Network devices are those which are used in networking to connected computers in local area network or wide area network. Without these devices you can't make LAN or WAN. 

This is the type of card which is connected on motherboard for local area network. This card is of two types first is ISA or second is PCI. ISA is 16 bit and connected to ISA slot of motherboard. PCI is the 32 bit lan card which connected to PCI slot of motherboard. PCI card are more reliable of faster than ISA lan card. This can transmit or receive the data 

This is the type of device which can be used for wide area network or internet. This device also transmit or receive the data . Modems are of two type external modem or internal modem. External modem is connected externally to the computer through the communication port. The internal modem is directly connected on the motherboard of computer.

The hub is a device used to centralize network traffic through a single connection point. Hubs can be of two types : Active and Passive hub. An active hub regenerates and transmits the signals. It require electric power to run. A passive hub acts as a connection point and does not amplify or regenerate the signal. Passive hubs do not require electric power to run. Signals after traveling some distance, become weak. Regeneration is the process by which the signals are given more power to travel further.