Welcome to Jeremy’s IT Lab. This is a free, complete course for the CCNA. If you like these videos, please subscribe to follow along with the series. Also, please like and leave a comment, and share the video to help spread this free series of videos. Thanks for your help. In this video we’ll take a look at the fundamentals of wireless networks. The exam topics we will cover are 1.1.d, access points, 1.11.a, nonoverlapping wi-fi channels, 1.11.b, SSID, and 1.11.c, RF. We will cover these and other wireless exam topics in greater depth in future videos, but this video will be a general overview and introduction to wireless networks. Here’s what we’ll cover in this video. I’ll introduce radio frequency, RF. RF is a range of electromagnetic wave frequencies which have been assigned for various purposes, including AM and FM radio, microwaves, radar, and Wi-Fi. The last one is of most interest to us, of course, because wireless LANs use Wi-Fi. I’ll talk about Wi-Fi standards as defined in IEEE 802.11. Just like various Ethernet standards are defined in IEEE 802.3, various wireless LAN standards are defined in IEEE 802.11. We’ll look at some fundamentals of wireless LANs and how they differ from wired LANs. We’re going to cover a lot of new concepts in this video, so I highly recommend taking notes as you watch. When learning new concepts taking notes is important to help you keep the new information organized without feeling overwhelmed. Make sure to watch until the end of the video for a bonus practice question from Boson Software’s ExSim for CCNA, my recommended practice exams for the CCNA. First let me introduce wireless networks, specifically wireless LANs. Although we will briefly look at other types of wireless networks, in this section of the course we will be focusing on wireless LANs using Wi-Fi, because that’s what you need to know for the CCNA. The standards we use for wireless LANs are defined in IEEE 802.11, just like how wired Ethernet LANs are defined in IEEE 802.3. Note that the term Wi-Fi is a trademark of the Wi-Fi alliance, which is not directly connected to the IEEE. The Wi-Fi Alliance tests and certifies equipment for 802.11 standards compliance and interoperability with other devices. Devices which have been Wi-Fi certified can use the Wi-Fi certified mark like this. For example, this is a photo of the back side of one of the Cisco wireless access points that I will be using to make these videos. As you can see, it has been certified by the Wi-Fi alliance. So, although the Wi-Fi alliance certifies devices for compliance with the 802.11 standards, Wi-Fi isn’t technically the correct term to refer to 802.11 wireless LANs. However, Wi-Fi has become the common term that people use to refer to 802.11 wireless LANs and I will use both terms throughout these videos. Wireless networks have some issues that we need to deal with. First of all, all devices within range receive all frames, like devices connected to an Ethernet hub. When using an Ethernet switch, the switch is able to forward frames only to the intended recipient. In addition, switches allow devices to function using full-duplex, so devices can both send and receive frames at the same time and collisions shouldn’t occur unless there is some problem in the network. However when using an ethernet hub, the hub will always flood all frames it receives, and collisions can occur when multiple devices try to send and receive traffic at the same time. Like devices connected to an Ethernet hub, when a wireless device transmits a frame all wireless-enabled devices within range will be able to pick up that frame. The signal isn’t contained within a physical wire, because the signal consists of electromagnetic waves radiating out from the transmitting device. This can lead to data privacy concerns, as well as collisions when devices communicate on the same channel at the same time. So, because all devices within range receive the frames, privacy of data within the LAN is a greater concern. In wired networks we don’t usually encrypt data within the LAN, only when sending data over a shared network such as the Internet. However, for wireless networks it is very important to encrypt data even within the LAN, or else anyone with a device in range of the transmitter can access that data. Also, to avoid collisions and facilitate half-duplex communications, CSMA/CA, carrier sense multiple access with collision avoidance, is used. That’s similar to another term I mentioned earlier in the course. CSMA/CD is used in wired networks to detect and recover from collisions. CSMA/CA is used in wireless networks to avoid collisions before they occur. Basically, when using CSMA/CA a device will wait for other devices to stop transmitting before it transmits data itself. Let’s look at a simple flowchart of the process. The transmitting device assembles the frame, prepares it to be sent. Then it listens to check if the channel is free. If the channel is not free, it will wait for a random period of time. Then it will listen again. If the channel is free this time, it will transmit the frame. Note that this is a simplification of the process, and there is an optional feature in which the transmitting device sends a ‘request to send’, RTS, packet and waits for a ‘clear to send’, CTS, packet from the receiver before actually sending the data packet. But this is just extra information, not something you need to know for the CCNA. But make sure you know the term CSMA/CA and that it is used in wireless LANs to avoid collisions. Another