1. 8.0 Demystifying Wireless Networks
Our network is becoming increasingly congested as more smartphones, laptops, and other devices connect to the Internet of Things. We need to be super familiar with wireless LAN concepts, and that’s what we’re going to be doing in this module. Specifically, we’re going to be understanding how data is encoded wirelessly, what frequencies are available, and what’s offered by some of those different wireless standards that we can select from, for example, WiFi 6. What’s that all about? So let’s begin our wireless discussion by identifying some different types of antennas that we’re going to find on our wireless gear.
2. 8.1 Introduction to Wireless LANs (WLANs)
In this video, let’s take a look at some different types of wireless LANs that we might have. First up is an ad hoc wireless LAN. Now, this is not going to be a large enterprise solution. This is when we have two devices and they simply need to transfer data between themselves. At the moment, as an example, maybe you have something like an Apple iPhone and you’re doing an airdrop to someone. Well, that’s a basic example of an ad hoc wireless LAN.
We can use either Bluetooth or the AE800 and AE211 standards to do this ad hoc communication. And the big distinction here is that there’s nothing in between. We’re not connecting to an access point or any sort of wireless router. We’re just talking to each other for the occasional file transfer. What is more common is a wireless infrastructure. Here we have one or more access points, and our wireless clients can communicate with those access points. And that access point connects out to the wired network. Here we have an Ethernet switch. So the wireless clients go to the access point, which then sends their data out to the switch and out to the rest of the world. And again, we might have a single access point or we might have multiple access points. And if we do have multiple access points, one challenge we might have is that not every access point might be in close proximity to an Ethernet jack. How do we plug some of those access points into an Ethernet switch? A wireless mesh network would be a good solution. As long as the mesh access points are powered, they can relay data among themselves.
The wireless client is going to talk to one mesh access point, and without necessarily having an infrastructure connection, it can talk to a neighboring mesh access point, and it can just be relayed hop by hop until we get to our destination. Of course, one of these mesh access points must be connected to the wired network, or we will never be able to leave it. But we can have some access points that are simply mesh access points. They’re going to get to the wired network via another access point. And when we start to have multiple access points, the way we administer an access point might change in a home environment or a small office environment. We may have one or a few access points that we manage individually. If you want to extend your coverage area across the floor of a building, perhaps that’s where your company is located. You might have three different access points on that floor to give you complete coverage. And it’s common to administer those three or so access points individually.
In that approach, we’re talking about autonomous access points. We call them autonomous because they are independent of one another. In other words, the configuration of one does not impact the configuration of another. If we want to have the same wireless network name show up across this big floor of our building, we would go configure identical settings in each of these access points. And then as we roamed around that floor with our laptop or our smartphone, we would just rehome to the nearest access point, and it would be seamless to us as the user, but we would have to, as the administrator, do three separate configurations if we wanted to scale beyond about four or so access points. The recommendation is to use lightweight access points. with lightweight access points. We are not required to administer those APS individually. Instead, we have a single point of administration. It’s called a wireless LAN controller.
And that wireless LAN controller is going to reach out, and it’s going to configure all of the access points for us. So if I want to set up one or a few wireless networks instead of having to do an identical configuration on every single access point, I could just configure the wireless LAN controller once, and that configuration would then be pushed out to all of the access points. And there’s a protocol running behindthe scenes that does that communication.as well as in older wireless Lan controllers That protocol was the LWAPI Lightweight Access Point Protocol. But today, we’re more likely to find a Capwap, which stands for Control and Provisioning of Wireless Access Points. Again, these are protocols used to communicate between a wireless lane controller and the lightweight access points that it’s configuring.
3. 8.2 WLAN Antennas
in a wireless network. We have to have antennas to transmit and receive the radio waves that we’re using for communication between an access point and a wireless client. And in this video, we’re going to consider some different types and characteristics of wireless network antennas, ants. And one of the big things to understand about an antenna is its coverage area. Different antennas are going to be appropriate for different implementations. So let’s talk about that coverage area. What we’re going to be doing is representing the radiation pattern that’s the signal strength coming out from the antenna. We’re going to plot that on a graph. And we need to go beyond the traditional two-dimensional XY graph. We need to have a z-axis. We have to be in three dimensions.
