[aprssig] Aprs-is / aprs-vhf packet rate limit guidelines

Robert Bruninga bruninga at usna.edu
Thu Jan 8 10:18:14 EST 2009

> I've recently been experimenting with 
> having new objects created when a power 
> outage in British Columbia is detected,  
> but am concerned about a high rate of 
> item creation via APRS-IS.  

I would be concerned too.  But maybe we don't need such
automatic objects.  

That is what is fundamental to the APRS "Net Cycle Time"
concept.  This is the well defined standard beacon rate for
stations.  Some newcomers frequently do not understand this
concept and wonder why they need to see someone's home station
on the map 24/7/365.  Or they set their beacon rate to 1 per
hour or something.

The net cycle time is the standard for the minimum rate an
unattended station reports its participation on the net.  APRS
is a two-way network of stations sharing the local tactical
situation.  These minimum net-cycle time beacons let everyone
know what stations are on the air and participating in the net.

Back in around 2002, we added the Operator-present bit so that
we could also tell what stations had an operator present.  When
an operator is present, for example in APRSdos, the minimum
net-cycle time is upped to 10 minutes.

THen in April 2007, the proposal for OVERLAY characters for ALL
symbols was added to APRS1.2.  This allows for the operator
present "O" overlay or an alternative energy overlay to be added
to the basic station symbol.  Thus, a home station that has lost
primary power and is operating on back up power can change to
the emergency power overlay ("E") so that his status is
available to all viewers.

So, given that, APRS already reveals some info on power outages:
1) By the ABSENCE of stations in the affected area
   (after 30 minutes)
2) By the PRESENCE of stations with the "E" overlay...

Anyway, that is something to think about.... In fact, we
probablly need to better define what "E" means.  Originally, I
was thinking it would mean that the station is "capable" or
emergency power so that we know in advance what capabilies
exist.  Maybe we need another symbol that means "running on E
power because the Mains are OUT!"...

> lat/long with X KM radius or only presenting 
> a new object if a certain number of 
> customers are affected),

Translating power outages to area objects would then be done by
a human with the ability to draw a shape object and be there to
update it as the outage geometry changes...

> ... but would like to get a sense for what is
> considered 'excessive' in terms of a single 
> node transmitting new objects via APRS-IS 
> and APRS-VHF/1200.

Now, ignoring my proselitizing above, such an automatic object
generator could be valuable and the net cycle time is already
defined in APRS.  Make it a LOCAL packet every 10 minutes in the
affected area (1 hop), and make it a 2 hop packet once every 30

But maybe consider re-using the same object name so that as the
outage area changes and is updated, then the current symbol on
all maps is still current and the maps are not cluttered up with
all kinds of older copies.

Something like that anyway...


I'd say it is already well
> For example, is 100 objects in a single hour to spammy?  
> Anyone have some thoughts on this?  I am looking for 
> distinctions between APRS-IS and transmitting to RF as well.
> Thanks
> Matthew
> --
> Matthew Asham
> British Columbia Wireless Network Society
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