[OZAPRS] APRS with Foundation license

[Ray Wells]

Daryl,

Congratulations for stepping up the ladder.

The ax25 specification set the six character limit for the callsign, 
plus the SSID which is in the range 0 - 15. The v2.0 specification we 
still use today emerged in 1984. I can't remember what limits, if any, 
existed in the father of packet, the Vancouver Protocol or the original 
V1.0 ax25 specification that displaced Vancouver. I do remember the hot 
debate about which was best, Vancouver or ax25 - this was circa 1983.

I have to confess I do not know what would happen with a seven character 
callsign but given that the last character ends up where the SSID is 
expected, one could expect packet corruption. I'm just looking at the 
v2.0 (1984) specification and the source address field is seven octets 
long. The first six are for the callsign, the seventh for the SSID. For 
a callsign with less than six characters, the space to the right of the 
last character is padded with ASCII spaces. The dash, between the 
callsign and the SSID is not mentioned but appears to be a delimiter 
after the callsign. Given that the SSID field expects certain ASCII 
characters and, another letter may not meet the requirement, I stand by 
my assumption that packet corruption is a possibility.

In connected mode and, assuming a connection could be established, such 
a frame could provoke a REJ frame from the destination station. Given 
that aprs uses unconnected mode the packet would probably just head off 
into the ether, never to be seen or heard again.

Perhaps someone who has delved deeper into the specification would like 
to comment.

Could it be that the ACMA was aware of the six character limit for ax25 
when they allocated a seven character callsign, a deliberate act to 
prevent the use of ax25 by Foundation Licensees?

Ray vk2tv

On 06/10/10 00:37, Darryl Ross wrote:
> I'll have to second Ray's note about thank you for asking questions
> before you get on-air Andrew. Much better to understand than potentially
> break the rules / law.
>
> Using the digital modes is a good reason to upgrade. I've done the
> Foundation ->  Standard ->  Advanced thing (in about 18 months from
> starting). The first upgrade purely so I could play Packet/APRS and the
> second upgrade for the 2 letter call ;)
>
> Changing the topic slightly away from the legal side of things, isn't
> the maximum length of a callsign in AX.25 6 characters? By my count,
> foundation callsigns are 7 characters, and so _can't_ appear on RF anyway?
>
> Whether the callsign is truncated to 6 characters is a separate issue
> and would be classed as a bug in the particular client...
>
> -Darryl, VK5HZ
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