Information transfer protocols for the broadband ISDN

A refinement of the OSI (open systems interconnection) reference model for broadband ISDN (integrated services digital network) is presented which introduces several additional sublayers in the network layer and one additional sublayer in the link layer. The purpose of these sublayers is to enhance the performance of the network, especially availability, while at the same time reducing capital and operational costs. Central to this improved performance of the network is the concept of a virtual direct route, i.e. a virtual circuit connection between two nodes in the network which is used by one or more calls as though it were a direct route. One of the sublayers in the proposed broadband ISDN reference model corresponds to the transfer of packets on virtual direct routes. The other sublayers all relate to service protection, i.e. techniques for maintaining service in the presence of equipment failure