The Hybrid Fiber Coax (HFC) Outside Plant (OSP) Power Supply to Transponder Interface Bus (PSTIB) Specification is part of the suite of specifications developed by the Hybrid Management Sub-Layer (HMS) subcommittee under the SCTE. The purpose of the HMS specifications is to support the design and implementation of interoperable management systems for evolving HFC cable networks. The HMS Power Supply to Transponder Interface Bus (PSTIB) Specification describes the physical (PHY) interface and related messaging and protocols implemented at the Data Link Layer (DLL), Layers 1 and 2 respectively in the 7-layer ISO-OSI reference model, that support communications between HMS-compliant transponders and the managed OSP power supplies and other related power equipment to which they interface.