Cisco CCIE Enterprise 350-401 Topic: Infrastructure Part 7
December 14, 2022

46. Interference & Effects of Physical Objects

Next topic. Interference and the effect of physical objects are present. Now, interference is nothing but noise, and this noise means that you are sending some signal and it has some overlap. You can see that there is some overlap with the same channel here. So different transmitters have the same channel, and they are overlapping. Now, in the real world, this panel interference is often a necessary evil that is too bad. Your signal will be degraded to the extent that we have planned. We should set up the access point in a proper manner.

So there should be less interference or no interference. Now, that’s the one thing. So here you can see that two nearby transmitters should never be placed in the same channel because their strong signals would be more likely to interface. That’s the one case. The second case we have is if we have neighbouring channel interference. So what is happening right now? I have transmitter A on channel six and transmitter B on channel seven. And they have the same overlap in the 5 GHz band. Still, we know that it has a long list of channels. It has so many different channels that the chances that they can overlap are smaller. Still, the best practice suggests that you should avoid placing a neighboring access point on the list of nearby access points, even if it is a 5. If you think there is still a chance of interfering, However, you should plan the access point’s placement so that it does not interfere with or disrupt the signal of any neighboring access point or the channels or bands. All right, next topic. We have the effect of physical objects.

So what is happening is that you place your access point, and then it is in contact with a surface that is reflecting the wave. It’s very much like light. We know how the light waves are reacting. If you put something lightweight in front of a mirror and at a certain angle, it will reflect even if your surface is smooth. In that case, the signals—RF signals—will also reflect or get reflected. Now, you can see in this diagram that, okay, there may be a chance that the receiver is minor, with multiple inputs and multiple outputs. So, as shown in the diagram, the sender sends the signal in three different directions, and the receiver knows how to get it from the multipath. Still, this situation is okay. But suppose you have a single review chain, or the receiver has only a single review chain capability, which means they can take the signal just from one source. So in that case, it will become worse. Obviously, you can see the signal will get degraded. So, in the case of A and C, if you have ABC-like that, the second thing to consider is absorption. What will happen in absorption is that the signal will get reduced. So you have some dense media, and behind the dense media you have put your access point. So in that case, the signal will be reduced. We should not place our access point in a way that it will get reduced. Then we have the scattering. If you have any sharp edges, So at that point in time, if the signal lands, it will get reflected. Obviously, the distortion of the signal will be there. Then we have reflection. Reflection means that your signal, the actual physical meaning, will be distracted once more. Or if you go and check the physics book, you’ll find that when an RF signal meets the boundary between media of two different densities, As a result, if one location has a higher density, another location has a lower density. for example, air and water.

So air has a low density, and water has a higher density. And if the signal travels on those media, obviously it will get refracted. Okay, so these are the evils we have here. Reflection, absorption, scattering, and refraction are all visible. And then finally, we have the refraction as well. Assume you have some OPC or a void in between signals on a line. So in that case, the signal will get you started; it will get refracted and diffracted. Suppose another signal approach is an OPAC object or one that is able to absorb the energy. So that’s the case; you have the diffraction. Obviously, the signal will get degraded. One of the important concepts we have here is the fringe zone. What is the fringe zone? Before going to that, you can see an example of diffraction where you have the obstacle, you’re sending the media, you’re sending the frequency, the waves, and you have the media in between. Who is decoding the signals? Obviously, the signal is getting diffracted. That’s the one thing. So what is the solution to that? that a wireless signal with line-of-sight can be used So there are two large towers with nothing in between. So there is nothing in between, which means there is no object or abstraction. As you can see, there is no large tower between those two buildings. As a result, your signal can be transmitted and received from here. That is one of the solutions. But again, what Francis Law is saying is that according to Frenzil, the rule is that even a narrow line-of-sight signal can be affected by the fraction. Even if an object does not directly block the signal, there is an elliptical-shaped volume around the line of sight that must also remain free of obstruction.

