Recent comments in /f/explainlikeimfive

Leucippus1 t1_jdshuah wrote

Reply to ELI5 How do undersea internet cables handle so much traffic? by RickTitus

There are a lot of them, and one cable will hold about 72 individual fiber strands, that is a lot of full optical bandwidth. Space division multiplexing is a way to make more then one link over the same fiber strand, so you can squeeze a lot of bandwidth over one strand of fiber optic.

(https://community.fs.com/blog/application-of-space-division-multiplexing-sdm-in-submarine-optical-cable.html)

Due to the distributed nature of the internet, you don't actually have to cross undersea cables very often. There are caching points and content delivery networks so you are usually not more than a few hops away from your content. This can be arranged through something called 'transit agreements' and 'peering agreements'; that is an entire essay unto itself, but suffice to say almost every modern ISP POP (internet service provider point of presence) has a Netflix caching server in a server rack plugged directly into the service provider equipment. That shortens the distance between the content and the subscriber.

Source: I work for one of the major US ISPs.

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Ape_Togetha_Strong t1_jdshffq wrote

Reply to ELI5 How do undersea internet cables handle so much traffic? by RickTitus

Information is encoded by changing the signal that is being sent. The amount of data you can transfer per second is a function of how often you can change the signal being sent, and detect the change on the other end. We can do this really, really, fast.

Once you've reached the limit of your ability to make the signal change more often, you can increase the amount of information transferred by making each unit of this signal contain more information than just "on" or "off". Instead of a signal where everything above a certain amplitude is a 1, and below it is a 0, you can split the amplitude into more sections, each one encoding multiple binary digits. You might split it into four different amplitudes corresponding to 00, 01, 10, 11.

You can build more and more advanced ways of encoding more information into the signal. For example, you can also send multiple signals of the same wavelength that are out of phase with each other, and if you have two signals, and one encodes phase angle and the other amplitude, now you can combine those signals to create a "line" that points to a location in 2D space. Then you can construct a grid of possible combinations of bits, 0000, 0001, 0010, 0011, etc. in that 2D space that each unit of the signal "points" to.

On top of that, you can send multiple different data streams through the same fiber at the same time by using different wavelengths of light for each of them.

And then you have many, many fibers in the same cable.

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therouterguy t1_jdsh75j wrote

Reply to ELI5 How do undersea internet cables handle so much traffic? by RickTitus

First of all a lot of data is cached locally. It is unlikely the data is transferred just for you from Europe to the US. Each cable consists of multiple fiber optic wires. each wire can handle multiple colors and each color can handle 10s of gigabit/s per second. Depending on the distance 400gbit/s per fiber is not unheard of. 100s of these fibers per cable gives a lot of capacity. But again your youtube video will not be streamed on demand from Europe to the US it will be there already.

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JohnnyJordaan t1_jdsgphd wrote

Reply to ELI5 How do undersea internet cables handle so much traffic? by RickTitus

Note that what's called a 'cable' is not just one single transmission line, it's a bundle of tens of fiber optic cables (strands of transparent plastic). They work by laser light that's shone through them and flickers in an extremely high frequency to deliver gigabits or even terabits of data per second per fiber. Modern versions even use multiple lasers with different colors to transmit multiple streams of data through the same fiber. As the plastic isn't perfect, after a distance of a few hundred miles they need a receiver (an electronic 'eye' to see the laser signals) connected to a new set of lasers to 'repeat' the data for the next few hundred miles. These are powered by separate power lines in the cable, with a very high voltage to be able to travel such a long distance without losing too much power in the cable itself.

As a sidenote, specifically for repetitive stuff like cat videos or your latest Netflix series, video websites and streaming services use local servers in every part of the world to serve the content to the local users. They in turn request the data from centralised servers, but that only has to be done once per chunk of video, saving a lot of bandwith. This is called 'caching' and removes the need for most of the basic internet stuff to have to cross the Atlantic all the time. It's also noticeable when you watch more obscure videos or listen to less popular music that it sometimes takes a few extra seconds to start playback. This is caused by the local server not having the content ready and first has to get it from the central server(s).

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EffeteTrees t1_jdsg5ql wrote

Reply to ELI5 How do undersea internet cables handle so much traffic? by RickTitus

The cables are bundles of incredibly fine fiberoptic strands. Each strand is used to the maximum- i.e. very fast state-of-the-industry optical switches cramming as much data through as possible. In terms of privately-owned globe-spanning infrastructure, I can’t imagine something more vital than these undersea cables at the moment.

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dingus-khan-1208 t1_jdsg207 wrote

Reply to comment by outofmemory01 in Eli5 what does the expression “daisies won’t tell” mean? by Entire-Pin264

There's another one from 5 years later in 1913: https://lyricsplayground.com/alpha/songs/a/alwaystakeagirlnameddaisy.html

ALWAYS TAKE A GIRL NAMED DAISY ('CAUSE DAISIES WON'T TELL) (Music: George W. Meyer / Lyrics: Alfred Bryan & Sam M. Lewis)

Jimmie Hodges - 1913 Albert Campbell & Henry Burr - 1913

Handsome Harry, handsome Harry Thomas
He was sued, yes, sued for breach of promise
He took Mary walking through the dell
And said, "Now don't you dare to tell"

Mary went right home and told her mother
Ma told Pa and Pa then told her brother
Brother told the preacher
And the preacher went and tolled a wedding bell

Never take a walk with Mary
Never take a walk with Sue 
Never take a walk with Maude or Carrie
That's the kind of girl you'll have to marry

If you take a girl out walking
Down a little shady dell
Always take a girl named Daisy 
'Cause daisies won't tell 

Harry's married life was pure and simple
Till he met a girlie with a dimple 
She said, "Dear, I'm not acquainted here 
I just came down from Beaver Fall"

Harry winked and said, "Why silk and satin
To this girl would be like Greek and Latin"
Harry felt like fainting 
When he missed his little dollar Ingersol

Never take a walk with Mary
Never take a walk with Sue 
Never take a walk with Maude or Carrie
That's the kind of girl you'll have to marry

If you take a girl out walking
Down a little shady dell
Always take a girl named Daisy 
'Cause daisies won't tell

That one's clearly not quite as innocent.

So I would guess that it was a phrase from the time when casual sex and premarital sex simply were not socially acceptable, and even being alone with someone of the opposite gender had implications. So people would sneak off and meet up in a field somewhere where they thought no one would see them together and tell.

But that's just a guess based on those two songs.

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zhonzhon t1_jdsb7e1 wrote

Reply to ELI5 Why is there a a crawl space under houses? by PetertheRabbit321

in general, there are a few different types of "foundations" used for housing. you have a raised foundation, where there are concrete posts with wood panels built on top of them. this type of foundation creates the "crawlspace" which can be used to access below the floor. this is a cheap method of building houses, and might be suitable for areas with flooding.

the other type of foundation is a solid concrete slab. this is just as it sounds, and costs more (because concrete expensive) and can be prone to flooding if the water level rises above the slab. but is more sturdy.

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