[aprssig] APRS Message Callsign SPEC- Ambiguity
scott at opentrac.org
Mon Apr 25 19:24:47 EDT 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
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
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
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