SIM-101 is a professional IEC 60870-5-101 protocol simulator for Windows, developed by SIM SYSTEMS for SCADA testing, commissioning, maintenance, training, and troubleshooting. It supports Master, Slave, and Monitor modes, enabling users to emulate controlling stations, RTUs, or passively analyze existing communication. Key features include balanced and unbalanced operation, serial and TCP/IP connectivity, automatic point-database generation, real-time traffic visualization, protocol decoding, graphical trends, command testing, general and counter interrogation, clock synchronization, event generation, configurable Class 1 and Class 2 buffers, IPv4/IPv6 support, and persistent packet recording. SIM-101 is suitable for FAT, SAT, interoperability testing, SCADA migration projects, device development, communication diagnostics, and reproduction of field scenarios without physical equipment.