[drats_users] TNC Port Support

[Tony Langdon, VK3JED]

At 04:41 PM 5/28/2009, you wrote:
>Dan:
>
>Having discussed the high speed data path idea with you in Dayton, you
>know I fully support the inclusion of a TNC channel.  I think it is
>great and would open up new possibilities for data transfer beyond the
>slow speed D-STAR data path and the D-STAR DD channel.  We too have
>lots of ARES members with TNCs. You would bring lots of our ARES
>members to D-RATS if you did include a TNC port.

Hmm, I like the TNC idea.  Funnily enough, I'm also looking at doing 
something for the text box on Echolink. I will be using AX.25 UI 
frames for that project.


>As for AX25 frame support, you might start with unproto frames first
>and avoid all the callsign routing stuff.  You have all the logic built
>in to deal with the ARQ aspects of the channel and don't necessarily
>need callsign routing.

I thought UI frames were just sent, with no ARQ.  If the frame was 
corrupted, then it's simply lost.


>In the long run, I believe there is value in making it AX25 aware.  In
>Missouri we have a state-wide packet net built on TheNet type nodes.
>Routing is not automatic but you can manually build a connection across
>the state by sequentially connecting the nodes that you need to create
>an end to end channel.  Basic AX25 support would allow you to use this
>and other digipeater networks. It doesn't require full AX25.

Also, it means it's simple to get field stations participating.  All 
they need to do is configure their TNC right, and they can transmit 
the right UI frames from a terminal emulator.  I haven't given any 
thought to routing yet.

Anyway, I think TNC support is an excellent idea, and that it's worth 
investigating the potential of using AX.25 UI frames on the packet side.


>I personnally want to build an AX25 stack over a high speed digitally
>modulated signal.  Packet radio needs an overhaul with newer digital
>modulation schemes.  I am studying several digital modulations schemes
>for one that is appropriate for my purpose.  D-STAR uses OFDM with GMSK
>carriers.  I read some comments that lead me to believe someone has
>written sound card libraries to encode and decode OFDM/GMSK.  If anyone
>knows who is doing this work, I would love to meet them.

Hmm, D-STAR does not use OFDM, it uses single carrier GMSK.

73 de VK3JED / VK3IRL
http://vkradio.com