We use many different technologies on our wireless networks. In this video, you’ll learn about frequencies, channel bandwidths, service sets, MIMO, and more.
When working with 802.11 wireless networks, you’ll see a lot of different technologies being thrown around. So let’s step through what some of these are and get a better understanding of their definitions.
Let’s start with the frequencies that are in use. You commonly see 802.11 networks operating at either 2.4 gigahertz or 5 gigahertz. And sometimes, both of those are able to be used on the same access point. On some very specific occasions, some of these standards even support communication over additional frequencies, although that’s certainly not something that you would commonly see.
Instead of using the specific frequency in the 2.4- or 5-gigahertz range, we tend to refer to these sections of frequencies used by our wireless networks as channels. These frequency groups are numbered and assigned by the IEEE. So if you’re using a 2.4-gigahertz network and you’re referring to channel 6, then it’s always going to be the same channel 6 across all IEEE 802.11 2.4-gigahertz devices.
Some of these channels overlap with each other. And that’s why we’ll often say that it’s best if we can use frequencies on multiple access points that do not overlap or conflict with each other.
These ranges of frequencies that we are able to use are dependent on the channel width. This is sometimes referred to as the bandwidth or the amount of frequency that would be in use. On 802.11 networks, you often see a 20-megahertz, 40-megahertz, 80-megahertz, and 160-megahertz bandwidths.
Here’s what we mean when we talk about the bandwidths and the number of frequencies available in the 2.4-gigahertz range and 5-gigahertz range. Let’s talk specifically about the 2.4-gigahertz spectrum that’s being used by our 802.11 networks.
There are three non-overlapping channels available in North America– channel 1, channel 6, and channel 11. They are grouped in 20-megahertz blocks. If you’re using non-overlapping channels, there are three separate 20-megahertz blocks. And they’re in the 2.4-gigahertz range between 2,412 megahertz through 2,482 megahertz.
When we introduced the 5-gigahertz range, we also introduced a large number of available frequencies. Everything here that is not the red color is available for use in 802.11. And you can see there are many more frequencies available in the 5-gigahertz range, certainly more than the three 20-megahertz non-overlapping groups that we might have in 2.4 gigahertz.
Not only are we using these 20-megahertz channels, but some of these wireless standards allow us to use larger bandwidths, such as the 40-megahertz bandwidth. And we’re using a lot more of the available frequencies when we increase the total amount of bandwidth.
We also have some standards that support 80-megahertz bandwidths– you can see the different channels and frequencies available for those– and, finally, the very large 160-megahertz bandwidths. And when you get that large, you can see there are only two contiguous 160-megahertz channels available on the 5-gigahertz spectrum.
802.11a, 802.11b, and 802.11g used channel bandwidths that were around 20 megahertz, 20 megahertz for a, 22 for b, and 20 megahertz for 802.11g. When we introduced 802.11n, we also increased our options for the amount of bandwidth that we could use. For example, we could use 20-megahertz, 40-megahertz, or 80-megahertz channel widths.
Some of these channel widths are, obviously, only available if you’re using the 5-gigahertz frequencies. For example, we don’t have 80 megahertz of frequencies available on the 2.4-gigahertz range. We would have to use 5 gigahertz to support that larger bandwidth.
802.11ac also uses 20-, 40-, and 80-megahertz channel bandwidths, but also allows us to bond together two separate 80-megahertz bandwidths that are not contiguous. And we can, of course, use one single, contiguous 160-megahertz bandwidth in the 5-gigahertz range.
If you’re using the backwards compatibility of 802.11ac to connect 802.11n stations, then you only need 40 megahertz of a channel bandwidth. But a native 802.11ac device needs at least 80 megahertz of bandwidth as part of the standard.
Increasing that channel bandwidth up to 160 megahertz is optional whether you’re bonding together two separate 80-megahertz channels or using one contiguous 160-megahertz channel.
