DIGIS.TXT 6.0++ AUTOMATIC PACKET REPORTING SYSTEM DIGIPEATERS VER 6.0++ ADDED NEW SECTION ON "ALL"net ROMS. SEE END OF THIS FILE. To satisfy the objective of instantaneous response, APRS stations are designed to begin operating without any prior knowledge of the network. For this reason, all APRS stations are initialized with the digi alias of RELAY and to send all UI frames via the path of RELAY. With this form of generic alias callsign (RELAY) and wildcard digipeating (RELAY), a mobile, or new station on the air does not have to know anything about the network in advance, but to simply turn on his computer to be seen by adjacent nodes. After 10 minutes and his map begins to show the location of all stations and digipeaters on frequency, he can customize his outgoing Unproto path to specific digipeaters to cover his intended area without as much QRM. It is important in any APRS network to avoid using the wildcard addressing, when possible, to minimize unnecessary QRM on frequency. The DIGIPEATER LIST command lets you see what digipeater paths other stations are using and in version 5.7b, users can store up to 13 different DIGIpeater paths. Then they can select any given path that is optimum for their present application with a single key stroke. This version also added range plotting for all stations that include the new format for their transmitter power, antenna height above average terain, and gain. Users can use these plots to estimate what paths, through what stations, might be useful. Although digipeaters work poorly for AX.25 level 2 connections, they are ideal for APRS operation using UI frames only. In the Washington DC area and Chesapeake Bay area, we are establishing a network of WIDE area DIGI's on the simplex packet frequency of 145.79. This frequency is for Keyboard QSO's and all UI frame applications. Even leaving Personal mail boxes on the frequency is welcome, since mail is posted at keyboard rates and is read off-the-air by the mailbox owner without QRM. The normal CONNECTED operation of BBS's, mail forwarding, file transfers, TCP-IP and DX clusters are discouraged! WILDCARD DIGIPEATING: To make these WIDE area digipeaters respond to mobiles and new stations, all wide area digipeaters have the same alias of WIDE in addition to their normal FCC callsign. This second generic alias of WIDE adds tremendous flexibility to APRS networks by significantly extending the ranges for wildcard digipeating using well situated permanent digipeaters. These wide area Digi's are spaced several tens of miles apart so that they are not too close, but that they can hit their adjacent other WIDE digi's. Assuming WIDE area digipeaters are about 30 to 50 miles apart it is very easy to select an UNPROTO path prior to a road trip which will assure that your location packets will always get back to your home area. The following example shows a string of digipeaters along the east coast. The HAM calls of SOUTH and NORTH are used for clarity. CALL: NORTH-3 NORTH-2 NORTH-1 HOME-0 SOUTH-1 SOUTH-2 SOUTH-3 ALIAS: WIDE WIDE WIDE RELAY WIDE WIDE WIDE If the mobile is going south for the day, and will be operating in the vicinity of SOUTH-3 digipeater, the operator can preset his UNPROTO path to be via WIDE,SOUTH-2,WIDE. Notice that not only will his packets make it back to home from the area of SOUTH-3, but also from the area of SOUTH-1 since SOUTH-1 will also respond to the first WIDE in the list. Similarly, stations in the vicinity of SOUTH-3 are alerted to his movements as he leaves home, since the WIDE,SOUTH-2,WIDE specification is symetrical. If he set the UNPROTO path to SOUTH-3,SOUTH-2,SOUTH-1 in the usual manner, he would not be tracked at his home until he actually arrived at his destination. As you can see, having the flexibility to alternate the generic alias's of RELAY or WIDE with other known sites gives a good degree of flexibility without having to change the UNPROTO path while on the road. Using the three digipeater string, he can wander up to 150 miles in his planned direction and still be tracked by the XYL. If he has no idea where he is going, he can always use the path of WIDE,WIDE or even WIDE,WIDE,WIDE and go anywhere, but with greater QRM on the channel. Yes there are multiple collisions, and repeats, but the packet does get out to the third tier! DEDICATE WIDE AREA APRS DIGIPEATER SET UP To set up a WIDE area APRS digi, simply connect a TNC to a radio, and put it as high as you can get it. Set the following minimum commands: cmd: MY W3XYZ-x (the digipeater call and SSID) MYA WIDE (this makes it digipeat WIDE packets) UNPROTO APRS VIA WIDE,WIDE (so everyone sees it) B E 60 (Sets Beacon to once every 10 minutes) BT !DDMM.mmN/DDDMM.mmW#Pwr5360/WIDE...