CWNP CWNA – WLAN Topologies

1. WLAN Topologies

Now, in this module, we’re going to take a look at some of the different types of topologies we can have with the wireless local area network. So that means we’ll look at those topologies and talk about some of the eight or 211 options that we have and the 800 and 211 configuration modes that we have both for clients and for an access point.

2. Wireless Networking Topologies

So when we talk about wireless networking topologies so far, we’ve really only talked about what we would call the wireless LAN or the WLAN. But there are other types of wireless technologies like cellular telephones, Bluetooth connectivity, zigbee for larger areas that we want to go to.

So there’s four major types of topologies. There’s the wireless wide area network that we can work with, the wireless metropolitan area network, the wireless personal area network, and then, of course, the one we really focus on, which is the wireless local area network or the W LAN.

3. Wireless Wide Area Network (WWAN)

Now the wireless wide area network provides and generally speaking, just for a wired connection. The Wan is trying to provide coverage over a vast geographical area. I mean, that’s an area that might go across an entire state or region or country or even worldwide depending on how far we need to have our communications go. So with the wireless Wan, we can can also cover a broad geographical boundary. But obviously it’s going to use wireless instead of the wired medium. And believe me, that certainly can happen because we can bounce these wireless signals off of satellites that are like 25,000 miles above the surface of the Earth in outer space.

Now, your cellular providers like Sprint, Verizon, Vodafone, wherever you go in the world, use a variety of different types of technology to carry the data. Now, some of you might remember, at least in the United States, that we had a couple of earlier versions like the Code Division, multiple Access, the CDMA for a while. Some went to the General packet radio service, the GPRS. There was also one that you probably didn’t hear about a lot the Time Division, Multiple Access. And of course, we’re all moving to LTE, which right now stands for Longterm Evolution. And what’s cool about LTE is that they’re trying to make sure that your voice is going to go across as IP packets instead of trying to actually convert the analog into digital through some other medium.

4. Wireless Metropolitan Area Network (WMAN)

The wireless metropolitan area network gives you RF covered verge to a just what it sounds like metropolitan a city or even maybe a city and surrounding suburbs. The idea about the metropolitan area network is that it was supposed to be a short geographical distance with high speed connectivity.

Now, one of the types of wireless technologies that we often associate with that is defined by the 800 and 216 standard for that type of coverage. The standard defines broadband wireless access and sometimes it’s called WiMAX, which is the worldwide interoperability for microwave access.

5. Wireless Personal Area Network (WPAN)

Now, on the personal area network, we’re talking within ten to 30 meters from wherever the one point is to the other. So we call it the wireless pan. And it again, is a wireless computer used for communications between computer devices within close proximity of the user. As an example, your bluetooth. For those of you who used to put the little bluetooth earpiece in your ear so you could answer the phone or call somebody on the phone and not have to have the phone right next to you that worked very well, or even inside your home. You might be using Bluetooth or even infrared to be able to connect to, let’s say, a printer or some other computer or something else in your room or in your house that’s not very far away. Now, infrared, remember, is a light based medium. Almost always have to have a line of sight to be able to use it, whereas bluetooth is a radio frequency medium that uses the frequency hopping spread spectrum, believe it or not, often on the same two 4 GHz channel to be able to communicate with those devices that are in close proximity.

6. Wireless Local Area Network (WLAN)

The most common that we see is the wireless Local area network or the wireless LAN. These are what we have at home. These are the purposes of access points in the office. They have a greater range than a personal area network. And certainly we’re designed for higher speeds, designed to be able to connect more than one client to the access point.

And it’s basically is a perfect fit for replacing or adding to your already existing local area network simply because of the range and the speeds that are defined, especially when we get into things like eight or 211 AC with very high throughput. And that makes up the majority of the different types of wireless network deployments that we see.

7. 802.11 Topologies

Now, when we get into the topologies, basically we have a couple of components. The first and most important is the wireless radio, which some of you call the access point. But by the 800 and 211 standard, they just call it a station. Or you might see it abbreviated as sta. Now, there are a couple of different types of topologies that we could use. One is the basic service set. And we’re going to go into each each of these so you can see what it does.

The extended service set, the independent basic service set, which, by the way, does not need an access point and the mesh basic service set. Now, one thing to remember unlike your wired networks, at least in today’s wired networks, unless you have some really old equipment, everything operates in half duplex. That means you can either send or you can receive, but you cannot do both at the same time. Where in our typical wired networks today, we have a full duplex where you can transmit and receive simultaneously.