And in 802.11x, that standard uses exactly the same channel bandwidths as 802.11ac– has 20-megahertz, 40-megahertz, 80-megahertz, two bonded 80-megahertz channels, or a single 160-megahertz channel.
In many conversations about 802.11, you’ll often talk about an access point or wireless router or some other piece of infrastructure device that sits in the middle of the communication. But 802.11 also supports the ability for two stations to communicate directly to each other without using any type of access point. This is an Independent Basic Service Set, or IBSS, using this ad hoc or direct communication between two devices.
Ad hoc means that we’re creating this connection for a particular purpose, and we didn’t have to plan out or implement some type of access point to make that communication occur. This ad hoc communication could be a permanent communication if only these two devices were on a particular network and there was no need to have an access point. But we can also use ad hoc communications on a temporary basis to configure a separate device and allow it to connect to a wireless network that did have an access point.
We would connect to this device over an ad hoc connection. We would assign it the proper configuration for the access points in our area. And then we would reboot that device. And it would then connect to a wireless network over an access point.
When you’re connecting to a wireless network, you’ll notice there’s usually a name that’s listed in the operating system. This could be a network such as SGC1 or Guest. That wireless name is referred to as an SSID, or a Service Set Identifier. We often just refer to that as the wireless network name.
If you’re in a larger organization, though, you’ll notice that wherever you happen to go in whatever building you’re visiting– that the wireless networks are all named the same. Obviously, there’s not a single access point supporting all of those different buildings. There are multiple access points. They all have the same SSID name. But they have a different BSSID, or Basic Service Set Identifier. You can think of this as the physical address or the media access control address of this wireless access point.
So when you’re connecting to this wireless network, you’re commonly just using the SSID. But behind the scenes, you’re actually connecting to this MAC address, or BSSID, of the access point.
As we mentioned earlier, most organizations have more than just a single access point for an SSID. In many cases, they might have tens or even hundreds of access points that are spread across many different parts of the organization. This is why we commonly use a wireless name to connect to the wireless network rather than using the MAC address of this access point. And by using the wireless name, it makes it much easier for us to move from access point to access point as we’re walking through the building.
When we share a network name across multiple access points, we refer to that as an ESSID, or Extended Service Set Identifier. If you connect to the ESSID on one end of the building and you begin walking through the building, you may find yourself roaming, or automatically switching, from one access point to the other. This all happens behind the scenes. You have no idea that the switching is taking place. All you know is that you’re always connected to an access point that’s able to provide you with connectivity.
Here’s a very simple design of an ESSID in action. We have a network switch here at the top. And this network switch is connecting to two different access points. You can see those access points have very different BSSIDs, very different MAC addresses associated with those.
Although these two access points are two separate physical devices, they both share the same SSID. Both of these are on the SGC1 wireless network. And there are devices in both of these areas of the building that are communicating to whatever access point may be local to them.
If you’re in the building with your mobile device connected to one access point and then you walk to the other end of the building, you’ll find that you no longer have connectivity to the original access point. But there is an access point closer to you that has the same SSID. So behind the scenes, your device will automatically connect to this access point because it has exactly the same configuration as the ESSID that you originally connected to.
Many of us might even do this in our homes, where we have an access point on one end of the house and another access point on the other end of the house. We can configure the SSID and security information to be identical between those. And wherever we happen to go, our device will automatically roam properly to the access point that’s closest to them.
In a previous video, we talked about the 802.11n, 802.11ac, and 802.11ax standards as supporting multi-user MIMO. This allows us to send multiple streams of information over the same frequency at the same time. In 802.11n, we support very simple MIMO, or Multiple-Input, Multiple-Output. In 802.11ac, we support a downstream version of multi-user MIMO. And in 802.11ax, we support both downstream and upstream multi-user MIMO.
To be able to send and receive information simultaneously, we need to have the proper number of antennas and support the proper number of streams. If you’re looking at a wireless device, you may see that it supports 2 by 2:2 or 4 by 4:4. The first number refers to the number of antennas on the access point. We put an x. And then we refer to the number of antennas on the client. And then after the colon are the total number of streams supported for that device.
