Can you give a brief explanation about ip telephony concept?

For many people, Internet Protocol (IP) is more than just a way to transport data, it's also a tool that simplifies and streamlines a wide range of business applications. Telephony is the most obvious example. VoIP—or voice over IP—is also the foundation for more advanced unified communications applications—including Web and video conferencing.

VoIP refers to a way to carry phone calls over an IP data network, whether on the Internet or your own internal network. A primary attraction of VoIP is its ability to help reduce expenses because telephone calls travel over the data network rather than the phone company's network.

Basic consept of IP telephony is very simple. Voice is transfered just like how we transfer data over data line. But we cant consider voice data as normal data so we have to give more preference to voice data to avoid the laging in communication, for this purpose we use QoS (Quality of service). We can use Stand alone IP phones or Software ip phones for the communication an ip address is assigned to the phones.