And now that we have understood the concept of cellular networks in a structural way. Let's try to take a broader ten thousand foot view at how modern day cellular networks look like. Now, regardless of the generation be it, 2G, 3G, 4G or 5G, which are the generations of cellular communications as some of you may know already. Although there are structural and functional differences at the high level, their network architectures have many commonalities. And if you extract all those commonalities and try to plot a generic cellular network architecture of today, this is how it will look like. In that, there is your phone on one end and at the other end there are all the services that your phone is trying to access. Be it news, be it whether, be it email or be it video streaming, be it picture sharing or be it video telephone, etc. Whatever those services are, those services are present at the other end of the connection. And in between is what we proverbially call the cellular network that is deployed by your cellular network operator. Now, a cellular network has two fundamental components, one is called RAN or Radio Access Network, the second is called Core Network. Let's try to understand those one at a time. The RAN comprises multiple base stations or cell towers and these are the entities as we have seen that exchange wireless signals with your phone. So when your phone powers up and tries to send wireless signals somewhere, a base station that is nearest to your fourth is the entity that ultimately receives those wireless transmissions. And as I also mentioned at a given point in time, you will be served by the base station that is closest to you. But when you move you may be handed off from one base station to another. And for that purpose two things have to happen, your network operator has to have a nationwide deployment of such base stations. And secondly those base stations have to be interconnected to each other directly or indirectly so that they can communicate with each other. So that they can ensure that your handover will be successful when you move from one base station to another. And just to give you a context in the country the size and shape of the United States. A typical network operator in order to provide nationwide coverage might end up deploying literally tens of thousands of base stations. So all those base stations comprise what is known as the RAN or Radio Access Network. And those are the cell towers or the base stations that we see all around us as I mentioned earlier. Now, when you, for example, go to a cellular network operator store and purchase a subscription you get the same card. The network operator assigns you certain credentials. Are those credentials stored with every base station? No, not really, those credentials are stored in a central repository that is a part of the second half of the cellular network that is called the core network. So core network is the central repository where the data regarding your subscription etc will be stored. And apart from that, core network has another important functionality in that it is supposed to be the routing bridge between your phone and the services network over here. And if that sounded a little confusing, let me elaborate. Let's say that you are trying to check your email, so you will open up your email client. But keep in mind that your email server which hosts your email isn't located here or even in the Core Network, it is located in the services network. But on the other hand, your services network doesn't know where you are located or what base station you are being served by. And that is where Core Network steps in, it acts as the middleman between your phone and the services network. That way, when the email server in the services network sends your individual email package to you, they first land on the Core Network. Core Network forward those email package to the precise base station that is serving you at that point in time. And that base station sends you those email package over your wireless channel, so this is how cellular communication works into it. And this is the rule that Radio Access Network and Core Network in the overall sentiment procedure, both of which are part of modern cellular networks. And as we'll see in the later chapter, when we try digging into the specific network architecture of a modern day 5G network. We will see that it utilizes the essence of the same basic network architecture while making certain improvements for performance purposes. And that will be the focus of some of our subsequent modules.