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Re: Screen shots

"John D. Hays" <john@...>
 

Hi John,

We've been thinking about some of these ideas as well.  In the design of the UDR56K-4 we really are shooting for the "sweet spot" between data rate, bandwidth, propagation, and utility.

70cm was chosen as the band because we can run at 56 K bauds and up to 100 Khz of bandwidth (Part 97.307) which is sufficient for many data transfer applications like text email. The band has decent propagation (compared to 33/23 cm) and is less crowded than 2 meters in most areas (especially in the 420-440 segment).  Lower loss cable, connectors, etc. and reasonable gain antennas are easier to work with than at higher frequencies.   A lot of people have said why don't you put it on 2 meters?  Well, we would have to cut back to 19.2 K bauds and the band is too popular with little room for additional modes.

So the main difference between DV and  DD, as far as the bits go, is 1 bit flag in the header and the payload.  So theoretically one could do a 4800 bps DD signal through a DV repeater.  Where it gets tricky is we don't know where in the Icom chain things might fall apart:
  1. Do  the DV radios honor the header flag bit and not try to decode the payload of a DD packet?  If so, then you wouldn't hear anything on a Voice channel when the bit was set.  Also Icom uses its digital coded squelch, which everyone leaves at 00, so would that also help filter out DD?  We'll know more about that when we start generating some 4800 bps DD on a channel.
  2. Does the Icom repeater look for the bit when repeating DV?  If not then local repeater use should be possible on current Icom repeaters.
  3. Does the RP2C require the bit to be set or unset when a port is designated for DV or DD in setup?
  4. Does the RP2C send to different ports on the gateway for DV vs DD data.  We know different ports (UDP 40000,40001) are used for DV and DD going to and from the gateway over the Internet.
  5. What exactly would the Icom G2 gateway do with a signal where the header bit is set opposite of what the module was designated for, e.g. DD on a DV module or DV on a DD module?
So much of this is just a black box on a platform like Icom G2.

Clearly on open source gateway and repeater controller software we could adapt to multiplex DD and DV on the same repeater or half-duplex channel, but we won't know on the Icom stuff until we're able to test. (We do have access to some RP2C / G2 gateway systems for testing.)

One thing about DD is it is callsign addressed, so if the reflector code would only pass DV traffic with CQCQCQ (or the reflector designator) in the UR field, one could multiplex without affecting links or reflectors.

The other concern with very low rate DD is buffering traffic from higher speed systems, e.g. trying to squirt a 56 or 128 K DD packet through a 4800 bps channel should work, but timings for TCP ACK packets, etc. would get a little crazy.

John D. Hays
K7VE
PO Box 1223, Edmonds, WA 98020-1223 
  



On Sun, May 27, 2012 at 9:27 AM, john_ke5c <ke5c@...> wrote:
 

> In general, I'm very interested in the UDR, I've done a good bit of testing (with Darren, G0HWW) of DTN, NORM, IPv6 and other protocols over 9K6 AX.25, D-Star DD mode, and to me it seems that it may hit a sweet-spot between RF range and data throughput (if there is indeed such a thing). I guess EmComm would be my main use/interest for it.

I too have been wondering about 9600 (or thereabouts) data. We might be able to take advantage of the gateway/internet infrastructure if a "Dd" DStar packet could be defined that would use all bits for just data, no voice. I'm guessing (hoping actually), the band modules and gateways would pass those so long as the headers were okay. Of course, it would sound like garbage to DV radios, but you could commit band modules to data only. dplus might burp, but you would probably callsign route such "data" packets anyway. Just brainstorming,

73--john
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