Module 5 - Selecting WAN Technologies

1. 5.0 Selecting WAN Technologies

A business with multiple locations needs a network that not only interconnects computers, printers, and other network devices within a building, but also They need to interconnect the buildings at their different sites, maybe over a large geographical area. That's what wide area networks, or WANs, can do for us. And that's the folks of this module. And this might involve bouncing signals off satellites using a cable modem being assigned her own wavelength or lambda in a Metro Ethernet network. So join me in our next video as we contrast packet-switched networks with circuit-switched networks.

2. (N10-007 ONLY) 5.1 Packet Switched vs. Circuit Switched Networks

In this video we want to compare a couple of different categories of technologies for wide area networks, and those two categories are circuit switched and packet switched. A circuit switch is much like a traditional telephone call. A circuit or a call is going to be set up before we send any data. This is what was happening with the older dialup modems that we had. We would dial up an internet service provider, maybe like America Online, and a circuit would be established for the duration of the call. This might also be used with ISDN circuits. Those are digital circuits that carry voice, data, and video. As a couple of examples of circuit switching, I want you to think of telephone calls and ISDN, which stands for Integrated Services Digital Network.

That's a technology that goes back a few decades and it could carry voice or video or data. And you could bring up a circuit on demand because, back in the day, you might be paying for the amount of time that the circuit was up. So if you didn't need the circuit at the moment and didn't want it to be up, that was a great fit for a circuit switch network because we wanted to bring the circuit down when it's not in use. And these circuit switch networks gave us dedicated bandwidth. So if we brought up that ISDN connection, that was our bandwidth and we were not sharing it with anybody else. Same thing with a dial-up modem. But on today's wide area networks, we are much more likely to find some sort of packet switching technology.

This is a connection that is always on. We're not trying to build and then tear down circuits. And like circuit switched, we can carry a variety of media such as voice, video, and data. As a few examples, cable modems that you might have in your home or your local cable company might be your Internet service provider, or you might connect to a wireless network or your local area network. All of those are examples of packet switch networks, where our data, voice, or video gets packetized. These packets can be routed throughout a network. But in a network like this, typically bandwidth is going to be shared between different clients and servers on that network. For example, we might have several devices connected to a local area network, and we hopefully have enough bandwidth to support the operation of all those devices simultaneously. And that's a comparison between circuit-switched and packet-switched networks.

3. 5.2 Cellular

In some cases, the best way to get out of the internet is to use cellular technologies. Maybe you've got a smartphone and you send your data to a cell tower, which communicates with a service provider that gets you out onto the internet. And I say it may be the best way because you may not be in an area that has Wi-Fi access. And it's not just a smartphone that can communicate with a cell tower. You might have mobile hotspots. Many people that don't have broadband access will have a mobile hotspot that connects via cellular technologies to their service provider and devices around their home, like their laptops, maybe their smarts, that connect to that mobile hotspot. Even vehicles of today might have cellular technology built in. This is where the car itself becomes literally a mobile hotspot. And your passengers with you in the car can connect their devices to the car acting as a mobile hotspot, which gets them online using cellular technologies. And in this video, we want to take a look at some of the different generations of cellular technologies we've had over the years. And you're going to see the term "g" used a lot. The g refers to the generation, and we're going to start with the first generation, or one g. This did not have data. This was a strictly analogue voice.

Data was possible with the second generation, or 2G. This added support for data standards such as GSM Global System for mobile communications and CDMA code vision. Multiple access and which one you used depended on your carrier. And the second generation was improved somewhat with the GPRS standard. And this is what many people call 5G. This added a packet switching service as opposed to a circuit switching service for data. And it got even better with 275 gin in the Edge network, where Edge stands for fore enhanced data rates for GSM evolution. You might have heard of the Edge network if you watched Steve Jobs' famous announcement of the original iPhone back in 2007. He said that the original iPhone was going to use Edge for cellular data, and he explained how much better that was than two g. And he said they didn't want to use 3G in the original iPhone because of the power consumption. So Edge was the technology in the original iPhone, despite the fact that 3G existed at the time. And as technology improved, more and more smartphones began to adopt 3G, which, of course, gave us better data rates.

