The AX88872 10/100Mbps Dual Speed "Swipeater" Controller is "a dual speed repeater with build in 4-ports switch function" It is design for low cost dumb HUB application. The AX88872 directly supports up-to eight 10/100Mbps automatic links RMII interfaces. Maximum up-to 96 repeater ports can be constructed by stacking 1 AX88872 and 2 AX88873 chips horizontally and then cascading 4 horizontal boards vertically. About the build in 4-port switch: The switch port3 is fixed to 10Mbps speed and connects to 10Mbps repeater segment, The switch port2 is fixed to 100Mbps and connects to 100M repeater segment. The switch ports 0 and 1 are connected to external MII or RMII interfaces for various applications. For example, one port is used for down link and the other is used for up link to extend the network topology. The other case is one port for up link and the other port for server. The AX88872 is designed base on IEEE 802.3u clause 27 " Repeater for 100Mb/s base-band networks" It is fully compatible with IEEE 802.3u standard. Please refer Ax873-12.doc to get more information about AX88873.