So what does it mean, and let’s call it the French jewel? You can see here that I have a transmitter and receiver in the diagram. But when you send the light, when you send the signal—not light but our radio frequency signal— So when you send the radio waves at that time, what will happen? That it will create some sort of cylindrical volume across it because there is still air in between, gravitational force, and some invisible obstruction that you can see in between. Maybe in some places we have so much pollution that the heavy particles can collide, and there are so many factors for that. In that case, what will happen is that they will form a cylindrical structure in between. Again, you can see that you have a small building in between that and the highway. So it is still going to degrade the quality of the signal. And then you can see that this curve indicates that there should be no obstructions in this curve. and that’s again coming from one of the formulas. Okay, so these are the things related to the interference and related to the objects—physical objects—in between. And, once again, if you look into reflection, refraction, absorption, and other phenomena, you will find that they are derived from physics. We learned a lot about all these theorems and theories related to various diffraction and signal transmission in our maybe twelve years or at graduation. Alright, so let’s just stop here.

47. Antenna Characteristics

The antenna and its various types are the next fundamental topic. So, let’s understand about antennas as well. You can see that we have different types of antennas, and there are actually different types of requirement is there.That is why we have various types of antenna. Sometimes a focused beam is required, while other times a smooth, surrounded, or equally spaced RF frequency or beam is required. Sometimes we want long-range radio frequencies, and sometimes we need short-range radio frequencies that will be inside the room. So, that’s the main reason you can see that we have different types of antennas because the requirements are also different. According to that, we will go and see what kinds of antennas are available and what frequency ranges they have. Before that, let’s try to understand a few of the basic things.

So, first of all, here you can see that we have the isotropic antenna, where we have an example here in the diagram, and you can see that you have x, y, and z directions. Assume I have two sections at this point, one in the x direction, which is horizontal, and one in the y direction, which is vertical. And suppose the requirement is that there be an equal amount of radio frequency. So what does it mean? Simply put, the access point is in the center, and the radio frequencies are distributed in a circular fashion from that access point. So whatever object enters that circular radius in that specific premises will receive the radio frequency equally. That’s the whole idea behind the isotropic antennas. However, it is not possible to create isotropic antennas that meet all of the requirements. So, that’s the reason we have different types of antenna categories. Now, here you can see in the diagram that you have the horizontal direction, which is asimuthal, and then we have the elevation plane as well. That is the E plane.

So we have two planes, basically the H plane and the E plane. And based on that, if you do the cross section, if you do the section here in the bottom diagram, let me try to highlight. So here you can see how the frequencies in terms of DB are increasing as we go outside the circle. So here you can see that the outermost circle usually represents the strongest signal strength. And the inner circle represents weaker signal strength because they are in the minus 30 range, which is less than minus five, which is obviously bigger than minus ten, et cetera correct.So outer circles represent a higher signal. And that’s one of the important points that we should know. So, now we understand about the isotropic antenna, and that’s actually not possible to build. We have different types of antennas. Then we have the edge of methyl and the E plane. Then we know that okay, moving forward, your signal strength will increase as per this section, as per E and H or H or E. Then what is gained? Now, gain is nothing, but it’s the focus. Suppose you have an antenna. What is the focus of that the focal?So, again, what does it mean? It simply means we can think like this. We know at this point in time that we have seen the antenna. Assume you have a parabolic antenna, and in the center, you have the central knob or the center. In between indicates that you are focused on something. As a result, the frequency at which you are focusing is referred to as a gain. We’ll also see that different antennas have varying gains and capabilities. OK? All right. So here we can see in the diagram different types of antennas. Either isotropic, omnidirectional, or directional, you can see the gain because the focus is changing. And that’s why the gain of the antenna is changing. Again, the new term we have is the beam width. So, what is the beam width? Manufacturer. Manufacturers list the beam width of antennas as a measure of antenna focus. Okay.

So again, two-term gain is a measure of how effectively it can focus RF energy in a certain direction. So that’s the gain. You focus in a certain direction or direct your energy in certain directions. And then there is the beam width; the beam width is nothing but the focus. So your focus and energy are on that particular focus. So your focus is your beam width and energy, and the signal in that particular focus is nothing but the gain. Alright? So now that we understand these many terms, we can do that. Now we can understand the types of antenna. We know that we have polarization. So that electromagnetic wave is nothing but the polarization. Earlier, we discussed that we have the electromagnetic wave and the magnetic wave. So we have electromagnetic waves and magnetic waves there in the 90 direction. So the angle between these waves is 90 degrees. All right. So knowing these many facts, now that we know what we can do, we can go and learn about the antenna. Again, if the electromagnetic wave is travelling in the horizontal direction, that is horizontal polarization. If it is in the vertical direction, that will be the vertical polarization. and that is shown here in the diagram. So, if the signal is going vertically, you can see the signal received; this is the vertical direction, or it can be in the horizontal direction. Great. So now, let’s focus on the antenna. We have two types of antenna. You will see those subcategories. Inside these types, we have the omnidirectional and the directional. Now, as its name implies, it will be at equal distances, correct? So, let me quickly demonstrate a dipole antenna, which is an example of an omnidirectional antenna. Dipole antenna. And you can see in the diagram that they are at an equal distance from the centre and have a gain of around. Again, we know what this is again.So the gain is around +2 to +5 DB. Okay, again, you can see the E and H. The horizontal is the edge of the T and E elevation planes. And this is the cross section in the diagram. Now in Omnidirectional mode.

