Wireless Review

Wireless and the OSI model

When it comes to the OSI model we have different layers. The first layer is the physical layer, the second layer is our data link layer, and the third layer is the network layer. I'm not going to worry about the other layers that we have — the seven different layers — but for the most part, when we're talking about wireless, we live here in layer one and two. Wireless lives in layer one and two.

Layer two is split up into two different sub layers, and one of the reasons why is because protocols such as Ethernet and wireless operate within those two layers, but not all of layer two. So that's what the reasoning is for that. The LLC sub layer is defined by IEEE 802.2. We see that Ethernet is defined by 802.3, and we see wireless networks that are defined by IEEE 802 — and specifically the things that define a wireless LAN are defined by 802.11. There's a lot of different ones: a, b, c, d, e, f, and then we get into this AC. That's not A and C, that is AC. There's a lot, and the list keeps growing — they keep continuing to add to this. So these are the protocols that define this wireless LAN.

Frequency

I won't get in depth into the physics between electromagnetic fields and how they operate; that's pretty in-depth stuff. I do cover that real briefly in my network fundamentals course, but for the purpose of this we're going to jump straight into frequency.

Frequency starts out really low. Here we have these extremely low, very low frequencies, and here we have 50 hertz right here — that means that frequency is cycling 50 times per second. This one right here, one million times per second. 500 million times per second. One billion times per second. So we've got these different frequencies within here.

Now what they've done is they've said, we're going to allocate certain frequencies for certain purposes, because these frequencies will interfere with each other. What they don't want is — there's some communication out there they don't want disrupted, so things like major satellites and some government communication that's happening. They want to specify these channels right here can only be used for these purposes. So they've defined what different frequencies can be used for these different purposes.

You've got radio transmissions, and within some of these are licensed bands, where if you want to start a radio tower and want to start a radio program, start a radio channel, you can't just go out there and start broadcasting at really strong levels to put your channel out there. You actually have to go and license that channel, and you are licensed for a certain strength of signal that goes out, so that will only go a certain distance out.

The key is, when we see 2.4 gigahertz and 5 gigahertz frequencies, the reason why we see that a lot is because those frequencies are the unlicensed band. It's what they have opened up and said anybody can use — you can create equipment in these bands. So when wireless phones came out, the wireless phones used those bands. Microwaves will use the 2.4 gigahertz frequencies, and one thing that's been added to that is these wireless access points, or wireless LANs, use that 2.4 and 5 gigahertz frequencies.

There are other amazing bands, but some of them are too low — the frequency is too low, and that low frequency doesn't allow us to have a lot of data go across it. And then if you get too high with those frequencies, then it doesn't penetrate walls very well. Essentially that is the reason why wireless LANs use 2.4 and 5 gigahertz frequencies: it is an unlicensed band, and it allows the amount of data and facilitates being able to penetrate walls and that type of stuff.

But for that reason, because they're unlicensed, sometimes there are things that step on each other's toes. You start up your microwave — this used to happen more — and it would send out these 2.4 gigahertz frequencies that would interrupt wireless communication. So if you were talking on one of those old cordless phones and somebody started up the microwave, it caused some problems. So that is the frequencies, and that's why we use 2.4 and 5 gigahertz.

Conveying information across a frequency

Somehow we have to convey information across these electromagnetic fields, and we have a couple of ways we can do that. One is we can adjust the amplitude. This is an example of adjusting the amplitude of that frequency. If you notice, the frequency doesn't change — the cycles per second stay the same this whole time — and what does change is the amplitude, or the volume, of these waves that are being sent out. So that's one way that we can convey information.

The other way is we can change the actual frequency. This is where you see that the frequency actually goes up right through here — we have a higher frequency through here — and then it goes back to a lower frequency. Essentially what this will do is, this has what we call channels that it operates within, and it will vary that frequency within there to send that data across and to transmit these ones and zeros. That's essentially what we're trying to do with it, right — it's to transmit the ones and zeros, the bits that go between the computers.

Frequency modulation is where a lot of our communication happens. If you've listened to an AM radio station versus an FM radio station, there are some limitations that AM has that FM doesn't, that FM compensates for. So when we transfer data, a lot of times we like to do that through FM signals, or frequency modulation.

Channels

Here we've got that 2.4 gigahertz frequency range, and it's not just exactly 2.4 — it's a whole range that we have within that 2.4 that we have to work with. But we have to carve out a whole channel, what we call the channel, in order to be able to communicate, because we're varying the frequency to send those little ones and zeros. So that's what you see right here: 2.412 is devoted to that first channel right there, but that channel has a range to it.

