Network Interface Card (NIC)
Most modern computers have these devices built into the motherboard, but in some computers you have to add an extra expansion card (small circuitboard)
Cables are still used in most networks, rather than using only wireless, because they can carry much more data per second, and are more secure (less open to hacking).
The typical use of a hub is at the centre of a star network (or as part of a hybrid network) - the hub has cables plugged into it from each computer.
The typical use of a switch is at the centre of a star network (or as part of a hybrid network) - the switch has cables plugged into it from each computer.
A switch is a more ‘intelligent’ device than a hub: if it receives a message, it checks who it is addressed to, and only sends it to that specific computer. Because of this, networks that use switches are more secure than those that use hubs, but also a little more expensive.
A common use of a router is to join a home or business network (LAN) to the Internet (WAN).
The router will typically have the Internet cable plugged into it, as well as a cable, or cables to computers on the LAN.
Other computers can request a web page via the proxy server. The proxy server will then get the page using its Internet connection, and pass it back to the computer who asked for it.
Proxy servers are often used instead of router since additional software can be easily installed on the computer such as anti-virus, web filtering etc.
If you wish to protect your whole LAN from hackers out on the Internet, you would place a firewall between the LAN and the Internet connection.
The problem with using telephone lines is that they are designed to carry voices, which are analogue signals. They are not designed for digital data.
A modem contains a DAC and an ADC.
The DAC in the modem is required so that the digital computer can send data down the analogue telephone line (it converts digital data into noises which is exactly what the telephone line is designed to carry.)
The ADC in the modem is required so that the analogue signals (noises) that arrive via the telephone line can be converted back into digital data.