issue that we must deal with is that wireless communications are regulated by various international and national bodies. You aren’t allowed to transmit data on any channel you want, and which channels you are allowed to use can vary depending on the country. Fortunately, the 802.11 standard outlines which frequencies can be used for wireless LANs, and devices are designed to use those frequencies. We also must consider the wireless signal coverage area. In wired connections we do have to consider the cable length and in some cases electromagnetic interference, but with wireless connections there are other factors we must consider. First of all, the signal range, how far the signal can actually travel. And there are several factors that effect how far a signal can travel intact. Absorption, reflection, refraction, diffraction, and scattering. Let’s briefly look at each of them. Absorption happens when a wireless signal passes through a material and is converted into heat, weakening the original signal. Here’s an example. By the way, I took this screenshot from EMANIM, which can be used to animate electromagnetic waves. Check out the link I put below the image to use EMANIM, it’s free. So, a wireless access point sends a signal, but the receiving laptop is on the other side of a wall. The wall absorbs some of the signal, resulting in a weaker signal by the time it reaches the laptop. That’s absorption. Reflection happens when a signal bounces off of a material, for example metal. This is why Wi-Fi reception is usually poor in elevators, because the signal bounces off the metal and very little penetrates into the elevator. For example if there is a metal wall between an AP and a laptop, most likely the laptop will not receive a good signal from the AP because much of the signal will bounce off of the wall. Refraction happens when a wave is bent when entering a medium where the signal travels at a different speed. For example, glass and water can refract waves. Try putting a straw into a clear glass of water. It will appear as if the straw is bent. That’s because the light waves travel at a different speed in water than in air. That’s refraction. Diffraction happens when a wave encounters an obstacle and travels around it. This can result in blind spots behind the obstacle. For example, this PC is blocked by some object, and the signals from the wireless access point travel around the object to some degree, but the PC is in a blind spot and doesn’t receive sufficient signal from the access point. That’s diffraction. Scattering happens when a material causes a signal to scatter in all directions. Dust, smog, uneven surfaces, etc can cause scattering. Forgive the unprofessional diagram again, but when a signal from this wireless access point strikes this uneven surface, the signal is scattered in all directions. That’s scattering. All of those, absorption, reflection, refraction, diffraction, and scattering, can affect the quality of a wireless signal. When planning the positioning of wireless access points for a network, you have to take all of these into account. One more issue I want to mention is interference. Other devices using the same channels can cause interference. For example, a wireless LAN in your neighbor’s house or apartment. So, I think you can see that there are various things we have to take into concern when building a wireless network that we don’t have to think about with wired networks. Now let’s talk about radio frequency, and electromagnetic waves in general. To send wireless signals, the sender applies an alternating current to an antenna. This creates electromagnetic fields which propagate out as waves. Electromagnetic waves can be measured in multiple ways, for example amplitude and frequency. Amplitude is the maximum strength of the electric and magnetic fields. For example, look at these two waves. The red one has a higher amplitude, and the blue one has a lower amplitude. Although these two waves have different amplitudes, they have the same frequency, which is the next term we’ll look at. Frequency measures the number of up/down cycles per a given unit of time. the most common measurement of frequency is hertz. Hertz is simply the number of cycles per second. Then of course there are kilohertz, thousands of cycles per second. Megahertz, millions of cycles per second. Gigahertz, billions of cycles per second. And terahertz, trillions of cycles per second. Of course there are more, but these are the common ones. Look at these two waves. Although they both have the same amplitude this time, the red one has a higher frequency and the blue one has a lower frequency. The red one goes through more cycles per second than the blue one. Look at this wave. Let’s say this represents one second. What is the frequency of this wave? Well, this is one cycle. This is a second cycle. A third cycle. And a fourth cycle. So, this is 4 cycles per second, 4 hertz. By the way, another important term is period, the amount of time of one cycle. So, if the frequency is 4 Hz, the period is 0.25 seconds, one quarter of one second, because 4 cycles occur in one second. The visible frequency range is from about 400 THz to 790 THz. But the range we’re concerned with, radio frequency, is from about 30 Hz to 300 GHz, and it’s used for many purposes. Actually we’re only concerned with a couple small bands of this range. Thanks to Wikipedia for this chart of the radio frequency spectrum. The text is a bit small so it might be hard to read, but that’s okay. I just want to