View source for Automatic Packet Reporting System

{{Short description|Amateur radio telemetry forwarding protocol}}

[[File:Byonics AIO.jpg|thumb|right|200px|APRS beacon transmitter with GPS receiver.]]

'''Automatic Packet Reporting System''' ('''APRS''') is an [[amateur radio]]-based system for real time digital communications of information of immediate value in the local area.<ref>{{cite web|url=ftp://ftp.tapr.org/aprssig/aprsspec/spec/aprs101/APRS101.pdf|date=August 29, 2000|editor=Ian Wade|title=APRS Protocol Reference|publisher=[[Tucson Amateur Packet Radio]]|archive-url=https://web.archive.org/web/20210227223020/ftp://ftp.tapr.org/aprssig/aprsspec/spec/aprs101/APRS101.pdf|archive-date=2021-02-27|url-status=dead|access-date=May 19, 2012}}</ref>  Data can include object [[Global Positioning System]] (GPS) [[Coordinates (geographic)|coordinates]], [[non-directional beacon]], [[weather station]] telemetry, text messages, announcements, queries, and other [[telemetry]]. APRS data can be displayed on a map, which can show stations, objects, tracks of moving objects, weather stations, search and rescue data, and direction finding data.

APRS data is typically transmitted on a single shared frequency (depending on country) to be repeated locally by area relay stations (digipeaters) for widespread local consumption. In addition, all such data are typically ingested into the APRS Internet System (APRS-IS) via an Internet-connected receiver (IGate) and distributed globally for ubiquitous and immediate access.<ref>{{Cite web|url=http://www.aprs-is.net/Specification.aspx|title=APRS-IS Specifications|website=Aprs-is.net|access-date=2016-10-02}}</ref>  Data shared via radio or Internet are collected by all users and can be combined with external map data to build a shared live view.

APRS was developed from the late 1980s forward by Bob Bruninga, [[call sign]] WB4APR, a senior research engineer at the [[United States Naval Academy]]. He maintained the main APRS Web site until his death in 2022.<ref>{{cite web|url=https://twitter.com/Pat_Kilroy/status/1491204945030565888|title=SAD NEWS Bob Bruninga, WB4APR, SK: Bob's daughter said he passed away peacefully yesterday following a two-year struggle with cancer, and Covid to top it off.|website=Twitter.com|access-date=2022-02-14}}</ref><ref>{{Cite web|url=https://annapolisfriends.org/celebration-of-the-life-of-bob-bruninga/|title=Celebration of the Life of Bob Bruninga - Annapolis Friends Meeting|date=July 16, 2022}}</ref> The [[initialism]] "APRS" was derived from his call sign.

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==History==
Bob Bruninga, a senior research engineer at the United States Naval Academy, implemented the earliest ancestor of APRS on an [[Apple II]] computer in 1982.<ref>{{Cite web|url=http://www.arrl.org/news/aprs-developer-bob-bruninga-wb4apr-sk |title=APRS Developer Bob Bruninga, WB4APR, SK|website=Arrl.org |access-date=2022-02-11 }}</ref> This early version was used to map [[high frequency]] Navy position reports. The first use of APRS was in 1984, when Bruninga developed a more advanced version on a [[VIC-20]] for reporting the position and status of horses in a {{convert|100|mi|km|adj=on}} endurance run.<ref>{{Cite web|url=http://www.aprs.org/APRS-docs/ARTICLES.TXT|title=APRS history|last=Bruninga|first=Bob|website=Aprs.org|access-date=October 2, 2016}}</ref>

During the next two years, Bruninga continued to develop the system, which he then called the Connectionless Emergency Traffic System (CETS). Following a series of [[Federal Emergency Management Agency]] (FEMA) exercises using CETS, the system was ported to the [[IBM Personal Computer]]. During the early 1990s, CETS (then known as the Automatic Position Reporting System) continued to evolve into its current form.

As GPS technology became more widely available, "Position" was replaced with "Packet" to better describe the more generic capabilities of the system and to emphasize its uses beyond mere position reporting.