In fact, picture a large beach ball, if you will, with a total spherical area. And if we were to take that beach ball and cut it in half, not top to bottom but left to right, Assuming the beach ball did not deflate, it would look something like this: We would have half a sphere at the bottom. And if we looked down on that cross-section of this sphere, we would be looking at what’s called the H plane, or the horizontal plane. So this is if we’re looking down on that antenna’s radiation pattern; what if we took a look at the side? Let’s imagine we took that beach ball that did not deflate when we cut it, and we cut it from top to bottom. In that case, we will be looking at a cross-section from the side view. This is called the E plane or the elevation plane.
And we can use what’s called a plot graph to represent the signal strength both for the H plane, where we’re looking down on the antenna, and the E plane, where we’re looking at the antenna from a side view. Let’s take a look at some sample plot graphs. First, consider an omnidirectional antenna. An omnidirectional antenna is designed to send approximately the same signal strength out in all directions. We’re not trying to interconnect buildings or go down a hallway. We’re just putting this omnidirectional antenna in the center of an area that needs coverage. And we’re trying to radiate out approximately equal signal strength in all directions in that spherical shape. And an example of that would be a dipole antenna.
These are common features on consumer-grade wireless routers that you might buy. And if you were looking down on the top of this antenna, each view you would have of the signal strength would kind of look like a circle. But if you were looking at the side, it would have some low signal strength at the top of the antenna and at the bottom of the antenna. In other words, those dipole antennas don’t do a great job of sending signals straight up or straight down. So what you’re left with is sort of a doughnut-shaped coverage area. That’s one example of an omnidirectional antenna. You might also see an access point mounted to the ceiling that looks something like this. This can include multiple Omnidirectional antennas to provide the spherical coverage area that an Omnidirectional antenna is supposed to provide. Again, Omnidirectional. We’re trying to send approximately equal signals in all directions. However, sometimes we want to focus our signal strength in a specific direction. For that, we can use a directional antenna.
And here we see a few different options. Now, a patch antenna is not extremely directional. We are focusing the signal strength in a general direction. It’s not spherical, but it’s not focused on one tight point. It’s sort of an area; for example, as we radiate it out from the patch antenna, we may be sending signal strength over maybe a 60- or 90-degree range. So it’s almost like a wedge of that sphere. It’s not really focused. A Yogi antenna is now extremely focused. This is going to be able to communicate between nearby buildings. As an example, you can point these Yogi antennas towards one another or a dish antenna.
We have this parabolic-shaped dish with the receiver and the transmitter on the opposite side of that parabola. And that’s going to be able to give us even more focused signal strength, allowing us to give COVID an even longer range. Let’s check out the plot of a directional antenna. Like a Yogi antenna, it might look something like this: We’re focusing our signal strength in one direction—down a hallway, for example. So we’re not going out in all directions. To summarize what we’ve discussed in this video, we said with antenna types. We have two basic types. We have omnidirectional technology, which will provide us with less gain in any one direction. We’re not focusing on our signal strength, but it’s going to be good for covering a larger area. We typically put one of these in the middle of an area that we want to give wireless coverage to. However, a directional antenna There we are going to be focusing our signal strength, giving us a higher gain in a particular direction. As an example, we could use that to connect buildings or a long corridor.
4. 8.3 Wireless Range Extenders
As the client moves further and further away from its access point, the signal strength between those two devices is going to drop. And in this case, let’s pretend that the client has wandered so far from its access point. When it sends a signal to the access point, it largely fades out before it ever gets there. We’re not going to have communication. So what we can do instead is install a wireless range extender. Here’s an example of a Linksys wireless range extender. We can plug it in an outlet, and it is going to receive the transmission from the client, regenerate it, and send that to the access point. That’s going to give that client a longer range from the access point because its signal is being repeated and therefore the range is being extended.