point out the two ranges used for wireless LANs. IEEE 802.11 wireless LANs use a few sections of the ‘ultra high frequency’ and ‘super high frequency’ ranges. Wi-Fi uses two main bands, meaning frequency ranges. First is called the 2.4 GHz band. The name is 2.4 GHz, but the actual range is from 2.4 GHz to 2.4835 GHz. Then there is the 5 GHz band. This time the actual range is from 5.150 GHz to 5.825 GHz. But it’s further divided into four smaller bands. Note that you don’t have to memorize any of these band ranges, just remember the two main ones. 2.4 GHz and 5 GHz. If you want to become a wireless network expert you might want to remember the exact ranges and bands, but for the CCNA that’s not necessary. The 2.4 GHz band typically provides further reach in open space and better penetration of obstacles such as walls. However, more devices tend to use the 2.4 GHz band so interference can be a bigger problem compared to the 5 GHz band. Modern devices typically support both, and it’s up to you which you want to use. Note that Wi-Fi 6, which is IEEE standard 802.11ax, has expanded the spectrum range to include a band in the 6 GHz range. I’m not sure if you’ll be asked about the 6 GHz range in the CCNA exam, but I’m mentioning it just in case. Now, each band is divided up into multiple channels, and devices are configured to transmit and receive traffic on one or more of these channels. I say ‘or more’ because something called ‘channel bonding’ can be used to combine channels together, but I don’t think you need to know that for the CCNA. For example, the 2.4 GHz band is divided into several channels, each with a 22 MHz range. Here are the channels, and note that it differs by country. Thanks to wikipedia for the chart again, by the way. Note that the ‘11b only’ here for channel 14 in Japan refers to 802.11b, which is an old and slow standard not used much any more. Now, an important aspect of these channels is that they overlap. For example, channel 1 is from 2401 MHz to 2423 MHz, which has some overlap with channels 2, 3, 4, and 5. To avoid interference between adjacent wireless access points, we have to carefully choose which channels we configure our access points to use. In a small wireless LAN with only a single access point, you can use any channel, because there are no other access points that can cause interference. However, in larger wireless LANs with multiple APs, it’s important that adjacent APs don’t use overlapping channels. This helps avoid interference between devices transmitting on the same channel. If overlapping channels are used, it will result in reduced performance and a worse user experience. In the 2.4 GHz band, it is recommended to use three channels, 1, 6, and 11. Here is a diagram of the channels in the 2.4 GHz band. Notice that channels 1, 6, and 11 don’t overlap with each other. So, we can have an AP using channel 1, an AP using channel 6, and an AP using channel 11 and they won’t interfere with each other. Note that outside of north america you can use other combinations, but for the CCNA you should really remember the 1, 6, and 11 combination. And as for the 5 GHz band, it consists of non-overlapping channels, so it is much easier to avoid interference between adjacent wireless access points. Using those three channels in the 2.4 GHz band, you can place APs in a ‘honeycomb’ pattern to provide complete coverage of an area without interference between channels. The diagram on the left shows how you can do that with channels 1, 6, and 11, as well as other patterns for those outside of north america. Here’s a large version of the 1-6-11 honeycomb pattern. Note that the coverage area of each AP overlaps to provide complete coverage of the area, but the frequencies don’t overlap, which helps avoid interference between the access points. When you have to provide wireless coverage over a large space, you should arrange your access points like this. Just like there have been various 802.3 Ethernet standards, there are plenty of 802.11 Wi-Fi standards too that use different frequencies and provide different data rates. Starting with the original 802.11 which was released in 1997 all the way to 802.11ax, also known as Wi-Fi 6, which was released in 2019, here are the 802.11 standards you should know. I know it’s a lot of work, but I do recommend memorizing these standard names, the frequencies they use, and their maximum theoretical data rates for the test. Note that these maximum data rates are theoretical. For many reasons you’re probably going to get much lower data rates than the theoretical maximums. Also notice that 802.11n is known as Wi-Fi 4, ac is known as Wi-Fi 5, and ax is known as Wi-Fi 6, however there is no official Wi-Fi 1, 2, or 3. That’s all I have to say about this. Take some time to memorize these different standards and their characteristics. Of course, I recommend using the flashcards to help you do that. By the way, 802.11-enabled devices might support one of these standards, some of them, or all of them. So, I recommend checking which standards are supported before you buy a device. Also, for some homework try looking up the WiFi standards supported by the wireless devices you own. For example, if you have an iPhone you can check Apple’s website to see which standards it supports. Here’s an example for the iPhone 10. It supports 802.11 A, B, G, N, and AC. Finally let’s look at another important part of 802.11, service sets. 802.11 defines different kinds of service sets which are groups of wireless network devices. There are