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[aprssig] APRS Digipeter Design Questions

Robert Bruninga bruninga at usna.edu
Fri Apr 29 12:50:16 UTC 2005


>>> hansen at fredonia.edu 4/28/2005 10:02:09 PM >>>
>Currently... properly doing callsign substitution (up to 8)

Be sure this pre-empts UIFLOOD and UITRACE

>I've implemented 4 beacons,

Only ONE is needed.  In fact if there are 4 then they
all have to be indentical, since nothing in APRS can have
more than ONE position (and position comment) at a time
and we dont want "cycling" positions reports because the
constant change FILLS up all position logs...

>1.  Currently I've not implemented TRACE.  

EVERYTHING is obsolete except for WIDEn-N
there is no more future need for RELAY, WIDE,
TRACE, TRACEn-N, nor SS.  There are only 
two mechanisms.  UIFLOOD with ID and UITRACE

> Is there any reason for me to include support for TRACE?

Be very careful with terms.  There used to be TRACE
and TRACEn-N.  Both are totally different processes.
"TRACE" is completely obsolete.  "TRACEn-N" using
the UITRACE paramete is being replaced by SSn-N 
where SS is the state or section abbreviation.

>2. I've allowed for 4 different Beacon texts.

See note above.  The ONLY reason we use 4 texts
(and make them all  identical) is because we neeed
the 4-RATES and 4-PATHS so that the beacons of
the digi can be sent at different distances and
different rates.  Every 10 minutes DIRECT, every
30 minues via 1 hop and every hour via 2 hops.

Rather than KLUDGING up the 4  identical TEXTS, 
and 4 diferent PATHS and 4 different  BLT RATES,
and 4 differeent offsets,  it would be better if you
 just set up this multi-rate-multi-path for ONE text.

The other TEXTS can be used for DIRECT identification
of thinks like IRLP, ECHolink or WINlink stations or
for local APRS voice repeaters...

>2B.  UIDigi allows for a different path for each Beacon. 
> How important is this?

VERY important if we have to use the present 4-way
kludge noted above.   But can be abandoned for this
scheme:

TEXT one every 10 min direct, every 30 min via
WIDE2-1 and every hour via WIDE2-2.

TEXT 2,3 and 4 may need to go direct or one hop
depending on what objects they may indicate.
So I guess they all do need 4 paths and 4 rates.

>2C.  How many digipeters should be allowed in a path

No more than 4.  Typically 2, but allow for 4.

>3A.  UIDigi does this by time interval. ...I would like to 
>implement this... with the last X received packets 
>where X is user settable.

Seems easy on the surface, but may have a fatal flaw?.  Iin 
a remote area  where there may be few packets, this
would completely block someone.  Or in a busy area where
a few critical digis went out due to power outages and then
there were not enough packets to clear the X count, then
again, someone is locked out for an unknown time.  It may
work, but needs study...

>3C.  What parts of a packet should I include in the CRC?

The FROM, TOCALL, and DATA only.  Nothing in the digi fields.

Also, with regard to this I'm concerned about what
happens when a ... message ... isn't acked.  ... the 
dup checker would... not digi it?

Yes, this is the reason that 30 seconds of TIME is used for
the dupe check.  So that people have a determinant 
TIME to know will work for a retry.

>4.  UIDigi ignores packets that are not UI frames.

Should be sysop configurable.  And even ideally,
remote configurable.  So it can be "monitored" and
controlled...

Plesase reveiw the New N Paradigm that is the
basis for the future of APRS:

http://www.ew.usna.edu/~bruninga/aprs/fix14439.html

I think I covered most of the key elements above that
are in the New N Paradigm...

thanks!
Bob





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