I've enabled tcp keepalives on the live tmc.openvehicles.com, at 4min intervals. It appears to be 80 bytes (40 in 40 out) every four minutes of no other data. Looking through the logs, this appears to be affecting at least 3 mobile operators (T-mobile USA, AT&T USA in one location, and a Guam provider). Hopefully the keepalives will resolve it. I could enable it selectively on individual cars, but thought it better to globally enable it for the moment to see how things behave. I suspect that it is affecting more cars than I can easily see. I don't anticipate any problems, but if anyone sees any issues, please let me know. Regards, Mark. On 19 May, 2012, at 11:49 PM, Mark Webb-Johnson wrote:
I've been working on a weird problem with a Tesla in Guam. Yep, they have Teslas in Guam, apparently.
Anyway, the problem is the user gets weird app behavior with the car disconnected a lot of the time.
A lot of hunting later, and I find his car reconnects regularly every ten minutes. The old connection is still open to the server (not torn down), and a new connection appears almost exactly ten minutes after the first one. Not an issue for the server (as it interprets that correctly and kicks off the first connection), but uses up bandwidth anyway and means the car is often disconnected (especially if you contact the car in the top half of the ten minute window.
More hunting, and I find 2 others cars with similar behavior. I'm chasing down the owners to find what cellular provider they use to see if there is anything in common.
It seems that the cellular providers are killing the OVMS TCP/IP connection after ten minutes (or so).
A google search came up with this:
http://web.eecs.umich.edu/~zmao/Papers/netpiculet.pdf (search for "10 minutes" in the document to find the relevant comment)
This seems really dumb, but possible I guess.
The solution is to be PING the car from the server, more frequently, but I hate using more bandwidth. Perhaps I can come up with an adaptive algorithm to do this only for cars that connect without disconnection of the previous connection a lot.
Anyone heard of this?
Regards, Mark.
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