Is this NAT-hell only? In principle it shouldn't happen on a real IPv6 network, which we'll hopefully be able to assume in a few years...
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An IPv6 network without stateful firewalls shouldn't have this issue, but stateful firewalls will still end up dropping old / inactive connections. There's also just a whole lot of broken stuff. I think there are a lot of pure IPv6 mobile networks already and it still happens.
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Why would you put stateful firewalls on an IPv6 network with millions of nodes? Do they just *want* to burn money and spew CO2?
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I don't know what they are doing or why, but carriers love dropping connections. *shrug*
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en.wikipedia.org/wiki/Carrier-g is definitely the main issue, but IPv6 definitely isn't 100% reliable either. The code really needs to be designed to actively figure this out.
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Shouldn't TCP keepalive at the kernel level be able to handle it?
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The device goes to sleep though and that's not going to wake it up. The only way it could work is if it was offloaded to hardware that kept running. It's totally possible that exists, I don't know.
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But kernel can and *should* schedule periodic wakeups just to do stuff like keepalive. Unlike gigantic userspace apps it could do it very efficiently.
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Apps aren't allowed to keep the device awake or trigger waking it up whenever they want though, so it can't apply to every usage of stuff like TCP keepalive. It's also really best if every single app needing push notifications isn't trusted to do it right themselves.
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Well now we're getting into the domain of Android policy (and why it's idiotic). Mobile OS should just force-suspend any app that consumes more than X% of cpu while in background, letting them use standard APIs like TCP keepalive but suffer consequences if they do it wrong.
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Waking up the device frequently is a bigger battery drain than doing it very infrequently but using a lot of CPU. It gets to sleep for long periods of 30+ minutes at a time on a reliable network. It always tries to get back to sleep very fast but apps will stop that.
Most apps will ruin battery life if given the opportunity. Simply something like an email app that wants to poll every minute and is too lazy to come up with a push system for email since it's not part of the baseline email standards and they don't want to run a push server, etc.
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And it's basically every app that will do it, so if the user has 50 apps they've got 50 things keeping the device awake with wake locks or constantly waking it up, with the intervals not lining up well. OS has to be heavily involved in scheduling / alarms / timers to work well.
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Well yes. I would include the cost of wakeup in the accounting of cpu time.