OPS.TXT APRS OPERATIONS NOTES Document version: 8.6.7 1 Dec 2003 Previous was 8.3.4 of 7 Mar 99 Author(s): Bob Bruninga, WB4APR ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FOR a general APRS overview see APRS.txt. FOR MOBILE Operations, see MOBILE.txt For operations with ALiases or MARS see ALIASES.TXT or MARS.TXT FOR HF Operations, see HF.txt FOR an APRS command summary see HELP.txt FOR multi-PC operations on a piece of ZIP cord, see ZIP-LAN.txt OVERVIEW: This OPERATIONS file may help you to understand the finer points of operating an APRS net both ROUTINE and SPECIAL EVENT. Since APRS was designed to facilitate real-time tactical communications, operating APRS on a routine basis is sometimes like watching the grass grow! The reason for building a routine APRS net is primarily for operator training and familiarity. If your operators are not familiar with APRS in a benign environment, then they will not be able to use it under stress! Although APRS is desiged for local real-time operations under stress, it does extend worldwide via the IGate system. Using APRS on-line lets you see any of the 30 thousand or so other stations. On RF, although you only see your local RF area, you can still keyboard with anyone on the globe because of teh automatic linking of the IGates. And if you are in message QSO with a distant station, the local IGate will send you a courtesy position report of the distant station. Again, the worldwide aspect of APRS is only there to give you something to practice with. This is not the design objective. SImilarly, GPS is a powerful tool linked to APRS. But, do not think that you need GPS for tracking special events. It is so easy to update your vehicle's position just by moving the cursor on your map and hitting the INPUT-MY command, that the only stations that need GPS are the ones that are lost! Use APRSmax for routine FIXED station operations to see more stations. Use APRSdos when all commands are needed and fewer stations are needed. DIGIPEATER RULES: APRS typically uses a fixed general path such as WIDE2-2 to cover a large local area with redundancy and repetition to assure that all stations can see everything. But this is not efficient for point to point messages because it floods packets everywhere. For messages it is best to CHOOSE a SPECIFIC PATH TO THAT ONE STATION. Your messages will go faster and will be less QRM to others. Watch the DIGI page, and if you can work him direct, DO SO! DIGIPEATERS AND MOBILES: The greatest advantage of APRS is in the use of generic alias digipeater paths so that mobiles do not have to change their paths as they move from area to area. In the 7 high density areas in the USA, WIDE2-2 is recommended to cut congestion. WIDE3-3 should only be used far away from these metro areas. FILL-IN DIGIS: Occassionally, a mobile needs some help getting out of an area and so he can use the path of WIDE1-1,WIDE2-1 to digipeat via a local home station set to WIDE1-1. ANy TNC can serve as a WIDE1-1 digi. See PATHS.TXT and DIGIs.txt. FIXED stations should NOT use WIDE1-1 to avoid QRM. See DIGIS.TXT and PATHS.TXT. THE NEW-N PARADIGM: A great effort was made starting in 2004 to get rid of old legacy paths of RELAY, WIDE and TRACE. Now only WIDEn-N is supported since it is much more efficient at eliminating dupes. It is important to keep digipeaters well separated to minimize duplicate repeats. ALTERNATE PATHS: In APRSdos prior to version 860, you could store up to 12 different, frequently used DIGI paths using the OPS-DIGI command for instant recall to tailor your DIGI path for the exact calls and path for effeciency each QSO. But under the new N-N Paradigm of 2003, and use of WIDEn-N and SSn-N, multiple paths are not required. The following paths are reasonable under the circumstances shown: WIDE2-2 - Default. Good starting place to see whats out there WIDE3-3 - in rural areas WIDE1-1,WIDE2-2 - May be needed in some remote areas for mobiles. The following paths are NOT considered good practice and should not normally be used... and if you do, some Do-gooder will fuss at you... xxxx,WIDE1-1,...- Never putWIDE1-1 anywhere other than the first hop! You may key up every station in hundreds of miles! WIDEn-N,GATE - QRMs the HF net which you cannot hear! ...GATE,GATE,WIDEn-N - QRMs every APRS net in the country! HOW ACKS WORK (or dont work): Users must understand that they are responsible for setting their outgoing VIA path so that their packets hit the intended area of interest. APRS is an unconnected broadcast protocol only and each station's packets will only go via the outgoing path set up by that station. If your station receives a duplicate APRS MSG packet more than twice, it gives you a beep and an alert that your ACK's are probably not being heard by the other station and that you should check your outgoing VIA path to make sure it gets to the sender. APRS helps you determine the best path between stations using the Power- Height-Gain data in each position report that plots range contours around all stations. Of course, Height here is height above AVERAGE TERRAIN, not above sealevel or tower height! If you do not understand the difference, ASK! See DIGIs.txt for the format. CAUTIONS ABOUT APRS MESSAGES: Remember that multiple digipeater hops has long been condemned in the packet community because the probability of success for CONNECTED packets goes down drastically because all ACKS must be successfully returned or packets get re-tried over and over. This is generally NOT a problem with APRS operations which use UI frames without acks. HOWEVER, APRS one-line MSGS are ACKED, and the