 We'll now look at the transition of IP networks to NGN. IP is at the core of the IP multimedia subsystem and of course the next generation network. But regarding IPv4 in particular and we'll see shortly IP version 6, we need to have a complete roadmap after understanding different aspects related to this transition. So we are going to look at the transition of IP networks to NGN in the form of these topics. The main idea of transitioning is that IP based next generation networks would essentially imply some major transformation. This transformation is going to be at the network level of course, the network being part of a service provider and in addition the way usual business runs, it's also going to be changed. We know that next generation networks is essentially a converged network, whether it is the convergence of the core and transit parts, whether it is the applications or services or it is the integration of voice, video and data. So in order to transition, the principle is going to be change the network structure and their interconnections. From the NGN reference architecture, we know we had the service stratum and the transport stratum. So we'd like to align the IP networks with essentially these two strata. Following the structure of the network, whatever IP network essential elements may be, for instance, if synchronous digital hierarchy, sonnet or any other underlying technology is being used, the first step is going to be to replace or change the underlying architecture with IP routers. This is going to result into the network ready for being declared as NGN known as the next generation access network. This is going to involve the core network as well as the transit network. Then we are going to look at the way ISP runs a certain network as a autonomous system. Traditionally, an autonomous system is defined internally by whatever intra autonomous system protocol. Externally, it is BGP that carries network related information to other networks. But now we are talking about NGN reference model. So the entities such as the resource admission control function, network attachment control function and home subscriber station like entities have to be brought into existence here as well. With these three most important entities of the reference architecture, we are going to interrelate the transport network services and the end users. IP multimedia subsystem is not only important and relevant for PSTN, PLMN migration to the NGN, but it's equally important for IP networks as well. So here we are going to need IMS implementation for AAA for the users and the resource request made by the users. IMS is going to be essentially incorporating SIP signaling and the radius advanced form known as diameter for communication between entities and databases. For instance, accessing the user profiles and their corresponding service profiles. Interconnection being a very important aspect of an IP network has now to be changed in accordance with the new requirements of NGN. For instance, in IP interconnection, ISPs traditionally work on the basis of BGP and the IP addressing is pretty straightforward because it does two things. It localizes the entity to whichever IP address is assigned and then it gives it an identifier. Here we need to provide mechanisms through which interoperability can be achieved between different NGNs each speaking its own language at the service level, control level and the transport level. Then we need mobility control function for mobile environments. And most importantly, we are going to introduce standardized interfaces. If you recall, application to network interface, network to network interface, service to network and user to network interface. Now let's look at the visual of the architecture for NGN interconnection as in IP. As we might expect, we have the customer premises, we have the edge network and we have the core network. We are going to incorporate corresponding interfaces like user to network interface, network to network interface and the application to network interface. So whatever we incorporate, we see that using standardized interfaces allows a smooth transition of IP networks to NGN.