[aprssig] Level 4 Routing ?

William McKeehan mckeehan at mckeehan.homeip.net
Tue Jan 30 12:29:21 CST 2007

Today I was doing some research on digipeaters. In doing that I read Bob's doc:

At the bottom is a section that I found very interesting:

These concepts were proposed in the early days of APRS (1994) but
have never caught on...  THey are retained here for historical purposes.

Since NODES are smarter than digipeating, the ultimate we should have
NODES do all UI frame routing via high speed  backbones.  The APRS
station simply sends his UI frame TO APRS VIA HOME;  Any NODE hearing
that transmission that has knowledge of the route to HOME, will send
the single packet via the NODE network (level 4) to the HOME node!
When it arrives at the HOME node, it is transmitted once as a UI frame.
With this arrangement, a mobile only has to specify his one intended
destination, no matter where he travels!  In this example I use
the DIGI call of HOME just to represent the digi near someone's HOME...

DIGI/NODE COMPATIBILITY:  Mobiles should be able to specify a path that is
compatible with both nodes and digipeaters.  The nodes should only look at
the LAST digi field in an UNPROTO list for the final NODE destination.
Any preceeding fields are assumed to be DIGI's only.  This way a path of
APRS VIA WIDE,HOME would be repeated by any WIDE that heard it, but any
level 4 node that heard it would forward it to the HOME NODE.  If only one
field is included in the digipeater string, it would be interpreted as
both a digi and a HOME destination without any difficulty.  Digi's and
NODEs would digipeat it, and nodes (hearing it direct) would forward it at

What would it take for this to be implemented?
Can current day (new paradigm WIDEn-N) digis be upgraded to be a NODE while
remaining a DIGI with the NODE routing overriding the DIGI routing?

William McKeehan

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