three main types, independent service sets, infrastructure service sets, and mesh service sets. All devices in a service set share the same SSID, service set ID. You might have heard that term before. The SSID is a human-readable name which identifies the service set. And it does not have to be unique, although it’s best to configure unique SSIDs since that’s what you’ll be looking at when you select which network to connect to. Here are the SSIDs my phone can detect as I sit here at my desk. Now, I said SSIDs are human-readable, meaning they can be given easy-to-read names like ‘Jeremy’s Wi-Fi’ or something like that. In this case, these names aren’t exactly the most easily readable. However, I could easily change the SSID of my wireless LAN to something simpler. Anyway, let’s look at the different types of service sets. First, an IBSS, independent basic service set, is a wireless network in which two or more wireless devices connect directly without using an AP, access point. These are also called ad hoc networks. They be used, for example, for file transfer such as when using Apple’s airdrop. However they are not scalable beyond a few devices and are typically only used for limited purposes such as quick file transfers like airdrop. Next, a BSS, basic service set, is a kind of infrastructure service set in which clients connect to each other via an AP, access point, but not directly to each other. Remember I said there are three kinds of service sets? First is independent, which I just showed you, and second is infrastructure. BSS is a kind of infrastructure service set. The AP serves as network infrastructure connecting different wireless clients together. A BSSID, basic service set ID, is used to uniquely identify the AP. Other APs can use the same SSID, which is Jeremy’s Wi-Fi in this case, but not the same BSSID. The BSSID is the MAC address of the AP’s radio, and as you know MAC addresses are unique. To be part of the BSS, wireless devices request to associate with the BSS. Wireless devices that have associated with the BSS are called clients or stations. Another important term is BSA, basic service area. This is the area around the AP where it’s signal is usable. What’s different between a BSS and a BSA? Well, a BSS is a group of devices which are wirelessly connected via an AP. BSA just refers to the physical area around the AP where devices will be able to associate with the AP and join its BSS. So, BSS is a group of devices, and BSA is a physical area. And note that clients must communicate via the AP, not directly with each other. The traffic must flow through the AP before going to the other client, even if the other client is in range of the sender’s signal. To create larger wireless LANs beyond the range of a single AP, we use an ESS, extended service set. This is the second kind of infrastructure service set. Note how there are two BSSs, BSS1 and BSS2, but together they form an ESS. APs with their own BSSs are connected by a wired network. Notice how the APs for BSS1 and BSS2 are connected by a switch. Each BSS uses the same SSID, Jeremy’s Wi-Fi in this case. However each BSS has a unique BSSID, notice how they are different in the diagram. Also, each BSS uses a different channel to avoid interference. Notice that BSS1 is using 2.4 GHz channel 1, and BSS2 is using channel 6. Clients can pass between APs without having to reconnect, providing a seamless Wi-Fi experience when moving between APs. This is called roaming, when you move between two APs in an extended service set. Note that there should be some overlap in the BSAs, about 10 to 15 percent, or else the connectivity can be lost when moving between APs. The final kind of service set we’ll look at is an MBSS, Mesh Basic Service Set. An MBSS can be used in situations where it’s difficult to run an Ethernet connection to every AP. The mesh APs use two radios. One to provide a BSS to wireless clients so they can connect to the network, and one radio to form the mesh network between the APs, to form a backhaul network which bridges traffic from AP to AP. For example if this PC wants to send traffic to the Internet, it sends traffic to its nearest AP, which then bridges the traffic from AP to AP over the backhaul network back to the switch. At least one switch is connected to the wired network, and it’s called the RAP, root access point. This is the RAP in this network. The other APs are called MAPs, Mesh Access Points. A protocol is used to determine the past path that traffic should take through the mesh, similar to how dynamic routing protocols are used to determine the best path to a destination. Now, most wireless networks aren’t standalone networks. Rather, they are a way for wireless clients to connect to the wired network infrastructure, and the AP serves to translate between the two mediums. In 802.11, the upstream wired network is called the DS, distribution system. Each wireless BSS or ESS is mapped to a VLAN in the wired network. Here’s an example. The SSID Jeremy’s Wi-Fi is translated to VLAN 10 on the wired network, which is the distribution system. The wired hosts in VLAN 10 will be able to communicate with the wireless hosts in Jeremy’s Wi-Fi. And it’s possible for an AP to provide multiple wireless LANs, each with a unique SSID. This is the same as how a switch can divide a single physical wired network into multiple VLANs. Each wireless LAN is mapped to a separate VLAN and connected to the network via a trunk. Here’s an example. There are two wireless LANs with their own SSIDs, Jeremy’s