[aprssig] APRS Priority bit

[Robert Bruninga]

Regarding the Priority Bit (signalled by lower case Overlay).

> I foresee two issues (may be overcome...)
> First is that the compressed posit format 
> ... uses overlays a through j to represent 
> actual overlays of 0 through 9.  

Good point.  Only alternate symbols, and only symbols with ALPHA
overlays can be used if PRIORITY is required.  The sender has
the choice.  Hopefully there are enough alternate symbols to
match primary symbols to be useful in many cases.  But thanks
for the clarification, I will add your finding above to the web
page.

> Second is the concept that digipeaters will 
> now have to decode the data portion of the 
> AX.25 packet if they are to implement these RF 
> pacing algorithms.  

Agreed.  This point is also well taken.  I guess our hope was
that at least for extremely overloaded areas or specific event
areas, unique and special digipeaters could be coded to handle
these unique requirements.  I did not expect this feature to
apply to the broad spectrum all across APRS... 

I'll add these comments as well to the document.

Bob, WB4APR