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Comment Re:Just two days of service? (Score 1) 183

My ISP for my server had an outage for a couple of hours. They then mailed their customer base that they'd refund a whole month of service. I'm guessing that mail went out to more than the affected customers: My server didn't go down. A couple of days later I got the invoice for that month. Full charge. Two days later: full credit. I'm guessing they did the right thing and credited everybody who got the mail, even if they sent it out to customers that weren't affected.

Comment Yes I got something without asking.... (Score 1) 183

> When was the last time a telecom provider gave you a discount on your bill without you asking for it?

My cellphone was down for a day this summer. They apologized and offered a "free 500Mb of internet" for the September billing cycle.

I buy "internet service" on my phone with lots of margin. They charge like 100 times more for the "over your limit" traffic, so I rarely use the upper 500Mb of my "prepaid" 1G limit. It's cheaper to pay 12 months for 1Gb/month than to pay for 500Mb and go over the limit once a year.

So their "free 500Mb of internet traffic" is indeed completely free... for them.

Comment Re:Futurologists and transportation. (Score 1) 252

The "1/hr" argument is in my "quantization". The larger the quantization, the larger the margins have to be to make sure you catch the bus. When I have an appointment in Rotterdam, I take the train to Schiedam and then the underground to the center. When I try to be at the station 5 minutes before the train leaves, two minutes extra "margin" make me catch the train earlier. I've given up on schedules and just go there and take the first train. When a train or bus goes once every 15 minutes you get there with 3-5 minutes to spare. If it goes every hour, you need about 5-10 minutes, and if it goes once a day you need to aim for being there 15 minutes before it leaves, because getting stuck in traffic for 5-10 minutes should be tolerable....

Self driving cars would still be an option in the country as long as you tolerate having a slightly longer lead time.

Comment Futurologists and transportation. (Score 2) 252

What is it that notorious car-drivers hate about public transport, so that they end up spending like 5-10 times more money than what public transport would have cost them?

That is the question that you need to answer before you can make predictions like in the slashdot summary.

Public transport has "quantization noise". If you leave for work 3 minutes later, you'll miss the bus, and end up at work 15 minutes later. Sure you can prevent that. Just be at the bus stop 5 minutes before the bus. This means you invest 5 minutes every day to prevent a 15 minute occasional delay.

Second: when you use public transport, you don't have "your own space". This means that if you leave your wallet, ipad or whatever lying around when you step out of the vehicle, barring exceptions, it is gone. If you have your own "transport space", you can also stock it with stuff you might need while travelling (e.g. my brother has mints in his car), of that you might end up needing at the destination (e.g. umbrella).

Third there is a cost issue. If you see the cost to you every time you move, that makes you consider it more. People ignore the: "the car needs xx petrol to drive this far, so it costs me at the least yy to make this trip". They see the filing up and paying whatever that takes as something that must be done, and then they pretend driving the car is free.

Those are the things the car-drivers will need to have satisfied before they can be converted. And if you don't convert the car-drivers you will not have the economy of scale to have "leaving out the steering column" make a difference.

The current topic will "solve" the quantization noise. You hit a button in your house a few minutes before you leave, and the system will get a self-drving-car on your driveway before you close the door. It does not solve the other problem. You cannot leave the umbrella in the car "in case it rains when I get there". You forget your stuff and the next occupant might take it. (or at least "where is my presentation" is not solved with a run to the car park).

The "self driving" and "semi-public-transport" ideas will only work if everybody gets to keep their private module. Those could be powered with say a small 1kW motor and have a 40km/h (25mph) speed limit. Then when they end up at the freeway, a bunch of them group together with a "power-unit" and they can travel on the freeway at high speed. (Pay more and the "maximum grouping delay" goes down).

Comment Confusion of terms. (Score 1) 233

The article claims that NTP is the cause of the leap second. NTP is just a protocol that handles keeping computer clocks in sync with each other and with the official time (UTC, IIRC).

If NTP handles leap seconds by increasing update frequency and then coming to the conclusion: "Whoa! my offset just went from 0.3 ms to 1000.25 ms, lets step the clock a second once we're sure this was not a fluke measurement". then that's a bad way of handling it in my opinion. (also suddenly speeding up does not provide a smooth-enough transition).

One of the things that is bad about this is that when normal operation can handle (the bandwidth of) most hosts updating every 1024 seconds, and a few hosts (just rebooted, just installed, sync lost, whatever), now all of a sudden a synchronized (pun intended!) attack will take place where many many hosts will increase their update frequency by several order-2 magnitudes.

For google, they internally have needs for synchronized clocks. Why I don't know, and I don't care. They have decided to handle the leap second in a more controlled way. It's actually not that hard. Just make sure that everything syncs off one level-0 server, and during the 20 hour period leading up to the leap second, add a variable number of microseconds to the exported time.

Comment Re:Doesn't matter, so why do it? (Score 1) 233

The thing that people-who-don't-know-better are suggesting is that the second will be the same all the time.

They think that nothing bad will come from "thirty years from now, the sun is in the south at 11:59:30" (assuming an average of 1 leap-second per year).

(I can't think of anything bad that would happen... but I know my limitations. It's probably annoying as hell to /some/ fields of research or something....)

Comment Re:Infinity (Score 1) 1067

Suppose I have a variable A that ends up with the value Y*X. (Y might be a difficult calculation). Next I want to calculate B = A/X .

