Network Devices

To build a network, computers must be connected and the signals passing between them must be directed and, where needed, strengthened. This is the job of network devices. The main ones are the following.

1. Network Interface Card (NIC). The NIC is a circuit board or chip fitted inside each computer that lets it connect to a network and gives it a unique hardware address (its MAC address). Every computer needs a NIC — wired or wireless — to join a network.

2. Hub. A hub is a simple device that joins several computers together in a LAN. When data arrives at the hub, it copies that data to every other computer connected to it, whether or not the data is meant for them. Because it broadcasts to all, a hub is slow and not secure, and it is now largely replaced by the switch.

3. Switch. A switch also joins several computers in a LAN, but it is more intelligent than a hub: it reads the address on the data and sends it only to the computer it is meant for, instead of to everyone. This makes a switch faster, more efficient, and more secure than a hub.

4. Router. A router connects two or more different networks together and finds the best path (route) for data to travel from one network to another. A router is what connects your home or office LAN to the Internet. It decides, for each packet of data, where to send it next so that it reaches the correct network.

5. Modem. The word modem comes from modulator–demodulator. A modem converts the computer's digital signals into a form (analog) that can travel over a telephone or cable line, and converts incoming signals back into digital form for the computer. It is what allows a computer to connect to the Internet over a telephone or cable connection.

6. Repeater. A repeater regenerates and strengthens a weak signal so that it can travel a longer distance. Over a long cable a signal grows weaker (it attenuates); a repeater boosts it back so the network can extend further without loss.

7. Bridge. A bridge connects two LANs (or two parts of the same LAN) and passes data between them, filtering traffic so that only data meant for the other side crosses over.

8. Gateway. A gateway is a device (or software) that connects two networks that use different rules or protocols, translating between them so they can communicate. It acts as an "entrance" between two dissimilar networks.