inefficiency of multi-hops DOES APPLY! If you do a lot of one-line messages between operators, you will experience the same hopeless probabilities of success as with conventional packet. But, in general, NEVER expect an APRS MSG to be successful beyond 2 digi's except if everyone else is off the air! Operator messages are a secondary function of APRS, and should not be used as a primary means of passing traffic! One further caution, since APRS suspends all packet processing while waiting for the operator with a BOXED prompt, never linger in a prompt. The SEND command is a BOXED prompt and should not be left un-completed! ACKS THAT DONT MAKE IT: Just like connected packet, the chance of a message packet getting through is usually the same as the chance that the ACK will get back. If the radio path is only 50%, that means that the receiver will probably get the message by the second transmission, but that the sender may not get an ACK until after his 4th! This is because the sender had to send 4 packets to get two through and the receiver then ACKed twice in order to get one through. You see this effect frequently on APRS, when you are talking with a station over a long poor path. You will notice that the person at the other end has already responded to your message even before you get an ack from your outgoing message. BUT your next line will never go out UNTIL it gets that ACK. The reason that you will probably get his response message before your ack, is because his response message is being repeated over and over in the usual APRS decayed algorithm, but his ACK is ONLY transmitted once each time he gets a dupe of your message line to him. What this means is that whenever it is obvious that the other station has responded to your message line, you should ERASE it so that APRS will move on to the next line. Sometimes if you know that the other station is probably hearing the digi better than the digi is hearing him, and you are not getting ACKS, then simply send him messages in the blind. Let each line will be transmitted for 6 minutes and then you can erase it. APRS will then move on to the next line. Remember that APRS will have transmitted 6 times in the first 6 minutes, but that it will then be over 3 minutes, then 6 and then 12 minutes for further transmissions. To improve on this effect of lost ACK responses, APRSdos recognizes a duplicate message, and not only sends out the usual ACK, but stores a copy for transmisssion in the blind 30 seconds later. The 30 second delay is to avoid cluttering up the frequency if the path is good, since the sending station will have sent the message at least twice in the first 30 seconds. After the third transmission, it is clear that the ACKs are getting lost and it is time to double up. This algorithm has the potential of doubling throughput on a poor channel! REPLY ACK: In the year 2000 time frame, APRS added embedded ACKS in reply messages so that for only 2 more bytes in a message in a dialog between 2 users, an extra ACK gets a free ride. This vastly improves the reliability of ACKS in a dialog. Only APRSdos and a few other versions have implemented this, but between those stations, combined with the APRSdos decaying retry algorithm results in an ORDER OF MAGNITUDE faster message dialog than other client software that does not use these two fundamental communications techniques. SHORT MESSAGES: Especially on HF, the shorter the packet the better. With 25 characters of overhead, however, there is not much sense in making the message part much shorter than a half line (40 characters). A trick that I frequently use whenever I know that a station is not currently on the air, or the path is not currently good, is to send the first message line with only the word "test" followed by additional lines with the body of the message. This way, only the very short "test" line is transmitted (often for hours on HF) until the band opens, and then once the station ACKs that line, the remaining lines are transmitted. BULLETINS: Bulletins are sent to the callsign of BLN# where # is a line number from 1 to 9. Like any other message, these BULLETIN lines will be transmitted on the decaying time period and will soon fade out of the system. If you want the bulletin to remain at about a 15 minute rate, then instead of using numerals in the BLN# mesage, use a LETTER. This way, new stations joining the net will quickly pick up the BULLETINS. Since lines are sorted onto the receiver's BULLETIN page, a new BLNx line will overwrite any previous BLNx at all stations making changes and corrections easy. If your bulletin is time sensitive, be sure to include the TIME in the text, since BULLETINS are not time- stamped. When your BULLETIN is no longer needed, simply ERASE your outgoing BLN#. This will stop your transmission of the BULLETIN lines. Receiving stations can erase all old bulletins by using the ALT-E command. GATEWAY RULES: It is very important that users understand that HF GATEWAYS ARE ONLY INTENDED TO LINK HF ACTIVITY INTO LOCAL VHF NETS. NOT THE REVERSE! IT IS INNEFFICIENT, DISCOURTEOUS, AND MAYBE ILLEGAL TO LINK from VHF to HF. Linking HF into every local VHF APRS net in the country is not a problem, because the slow 300 baud data rate could never saturate ANY 1200 baud local net. HOWEVER, linking just ONE active VHF net ANYWHERE in the country out onto HF WOULD CERTAINLY BLOCK ALL HF OPERATIONS NATIONWIDE! DO NOT ABUSE IT, OR WE WILL LOOSE IT! See HF.txt. GATE SUMMARY: On HF, use the path of GATE,WIDE2-1 and everyone in the country within one hop of a GATE will likely see you. *Never* use GATE,WIDE2-2 or greater