[aprssig] APRS Message Callsign SPEC- Ambiguity

Scott Miller scott at opentrac.org
Mon Apr 25 18:24:47 CDT 2016


If you're talking about AX.25 TOCALLs it's not fair to say that it's a 
limitation of the TNCs - upper case callsigns are required by the AX.25 
spec:

3.12. Address-Field Encoding
The address field of all frames consists of a destination, source and 
(optionally) two Layer 2 repeater subfields.
Each subfield consists of an amateur callsign and a Secondary Station 
Identifier (SSID). The callsign is made up
of upper-case alpha and numeric ASCII characters only. The SSID is a 
four-bit integer that uniquely identifies
multiple stations using the same amateur callsign.

That doesn't apply to the APRS message spec, of course.  And if you're 
dealing with a TNC in converse mode on the receive side you can spoof 
AX.25 TOCALLs, too.  Embed a CR/LF in the packet payload and insert a 
TNC2 style header and your converse-mode connected software can't tell 
that it's not another packet, assuming the TNC is passing the CR/LF 
characters.

Scott
N1VG

On 4/25/2016 2:07 PM, Robert Bruninga via aprssig wrote:
>
> There is an unintended ambiguity in the APRS SPEC regarding the 
> addressee in the APRS MESSAGE format.
>
> It was intended that the TOCALL of any transmitted message could be 
> sent to ANY 9 character callsign field and this included mixed-case.  
> Although TNC’s have historically forced callsigns to UPEPRCASE only, 
> this is only a limitation of TNC’s and was not intended to be a 
> limitation of APRS.
>
> STATION names, OBJECT names, ITEM names were intended to be a general 
> 9 character mixed case field in APRS padded to 9 with spaces.
>
> We just noticed that some radios do not allow sending an APRS message 
> to a mixed case address.
>
> Unfortunately, the QIKCOM-2 satellite which does DTMF-to-Voice and 
> APRS-to-voice has a special message address of “QIKCOMsay” for all 
> messages it is expected to speak.  So some people will not be able to 
> exercise this text-to-voice messaging capability.
>
> I wont make this mistake in any future satellite, but we are stuck 
> with it.
>
> SO, we might ought-to-identify all APRS radios and APRS clients that 
> have this uppercase-only restriction on MESSAGE Callsigns.
>
> I can say the Kenwoods have it.  Others?
>
> See http://aprs.org/aprs11.html and specifically, see:
>
> See http://aprs.org/aprs11/aprs-names-and-spaces.txt
>
> Bob, WB4APR
>
>
>
> _______________________________________________
> aprssig mailing list
> aprssig at tapr.org
> http://www.tapr.org/mailman/listinfo/aprssig

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tapr.org/pipermail/aprssig/attachments/20160425/fac4d0f8/attachment.html>


More information about the aprssig mailing list