Wi-Fi and Guest Wi-Fi. Although as I said before, SSIDs don’t have to be unique, but usually they are. Jeremy’s Wi-Fi is mapped to VLAN 10, and Guest Wi-Fi is mapped to VLAN 11, and the AP is connected to the switch via a trunk which allows both VLAN 10 and 11. Also, notice that each wireless LAN uses a unique BSSID, usually by incrementing the last digit of the BSSID by one. So, the BSSID of Jeremy’s Wi-Fi ends with 3456, and the BSSID of guest Wi-Fi ends with 3457. The final thing we’ll cover is a few more modes that APs can operate in. First, an AP in repeater mode can be used to extend the range of a BSS. Here’s an example. The repeater will simply retransmit any signal it receives from the AP, which will extend the range of the AP’s BSS. A repeater with a single radio must operate on the same channel as the AP, but this can drastically reduce the overall throughput on the channel, since the repeater will be repeating the AP’s signals back to it using the same channel, keeping the channel busy. This cuts the effective throughput of the channel by 50%. A repeater with two radios fixes this weakness, because it can receive on one channel and then retransmit on another channel. So, that’s how a wireless repeater works. Next, an AP operating as a workgroup bridge operates as a wireless client of another AP, and can be used to connect wired devices to the wireless network. In the example below, PC1 does not have wireless capabilities and also does not have access to a wired connection to SW1. However, PC1 has a wired connection to the workgroup bridge, which has a wireless connection to the AP. Now, there are two kinds of WGBs. Universal WGB, uWGB, is an 802.11 standard that allows one device to be bridged to the wireless network. However what Cisco simply calls WGB is their proprietary version which allows multiple wired clients to be bridged to the wireless network. To summarize, this is a solution which allows clients that don’t support wireless connections to connect to the wireless network via an AP operating as a workgroup bridge. The final mode I’m going to introduce is outdoor bridge. An outdoor bridge can be used to connect networks over long distances without a physical cable connecting them. The APs will use specialized antennas that focus most of the signal power in one direction, which allows the wireless connection to be made over longer distances than normally possible. The connection can be point-to-point as in the diagram, just two sites being connected. Or it can be point-to-multipoint, in which multiple sites all connect to one central site, forming a hub-and-spoke topology. Okay, since we covered so many different topics in this video let me summarize all of them with a lovely wall of text. Here it is. Now, although this summarizes the topics in this video, make sure you know the details of each topic that we covered. If you didn’t take notes I recommend going back in the video to take your own notes, and also using the flashcards to memorize some of the details. Okay, in this video we covered the basics of wireless networks, specifically wireless LANs, including radio frequency, wi-fi standards, and wireless LAN fundamentals such as service sets. There is still a lot more to cover about wireless networks including wireless network architectures, wireless network security, and wireless network configuration. Those topics will be in the next few videos. As always, watch until the end of the quiz for a bonus practice question from Boson Software’s ExSim for CCNA, the best practice exams for the CCNA. Okay, now let’s go to quiz question 1. When using the 2.4 GHz band, which channels should be selected when using multiple APs? Pause the video now to select the best answer. Okay, the answer is B, 1, 6, and 11. As this diagram shows, channels 1, 6, and 11 do not overlap, so even if APs are near each other interference can be avoided. Okay, let’s go to question 2. If an enterprise’s network is mostly wired, what is the purpose of an AP in the network? Pause the video now to select the best answer. Okay, the answer is to connect wireless devices to the wired network. In 802.11, the wired network is called the DS, distribution system, and the AP’s main role is to connect wireless devices to the wired network. Okay let’s go to question 3. Which of the following bands are commonly used by wireless LANs? (select two). Pause the video now to select the best answers. Okay, the answers are A, 2.4 GHz, and D, 5 GHz. These bands are divided into channels which are used by wireless devices to send and receive wireless signals. Okay, let’s go to question 4. Which of the following statements about an ESS are true? (select two). Pause the video now to select the best answers. Okay, the answers are B, each BSS uses a unique BSSID and C, roaming can provide seamless connectivity when moving between APs. A is not correct because each BSS in an ESS should use the same SSID, and D is not correct because adjacent APs should use nonoverlapping channels to avoid interference. Okay, let’s go to question 5. Which of the following statements is not true about an AP that provides multiple BSSs? Pause the video now to select the best answer. Okay, the answer is B, each BSS shares the same BSSID. Although it is possible for each BSS to share the same SSID, they must have unique BSSIDs. With that said, however, it is best practice to also use a unique SSID for each BSS. Okay, that’s all for the quiz. Now let’s try a bonus practice question in Boson Software’s ExSim for CCNA.