WHATS WRONG WITH THE RELAY,WIDE PATH? 31 March 2005 -------------------------------------------------------------------- >Please explain how RELAY causes DUPES in the USA? Thanks for asking, because it is important that eveyone understand this and it is why RELAY in our current overloaded nets is now part of the problem and not the solution... The problem is that in the USA, Kantronics implemented my WIDEn-N suggestions in 1998 over the top of the previous legacy RELAY-WIDE system independently. A packet digipeated with RELAY, or WIDE in the path is not compared with a subsequent WIDEn-N copy of the same packet. Thus dupes can be generated. Lets assume a mobile is using the path of RELAY,WIDE: If all he hits is a rare RELAY-only digi in the boonies, then there is one copy digipeated and then that copy is then digipeated by lets say 3 other WIDES. Those are all 4 copies of the original packet, one for each digipeater. We dont call those dupes. Those are what we want. 4 copies, one for each of the 4 surrounding digis. That's good. MOBILE>APRS,RELAY*,WIDE MOBILE>APRS,RELAY,DIGI1* MOBILE>APRS,RELAY,DIGI2* MOBILE>APRS,RELAY,DIGI3* But all the other 95% of the time while the mobile is driving around town his RELAY,WIDE packet is being heard by lets say 3 other digis. Now then here is what we see: MOBILE>APRS,DIGI1*,WIDE MOBILE>APRS,DIGI2*,WIDE MOBILE>APRS,DIGI3*,WIDE MOBILE>APRS,DIGI1,DIGI2* MOBILE>APRS,DIGI1,DIGI3* MOBILE>APRS,DIGI2,DIGI1* MOBILE>APRS,DIGI2,DIGI3* MOBILE>APRS,DIGI3,DIGI1* MOBILE>APRS,DIGI3,DIGI2* for a total of 9 packets. Three are the intended packets from the 3 surrounding digis and the other SIX are "DUPES". Each digipeater is digipeating the same packet TWICE because it does not compare the RELAY digipeated packet to any that it has also digipeated vis WIDEn-N. Now imagine each time that mobile passes by a HOME RELAY, that adds another original for each of the digis to also digi a 3rd time (total of 12 packets). Not only is this so obvious to see happening and so obviously a waste of bandwidth by causing a factor of 3 dupes on every packet transmitted, but the stations doing it the most are MOBILES which already generate 10 to 20 times as many positions per hour as any other stations. It is this totally unneeded multiplication of DUPES from RELAY,WIDE paths that is the biggest load on the APRS channel in the USAand also the *easiest* to get rid of. Some people say that they have to have a RELAY in a certain area because it is a dead zone. True, but the "cost" of having mobiles use the RELAY,WIDE path just for that one packet in the morning and that one packet in the evening in that "hole" is causing the other 40 of his commute packets to be generating over 240 "DUPES" all the rest of the time when he is closer to town on his 20 minute commute. We must get rid of RELAY (and WIDE) which have no dupe elimination algorithm. Besides, we can still have FILL-IN digis by just swapping WIDE1-1 in place of the RELAY alias. To me, we are shooting ourselves in the foot with all these mobiles driving around using a RELAY,WIDE path. Yes, I advocated that for years for backwards compatiblity with all the RELAY-only and WIDE only TNC's we had back here on the east coast. But it is time to move beyond that. In fact, we should have done it years ago. But I have to admit that since I have been spending 12 hours a day for the last 4 years building satellites, I had not been watching what was going on on the local 144.39. A few months ago, I had a weekend lull and was watching RAW packets and was *astonished* at what I saw from all the dupes of all the RELAY, and WIDE paths in our area. By the way, WIDE,WIDE does exactly the same thing. If there are 3 digis that hear that path, then there are the potential for 9 copies just from the first 3 digis. We MUST phase out WIDE completely and discourage any routine use of RELAY. On the other hand the path of WIDE2-2 goes just as far, but because the WIDEn-N algorithm has perfect dupe elimination, then if