So you can see that omnidirectional, and one example is a dipole. And again in omnidirection, the other example is the monopole. Okay, one of the Cisco vendors is a major networking vendor, as is one of the APINS vendors. Cisco’s access point contains six tiny monopole antennas. By the end of this section, we will have a summary of whatever we are going to discuss here. In the summary section, we’ll learn more about that. Now, what is happening, for example, in monopoly? And then, let me quickly show you the summary I have. So here’s the gist of it. We have a dipole monopole and an integrated dipole in Omnidirectional. We have discussed that the gain is 2.2 up to 3.5 monopoles. You can see that in 2.2.2. So we have two spectrums, 2.4 and 5 GHz. Obviously, at 5 GHz, you’ll find much stronger signal strength. 2.4, you have less signal strength. But there are vendor-made access points; maybe Cisco or any other vendor is making these access points. They support both the 2.4 and 5 GB standards for access points. Okay? All right, then you have the monopoly. After that, we have the directional antenna. Why do we have a directional antenna? Because we require significantly more gain in certain directions. So here, you can see that we have the Cisco patch antenna. And the gain for that Cisco patch antenna is six to eight DB. Okay, this is supporting two 4GHz, which again is six to eight. They have seven to ten DB of support at 5 GHz. And here we can see the diagram. This diagram clearly shows that the focus is in one direction. If you go and see the other direction, you can see they are at an equal distance. They are mostly equidistant in the case of only directional If I go back, they are mostly the same distance.

But if you go and check the directional antenna, you’ll find that the focus is in one direction. So for this antenna, this is the patch antenna. You can see the gains. Next we have the Yagi antenna. Again, the name of the inventor is Yagi. So that’s why this is the Yagi antenna in a Yagi. Again, you can see this is very much focused in one direction. And again, for these antennas, the numbers are 10 to 14 for 2.4. and we can see the list as well. Cisco does not support or offer 5 GHz. Cisco is not supporting the five-gig herd, Yogi. So that’s why it’s not there for 5 GHz, but I can see that’s 10 to 14 for Yogi. And if I go and check the list, 5 GHz is not supported, so it is not listed there. All right. Then finally, we have the parabolic dish antennas. Again, the gain will increase because the focus will shift in certain directions. In this case, you can see the linear type of azumuthal as well as the horizontal elevation plane and the e plane, elevation plane. Now the focus is quite linear, but you can see what gain we have on the other hand. The gain is 20 to 30 degrees, and that’s a lot. Again, in this summary slide, you can see the parabolic’s directional attainment for two and four gig. They have 20 to 35 gigabytes. They also have a 20-to-30-point gain in the range. So you can take this particular chart as a reference, and we have discussed, first of all, the terms used inside the antenna, like what is being built, what is gain, what is polarization, what is mutual, what is e-planet, etc., etc., etc. Then we went through and checked the different types of antenna in every direction. We have dipole, monocle, integrated, indirectional, patch Yogi, and parabolic antennas.

48. Types of Wireless Networks

So what type of wireless network do we have? Let’s understand the different types of wireless networks, and then we’ll focus on wireless LAN. So, in the diagram, you can see that the personal area network begins with a small WPAN and then progresses to a wireless LAN, then a W Man, and finally a W Van. An example is Bluetooth. The distance is 20 to 30 feet, or seven to 10 meters. Then we have wireless land that we are going to study in this particular course.

That range is 100 meters, and we know that we have banned the 2.5 and 5 GHz bands. Apart from that, we have the metropolitan area network as well. Y Max is a good example of this. Obviously, it is for a wider range, and then we have the wide-area wireless network as well. That is again for a broader area. Example: mobile services, mobile towers, etc. Let us now concentrate on the wireless local area network. Now that we know that we have a transmitter, we also have a receiver, right? A transmitter. They are going to send their electromagnetic wave receiver. They have to be in line to receive those signals. If in between there is any interference, any obstacle, any problem, or any type of object, then the signal will be degraded, the frequency will be degraded, and the overall performance will be degraded. Right? Now we may have one-way communication or we may have two-way communication. And suppose you have a larger number of devices in a group, in a specific wireless area landgroup, and there is so much interference and the problem that, just to mitigate this particular problem, we need one centralised device that can work on behalf of all the devices, right?