because your packets will now go 2 or more hops on VHF and be seen MULTIPLE times from multiple gates! No one can tell where the GATE is and it is just a BIG MESS. Believe me! Second, never routinely go through a GATE on VHF to HF. USING THE OPS-COMM-TNC dumb terminal mode. Learn to use your TNC in conventional connected mode and use that mode for point-toppoint messaging and files and on a different frequency. OBJECTS: Anyone may place an object on the map for all to see and on the P-List the packet is marked with the last three letters of the originating station. Any other station that has more current information on that object can also update its position by SELECTing, moving the cursor, and then hitting the insert key. His station will begin uplinking the new posit, and all stations, will update their P-list entry for that object INCLUDING THE ORIGINAL UPLINK STATION! Since the new position overwrites the old one, the original originating station will now no longer uplink it. Thus we are not dependent on the original station for future updates. Old objects no longer being uplinked by anyone will fade to dark gray after 80 minutes to show they are old. Use the CONTROLS-FADE command to bring them back to bright colors, or use the J command to see JUST- the-LATEST symbols. The KILL function permits the originator of an OBJECT KILL it from all displays on the net. His station will continue to uplink the object, but tagged with a special KILL flag to suppress its display on all screens. It remains in everyone's P-lists, though, so they can refer back to it if needed. They must still manually DELete it from their P-list as needed. Once the originator has KILLED an object, he should let it remain on his P-list for at least 6 minutes to be sure everyone has received the KILL indicator; then he can delete it from his list. NEAT OPERATOR FEATURES: CONTROLS MENU: Set filters and how you want packets displayed. MAPS: Turn on or off map features plus overlay data files on the maps such as DIGIS, Radio Shacks, etc RADAR ALARMS: Use INPUT-MY-RADAR to set your"airspace". POSIT ALARMS: Set ALARMS on any mobile which will alarm if he moves. WX ALARMS: Set Weather alarms on temps, winds or rain... TRACK MODE: Lock on to one station and keep map centered SPECIAL MARKS: Mark any station on the P-LIST for SPECIAL highlighting Then you can see only those stations with JUST-S SPECIAL EVENT OPERATIONS: The alt-SETUP-MODES-SPECIAL command sets up an APRS station to send TO the UNPROTO address of SPCL... and to ignore all other packets NOT addressed to SPCL. This allows the event participants to keep their screens and lists clear of unwanted data while tracking the event normally. But all other stations watching the event will still receive all SPCL event packets normally. But they will also be marked with the # for special display using the JUST-SPECIAL command or SPACE bar. SYMBOLS: APRS now permits HUNDREDS of different mobile symbols by using the NUMERIC OVERLAY capability. This makes it easy to distinguish mobiles even with CALLSIGNS-OFF to reduce clutter! EMISSION CONTROL: Observers of an event can set their transmitter off using the CONTROLS-X command to minimize QRM on channel. They can still transmit under manual control by using the X key. LOAD SHARING: Since any station can take over reporting of any objects, one approach is to let only one station SELECT every symbol that comes in and then he becomes the reporting repsonsibility. The original station that uplinked the report in the first place will fall silent when it sees the report comming from the designated Net Control station. This way all positions are reported by only one station on frequency, although all other stations can still update the positions as needed. Remember that the last station to report the position of an object will be the one that continues to report it! APRSdos has a NET-CONTROL feature for OBJECTS that automates this process. MARINE CORPS MARATHON: See MARATHON.txt for the lessons learned. ZIP_LAN MODE AND EMERGENCY OPERATIONS CENTERS: Dont overlook, that a handful of separate PC computers can ALL BE CONNECTED TO A SINGLE TNC AND RADIO! The ZIP-LAN can be used to create quite an impressive multi-station tactcal communications system that will rival some 911 consoles! No special LAN hardware is required other than a serial port and as much two conductor zip cord as you need. See ZIP-LAN.txt This ZIP-LAN capability is not backwards compatible to any software prior to APRS800, Mac/Win prior to 2.09 and APRSa4 ver 0408. With a ZIP-LAN, ALL consoles see the tactical picture, and these PC's are at the individual operator's disposal to zoom in, and hop from screen to screen to give them access to what ever info they need! Do not think that a big screen display is better. A single big screen is impressive, but actually useless. Only the person at the KEYBOARD of an APRS system can actually get useful info from APRS. In our county, you need to be below the 8 mile scale to get an idea of what is going on at a crisis, and while you are zoomed in there, others need to be focusing on other parts of the county, or different screens. You can wire every PC in the building using cheap 2 conductor speaker ZIP cord! You can carry hundreds of feet of this stuff in your briefcase with your portable laptop! This is a TREMENDOUS capability, since these days PC's are much more plentiful than TNC's and all available assets can be brought into the picture. Every SLAVE operator has his own INDEPENDENT access to all of the APRS info without bothering the APRS operator. See ZIP-LAN.TXT de WB4APR, Bob