If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Wires, cables, and WiFi

Software engineer Tess Winlock introduces how the physical infrastructure of the Internet moves information. 

Want to join the conversation?

  • aqualine seed style avatar for user Aku Ankka
    So I'm not sure if this is related to internet connection but I try my luck. So suppose that you have headphone that you can listen music by connecting it to your mobile phone via cable or wireless bluetooth connection. Why the cable in general gives you better sound quality than bluetooth? I suppose that cable use electricity and bluetooth use radio waves...
    (55 votes)
    Default Khan Academy avatar avatar for user
    • leafers ultimate style avatar for user Diogo Ribeiro
      The cable has no interference. Try to speak with another person when you're alone and when you're in the middle of a crowd. In which situation can you understand the other person better?
      The cable is connected to the headphones and mobile phone only, while the space around you is being used all the time by multiple devices.

      Another thing that differenciates both cases is that the signal strength for wireless comunications drops a lot, while in comunication by cable it doesn't.
      (114 votes)
  • leafers ultimate style avatar for user Justin
    Wow, are fiber optic cables across the ocean floor really what connects each continents to the internet?
    (17 votes)
    Default Khan Academy avatar avatar for user
  • starky tree style avatar for user Hitoshi Sasaki
    This may be silly, but if I were to play a game with high fps and ability to talk with teammates, how dose the level of WiFi I receive affect my experience?
    (9 votes)
    Default Khan Academy avatar avatar for user
    • male robot hal style avatar for user Cameron
      The main issue concerning gaming over networks is high latency (aka "lag")
      Latency is the time it takes data to travel across the network.

      WiFi typically has more latency than a wired network, but the increase in latency may or may not be significant enough to affect your gaming experience.

      How can we figure out if WiFi is resulting in unacceptable latency ?
      We can try to measure the latency by using the "ping" command, which measures the time for a chunk of data to be sent from your computer to its destination and receive an acknowledgement back.

      If the ping to the game server takes > 100 ms it may start to become noticeable (Some people are more sensitive than others).

      But we need to ping the local router to determine if the source of that latency is the local network.

      A wired connection typically has a ping time to the local router of < 1ms.
      A good wireless connection will typically have a ping time to the local wireless router of < 10 ms (should be unnoticeable).
      A poor wireless connection can have ping times to the local wireless router > 100 ms (may cause noticeable lag).

      Hope this makes sense
      (30 votes)
  • aqualine ultimate style avatar for user Brian Trinh
    Why do some places have weaker or stronger wifi signals than others?
    (7 votes)
    Default Khan Academy avatar avatar for user
  • old spice man green style avatar for user 时若斯/anonymous
    Is computer science about the history of computers?
    (4 votes)
    Default Khan Academy avatar avatar for user
  • male robot hal style avatar for user Rohan
    How Li-Fi differs from Wi-Fi?
    (4 votes)
    Default Khan Academy avatar avatar for user
  • winston default style avatar for user Mysterious Mind
    Can someone explain this to me. My internet is very bad right now so I can't watch this video.
    (5 votes)
    Default Khan Academy avatar avatar for user
  • marcimus purple style avatar for user KYLEG
    I want to be a Red Hat Hacker
    (4 votes)
    Default Khan Academy avatar avatar for user
  • duskpin ultimate style avatar for user Debanil
    Wouldn't hexadecimal system transfer more data than binary in the same time? In binary, everything is encoded in ones and zeros but there are 16 symbols for encoding data in hexadecimal.
    So why don't we use hexadecimal?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • leaf green style avatar for user Kelly Loum
      Good question. The short answer is, "Yes, you can convey more information using the same space".

      But the long answer is that there is a limit to how much information can fit in a given space, whether its the space on a piece of paper, the space on a hard drive, or the "space" in a data stream on a computer network. And it depends on how much "noise" there is in that space.

      There's a whole science called "information theory" that deals with how much information can be stored in or sent through what's called a noisy "channel" (and every channel has noise). Information theory includes concepts like bits, symbols, data compression, error correction schemes (like sending redundant data), etc.

      When you write a sequence of decimal or hexadecimal symbols on a piece of paper, you are using only a small part of the data "channel" that is the paper. Hexadecimal uses more of the channel than decimal because there are more symbols even though each symbol uses the same space. You can keep improving the symbols and adding more of them to your scheme (or drawing them smaller) to squeeze more and more information in the same space, but eventually the various imperfections in the paper (the "noise") prevents you from using more symbols or drawing them smaller because then the symbols couldn't usually be discriminated from each other. The same goes for electronic circuits. Analog electronic data (like radio signals) allow any number of symbols, but after you define too many symbols they can't be discriminated from each other because there is always some level of noise (from the circuit, or radio noise) that distorts each symbol. Digital circuits (like a circuit to store a computer file or send data over a network), are designed so each bit uses enough of the channel so the noise very rarely, if ever, damages that bit.
      (4 votes)
  • leaf grey style avatar for user Joe
    How fast does electricity move through a wire?
    (3 votes)
    Default Khan Academy avatar avatar for user
    • purple pi purple style avatar for user APDahlen
      Hello Joe,

      A signal in a wire travels very close to the speed of light.

      Grace Hopper had a good visualization. In lectures for early computers she would hand out “nanoseconds” to each member in the audience. The “nanosecond” she handed out was length of wire about 12 inches long. You see, a signal will travel about 12 inches in one billionth of a second.