The 2.4 gigahertz frequency, depending on what country you're in, will have one to maybe 11, possibly up to 14 different frequencies that it can communicate across. But the problem with these is these channels actually overlap. You can see that two overlaps with one and three overlaps with one, and so now we cause problems here. We don't find channels that don't overlap until we get to this 1, 6 and 11, or 2, 7 and 12, or 3, 8 and 13. Many countries don't have these last ones on here, so 1, 6 and 11 are typically the frequencies that we will work with when it comes to wireless LANs, and we only have three.

Now this is not a problem if you don't have a lot of wireless networks all in one little area, but what will happen is they will start stepping on each other's toes if they have to use the same channels.

So here's an example of a headquarters office that maybe I want to set up a wireless LAN on. We're going to set up an AP — maybe the AP is right about this location — and this is the broadcast area that gets sent out from that one location. Maybe I set up another one right here, and this is the broadcast that's sent out from that area. It's going to have a certain distance that it's going to go out, and the distance that it goes out is going to depend on the power that we have each one of those set to.

So the problem with that is, if I have channel one assigned here, and this one would be, let's say, six, and this one right here would be 11. Now I have this one right here that I can't assign to one because it overlaps one, or six because it overlaps six, or eleven because it overlaps that — so it overlaps all of these. So I've got to choose something. Well, in this case right here it only overlaps the six just a little bit, so maybe I can get away with doing the six right there, and then this one right here I can go back to one right there. You can see that if I were to get any more into here it would cause some serious problems with this network, and so we have to really plan this out.

2.4 gigahertz versus 5 gigahertz

That's more of an issue with the 2.4 gigahertz, and the 5 gigahertz range opens up and we have much more channels, so it gives us a few more options with that. There are other advantages as well.

So the 2.4 gigahertz range has too many overlapping channels; the 5 gigahertz range opens that up so we have a lot more options. But there are some other differences between these as well. The 2.4 gigahertz range is a longer wavelength, and those longer wavelengths are associated with lower frequencies. The longer wavelengths will penetrate objects better. What I mean by that is it will go through walls better, it will go longer distances, the signal won't deteriorate as much. So when you're dealing with 2.4 gigahertz it's nice if you have any kind of distance, or if you're penetrating a lot of walls and there's a lot of objects and stuff, then it's to advantage to use the 2.4. So there's a larger coverage area, less susceptible to obstructions. One of the problems though is it's a crowded space; there's a lot of things that will use this 2.4 gigahertz frequency.

So we prefer to use a 5 gigahertz frequency. It has higher data rates — we can send more data across the 5 gigahertz signal than we can at 2.4 — and this says less, but it's actually more susceptible to interference. So that's one of the disadvantages: it doesn't go as far, and there are things that will obstruct the signal.

So really an ideal would be a combination of both 2.4 and 5 gigahertz frequency, which is why we still have a lot of this 2.4 gigahertz frequency. Some of the older equipment doesn't even have a 2.4 gigahertz frequency radio inside of it, or a few things that are the IoT items that you have out there don't have a 5 gigahertz, so they only have a 2.4. So a lot of times you still have to support this 2.4 gigahertz on your networks even though 5 gigahertz is really the ideal on them.

SSID and CSMA/CA

We have this thing we call SSID, or service set identifier. What a service set identifier is, is that is the wireless LAN that you're defining with this. So this possibly is getting broadcasted out; it will broadcast an SSID so that way these computers know what they're actually trying to connect to. So SSID is service set identifier — that is the name of the wireless LAN that you're connecting to.

CSMA is carrier sense multiple access. The multiple access, because you have a lot of devices that are connecting onto this wireless LAN. The carrier sense is because before they connect they're going to sense to see if somebody else is speaking, if somebody else is talking. So carrier sense multiple access is a mechanism designed for multiple devices to be able to communicate on a network that's shared. The key point to this is it's shared, meaning that if this laptop communicates and this laptop is communicating at the same time, that is going to be a problem. If they're communicating at the same time, those frequencies cancel each other out or interfere with each other, and then the signal gets disrupted, and then you don't have communication happening — the wireless access point here is just hearing some problematic, or some garbled, messages. So what this computer will do before it tries to communicate is it will listen. So the carrier sense is just listen: am I hearing anything, can I communicate at this time, before it even tries to communicate.

Then we have this thing called collision avoidance. There is collision detection, which is what our Ethernet uses, and collision avoidance. The collision detection is just computers are going to try to talk and they're going to just say what they need to say, and if it causes a problem then they'll back off. There's this backoff algorithm that happens, and they wait for a random period of time and then they'll try communicating again. The problem with wireless is that it's a little more sensitive, and so this collision avoidance is each of the machines will just say, hey, can I speak, am I allowed to speak, and they'll just kind of slip it in there. It's a small little just "hey, can I speak", and then they will get permission to speak if they can speak.

