aprsdigi - APRS(tm) digipeaterSYNOPSIS
aprsdigi [-mDM] [-a call] [-n|s|e|w path] [-d digipath] [-f call] [-t tag] [-k secs] [-l logfile] [-i interval] [-k keep- for] [-r rxport] [-x txport]DESCRIPTION
Aprsdigi uses SOCK_PACKET facilities to act as a digi- peater for UI frames. In addition to conventional TNC-style digipeating, in which a packet is digipeated if the next non-repeated digipeater callsign matches the ax.25 port's callsign and SSID or an alias specified with the -a option, aprsdigi implements the Automatic Position Reporting System's (APRS) SSID-based and WIDE-N flooding algorithms as described in the APRS README/MIC-E.TXT document. Aprsdigi also translates "APRS MIC Encoder" compressed position and telemetry packets into conventional "MIM" packets. SSID-based routing uses a non-zero sub-station ID in the destination callsign, along with an empty digipeater path, to indicate that the APRS digipeater should repeat the packet after filling in an appropriate digipeater path. For example, a packet sent to "APRS-3" would be repeated with a modifed destination of "APRS VIA WIDE-3" (in a net- work that supports WIDE-n flooding). A packet sent to "APRS-11" would be repeated to the West unproto path, as defined with the -w option. A table of SSID values and their paths follows: SSID unproto path ---- ------------ 0 none 1 WIDE-1 2 WIDE-2 3 WIDE-3 4 WIDE-4 5 WIDE-5 6 WIDE-6 7 WIDE-7 8 NORTH UNPROTO path 9 SOUTH UNPROTO path 10 EAST UNPROTO path 11 WEST UNPROTO path 12 NORTH UNPROTO path + WIDE 13 SOUTH UNPROTO path + WIDE APRS WIDE-N (or flooding) digipeating works by repeating any received packet that has exactly one digipeater, that digipeater callsign or alias was specfied with the -f option, and the SSID is 1 or greater. The SSID is decre- mented by one, and the packet is repeated. Furthermore, recently transmitted packets are remembered for a period of time specified by the -k option and are not repeated if they are heard within that time period (default is 20 sec- onds). Unlike conventional digipeating, in which the digipeater callsign/alias is flagged as "repeated", neither SSID nor WIDE-N modes do this. The SSID mode is designed to be used as a means of allowing extremely short packets used by GPS-based mobiles operating on voice frequencies. The WIDE-N mode will eventually become a conventional WIDE path when the SSID decrements to zero and will then be flagged as repeated by the final digipeater to repeat it. The WIDE-N flooding algorithm is meant to address the com- binatorial explosion caused by the use of, for example, a "WIDE,WIDE,WIDE" path in which all two or three nearby WIDE digipeaters can hear each other and keep repeating the same packet. Using WIDE-N, a packet can be digipeated further outward throughout the APRS network while limiting unneccessary repeats. Aprsdigi also fits into a non WIDE-N network by using the same algorithm for selection of subset of digipeaters from a list supplied with the -d option as the MIC-E. That is, SSIDs of 1, 2 or 3 select that number of digipeaters from the first three digipeaters in the -d list. SSIDs of 4, 5, 6, or 7, start at the fourth digipeater in the list.OPTIONS
-a alias Add alias to the list of callsigns aprsdigi will respond to. The port's callsign is included automatically. -m Selects Paccomm-style replacement of the digi- peated alias with the station callsign (mycall). For example, if one of aprsdigi's aliases is RELAY and it receives a packet that has RELAY as the next digipeater to use, it will replace RELAY with the station callsign. This aids in tracing which stations actually repeated packets addressed to generic aliases (and also enables legal IDing in the US without having to transmit addition ID packets). Specifies the North, South, East, and West digi- peater paths for SSID routing. -d digi1 digi2 ... digi7 Specifices the omnidirectional digipeaters paths for SSID routing in a non-flooding (non WIDE-N) network. -f alias Add alias to the list of WIDE-N flooding aliases. Current practice is to specify -f WIDE as the flooding alias. -t tag Defines a message to the tagged on to the end of all SSID-mode repeated packets. Useful when operation a split frequency digipeater that is listening on a voice input frequency and trans- mitting on a digital output. The tag can iden- tify where the packet was heard. -k seconds Sets the number of seconds to remember flooded packets. Default is 20. -D Enables duplicate detection for conventional digipeating. Remembers duplicate packets for the number of seconds give by the -k option and will not repeat them more than once. This reduces conjestion caused when several WIDEs can hear each other, causing geometric duplication of packets address via "WIDE,WIDE" for example. -r port Port is the receive-only (usually voice repeater) ax.25 port as defined in the axports file. -x port Port is the transmit/receive (usually 145.79) ax.25 port as defined in the axports file.FILES
/etc/ax25/axportsSEE ALSO
call(1), listen(1), beacon(1), ax25(4), axattach(8), aprsmon(1), http://www.tapr.org/sigs.htmlAUTHORS
Alan Crosswell N2YGK (aprsdigi) Bob Bruninga WB4APR (APRS(tm))