The Telecom Switched Services Interoperability (TSSI) Program includes interoperability certification of DoD's voice, video, and data services across the circuit switched network. The circuit switched network comprises the Defense Switched Network (DSN) and customer premise equipment (CPE). As "approved by Office of the Secretary of Defense (OSD)", the DSN, is an interbase, nonsecure or secure Command & Control (C2) telecommunications system that provides end-to-end command use and dedicated telephone service, voice-band data, and dial-up video teleconferencing (VTC) for C2 and non-C2 DoD authorized users in accordance with national security directives. Non-secure dial-up voice (telephone) service is the system's principal requirement.MISSION
The mission of the DSN is to provide rapid, low cost, long-distance, voice, secure voice, data, and video service for DoD elements and for other organizations (when authorized by DoD). The prime use is to support Special C2 and C2 users during peacetime, crisis, or conventional war.