This 1-minute instructional video shows how to do track history lookups on aprs.fi. I made it quickly one morning as an answer to a question from an user on APRSSIG.
The news of https://aprs.fi/ - new features and interesting attractions found in the APRS and AIS worlds.
Showing posts with label video. Show all posts
Showing posts with label video. Show all posts
Monday, October 10, 2011
Wednesday, March 16, 2011
Kantronics KPC3+ KISS considered harmful - demonstration videos published
[UPDATE: Do read the comments below the post too, for workaround suggestions.]
If you happen to have a Kantronics KPC-3+ TNC, please do not use it for your APRS igate. It appears to have a software bug which causes delays of over 10 minutes when receiving packets from the radio and then forwarding them to the computer, which then forwards them to the Internet (or possibly retransmits the old packets back to the radio channel, if digipeating).
This is a very bad thing to do, as the greatly delayed packets cause network overload and make moving vehicles jump back and forth between their current positions and the past positions. Looks very funny when aprs.fi tries to draw a track line between the received positions.
For years there have been anecdotal stories and suggestions about a possible problem. Yesterday Alan (radionerd1) has uploaded three videos to Youtube demonstrating the problem. This serves as a nice technical proof that the problem is real, and demonstrably a problem of the KPC-3+. There have been hints that the bug could be in UI-View32 (when using it with the KPC-3+), but Alan demonstrated the problem without involving UI-View.
Alan ran APRSIS32 on a computer, and connected it to two APRS receivers. One used a KPC-3+ and one used AGW packet engine (sound card packet decoder). At first, the two ports received the same packets at the same time. After about a week the KPC-3+ started to misbehave - the received packets were given to the computer only after they had been held as hostage for over 10 minutes. Some people have reported that it can go in this delaying mode within hours or days - it might be due to bad luck, or due to the amount of traffic received. The KPC-3+ did put out a KISS packet to the computer every time a packet was heard from the radio, but it was an old one. When the TNC was reset, it started performing well again.
My guess, as a programmer, would be that the KPC-3+ looses count of the packet it should be transmitting on the serial port. It receives a packet on the radio port, puts it in the received packets buffer, and then prints the wrong packet on the serial port. It might be the oldest packet in the buffer, or thereabouts. The amount of perceived delay would depend on the amount of traffic received in your area.
So, I repeat: If you have a KPC-3+ on your igate in KISS mode, please switch it to something else as soon as possible (KPC-3, OpenTracker, TinyTrak, TNC2 clones, whatever). If you wish to continue using it later, please contact Kantronics at service@kantronics.com and ask them to fix the software bug.
It has been said that the problem only exists in KISS mode. So if you're using the KPC-3+ as a stand-alone digipeater, it should be fine (in this respect). If you're using it as a digipeater in KISS mode, with the digipeating happening on the computer (digipeating enabled in UI-View32 or APRSIS32), the effects are seriously bad, as you're transmitting old packets on the radio channel.
If you happen to be Kantronics, please fix the bug. It's causing a great deal of havoc to the APRS network, and it's messing the contents of the aprs.fi database. Thank you!
If you happen to have a Kantronics KPC-3+ TNC, please do not use it for your APRS igate. It appears to have a software bug which causes delays of over 10 minutes when receiving packets from the radio and then forwarding them to the computer, which then forwards them to the Internet (or possibly retransmits the old packets back to the radio channel, if digipeating).
This is a very bad thing to do, as the greatly delayed packets cause network overload and make moving vehicles jump back and forth between their current positions and the past positions. Looks very funny when aprs.fi tries to draw a track line between the received positions.
For years there have been anecdotal stories and suggestions about a possible problem. Yesterday Alan (radionerd1) has uploaded three videos to Youtube demonstrating the problem. This serves as a nice technical proof that the problem is real, and demonstrably a problem of the KPC-3+. There have been hints that the bug could be in UI-View32 (when using it with the KPC-3+), but Alan demonstrated the problem without involving UI-View.
Alan ran APRSIS32 on a computer, and connected it to two APRS receivers. One used a KPC-3+ and one used AGW packet engine (sound card packet decoder). At first, the two ports received the same packets at the same time. After about a week the KPC-3+ started to misbehave - the received packets were given to the computer only after they had been held as hostage for over 10 minutes. Some people have reported that it can go in this delaying mode within hours or days - it might be due to bad luck, or due to the amount of traffic received. The KPC-3+ did put out a KISS packet to the computer every time a packet was heard from the radio, but it was an old one. When the TNC was reset, it started performing well again.