And some of these wireless range extenders also have one or more Ethernet ports, which is really convenient if I have a device that needs to be wired into the network. In other words, it doesn’t have a wireless network interface card, but we have no wired connections nearby. Maybe I have a printer as an example. That printer with an Ethernet port might be able to plug into the Ethernet port on that wireless range extender, giving that printer connectivity with the rest of the network.
5. 8.4 WLAN Frequencies and Channels
Wireless networks use frequencies in one of two bands. Primarily, those are the 2.4 GHz band and the 5 GHz band. And when you’re doing your configuration on your access points, you may be in different configuration modes, one for 2.4 GHz and one for 5 GHz. So I wanted you to be aware that these are the two ranges that exist. But also be aware that we’re not talking about all of the 5 GHz traffic operating at exactly 5 GHz. There’s a range of frequencies around 5, and there’s a range of frequencies around 2 and 4 GHz. It’s not just that specific frequency. First, let’s consider the two 4 GHz bands. Now, technically, we have 14 different channels, and for channels 1 through 13, we have 5 MHz between each channel. The exception is between channels 13 and 14, where there’s 12 MHz. By the way, Channel 14, you will probably never use it. If you use it, then two things are probably true. Number one, you’re in Japan. And number two, you’re using the very old ISO 800 and 211 B standards. So you’ll probably not be running into Channel 14. And we want to have nearby access points on different channels so they don’t interfere with one another. We call that having non-overlapping channels.
And a misconception is that if I put my access point on channel 1, you could put your access point on channel 2 to avoid that overlap. Well, that’s not the way it works. When we say we want non-overlapping channels, we have to realize that when we say, “I’m using channel one or channel five or whatever,” we’re actually centered on that channel. But the actual frequency range that I’m using spans 22 MHz. So if I say I’m using channel one, that’s going to extend a little bit above channel three. So we could not even have channels 1 and 3 active at one time without some interference. In fact, in order to maximize our no overlapping channels in the 2–4 GHz range, we want to have five channels of separation. As a result, channels 1, 6, and 11 are frequently used. Notice that these channels, which are spanned by the center channel of 1, 6, and 11, are not overlapping and are not interfering with one another. Now we could, if we were using channel 11b in Japan, have another channel of 14 that would not overlap, but it’s unlikely we’re going to have that. I just mentioned that for completion. So within my design, how do I have multiple access points to expand my coverage area while not overlapping?
Well, we just want to make sure that channel one is only bordered by channels six and eleven, and that channel six is only bordered by channels one and eleven, and that channel eleven is only bordered by one and six. Think of this honeycomb-style design. Let’s start with channel 1. We call the area in the middle a cell of coverage. Well, we do not want any neighboring cells of coverage to be using channel one to avoid that overlap. So maybe I put a cell using channel six above, a cell using channel eleven below, and then between channels one and six we’ll put channel eleven. So there’s no overlap between either one or six. And between one and eleven, we’ll put channel six there. So notice in this honeycomb-style pattern that the channel used by each cell is only bordered by cells using a different channel. And you could continue to expand this honeycomb design indefinitely. But with two 4 GHz bands, we need to be really careful not to have overlapping channels. The good news with 5 GHz is that we have much more elbow room. We have many more channels to select from. In fact, what I normally do is just tell my access point to listen to the radio waves and select the best channel.
And here is a screenshot of a wireless network analyzer I had running on my PC. And it’s showing the wireless environment; it’s showing what wireless networks are using and what channels. And you might think these channels seem to be spanning at quite a range. Well, if you notice in the lower right-hand corner, it says we have a channel width of 80 MHz. What we’ve done there to increase throughput is take four of the 20 MHz channels and logically bond them together. It’s called channel bonding. And as a result, instead of having a 20 MHz channel, I’ve got an 80 MHz channel, and that’s going to support more simultaneous communication. But to wrap up, we said that we have two primary frequency bands for wireless networks, the 2 GHz range and the 5 GHz range. And when we do our channel selection with the 2.4-gig range, we want to have five channels of separation. In addition, we frequently use channels 1, 6, and 11. But we don’t have to be quite so cautious with the 5 GHz channels because there are so many of them.
