Sending digital information over a wire | Networking tutorial (1 of 13)

Sending digital information over a wire | Networking tutorial (1 of 13)



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We start our exploration of computer networking with the basics of sending digital information with a copper wire.

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This video is part 1 of an intro to networking tutorial:

so if you've connected to a network before you're likely going to recognize what we're looking at here these are pictures of a cable that's used very often to connect computers to a network and this particular type of cable is often called an Ethernet cable well we want to focus on here is how this cable is able to carry information from one computer to another so if we cut away the outside jacket here we can see that the cable is made up of it's actually four pairs of copper wires those eight wires here total and in future videos we'll get into the details of why that is and what all these different wires do but for now let's just think about kind of the most basic way that we can imagine to use this to send information you know so probably the simplest thing we can do is to just apply a voltage across two of these wires just so connect some voltage here and then we can vary the voltage to send information to the other end so for example maybe we'll vary the voltage between zero volts and 5 volts and so then we can vary this over time so this is time going off here to the right you know maybe you know maybe we start at 0 volts for a second and then we switch this to 5 volts for for a second and then maybe it goes back to 0 volts for 2 seconds and then up to 5 volts for a second and then 0 volts for a second and then 5 volts for 2 seconds and so if we look at what we did here we've got basically two different states that this can be and we can either be at 0 volts or we can be at 5 volts and so we actually call these states we have a term for this we call these state symbols so 5 volts and 0 volts are both two different the two different symbols that we have and we call these symbols because we can use them to represent information like a number so for example we could say that 0 volts is a symbol that represents the number 0 and that 5 volts is a symbol that represents the number 1 and so if we look at the voltage here once per second we've got 0 1 0 0 1 0 1 1 which we could actually interpret this now is a binary number if we wanted to we could even write this number as a decimal and so 0 1 0 0 1 0 1 1 converting that to decimal that actually equals the number 75 so I just want to take a moment and go over some terminology here so like as we mentioned the different states here are called symbols and the rate that we're sending these symbols is called the symbol rate so in this case the symbol rate would be one symbol per second you might also see this sometimes referred to as baud and baud is a term that literally means the symbol rate in symbols per second so in this case you know with the one symbol per second we refer to this as a sending this information at one baud so if we were sending this 10 times faster at 10 symbols per second so each of these were a tenth of a second long then we would be this would be a we'd be sending information at 10 baud so this is interesting so hopefully you can see how this lets us send whatever number we want to send but what if we want to send text well since we can send numbers really all we need to do to send any message we want is to agree on a mapping between a number and then a letter or symbol or some other character and so one of the most common sort of agreed-upon mappings is ASCII and I got this from Wikipedia is a just example of what ASCII looks like and it's just this table that maps between numbers and they call a glyph but it's basically just a character a letter of some sort so for example this 75 that we had up here maps to in ASCII 75 decimal maps to the letter K and you can see they also have it here in binary this this is this is what we what we have up here the 1 0 0 1 0 1 1 is is the binary letter for K and so you can see that by using this mapping and by varying voltages like this we were able to we could you know send any information that we wanted to

43 Replies to “Sending digital information over a wire | Networking tutorial (1 of 13)”

  1. EllipticGeometry

    1:27 If you look at what we did here, we played a paradiddle on the wire. I couldn’t help but notice the resemblance to the drum rudiment, RLRR or LRLL, often with the two played in succession.

    Let’s see if I’ll learn something. I’m pretty familiar with all the layers except the physical layer. It should be interesting to see what traffic actually looks like on the wire.

  2. ELEMENT-

    So if I want to send a word – for an example CAT (10000011 10000000 1010100) . How can I send one letter and group it together as word?

  3. TheDroidBay

    Did you cover UDP at some point too? I have a PC controlling a CNC machine that works on UDP and I would love to know more about it 🙂 I know its not as relaible as TCP but UDP is just what's used in this application.

  4. Ryan Roberson

    what i never understood is why you need 4 PAIRS. if current is a flow, then why not have 4 wires that send current one way, and one main dump wire that balances them in net.
    at least in water systems, this should work just as well as the pairings since you only detect voltage differences across one of the four and the main dump

  5. Shea Layton

    I know almost nothing about electricity and networking and this video just blew my mind, haha. As soon as he drew the 0V-5V graph it hit me that he was gonna write binary below and my world just expanded so much.

  6. Richard Walters

    excellent video … nice example … but, makes one think about how you got the number 75 in binary … as, in your chart of time vs voltage … the most significant bit and the least significant bit were switched … unless you were to fill up a buffer or something in reverse order, and extract that … just thoughts … looking forward to proceeding with the rest of the videos … great series !!!!  Thanks so much for sharing …

  7. houkensjtu

    Hi thx for your amazing explanation. I came up with an idea that if the physical basis of signal is just voltage, why can't we use audio cable (like common ones used for earphone) to convey data? Is it because the sound card are not able to produce such digital voltage waves?

  8. Thisun Pathirage

    I watched all the 13 episodes. This is awesome. Really understandable. Thank you very much. This is one of the best youtube tutorials I have ever watched!

  9. p4p1

    OMG thank you so much now I undserstand what is the bauds in arduino 🙂 you do really good videos man thank you for all of this knowledge

  10. The Chosen one

    Awesome Explanation,Very well Explained….I am Impressed very much on how you carried yourself explaining each topics with clarity & simple to understand…….I am SO happy

    I am Very much expecting your similar videos on TCP and other stuffs

  11. Brannon Wadforth

    Thank you so much for this series man, it has given me much more clarity in the field of computer networks and how things operate on the physical layer.

  12. Green Coder

    Hey! Thanks for this video series. It was always hard for me to start in this topic although I am very interested because I didn't know where or how to start and it was very confusing. I only knew the very top layer (application) and the physical layer but wondered how it works between. You helped me a lot! 🙂

  13. Tom Heylen

    Wow man. Just watched the 13 episodes without a break. Awesome. Going from 5 volt trough a cable up to understanding the internet protocol. All clear explained and very understandable.
    Great work!

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