there are 3 digis, then there are only 3 copies (no dupes) heard in the original area of packet origination. Copies only radiate outward and never fold back. Whereas with RELAY,WIDE and WIDE,WIDE paths there will always be dupe multiplicatiion. But you ask, what about callsign-substitution? Isnt that supposed to eliminate dupes and keep a digi from digipeating something it has digipeated before? Yes, but look back at the original 6 dupes in the original example above. Notice that none of the 6 dupes was ever transmitted by the same digi twice. Those would look like MOBILE>APRS,DIGI1,DIGI2,DIGI1* and you dont see those, beause substitution prevents it. But that only protects after the 2nd hop. Most dupes are caused after the first hop! There, could be as many as 15 copies (3 desired and 12 dupes) heard from these 3 digis when only 3 would be heard if WIDEn-N were used. MOBILE>APRS,DIGI1*,WIDE,WIDE MOBILE>APRS,DIGI2*,WIDE,WIDE MOBILE>APRS,DIGI3*,WIDE,WIDE MOBILE>APRS,DIGI1,DIGI2*,WIDE MOBILE>APRS,DIGI1,DIGI3*,WIDE MOBILE>APRS,DIGI2,DIGI1*,WIDE MOBILE>APRS,DIGI2,DIGI3*,WIDE MOBILE>APRS,DIGI3,DIGI1*,WIDE MOBILE>APRS,DIGI3,DIGI2*,WIDE MOBILE>APRS,DIGI1,DIGI2,DIGI3* MOBILE>APRS,DIGI1,DIGI3,DIGI2* MOBILE>APRS,DIGI2,DIGI1,DIGI3* MOBILE>APRS,DIGI2,DIGI3,DIGI1* MOBILE>APRS,DIGI3,DIGI1,DIGI2* MOBILE>APRS,DIGI3,DIGI2,DIGI1* That is why I say that any use of RELAY or WIDE paths is causing 2 to 5 times the duplication of every packet transmitted in the USA. These are unnnecessary DUPES and not just COPIES I am talking about. They are just wasted QRM... >So, if home RELAY fill ins are spaced properly, what is the problem? >They are doing what they were put there to do... So true. But is the other 95% of the time that that mobile is transmitting RELAY,WIDE and hitting the big digis direct that is causing horrendous duplication all the rest of the time when he *is* in range of digis that is the problem... >I fail to understand your statement that home RELAYs >cause so much duplication.. They don't. What I was meaning was that the "concept of home RELAYS which is the basis for mobiles using the RELAY,WIDE... path is causing horrendous duplication most of the time when the mobile hits other digipeaters directly" is the better way to say it. Its not the home "RELAYs" but the use of the RELAY,WIDE... path that is the problem. >So in short, a DUPE to me is a packet sent by a RELAY >that was received from another RELAY. It is not a DUPE >if two RELAYs attempt to digipeat the same received >direct from the tracker's packet. Yes. A DUPE is the same digi digipeating the same packet more than once... >Simple solution is to limit unnecessary home RELAYs. No, Best solution is to eliminate the use of the RELAY,WIDE and WIDE,WIDE paths completely in the USA. This will cause a huge 2 to 5 TIMES reduction in dupes. This means the network load could go down to 50% or even 20% of what it is now. With that kind of a quiet channel there probably is no need for many of the fill-in digis in the first place, because now the regular digis might hear enough dead silence to hear the mobile in what used to be called the dead zone in the first place. And if the dead zone is really dead, then simply replace the RELAY alias with the WIDE1-1 alias. It will work just as well, but being of the WIDEn-N family, the perfect dupe-elimination filter in the digis will not generate the wasteful dupes. Thus, users that need to use FILL-IN digis can use the dual entry WIDE1-1,WIDE2-1 path. Notice the second entry starts as 2-1 so that only one additional hop is used for a total of 2 which is about right in most areas. A mobile path of WIDE1-1,WIDE2-2 would make 3 hops on every packet. OK in remote rural areas, but not desired in the seven major APRS metro areas or California or any other populous state with big mountain digis. NEVER use WIDE1-1 anywhere except the first hop in a path. Just like RELAY was never used beyond the first hop, or it generates horrendous QRM. Hope that clears it up. Bob, WB4APR