1.General Information:
VoiP is the technology that changes the meaning of "telephone call". It stands for voice over Internet protocol, means voice transmitted over a network or voice travels by way of the same protocols used on the Internet. VoiP referred to IPT (IP telephony) because it uses Internet protocols to make enhanced voice communications possible. VoiP unites many locations into a single converged communications network and provides a range support services and features unequalled in the world telephony. IPT uses in big buildings, a campus-like network, or even a LAN. When IPT crosses from the LAN to the WAN network (wide area network), it becomes VoiP.


2.POTS:

POTS stands for "plain old telephone service". POTS runs over a network called PSTN, public switched telephone network. These system use the tried-and-true method of telephone service known as circuit-switched telephony. People have to rely on their "bottom line-POTS" which means that if the line is cut they can not communicate any more. Besides that POTS also costs a lot of money compared with VoiP. Moreover VoiP also has better quality.
3.Packets:
VoiP technology enables traditional telephony services to operate over computer networks using packet- switched protocols. Packed-switched VoiP puts voice signals into packets, similar to an electronic envelope. VoiP packet includes both caller's and receiver's network addresses. Because it uses packets, you can carry more information compared to traditional telephony system. In POTS world, if one line is down then the call can not go through. On the contrary, in a packet-switched network, the packet can switch to another working route to keep the call continue.VoiP are also portable, they will work with any IP-enabled device such as an IP telephone or PDA. All IP telephone has network interface card and is it the same as a physical address to communicate over the network. The address is called MAC address.
4.Server:
They are just like personal computers except that they have more memory speed and capacity. Depending on the numbers of users or the size of the LAN, we need switches. They are boxes for and have several ports for many LAN to connect.