As approved by the Office of the Secretary of Defense (OSD), the DSN is an interbase, non-secure or secure command and 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.

The primary function of the DSN is to provide non-secure dial-up voice service. The DSN provides rapid, reliable, survivable, non-secure / secure, and economical C2 telecommunications. To take advantage of economies of scale, the DSN also provides service to non-C2 users on a not-to-interfere basis.

The DSN system is used only for official business or in the interest of the government and is the first choice for all switched voice and dialup video telecommunications between DoD user locations.

The Defense Information System Network (DISN) provides secure voice services using the Joint Staff Defense Red Switch Network (DRSN). This global, secure voice service provides the President, Secretary of Defense, Joint Chiefs of Staff, combatant commanders, and selected agencies with command and control secure voice and voice-conferencing capabilities up to the Top Secret SCI level.

Department of Defense and federal government agencies that have Joint Staff approval can access the network. Joint Staff policy for obtaining service is in Chairman of the Joint Chiefs of Staff Instruction (CJCSI) 6215.01, dated Sept. 23, 2001. Upon approval by the Joint Staff, DISA will work with the customer and the appropriate military department to arrange for service.

VoIP technology is proliferating in the DoD. VoIP should only be employed where there is logical business case which makes it less expensive than traditional Time Division Multiplexing (TDM) technology. DoD policy currently allows the use of VoIP products which have been certified by the Joint Interoperability Test Center (JITC). These products can only be used for local “line-side” service with the Defense Switched Network (DSN), due to important information assurance reasons and to preserve military unique telecommunications features in the DSN. The current listing of JITC-certified products can be found at the JITC Approved Product List Web site.

For several years, DISA has led an effort with the military services to fully migrate the DSN to VoIP technology which will allow end-to-end IP calls over the DISN. This effort was called “Real Time Services” (RTS) until recently, when it was renamed “Unified Capabilities” (UC) to reflect the expanded features offered by the next generation of integrated VoIP products. UC will allow DoD organizations to connect VoIP products directly to the DISN-NIPRNet for DSN service. Pilot testing of UC will begin in late 2009 with European involvement scheduled in 2010. Over the next 10 years, the DSN backbone is expected to largely migrate to UC.

For up to Secret-level voice service, the DoD has a separate global network known as VoSIP. VoSIP is VoIP technology over the SIPRNet. DISA owns and operates the backbone of the VoSIP network which connects VoSIP enclaves to the rest of the network.