Bruninga has also stated that APRS was not meant to be a vehicle position tracking system, and can be interpreted rather as "Automatic Presence Reporting System".<ref>{{cite web |title=2011 DCC - Sunday Seminar Part 1 - WB4APR and APRS |url=http://www.youtube.com/watch?v=TfArEGYgw6I&t=11m0s |website=Youtube |access-date=13 April 2020 |date=2011}}</ref>

==Network overview{{anchor | Network Overview}}==
APRS (Automatic Packet Reporting System), is a digital communications protocol for exchanging information among a large number of stations covering a large (local) area, often referred to as "[[Internet Protocol|IP]]-ers". As a multi-user data network, it is quite different from conventional [[packet radio]]. Rather than using connected data streams where stations connect to each other and packets are acknowledged and retransmitted if lost, APRS operates entirely in an unconnected broadcast fashion, using unnumbered [[AX.25]] frames.<ref name="ARRL2006">{{cite book|title=The ARRL handbook for radio communications|year=2006|pages=9.22|isbn=978-0-87259-948-2|editor=R. Dean Straw |location=Newington, CT |publisher=American Radio Relay League}}</ref>

APRS packets are transmitted for all other stations to hear and use. Packet [[repeater]]s, called digipeaters, form the backbone of the APRS system, and use [[store and forward]] technology to retransmit packets. All stations operate on the same radio channel, and packets move through the network from digipeater to digipeater, propagating outward from their point of origin. All stations within radio range of each digipeater receive the packet. At each digipeater, the packet path is changed. The packet will be repeated through only a certain number of digipeaters&nbsp;— or hops&nbsp;— depending upon the all-important "PATH" setting.

Digipeaters keep track of the packets they forward for a period of time, thus preventing duplicate packets from being retransmitted. This keeps packets from circulating in endless loops inside the ad hoc network. Eventually, most packets are heard by an APRS Internet Gateway, called an IGate, and the packets are routed on to the Internet APRS backbone (where duplicate packets heard by other IGates are discarded) for display or analysis by other users connected to an APRS-IS server, or on a Website designed for the purpose.

While it would seem that using unconnected and unnumbered packets without acknowledgment and retransmission on a shared and sometimes congested channel would result in poor reliability due to a packet being lost, this is not the case, because the packets are transmitted (broadcast) to everyone and multiplied many times over by each digipeater. This means that all digipeaters and stations in range get a copy, and then proceed to broadcast it to all other digipeaters and stations within their range. The result is that packets are multiplied more than they are lost. Therefore, packets can sometimes be heard some distance from the originating station. Packets can be digitally repeated tens or even hundreds of kilometers, depending on the height and range of the digipeaters in the area.

When a packet is transmitted, it is duplicated many times as it radiates out, taking all available paths simultaneously, until the number of "hops" allowed by the path setting is consumed.

==Positions/objects/items==
[[File:Xastir-screenshot.png|thumb|right|200px|Screenshot of an APRS display in XASTIR, an APRS software system for Linux/Unix. Station positions, objects and items are displayed on a map overlaying counties around New York City. Raw APRS messages are displayed in the terminal window on the lower right.]]

APRS contains a number of packet types, including position/object/item, status, messages, queries, weather reports and telemetry. The position/object/item packets contain the latitude and longitude, and a symbol to be displayed on the map, and have many optional fields for altitude, course, speed, [[Effective radiated power|radiated power]], [[antenna height above average terrain]], [[antenna gain]], and voice operating frequency. Positions of fixed stations are configured in the APRS software. Moving stations (portable or mobile) automatically derive their position information from a GPS receiver connected to the APRS equipment.<ref name="ARRL2006"/>

The map display uses these fields to plot communication range of all participants and facilitate the ability to contact users during both routine and [[Amateur radio emergency communications|emergency situations]]. Each position/object/item packet can use any of several hundred different symbols. Position/objects/items can also contain weather information or can be any number of dozens of standardised weather symbols. Each symbol on an APRS map can display many attributes, discriminated either by colour or other technique. These attributes are:

