[aprssig] back to tactical aprs
Andre v Schaijk
aprs at pe1rdw.demon.nl
Fri Dec 10 05:57:01 CST 2010
Bob has been sharing his frustration that aprs has become unusable for
tactical communication thanks to the abundance of mobile trackers.
Offcourse splitting tactical and tracker trafic (and combining them on
uhf) is a good fist step but over the years another problem has made
it's way into the network.
It starts with using level 2 routing where it should be handled at level
3 and set at level 7, for those not familair with iso network layers
level 1 is the hardware (radio/audio/1k2/9k6/etc) level 2 the transport
protocoll (ax25) level 3 is routing (net/rom flexnet inp3 ip etc) level
4 transport (tcp aprsobjectname etc) level 5 session (end to end
connection etc) level 6 presentation (aprs data text etc) level 7
aplication (win aprs, ui-view etc).
right now we are setting the number of hops you want to go at level 2
(wide2-2) but for tactical use we should not have to worry about the
network, all we care about is how far it gets, this should be a setting
in level 7 that is forwarded to level 4 and used by level 3 (the digi
checks how far it is from the sender and decide if it has gone far enough)
On a transport level we are handeling duplicate reduction of level 2 by
abusing a level 1 setting (setting dwait to 0 making sure we get on air
collisions, this is against normal network planning, it make much more
sense to use the digi software to decide if a packet is a duplicate or
not (like digined does) this will safe onair time compared to using
level 1 collisions because FM capture is not perfect and leads to
undecodable packets and time shift between digis thanks to differences
in txdelay and difference in reception of hidden nodes.
I'm fully aware that it grew this way because at least in the usa a lot
of sites depend on embaded hardware to do everything but today it makes
no sense to stick to outdated hardware (8bit z80 based tncs) where
embeded pc systems have simular power consumption and can do a lot more.
73 de Andre PE1RDW
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