A Pascal extension for formal specification of computer networkprotocols. Protocols are described by modules which are communicating NFAs. Modules are arranged in a dynamic hierarchy and communicate at named interaction points. EstPC (ftp:osi.ncsl.nist.gov/pub/osikit/estpc) Compiles Estelle into C. petdingo Translates Estelle into C++ Adopted by ITU-T. ISO 9074 (1989). ["The Formal Description Technique Estelle", M. Diaz et al eds, N-H 1989].