8. Access Points

Now the definition of an access point. It’s a wired infrastructure device typically associated with half duplex communications, like an Ethernet hub would have done. I don’t remember or know if any of you remember what the Hub is. You probably can’t buy one unless you go online somewhere and try to find somebody who’s hoarding old equipment. The idea with a Hub was that you had to share the and with. In other words, you might have four, six, eight computers connected to the same box.

But if any one of them transmitted, nobody else could. They had to wait for the line to be clear so that they could transmit again. Going back in history, and I’m really aging myself, some of you may once in your life had what we call a landline, a telephone that was plugged into a four wire jack in your house. And it was not cellular, it just went straight to the central office switch.

And then you might have said, you know what, besides having a phone in my kitchen, I would like to have one in my bedroom, I’d like to have one somewhere else. And so when they added those in, you were all on something like a Hub, which meant that only one of you could use the phone at a time. If somebody else picked up the phone, they could listen to your other conversation that was going on. So it was a shared bandwidth and it was great at the time, don’t get me wrong, but it certainly did not help us with communications.

Now, the original CWMP definition of an access point was that it was a half duplex device, much like I’ve just been describing, but it still had a switch like intelligence. Now, when we say switch like instead of a Hub, when we move to a switch or a bridge, we no longer had to share bandwidth.

Every device could communicate at the same time without any fear that there would be a collision or interference. So again, go back to my landline description. If somebody was on the phone in your house and you didn’t first listen to see if the line was clear and you picked up your handset and started dialing numbers, you’re basically putting those tones in everybody’s ears and causing a collision with the access point. We still can, on the radio frequency side of it have those collisions, but once it’s going to get converted from wireless to wired, that’s where the access point and whatever switches it’s connected to is actually going to make forwarding decisions based on Mac addresses, assuming that you’re connected to an Ethernet network.

So we can still use that definition to characterize the current autonomous systems, or what we call the autonomous access points, and we’ll talk about the difference between that and a lightweight one later. But there are some differences. In other words, we’ve put into the technology methods to try to prevent that interference. So the best example, then, like I said, of a switch like intelligence that are used by access points or wireless LAN controllers is to basically send information based on the address to the actual device on the wired network at layer two.

Layer two in Ethernet means we use a Mac address. Now, with the wireless, we still have Mac addresses, but we’re going to have a chance to talk a little bit more about the different types of Mac addresses we might see. Now the upper layer information, the IP address, the transport protocol, the data that’s not going to change. What we really have to manipulate is what we would call layer two on the OSI model, which generally, again, is speaking as the Mac address. So the upper layer information that is contained in the body of a wireless data frame, we’re going to call that the Mac Service Data Unit or the MSDU.

9. Distribution Service

Now, at some point there has to be a distribution service. The distribution service is how we are able to get the data that comes into the access point sent basically to the eventual destination, whether it’s on a basic service set or even an extended service set. And often we call the medium that we use for that distribution the DSM or the distribution system medium for almost every single one of our deployments. That medium is going to be Ethernet.

10. SSID

One of the other parts of the wireless network is a way of giving it a name. And we call that the Service set Identifier or the SSID. And really all it is is a logical name used to be able to identify a particular wireless network. If you really want to get into it, you could have multiple access points that can hear each other and actually have the same SSID. So one of the other things that we use to identify a specific network is what they call the basic Service Set ID, which is really just the Mac address of the access point. But for most end users, they might see, let’s say they’re at a coffee shop, they might see an SSID that says coffee shop, another one that says coffee shop.

And unless they really know how to dig into that, they’re not going to really know which one they’re connecting to, which can, for many people in identity theft, be a big blessing for them to be able to commit their crimes. So you can think of the SSID wireless network plus that Mac address as being comparable to a Windows workgroup name.

The big hope is that everybody has a different SSID. Now, in case you’re worried about people joining your network without having permission, there is the ability for what we call a cloaking, where the app access point can actually stop sending out their SSID in a frame. Later you’ll learn it’s called a beacon. But it really is just a warm, fuzzy feeling of security because, again, somebody who knows what they’re doing is going to know how to send a probe or just listen to the traffic and be able to figure out what the SSIDs are. So anyway, it’s not a password or anything like that, it’s just the name of a network.

11. BSS

When we look at the different types of topologies, the first one, the one that most of us have at home, is the basic service set and it is kind of the cornerstone of a topology. For the eight or 211 network. That really means that you have just one access point that your clients are going to connect to. There’s no other ones. So if somebody decides to move off somewhere else and get outside of the range then they’ve lost their wireless connectivity there’s and of course this access point don’t forget is connecting to a wired almost always an Ethernet network to be able to get their communications going. So really a basic service set is as simplistic of a wireless network that you can make and again, it’s just one and only one AP radio with more than one client trying to connect to it.