Error Detection and Flipping the Bits - Computerphile

Devising codes for different weather states is all well and good, but what if the weather strikes back? Electrical storms can distort codes and noisy lines can confuse things, Professor Brailsford shows us one way of building redundancy into the system.

This video was filmed and edited by Sean Riley.

[lejink]

This is my new favorite channel of yours Brady, glad to see so much activity with it lately

[heyandy]

I love error correction. When I learned about it in Digital Logic, I was pretty floored that the simple rules could detect, and (in the case of Hamming code) even correct the error! I was floored. Of course, it's not practical, as I have the full network stack between me and the bits. But it is shades of things to come as far as what can be automated.

[chrisharrison]

Another excellent video from Brailsford. When Computerphile was announced, this is exactly the kind of video I envisioned the channel would be creating. Nice work!

[Truthiness]

Been writing an RLE solution for a program I'm working on (probably why YouTube recommend this), and this was JUST what I needed to see. Very, very good thought provoking discussion here, I was so worried about compression I forgot all about error proofing and recovery.

[iabervon]

Details: use GF(2^n) instead of normal arithmetic, which means that addition, subtraction, multiplication, and division all "work" and don't require more than n-bit numbers. Treat your 15-number sequence as a big number without carrying from one place to another. Valid sequences are multiples of 1, 1, 1, 1. Invalid sequences are a multiple of 1, 1, 1, 1 plus a<<b plus c<<d, and you can solve for a, b, c, and d to correct 2 errors.

[riskinhos]

really. this guy is great. makes this things look so easy. love it.

[Random]

Yes, a video on forward error correction and/or cyclic redundancy checks would be a very nice sequel to this video.

I doubt the channel takes suggestions, but I'll still leave it here :)

(Also, good job so far on the videos, keep up the good work!)

[benjaminjarrell]

Wow, i've never thought of that was to preform the xor logic function, adding the 2 inputs together and rather or not the sum is even is the exact same output as an XOR function

[ragnkja]

That was discussed in the video about compression; if you sent a 1, it could, in your system, be either "foggy" or the beginning of "cloudy" or "rainy". If the system needs to be able to send many messages with as little space between them as possible, they need to be possible to identify without wondering whether the next bit is part of the message or not.

[AdamBreitkreutz]

I was expecting to hear about that too. If you're interested, error correction (and detecting multiple errors) is done with a cyclic redundancy check (CRC).. There are longer and shorter CRCs that can detect/correct more or less errors in the transmission.

[MrShysterme]

I love these information theory videos. Information theory is so rich. It is useful in many fields besides data compression and signal transmission. For example, an important part of statistics is going toward information theory.

[TensionFreeTape]

Sure are. One really simple extension of this idea is to use a "distance 3" coding, which means that each valid code has at least 3 digits different to any other code.

Now if any single digit is flipped, the error can be detected in the same way as explained in the video. This time though the received message will differ from the correct code by only 1 digit, but differ from every other code by at least 2 digits.

This new system can detect errors of 2 digits, OR correct single digit errors.

[trefod]

If only all teachers were as clear and understandable as this guy, far more people would know far more stuff.

[flatdragonfruit]

Seriously dude... This channel is about computer science, and comuter science is all about thinking. :)

[MrShysterme]

This channel has a different intended audience. I'm sure you can find tons of other videos on youtube that fit your needs.

[Aroboy]

I can explain that in a sentence. IP's aren't distributed randomly, they are assigned: certain countries get a certain batch of codes, certain ISPs within get a subset of those codes, and so on, so one can easily look up which country, region, ISP, etc. your IP belongs to. However ISPs *do* assign them randomly, so at best someone can find out where the last non-random element along the line was.

[instormental]

This video takes me back...to the digital systems test I had this morning. Maybe I should've been watching this yesterday instead of studying and avoiding YouTube :P

[jeanguylouisbourg]

man, i could listen to this guy talks for hours on ends. this stuff is super interesting!

[utkua]

sound file is transmitted as smaller blocks called bytes, 8 bits, which are validated just like weather codes, so the same thing. TCP stands for transmission control protocol, you have botch control and acknowledgment support, which is how internet works.

[TheOverCaste]

The receiving end calculates the bit aswell, and if they don't match it's changed.

If what you're asking is if two total bits get changed, that can't be detected with this method, but the odds of that happening are of course quite a bit lower.