This could happen for example when I'm doing physics calculations where the parameter X eventually cancels out.

Anyway, this will end up with B = Y if you do the math and cancel out the X. However, if you let a computer follow through with the calculations, when X=0, you'll end up with a variable A with the value zero. And if you assign a value of "1" to 0/0 you'll silently get a wrong result when Y != 1.

So: The computer should throw an error. There is no way a compiler can come up with a reasonable answer for the variable B.

If you want it your way, you write B = X?A/X:1; If you want get rid of that expression everywhere in your code, you get a few choices. In C++ you could probably define a "myfloat" that overloads the division operator. Or you could make a "mydiv" function.

Comment Re:Opportunities as well as problems (Score 1) 98

Directional is an option for the satellites. But on the ground you'd have to be tracking all the time, and you'd have a dropout the moment one satellite goes away and another comes into view.

Oh, about the height. Suppose you're at 1000km. Then the area that can see the satellite at at least 45 degrees above the horizon is about 1000km in diameter. This covers an area of about 3 million square km. The earth is about 450 million square km. You'd need about 300 satellites to cover the earth with each spot getting on average two satellites (hopefully you can then arrange for every spot to get at least one satellite). If they need 4000 satellites they are apparently aiming for about 300km height! -> my calculation comes to 3000 satellites, they probably have a few in reserve, require a higher number of satellites to cover everywhere all the time etc.

Anyway, that would come to "too low" for the drag/orbit deay reasons..... So that would mean they are aiming for "the lowest the orbit-decay will alow".

Comment Re:Challenges... (Score 2) 98

Older satellite internet systems used technologies borrowed from "TV broadcasting". What they effectively did is broadcast everybody's downlink via the satellite and everybody-for-himself had to use a land-line for the uplink. The idea being that you like having a big downlink pipe and it might be acceptable to have "only" 56k uplink.

All that is going overboard, as I understand things. Yes, people are going to transmit their uplink bits to the satellites: the stated goal of these projects is "internet everywhere", even where landlines don't come. So on most my calculations (I hope all of them :-) ) I calculated the round-trip delay via satellite.

On the other hand, I did not take the groundstation-to-destination delays into account. Those are on the order of 60ms minimum for a transatlantic link, for exactly the same reason that a transatlantic satellite link will take that amount of time: the light speed.
(I just tried tracing packets to three American companies from Europe. All were reachable in less than 10ms (not enough to cross the ocean), with google performing worst from the three I tried: google, nbc, cnn. Apparently they all have servers serving european users here in europe).

Comment Challenges... (Score 5, Informative) 98

Google and facebook have realized that some problems are not (economically) surmountable.

The problems are the following: The closer you fly your satelite to the earth, the more resistance it has from the atmosphere. The density of the atmosphere reduces by a factor of 100 each 46 km of height. So at "100km", you have about 10000 times less air than at the surface. Some people call that space. At 200km the air pressure is about 100 million times less than what it is over here. That is enough to have a reasonable decay rate of weeks/months/years. "skylab" came down after a few decades, right?

The further away you fly your satellites, the longer the travel times will be for the signals. This equates to ping-times. Hmm. 200km is 0.6 ms, quite acceptable. Both ways. 1.3ms. Still fine. Double the distance to 400km for slower decay times, and you're still about 10 times faster than a normal ADSL line. Acceptable. Not a problem. (the problem here is the same for everybody. The satellites will then play "pass the hot potato" to one that's flying above the ground station and beam your packet down to earth. Assuming your halfway around the globe, that will be about 10000 km. That's with 66ms (round trip) already more than what you get with a residential ADSL line. Still not too shabby.)

The problem with putting satellites high is that the distance to the user becomes large. You want them as close as possible.

The closer you put them, the more you need. -> 4000 of them. This however is not just a one-time investment: because they are low, their orbits decay and they fall back to earth on relatively short notice. If you need 4000 of them, they are not going to be large. So they are small. If you have a cubesate (10cm cubed) weighing 1kg, its orbit will decay just like a 100kg satellite of 10x100x100cm (flying the wrong side towards the front). But a bigger satellite is likely to be 100x100x100cm and weigh not 100, but 1000kg. The extra weight helps keep it in orbit, the extra size in the flying direction does not make a big difference. So the small satellites decay fast as well!

Comment Next time.... (Score 1) 535

... arrest the 5-year-old with glasses in a superman costume. Everybody knows that Superman's glasses are a lethal weapon.

The shoot first, ask questions later attitude in the US is making me afraid. And the willingness of the police to come up with "charges" when they find nothing out of the ordinary.

The idea of a free country is that you can go about your business without getting arrested and thrown in jail for nothing. That "business" should include say hobbies that not everybody shares. Some people like to dress up. Some girls "fancy", some guys "as girls" and some nerds "as TV characters".

If on the report of a "gun sighted" the police rush out: Great. If they then arrest him, take him to the police station and then tell him: You had us scared for a moment, please don't do this again, that's "so so". But if they then CHARGE him with things just to make their trip seem useful then that's bad.

If they tell the man who reported this: Hey, that was just a guy in a costume from a TV show, please look better before you call us over. Then that's good. If they tell him: "great! we arrested the guy", then that's bad.

Be careful when a loop exits to the same place from side and bottom.