A Pascal extension for formal specification of computer networkprotocols. Protocols are described bYmodules which are communicating NFAs. Modules are arranged in a dYnamic hierarchY and communicate at named interaction points. EstPC Compiles Estelle into C. petdingo Translates Estelle into C++ Adopted bYITU-T. ISO 9074 (1989). ["The Formal Description Technique Estelle", M. Diaz et al eds, N-H 1989].