For example, you can have two antennas on the access point, two antennas on the client, and a total support of two streams for that particular access point. There might be three antennas on the access point and three antennas on the client, but that device may only support two separate multi-user MIMO streams, or you may have a larger device that has four antennas on the access point. You might have a client that has four antennas on the client, and you’re able to support four separate streams on that access point.
This multi-user MIMO is an important addition to the 802.11 standard. Before 802.11n, we would have one access point and a single device at the end. And we were able to send information from one device to the other without any type of multi-user capability.
MIMO works completely differently. We can send information between devices using multiple antennas. The data is bounced off of the other devices that may be nearby, but eventually make their way to the antennas that are in the receiving device. And that data is reconstructed using advanced digital signal processing.
When we introduced MIMO, we were able to send a lot more traffic between two devices at the same time, multiple streams of traffic using Multiple-Input, Multiple-Output. So we might have an access point that could send a large amount of information to a laptop. Then it could send a large amount of information to a mobile phone. And then it might send a large amount of information to a streaming device. And as the devices needed more data, it was able to send all of that data using Multiple-Input, Multiple-Output.
When we introduced multi-user MIMO, we were able to split those streams up so that we could send information at the appropriate rate, depending on what type of data was required. For example, an access point that supports multi-user MIMO might have two streams that are constantly communicating to a laptop, a single stream that is communicating to a mobile phone, and another stream that’s communicating to a streaming device, like a television. All of these can be operating at the same time with the multi-user capability. And it’s taking advantage of Multiple-Input, Multiple-Output.
The multi-user MIMO that’s in 802.11ac can also send different amounts of traffic in each one of these streams. A mobile phone, for example, doesn’t need as much data as a laptop may require. But with 802.11ac and the multi-user MIMO, an entire stream of traffic is required to send data to a mobile phone even though that mobile phone may not require all of that bandwidth.
To more intelligently send data over these multi-user MIMO networks, we can use 802.11ax, which introduces OFDMA, the Orthogonal Frequency Division Multiple Access. Here we can send multiple streams of data. But we can break those streams into smaller pieces and send only the data required for the individual devices.
If the laptop needs more bandwidth, we can send this fractional data within the streams to provide that information to the laptop or, at the same time, provide data for the mobile phone and the television. This means that the end stations can receive exactly the right amount of data and efficiently use the wireless frequencies to be able to support that. This also means that we can have many more users communicating at the same time on the same 802.11n wireless network, supporting larger densities of users from a single access point.
If you look at the antennas that are included on traditional access points, these are omnidirectional antennas. They’re very common, something you’ll find when you purchase an access point off the shelf. And the signal is distributed evenly on all sides of the antenna. That’s where we get the “omni” from omnidirectional.
This is a good choice when you’re putting the access point in the middle of the building and you want it to have the same coverage all the way around the access point evenly. Unfortunately, this doesn’t give you a lot of options for focusing the signal. So if you want to have a very directed 802.11 signal, you want to use a different type of antenna.
A directional antenna allows you to focus that signal. And it’s commonly used when you need to extend this 802.11 wireless network over a longer distance. You can send and receive data over this single connection. And it’s common to see these directional antennas used between buildings, for example.
This antenna performance is usually rated as a number of decibels. If you double the performance, you can increase the decibels of the signal that you’re sending or receiving. And using those measurements, if you increase the signal strength by 3 decibels, you’re effectively doubling the power of that signal.
Yagi antennas are very common. They don’t take up much room. They’re able to send information very directionally and usually give you a very high gain.
If you’re sending information over a much longer distance, you may want to use a parabolic antenna, which has a bit higher gain and focuses the signal to a single point. The signal would be bounced off of the parabola and bounced into the feed horn that’s in the front, allowing you to focus that signal and get much better gain.