting everything that the master was seeing but couldn't actually transmit back out to the network.  I was actually making this happen by adding my phone's callsign into the nws-stations.txt file that forces the client to transmit those packets, as third-party packets, over the air.


So there you go, Enable Server Ports is a pretty neat feature but one that will require a bit of work to understand the limitations.  Sharing a single RF connection with a bunch of APRS clients could be very useful.  I'll continue to test out the functionality and see how much of a load I can put on the server.  Updates to this article will be forthcoming...