 In this module, we shall understand what is an end user and in the NGN reference architecture what functionality is assumed for the end user function implementation. An end user is essentially a device. It could be a laptop, a desktop, a smartphone or any other kind of user equipment that is authenticated and is allowed to access the network functionality. The functions that need to be implemented by the end user are supposed to interact both with the service and transport stratum. It means the end user equipment is going to interact on need-to-do basis with some modules in the services stratum and some modules in the transport stratum. While doing so, it has to have its own identity because after all it's an entity so the identity management module also has to interact with. Let's look at the end user functions which are shown to you on the left-hand side at the bottom. Here we can see that it has various kinds of interfaces. The strongest interface that it has is via a user-to-network interface with the transport stratum. At the same time it has interfaces directly with the transport control functions with the service control and content delivery functions and it also has definitely interaction with the application support functions. Now with these different kinds of interfaces, the end user is able to implement the user functionality necessary to let the user interact with the system and run an application of its own liking. The interactions for end user functions are within the data plane, at the transport stratum and the services stratum as we just shortly said. In the data plane, the responsibility is essentially to carry the user traffic via the transport functions. For that, the user-to-network interface is invoked to let the transport carry data coming from the application that the user is controlling. The transport stratum essentially is related to the call control signaling, for example the session control, session initiation, termination, etc. And in the services stratum, the service control function and content delivery function are also interacting with the end user functions. Now you may see and appreciate from the previous lectures that the services control function was related to the resource and admission control. After all, the sparing of resources and allotment of resources is an important functionality of the services stratum, which is implemented by the service control function. And the content delivery function is related with taking the data from the particular application on behalf of the user.