Kantronics KPC–3 Plus User Manual page 99

Using generically named digipeaters does result in wider coverage of GPS stations, but
several inefficiencies may arise from this common practice (depending upon the
availability and names of the digipeaters).
Among the problems that may arise in this situation are that: (1) UI packets can be
repeated much more than necessary, by the same or by different digipeating stations
with the callsigns RELAY, WIDE, or TRACE clogging up the airwaves, and that (2)
several stations may re-transmit the same packet at the same time, resulting in a
combined signal that cannot be copied by other stations.
Kantronics' TNCs have a suite of UI digipeating commands that can be used to deal
with inefficiencies that can arise when a number of digipeaters are transmitting in the
same area, at the same time, using the same generic names.
Overview of UI Digipeating Commands
The following UI digipeating commands support advanced GPS (or APRS) digipeating
capabilities.
The UIDIGI command may be used to set up to four additional aliases/call signs for
―special‖ digipeating service. To-be-digipeated packets received containing one of these
aliases will be repeated (once) with the call sign (MYCALL) of the digipeater substituted
for the alias in the digipeated frame. See the example shown below and the command
description for more detail.
UIFLOOD and UITRACE are a bit more exotic. Each provides for multi-hop digipeating
with just one digipeater address per packet, thereby keeping the transmission time
short. For example, to digipeat through three TNCs supporting the UIFLOOD command,
the reporting station might set a GPS position path as follows:
LTP 1 GPS via wide3-3.
A digipeater TNC supporting ―wide‖ set by the UNIFLOOD command and hearing the
reporting station's transmission would then digi the UI location packet (assuming it had
not done so already, within a preset time), using an address of wide3-2. In turn each
similar digipeater down line would digi the reporting station's UI packet and reduce
(decrement) the ssid of the digipeater address again. A TNC using UIFLOOD has the
option of inserting MYCALL, creating two rather than one digipeater addresses in each
transmitted digi packet.
With UITRACE, each time a packet is digipeated, each TNC adds its MYCALL, thus
creating a ―trace‖ or return path. In effect, the size of the packet grows by one
digipeated address with each hop. A parameter, n, sets a delay time ―do not digipeat
within n seconds.‖ Again, see the examples below and the command descriptions for
detail.
The current setting of UIDWAIT determines whether or not a delay is added to UI
digipeat packets (those formed by UIDIGI, UIFLOOD, or UITRACE) before
transmission, once the channel is clear. If UIDWAIT is ON, the delay is determined by
slottime or persist settings.
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