 with such a good understanding of the NGN recommendations in the Y-Series and with an overview of all the organizations where the regional or global and their roles that they have played in developing such standard and its recommendations. Now, let's look at the overall shape of the NGN that is based on the layer 3 IP based principle. So in this module, we'd have a look at the all IP concept of NGN. How naturally every technology slowly moved towards adopting IP and IP became the centerpiece or we can say the center stage for the NGN. So we'll start with appreciating that it was not a one-day revolution, but it was a technology evolution that took decades to materialize. And then we'll see the adoption of NGN as a standard does not necessarily mean an overnight action. It has to be a transitive migration. So how this migration has already taken place in various parts of the world and how this is in an ongoing phenomenon we'll appreciate it in this module. First, we must convince ourselves that NGN are all IP. What it means is that preferably starting from the customer premises on one end to the network on the core side and the customer premises or the server premises on the other end, it has to be all IP. Sometimes there could be a translation mechanism that is supporting IP, but essentially IP lies there at the center and it cannot be simply avoided in NGN. So how did this evolution take place? First, let's understand it from the original circuit switch networks. In PSTNs and PLMNs, it was widely understood that the users are going to be given a TDM, FDM or any other kind of let's say space division or core division multiple based access and at the same time internet as a data technology was being promoted and marketed and provided through the internet service providers. So to begin with these two perspectives were existing. The circuit switch users were there and the packet switched users were meant for the internet only. Now slowly, they all started moving towards IP. How? It's very interesting. First, the PSTNs and PLMNs started realizing that as compared to fixed circuit switching, they could somehow come up with a more smart switching mechanism or a multiplexing scheme that can cater for a larger user base. For that, first they converted their technology into packet switching and then packet switching started getting improved or got dove-tailed with the statistical multiplexing. So using the statistical multiplexing technique, more number of users were accommodated with lesser number of resources when all the users were not active. So we see that PSTNs and PLMNs started moving towards packet switching and eventually IP. Now since NGN is all based on IP and the legacy networks such as the PSTNs and PLMNs have existed before number one the internet and number two the NGN. So they have an influence. Now this influence actually dictates the quality of service. The quality of service in the absence of internet was based on dedicated resources. So naturally it had better performance. Now with their influence, the bar has been set very high. So it means NGN is now giving due consideration to the standard, I would say the gold standards which were set by these native networks to provide quality of service. Especially this quality of service becomes more important when it comes to real-time services like voice over IP and the IP TV broadcasting. This figure which is again from the NGN architecture protocols and services by Tony Jowinski gives a good overview of how technology migration takes place in steps. I call it the transitive migration. Let's look at the figure from the left-hand side. What we see here is a network based on traditional telecommunication infrastructure. We have the call signaling control that is SS7. We have a circuit switching infrastructure comprising switches and exchange points. Then we have the digital hierarchy that is E1s and T1s, the SDH, the SONET, OC3, OC12, OC48 and they appropriate interfaces to carry individual user data streams or corporate data. Now this was the traditional telecommunication perspective. Now when NGN adoption started taking place we see that gradually these traditional devices were replaced by IP-based systems. For instance, the traditional SDH-based hierarchy was replaced by the dense wavelength division multiplexing. The DWDM, the E-PON, G-PON, the passive optical network, that particular core and distribution network. Then we see circuit switching was replaced by the MPLS, the multi-protocol label switching, which is a layer 2.5 technology. It is slightly above layer 2 and slightly below layer 3 because an IP packet gets encapsulated into shim header-based structure, which is carried by the MPLS domain. Then the SS7 signaling was replaced by the SIP, Session Initiation Protocol-based signaling, the IP multimedia subsystem and all these. So we see that depending upon the requirements the migration took place and eventually a complete IP-based infrastructure was realized that is NGN by the gold standard or by the purest definition. Let's look at now an example of TV broadcasting. To begin with, in the old way or the traditional way, the TV transmission was distributed over separate networks to meet different customer requirements. For instance, we had the terrestrial television, which we call the typical TV broadcasting. Then we had the satellite TV, we call it the dish television, and then we had the cable operator-based TV channel distribution. This was the traditional way. Now, what is common to all of them? Number one, they all use the TV color carrier and the audio carrier and the spectrum was six megahertz. So it was analog transmission. Then we also had digital television. The digital television was based primarily on the analog technology getting translated into digital signals. But essentially it was digital, it was still not packetized. Now, the new way of transmitting the same TV to television transmission to these customers is now to digitize and packetize the television transmission before sending it on to any specific network. Now, when something gets packetized, it means it gets ready to be encapsulated into an IP packet. Good for us that with IP at the heart of NGN, it can carry television over the different distributions and different customers can be provided these services. An interesting observation here is that the television transmission was the last for adoption in terms of migration to NGN as compared to voice and data. Because translating voice and data into packets means, yes, an increase in bandwidth, but not that much. But when we talk about television, TV broadcasting means very high-fidelity audio and video. Now, let's look at how we moved from the typical silo effect in which we had the voice, data and TV and radio, that is both voice and video broadcasting, which were carried by these different networks. We see that voice was carried by the PSTNs, the mobile networks, the integrated services, digital network. See that now the data was also carried by ISDN sharing it with voice. And then we have data carried by Ethernet as well. The TV broadcasting was carried by TV broadcasting as in satellite, cable or things like that. Then we also see that the data is in the middle of voice and radio. What we observe from here is that anything that can be digitized is nothing but data. So the data part in these three voice, video and data services is central to what internet can carry. So a digital packet, which is switching packet from the beginning is the internet. So statistical multiplexing can take place and consequently everything can be moved on to IP. So with this silo, we were living in isolated islands. Now we have the NGN effect. You see, instead of horizontal silos, we have the vertical layers. These layers are actually horizontal separation of the services, the applications and networks. So we can have the plug and play. We can change the applications. We can change the services and we can change the networks as long as all these are IP compatible. Now this is what is known as the NGN effect.