* Moving or fixed
* [[Dead reckoning|Dead-reckoned]] or old
* Message capable or not
* Station, object or item
* Own object or other station object/item
* Emergency, priority, or special

==Status/messages==
The Status packet is free-field format that lets each station announce its current mission or application or contact information or any other information or data of immediate use to surrounding activities. The message packet can be used for point-to-point messages, bulletins, announcements or even email. Bulletins and Announcements are treated specially and displayed on a single "community Bulletin board". This community bulletin board is fixed size and all bulletins from all posters are sorted onto this display. The intent of this display is to be consistent and identical for all viewers so that all participants are seeing the same information at the same time. Since lines are sorted onto the display, then individual posters can edit, update, or delete individual lines of their bulletins at any time to keep the bulletin board up-to-date to all viewers.

All APRS messages are delivered live in real-time to online recipients. Messages are not stored and forwarded, but retried until timed out. The delivery of these messages is global, since the APRS-IS distributes all packets to all other IGates in the world and those that are messages will actually go back to RF via any IGate that is near the intended recipient.

=== Email ===
A special case message can be sent to EMAIL where these messages are pulled off the real-time APRS-IS and wrapped into a standard email message type, and forwarded into regular Internet email. This was done by the WU2Z email engine until 2019 , when it was replaced by the javAPRSSrvr [[Message transfer agent|email gateway]].<ref>{{Cite web|title=Email Services|url=http://www.aprs-is.net/Email.aspx|website=Aprs-is.net|access-date=2020-05-24}}</ref>

==Capabilities==
In its simplest implementation, APRS is used to transmit real-time data, information and reports of the exact location of a person or object via a data signal sent over amateur radio frequencies. In addition to real-time position reporting capabilities using attached GPS receivers, APRS is also capable of transmitting a wide variety of data, including [[weather]] reports, short text messages, [[Direction finding|radio direction finding]] bearings, [[telemetry]] data, short e-mail messages (send only) and storm forecasts. Once transmitted, these reports can be combined with a computer and mapping software to show the transmitted data superimposed with great precision upon a map display.

While the map plotting is the most visible feature of APRS, the text messaging capabilities and local information distribution capabilities, combined with the robust network, should not be overlooked; the New Jersey Office of Emergency Management has an extensive network of APRS stations to allow text messaging between all of the county Emergency Operating Centers in the event of the failure of conventional communications.

==Technical information{{anchor | Technical Information}}==
{{Listen
|filename=AFSK 1200 baud.ogg
|title=1200 baud APRS signal
|description=Example of a 1,200-baud AFSK modulated APRS signal.
|format=[[Ogg]]}}

In its most widely used form, APRS is transported over the [[AX.25]] protocol using 1,200-bit/s [[Bell 202 modem|Bell 202]] [[Frequency-shift keying|AFSK]] on [[frequency|frequencies]] located within the [[2-meter band|2-meter amateur band]].

