LAN - Local Area Network
A LAN is probably what you use at school or if you have a number of computers at home connected via a wireless connection. It has all the machines close together, and is probably hard wired using cable or is connected via a wireless system. The data in a LAN is far more secure as long as it is not connected to a WAN like the Internet.
WAN - Wide Area Network
The most common type of WAN is the Internet. The WAN tends to be spread more remotely than the LAN, and probably uses a communication system that is not owned by the owners of the computers – in the case of using the Internet it would be a telecommunications company like BT. It probably uses a public communications medium so it is easier to intercept messages.
NIC - Network Interface Card
Machines will need a device called a Network Interface Card, through which al communication with the network is carried out. This NIC will use a medium, either by being connected to a cable or by being connected to a wireless antenna so that the messages can be passed, and to software that can control the whole process.
Serial and Parallel Data Transmission
If data is going to be transmitted then the bits have to be sent from one machine to another.
One way of doing the transmission would be to send the byte, one bit at a time, through a single wire.
Another way would be to use a number of wires, one for each of the bits in the byte. This is known as parallel transmission of data.
Parallel transmission is much faster than serial transmission but serial transmission is safer because it is difficult to keep all the bits together as they will naturally be transmitted at slightly differing rates.
Direction of Data Transmission
If the transmission of data is only ever in one direction like the transmission of data from a mouse to a computer, it is known as simplex data transmission. Most of the time however, the transmission needs to be in both directions. If it is possible to transmit data in both directions at the same time it is called duplex (or full duplex) transmission. If, however, the transmission can only be in one direction at a time it is known as half duplex.