The overall system architecture of the INTELSAT satellite-switched time-division multiple access (SSTDMA) headquarters subsystem (HQS) is described. The HQS is the central control and monitoring facility for INTELSAT's three 120-Mbit/s TDMA networks, and was formed by aggregating the INTELSAT Operations Center TDMA Facility (IOCTF) with elements of the INTELSAT Satellite Control Center (ISCC). To support operation in the SSTDMA era, the IOCTF was augmented to become an active, on-line system that performs several critical SSTDMA network functions in close interaction with the ISCC. It also serves as the central data communications hub for computer-to-computer communications between TDMA reference and monitoring station sites; nonreference diagnostic equipment sites; IOCTF; ISCC; and telemetry, tracking, command, and monitoring sites. This paper describes the changes made to the IOCTF system to significantly improve overall system availability by operating the major computer systems in an on-line/standby configuration with either automatic or manual switchover capability. The augmented role of the IOCTF is discussed, and examples are given of how SSTDMA-specific functions are performed, including burst time plan change management, anomaly event handling, central data flow control, and Universal Time Coordinated (UTC) synchronization. Finally, the new IOCTF-based data communications subsystem is described, and the role played by the IOCTF internal Ethernet bus in providing IOCTF inter-subsystem data communications is discussed.