The name of the centred device is access point. Now here in the diagram, you can see that all the devices, all the wireless devices, are end points. They are going to connect to the access point. Now there are so many different terms that we should understand at this point in time. So, in the diagram, you can see that there is only one circle, and that circle represents nothing more than, say, this point in time; this is the wireless area, as in OSPF, at this point in time. Just think of this as one of the areas. For example, area zero. Inside area zero, you have different endpoints, and you have the AP. So for this AP, the BSSID is nothing but the Mac address of the access point. Obviously, Mac addresses issues specific to physical devices. So the physical ID that this device has is the BSSID. Here, you can see that you have the basic service set. So complete area zero makes you think that the standard inside complete area zero is the basic service set. So we have the basic service set, we have the access point, and we have BSSID. What is happening and what is important here is similar to routers, what routers do. They are promoting their network in the same way that an access point would. He will advertise his network, and his network identification is nothing but SSID. So the SSID he is advertising is to whoever endpoint associates that specific SSID that will become part of that group, part of that set. Correct? And that’s actually the truth. So here you can see that you have the basic service set (BSS).Inside BSS. You have the BSSID.

That’s the AP ID. And this AP is advertising its network, and all the endpoints are going and connecting with that particular network, and that network is nothing but the service set identifier. Again, the endpoints that are members will go and associate with that particular network. Obviously, they will do some sort of negotiation between that and having to associate with that particular network. Now, if you want to do some sort of access control from AP, we can do that. So in the diagram, we can see that certain groups of devices can communicate, certain members can communicate with each other, and certain members will not communicate with each other. Later on, we’ll discuss more about the packet type, communication, et cetera. So far, we’ve learned what an AP is, what members are, what an SSID is, what a BSD is, and what a BSS is. Now, it is critical to note that the core is required for every wireless network. And that core is nothing but a wired network. So behind every wireless network is the backbone of a wired network. That backbone wired network was known as a distribution system, or DS. So here you can see in the diagram that you have DS. And again, behind that, you have router switches, a firewall, etcetera, etcetera. So, how is the connection? We have BSS connected to DS, which could be a Neil 2 or L 3 switch. And suppose if you have multiple VLANs, with one VLAN representing one of the SSIDs and another VLAN representing another SSID, or maybe you have multiple VLANs across your SSID, depending upon what design you have. In that case, a trunk link should be established between the BSS and the DS. So we know this concept from our VLAN concept: if you have multiple VLANs, there should be a trunk in between to allow those VLAN frames. Okay? So that’s the concept of DS and the connection with BSS. Now, the next concept we have is the extended service set. So what does it mean?

Now, if you look at the diagram, you’ll see that you have two BSS, BSS. Having BSS obviously implies having BSSID. So that means they have their own unique Mac addresses. To put it simply, you have two different access points on the same network. So their network is nothing more than an SSID. So they have the same SSID and are linked to the DS distribution system or switch. So the BSS, or collection of BSS, can now be thought of as an extended service set. So BSS plus BSS is equal to ISS Extended Services. Now, if I have one user here who is associating with one of the APs, and then he’s going to the other AP, and he’s associating with the other AP, This was referred to as “roaming” at the time. So the user is roaming across the network. But we can say that throughout, it may have different AP credits. You can see that it has different APs, but they are all part of the same network. So that concept is nothing but Roman. All right, so let’s just stop here. We have covered the basics of the wireless LAN so far.

49. 802.11 Frame Format

The 80-2, 11-frame format is next, though we already know how the item-based format, 80-2.3, works and looks. So you can see that you have preamble the source,  destination, and address, and then you have the data field plus the FCS switch used to learn all these end host machines. And, depending on the situation, do we have L-3 communication or L-2 communication for L-3 communication? Again, if you’re crossing the boundary, then the router will come into the picture. But that’s the way that the land and broadcast networks used to work in wireless networking. The communication is very different. Why? Because we know that all these end systems first of all have to learn the SSID, which is nothing but the advertisement network from the access point, they have to learn, associate, and authenticate this SSID. They will then begin communication because we have a society in the picture because we have various types of wireless clients or end systems.

