The DCS is a composite of certain Department of Defense (DOD) communications systems and networks. The system provides long-haul, point-to-point, and switched network telecommunications. The Defense Information Systems Agency (DISA) provides centralized management and command, control, communications, computers, and intelligence (C4 ) systems of the DCS.
Defense Switching Network (DSN). The DSN is the principal common user, switched, nonsecure voice communications network within the DCS. It consist of a worldwide network of commercial leased and government-owned facilities. Tactical DSN subscribers normally gain access through the Theater Communications System (TCS) using the AN/TTC-39 circuit switch. The TCS provides circuit or message switches and direct access to many worldwide DOD networks.
Defense Information Systems Network (DISN). DISA integrated the Defense Data Network (DDN) packet switching networks under the DISN. DISN provides DOD worldwide packet switched data communications through four physically separate networks. These networks were implemented with technology developed by the Advanced Research Projects Agency (ARPA) using packet switch nodes (PSNs). These PSNs accept inputs using the international standard x .25 set of protocols. Until completely replaced by DISN, the four networks are managed together as the DDN:
Under DISN, the four DDNs will remain physically separate and the x .25 PSNs replaced with commercially available Internet Protocol (IP) routers. Each network will employ IP routers to perform switching and routing functions. The trunk circuits that interconnect the routers may be shared by multiplexing the encrypted outputs of the routers. DIA will transition DSNET3 to an IP router network under the auspices of the JWICS program.
Automatic Digital Network (AUTODIN). DISA operates the AUTODIN system. AUTODIN is the DOD common user store-and-forward message switching network for all record message traffic. It consists of a network of fixed and mobile AUTODIN switching centers (ASCs) and AUTODIN communications centers. The current AUTODIN system evolved from the consolidation of the Defense Special Security Communications System (DSSCS) with the General Services (GENSER) AUTODIN system in the mid-1970s. While the two independent systems have been merged, each system has retained its own identity and mission function. GENSER AUTODIN (referred to as the "R" side) handles UNCLASSIFIED through TOP SECRET record message traffic including special category (SPECAT) type messages. DSSCS AUTODIN (referred to as the "Y" side) handles record message traffic containing SCI information. DISA is replacing the aged and inefficient AUTODIN with the modern E-mail based Defense Message System (DMS).
Users require an AUTODIN routing indicator to exchange information. Router indicators identify the relationship of subscribers to their parent message switching center. As stated above, the "R" routers access the collateral security level record message traffic of the worldwide GENSER AUTODIN network, and the "Y" routers access the DSSCS for SCI AUTODIN message traffic.
Defense Message System (DMS). While the DMS is a system in the sense that its components work together to provide message services, it is and will continue to be the composite result of many coordinated service and agency development and acquisition projects. DMS supports two classes of messages: organizational messages (formal record messages) and individual messages (informal E-mail). Its distributed message system supports on-line message preparation, coordination, and release of organizational messages. The DMS will replace the centralized AUTODIN message system, the DDN E-mail components, and the formats and procedures of the current message distribution baseline.