 Web Services is a well-known concept in the overall internet community, but when it comes to NGN, the ITUT came up with standardizing the access of web services. So in this module, we are going to look at the formal definition of web service, how these can be extended from the traditional best effort internet to the NGN. And what are the implementation options that we have? So the precursor to the web services is actually the web. When I say web, it actually means HTML pages, the hypertext markup language based static pages, which included the text and some illustrations. So HTML pages were best suited for delay tolerant applications such as browsing, which was based on HTTP. The concept of adopting the HTTP subsequently for web service comes with a lot of advantages because the overall legacy of technology helps us to embrace the benefits that we have seen in maturing HTTP because HTTP moved from 1.0 to 1.1 to HTTPS. So it means that it's a very matured technology. So once we talk about generalizing or abstracting the concept of service because we are moving from web browsing to literally any browsing, this helps us to take benefit of the existing architecture. In existing networks, when we talk about the interaction that takes place between the browser, user equipment, which resides in user equipment and the web server, it is based on the concept of cookies, which provide some pleasant user experience and historical logging through cookies. But cookies have their own limitations because they are strictly tied up with the concept of web pages. But so how these are extended, we will see in a while. So web services actually are formally defined as a service, literally any service, which is provided by using the system of browsing or the web. This means we are going to use the concept of request and response. We are going to look at the concept of URL, which is resolved using the domain name system. And then we are going to look at the concept of the server, which is available 24 seven. So once we have adopted these three essential features of services on web, we can extend them to literally any service. So the web services, which are actually adopted by ITUT and NGN make a more generalization up a good generalization to the web pages by assuming that the relationship between the request and the response is determined real time. Like if you are making a request for a web page, you are expecting that particular web page to arrive and you the parameters that you've passed in that request are straightforward. But once you loosen up the relationship between the request and the response, this allows a variety of features that can be incorporated in real time. This can be implemented through XML, which is a extensible markup language. It's a much more powerful feature feature based variant of HTML in which the user literally can define anything in HTML kind of tags. So if you have such a mechanism, then you can incorporate these web services to provide literally any service using the web. For instance, there is a protocol known as simple object access protocol as the name implies, it's an application layer protocol that works over HTTP, so you are encapsulating the SOAP message in HTTP payload to carry traffic that literally can pass any kind of service from the service provider end to the service user end. So now if you want to publicize or publicly make a web service available, then for that NGN provides us the standardized interface of the ANI or the application to network interface. So when ANI is used, it means any web service that has to be serviceable over NGN has to be registered. The registration format is defined by Wastel or the web service description language. It is a kind of a variant of XML that is machine readable. It contains the metadata of the service. For instance, how to discover a service, how to make a call, how to activate it and how the service can be altered or the if it if it has certain parameters that can be tweaked and particular data structures. So once we have the ANI application to network interface, so the XML based web service registry process in Wastel helps the web service to be present. Once a web service is present, then the web service provider actually looks for these services because these services can be coming from third parties. So it means that some kind of web service provider will make a pool or a list of all the services that it will provide to the user that makes a request. So it means that there is going to be an entity known as the registry entity or you can call it a directory agent that keeps track of all the web services which are present in NGN and then web service providers are going to discover these services and are going to share them with the clients. And of course, once these services are discovered, then the service providers can use SOAP to share these services with the service requesters. When we look at the web services, we can think of literally any service that starts off as being simple HTML page to more complex services like IPTV, the PSTN or the digital network like integrated services, digital network kind of emulation service that behaves or performs like a real PSTN or a digital video broadcast network or probably voice over IP service. So it means if you start thinking about all these services, they're all web services, but web service as such still allows you to do something new and advanced. So let's look at the architecture. In this architecture, we have, if you look at figure, the two rectangles are the NGN architecture in the core, we have the service stratum, we have the transport stratum. The service stratum now has the application support functions and service support functions, which are now going to interact with the web services through the application to network interface. The web services are there, discovered and available for use by the providers. They are discoverable through their respective wasteels. The registry service keeps track of all the possible web services that the web service providers can discover and subsequently provision to the end users. So there's a repository. Then we have the requester or the end user equipment. So above the application to network interface line, you can see the complete architecture. It's actually known as the service oriented architecture. If you look at this, you will understand that the abstraction of web service is such a great breakthrough or an advancement for providing literally any kind of service over the amazing NGN architecture that is geared to provide quality of service suited to the web services individual requirements.