[aprssig] Did ICOM DSTAR ever take off ? can it be used for APRS ?
Gerry Creager N5JXS
gerry.creager at tamu.edu
Tue Jun 21 22:20:08 CDT 2005
First things first: "Am I on the right track?": No, I'm afraid not.
Wes Johnston wrote:
> I've never touched a Dstar rig, but my understanding is that while you
> talk in low speed data mode, 1/2 of 9600 is used for voice, the other
> 1/2 is used for 4800 baud serial data... so in an ideal world, I could
> hook my GPS up to the serial port and while I'm talking 100% of my GPS
> sentences are passed thru to all receivers as if the TNC were in
> converse mode.
Your first part of the understanding is essentially correct, save the
voice component is 4800-baud effective 2FEC. Correcting bit errors on
the fly helps with the audio. The remaining 4800-baud data stream is
*still* addressed in a virtual circuit manner using ATM over radio.
Because they're using "permanent" (as in, for the period of the
transmission) virtual circuits, the connection from sender to receiver
is end-to-end connected and *not broadcast generally. It's like
converse mode only between the 2 (connected) stations.
> I"m gunna ask the dumb question....
> How do you know WHO is sending the data? If it's converse mode, only
> the data portion of the packet shows up, none of the headers show up.
The circuit is nailed up when it's needed and torn down at the end of
the transmission. Both sides know who's talking to whom.
> Sounds like we need to take GPS data and encapsulate it in a 3rd party
> formatted frame.... sounds kinda clunky.
But that's what we're doing on AX.25. It's clunky but that's how a
layered system works.
You know, like IP.:-)
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.847.8578
Office: 903A Eller Bldg, TAMU, College Station, TX 77843
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