Re: [Xastir] Weird plotting
On 3/1/07, Tom Russo <[EMAIL PROTECTED]> wrote: This looks suspiciously like a digi that's holding packets too long before digipeating them. My memory's kinda dim on the subject, but as I recall it is stale packets being re-transmitted long after later posits are created. If you're seeing the behavior in a specific location, it's likely that the nearby digi is malfunctioning somehow. You might try searching the APRSSIG archives for details, as I don't remember exactly what the mechanism is or what the comment traits were. Mountaintop digipeaters that can hear far too much will exhibit this phenomenon. Let's pretend for sake of simplicity that all APRS users set their path for 1 hop, making use of the digipeaters to simply digipeat once and once only. The i-gates grab this information and forward it on to the APRS-IS. So, let's also look at the situation where Dave KJ5KG is driving along near BIGDIGI. BIGDIGI can hear 5 other digipeaters. As Dave drives along, he can be heard by the digipeater, and also a local i-gate. As Dave drives along, his packets get digipeated and gated to the APRS-IS. However, in one location Dave only gets heard by BIGDIGI... he is shadowed from the i-gate. BIGDIGI attempts to gain access to the channel, however the neighboring digipeaters are busy making noise. BIGDIGI has to wait for a chance to get on the air. Meanwhile Dave's tracker pumps out another position report which is heard by the i-gate. Finally BIGDIGI finds a spot to digipeat the packet it has been holding, and does so. The i-gate dutifully sends the packet along to the APRS-IS. This easily shows how packets can be sent 1 - 2 - 3, and get heard on the APRS-IS in 1 - 3 - 2 order. In a quiet area, it is rare to see packets get out of order, but in higher density areas, it can happen on a regular basis. One thing that quite often happens though is that people think that their local digipeater is not heavily used when in fact the digipeater is hearing a very active channel. Remember the assumption above about single hop paths? I did that specifically to get you thinking about channel usage with used up paths. BIGDIGI would never act upon any packets except those that it heard locally. It would never need to digipeat packets already handled by another digipeater. However, those digipeaters within earshot still use up local airtime according to the local digipeater. It may sound like a really quiet channel on the ground, but that digipeater up on the mountain, or on that huge tower doesn't hear as quiet a channel. Digipeaters with incorrect DWAIT and SLOTTIME or TXDELAY settings can wait for quite a while in a noisy area. The noise level is determined by adding the activity on your local digipeater PLUS all the activity on ALL digipeaters that the local digipeater can hear. When you use a single hop path, you affect the channel load for the local digipeater, and also those it can hear. When you use a 2 hop path you affect your local digipeater, all digipeaters that can hear the local digipeater, and also all digipeaters that can hear the digipeaters that heard your local digipeater. You affect people one hop further than the number of hops you are using. James VE6SRV ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Weird plotting
On Thu, 1 Mar 2007, Tom Russo wrote: > This looks suspiciously like a digi that's holding packets too long before > digipeating them. Stuff like this has shown up in discussions on APRSSIG > from time to time. My memory's kinda dim on the subject, but as I recall > it is stale packets being re-transmitted long after later posits are created. > > If you're seeing the behavior in a specific location, it's likely that the > nearby digi is malfunctioning somehow. You might try searching the APRSSIG > archives for details, as I don't remember exactly what the mechanism is or > what the comment traits were. By any chance have you clicked on "Disable Posit Dupe-checks" in the File->Configure->Defaults dialog? Having this feature _enabled_ will at least prevent you from backtracking if repeaters are sending you an old packet that you've already received. Won't solve the entire problem though, but it might help. In other words, make sure the togglebutton is _not_ clicked to enable it. -- Curt, WE7U. archer at eskimo dot com http://www.eskimo.com/~archer Lotto: A tax on people who are bad at math. - unknown Windows: Microsoft's tax on computer illiterates. - WE7U. The world DOES revolve around me: I picked the coordinate system!" ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
Re: [Xastir] Weird plotting
On Thu, Mar 01, 2007 at 07:24:37PM -0500, we recorded a bogon-computron collision of the <[EMAIL PROTECTED]> flavor, containing: > Good afternoon folks, > > Has anybody noticed anything weird with plotting tracks? I have 1.8.5 > (latest CVS) running on both my home and work Fedora Core 5 boxes. I > notice that the tail sometimes has two coursed plotted from the same posit > but going in different directions and other weirdness. Rather than trying > do describe it, check out > > http://www.kj5kg.net/snapshot.png > http://www.kj5kg.net/snapshot2.net > > I'm pretty sure that I'm not driving like my trail would suggest! It's > also interesting to note that Mike's K9MTN trail shows the same behavior > in the same place! > > The data in snapshot.png is from my TNC at home and snapshot2.png is via > APRS-IS at work. > > Also, the same phenomena happen when I download my track from findu. This looks suspiciously like a digi that's holding packets too long before digipeating them. Stuff like this has shown up in discussions on APRSSIG from time to time. My memory's kinda dim on the subject, but as I recall it is stale packets being re-transmitted long after later posits are created. If you're seeing the behavior in a specific location, it's likely that the nearby digi is malfunctioning somehow. You might try searching the APRSSIG archives for details, as I don't remember exactly what the mechanism is or what the comment traits were. -- Tom RussoKM5VY SAR502 DM64ux http://www.swcp.com/~russo/ Tijeras, NM QRPL#1592 K2#398 SOC#236 AHTB#1 http://kevan.org/brain.cgi?DDTNM "And, isn't sanity really just a one-trick pony anyway? I mean all you get is one trick, rational thinking, but when you're good and crazy, oooh, oooh, oooh, the sky is the limit!" --- The Tick ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
[Xastir] Weird plotting
Good afternoon folks, Has anybody noticed anything weird with plotting tracks? I have 1.8.5 (latest CVS) running on both my home and work Fedora Core 5 boxes. I notice that the tail sometimes has two coursed plotted from the same posit but going in different directions and other weirdness. Rather than trying do describe it, check out http://www.kj5kg.net/snapshot.png http://www.kj5kg.net/snapshot2.net I'm pretty sure that I'm not driving like my trail would suggest! It's also interesting to note that Mike's K9MTN trail shows the same behavior in the same place! The data in snapshot.png is from my TNC at home and snapshot2.png is via APRS-IS at work. Also, the same phenomena happen when I download my track from findu. 73 Dave ___ Xastir mailing list Xastir@xastir.org http://lists.xastir.org/cgi-bin/mailman/listinfo/xastir
