architecture consists of five major systems. Four of these systems are the information processing systems that reside at the central dispatch office (the Central Dispatch Computer), on-board locomotives (the On-Board Computer), on-board work vehicles (the Track Forces Terminal) and in the field (the Wayside Interface Unit). These systems collect, process, and distribute data with minimal input from dispatchers, enginemen, and foremen. The fifth system and the ATCS keystone, is the modern data communications system, which ties the various information processing systems together and significantly reduces the need for voice communications. ATCS has been designed for modular expansion, which allows for varying levels of operational sophistication. Three basic levels of operation have been identified, although many hybrid configurations are expected in actual installations. The Base Communications Packages (BCP) interface the ground segment to the RF segment of the communications system. Mobile Communications Packages (MCP) interface clients to the RF segment of the communications system or (optionally) to the ground system directly. MCP clients include wayside interface units, on-board computers, and track forces terminals. The RF segment operates at 4800 bits per second in the 900 MHZ radio band. The Association of American Railroads' Task Force on Locomotive Systems Integration (LSI) has the mission to "develop a practical approach to the integration of the new electronic and mechanical components on locomotives" (per Minutes of Locomotive Systems Integration Committee Briefing to Locomotive Suppliers, September 5, 1991, Montreal, Quebec, dated September 11, 1991). An architecture to achieve this mission has evolved in the LSI Specifications which describe multiple configurations of electronic and mechanical components in a locomotive cab. See also Positive train control Train protection system References External links "What is ATCS?" - Background and technical data Automotive standards Train protection systems