[aprssig] What is "TNC Channel Switching"?

Andrew Pavlin AndrewEMT at hotmail.com
Fri Apr 11 09:54:58 CDT 2014


Actually, there would be a reason to prohibit if the Kamtronics units couldn't handle it; they couldn't _transmit_ such packets to RF. 

But what software could attempt to send such packets in Command or Converse mode on a KPC? Nothing modern. KISS mode wouldn't have a problem.

Andrew, KA2DDO
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Rick Green <rtg at aapsc.com>
Sender: aprssig-bounces at tapr.org
Date: Fri, 11 Apr 2014 10:44:37 
To: TAPR APRS Mailing List<aprssig at tapr.org>
Reply-To: TAPR APRS Mailing List <aprssig at tapr.org>
Subject: Re: [aprssig] What is "TNC Channel Switching"?

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 
packets?
   To answer this, I feel we need to know the answers to two other 
questions:
   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

We, the People of the United States of America, reject the U.S. Supreme Court's
  Citizens United ruling, and move to amend our Constitution to firmly establish
  that money is not speech, and that human beings, not corporations, are persons
                        entitled to constitutional rights.

 			http://www.MoveToAmend.org


_______________________________________________
aprssig mailing list
aprssig at tapr.org
http://www.tapr.org/mailman/listinfo/aprssig


More information about the aprssig mailing list