Cisco QSGMII Specification.pdf

The Quad Serial Gigabit Media Independent Interface (QSGMII) is designed to satisfy the following requirements:
•Convey 4 ports of network data and port speed between a 10/100/1000 PHY and a MAC with significantly less signal pins than required for GMII & SGMII.
•Operate in both half and full duplex and at all port speeds.
•This implementation can be extended to other port to channel ratios. However, this is outside the scope of this document.