Figure 1 A model three-layer architecture for the NII. Bitways provide the communications substrate, the applications layer supports the implementation of the NCs, and the services layer provides the bridge between communications and information. (a) Despite the need for similar application-enabling services, each NC sector might reimplement these from scratch, yielding overlyexpensive stovepipe systems if there were no common services layer. (b) A common services layer coupled to toolkits for building applications.