Network interworking for narrowband services over an ATM network

In the evolution towards the broadband integrated services digital network (B-ISDN), the existing services and applications, which are used in N-ISDN, should be provided through the interworking function. Network interworking between N-ISDN and B-ISDN is one of the most important technical issues to provide existing N-ISDN services for N-ISDN users. As a trunking method to fulfil the interworking function (IWF), we present a network interworking mechanism based on the service interworking scenario specified by the telecommunication standardization of the International Telecommunication Union (ITU-T). It provides network-to-network interface (NNI) signaling protocol conversions between N-ISDN and B-ISDN, and it can make it much easier to extend the network interworking function to the service interworking function which allows communication between N-ISDN users and B-ISDN users. Therefore, the proposed interworking mechanism, when compared to other trunking methods, can be regarded as an efficient way for a step towards a future universal communication network. For network interworking, we describe the technical aspects to implement the IWF in terms of hardware and software. We particularly address the call/connection control for the interworking between the N-ISDN service and the B-ISDN service, and the signaling conversions of network interface protocols between N-ISDN and B-ISDN. We also discuss several restrictions and benefits of the proposed network interworking method.