--- In [email protected], John Hays <j...@...> wrote: > > Hi Simon, > > Good questions. It's nice to see someone actually looking at the spec :)
Yes, but I wish the spec was a little clearer. They also appear to muddle bits and bytes. > > Q1: The DD (Digital Data or Data-Only) mode, is specified in the > header, as you noted. This mode is currently only implemented at > 128kbps on 23cm in the Icom ID-1. So it's 'Ethernet-over-DStar', make sense I guess. > the > remaining 1200 bps of the 4800 bps (6.25 kHz wide GMSK) data stream is > available ... > with no > error detection or correction in the protocol. > Some applications such > at D-RATS (http://www.d-rats.com) add these features at the > application level. I'll have a look as D-RATS. So am I right in my understanding that a DStar 2m radio (such as IC-V82 + UT-118) will send (or can be made to send) unadulterated data over the voice+data channel? Does this mean whatever it receives on the serial port is sent out as additional data on voice+data more, or is there a comms protocol on the ICOMs to 'poke' data bytes into a message queue? Now for the big question.... :-) Q. How useful/important would it be for transmission integrity to include compression/FEC of 'simple data' on the voice+data link. The reason that I ask is that (in one of my other areas of interest) there is a scheme for compressing ASCII (binary, C40, etc) for use with IEC16022/ECC200 2D barcodes. Basically the data stream is encoded into a sequence of codewords and with FEC data appended to the end. Codewords/FEC lengths are predefine for different barcode geometries, but allow up to 3116 numbers in a single codeword sequence (more can be 'paged' together up to 16 pages). It just struck me that this might be an obvious match for a modified D-Star scheme. It is pre-defined and there is open code for making it happen.... Compression ratios depend on source data and chosen mode, although it is possible to switch between modes with a little overhead. The C40, X12 and EDIFACT 'alphabets' also have a shift character where another character set can be obtained with an addition codeword. ASCII, ASCII character 0 to 127, 1 characters per CW ASCII extended, ASCII character 128 to 255, 0.5 character per CW ASCII numeric, ASCII digits, 2 characters per CW C40, Upper-case alphanumeric, 1.5 characters per CW TEXT, Lower-case alphanumeric, 1.5 characters per CW X12, ANSI X12, 1.5 characters per CW EDIFACT, ASCII character 32 to 94, 1.33 characters per CW BASE 256, ASCII character 0 to 255, 1 characters per CW Codeword+FEC sizes are dependant on message length, but range from 3+6 to 1558+620. Cheers, Simon VA6SDW
