The Serial-GMII (SGMII) is an alternative interface to the GMII/MII that converts the parallel interface of the GMII into a serial format. This radically reduces the I/O count and is therefore often favored by PCB designers. This is achieved by using a serial transceiver. SGMII can carry Ethernet traffic at 10 Mb/s, 100 Mb/s, and 1 Gb/s.
The SGMII physical interface was defined by Cisco Systems, Inc. The data signals operate at a rate of 1.25 Gb/s. Differential pairs are used to provide signal integrity and minimize noise. The sideband clock signals defined in the specification are not implemented in the subsystem. Instead, the transceiver is used to transmit and receive the differential data at the required rate using clock data recovery. For more information on SGMII, see Serial GMII Specification v1.8.