And those 3G devices might use standards such as UMTS (Universal Mobile Telecommunications System) and CDMA2000, an updated version of Codi vision multiple access. More recently, though, we have had four g. And four, technically, requires your provider to give you at least a network that can do 100 megabits per second at a minimum. But many of the 4G providers out there didn't really do 4G. They did something close to 4G. They were trying to get to 4G, but they would call it something like 4G. They were all LTE, where LTE stands for Long Term Evolution, implying that they were evolving towards faster speeds, but they weren't up there yet. So, while 4G technically required a minimum download speed of 100 meg, 4G LTE typically had speeds ranging from 20 to 100 megabits per second, which is where four G began.

More recently, we've had 5G advertised. This gives us much higher speed and very low latency, which is critical for applications such as autonomous driving. Your smart car wants to have minimal delay if it needs to know how to react to a certain condition on the road. And there are two different flavors of what you might hear about. There aremillimeter wave and sub-six frequencies. Now, millimeter waves are the faster of the two. The downside to millimeter wave is that it cannot use the existing cellular infrastructure where we have cell towers all over the country. They're going to have their own antennas and they're going to have a much shorter range because they're using really, really high frequencies. And these waves are going to bounce around inside an office environment. And you've got to have a fairly tight density of these millimeter wave antennas. in a city. You might see millimeter wave antennas on the top of light posts or traffic lights as a couple of examples. More commonly today, we have sub six,which means sub or below 6 GHz. This can use some of the existing cellular infrastructure and still give us better speeds than 4G, but not quite as good as millimeter wave. You typically have some somewhere in between, typically someplace above 4G but below millimeter wave. And that's a look at some of the different generations of cellular technologies we've had over the years.

4. (N10-007 ONLY) 5.3 Frame Relay

When I was working with wide area networks in the 1990s, there were two primary ways of interconnecting different business locations. You might have a headquarters and a couple of branch offices. One option was to have a dedicated line, maybe from the headquarters to the branch office one and another lease line over to branch office two. However, in some cases, instead of paying for a dedicated line from the headquarters out to each remote site,it was more cost-efficient to have a single connection into a service provider's frame relay cloud. In this example, HQ can send traffic directly to BR One and BR Two can send traffic directly to HQ and vice versa. In fact, even BR One can talk directly to BR Two. How is this possible?

They each have a single connection to the wide area network. But if you notice the dashed lines, those represent permanent virtual circuits, or PVCs. These are virtual circuits that can live on a single physical circuit. Notice that HQ has a couple of these virtual circuits and they're identified with Dells DLCI. That stands for Datalink connection identifier. And that Delco of one two is going to connect into a frame relay switch that lives in that service provider's cloud. And then a switch in the service provider cloud is going to have another permanent virtual circuit out to be our one, and it uses Delco 20 for one different Delco number. In the end, these are different virtual circuits that are being tied together with the Framing League switch in between. But by having the service provider do some configuration on their frame relay switch, we can have virtual connections and not have to purchase additional physical connections. And that's a look at a somewhat legacy wide area network technology called frame relay.

5. (N10-007 ONLY) 5.4 ATM

In this video we want to consider the asynchronous transfer mode, or ATM for short. ATM is unique among wide area networking technologies in that it uses a cell to transport data rather than a packet, as most Wayne technologies do, where those packets can be of variable size. And that cell is of a fixed length. And that length is 53 bytes. The 48 bits comprised the payload. And we've got five bites of header for a grand total of 53 bites. And at 48 bits, that might seem like a somewhat random number, but it was actually based on a compromise between people that wanted to use this for voice communication. They preferred smaller payload sizes and data communication; those people preferred larger payload sizes. So they compromised and came up with 48 bytes of payload. And ATM allows us to have a single physical connection from our site into an ATM service provider's cloud. And even though we have a single physical connection, we can have multiple virtual connections running over that single physical connection.

And the way we identify one of those virtual circuits is based on a VPI VCY pair. An example of a virtual circuit identifier might be 100, 110. 100 is the VPI, the Virtual Path Identifier, and VCI is the Virtual Circuit Identifier. And we can have multiple VCIS, as you see on screen, belonging to a single VPI. But that's the way that we organize and address the different virtual circuits within ATM. And to zoom out and consider how we communicate across an ATM service provider cloud, a couple of terms I want you to know when we're connecting from our site where client one is, we'll say,into the ATM service provider switch. That type of ATM connection is called a unitconnection. That’s a user-to-network interface where the user is the customer and the network is the ATM cloud. Now, between ATM switches within the cloud, that's called an in connection. That's a network-to-network interface. And then we exit the ATM cloud and go to the destination where client two is on another machine and I, another user on the network interface. And that's a look at the fixed-length sell Wayne technology of ATM.

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