[aprssig] What is "TNC Channel Switching"?
rtg at aapsc.com
Fri Apr 11 09:44:37 CDT 2014
On Fri, 11 Apr 2014, Stephen H. Smith wrote:
> The Kantronics "stream switch" characters were a way of accommodating
> multiple logical channels in the 7-bit ASCII world that predated KISS, by
> using two typeable characters that were not used much (at least in American
> English and if you weren't a Unix programmer!).
That doesn't answer the OP's real question. Is it necessary to treat
these characters as 'reserved', and prohibit their use within APRS
To answer this, I feel we need to know the answers to two other
Were the Kantronics dual-TNCs sensitive to these characters in received
data on the radio side? Would they cut off the current stream and switch
the received data to the other radio in mid-packet??
Did the Kantronics command language provide any way of 'escaping' these
characters so that they could be embedded within packets? It was
mentioned that in practice they were 'prefixed' to a command to indicate
which stream this command is to apply. Is it possible that the TNC was
ONLY sensitive to a stream switch character immediately after a ctrl-C as
it enters command mode, or immediately after a carriage return if already
in command mode?
If it can be shown that the Kantronics TNCs are only sensitive to these
characters on the serial side, and as a prefix to a command, then there
is no reason to prohibit their use within the protocol itself.
Rick Green, N8BJX
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