;Sample APRS VHF frequencies
* 144.39&nbsp;MHz&nbsp;: [[North America]], [[Argentina]], [[Colombia]], [[Chile]], [[Indonesia]], [[Malaysia]], [[Singapore]], [[Thailand]]
* 144.575&nbsp;MHz&nbsp;: [[New Zealand]]<ref>{{Cite web |url=http://www.nzart.org.nz/maps/2010/d1-ni.pdf |title=Archived copy |access-date=2010-09-17 |archive-date=2010-09-26 |archive-url=https://web.archive.org/web/20100926014321/http://nzart.org.nz/maps/2010/d1-ni.pdf }}</ref><ref>{{Cite web |url=http://www.nzart.org.nz/maps/2010/d1-si.pdf |title=Archived copy |access-date=2010-09-17 |archive-date=2010-09-26 |archive-url=https://web.archive.org/web/20100926033414/http://nzart.org.nz/maps/2010/d1-si.pdf }}</ref>
* 144.64&nbsp;MHz&nbsp;: [[China]],<ref>{{Cite web |url=https://www.iaru.org/wp-content/uploads/2020/01/R3-004-IARU-Region-3-Bandplan-rev.2.pdf |title=IARU Region 3 Interim Band Plan |access-date= }}</ref> [[Taiwan]]
* 144.66&nbsp;MHz&nbsp;: [[Japan]]
* 144.8&nbsp;MHz&nbsp;: [[South Africa]], [[Europe]],<ref>{{Cite web|url=http://dididahdahdidit.com/eurofreq.php|title=APRS Frequencies World-Wide|website=Dididahdahdidit.com|access-date=14 February 2022}}</ref> [[Russia]]
* 144.93&nbsp;MHz&nbsp;: [[Uruguay]], [[Panama]]
* 145.175&nbsp;MHz&nbsp;: [[Australia]]
* 145.57&nbsp;MHz&nbsp;: [[Brazil]]
* 145.825&nbsp;MHz&nbsp;: [[International Space Station]]<ref>{{cite web |url=http://www.ariss.org/current-status-of-iss-stations.html |title=Current Status of ISS Stations |author=<!--Not stated--> |date=April 17, 2017 |website=Amateur Radio on the International Space Station (ARISS) |access-date=November 16, 2017 }}</ref> and other satellites
<!-- (Not VHF frequencies) * 430.5125&nbsp;MHz&nbsp;: [[Netherlands]] (UHF) (Phased out due to transition to 432.5&nbsp;MHz.)
* 432.5&nbsp;MHz &nbsp;: Europe (UHF)<ref>{{Cite web|url=https://www.iaru-r1.org/index.php/spectrum-and-band-plans/uhf/70-centimeter|title=430-440 MHz - International Amateur Radio Union - Region 1|website=Iaru-r1.org|language=en-gb|access-date=2018-10-19}}</ref>
-->

An extensive digital repeater, or "digipeater" network provides transport for APRS packets on these frequencies. [[Internet]] gateway stations (IGates) connect the on-air APRS network to the APRS Internet System (APRS-IS), which serves as a worldwide, high-bandwidth backbone for APRS data. Stations can tap into this stream directly, and a number of databases connected to the APRS-IS allow Web-based access to the data as well as more advanced data-mining capabilities. A number of [[Low Earth orbit|low-Earth orbiting]] [[satellite]]s, including the [[International Space Station]], are capable of relaying APRS data.

==Equipment settings{{anchor | Equipment Settings}}==
An APRS infrastructure comprises a variety of [[Terminal node controller|Terminal Node Controller]] (TNC) equipment put in place by individual amateur radio operators. This includes sound cards interfacing a radio to a computer, simple TNCs, and "smart" TNCs. The "smart" TNCs are capable of determining what has already happened with the packet and can prevent redundant packet repeating within the network.

Reporting stations use a method of routing called a "path" to broadcast the information through a network. In a typical packet network, a station would use a path of known stations such as "via n8xxx,n8ary."  This causes the packet to be repeated through the two stations before it stops. In APRS, generic call signs are assigned to repeater stations to allow a more automatic operation.

===Recommended path===
Throughout North America (and in many other regions) the recommended path for mobiles or portable stations is now WIDE1-1,WIDE2-1.<ref>{{Cite web|url=http://aprs.org/fix14439.html|title=FIXING DIGIPEATERS|website=Aprs.org|access-date=14 February 2022}}</ref> Fixed Stations (homes, etc.) should not normally use a path routing if they do not need to be digitally repeated outside of their local area, otherwise a path of WIDE2-2 or less should be used as requirements dictate. The path parameter{{clarify |reason=which one?|date=August 2017}} reflects the routing of packets via the radio component of APRS, and fixed stations should carefully consider their choice of path routing. Any path selection for stations that do not require it contributes to congestion of the APRS frequency and may hinder other stations' reporting. Aircraft and balloon APRS stations should avoid beaconing with any path at altitude since digipeating may not be necessary due to their antenna height and likelihood of reaching multiple wide-ranging digipeaters and IGates. Mobile stations in congested areas or more populated areas may consider using only 1 hop (WIDE1-1), as there are usually enough Internet gateways nearby that no path routing is needed. One solution to the path selection is proportional pathing<ref>{{cite web|url=http://www.aprs.org/newN/ProportionalPathing.txt|format=TXT|title=Proportional Pathing and Decayed Beaconing |website=Aprs.org|access-date=2022-02-14}}</ref> if the user's equipment is capable.

