[aprssig] On flow control/smart beaconing...

Jim Lux jimlux at earthlink.net
Thu Mar 23 13:42:11 CST 2006

Date: Tue, 21 Mar 2006 10:56:01 -0800 (PST)
From: "Curt, WE7U" <archer at eskimo.com>
Subject: Re: [aprssig] On flow control/smart beaconing...

 >On Tue, 21 Mar 2006, Jim Lux wrote:
 > One might argue that this is an anomaly.. I'm running a 5W transmitter, and
 > the digis see hundreds of miles, and dozens of 50W transmitters,

It's not an anomaly.  Perhaps the real solution here is to optimize
these yet-to-be-invented smart digi's so that they keep xx% of the
air-space available for these stations to make it into the network.
That'd save having to create a separate input channel for the
low-power stations.

Just a few stations transmitting often can ruin it for everybody
this way though, particularly if they are running higher power or
have an antenna/height advantage over others.  The digi's would have
to attempt to rectify that situation too, but there's only so much
they can do in that instance.

I can see human nature getting in the way of this scheme though:  If
people try a few test transmissions and some of them don't get
digipeated because the digi's are throttling back to make airspace
available, these people will most likely crank up their power level
and/or reduce their interval until they get "enough" packets

Perhaps what's needed is active management of the end nodes by the digis, 
much as the cellular system does.  One could do active acknowledgement..
When a digi successfully receives a packet from the tracker, it 
acknowledges it, so the tracker knows that it got in, and doesn't need to 
keep blindly transmitting.    In fact, the digi does this now, because it 
retransmits the packet, and if the tracker hears its own packet repeated, 
it should then use a longer interval until it bursts forth again.

One could also implement some form of power management/rate management 
feature where the digi could send explicit cues to the trackers about 
"preferred rates" (much as cellular systems tell the handset to reduce 
power if the receieved signal strength at the cell site is high).  A lot of 
the newer radios have the ability to change Tx power over their control 
interface, so a mobile that can run at 50W could ramp back, if it heard 
from the digi that it as 20overS9.

This could either be explicitly managed by the digi (or, even, a 
centralized network controller, where there are multiple linked digis) OR 
more passively managed if the digi added something to the packet when it 
retransmits indicating the received signal power, then the mobile could, in 
addition to knowing that its packet was received, could also manage its Tx 
power (which would help with battery life, too!)

Right now, this sort of network management function is done in an adhoc, 
very slow  response time (days) sort of way (someone uses long packets, 
very frequently, at high power, and gets chiding emails about being a pig, 
so they scale back, etc.)


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