 The method in the implementation of the engine reference architecture is key to how different functions are organized in the layers and the strata. The service stratum functions are grouped into the application and service control functions, the service control and delivery functions. We are now going to look at each one of these in due detail. The application and service support functions are essentially related to how the application and the service are provided by the engine reference architecture. Remember that two important functions that is the end user, how the end user wants the network to execute its service or the application and the second is the application or service itself. It means the application and service support functions comprise all the functions which are related to the implementation of the smooth functional aspects of the applications. For that, the application and service support function to begin with interacts with the application itself. Now how the application is integrated into the system, how is it initialized, what all initial parameters it is passed to and what all arguments does it pass to the system is implemented via the application to network interface. Then the application and service support function also interacts with the end user. Now the end user is identified by the person or a system for that matter which is trying to utilize a certain service provided by the engine. Now the user is going to interact with this application and service support functions through the user to network interface. Now these interfaces that we have discussed before also are important to the implementation of the application and support functions. Now the functions at the application layer specifically include, imagine any application that needs to be provided on NGN, it has to be registered first. If it's an unregistered service, it won't be provided on NGN. Likewise, if a certain version or a certain release has to be registered, then it has to be registered with its own version number, release date and the particular bindings that it has to make to run smoothly. Then the application has to be authenticated as well that specifically is this application legitimate or permissible to be allowed on this network and then who all are allowed to use this particular application that comes under the umbrella of authorization. Now the end user functions are controlled by the service control function. The service control functions are as you can see we have the service stratum. The service stratum has two parts, the application support functions, the service support functions. The service support functions in turn utilize the service control and content delivery system. The service control and content delivery functions implement the all the necessary functionality that the user is needing to execute that particular service. We shall look at it once it's required. Now the service control and delivery function are related to two important aspects. Number one, a service needs to be controlled that is a service needs to be activated. It has to be stopped. It has to be resumed. It has to be controlled by a group of users like a user group. Then the content has to be delivered. So specifically the service control is regarding the control of the service and the content delivery is related to the content delivery functions. Now the service control functions are implemented to actually manage the resources which are required for the service execution. This certainly relates with if you remember the transport stratum we covered the resource and admission control functions in the transport stratum. So there is going to be some kind of interaction between the service control function and the resource and admission control function. When we had discussed the radio the resource and admission control function in the last module we had also discussed the interaction from the RACF viewpoint. Here we are looking at it from the SCF viewpoint. Essentially these interactions are bi-directional. Again with regards to the service the service has to be authenticated that is only an authenticated service can be run in the NGN framework. Then it has to be authorized for a certain number of users. Now we have discussed it before there is a notion of a database that is a list of records that keeps track of all the registered services and applications and all the authorized users who can access these applications and services. And lastly the content delivery function is very important. The content delivery function is a function or it is an implementation that interacts with the application support function and service support function regarding the content. The content is stored in a certain format. It means some kind of encoding, decoding or transcoding mechanisms have to be activated. The end user functions which are actually managed by the upper layer the service application and service control functions. Now interact with the underlying transport functions to get the content from the application and deliver it into the network. Let's quickly go back and look at the overall concepts that you've studied here. As you can see we have quickly looked at how service stratum is organized. We have the application and service support functions. Then we have the service control functions content delivery functions the content delivery function in in turn interacts with the transport stratum and the service control function utilizes the functional database that needs or that contains all the necessary authentication and authorization mechanisms. It means that we have now summarized how the service stratum is organized. We have already seen how the transport stratum is organized.