6. 8.5 WLAN Standards
In this video, we want to talk about some different WiFi standards. These are things you might look for when purchasing something like a wireless access point or a wireless lane controller, and they will give you a bit of a history lesson. In fact, let’s do that right now. Let’s go way back to 1997 and the original 811 standard for wireless networks. And this standard operated on the 2 and 4 GHz bands, not the 5 GHz band. It had a fairly limited throughput, with a maximum bandwidth of about one or two megabits per second. And the way ones and zeros were encoded was either using direct sequence spread spectrum (DSS) or the more secure frequency hopping spread spectrum (FHS). and we’ll discuss those a bit later in this video.
Then, a few years later, the 800 and 211 A were released, which only operated on the 5 GHz band and had a much higher throughput—54 megabits per second, in theory. And the transmission method, the method of encoding data, was OFDM (Orthogonal Frequency Division Multiplexing), which we’ll discuss in this video. In addition, in 1999, the then-popular 800 and 211 B standards were released; these only operated on the two 4 GHz bands. It had eleven gigabits per second throughput, and it used, just like the original 800 and 211 standards, direct sequence spread spectrum. A few years after that, 800 and 211 GHz were released in 2003, operating just on the two 4 GHz bands with a maximum throughput of 54 megabits per second. This is the first time that bandwidth has been achieved with the two 4-gig bands. Do you remember dot eleven A? It did 54 meg in the 5 GHz band. In addition, eleven to eleven g of DM orthogonal frequency division multiplexing was used. Then, quite a few years later, 800 and 211 N were introduced in two-nine. And here we could use either the two-gig band, the five-gig band, or both simultaneously.
And this had a throughput of 150 megabits per second. Again, using OFDN. In 2014, 800 and 211 AC were released operating on the 5 GHz band with a massive leap in throughput—three gigabits per second in theory—still using OFDM. We’ll talk in this video about how that dramatic leap in speed was possible. Then, in 2019, the 800 and 211Ax were released, which could use either the 2.4-gig band or the 5-gig band, or both. And it took another quantum leap in transmission speed—9,6 Gbps. And this is not a typo. This is actually OFDMA. Not OFDM. That stands for orthogonal frequency division. Multiple access. And we’ll discuss the magic behind the Eleven Ax Standard in this video. But let’s go way back in time. First, understand how direct-sequence spread spectrum works. With direct sequence spread spectrum, or DSSS, a frequency range of 22 MHz was used to communicate a binary one or a zero, and that binary one or a zero, technically, could be sent in only 2 MHz of bandwidth. That would use only 2 MHz to send a single bit. However, in order to do error detection and correction, eleven B, as an example, used something called Barker eleven encoding. That meant we transmitted one bit of data along with ten extra bits. Those extra bits that were there for error detection and correction were called chips.
Those were to help protect us against interference. And this series of eleven bits—that was called a symbol. But we had this entire 22 MHz channel sending a single binary one or zero. And as I mentioned, this was used in the older 11-B standard. And this is a direct sequence spread spectrum, meaning that we had a predictable carrier frequency for this data. We also saw a reference earlier in the video to frequency-hopping spread spectrum. The theory of operation was the same, except the carrier frequency would hop to something that would not be guessable by anybody trying to eavesdrop on us. So frequency hopping spreads the spectrum, which is a similar technology, but it adds an element of security by making the carrier frequency hop appear seemingly random to anyone attempting to eavesdrop but known to the sender and receiver. But as chip design developed over the years, we had less of a need for all of this. Error detection and wireless equipment started using a 20 MHz channel width. instead of using the 22 MHz that we talked about earlier. With 20 MHz, we could send ten individual binary ones or zeros, remembering that a binary one or zero could be communicated with a frequency width of just 2.
