What Is Internet Telephony ?

In a simple definition, Voice over Internet Protocol (VoIP) or internet telephony is a telephone network over the internet (TCP/IP) network. Thus, you could use VoIP anywhere as long as you are connected to the internet.

There are two main internet telephony technology, i.e., H.323 and Session Initiation Protocol (SIP) that are frequently used. The former is an older standard developed by the International Telecommunication Union
(ITU), the leading United Nations agency for information and communication technology issues.

The latter, SIP, is a more advanced technology developed by the Internet Engineering Task Force (IETF), a large international community concerned with the internet architecture and its development.

In short, it is sufficient for you to know that these protocols are the main engine of VoIP
communication. This book will concentrate on SIP technology as it is currently the main engine behind many
advanced VoIP deployment on the Internet.

How good the quality of VoIP communication depends on the type of Codec employed in a given
communication. Short for Coding­Decoding, Codec is a process of turning analog signal to digital
signal vice versa, allowing audio and video to be sent over the computer network. In such process, codec minimize the use of bandwidth for transferring the signal data while ensuring that the voice received remains clear. A variety of codecs have been developed.

Despite that VoIP communication can be provided for free, you still need to meet some basic
requirements. They include the required equipments and software. At the very least, you need an IP­ based network using TCP/IP and a computer with sound cards, headsets, microphone speaker and have the computer be connected to a network or the Internet. Softphone, the software required for VoIP communication, is provided for free.

If you have more money to spend, you can buy VoIP­ready equipments that can be operated with no need for configuration or very minimal configuration. In addition, you can avoid the hassle of turning on your computer each time you want to communicate through VoIP. At the minimum, you can buy an IP­Phone, a phone that can be plugged into LAN network. Some of these IP Phones have WiFi capability, allowing you to use the phone when connected to a hotspot network. There are many devices enabling VoIP communication, some of which may or may not need configurations.

If you're building a much more complicated network, you can implement IP PBX or Internet Telephony Gateway also known as Analog Telephony Adapeter (ATA), a medium between internet telephony network and conventional phone network.
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