===Old path===
Early on, the widely accepted method of configuring stations was to enable the short-range stations to repeat packets requesting a path of "RELAY" and long-range stations were configured to repeat both "RELAY" and "WIDE" packets. This was accomplished by setting the station's MYALIAS setting to RELAY or WIDE as needed. This resulted in a path of RELAY,WIDE for reporting stations. However, there was no duplicate packet checking or alias substitution. This sometimes caused beacons to "ping pong" back and forth instead of propagating outwards from the source. This caused much interference. With no alias substitution, one could not tell which digipeaters a beacon had used.

===New path===
With the advent of the new "smart" TNCs, the stations that used to be "WIDE" became "WIDEn-N." This means a packet with a path of WIDE2-2 would be repeated through the first station as WIDE2-2, but the path will be modified (decremented) to WIDE2-1 for the next station to repeat. The packet stops being repeated when the "-N" portion of the path reaches "-0." This new protocol has caused the old RELAY and WIDE paths to become obsolete. Digi operators are being asked to re-configure fill-in "RELAY" stations to instead respond to WIDE1-1. This results in a new, more efficient path of WIDE1-1,WIDE2-1.

===Amateur Radio High Altitude Balloons===

Testing radio range is often a large component of these hobbies. Amateur radio is often used with packet radio to communicate at 1200 baud, using the Automatic Packet Reporting System back to the ground station. Smaller packages called micro or pico trackers are also built and run under smaller balloons. These smaller trackers have used Morse code, Field Hell, and RTTY to transmit their locations and other data.<ref>url=https://arawr.ca/?page=payloadtitle=|date=26 April 2024</ref>

==Related systems==
The APRS protocol has been adapted and extended to support projects not directly related to its original purpose. The most notable of these are the FireNet and PropNET projects.

* '''APRS FireNet''' is an Internet-based system using the APRS protocol and much of the same client software to provide fire fighting, earthquake, and weather information in much higher volume and detail than the traditional APRS system is capable of carrying.
* '''PropNET''' uses the APRS protocol over AX.25 and [[PSK31]] to study radio frequency propagation. PropNET "probes" transmit position reports, along with information on transmitter power, elevation, and antenna gain, at various frequencies to allow monitoring stations to detect changes in propagation conditions.<ref>{{Cite web|url=http://www.propnet.org/|title=The PropNET Project|website=Propnet.org|access-date=14 February 2022}}</ref> It is based on ACDS, a special client program running under Microsoft Windows.

==See also==
<!-- Please respect alphabetical order -->
* [[APRS Calling]]
* [https://github.com/wb2osz/aprsspec APRS Documentation Project - includes latest protocol specification]
* [[Automatic identification system]]—position reporting system used for marine traffic
* [[Spartan Packet Radio Experiment]]—an experiment intended to test the tracking of satellites via amateur packet radio, flown on [[Space Shuttle]] mission [[STS-72]].
* [[Traffic collision avoidance system]] (TCAS)

==References==
{{Reflist}}

==Further reading==
*{{Cite book|author=Stan Horzepa |title=APRS Tracks, Maps and Mobiles|publisher=[[American Radio Relay League ]]|year=1999|isbn=978-0-87259-774-7}}

==External links==
* [http://www.aprs.org/ www.aprs.org]&nbsp;— Automatic Packet Reporting System site
* [http://www.findu.com findU] is a database archiving weather, position, telemetry, and message data.
* [http://aprs.fi/ aprs.fi]&nbsp;— OpenStreetMap map-based tracking/mapping
* [http://www.pinpointaprs.com/ www.pinpointaprs.com]&nbsp;— A free Windows based desktop APRS client with built-in mapping.
*[https://github.com/wb2osz/direwolf Dire Wolf] is a free open source software replacement for the 1980s technology TNC.

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