[aprssig] APRS Priority bit

[Robert Bruninga]

APRS needs a priority bit so that the network can make decisions
about traffic during times of stress.

We have been looking for a way to include a PRIORITY bit in all
APRS packets for many years, and there are 3 available bits in
the standard packet, but they cannot be used until UI-view is
obsolete.

This last week we did find that one of these bits IS backwards
compatible with UI-view and so we would like to move forward on
this issue.  Please read:
http://aprs.org/aprs12/priority-bit.txt

Basically, we will use the CASE of the OVERLAY byte to indicate
ROUTINE or PRIORITY.  If the overlay byte is UPPERCASE or
missing, then the packet is ROUUTINE.  If the case of the
overlay byte is -lowercase- then the packet is PRIORITY.

Last week testing confirmed that UI-view and most other clients
will display these lower case overlays, or can be updated to do
so, so this has now been added to the APRS12 addendum.
www.aprs.org/aprs12.html

This combined with the OPERATOR PRESENT bit which has been
defined for years, gives operators an easy way to differentiate
assests of immediate value during times of stress and to
minimize or ignore routine or unattended systems as needed.

DIGIPEATER code can add a SYSOP parameter that allows a sysop to
designate a local emergency and to implement a MINIMIZE function
that lets the digipeater make decisions on traffic load based on
packet priority or other parameters.

Bob, WB4APR