come inHubs are essentially repeaters, operateing on bits. layer 1 device; taking an input and retransmits the input on the hub's outgoing ports. Bridges are layer 2 devices. using the concept of store-and-forward transmission. interconnecting networks. Routers are layer 3 devices. interconnect physically different networks that support different network protocols. store-and-forward packets using network-layer addresses. (bridge forwards packets using LAN addresses.) 不知道用中文怎么讲，你将就着看吧。 正好帮我复习一下。^-^