Gradually, the directory, addressing and routing functions separated from the interface and became part of the network services while the interface became the next generation application. Applications will often be built on top of other applications, which in turn, may be composed of still other applications. An application, that is originally written for one or two parties, can evolve to a service, as more people and organizations begin to use it. Services can either be shared by several applications or be specific to a single application. The aspect of the NII that is critical and most difficult to realize is the development of a services infrastructure.
Services support a variety of activities.
Some help users to move and navigate between different networks and information resources. Others simplify applications programming by hiding many of the lower level systems details from the developer. The NII must have built-in privacy safeguards to allow individuals and companies to conduct business with the confidence that data and information are private, authentic, and secure. The services layer must therefore also include services that implement privacy and trust mechanisms as well as defensive software organized to protect the infrastructure from intrusion and attack. The services provided by the information infrastructure must be accessible by users with widely varying skills, experiences, abilities and backgrounds.