Technically, these are not overlapping subchannels that we’ve created where we can have ten different conversations going on here at any one time. However, these subchannels are right next to each other. There is going to be some interference. So to reduce that interference and allow these ten different streams of communication to occur simultaneously, a variant of frequency division multiplexing was used, and that’s called orthogonal frequency division multiplexing. Now, orthogonal is a concept you might remember from your high school math class. Orthogonal simply means at right angles to, or in other words, at 90 degrees to one another. So if you look at a plus sign, for example, that vertical line and the horizontal line are orthogonal to one another. You might remember from trigonometry, though, that the waveform that I have on screen right now is called a sine wave. And do you remember what a sine wave looked like? It was the same shape as a sine wave, except it was phase-shifted by 90 degrees. So here, the red line represents the cosine, and the blue line represents the sine. What have we done? We have made those two waveforms orthogonal to one another. They are 90 degrees apart.
What is the advantage of that? Take note whenever one of the waves peaks in either the positive or negative direction. The other wave is at zero signal strength. Check it out. At zero degrees, the cosine signal strength is at its maximum, but the sine signal strength is zero. And if you look at 90 degrees, the sine wave is at its peak transmission power, but the cosine wave is zero. And the same thing happens in the negative direction at the 180 and 270 degree marks. By making our adjacent channels orthogonal to one another by phase shifting them by 90 degrees, we can have them sit side by side in that 20 MHz channel width without interfering with one another. But let’s take this a step further. Instead of representing just a single binary one or a zero in that 2 MHz, what if we had a way of encoding more information? Imagine that we had a dartboard and that we had these 16 dots on the dartboard, and you took a dart and you threw it, and you hit one of those blue dots on the screen. And let’s say that if you hit that dot in the upper left, that represented four binary bits, 1011; if you hit the blue dot in the upper right, that would be the four binary bits of 0011.
Well, here’s the question. What if we took that 2 MHz channel width that we said could send a single bit? And what if we did something about that? What if we phase-shifted it a bit? What if we also adjusted its amplitude and signal strength? What we could do is logically throw a dart and hit one of these dots. Let’s say that we wanted a waveform to represent the binary bits of 1100. What we could do to that waveform is phase shift it 225 degrees and then reduce its amplitude to 25%. And that’s going to equal, and I’m showing you just a sampling here on the screen, but that would equal 1100 in binary. And to make it easy to see, we only have 16 dots here on the screen; we could have many more dots. And if we had lots more dots, that would mean we could represent more bits by hitting one dot. And once you have a lot of dots, it almost starts to look like a star field. And it’s literally called a constellation. In this way of encoding data, we adjust the phase and the amplitude of our waveform, and that’s called qualm. Now, if we have 16 dots on the screen, that’s called 16 quam.
We’ve identified 16 different targets. And how many binary bits does it take to give us 16 possible values? Four, because two raised to the power of four is 16. And something else we can do to increase the overall throughput of our wireless network is to take our 20 MHz channels and logically group them together. If I took two of these 20 MHz channels and bonded them together, that would give us a 40 MHz channel, allowing more simultaneous communication. Because when we bond together two of these 20 MHz channels, instead of having ten subchannels, we now have 20 subchannels, so we can have more simultaneous communication, and some standards allow us to bond together four of these 20 MHz channels, which will give us an 80 MHz channel. And some standards even allow us to bond eight of these 20 MHz channels for a whopping 160 MHz channel width. And by bonding these channels together and using quadrature amplitude modulation with more dots, that’s one of the main ways that throughput is being increased in these more recent wireless standards. As an example, just taking three of the recent wireless standards into account—800 and 211 N use a 64-bit quantum—and two raised to the power of six is 64.