One of the problems with this is that as this computer is speaking and this computer is listening — that carrier sense — this computer may be too far away and not hear that, which is one of the importances of this collision avoidance. This asking to speak is because this computer then can just ask, hey, am I allowed to speak, is this a good time to speak, so that way it tries not to step on the toes of any other devices that are speaking at that time. So that's carrier sense multiple access collision avoidance.

Security

Since everybody's speaking all at the same time, or can speak, all the other devices — or many other devices at least — can hear what is being said. That is the importance of security.

In its nature, wireless communication is out in the open, and anyone can pick up those signals and be able to listen in on a conversation. That is why it's so important to create security on your network — and not just from an authentication standpoint, are you allowed to be on my network or not. No, you have to actually encrypt the data. It's really important that you encrypt the data. So we do that through other mechanisms such as WEP, which was cracked. WPA is another method that we can encrypt this data. There's WPA2, which is a better method — obviously it's a more recent method — and now they have WPA3. So obviously they're continually evolving this and making sure that there's a level of security with wireless, since inherently it's insecure.

Wireless router versus wireless access point

Often there's a misconception between what a wireless router is and a wireless access point, and they're used incorrectly at times.

So first of all, what you're probably most familiar with is a wireless router. This is an example of a wireless router. With this wireless router it has routing capabilities on it and it will actually route data. It also has a built-in switch — you can see that there's multiple ports here that show up on the LAN side of this. There's also a WAN side of this. The WAN and LAN side is because it's got the router functionality; this LAN side is a built-in switch into it. And then it also has the capability of wireless connection, which is why you see these antennas on it. So I can set this up in my home or small office, I can plug it into my network connection or my internet service provider, and be able to get a network onto my device.

Now I also have seen quite a few times when they plug this WAN connection into whatever router or whatever modem that their internet service provider is providing them. Often that has a built-in router in it as well — I'd say a large portion of the time that's got a built-in router into it. So now if you do that, you're doing double routing, which causes also some communication delay on your network, and especially the gamers, who it's really sensitive for and needs really high speeds when they're playing their games, that can be problematic.

So this is a wireless router, and this is what you commonly see. It's more of a consumer level grade here, where you don't see these in businesses — maybe as a backup link, or really small businesses, this is the type of equipment that you would see. But this is not something that you necessarily want supporting your enterprise network.

What you really want is an access point. So here's an example of an access point right here. This access point, first of all, comes with a mounting bracket to mount it to ceilings and that type of stuff. You'll notice that on here I've got only two ports, and one is to link it to another device and the other one is the main connection that you plug into your network. So you plug this access point into the network, and then it's for the sole purpose of providing an access point for your devices.

Now what are some of the differences? I actually bought this for a lot cheaper — this was a $25 router that's right here — and this is more than a hundred dollars for this access point right here. So this performs more functionality and has more functionality than this access point, but this access point costs more. One of the reasons for that is because it's purpose built for specifically just providing access to different devices. It has a better built-in antenna; it can pick up and do better signaling than this device right here, and I can get more devices communicating using this right here. Now wireless is not magic, so I can't connect just hundreds and hundreds of people to this one device right here, but these Ubiquiti devices are awesome.

But that's the difference between a wireless access point, that just provides a wireless LAN for your users that are on your network, and a wireless router, which performs a lot of different functions. But I would say that cheap router probably doesn't provide great functionality if you had quite a few people on your network — it wouldn't quite meet that standard.

What that looks like on your network is a wireless router sits in the middle of all your network, and then a wireless access point just adds to it to create some sort of functionality.

Wireless LAN controller

Then we have a wireless LAN controller. A wireless LAN controller is used to manage your different wireless devices on your network. So this device right here is a wireless access point, and this is a wireless controller. What will happen is that this controller will tell this wireless access point what kind of wireless networks it's going to be facilitating, and the details of how that wireless access point is going to operate.

Now it could just give those instructions. I've seen wireless controllers that just give instructions to this wireless access point, and then the wireless controller steps out of the picture and is no longer used. But also what can happen is all the traffic from this wireless access point could be tunneled back to the controller on a specific VLAN or using specific protocols, and then this controller determines what networks those are supposed to be on and then puts it onto the switch onto those networks, or out to the rest of the world. So then what happens with this is you're able to segregate your traffic better, you're able to separate that traffic out and keep it separated, and have more control and more security over your different networks.