[aprssig] Why do stations send telemetry parameter messages to themselves?

[Lynn W Deffenbaugh (Mr)]

On 11/19/2024 7:08 PM, John Gorkos wrote:
> inline comments
ditto
>
>
> On 11/17/24 8:23 PM, Lynn W Deffenbaugh (Mr) wrote:
>> Read chapter 13 of aprs101.pdf.  It describes the "On-Air Definition 
>> of Telemetry Parameters" which are specially formatted messages 
>> (PARM, UNIT, EQNS, BITS) sent via APRS message format packets from a 
>> station to itself.   The T datatype only carries values, not the 
>> definitions of how to interpret those values.
>
> Ok.  So we have 4 specifically spec'ed, formatted messages that use no 
> DTI, and cause parsers to specifically have to look beyond char[0] of 
> an on-air message to see what they really contain and if they need 
> special handling.  That's probably not the worst thing in the spec, 
> but it's in the running...

What null are you trying to parse beyond?   There isn't a null in the 
telemetry definition messages.   At least, there's not supposed to be.   
What is a "DTI"?   I'm not familiar with that TLA (Three Letter Acronym).

>
>
>>
>> As for RXTLM-1, technically that would be an Alternate Net identifier 
>> of RXTLM since it doesn't start with AP.   You can read about these 
>> on Page 15 of chapter 4 in aprs101.pdf.
>>
>> The -1 would be a Generic APRS Digipeater Path also discussed on page 
>> 15 in chapter 4 of aprs101.pdf.   The -1 would technically be the 
>> same as a WIDE1-1 path.
>>
>> However, that said, I suspect that the RXTLM-1 is actually not 
>> meaning that but is being mis-used by some software somewhere.
>>
>> Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
>>
>>
> And I still don't see the purpose of wrapping the telemetry specs in a 
> message and sending it to yourself.  that triggers all kinds of 
> third-party message handing in the network that doesn't need to be 
> woke up.
If we had been around when aprs101.pdf was being authored, I'm sure we'd 
have learned the reasoning behind it.   But coming on the scene later 
than that, we pretty much have to live with it.

My first check in message packet handling: If the source callsign-SSID 
is the same as the addressed callsign-SSID, process it as a telemetry 
definition or ignore it entirely as needed. These should NEVER be gated 
to RF from the APRS-IS, IMHO, if for no other reason that if the 
addressed callsign-SSID was recently heard on RF, then the source 
callsign-SSID must also be on RF (it is the same, after all) and so it 
won't need these messages gated to it.

>
> I'm torn between being a spec-Nazi and just throwing my hands up and 
> saying I can't fight 40 years of momentum.

Like all specifications, implementers have the choice to be compliant or 
non-compliant.   But if you expect to handle telemetry and present it to 
the user in readable (read: converted) format, then you'll need to 
process the definitions.

And if you're doing IGating, then you need to consider these definition 
and see how a message sourced by and addressed to the same callsign-SSID 
would be handled in your logic.


Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32


>
>>
>> On 11/14/2024 4:15 PM, John Gorkos wrote:
>>> I'm back into the deep, ugly guts of parsing the full APRS-IS 
>>> stream, and I keep seeing messages like this:
>>>
>>>
>>> EL-OK1BY>RXTLM-1,TCPIP,qAR,OK1BY::EL-OK1BY:UNIT.RX Erlang,TX 
>>> Erlang,RXcount/10m,TXcount/10m,none1,STxxxxxx,logic
>>> ER-F5ZVB>RXTLM-1,TCPIP,qAR,F5ZVB::ER-F5ZVB :UNIT.RX Erlang,TX 
>>> Erlang,RXcount/10m,TXcount/10m,none1,STxxxxxx,logic
>>> KI0AU-1>APMI06,TCPIP*,qAC,T2BC::KI0AU-1 
>>> :UNIT.C,Pkt,Pkt,Volts,Volts,N1,N2,N3,N4,N1,N2,N3,N4
>>> GM7AFE>APMI01,TCPIP*,qAS,MB7UZL::GM7AFE 
>>> :UNIT.Pkt,Pkt,Pcnt,Volts,Volts,Off,On,On,On,Hi,Hi,Hi,Hi
>>>
>>> Why are stations wrapping telemetry parameter messages in APRS 
>>> Messages and then sending them to themselves?  At least they're not 
>>> asking for acknowledgements.  Can anyone explain this behavior and 
>>> what it's intended to do, versus just using a :T telemetry message, 
>>> per spec?
>>>
>>> While we're at it, what does the RXTLM-1 tocall tell me? Clearly 
>>> something to do with Receive Telemetry (i.e. erlang values, etc).
>>>
>>>
>>> Thanks de AB0OO
>>> John Gorkos
>>>
>>>
>>> _______________________________________________
>>> aprssig mailing list
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>>
>>
>>
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