So if we hit one of those dots by adjusting the phase and the amplitude, that one waveform suddenly represents six bits. And we have the option of bonding together a couple of the 20 MHz channels into a 40 MHz channel. With 800 and 211 AC, we have 256 quantum bits. That’s how many dots we have in that constellation. And that’s going to give us eight bits with a single waveform hitting one of those dots. And some equipment will allow you to bond together 820 megahertz channels, giving us a 160 MHz channel. And, with the more recent 800 and 211 ax, we can adjust the phase and amplitude of the waveform, allowing us to hit one of those 1024 dots on our metaphorical dartboard. Once we do that, that dot represents ten bits. We could bond together as many as 820 megahertz channels, giving us an effective channel width of 160 MHz, thanks to two raised to the power of 1024 and 11 AC. Something else that we can do with more recent standards is something called beam forming.
This is where we can focus our transmission going to a client such that the signal strength is actually pointing towards that client. Here’s how that works: It uses a combination of constructive and destructive interference. Consider this waveform. If I had an identical waveform and overlaid it on top of the original waveform, those two waveforms would add to one another at each point along that waveform, giving us a resulting waveform that was larger in amplitude. That’s called constructive interference. However, if I had a waveform and played another waveform that was 180 degrees out of phase with that original waveform and wedded those two waveforms together, that would give me approximately nothing, a line of zero. In fact, that’s how noise-canceling headphones and earbuds work. They have one or more microphones that listen to background ambient noise, and they play that background noise into your ear, shifted 180 degrees, so that it cancels out a lot of that background noise. And by using this combination of constructive and destructive interference, we can focus our transmission going to a client on just going towards that client and not waste signal strength going somewhere else.
And this was the technology originally introduced in 8211 in.Of course, we see it in both AC and axe. And, because this technology was introduced in 11, we can expect 11-n access points to have multiple antennas. However, those antennas can only talk to one station at a time. That’s something called single-user MIMO, which stands for single-user multiple input and multiple output. That means we can only have one spatial stream at a time. So if this access point on screen wants to talk to both wireless clients, it’s going to have to send a stream to the top wireless client first, and then it’s going to send a stream to the bottom wireless client. But as of the second generation of eleven AC, some people call that “wave two” of eleven AC. We now have something called “mumimo mu MIMO.” That stands for “multi-user, multiple input, multiple output.” This can allow us to have multiple spatial streams. We might have two spatial streams; we might have three; we might have four. With this second wave of eleven AC So now if I have two spatial streams and this access point wants to communicate with both wireless clients, it can do so at the same time.
That’s going to give us a lot more throughput. Now let’s do a side-by-side comparison of the different spatial streams supported by our different standards. Specifically, with 11n, that’s really not mu MIMO. That’s sumimo; we have a single spatial stream going downstream. To put it another way, from the access point to the end client. With eleven AC, specifically wave two of eleven AC, we can support four spatial streams. This access point can communicate simultaneously with four clients. However, only one client at a time can communicate with the access point. However, as of November 8, we have a large number of spatial streams. Specifically, with the two 4 GHz bands, we have four spatial streams. But it’s not just downstream; it’s upstream and downstream.
That means that for the two 4-gig bands, we can have up to four clients sending data to the access point at the same time. Or the access point could be communicating out to four stations. With the five gigabands, we’ve got eight spatial streams, and again, we’re talking both upstream and downstream. The ability to do multiple upstream spatial streams—that’s a game changer. We did not have that in previous versions. So if you look at this, we’ve got a total of twelve spatial streams with eleven axes. That’s one of the things that allows us to get that incredible throughput. But the question is, how can I have multiple streams coming into the access point? Because prior to 11.x, the access point worked basically like an Ethernet hub. In other words, only one station could be transmitted at any one time. And what makes that possible is something called OFDM, which stands for orthogonal frequency division multiple access.
