APRS Packet Path Recommendations

Note: Bob WB4APR, the "father" of the APRS network, recently published some recommended changes of APRS packet path specifications (see Fixing The 144.39 APRS Network) that should be used by digipeaters and individual APRS users. The following is a discussion of proposed packet path changes and path settings to be used in the Rochester, Minnesota, area by Rob KCØFOW, chairman of the RARC Technical Committee.

The draft version of the APRS 1.2 Specification contains a new packet path recommendation to reduce RF traffic in congested areas.

The largest change for users of APRS in this recommendation is the elimination of the "RELAY" and "WIDE" paths. The use of these paths in areas where there are several digipeaters causes excessive duplication of the packet. The 1200 baud APRS network can only handle between 60 and 100 stations in any given local area and duplication of packets reduces that number considerably. The recommendation is that owners of APRS stations, both mobile and fixed, update their APRS stations.

The "RELAY" path was designed to link to fill-in digipeaters, low power digipeaters designed to link to the main digipeater network. Under the new plan, "RELAY" is replaced with "WIDE1-1".

The "WIDE" path was designed to be repeated by the main, or wide area, digipeater network. Under the new plan, "WIDE" is replaced by a "WIDEn-N" path like "WIDE2-1", "WIDE2-2", or "WIDE3-3", but *not* "WIDE1-1". The value for N should be 1, 2, or 3. The value for n should be 2 or 3, and equal to or larger than N.

Fixed stations in the Rochester area should use the path "WIDE2-2". This is a "2 hop" path, meaning that packets from the station will be digipeated twice, but only once by each digipeater that hears the packet. Fixed stations should transmit position and status no more than twice per hour, and weather stations should transmit the weather no more than 4 times per hour. Fixed stations should use no more power than is necessary to reach the nearest digipeater.

Mobile stations should use "WIDE1-1,WIDE2-1" or "WIDE1-1,WIDE2-2". The first is a 2 hop path and is ideal for people who spend time in metropolitan areas, Rochester included. The second is a 3 hop path and is better suited for areas where digipeaters are not so common. Mobile trackers should beacon no more than once every 2 minutes, and once every 5 minutes in APRS congested metro areas. Mobile trackers should normally run on low power, 5W or less, when in metro areas, including Rochester. In rural areas, it may be necessary to use more power to reach the nearest digipeater.

Mobile stations capable of digipeating, like laptops running UI-View or the Kenwood D700, are typically used as fill-in digipeaters to help digipeat special event trackers that might be running less than 1 watt power. The UIDIGI (D700) or Aliases (UI-View) should be set to include "WIDE1-1". For backwards compatibility, the UIDIGI or Alias of "RELAY,WIDE1-1" can be used by the mobile fill-in digipeater until all trackers are updated. The trackers should always have "WIDE1-1" as the first destination in the path.