Hubs, Repeaters, Bridges, Switches, Routers and Gateways

I have always wanted to do this. What better way to do this than when I am studying Computer Networks. Knowledge courtesy: Computer Networks by Tanenbaum.

Application Layer : Application Gateway
Transport Layer : Transport Gateway
Network Layer : Router
Data Link Layer : Bridge, Switch
Physical Layer : Repeater, Hub

Repeaters: Just amplify volts.
Hubs: Can connect many entities. Frames arriving from any one is sent out on all others.
Bridges: Bridges are used to connect LANs. They connect 2 ethernets. They do not examine packets. So they can transport any type of payloads - IPv4, IPv6, AppleTalk, ATM, OSI or any other kind. A bridge can have line cards for different network types and different speeds.
Switches: Switches also route on frame addresses. Swich is almost like a multi-port Bridge. However switches often are used to connect individual computers. Switches do not broadcast like hubs.
Routers: Examine addresses in packets and route based on them.