[Xastir] UDP frames

[Wes Johnston]

Perhaps we've meandered far enough it two days....

My goal when I brought this thread up was to create some widget (or a new port
type under xastir) that would connect to the aprs IS stream and pass that data
out on my local wlan (or lan for that matter) as UDP packets on port 14439.  In
the case of a wlan, the ssid could be APRS or AXU.  The point to this is that as
my laptop/pda/whathaveyou wanders in and out of hotspots around an event, I get
any and every packet that is available from the AP that is broadcast to
255.255.255.255:14439.

If we start talking about TCP packets, I may as well establish a connection to
some normal APRS software like xastir on TCP port 2023.  Problem is, in a local
event, there may be long periods of no traffic and I could not use (as a client)
the auto reconnect feature of most aprs programs because they would not know the
connection had dropped due to my wandering around, or if there had just been no
data for an extended period.  Even then, I have to reconnect and during the
unconnected time, I missed some packets.

I like the UDP method because there is no connected layer overhead, no ACKs
(well ok, there are ACKs in the 802.11 mac layer).  In the end, the software on
my PDA just listens promisculously on port UDP 14439 and scavenges anything it
can.  This is no different than APRS listening to PID F0 (UI frames).  There is
no setup of a connection that may fail in 2 seconds as I pass out of range of
the 802.11 ap... just catch as catch can.

I understand that 802.11 works a behind the scenes connection when you wander in
range of an AP... But I don't need to know about that in this context... all I
know is that I wander within range of a hotspot and like magic data starts
appearing on port 14439.  My not worrying about the behind the scenes
connection between 80211 devices and the AP, I closely mimic being connected to
a LAN cable and hearing the broadcast packets there.

Also by using UDP frames, we don't have to know which host to connect to...
which is a pretty major part of APRS... come as you are and hit the ground
running.  If I run TCP telnet connections to a host, I have to know the name of
the host, and program that into my client software.  A difficult thing to
convey.

I did like the analogy someone said about working packet this way would be like
meteor scatter.  That's true when driving a car.. but in/on/around the EOC,
anyone with a laptop in range of an AP could have the full aprs IS stream w/o
having to do anything other than turn on the network card.

I need to check Curt's suggestion of something simple like Netcat.

Wes
--



Quoting jeff at aerodata.net:

> Yes, now you are seeing the problem. I need to get in there, assoicate,
> get an IP address, and then dump my data to the APRS server stream.
>
> In the later case, making a more terse method to enter position reports
> makes sense (if it already doesn't exist).
>
> To associate quicker, you need to step up the 802.11b probe request rate.
>
> The IP address, not much we can do about that as that depends on the DHCP
> server. But we have control over the probe requests as well here.
>
> If you run windows, I'm sure you have heard of netstumbler. Its a AP/Adhoc
> scanning tool. Similar things exist for linux. What you may not have
> heard, is netstumbler has its own API...
>
> http://www.stumbler.net/scripting.html
> http://www.netstumbler.org/index.php?
>
> Which should allow you to use the GPS and AP data to more quickly connect
> and dump data to the APRS system.
>
>
>
> >>
> >> What if you are running adhoc?
> >>
> >
> > That's was the whole point of my earlier questions.
> >
> > I might be romaing around at 60MPH and see any given access point for only
> > seconds - if at all.
> >
> > I am interested in how connectivity will work with an access point at a
> > high
> > location and a beam pointing down at me. Over all, I suspect the whole
> > deal
> > might look more like meteor scatter than packet radio :-)
> >
> > Andreas, N6NU
> >
> > _______________________________________________
> > Xastir mailing list
> > Xastir at xastir.org
> > https://lists.xastir.org/mailman/listinfo/xastir
> >
>
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