1988 enhancement to CCITT Recommendation X.75: interworking protocol for the ISDN era

The author provides an overview of CCITT Recommendation X.75 and presents the latest enhancements that make X.75 a suitable interworking protocol in the integrated services digital network (ISDN) environment. He discusses the expansion of the scope of X.75 and its implications, the problems that this expansion created, and the solutions that were adopted. The addition of new utilities and the modification of several existing utilities to provide the OSI (Open System Interconnection) network service and to allow greater flexibility in exchanging information among networks are also discussed in detail. Packet layer changes in the following categories are examined: format changes, categorization of utilities, new utilities, modified/deleted utilities, network layer service support, and new cause code/error conditions