Secure communications interoperability in mixed analog and digital networks

The authors address the issue of interoperability of secure communications terminals in mixed analog and digital networks. Particular attention is given to the use of US Government standard secure telephone units (STU-IIIs), which were designed for global interoperability in the public switched telephone network. As digital networks are being developed, it becomes important to insure that reliable STU-III interoperation can be assured when both analog and digital systems are part of the end-to-end connection. The importance of standards to insuring transparent, uniform interoperability is emphasized, and specific signaling standards for providing secure interoperability through the transition to an all-digital world are discussed