Sending streams of information across a single network link requires the use of modulation. In this video, you’ll learn about multiplexing, analog modulation, and digital modulation.
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One of the challenges we have when communicating from device to device is there’s usually a single link between point A and point B. But of course we may be sending many different types of data and many different streams of information between those two devices.
One way to get data between these two devices and be able to maintain these multiple streams is to do something called “multiplexing” and demultiplexing.” This is when we take multiple streams of information, we combine them together in some fashion so that we can send it across a single stream, and then on the other side we break it out into its multiple streams again. You’ll sometimes hear this multiplexing process referred to as “muxing.”
There are number of different ways to multiplex data together. There’s time division multiplexing, or TDM. We use this a lot on our ISDN and SONET networks. You have frequency division multiplexing, or FDM. That’s commonly used for things like radio signals. You have a single radio inside of your car, and it’s able to receive a lot of different stations because they’re being multiplexed over many different frequencies. And then you have wavelength division multiplexing, which we commonly see to use across wide area network and fiber connections, where we’re using different wavelengths of light to communicate.
Here’s an example of time-division multiplexing. You can see I have a blue, a red, and a purple network. I have a multiplexer on one end that’s going to combine all three of these channels into a single communication channel. And you can see it splitting up the usage of this network by time. I have a blue, a red, a purple, a blue, a red, and a purple. On the other end there is a demultiplexer, and it’s going to separate out the blues, the reds, and the purples back onto theur original networks.
We also use two different ways to send the data across these mediums. We have analog modulation and digital modulation. For analog modulation, we are simply sending an analog signal over this analog channel. This is very commonly seen for things like AM and FM radio communications.
We also can communicate via digital modulation. In this case, we’re sending a digital signal over what is originally an analog channel. You can see this in something like satellite radio communication, where you’re receiving a digital signal on your satellite radio, but it’s being sent over this wireless analog channel.
When you’re sending digital signals over an analog channel, you have to convert these from this digital wave that we have here with the ones, the zeros, and the ones, into something that can be sent over the analog medium. So we need sine waves to replace these ones and zeros and ones.
And you can see if we were to take a representation of that, one way to do it would be to have a tighter wavelength for one, one that’s a little bit longer for zero, and then back to the shorter wavelength for another one. So you can send this over the analog channel, you can receive it on the other side, and reinterpret those sine waves back into the ones and zeroes for the digital communication.