A problem with the X.25 link access procedure
Jack Gostl · ACM SIGCOMM Computer Communication Review · 1977
In the first half of 1977 I was involved in the design and implementation of a network control program (NCP) which interfaced a PDP-11/70 Host computer to a packet switching network (similar to ARPANET (1)). The NCP was responsible for both Host to Host message control and Host to network link control. The Host to network interface used a subset of X.25 (2) for its Link Access Pro cedure (LAP). During the development and debugging of the NCP, it was discovered that the Host-network link could get into a deadlock condition which could not be rectified by any mechanism specified in the current X.25 protocol. The LAP, the problem and several possible solutions are described.