Network Fundamentals – CompTIA Network+ N10-006 – 5.2

| May 12, 2015


Most of our modern networks use some fundamental technologies to operate. In this video, you’ll learn about encapsulation, decapsulation, baseband, broadband, baud rate, bit rate, and wavelength.
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One of the key concepts of networking is this idea of encapsulation and decapsulation of your application data.

Here’s how this works. I’ve got a summary of the different communication layers at the left, there’s an application layer, a transport layer, an internet layer, and a link layer. And if you’re familiar with the TCP/IP model, that corresponds directly back to that model. Well, obviously, we’re trying to get data from your device and your applications, out to the network and to another device.

So we start with the application data, but that can’t go over the network by itself. As we send it down to the transport layer, the transport layer adds its own header on to this, it encapsulates your application data within a TCP header. So we can see the header at the beginning, and there’s your application data that’s still there. But we’re not done with the encapsulation process, because we have to go to the internet layer, where an IP header is now added. So we’ve now encapsulated this into IP header information. And now, we have, at the bottom, a link layer that needs to put link information on to this, and it encapsulates a frame header and a frame trailer and now is able to send all of this information across the network.

So if we expand out this process and look at it from both sides of the conversation, we have application data that starts on the source device, and we begin encapsulating it within the header information for transport, internet, and link. It is sent now, across the network to the other side. And now, the decapsulation process occurs. We remove the frame information at the internet layer. As we move up, we get rid of the IP header. And then, finally, our application removes the TCP header, and it’s now left with the original data, and now it can perform whatever task is required by that application.

When we talk about how we send traffic across a network, we’re really putting the categorizations into either a baseband network or a broadband network. A baseband network is usually a single cable, you’re sending a digital signal across this link. It can be copper or it can be fiber, because we’re really talking about the method of communicating over that medium.

On a baseband network, whenever we send signal out over that wire, or over that fiber, we are consuming 100% of the available bandwidth on that particular medium. And when you think about it, that is the utilization on our networks. It’s usually 0% or it’s usually 100%. And on baseband, if you send any signal, you are using all of the available bandwidth.

Just because you have a single wire whenever you communicate, you’re using all of the bandwidth, doesn’t mean that this is a one way path. You can have bi-directional communication over a baseband network, just not at the same time. The devices have to wait for everyone to finish talking before they are able to communicate over this medium. This is a very standardized way of communicating. If you’re using ethernet, whether it’s 100 megabit, a gigabit, or different formats of ethernet, you are using baseband communications to send that data.

On a broadband network, we’re not just sending a single signal over this link, we are sending many different signals over this connection, all running at different frequencies. That means that we can have different traffic types, or different communication channels, all occurring across the same medium at the same time. And again, the type of medium doesn’t matter. This could be a copper connection or a fiber connection.

The key with broadband is that each individual communication channel is just using part of the frequency available on that particular medium. That means that you can have many different communications going over this link simultaneously, and even in different directions over this link as well. Unlike baseband, on a broadband network you can have bi-directional communication, because one frequency may be sending traffic, and you may be receiving traffic on a completely different frequency.

A good example of a broadband connection is our cable modem and cable internet connectivity. We’re receiving television signals, our internet signals, voice over IP, all simultaneously over this very robust broadband network.

When you start working with networks, you become very accustomed to talking about how many bits per second, when you refer to speeds or bandwidth. But if you work a lot with modems, you’ll also see there’s a measurement standard called baud rate, which stands for bits of audio data. This is almost always seen with modems, and it’s referring to the communication of how many symbols you can move across the network at any particular time. The baud rate then would be the number of times that this signal rate changes during a particular time frame.

Because of the way the signaling works over these modem connections, a single symbol may represent a number of different bits. The number of bits that are traversing the link then would be the bit rate. If we had to extrapolate this into something that might be easier to understand, we can look at something like a train. As we see the different train carriages passing by, we can refer to that as the baud rate. But inside each carriage may be a number of people, and those may be the bits that are being communicated by those symbols, and the number of total passengers then would be the total bit rate for that connection.

We often discuss wavelength when we’re talking about are wired and our wireless networks. A wavelength is the length where the sine wave is repeating. So when you start to see a repeat, that is the length of that particular wave going through that medium. As the frequencies get higher, the wavelengths get shorter. So a 2.4 gigahertz wireless network will have wavelengths that are approximately 12 centimeters in length. And the reason this is important is that we need to have antennas that are properly tuned to send and receive this exact wavelength size.

When we start talking about sending light over fiber, we’re talking about extremely small wavelengths. For example, over a multi-mode fiber that’s using LEDs, you have 850 nanometers and 1,300 nanometers. To give you an idea, nanometer is one billionth of a meter. So that is a very small wavelength. Over single mode fiber, you can go all the way up to 1,550 nanometers. So the differences between a wireless network and one that’s communicating over light are very different when you look at the size of the wavelengths.

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Category: CompTIA Network+ N10-006

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