Now that we have seen what 5G is at a high level and what are some of the fundamental promises that it makes with respect to performance. Let's turn our attention to learn about how 5G networks look like and what are some of the fundamental features that enable 5G networks in this module, we will learn about the structure of general changing network at least at a high level. We will see a couple of important options using which 5G networks of today and tomorrow can be deployed. Then we'll turn our attention to a related point that is understanding some of the general networking principles underlying 5G deployments. And then we will focus on some of the specific features or techniques that help at 5G networks are substantially improved their performance on top of the Legacy Network performance. So this is how a general 5G network looks like at least at a 10,000 ft level, so to speak. And the good news is that if you eyeball the schematic, you will notice that it is very similar to the general cellular network structure. We have studied at the very end of module one in that you have a phone on one end and at the other end you have a services network where in all the services that your phone leverages such as email, web browsing, video streaming, etc. Those services are hosted in the services network now, although the general schematic is very similar in 5G. There are certain changes in that there are some specific network components and furthermore, some of the network components are given different names. For example, what we call the phone in five years technical parlance is called a U.E. or user equipment equipment that is ultimately operated by end users like you and I. That equipment is the user equipment. And although we show a phone over here, user equipment is the technical name for pretty much any equipment that an end user like you might use in the 5G network be it a tablet, be it a fitness tracker or be it any other device at the other end. As I said, there is services network, which in 5G parlance is called data network. Data network as you may have guessed, is the place that hosts your email server, your video servers etc. All the services that are ultimately used by the phone which we now know is called UE technical parlance. And what lies in the middle is the proverbial 5G cellular networks. As you know, it has two parts, one is the access network Called 5G RAN and the other is the core network in this parlance called the next generation core or NGC. Focusing on the RAN as you know, the RAN is what has the wireless channel with your phone. And in technical parlance, the wireless channel is also called the air interface. Now the principal component of a 5G RAN is called a gnode-B. And there is a little bit of history to that name in that the base stations in 3G were called node-B base stations in 4G. Were an enhanced version of the node-Bs and hence they were called in or Enode-Bs. And the base stations in 5G are the next generation of node-Bs in that succession. And that's why they are called the gNode-B. Node-B is essentially the cell tower or the base station In the 5G network. And to provide ubiquitous nationwide coverage. For example, you can pretty much guess that given network operator would have to deploy a nationwide network of these gNode-Bs. And a typical operator might have to deploy easily tens of thousands of such gNode-Bs to cover a country. with the size & shape of the United States for example. Now, as you know, at a given point in time UE is served by a given gNode-B typically the gNode-B it is located the closest to and as the UE moves from one point to another, as the user handling the UE moves. Then the 5G connection would be transferred, so to speak from one gNode-B to another in a process reminiscent of what we have learned earlier. It's called handover and to make a handover possible. You can also guess that these gNode-Bs would have to be interconnected to each other. So that is what gNode-Bs do as far as the wireless channel or the air interface is concerned. They are the wireless end of the 5G network at the other end. As you can see all the gNode-Bs are connected the 5G core network. But you see a couple of interesting lines here and those are for a reason you see one daughter line going from each gNode-B. And then you see one solid line and there is a reason for which there are two lines. General traffic in a cellular network is typically broadly classified into two categories. Data and control as the legend shows here now. Although the names are technical, it is easy to understand the essence of those ideas in general. Whatever that you see on the screen of your phone, be it a picture, be it an email, be it a webpage, be it a streaming video. Whatever you generally see on the screen of your phone as the user oriented content is in technical parlance known as user data or user plane. Okay, whereas the signaling that occurs in the background under the hood, so to speak, in order to bring that data from a data network to your phone. Once again be it a picture or an email, whatever signaling that it takes for the network to bring the picture or the email from data network to your phone is called control messaging or simply signaling. So there are two types of packages that are exchanged in the typical cellular network data is what you see on the screen of your phone. Whereas control messaging or signaling would be the part that is used to establish and manage the session that actually brings the content to you out from the data network. Another easier way to understand control versus data would be regular letter writing analogy suppose you write a letter to your friend. The content of the letter, what you write on paper would be of interest to your ultimate reader and that's why the content of the letter would be used for data in this context. Whereas the act of putting the letter in an envelope, writing your friend's address, going to the post office, getting a stamp and then mailing the envelope to your friends. All those auxIliary activities that ultimately help your friend get the letter. Those auxillary activities could be seen has control messaging or signaling. So that is a fundamental reason why there are two lines in this figure. Another interesting thing that you will notice with respect to core network and these lines is that the dotted lines go to a component called the AMF and the solid lines go to a component called use user plane function. And this is what brings us to this because the core network. Now a typical core network be it 4G or 5G contains easily more than a couple of dozen components but we will only focus on some of the key components are here today. Because they happen to be the most prominent and the most consequential components so to speak. At least as far as today's curriculum is concerned. So the three components, we will focus on AMF. Smf and user plane function once again noting that these aren't the only components. There are many other components are present. What is AMF, it is access and mobility management function as the note says here. And the name is pretty self explanatory whenever your phone needs to access the network for a given service, it needs permission so to speak from AMF and once AMF has permitted the to access the network. The data session is established and managed by SMF which stands for session management function. Once again name is self explanatory. So session management function has responsibilities like bringing up your session, assigning your phone and IP address and managing and ultimately tearing down your session and the actual data. The actual content you see on your screen, be it a picture or an email that is handled by user plane function. And in this context, the name, once again maybe self explanatory because this network function handles user data whatever you see on your screen. That is called user plane function and that is the ultimate reason why you will see user plane function has data connectivity with the services network or the data network. So your picture goes from the data network to your UPF from UPF to your serving gNode-B and from your serving gNode- B or the wireless channel careful as always. There is an easier way to understand AMF. SMF and UPF, let's say that you're trying to apply to college or grad school. The first office in the university that you communicate with is usually the admissions office. They determine whether they can admit you to their university or not. And once you have been admitted by the admissions office you then go to the student services office on the first day of school to get your student ID. And to get your classroom scheduled and once you have your classroom scheduled you go to your actual classroom where classes are taught ie where the content that you're interested in is actually disseminated. So in that analogy your AMF would be the admissions office, the SMF would be the student services office and the UPF would be the actual classroom where the actual data transmission and reception happens. And now that we have got a broad overview of 5G network architecture, let's try to translate that knowledge and practice and see how 5G networks can be deployed in reality.