(identifying comments)... | | | | |||| |_____ makes station show up green | | | | ||||________ Omni (Direction of max gain) | | | | |||_________ Ant gain in dB | | | | ||__________ Height = log2(HAAT/10) LAT LONG | | |___________ Power = SQR(P) | |_____________ Power-Height-Gain PHG indicator |_______________ # is symbol for digipeater As you can see by the integers in the Pwr string, there are only 9 plus 0 possible values for each of these fields as follows: DIGITS 0 1 2 3 4 5 6 7 8 9 as used in the Pwr field ------------------------------------------------------------------------- POWER 0, 1, 4, 9, 16, 25, 36, 49, 64, 81 watts SQR(P) HEIGHT 10,20,40, 80,160,320,640,1280,2560,5120 feet LOG2(H/10) GAIN 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 dB DIR 0,45,90,135,180,225,270, 315, 360, . deg D/45 This offsets the range circle in the indicated direction NOTE ABOUT POWER LEVELS: There is little justification for making a WIDE area digi run any more power than an average mobile rig. The function of the WIDE digipeater is to pick up signals from mobiles and to relay those posits to fixed stations. The mobile is usually at ground level and is using an omni directional whip. If his path gets him into the digipeater, then he should be able to hear it. Home stations, however, usually run higher antennas and will easily be able to hear the digipeater. Both WIDE area APRS digipeaters that I have installed use only 1 and 5 watt radios. Running real high power just adds QRM beyond the effective range of the repeater. If you are concerned about linking to the next WIDE, forget it. If your digi can hear it, then it should be able to hit it with 10 watts! PREMPTIVE DIGIPEATING: THIS SECTION IS O.B.E By the NEW "ALL"net ROM IDEA at the end of this file.... The ultimate APRS digipeater configuration is (WAS) to have modified TNC-2 digipeater code so that any digipeater hearing a UI frame with its callsign anywhere in the UNPROTO path will pause for a reasonable time and then digipeat the packet as long as it was not previously digipeated by any stations earlier in the list. This way, to always report your movements back home, you always place digipeaters in your UNPROTO command in the reverse order of your travels. Your packets will be digipeated back to your home area as you enter each new digipeater in your direction of travel. For example, if you live in the vicinity of DIGI-1 below and routinely travel in the direction out to and including DIGI-3. DIGI-1 DIGI-2 DIGI-3 etc If we can get TAPR to modify the code, the mobile could specify the UNPROTO path of VIA DIGI-3,DIGI-2,DIGI-1 in order to be tracked anywhere all the way out to the area of DIGI-3. If only DIGI-1 hears the packet, it will pre-emptively digipeat the packet and set its digipeat flag. If DIGI-2 also hears the original packet, DIGI-2 will pause for P seconds to see if DIGI-1 repeats it. If so, it does nothing, since DIGI-1 follows it in the list. If not, after P seconds, it digipeats the packet for DIGI-1 to subsequently further digipeat in the normal manner. Similarly, DIGI-3 pauses for 2*P seconds to see if DIGI-2 digipeated the UI frame. If so, it does nothing. If not, after the 2*P seconds, it digipeats the packet. Even if the packet pauses and comparisons are not performed, (to simplify the code) the worst case is that N duplicates will arrive at the destination for all N digipeaters that simultaneously heard the original UI frame. Since these are UI frames, any pauses in the network for the comparisons suggested, are not significant. The extra code to do the pauses and comparisions only protects against duplicates when two digipeaters hear the same original packet, and might not be worth the extra code. This algorithm works perfectly well in reverse. If a mobile desires to announce his progress forward in the direction of his