A modified ISDN network layer protocol suitable for implementation in hardware

The paper discusses a modified ISDN signalling system’s network layer protocol for point-to-point links suitable for processing in VLSI. A reduction to CCITT recommendation Q.931 is proposed. The need for bearer channel negotiations is eliminated by using a symmetric ‘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 a 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).