AbstractLANSF is a software package that was originally designed as a tool to investigate the behaviour of medium access control (MAC) level protocols. These protocols form an interesting class of distributed computations: timing of events is the key factor in them. The protocol definition language of LANSF is based on C, and protocols are specified (programmed) as collections of communicating, interrupt‐driven processes. These specifications are executable: an event‐driven emulator of MAC‐level communication phenomena forms the foundation of the implementation. Some tools for debugging, testing, and validation of protocol specifications are provided. We present key features of LANSF at the syntactic level, comment informally on the semantics of these features, and highlight some implementation issues. A complete example of a LANSF application is discussed in the App