They are part of a wireless network and can communicate with one another as well as the machine that is generating the wireless signal. Wireless will connect with wire, and then wire will be connected to some other host machine. So the bottom line is that you may have various modes of communication, and depending upon what type of communication you are doing, that’s why we have different types of addresses. So as you can see, you have four different addresses (1234, and then you have a duration. It is because this technology is based upon congestion avoidance (see the ethernet plan), which is something like collision detection, and this is actually collision avoidance, not condition collision avoidance. Now in the case of collision avoidance, what is happening is that you wait, you have some timers, you have some back-off algorithms, and you will see, so if it is clear to send, I will send. If the media path is not cleared, I will wait until that particular point in time, so that’s why there are calls and an avoidance mechanism. Now here you can see that you may have end systems—those are the wireless clients where you are doing the communication—or you are doing the communication with the machine that is behind this AP that is wired. So wired versus wireless, and that’s why we have this DS bit set, so either zero or one, so if you have two bits, then you can have four conditions. Now this means that two hosts are doing the communication; they are purely part of a wireless network. At this point, you can see that you are transitioning from a wireless to a wired network. Then you have this zero one, which indicates that the bits are arriving, the frame is arriving from the host from the wired network to the wireless, and finally, if you have access points A and B and they are communicating, that will be a one.

Okay. So, let us try to figure out what all of these address types are about. Yes, we have four different types of address type.Here you can see that first of all, they must have a TA, transmitter address, and receiver address. Now, one field in this address always contains RA, which is the receiver address. Now its extract contains may vary dependingon where the frame is headed. Likewise, address two always contains the letter T. As a result, two addresses are assigned, and address one is received. It is transmitted when two are added. Correct? Apart from that, obviously, when you are sending the frame, you should have the actual source address, the actual destination address, et cetera. So let me try to explain this with a diagram here. You can see and understand all of the address types in the diagram. Address numbers 1, 2, 3, and 4. Remember, in this diagram, I don’t have AP-to-AP communication. So that’s why address four is blank. Okay, now we have one case where host one wants to communicate with host two. So what will be the source, and what will be the destination? So here are the source addresses, the transmission address, and the destination addresses, which are the actual source and actual destination. Now who is the receiver? at this point in time? The access point is the receiver.

So that’s why his Mac address Okay, so clearly you can see first all the addresses and then the bits. So since you’re sending one to zero, that means wireless to wired. So that’s why you can see here that this is going to hit. Okay? And here you can see that address one is BSSID, address two is the TA, and then address three is the destination. Okay. The hosts are now going to respond. When host two responds, the source and destination addresses get changed. So now, who is the source? Who is the destination? When it comes to being a host, this guy is the ultimate destination. Now what about the Mac address of the BSSID or the AP? That will be the transmitter address. So he has received the address, and then he is transmitting. You can think of the logic like this: There is a transmitter address, a receive address, and a source address that are going to be changed. Now, which is the use case? This one. So you can see the address of one is RA, who will receive. Address two is BSSID, who’s going to transmit, and address three is the source address. Correct. And who is the source? This guy is the source. Although this is a bit tricky, So you can pause the recording, you can take snapshots, and you can do your mapping. But this is the way that the frame format looks, and the fields inside the frame format represent these addresses. 

50. 802.11 Frame Types

Let us understand the 80 two-point eleven-frame types. As you know, we have three different types of planes. SDMAs are frequently used as routers. So we have the control plane. We can think that for frames we also have a management frame, a control frame, and a data frame. Now, what is the use of a management framework and why is it important? So let’s try to understand all these options that we have. First of all, let’s start with the management framework. Now, this management framework is there to advertise the BSS and its capabilities to the clients. Now, what are those? First of all, you can see that you have a beacon. A beacon is something that will be sent by the AP. At this point in time, you can think that, okay, AP is sending the beacon to all of the clients. Clients can receive those beacons if they open and check their wireless network. Isn’t it now up to the client to decide whether or not to join? So if I go to my laptop and check my wireless connectivity, I can see a range of SSIDs or BSSIDs. Generally, those are SSID, not BSSID, but I can see all those SSID. SSIDs are nothing but the network advertised by the AP on the wireless network. So that’s nothing but the beacon; that’s one of the management frames. Then Probe. What is a probe? The probe is something you do if you want to join the AP, and then you send a request to the AP saying, “I want to join the AP.” And that’s why this is the passive. So Beacon is a passive scanner, and Probe is an active scanner. Okay, now for the authentication and authentication.