travel he can specify the digipeaters in the forward direction. Then using this algorithm, all of his packets will be repeated in the forward direction, no matter where he is along his route, but not in the backward direction. Until we get new UI forwarding algorithms in standard TNC's, however, the general aliases of WIDE and RELAY will do nicely. If fixed, known digipeaters are available, even with the generic alias of WIDE, it is best for fixed APRS stations to use the digipeaters unique callsign instead of alias to avoid any ambiguity. Also avoiding the wildcard addresses except when necessary, significantly reduces QRM on the channel. APRS now has a special command SETUP-WIDE that sets ones own station to the ALIAS of WIDE vice RELAY. This is so that an APRS station that is well situated, can serve as a WIDE digipeater. This special command is used to override the automatic TNC initialization routine that always sets APRS TNC's to the generic alias of RELAY. This command should be used with caution and with the understanding of all stations on the net. Too many WIDE's and too close together causes too much QRM. The command has to be used each time APRS is run, since the initialization routine will always reset your alias to RELAY. Also, if you use the Shift-F1 command, your symbol will be set as a digipeater and the word WIDE will be installed in your POSIT comment field so that your station will show up on all screens in green. This color (showing you as WIDE) will be lost, however, if you have a weather station hooked up to COM2, since it re-writes the POSIT string every few minutes. TheNET CONSIDERATIONS: I now understand that G8BPQ TheNET code for the DataEngine includes a DIGIon command that if set to 255 will permit Digipeating of UI frames only. Hopefully, other TheNET writers will include a UI frame only digipeat command. The problem, however, is that since the digipeat ALIAS is the same as the NODE alias, you cannot operate more than one NODE with the ALIAS of WIDE or it will totally screw up the NODE functions. We are asking NODES to consider permitting another ALIAS for UI frames only that is not tied to any of the node functions. Since NODES are so much smarter than digipeating, the ultimate solution is to have the NODES do all UI frame routing. The APRS station simply sends his UI frame TO APRS VIA HOME; Any NODE hearing that transmission that has knowledge of the route to HOME, will send the single packet via the NODE network (internode, level 4) to the HOME node! When it arrives at the HOME node, it is transmitted once as a UI frame. With this arrangement, a mobile only has to specify his one intended destination, no matter where he travels! DIGI/NODE COMPATIBILITY: Since the user should not have to change his digi path as he drives from one area to another, he should be able to specify a path that is compatible with both nodes and digipeaters. This is easily accomplished by assuming that the LAST field in an UNPROTO digi list is the HOME NODE and should be the ultimate destination for the UI frame through any level 4 network. Any and all preceeding fields are assumed to be DIGI's only. With this arrangement, the user could use an UNPROTO path of APRS VIA WIDE, HOME so that any generic WIDE digipeaters would repeat his position to their local area as would any WIDE NODES in the usual digi fashion. Only the node that hears the direct packet would also forward it through the network at level 4 to the HOME NODE. If only one field is included in the digipeater string, it would be interpreted as both a digi and a HOME destination without any difficulty. Digi's and NODEs would digipeat it, and nodes (hearing it direct) would forward it at level-4. It is important that NODES hearing digipeated UI frames from other digis do NOT enter the packet into the network, to eliminate duplication. Only the ones hearing the direct signal should be repsonsible for doing the level 4 routing.. EXAMPLE: A typical mobile just wanting to keep his spouse informed of his whereabouts might want to just use the UNPROTO path of APRS VIA HOME. Then his UI frames will be digipeated by the local HOME node or digi and will also be routed back to HOME by all NET-NODES along his travels. If he also wants to be seen by most HAMS in the areas of