Transmitting Signals

How is a signal transmitted across a network, e.g the internet?

http://curiosity.discovery.com/question/how-signals-transmitted-internet

Part of what makes the Internet so robust is the numerous ways data can travel across the system. There are physical lines that connect computers together -- these are usually made out of copper wire or fiber-optic cables. Radio towers, cell phone towers, 4G towers and satellites also can transmit data across the Internet. Then there are the thousands of computers that act as clients, servers or both. These computers are the connection points that allow information to pass from one computer to another, even if the two computers are on opposite sides of the Earth.

According to an online resource...

http://compnetworking.about.com/cs/routers/g/bldef_router.htm

Definition: Routers are small physical devices that join multiple networks together. Technically, a router is a Layer 3 gateway device, meaning that it connects two or more networks and that the router operates at the network layer of the model.