Now, in wireless networking, we have this authentication option that the clients can use to authenticate with the AP, and even they can do the deferred indication as well. So the first stage is that you can see N numbers of SSIDs or so many SSIDs on your laptop. Now, if you go ahead and click there, it will prompt you for a password. What is the password? If you enter the correct password, it will get authenticated. It will not be authenticated if you do not include it. Those are, in fact, the management framework. Then we have important terms like “association de” and “association reassociation.” So suppose once you are able to discover the network, you are able to do the authentication, and then you are going to do the association with the AP. Now, in this association phase, the access point is sending a unique association identifier to the clients who are going to do the association. Assume you want to leave and can do the reassociation. If you want to change one AP to another, you can do the reassociation. There are numerous terms associated with association. Now we have the action frame as well. Suppose you want to roam or you want to extend the wireless capabilities at that time. This action frame will come into the picture. So you can see that you have this management framework. Then we have the control frames; although there are nine control frames, these four are important.

So control frame again: it’s not the payload, it’s not the data, it’s the control mechanism. So for every frame we are getting acknowledgement, and that will provide, for example, availability in the channel. We are getting acknowledgement for blocks of data as well. Okay, then we have this power shape. Paul So, what does it mean for a framesent from client to AP to request the next frame that was buffered while the client’s review was turned on to be a power saving mode? Then finally, the important one, we have the RTS and CTS. The RTS and CTS are something like a timer. So it’s something like “request to send” or “clear to send.” These are the terms and why these terms have become important because requests to send and clear to send RTS and CTS are not only providing the timer to send the frames, but they are also used for collaboration and avoidance as well.So the RTS is a mechanism to do some sort of calling and avoiding in the channel as well. So finally, once you have your management and control done, the next thing is to send or receive the data. For that reason, the data frame will come into the picture. At this point in time, we know from our previous lessons that we have four different types of address build.So you have the source address, the destination address, the ap address, and then you have the destination behind the wireless that is in the wired network. So you have these four addresses, and then the actual communication can happen.

51. Client Scans for AP & Roaming

Let’s look at how the client searches for AP and roaming features. We have already discussed beacons and probes. We understand what “passive scanning” entails. “Passive scan” means the access point. Here, you can see that they are sending their beacon to the host for a set period of time in order to offer their network to the host. Now it’s up to the host; he can go select that network and then do the authentication and association. That’s the passive scan. Now, this passive scan is good, but still, the drawback here is that the host has to wait for a certain duration to get the network or to get the advertised network from the access point. Next, we have the activist, in which the client sends the probe and asks, “Who owns this network?” to which the access point responds, “OK, I’m there.” You want to authenticate; you want to associate. If you associate, you’ll get the unique association ID. Now, how will the host go and join a particular AP? So here, you can see that we have several steps. Step numbers one through five First of all, the host will handle the authentication request. Then he will get the response. Then he will fulfil the association request. He will get the association response and unique association identifier.

And then he’ll go and join that, okay? And all these steps are listed here. For example, point number five is the response that also contains the aid that uniquely identifies host one as an associated client. In effect, aid is host membership, etc. So these are the steps. Obviously, authentication requires a response, obviously, association requires a response, and finally, they will receive the unique ID. Now, if a host or client wants to leave it, he can do the de-association. Remember here that deauthentication and disassociation are different things. So if you’re deauthenticating, that doesn’t mean that you’re deauthenticating or that you have to authenticate again next time. You can be deassociated, but you are still authenticated. Correct? The next very important topic is roaming. So far, we have studied that if you are moving from one BSS or one area sale to another area sale, that means you are rooming. And suppose different APs have the same SSID, so you can roam from one place to another as per the signal capability. You will go ahead and connect the access point. That’s the technical term for association. Now you can see all of the steps that have been listed. What is the status of the roaming? First of all, say your signal strength is getting weak; your signal-to-noise ratio is getting weak. It’s time to go. If you are not receiving a proper signal, you can see that the client is on the edge, away from the AP but close to another AP.

