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[aprssig] Modification to AE5PL's routing idea

Wes Johnston aprs at kd4rdb.com
Tue Feb 15 15:08:49 UTC 2005


In a nutshell, in the winter 2005 PSR ftp://ftp.tapr.org/psr/Winter_94_2005.pdf
, Pete Loveall ae4pl suggests that digipeaters hearing any packet would remove
the path from the packet and substitute it's own callsign and mark that
callsign as having been digipeated.  Other surrounding digi's would be
programmed to recongize that original digipeater's callsign as "local" and
digipeat any packet marked with that digi's callsign.  Each digi in the system
would keep a checksum of the last 30 packets' data portion for dupe supression.

The thing I didn't like about this idea was that the users could not specify a
smaller area than the area of digipeaters who were programmed for a given area
- not that any of us ego-maniacs would want smaller coverage, right?? lol. 
Seriously though, what about the need for different coverage for different
services like NWS (which often one office serves two states).  Another drawback
to Pete's idea is that if someone adds a new digi, none of the other digipeaters
would recognize it until all the other digiowners programmed their digi to be
familiar with it - or maybe this isn't a drawback ... some digiowners put up
digi's for the sake of having thier call's attached to a digi.... we'll deal
with that later.

Anyway, the suggestion that came up (again) yesterday was to use a generic call
such as LOCAL, CITY, COUNTY, STATE.  If we combine Pete's excellent idea with
the suggestion from yesterday, we can make it fit in the AX.25 v2.2 spec which
limits us to 2 digipeaters instead of 7.

Here's how we do it...
A user transmits a packet with a path of COUNTY.
kd4rdb>aprs v COUNTY:my data here   (yes, I do mean the generic term COUNTY for
the sake of travellers who may not know what county they are in)

A given digipeater (kc4pl in this case) in the area hears this packet direct and
rewrites the path to include the specific county and as Pete suggests, puts in
the digi's callsign with the has been digi'ed flag set.
kd4rdb>aprs v SUMTER*,kc4pl*:my data here

Now, all other neighboring digi's that have been programmed to respond to SUMTER
alias will digipeat the packet and maintain a checksum of the packet's data
portion in memory for dupe supression.  They will simply digipeat the packet
per Pete's idea and not alter it in any way - the first digi did all the mod's
to the packet we'd need.

The same can work for NWS areas... all digi's in NWSCHS (nation weather
Charleston) would respond to NWSCHS... it works on a state level with all
digi's in a group set to respond to two letter state abbreviations, it works
for CITY too!!  If each digipeater were to have the ability to know to respond
to 6 or 10 such aliases, we'd have a winner!  The individual digiowners would
simply get together and determine the local convention for the spelling of the
various areas they wish to support.  The users don't need to know the
spelling/abbreviations because they just use words like CITY,STATE, LOCAL and
IGATE.

Now for the gotchas and details....
1)users could transmit a packet to RELAY,COUNTY instead of just COUNTY.
2)users could still specify a path which names specific digipeaters so they can
go further in one direction if needed.
3)digipeaters could analize paths such as WIDE2-2 and realize that is equivalent
to COUNTY and convert the WIDE path to Pete's path system on the fly.

This is souped-up subnetting.

Comments?  Jason?? Gerry? Eric? Pete?

Wes
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