That’s used by Eleven Ax but not by any of the previous wireless standards. In the literature, Eleven Ax is frequently referred to as WiFi Six. And the way this is possible is that instead of essentially acting like an Ethernet hub where only one device is allowed to transmit at any one time, with OFDMA used by WiFi 6, we give our clients a window in which they are allowed to communicate. It’s called a target wait time. Specifically, an access point tells a client that it’s going to be your turn to transmit at this point in time. And that way we don’t have clients simultaneously trying to transmit and having collisions, making the other one wait. No, they have their own slice of time where they can transmit. So there’s no contention. In fact, even though it’s for a very brief time, since a client knows that it’s not going to be its time to transmit, maybe for a few milliseconds, it can actually power down its wireless card to a low-power state ever so briefly. But over time, that saves power. And that’s one of the ways that we get such incredible throughput with the 800 and 211 AX, or WiFi Six. Another really cool feature with Eleven Axis is something called BSS coloring. BSS, that’s “basic service set.” What that means is if you’re in a very populated area with multiple access points servicing different wireless networks, like an apartment building, for example, you have people that live in apartments next to one another.
They each have their own access point; they’ve setup their own wireless network, but they might be using the same channels, and if they’re using the same channels, those could interfere with one another. Remember our desire to have no overlapping channels, but with BSS coloring, WiFi Six is able to identify that a particular waveform is associated with this specific SSID. That’s a service set identifier; that’s the name of a wireless network. That way, even though I have this interfering communication, I know I can ignore that interfering communication because it is not colored. In other words, it is not encoded in the header as being part of the wireless network to which I belong. And that’s a look at some of the different WiFi standards out there. By the way, when we say WiFi, we mean an alliance that can certify wireless equipment to operate according to certain specifications. So when we talk about WiFi, we’re really talking about an alliance that certifies equipment. But those are some of the WiFi standards, both old and new, that we might encounter.
7. 8.6 Regulatory Impacts of Wireless Channels
When we’re designing wireless networks, it’s important to understand that not every channel is going to be allowed in every country. And that’s the purpose of this video. This is more of a reference; you don’t have to remember everything we’re going to show you in this video. But this serves more as a reference for what channels are allowed with.Let’s start with three different standards bodies. And if your country is not included in this listing, you want to check with your country’s standards body.
But in North America, it’s the FCC, the Federal Communications Commission, that dictates what we can use different frequencies for. In Japan, you might see it abbreviated as MKK, and you see what MKK stands for on screen. But in English, we typically refer to that as radio equipment. Inspection, accreditation, and institute And in Europe, it’s the ETSI. The European Telecommunications Standards Institute Now let’s consider the 14 different channels we have under the two 4 GHz bands. And again, this is a reference; although this would be fairly easy to remember, in North America, according to the FCC, we should not use channels 1213 or 14. We should only be using channels one through eleven. Channels 1 through 13 are available in Japan, with one notable exception: channel 14. And that’s if we’re using 8211 B. But that’s sort of a legacy standard these days. We’re probably not going to be using those, especially in the new network designs. In Europe, we are permitted to use channels 1 through 13, but not channel 14. And we have many more channels when it comes to the 5 GHz band. Let’s take a look at those channels. And one thing that might seem curious is that we don’t seem to be going sequentially in increments of one. It looks like we’re jumping from channel 36 to channel 40, and then we’re jumping from channel 40 to 44. Those are actually sequential channels. We’re not skipping any. They’re just not numbered in increments of one.
And I certainly wouldn’t expect you to memorise all of this. Again, this is a reference. But I want you to understand that these different standards bodies we talked about for Japan, Europe, and North America say that some channels are allowed, some are not, and some are allowed under certain conditions. Maybe we’re indoors, or maybe we’re reusing DFS, TPC, or SRD. What are those things? Well, first consider DFS (dynamic frequency selection). There are some channels that are typically used for radar, but we can use many of those channels for our WiFi networks. It’s important to check, however, to make sure that those channels are not currently being used by radar in your area, such that the radar might cause interference. That’s going to open up some channels for us. TPC stands for transmit power control. That’s a WiFi feature that lets us reduce the power of channels to minimise interference with other channels. and the SRD short-range device. That’s a device that’s probably not going to interfere with other devices because it has very low power when it transmits. The maximum signal strength is 25 milliwatts, so we’re probably not going to be getting a lot of interference there. So, once again, our difference here is a comprehensive listing of what three standards bodies say about different channels in both the 2.4 and 5 GHz bands.