My guess, as a programmer, would be that the KPC-3+ looses count of the packet it should be transmitting on the serial port. It receives a packet on the radio port, puts it in the received packets buffer, and then prints the wrong packet on the serial port. It might be the oldest packet in the buffer, or thereabouts. The amount of perceived delay would depend on the amount of traffic received in your area.
So, I repeat: If you have a KPC-3+ on your igate in KISS mode, please switch it to something else as soon as possible (KPC-3, OpenTracker, TinyTrak, TNC2 clones, whatever). If you wish to continue using it later, please contact Kantronics at service@kantronics.com and ask them to fix the software bug.
It has been said that the problem only exists in KISS mode. So if you're using the KPC-3+ as a stand-alone digipeater, it should be fine (in this respect). If you're using it as a digipeater in KISS mode, with the digipeating happening on the computer (digipeating enabled in UI-View32 or APRSIS32), the effects are seriously bad, as you're transmitting old packets on the radio channel.
If you happen to be Kantronics, please fix the bug. It's causing a great deal of havoc to the APRS network, and it's messing the contents of the aprs.fi database. Thank you!
Sunday, October 10, 2010
Youtube: aprs.fi bookmark feature demonstration
Today I did a little exercise in creating an instructional video. In this Youtube video I demonstrate the new bookmarking feature.
Monday, September 27, 2010
Outage on Sunday (502 Bad Gateway)
One of the two aprs.fi web servers got stuck on Sunday afternoon (around 1300 UTC 2010-09-26) and started giving out 502 Bad Gateway responses. About half of the web requests for aprs.fi ended up on the stuck server, so sometimes you got the correct response page and sometimes you didn't. For some reason the automatic failover did not work – in exactly this sort of situation it should magically disable the second server and point all requests to the working one.
I happened to be driving back from the countryside when the problem appeared. After getting home in the evening and analyzing the situation I disconnected the server from the network remotely by shutting down the switch port, so that it would not interfere and that the other web server could handle all of the site visitors. At this point, when the server disappeared completely from the network, the other server automatically took over it's IP address and the service started working perfectly.
The next day, 15 hours after the disconnection, I went to visit the hosting site to bring the server back online, and took a couple of iphone video clips of the servers. First, the primary server (at the moment running the whole aprs.fi site and serving all visitors), and then the secondary server which had just been brought up and was receiving the past 15 hours worth of APRS data from the primary server. It was pretty busy at the time, but it took only an hour to copy over all the missing data from the primary.
After the replay was completed I started up the web service on the second server, too, and the service is now again running in a redundant configuration.
Root cause analysis continues. It was definitely a software glitch, probably something to do with me running a system process under gdb to analyze a SIGSEGV it gets every now and then. It might well have caused some services to freeze. The database didn't hang and continued to replicate until the disconnection, but the web service got stuck and I couldn't log in to the box using ssh, or through the serial console.
I'll also have to fix the health check used to trigger the automatic failover procedure, so that it will work next time this sort of problem appears.
The trip to the computer room gave me an excuse to quickly try out Apple's iMovie for composing a little video. Appears to work, but I guess I still prefer Vegas. There isn't much point in this silly video, but maybe it's interesting for some aprs.fi fans. :)
I happened to be driving back from the countryside when the problem appeared. After getting home in the evening and analyzing the situation I disconnected the server from the network remotely by shutting down the switch port, so that it would not interfere and that the other web server could handle all of the site visitors. At this point, when the server disappeared completely from the network, the other server automatically took over it's IP address and the service started working perfectly.
The next day, 15 hours after the disconnection, I went to visit the hosting site to bring the server back online, and took a couple of iphone video clips of the servers. First, the primary server (at the moment running the whole aprs.fi site and serving all visitors), and then the secondary server which had just been brought up and was receiving the past 15 hours worth of APRS data from the primary server. It was pretty busy at the time, but it took only an hour to copy over all the missing data from the primary.
After the replay was completed I started up the web service on the second server, too, and the service is now again running in a redundant configuration.
Root cause analysis continues. It was definitely a software glitch, probably something to do with me running a system process under gdb to analyze a SIGSEGV it gets every now and then. It might well have caused some services to freeze. The database didn't hang and continued to replicate until the disconnection, but the web service got stuck and I couldn't log in to the box using ssh, or through the serial console.
I'll also have to fix the health check used to trigger the automatic failover procedure, so that it will work next time this sort of problem appears.
The trip to the computer room gave me an excuse to quickly try out Apple's iMovie for composing a little video. Appears to work, but I guess I still prefer Vegas. There isn't much point in this silly video, but maybe it's interesting for some aprs.fi fans. :)
Wednesday, July 14, 2010
Video: Using aprs.fi to trace packet errors
radionerd1 has uploaded a video on Youtube, instructing how to trace down a faulty digipeater.
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