Or if he roams, he can get near the AP and decide he wants to go and associate with a new high-bandwidth network or get some high-frequency signals. So that’s why he went to his room to go to the other SSID. In this case, what happens is that the client sends the probe. He will now receive the probe response. Then here, you can see that the association request will be initiated. Okay? An association request will be initiated. And I want to emphasise point number five because it is critical. Now, in this case, when the client is doing the networking across the AP or across the wireless networks at that time, point number five is important. So whatever buffer and whatever information AP One has, he will go and pass the information to AP Two. And then he will use the DS distribution system. He will go and use the wired media to bypass and relay the buffer information. Finally, this client number one will be assigned to AP 2. Okay? So you can see all these steps. We know what to do if you only have one access point. You will be in charge of the authentication. You will respond to authentication requests and association requests. And you’ll be part of the network, or society, in the case of rooming. When you have some problems, you are roused, then you do the probing, and then you do the association. Then this APS will sync their buffer data, and finally you’ll be part of the new access point network. Correct? Alright.

52. Understanding Cisco Wireless Architectures

Let’s try to understand this wireless architecture. We have several types of wireless architecture within wireless architecture, and we can discuss what is suitable for enterprise level. We have some well-known ones, such as cloud-based architecture and Split Mac. So let’s understand all the different types of architecture. So first of all, you can see in the diagram that we have an autonomous architecture. Autonomous architecture means that you have an access point that is working independently. So here in the diagram, you can see that you have an access point connected to the distribution system or connected to the switch. The problem with this design is that although you can manage the SSID, all these access points have to manage their own management IP. As a result, there is no centralised authority from which to manage common work, the common security framework, IP management, and so on. So if the network will grow in this case, in this fashion, you’ll find that it’s difficult to manage and that it’s not a good design for a big enterprise network, or even when your AP’s number of AP will grow more than, say, from 30 to 75, or from 100 to 200, et cetera.

It’s fine, but only for very small types of infrastructure with a small number of endpoints and no need for a third party or controller type of device to manage all of these access points. So for that reason, it’s okay. So this is the first, which is the autonomous architecture. The next step to reducing complexity is cloud-based architecture. One of the popular cloud-based architectures we have is Cisco Meraki, where you have the cloud-hosted controller and then you have your Meraki waste access points situated in the branches, in the Lanare network, etc. And so here you can see that you are responsible, which means the APS is responsible for the dataplane traffic, but they are getting all the control information from the dashboard that is hosted in the cloud, or we have the cloud-hosted control plane. Although the good thing about this is that management is easy, we can easily manage our infrastructure from one single location. We can go and log in and check various reports, various configurations, etc. from one central place. That’s the key we have with the cloud-hosted control plan.

Again, when we are talking about a cloud-based controller, we have the control plane hosted in the cloud, and with the control plane, we can do various operations, such as configure, manage, monitor, and create reports. Even though we have some visual representation, we can do the troubleshooting as well. So we have long lists that we can do from the control plane. And again, it is the data plan that is responsible for passing the data. Okay, so now you can see that we have autonomous architecture that has evolved to cloud-based architecture, and finally, that is our interest in this particular course. is the split Mac architecture where we have the wireless LAN controller. So now, in the diagram, you can see that you have two access points. One is autonomous, which evolved from autonomous architecture. And then we have the lightweight access point where they have given their brain to the central location, which is the WLC. So from WLC, what are the things we can do? We can go, and we can do the RF management. We have the association and roaming management, client authentication, security management keys, et cetera. There are so many things that you can check from the WLC, and you can manage the number of access points or the data plan devices. Again, it depends on which version of WLCcontroller or LAN controller we are using. According to that capability, we can manage the number of lightweight access points.

Now, what data-plan device is doing that? They are doing the RF transmit to receive Mac management encryption, et cetera.So I’ve got one comprehension chart here, and you can see that the names autonomous WLAN and lightweight autonomous indicate that their autonomous access point configuration of each access point independent operation managed by Cisco works with LSE and WDS access point redundancy. These are the things that the WLC is in charge of on their own. So they are the lightweight access points configured via Cisco land controller, dependent on Cisco land controller management via Cisco wireless LAN controller redundancy. So, depending on the failure scenario, we may have a primary and secondary utter WLC in this architecture. All right, so here you can see that in this case the APS we are telling them is a lightweight access point, and they have to go and register with the central authority. That is the WLC. Now, it’s still a question of how the lightweight access point will go about registering with WLC. What about the traffic? how the traffic will move from one client to another if both are registered with WLC. So we’ll go over all of that, as well as the protocol between the LNP and the WLC, in the next recording with you. 

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