The IEEE 1588 standard defines a hierarchical set of clocks maintained by the use of the Precision Timing Protocol (PTP). In each timing domain, there is one or more Grand Master (GM) clock source usually synchronized to a GPS clock. See figure below. Cisco Connected Grid Switch (CGS) implements the 1588 Power Profile to act as a Boundary Clock device, interoperating with GM devices to synchronize its own clock and with Ordinary Clock devices (e.g. PMUs, IEDs) to provide them clock synchronization.