A subset of the ISDN network layer protocol suitable for implementation in hardware

A discussion is presented of the selection of a subset of the ISDN (integrated-services digital network) signalling system´s network-layer protocol for point-to-point links suitable for processing in VLSI. A symmetric subset of the CCITT Q.931 recommendation as it stood in August 1987 is proposed. The need for bearer-channel negotiations is eliminated by using a ´two-way independent channel selection´ technique in which each end of the link is master in the transmit direction and slave in the receive direction. A logical model for the signalling system´s network layer processor is developed to aid in understanding the Q.931 protocol. The model also serves as the initial functional partitioning for the VLSI implementation. The key element of the model is the separation of the network-layer processor into a protocol-specific module (PSM) and an application-specific module (ASM).<>