Network devices

Networks are built from several devices, each with its own job.

• Modem (modulator-demodulator): converts a computer's digital data into analog signals that can travel over telephone or cable lines, and converts them back at the other end.
• NIC (network interface card, or Ethernet card): fitted in a computer to connect it to a wired network. Every NIC has a unique MAC address. Network cables plug in with an RJ45 connector, which has 8 pins.
• Repeater: signals grow weaker as they travel along a cable; a repeater regenerates them, usually about every 100 m.
• Hub: connects several computers; it sends incoming data to all its ports, so everyone receives it, and signals can collide.
• Switch: also connects several computers, but it sends data only to the destination device, so the network is faster and less congested.
• Router: forwards data between different networks, choosing the best route. It connects a LAN to the Internet.
• Gateway: the entry and exit point of a network, through which all its data passes in and out; it usually includes a firewall for security.

A simple way to remember the first three: a hub shouts to everyone, a switch whispers to just one, and a router crosses between networks.