      Speaking of Amazing Grace, my favorite quote is: “It's easier to ask forgiveness than it is to get permission.” Also, she coined the word "bug."

      Do a bit of research on Admiral Hopper if you get a chance.


      (4 votes)

Video transcript

(upbeat music) - My name is Tess Winlock, I'm a software engineer at Google. Here's a question. How does a picture, text message, or email get sent from one place to another? It isn't magic. It's the internet. A tangible, physical system that was made to move information. The internet is a lot like the postal service. But, the physical stuff that gets sent is a little bit different. Instead of boxes and envelopes, the internet ships binary information. Information is made of bits. A bit can be described as any pair of opposites on or off, yes or no. We typically use a one, meaning on, or a zero, meaning off. Because a bit has two possible states, we call in binary code. Eight bits strung together, makes one byte. 1,000 bytes all together is a kilobyte. 1,000 kilobytes is a megabyte. A song is typically encoded using about three to four megabytes. It doesn't matter if it's a picture, a video, or a song, everything on the internet is represented and sent around as bits. These are the atoms of information. But, it's not like we're physically sending ones and zeroes from one place to another, one person to another. So, what is the physical stuff that actually gets sent over the wires and the airwaves? Well, let's look at a small example here of how humans can physically communicate to send a single bit of information from one place to another. So, say we could turn on a light for a one or off for zero. Or use beeps or similar sort of things of, like, Morse code. These methods work, but they're really slow, error-prone, and totally dependent upon humans. What we really need is a machine. So, throughout history, we've built many systems that can actually send this binary information through different types of physical mediums. Today, we physically send bits by electricity, light, and radio waves. To send a bit via electricity, imagine that you have two light bulbs connected by a copper wire. If one device operator turns on the electricity, then the light bulb lights up. No electricity, no light. If the operators on both ends agree that light on means one and light off means zero, then we have a system for sending bits of information from one person to another using electricity. But, we have a problem. Let's say that, we want to send five zeroes in a row. Well, how can you do that in such a way that either person can actually count the number of zeroes? Well, the solution is to introduce a clock or a timer. The operators can agree that the sender will send one bit per second and the receiver will sit down and record every single second and see what's on the line. To send five zeroes in a row, you just turn off the light, wait five seconds. The person on the other end of the line will write down all five seconds say, "Zero, zero, zero." And for ones do the opposite, turn on the light. Obviously, we'd like to send things a little bit faster than one bit per second. So, we need to increase our bandwidth, the maximum transmission capacity of a device. Bandwidth is measured by bit rate, which is the number of bits that we can actually send over a given period of time, usually measured in seconds. A different measure of speed is the latency, or the amount of time it takes for one bit to travel from one place to another. From the source, to the requesting device. In our human analogy, one bit per second was pretty fast, but kind of hard for a human to keep up with. So, let's say that you want to actually download a three megabyte sone in, like, three seconds. At eight million bits per megabyte, that means a bit rate of about eight million bits per second. Obviously, human can't send or receive eight million bits per second, but a machine could do that just fine. But, now, there's also a question of what sort of cable to send these messages over and how far the signals can go. With an ethernet wire, the kind that you find in your home or office or school, you see really measurable signal loss over just a few hundred feet. So, if we really want this internet thing to work over the entire world, we need a different way of sending this information really long distances. I mean, like, across an ocean. So, what else can we use? Well, what do we know that moves a lot faster than just electricity through a wire? Is, well, light. We can actually send bits as light beams from one place to another using a fiber optic cable. A fiber optic cable is a thread of glass engineered to reflect light. When you send a beam of light down the cable, light bounces up and down the length of the cable until it is received on the other end. Depending on the bounce angle, we can actually send multiple bits simultaneously, all of them traveling at the speed of light. So, fiber is really, really fast. But, more importantly, the signal doesn't really degrade over long distances. This is how you can go hundreds of miles without signal loss. This is why we use fiber optic cables across the ocean floors to connect one continent to another. In 2008, there was a cable that was actually cut near Alexandria, Egypt, which really interrupted the internet for most of the Middle East and India. So, we take this internet thing for granted. But, it's really a pretty fragile physical system. Fiber is awesome, but it's also really expensive and hard to work with. For most purposes, you're gonna find copper cable. But, how do we move things without wires? How do we send things wirelessly? Wireless bit-sending machines typically use a radio signal to send bits from one place to another. The machines have to actually translate the ones and zeroes into radio waves of different frequencies. The receiving machines reverse the process and convert it back into binary on your computer. So, wireless has made our internet mobile. But, a radio signal doesn't travel all that far before it completely gets garbles. This is why you can't really pick up a Los Angeles radio station in Chicago. As great as wireless is, today it still relies on the wired internet. If you're in a coffee shop using Wi-Fi, then the bits get sent through this wireless router and then are transferred to the physical wire to travel the really long distances of the internet. The physical method for sending bits may change in the future. Whether it's lasers sent between satellites or radio waves from balloons or drones. But, the underlying binary representation of information and the protocols for sending that information and receiving that information have pretty much stayed the same. Everything on the internet, whether it's words, emails, images, cat videos, puppy videos, all come down to these ones and zeroes being delivered by electronic pulses, light beams, radio waves, and, you know, lots and lots of love. (upbeat music)