his travels, then he sets his path to APRS VIA WIDE,HOME. If he travels through a region that has both DIGIs and NODES, he might choose APRS VIA WIDE,WIDE,HOME. This way any areas with digis would digipeat via WIDE,WIDE and if he gets to an area with nodes which are aware of the path to HOME, then they will forward his packet there. Finally, since I hope to build a regional area Tracking network, the node should also permit the SYSOP to turn off other level 4 routing if he wants to make a dedicated network of APRS nodes just for tracking. Such a network would be swamped if all of the BBS and other CONNECTED protocol users began to use it, and the original purpose of the network would be defeated. Still, most of these APRS support ideas could be included in all NODES so that a minimum of APRS tracking could be supported by ALL networks on all frequencies, especially where there is not yet a dedicated APRS TRACKING NETWORK. I think there are other undeveloped applications for shipping UI frames through ALL networks which have not yet been explored. The capability should be there, in any case, so that experimentation can proceed. Time will tell. These few paragraphs were primarily written to the NODE CODE writers such as John G8BPQ and Mr. Roberts of X1-J. But are included here in general distribution for all to read. SEE README.HF for setting up your UNPROTO path for HF and HF/VHF gateways.. ___________________________________________________________________________ *********** ALL-WIDE ROM ONE-TIME GENERIC DIGIPEAT! **************** This may be the simplest mechanism for making an order of magnitude improvement in APRS status and position reporting networks. I am calling it the WIDE-N ROM, since it could be made into a TAPR-2 compatible ROM for use in any TAPR-2 compatible TNC. In a WIDE-N network, each WIDE digi simply repeats ANY packet with the VIA address of WIDE-N; but ONLY ONCE. If it keeps a copy of the last 30 seconds of packets, and compares each new packet that it hears with the LAST one that it digipeated, then it could decide NOT TO TRANSMIT it again! This would completely eliminate the multiple round- robin multiplication of packets generated when a mobile station uses the generic path of WIDE,WIDE,WIDE. As it is now, such a 3 tier path launched in the middle of 3 WIDE digipeaters that all hear each other can generate as many as 3x3x3 or 27 duplicates in the area. If each WIDE-N only digipeated the packet once, then there would only be 3 local copies generated, but the packet would still propogate outward three levels in the usual manner! To make this work, there are two considerations. BONCE-LIMIT: Using the via path of WIDE-N, each DIGI that repeats the packet decrements the WIDE-SSID by one. This way, each packet carries along with it information on how many times it has bounced through the network. The user specifies how far it goes, by the initial setting of the SSID! If he sets it to WIDE-15, then the packet could be digipeated as many as 15 times outward. If he is doing a local test, or event, and wants to limit DX QRM, he simply sets his path to WIDE-1, and it only gets digipeated ONCE. AGE-LIMIT: The WIDE-N digi has to keep a copy of all digipeated packets for a brief period for comparison with new packets heard. This is the key to the WIDE-N algorithm. Every digi that hears a mobile POSITION report will digipeat it to ALL other DIGI's, BUT ONLY ONCE. There needs to be a limit on how long the DIGI keeps a copy of each packet. If the time is too long, then the list is big, and originating stations are prevented from repeating their SAME packet. If it is too short, then there is the chance that a packet may propogate in a circle and get repeated again. My guess is that 30 seconds is a good default value. Howie Goldstein, N2WX has improved the effeciency of this idea, by only saving and comparing the CHECKSUM of the packets, instead of the whole packet. If ALL APRS WIDE area digipeaters changed over to the WIDE-N code, we would HAVE THE ULTIMATE GENERIC MOBILE GPS NETWORK! Mobiles traveling within a 200 mile radius of home could simply set a path of UNPROTO APRS VIA WIDE-5 without fear of clogging the network! This WIDE-N ROM would not have to do anything else! It would be a cake walk to make it fit in any TNC.