 The concept of services and applications is central to the next generation networks. The ITU recommendations for NGN include the service capabilities and service architecture, which entail all the details which are related to what the service should be defined like, what are the components of a service, how the service should be delivered, through which interfaces should be the service accessed from and all these kinds of details. So in this module, we should briefly look at the concept of service capabilities and architecture from the specifications point of view. First of all, NGN recommendations define that a service needs to be made or it has to be considered different from what an application looks like. The World Wide Web, which is a well-known client server application, which has always been available on traditional internet, is an application because it involves a client and a server. As such, there isn't much of a responsibility on the underlying infrastructure or the network to provide any exclusive services. On the other hand, if you look at more complex applications such as providing voice over IP, we need some kind of signaling support. So a signaling service is required of the underlying infrastructure. In reality, NGN discusses and looks at services differently from applications because services are embedded in the network, whereas the applications are end-to-end. So the NGN recommendations state that a service needs to be elaborated in terms of the capability that either it provides or it requires. Specifically, for instance, let's look at the behavior of a service if it is a real-time service or a non-real-time service. Is this service meant for a machine or is it meant for a human being? So the concept of machine-to-machine communication comes into play, then machine-to-human or human-to-machine. Consequently, depending on the service type, underlying communication models would arise. So a service would be requiring a specific kind of communication model. And when a service is solicited or when a service is provisioned, a certain business model has to be adopted. So the recommendations give guidelines and give some details about what the business model and communication model should look like. An important aspect for services is that if a service is to be offered on NGN, if it was offered before on traditional network, on any legacy system like the Internet or any other like the traditional TV broadcast or radio broadcast or cable service, some standardization has to take place because if a service is to be offered on NGN, the user could be sitting on any proprietary or any exclusive legacy network. So a service needs to be equally accessible for that standardization has to be implemented. A key component of standardization is when a certain service is implemented using some standards, it has to be defined by interfaces. These interfaces need to be implemented. The implementation of these interfaces ensures that no matter who is accessing the service or from where the service is being accessed, it is interoperable and it is smooth. While a service needs to be considered for NGN, some backward compatibility has to be ensured as well. So it means the overall NGN architecture spells out service architecture that says a service which is implemented on NGN may offer advanced features, functionalities or implementation, but it has to provide the minimalist set of functions or features that it was providing in legacy systems. So that if the soliciting side is seeking some service or is providing some service, so a harmonized view or a consistent view is seen across all the NGN.